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Where are you based? Thanks for the reference on your dyno run which I had seen but didn't notice the spec on your car. We should get together for a run on the same dyno and the same day with Mel for something truly compareable.


I'll get around to it at some point.

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Lotus run the car rich for a reason. It doesn't run too rich. It is to add cooling at the flame front. Whether its the best way to cool is a moot point, but that is what it does. Overheating of the he

A stock V6S runs at WOT at redline an AFR of 10:1 on stock tune. A V6S with CAI, Larini headers, NO CATS, OEM backbox runs at WOT an AFR of 10.5:1 on stock tune.   Still seems pretty ri

Spent another day testing the intake at the track during the Lotus cup usa HPDE, zero issues with the intake, no CEL, no idle issues and the car felt fast again compared to the stock intake. I w

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Hi Trevor,


Indeed a with/without CAI test to TDI standard on a basic car would be good. Not even Radium did that!  And ensuring full on-the-move intake air flow to avoid engine heat effects, even better. (I have reported measurements re that here.)  Plus with/without a free flowing exhaust (and possibly no cat as in your case) might show that gives most CAI benefit.  All a lot of bother though!


I hope Radium see themselves as a professional operation with a reputation to protect. (Particularly in the US litigation context!) They would be on thin ice if their openly claimed 21.5 HP was not soundly drawn from the tests of their car - I guess a number of people were involved and know, so I'm happy to believe it.


Radium’s claimed +21.5 HP used a Larini exhaust. When I fitted my CAI I already had the possibly similar Lotus Sport exhaust. And, broadly speaking, the immediate “butt dyno” result convinced me - as many others have posted - that it was no trivial improvement. But I can say nothing re a standard car.  And as we know, peak power itself only counts for “autobahn flat out” figures. (By the way, re autobahns, there has been a post (this thread I think) of a satnav measured substantially higher than standard top speed with the CAI. Some 7-8 kph I think, anyway “a lot” in power terms.)


More generally it is the area under the torque curve that really matters, so a mod could be good overall whilst doing little for peak power. In principle it might even reduce it - unlikely to be marketed though! (I make our peak difference 6.5 Met HP by the way.) Did you notice any effect fitting your K&N filter? It’s in the Lotus GTN catalogue as “performance filter”, so it should be doing something. And as your car also is well up on basic power, it would be good to find out re your “possible decat". I’m considering adding that as people speak well of it, though not seen numbers.


And re torque, worth mentioning, for those who’ve not read the whole thread, that way back I reported (in detail) on my own before/after CAI road tests of single gear acceleration from 2000 rpm until the first rev warning light. (Reasonably carefully carried out.)  I compared my clear road gain with the Radium torque improvement measured at 500 rpm intervals on their graph. My road result corresponded quite well with the overall torque gain from the Radium graph - tests were not accurate enough to say more than that. They certainly can’t say anything about peak power though.


Hi Chris,


Sorry not to meet you. Two CAIs, with and without a Sports exhaust would have been really useful - as above! Pity we can’t draw any firm conclusions from your smaller power gain on a different dyno, but as above, it’s torque that matters.  (Metric or Imp HP? Corrected to standard environmental values? Tyres and pressures the same? We all three should note mileages too.  Have read a post saying their car performance seems to keep improving with mileage - at over 20Km I think. Mine 14,500m)


As with your test, for me, the AFR reassurance was really valuable. I’m not brave enough to try rotating my filter although I’ve marked the position as it is very plausible that it can affect the metering.  If you would like to adjust yours and let us know, it would be doing a real service to TLF!  Re that, while at TDI I took some details of the TDI symmetric circular filter which would avoid that uncertainty. It’s too big in diameter to fit on the inlet pipe directly but possibly good for future fun as Sam (TDI Tech Chief) has measured that it gives less restriction than Radium’s K&N filter at max airflow.  Looking at my results, the AFR becoming richer at highest revs does point to that possibility. I understand it is the bellmouth inside the filter that helps. Tempting! But changing anything there would call for retesting the AFR.



PS: Trevor, just seen your note to Chis re meet.  My view, not tell anything re fundamentals, which are my interest - too many variables between different cars. Re CAI, need an on/off on same car. But helpful to who? No one doubts a substantial gain. The exact amount depends on so much else - including the filter rotation!

Edited by mdavies
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Did you notice any effect fitting your K&N filter? It’s in the Lotus GTN catalogue as “performance filter”, so it should be doing something.

We dyno’d my car with an almost OEM filter to new K&N filter with no measurable change. This is expected as K&N claims less flow degradation over time, not more flow up front. By the way, Toyota OEM filters are not low quality.



Changing up at filter, such as bellmouth, should be far enough away from MAF to not affect AFR’s as long as your changes are not moving flow from side to side, as would an asymmetric filter.  If the MAF is correctly calibrated to the flow in its region and your changes only increase or decrease overall flow not distribution of velocity across section or induced vortices, them the AFR’s will come out.



Edited by Julian73
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Ditto, thanks Julian.


Just too busy at moment to update the TDI PLUS CAI thread with pics of their special filter (have got them as far as computer!) and to add a few words from my recent chat with them.


Have tried to feel around Radium K&N filter as fitted behind screen; there is more space right left and above, at least. Am pondering practicality of making/getting bellmouth to add to end of intake to copy TDIs and surrounding it with a larger adapted K&N filter.  Fabrication and material tricky, would demand care, for obvious reasons, including shockwaves at end.  But uncertain re "tuned length" effects of adding bellmouth - might negate tuning!  Need read up on that! Any experts here? 

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88 Esprit NA, 89 Esprit Turbo SE, Evora, Evora S, Evora IPS, Evora S IPS, Evora S IPS SR, Evora 400, Elise S1, Elise S1 111s, Evora GT410 Sport

Evora NA

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WOW, ta Mr Bibs.

For the couple of people that had asked to see the graphs from a recent rr session at TDI.
This is with a cold air intake fitted to replace the standard airbox.

3 runs


and AFR from that session



From the other thread.

My starting point was a factory S with no modifications that gave the following rr results at the hub.


and associated afr figures.


Over a period of time I experimented with different air box configurations.

The final result is as posted above.

The increase is from 256hp recorded to 312.8hp recorded. Torque has gone from 257.5 to 269.8. All figures taken on the same rolling road, same operator and same test methodology.

My conclusion is that it is worth fitting a cold air intake to the Evora S.

The bottom graph has a key to the left

Y1 is the black line-engine speed.

Y2 is the red line- wheel torque.

Y3 is the green line- Air fuel ratio. 


Just as a bit of background to those that haven't been following the various threads re CAI's on the Evora- mostly in the USA.

There has been one known engine failure on a car fitted with a commercially available cai made for the N/A Evora.
There are other factors involved but it has been stated as a result of that one failure that the Evora engine in both n/a and supercharged form can not utilise a CAI, for fear of it ruining the engine map and causing intermittent errors and eventual failure.
Some people have been experimenting with engine maps and air intakes, often, imo, not understanding the requirements of this engine in the form that Lotus have installed it. Using often quoted 'acceptable' afr figures in your re-map leads to a weaker than needed afr even when the figures look 'conventionally' correct.
I believe, but have no more than my own knowledge and gut instinct, developed on carburettor old school cars, that Lotus have had problems developing the expected power outputs from this engine, mostly due to heat problems. I also believe that they have taken a relatively well known route to alleviate/cure these problems by overfuelling the engine to help with flame front cooling. This is particularly important in supercharged cars where the additional charge compression generates extra heat, even before the extra heat from the higher energy burn after spark. Hence the pretty poor mpg and conventionally rich looking afr's from the factory.
My intention was to try and get more power from the engine but hold on to the Lotus 'rich' afr's to keep whatever 'magic' engine heat dynamics Lotus had introduced.
I think there is a lot more power to come from this engine but I don't want to risk the leaner conventional afr's that might expected to be seen.
The result is above. 


Originally posted by damurphster

Originally posted by bruss

I don't get it.

Are you saying that with CAI and mapping you went from 251bhp to 312bhp at the hubs???

That's exactly what happened, not just what I'm saying.

Surely that starting bhp has to be wrong - that's well less than 300 at the wheels from a reported 345bhp.

You might say that- and I did - to Lotus, who responded with a re-flash. After re-testing there was no change. Lotus then got quite aggressive in telling me that my car was performing normally and within their specifications. Casting around for other peoples rr results, the best I have seen on the TDI rig is just short of 270 at the hubs.

Thats mind blowing - you cannot be the only person [Censored] ed off by that.

Do Lotus not 'get' that their cars attract 'geeky' buyers who will 'talk' to each other and these type of things (and how they deal with them) will not go unnoticed.

I love Lotus but, like TVR, sometimes I really think that if they went under they would deserve it.

I wonder what bhp the press cars were running?

The car must feel night and day different.

Whats happening with your warranty - the car is 'modded' but to less than manufacturers spec?!?!?!

Yeah, that's a whole other argument, the difference between any manufacturers 'best' lab figures and what's actually achievable in practice. Lotus would probably defend their position by saying, correctly, that they run industry standard tests. Whether it's mpg or power or any other published test you have to take any manufacturers figures with a large pinch of salt.

I wouldn't accuse any manufacturer of lying, but I would argue that lab results on an engine on a test rig are never going to be achievable in a production car on the road. I'd fundamentally disagree that even if they were once achievable, they would never be consistent on a day to day basis. There are just too many variables. The only thing I have been able to do is bench mark my sample on one Evora S and then make changes that give me what I expected from the car. I have then published the results on this sample of one.
I doubt whether any but the largest manufacturer has conducted longitudinal tests over 6 or 12 months on mpg and power outputs on production cars. Certainly I don't think any would be brave enough to publish them. It'd be commercial suicide.

Regarding warranty. Any subsequent engine problems would be investigated by Lotus to see whether my changes had affected/caused any failure. I take that risk.

Yes if Lotus went under they certainly haven't helped themselves in terms of customer relations. On the other hand the help I have consistently had from motorsport and individuals on the production side is excellent. They really are good.
It's just the customer relations and PR side that needs massive improvement imo. 

I'd agree with the terminology. I used cai 'cos that's what everyone calls them. For me it was just about improving air feed at a controlled rate that allowed more air to get in without upsetting the ecu's ability to adjust within the Lotus map parameters.

Incidentally I think that the original apparent lack of power is exactly what you suggest - the timing being pulled as a response to some limiting factor. I would suggest due to heat but Lotus say not.

I found that to get the best consistency I could over a range of heat soaks, the position and size of the cone air filter had to be combined with the diameter of the connecting ally tube. Too much of one or the other triggered differences which couldn't be accommodated by the map. (mil light thrown). The other and probably more important factor was the relative position of the maf in the air flow. This was super critical.
I did also use a heat shield between the main engine compartment and the air filter, making a de facto separate air box from the air intake. I played with a canister type air box but didn't see any great improvement. There could be more to be gained with such a canister but I ran out of patience with swapping out different combinations for very small or no gains.
The final runs were taken after driving for 2 hours in traffic to get to TDI, and then sitting for 30 minutes. I then ran the car for 10 minutes at idle to stabilise the engine temperature before going in for the runs. The graphs should reflect a real world situation, as much as they can. 




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Paul, as a humble NA owner I can only comment with my face pressed to the glass of the S workshop (though amazed that your standard S kicked off at 251 Hub hp compared with my NA+Radium+sports exhaust at 266 Hub hp) but it may be relevant that, as I understand, for the Exige S, Lotus spent time with a hub dyno in connection with its intake system, and that - call it what you will - the intake tube and filter design were given close attention. I speculate that material in the TDI CAI Plus thread here and the Exige Cup R info (in Up Your S) is relevant. Noteworthy that Lotus quote a rather precise 366 hp for the Cup R. The Exige S cooling arrangements may be better of course, so allowing a higher state of tune, as you indicate.


On my NA I am presently playing with a larger cone filter than Radium provide (tight fit but possible) as there have been indications that there is some scope for greater airflow. Also trying what might be a slightly improved intake shape (my own). Not checked out yet and some way to go, but headed back to TDI idc. If things work out, I will put all details here.  More info on your much improved design would be interesting, unless it is proprietary of course, and I note the sensitivities you discovered and the great deal of work and testing involved.

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Experimental enhancement of Radium CAI filter. TDI Test 27 April 2013

My post 243 on the 30th March gives results of the TDI dyno test on my Evora NA (Lotus Sport exhaust) with the Radium CAI. I’ve now tried a larger K&N filter together with a simple bellmouth mounted inside it at the end of the intake tube. Thus is a report of the results of a TDI test of that modified filter. Relevant background is as given in the 30th March report, and not repeated here - except noting that the TDI dyno measures in metric HP (PS) (98.6% of Imperial HP).

The Radium CAI works well for me in its standard form, but as well as benefitting from any immediate gains I wanted to assess the scope for yet further development, perhaps using a different type of filter as mentioned by TDI at their Charity Dyno Day.

In summary, small but clear gains were measured throughout the rpm range, and notably above 6,000 rpm. The implications of the changes are significant however, and not well represented simply by peak torque and HP values. They are indicative of real effects which lead to my two primary conclusions, which are: a) the revised filter has positive effects, making its continued use beneficial and, b) it is clearly worthwhile exploring the use of a more sophisticated filter.

To provide good quality pictures of the bellmouth and the test results, I have provided them in a Photobucket folder.

The photos are self explanatory, but I am not necessarily encouraging anyone to copy the approach and so am not providing details here.

Revised Filter

1) The Radium supplied K&N RC-1637 filter was replaced with a K&N RC-4470, mounted with the same alignment of the offset. The RC-4470 has an insignificantly different offset, but a length of 167 mm as opposed to the 140 mm of the standard, so giving an extra 17% of filtering area. (Not the same as the ratio of the lengths, because of the taper.) I suspect there is probably a greater than 17% increase in “effective area” because, at the highest air flows, the filtering circumference closest to the intake tube requires air to turn through 90 degrees and so that area may be relatively less drawn through than the rest of the filtering area further away; the longer RC-4470 has more area “further away”. I assume these effects only come into play at high flows. The longer - and hence more slowly tapering - filter required care in positioning, calling for packing adjustment of the rubber mount and the removal of a little of the rubber edging from the rear of the Radium screen. It was also convenient to make the screen itself easily removable without disturbing the intake tube and filter, by removing the part of the bottom lug of the screen that otherwise lies below the rubber mount. (No substitute is actually necessary, although I used Velcro along the remaining bottom of the lug.)

2) I made a simple “bellmouth”, as illustrated. It is slit, allowing it to be compressed to fit inside the filter opening and then fitted back over the intake tube and clamped in position with the filter. (The photograph happens to show a standard filter - identical in that respect.) Also shown is the end of the intake tube, chamfered to blend in with the bellmouth and so eliminating the step of the tube wall thickness. The aims were - hopefully - to generally smooth the air intake flow, to enhance it by reducing turbulence at high flows (no 90 degree angle tending to “compress” the effective intake diameter) and no step; also to reduce the effect of the filter offset by giving a more balanced flow to each side of the intake tube. The circumferential “90 degree turn area” of the filter that is screened by the bellmouth was hoped to be more than compensated for by the extra length of the longer filter.

I cannot assess how the two factors might have performed independently. It seems unlikely that a larger filter alone would have actually reduced performance, but conceivably it may not have played any part in enhancing it. Thus it cannot be concluded that the standard RC-1637 is inadequate. Equally possible is that the bellmouth gave no advantage. Conceivably it even reduced performance, although (noting given the additional length of the RC-4470) that seems a fairly unlikely possibility. It may have added little or nothing and the performance effects would then have been given entirely by the larger filter. (Regrettably, resources limited the testing undertaken!) However, despite no firm evidence, it does seem more likely than not that different aspects of the effects discovered owe more to one component than the other.


See the three photographs of the graphs. (Also the 30th March AFR photo.)

Air - fuel ratio

It is important to note the effect on the AFR of the modified filter before considering torque and power changes. The AFR was made significantly richer in the key range from 3,000 rpm to 6,000 rpm. The graphs show the modified filter gave a ratio of approximately 11.5:1 rather than the 12.5:1 of the standard filter. However from 6,000 to 7,200 rpm the modified and standard filters are consistent and both give slightly less than a 11:1 ratio. Thus the modified filter:

a) moves the AFR towards the “rather rich” value (unknown to me) that several sources have stated that Lotus provide in their stock engine setup and,

b) moves the AFR away from the ideal that TDI “would aim for if developing a setup”, as found in the March test of the standard Radium filter. So, had the mapping been changed to maintain a 12.5:1 AFR, the modified filter would have given a greater gain than that measured. (This was discussed at the test with TDI who were quite clear that a meaningful increase would be obtained.)

Leaving aside whether it is optimum or not, in considering the power difference between the filters from 6,000 to 7,000 rpm it is highly relevant that the AFR was the same in both cases.

Peak torque and power.

Peak HP:

Radium CAI Filter: 300.1 mHP(295.9 Imperial) at 6,240 rpm

Modified Filter: 302.2 mHP(298.0 Imperial) at 6,330 rpm

Peak Torque:

Radium CAI Filter: 276.7 lb ft at 4,620 rpm

Modified Filter: 278.7 lb ft at 4,830 rpm

The torque graph shows that in the rpm range around the two peaks the modified filter gives a broader spread of increased torque than can be seen from the peak figures alone. Also important is the higher rpm at which the modified torque peak occurs and, with the increased torque, represents 5.3% greater power. (The modified 278.7 lb ft could, in principle, be “geared down” to the standard peak at 4,620 rpm to produce 291.4 lb ft, i.e. 14.7 lb ft more than the standard.)

Torque and power improvement

At both lower and higher ends of the rpm range there is a small but clear increase in torque and power, and generally more so than at the peak values. At the lower end the increase lies from 4 to 7 mHP. The greatest increase (with the same AFR), at the greatest airflow, is seen at 7,000 rpm with +7.5 mHP at the hub, equivalent to 8.5mHP at the flywheel.


With the AFR difference giving an undefined power reduction, the uncertainty regarding which aspect of the filter change was responsible for which effect, and further, how this may have varied with the airflow/rpm rate, some conclusions are highly tentative.

1. It is quite clear that the modified filter has positive effects and its continued use is worthwhile. (I believe I could subjectively detect the improved performance at peak rpm.) At the very least, there are small gains whilst the AFR is restored towards the Lotus norm.

2. As filter characteristics do have definite effects it seems there is clear potential for a more sophisticated filter to be worthwhile.

3. Another firm conclusion is that the AFR effect limited the increased power from the modified filter. (In contrast to the “ideal power ratio” at which the standard filter operated.) Something for the future, after further filter consideration.

4. On the basis that performance was improved even at the lowest airflow/rpm, when filtering area was not likely to have been a constraint, it seems highly probable that the bellmouth had a definite effect. The several possible effects seem likely in combination to have affected the metering of the air flow and so the AFR. Speculatively, perhaps the bellmouth gave a smoother cross-intake airflow that more closely approximated that of the stock intake and so gave closer to a stock AFR. From the basic geometry of the bellmouth protrusion inside the filter, the effect of the filter offset is likely to have been reduced as the bellmouth constrains and directs the airflow so that the “offset effect” becomes only that of the distance of the filter surface from the entry to the bellmouth. Also the bellmouth focuses the flow paths to be from the more distant parts of the filter which are more comparable side to side.

5. That the most substantial increase in power occurs at the greatest airflow/rpm is definite, although it seems unclear whether that is more likely to be due to the larger filter or to the bellmouth or to the combination. (At least the AFR is not a factor.) Further testing would seem necessary to resolve it. (None is planned.)

Edited by mdavies
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  • 1 month later...


Any update on your tweaked CAI? Still running well? Did TDI ever announce anything?

I still have the Radium as never got around to selling it so refitted about 250 miles ago, was missing the windows down noise. All fine until earlier today and noticed a rough idle a few times in traffic. A blat and it appears to have cured itself.

Most likely due to the fact I put £20 of normal unleaded in other day. Normally use VPower only but was getting low and local shell garage had none left. It's been run on VPower for 4000 miles in my ownership so it may have developed a liking for the finer fuel and have been disgusted as the normal stuff ;-)

Other suspects were dirty MAF or some gunk accumulated on the throttle body.

I will give the MAF a clean just in case. But car will have only done 400 ish miles with CAI fitted and 14500 in total so be surprised if its dirty already!

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Hi Raf,


Nothing to report - except it's great!


I've done about 1,000 miles with my "tweaked" version now, much on roads able to exploit it plus some with traffic clogged up and it's never missed a beat. ("tweaked"? Hmm....... "intelligently enhanced" I say!)   I sent my report as above to Radium - they said thank you, but I heard nothing more.  Now if they bring out a MK II with the same changes, they will hear from me again! But I don't expect it as the larger filter is a tight fit that needs careful adjustment of the mounting arrangement and the bellmouth is a fiddle to make. (By a process that needs care as it involves some potential danger!)


Always run on Shell V Power. (Very occasionally the BP Supreme, or whatever they call it.)  I don't measure fuel use accurately, but my impression is of slightly higher displayed consumption, which would fit with the richer AFR TDI measured. I am happier with that - and more relaxed whilst appreciating the now tiny interval between the first and third rev warning lights with Sport mode on!)  Find I occasionally hit the limiter, which I didn't used to do. Have to look it up but done about 6-7K miles with the CAI and approaching 16K altogether. Just had the 3 year service from B&C - no issues. (Warranty ended of course.) Re serious testing though I have not tracked it so can say nothing about sustained peak power use.


I'd be surprised if your MAF was dirty after just a few hundred miles. (Assuming the filter itself was ok - not rubbing anywhere and worn through? And no extra oil put on?) And always worth checking the MAF mounting bolts are tight, though if a leak it wouldn't likely remedy itself.  And without any warning light your fuel guess may be it, especially if came as shock to the ECU.


However, as TDI did not (have not yet?) come up with a commercial version of their prototype - need 20+ or whatever orders they said - I'm intending to see what more I can do. I have obtained one of the special filters they used (How much?.....!!) and am awaiting the making of a suitable connecting tube. Fitting, bracketing and mounting will definitely be tricky.  An uncertainly that concerns me is that it will extend the Radium tube. They put some R&D into that, so moving away from their length may negate any benefits from the special filter. Certainly a full TDI test will be needed and I'm prepared to revert to my "tweak".


You might be interested in this article - covers the ground!



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Blimey Mel, article over my head before the end of page 1 ;-) One for a read with a beer in hand and some free brain space!

I did think about rubbing and will take a further look at the weekend. I did notice slight rubbing after the first time I removed it but it was cosmetic, certainly no holes or anywhere near that.

I did some fine tuning so thought I had removed any chance of rubbing but worth a check while I clean the maf and check all screws etc.

I did 40 miles after the rough idles and no re-occurrence so fingers crossed it was just the fuel.

Good to hear your 'intelligently enhanced version' is going well.

Keep us all posted on any further developments, good to see the amount of thought etc that has gone into the application and that the results are positive.

Now that warranty is out perhaps worth proving some info to Lotus? As others have said earlier in thread cant believe they haven't introduced some approved mods in this area before now.


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Yes, I found that article needed some concentration too!  But interesting stuff re what the professionals do.


About the filter rubbing, I'm glad I modded the screen to allow it to be removed separately, as said in my report.  Can check things without moving the the mount.


Re Lotus, as you say, a CAI is something they could well exploit, as has been posted here many times.  But they certainly know already, from several sources. I spoke to someone senior enough a year ago who was already well aware. Lotus are bound by all the regs of course so it would have to be dealer fit. Two I know of have explored it, one practically, with a reputable fabricator, a while back, and I understood that project was with Lotus' interest. Don't know what happened there.  Another dealer recently mentioned considering something but I don't know the status. I was told that no interest was shown by some particular Lotus personnel in a serious suggestion a while ago, but they may have not been the right ones.


 Perhaps my type of tweak (that's ok!) giving a richer mix again would remove one concern. Certainly any significant dependence of the AFR metering on the angular setting of the filter would have to be removed.  I can't stretch to a lot of testing to see how sensitive mine is re that but, as my report said, I believe I have reduced it.


For the S engine, Lotus Motorsport have developed something on the intake side for the Exige Cup R as I've posted about (Up Your S, and again more recently) but that's rather different.


I will update here on anything useful that comes out of further work. Have to find a decent time slot - don't want the car off the road for long!

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  • 3 weeks later...

Just an update on my further CAI version. It is now fully built, running apparently satisfactorily and an appointment with TDI is in the diary.


Taking the car out after a week off the road it is bound to feel good and so I can't make any meaningful comparison with my previous "tweaked Radium", but it doesn't feel slower, anyway.  However I have restricted myself in trying peak revs and power as I don't know what the AFR looks like. I'm hoping it will remain slightly rich as before; certainly the new arrangement flows in from the entirely symmetric filter which includes a bell mouth that follows pretty well the optimum design described in the article I linked in my post 262 above.


However only the test runs will tell. If results are better than my tweaked Radium, I hope to give a full report here, but if not I will have to be careful about what I post. My development is constrained in test resources and by practical limitations - I can't test a range of lengths and diameters of intake pipes for instance and what I do has to be reversible. It would not be sensible or right to suggest that a particular filter is ineffective on the basis of my one-off amateur effort.


Something worth mentioning. I AGAIN discovered that one of the two bolts holding the MAF into the Radium intake tube was slightly loose. I have mentioned tightening these twice previously, once after the initial shakedown - fair enough - but again a year ago or so one had slackened slightly.  This time one bolt needed something less than a quarter turn but it certainly was not as I had tightened it. I can't quite recall but I believe there is a rubber seal included and possibly this is compressing. Or there may be some heating or vibration effect. Whatever the cause, any slight air leak at the MAF would be highly undesirable.


Re that though, should my new arrangement survive its test and I retain it, a new angle of the MAF will allow very easy checking in future!

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88 Esprit NA, 89 Esprit Turbo SE, Evora, Evora S, Evora IPS, Evora S IPS, Evora S IPS SR, Evora 400, Elise S1, Elise S1 111s, Evora GT410 Sport

Evora NA

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Loctite is a possibility but first I would like to know whether it is the bolt turning or the seal compressing. It might need tightening. So I have marked the bolt heads now - we will see.

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  • 2 weeks later...

Addition of Bellmouth to Radium CAI. TDI tested 11 July 2013. More Power BUT.......


My previous report (post 260) on my “enhanced Radium” (EnR) concluded that there was scope to explore further improvement.  After reading I wanted to try a new intake arrangement using a scientifically optimised true bellmouth on the Radium tube; a symmetric intake, of course.


In a move away from the "obvious" approach I mentioned a few posts ago involving extending the intake tube, I found a way of constructing it that did not extend the Radium tube length - which they state to be optimised - and which fitted in the available Evora space. My arrangement did indeed give more top end power, but testing showed up a flaw that makes it unusable - by me anyway. All very disappointing, given what I thought were rather neat solutions in practical implementation and which produced a successful working installation.


I am not going to report details of the design here, pleased as I was with it. It was not successful in the terms I sought - using the Radium inlet whilst being entirely reversible to standard.  Moreover, it would be inappropriate for me to suggest that the measurements made on my single vehicle of my constrained design form a basis for general inferences regarding the performance of any of the components, commercial products or approaches I used.


In my EnR report I stressed my attention to keeping a healthy air/fuel ratio. (For background, I found a decent summary of AFR matters, although fuel management systems and chemical mixes in the petrol add complexity.)  That reference includes a graph (from Toyota as it happens) that shows why I would only be happy with an AFR around 12.5 or richer.  All the following figures are given on the same technical basis as in my EnR report.


Under test by TDI the new bellmouth arrangement did give greater airflow and more top end power. However, below 3,750 rpm the AFR was substantially weaker than with either the basic Radium or my EnR; these were never weaker than 12.6 at any (full power) rpm.  At 2,000 rpm the new bellmouth arrangement sat just at (the only theoretically ideal) 14.7. With increasing rpm it steadily enriched but reached 12.6 only at 3,750 rpm. It remained about there until 5,500 rpm then enriched further up to peak rpm.  It always remained weaker than with the EnR however.


I am not going into detailed power results here, for the reasons I have already given.  Remapping the AFR would probably allow a true bellmouth to be used more successfully, possibly with quite different results.  But broadly, at peak torque and power it gave clear small gains over the EnR. However, below 4,500 rpm it gave virtually identical curves to the EnR. (Pleasingly for me, in a way.) Below 2,500 rpm it was slightly down on the EnR - AFR just too weak, I imagine.  The most significant gain over the EnR was at peak power, up by 6 bhp to 308.3mHP, 304.0 bhp, at the slightly higher rpm of 6,330; it maintained that advantage up to 7,000 rpm.


My disappointment at the AFR outcome is lifted a little by a few things. Firstly, a key conclusion of my previous report has proven to be true. There was indeed scope for seeking still more from the Radium intake and simultaneously avoiding the asymmetry of the K&N filter that it incorporates.  Secondly, I’m very happy with my EnR which I regard as very successful.  And thirdly, in replacing my EnR I was able to slightly modify and thus continue to use the new CAI screen I made for the bellmouth arrangement.  This weighs just 0.2kg whereas the Radium screen weighs 0.9kg. (I believe that Radium made theirs substantial enough to support an oil catch tank as a secondary capability.)  So, a success!

Insofar as it might be of interest, I don’t envisage undertaking any further explorations of this sort. Certainly a true bellmouth would be expected as a component of an optimum intake design, but probably only in conjunction with remapping and unconstrained overall design freedom.


As a postscript for the avoidance of doubt, and noting the possibility that my car may be on the market one day, I emphasise that at no time during my developments has any warning light appeared, and that I have run the engine only at low power prior to testing, and indeed afterwards in this last case, until I refitted my EnR!

Edited by mdavies
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They're for the NA cars. I'm pretty sure they don't play well with supercharger cars Ross I'm afraid.

88 Esprit NA, 89 Esprit Turbo SE, Evora, Evora S, Evora IPS, Evora S IPS, Evora S IPS SR, Evora 400, Elise S1, Elise S1 111s, Evora GT410 Sport

Evora NA

For forum issues, please contact the Moderators. I will aim to respond to emails/PM's Mon-Fri 9-6 GMT. 

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My understanding also is as Bibs says.  Radium themselves post on and are discussed a great deal on the US forum. I'm not up to date but they have said several times that if someone would supply them an Evora S on which to develop a similar intake they would consider it. No takers so far I believe.


There are potential issues however.  The S engine runs nearer its limits than the NA and cooling and AFR matters for example are much more complex. Having explored the NA situation, with its lower power and simpler basis, fairly fully myself, and chatted to others quite a bit, I would not casually modify an S in any way.  I believe it can only sensibly be done by a full scale properly equipped professional operation and engine remapping would be part of it. (Which opens up other questions!)


IMO it is a pity that Lotus themselves have not seen fit to give the Exige S Cup a little more than the basic S, perhaps as a dealer fit - would make it very desirable! (They have done for the Cup R - just from memory, 366 vs 345 ?)  Quite informally I have heard the words Larini, full system, and +40 bhp mentioned re the S but have no actual knowledge. Also the supercharger pulley size. Info about all that on other threads here I think.

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If you want a little more induction noise you could always have a oiled mesh filter rather than the OEM, like a K&N or Green Cotton?

88 Esprit NA, 89 Esprit Turbo SE, Evora, Evora S, Evora IPS, Evora S IPS, Evora S IPS SR, Evora 400, Elise S1, Elise S1 111s, Evora GT410 Sport

Evora NA

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Ok thanks. I had a supercharged Elise 111R before this and so am fully aware (after blowing it up!) the implications of increased power. I'll stick with my S as it is I think.

The way to improving the Evora S and getting mor power is through the exhaust system - either Supersrint or KomoTec.

If you have the choice between a Stairway to Heaven and a Highway to Hell don't forget the Nomex®!

Captain,  Lotus Airways. We fly lower! 

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