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Found useful power gains..


f1karting

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Sorry folks.. Ive been away... quite the commentary...

I am at 19 total degrees advance for one main reason and that was before we got to 12.5AFR (we were at about 13-13.5AFR) and getting detonation at spots along the peak torque range.. I have done some research and found 16-20 degrees of advance at peak boost/torque safe (without WI).. given factors like IAT and fuel. Once we get past the peak torque more can be added, but with the analog distributor it just isnt possible (as far as I can see) so I live with 19 (which is 3 degrees more than the book values for the fed spec distributor.

Without an intercooler and the stock 40trim compressor..the IAT gets up there. We measured close to 160F on the surface of the intake tube.. 160F is the limit before bad things can happen.

The OE trumpets sit less than 16mm from the plenum face which I thought was a bad design but figured that the blow-thru turbo setup needed to have some form of restriction to get a signal across the jets (a method I have read about for BT turbo VW and A-series mini engines) I decided to do a back to back test and honestly figured it would be unsuccessful because of that theory.. not so!! I now believe that lotus added the boost feed pipes to the carb tops to get a slightly higher pressure over the jets vs using restriction methods. Good on them if that is true!

I am still playing with jetting trying to get 12.5AFR across the board, but the top end is still too rich at about 10.5 to 11.5AFR I have ordered some 250 and 260 air correctors to see if we can flatten it out.

The 40hp drop off the end of the curve is the dump valve opening prematurely. We got one run where it held, and we got to 6500 before it popped. I will be changing the OE DV to something like the Hyperboost CORE DV

I am as surprised as you all are.. the car drives just fine and pulls like a freight train. Albeit I am still working on the idle circuit. Using 55/#1 I have had good results but will be trying 55/#7 to see if I can knock the last little bit of progression hesitation out of her.

The dyno runs were on an eddy current dyno at 10m/s load

all numbers are uncorrected.. add 15-18% to get FW numbers.

post-88-1193093283.gif

This shows the plenum clearance:

This shows the trumpet change:

As an added bonus the turbo spools up faster and delivers slightly more average psi up up to WG opening... :getmecoat:

Edited by f1karting

If you set no goals you shall surely reach them..

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Jan,

Absolutely stunning results!

Where did you get the 16mm trumpets?

My engine seems to be quite happy w/ a total of 32 degrees total advance @ 3000 rpm (12 static, 20 dynamic), dialed in on my Electromotive HPV-1. I didn't think ours would be that far apart though! I S/B detonating all over the place, but don't seem to have any problem. I'm trying to find out where I got the 32 degree figure from. I have much less weight in my car. Perhaps less load = more useable advance??? Any thoughts?

I have found that by going from a 52 to a 58 idle jet that it took the 'progression' hesitation out, however the WOT AFR went up significantly, so be careful there. Perhaps the power valve is kicking in @ 4500 rpm. Could you drop it's size down?

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This shows the plenum clearance:

post-88-1193093929.jpg

Blimey, never really looked at a turbo plenum before (my car was an NA), but no wonder there are flow issues with the velocity stacks that close to the wall!!!

Hilly

1981 S3 4.2 V8 6 speed (The Mutant)

Mutant V8 Conversion Thread

Knowledge is power .................... apparently.

 

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Jan,

Absolutely stunning results! NO KIDDING

Where did you get the 16mm trumpets? ORIGINALLY FROM DAVE BEAN BUT I THINK THEY ONLY HAD THE ONE SET.

My engine seems to be quite happy w/ a total of 32 degrees total advance @ 3000 rpm (12 static, 20 dynamic), dialed in on my Electromotive HPV-1. I didn't think ours would be that far apart though! I S/B detonating all over the place, but don't seem to have any problem. I'm trying to find out where I got the 32 degree figure from. I have much less weight in my car. Perhaps less load = more useable advance??? Any thoughts? MY CAR WEIGHS IN AT 2400LBS WHICH I THINK IS PRETTY DECENT..WE MUST BE PRETTY CLOSE?

I WOULD LIKE TO ADD MORE ADVANCE, PERHAPS 24 DEGREES, BUT THINK THAT THE CAM TIMING NEEDS TO CHANGE TO BE ABLE TO DO THAT.. I STILL HAVE THE RED DOT CAM WHEELS IN PLACE.. WHAT ARE YOURS AT.

I AM SURE THE ENGINE WOULD LOVE MORE ADVANCE BUT DONT WANT TO RISK DETONATION AT ALL AT THIS POINT. I AM AMAZED YOU CAN HANDLE 32 DEGREES.. I MAY PLAY WITH TIMING THE NEXT SESSION

I have found that by going from a 52 to a 58 idle jet that it took the 'progression' hesitation out, however the WOT AFR went up significantly, so be careful there. Perhaps the power valve is kicking in @ 4500 rpm. Could you drop it's size down? I HAVE A 55 IDLE AND ONLY 2.5 TURNS ON THE IDLE SCREWS(FINE THREAD) I AM AT 13.9 AFR AT IDLE. 2,5 TURNS ISNT MUCH. IF I GO TO 60 I GET RID OF HESITATION BUT MILEAGE SEEMS TO SUFFER. I JUST GOT SOME RICHER IDLE AIR JETS TO PLAY WITH... THAT SHOULD HELP WITH THE RANGE I HAVE PROBLEMS WITH BETTER THAN THE BIG IDLE JET.

I REALLY WONDER HOW MUCH THE IDLE JET EFFECTS OVERALL AFR, IF AT ALL? WITH THE AFR CHANGE WE GOT GOING FROM 1.70 TO 1.85mm MAINS (0.15mm) I CANT SEE HOW AN IDLE JET THAT INCREASES 0.06mm ON A SMALLER DIAMETER WOULD BE ENOUGH TO MAKE MUCH MORE DIFFERENCE THAN GOING FROM SAY A 1.70 MAIN TO 1.75 AT MOST. SINCE THE IDLE CIRCUIT OPERATES WITH THE THROTTLE PLATE CREATING A LOW PRESSURE OVER THE IDLE/PROG HOLES, I CANT UNDERSTAND HOW THE IDLE CIRCUIT WOULD EFFECT THE WOT AFR IF AT ALL. I CAN TELL YOU THAT THE PUMP JETS DO EFFECT OVERALL AFR. WE FOUND O.5mm INCREASE GAVE ABOUT 0.2 RICHER AFR AND QUITE A BIT ACCEL ENRICHMENT. THE "POWER JET" OR PUMP BLEED, AS I CALL IT, I BELIEVE SERVES TWO FUNCTIONS ONE TO ALLOW PUMP PRESSURE TO BYPASS THE PUMP JET ON ACCEL AND TO ALLOW FUEL TO BLEED TO THE PUMP JET AT WOT.. HOW MUCH I CANT SAY BUT IT WOULD BE AN INTERESTING EXCERCISE TO TEST IT OUT. ALL I KNOW IS THAT THERE SEEMS TO BE VERY LITTLE CHOICE IN POWER JET SIZES (NONE ACTUALLY) EVEN THO THE LOTUS BOOK SHOWS BLANK AND 110, NO ONE THAT I KNOW THAT SUPPLIES DELORTO JETS, HAS EVER KNOWN OF ANY SELECTION AVAILABLE. PERHAP LOTUS DRILLED OUT BLANK ONES

Edited by f1karting

If you set no goals you shall surely reach them..

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Jan,

My car now weighs in @ 1980 lbs. but I'm not sure it should allow that much advance. I'm really confused on this one. Someday I might have a chance to get the car on a dyno, but there are no chassis dynos within 150 miles of here.

I will certainly seek a source of 16 mm trumpets! My cam sprockets are still in the stock location for my car so nothing has changed there. :)

I don't have much experience or knowledge w/ air correction jets, etc., but my WOT AFR went from approx 12.5 to approx 11- 11.5. So the change certainly affected my mixture across the range. I also found that my mileage suffered almost proportionally. I think you might want to try 56's and play w/ the air correction. I wish I knew more! I plan on keeping my stock idle jets for the time being. They work OK, but I may go up one size, as my AFR @ 80 mph is roughly 15-16.

If you are interested, for experimentation, I may part w/ my 58's.

So to address your last paragraph, I believe that the idle jetting DOES significantly change the overall AFR, all else left the same. It is also very interesting that the pump jets would affect the overall AFR, just as I found the idle jets did. You would think there would be more of a disconnect between all these dedicated systems. If you had to venture a guess, would you deduct from your HP vs AFR graph that the power jet is coming online @ approx 4500 RPM?? That is where you really start to go rich.

Are you running the stock or aftermarket exhaust? I have a fairly low restriction exh. so it causes the mixture to lean out.

Another curiosity I've found is that running my engine lean does require more advance. This could mean high EGT, but If I reduce the timing, it tends to bog down. When I tied a map sensor in to my Electromotive to pull timing w/ boost, my engine lost so much power it was literally undriveable! This same problem also exists in two Mazda Miata's that I work on. One is a turbo, one supercharged; both are running only 5PSI boost. They both have an MSD boost retard device that pulls timing w/ boost. Obviously our cars would run fine on 5 PSI w/o pulling timing back, so why would they need it? When I first drove the turbo Miata, it felt exactly like my car w/ that damn map sensor hooked up. I simply took the vacuum line off the MSD and the car absolutely came ALIVE!!! After re-plumbing to streamline the system (incl. removal of the intercooler!) and removal of the boost retard, the car was VERY fast (for a Miata).

When my customer got the car back he was amazed, but what did he do? he put the boost retard back on and killed the power!! Claiming that he wanted to play it safe because someone said to on a Mazda forum. I'm thinking that if you experience detonation, your power would be reduced dramatically. Am I entirely wrong in thinking this way? It seems as if the rough running, bogging down and hesitation would be just as bad. The supercharged one also has a rising rate pressure regulator, the turbo one did not. 5 PSI is 5 PSI regardless. I know that his rising rate pressure regulator is way out of spec, so why not remove it AND the boost retard device, and regain all that lost power and mileage?!

My reason for rambling on is to illustrate the fact that factory settings can sometimes be very close to what we need to get the job done, the exception being the short trumpets! I wonder if they are there merely for the purpose of emissions control here in the states?? Are they the same size in the DOM/ROW cars?? Let us know!

Off now to search for those trumpets!

Edited by Esprit Aviation
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I actually started off with adding a Blackstone-Saab intercooler and found that just adding that gave the engine a noticeable increase in midrange torque which kinda confimed my thoughts that Lotus jets these engines rich out of the factory as a safety measure to ward of dettonation when using poor quality fuels.

Mine still runs on the factory stock timing specs of 1 degree initial which gives a total of 18 degrees at 5,000 rpm +.

I also increased to boost to 10 psi (still using the stock jetting) again giving a noticeable increase in urge (and also causing my 3,000km newish clutch to slip in 4th gear under hard acceleration.) I have heard no audable dettonation, and the plugs read OK(not white)

Although I have never run it on a rolling road, I did measure the intake temperature differences (with a digital Tyre Pyrometer teed into a vacuum port on the intake manifold)

That was 2 years ago, and of course I cant find the paper I wrote the result on, but I do remember it was around 30 degrees centigrade(about half the pre-intercooler temp)

I remember an article wrote by Tony Rudd about the Turbo Esprits carbs fuel spray giving an intercooler effect and adding power, so I also wired my carb fan to run constantly with the engine running, and another idea might be to run the fuel though a Moroso Cool Can to further bring the intake temps down.

Of course I suspect all this fiddling will eventually ruin my Citroen transaxle (the clutch slip is probably a warning), so I would advise anyone not to do these mods unless they are prepared for that eventuallity.

Edited by WayneB
SUNP0003-1.jpg
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Jan,

My car now weighs in @ 1980 lbs. VERY COOL.. I HAD ESTIMATED THAT I COULD GET MY PROJECT CAR DOWN TO ABOUT 21-2200, BUT 1980 IS FANTASTIC.. WHATS THE SECRET?

but I'm not sure it should allow that much advance. I'm really confused on this one. Someday I might have a chance to get the car on a dyno, but there are no chassis dynos within 150 miles of here. I KNOW MORE THAN 19 DEGREES ADVANCE WILL GIVE ME MORE POWER BUT ALMOST DOUBLE SEEMS UNREAL WITHOUT CAUSING GRIEF. I QUESTIONED ZENSPORT ABOUT ADVANCE AND THEY SAID THAT TUNER ENGINES WITH ABOUT 15-18PSI BOOST RUN ABOUT 24 DEGREES AT PEAK TORQUE (WITH KNOCK DETECTION MIND YOU) .. WE WILL TRY MORE TIMING ON OUR NEXT SESSION.

I will certainly seek a source of 16 mm trumpets! My cam sprockets are still in the stock location for my car so nothing has changed there. :fun: APPARENTLY THE 2.2 HAS THE SAME BORE, STROKE, ROD LENGTH CONFIGURATION AS A 283 CHEVY .. I HAVE A V8 TUNER FRIEND THAT SAYS THE OE CAM TIMING IS NOT GOOD FOR TAKING ADVANCE OR DEVELOPING DECENT HP.. HE GOT ALL DETAILED ABOUT THE EFFECT OF DIFFERENT MOP AND LOBE CENTERS WHICH I NOW FORGET. I WILL WRITE HIS IDEAS DOWN NEXT TIME I SEE HIM.

I don't have much experience or knowledge w/ air correction jets, etc., but my WOT AFR went from approx 12.5 to approx 11- 11.5. FROM AN IDLE JET.. THAT SEEMS A LOT!

So the change certainly affected my mixture across the range. I also found that my mileage suffered almost proportionally. I think you might want to try 56's and play w/ the air correction. I wish I knew more! I plan on keeping my stock idle jets for the time being. They work OK, but I may go up one size, as my AFR @ 80 mph is roughly 15-16. YIKES THATS LEAN!

If you are interested, for experimentation, I may part w/ my 58's. THANKS ..WE'LL SEE WHAT THE NEXT SESSION YIELDS.. I HAVE A DECENT SELECTION OF JETS TO PLAY WITH.

So to address your last paragraph, I believe that the idle jetting DOES significantly change the overall AFR, all else left the same. I AM GOING TO CHECK THAT OUT ON THE DYNO FOR SURE, AS I HAVE A HARD TIME BELIEVING IT COULD BE THAT SIGNIFICANT.

It is also very interesting that the pump jets would affect the overall AFR, just as I found the idle jets did. You would think there would be more of a disconnect between all these dedicated systems. AGREED.

If you had to venture a guess, would you deduct from your HP vs AFR graph that the power jet is coming online @ approx 4500 RPM?? That is where you really start to go rich. POSSIBLY.. BUT THAT IS A LOT OF FUEL TO DELIVER FROM A TINY NONE-DEDICATED JET... ESPECIALLY WHEN YOU SEE THE EFFECT OF AN AIR CORRECTOR CHANGE (WHICH ARE SUPPOSE TO EFFECT THE 5000RPM PLUS RANGE). IF THE ENRICHMENT ON THE GRAPH IS HIGH SPEED BLEED FROM THE PUMP JET, THEN THE AIR CORRECTOR WOULD APPEAR TO HAVE LITTLE EFFECT BY COMPARISON (FROM THE RESULTS WE HAVE SEEN FROM THE CHANGES WE MADE). IT JUST SEEMS WRONG SOMEHOW. HOWEVER, I DO HAVE TO ADMIT THAT WE HAVE HAD TO GET PRETTY RADICAL WITH AIR CORRECTORS TO GET THE HIGH SPEED AFR FLATTENED OUT.. BUT WE ARE HEADING THE RIGHT DIRECTION. IF I COULD FIND SOME SIZES OF PUMP BLEEDS TO TRY IT WOULD BE A VERY WORTHWHILE EXERCISE TO TEST THEM.

Are you running the stock or aftermarket exhaust? I have a fairly low restriction exh. so it causes the mixture to lean out. YES, TWIN BOX: 1- MAGNAFLOW PLUS 1-BORLA, STRAIGHT THRU

Another curiosity I've found is that running my engine lean does require more advance. This could mean high EGT, but If I reduce the timing, it tends to bog down. When I tied a map sensor in to my Electromotive to pull timing w/ boost, my engine lost so much power it was literally undriveable! APPARENTLY THAT IS THE CASE.

This same problem also exists in two Mazda Miata's that I work on. One is a turbo, one supercharged; both are running only 5PSI boost. They both have an MSD boost retard device that pulls timing w/ boost. Obviously our cars would run fine on 5 PSI w/o pulling timing back, so why would they need it? When I first drove the turbo Miata, it felt exactly like my car w/ that damn map sensor hooked up. I simply took the vacuum line off the MSD and the car absolutely came ALIVE!!! After re-plumbing to streamline the system (incl. removal of the intercooler!) and removal of the boost retard, the car was VERY fast (for a Miata).

When my customer got the car back he was amazed, but what did he do? he put the boost retard back on and killed the power!! Claiming that he wanted to play it safe because someone said to on a Mazda forum. SHEEP..

I'm thinking that if you experience detonation, your power would be reduced dramatically. WE NOTICED 10 HP SPIKES DOWN ON THE HP CURVE, BUT THE DIPS COULD BE FROM ONE CYLINDER ONLY IN A DET EVENT.. YOU COULD FEEL IT IN THE SEAT OF YOUR PANTS THOUGH. WE TUNED THEM OUT WHEN WE HIT 12.5AFR .

Am I entirely wrong in thinking this way? It seems as if the rough running, bogging down and hesitation would be just as bad. The supercharged one also has a rising rate pressure regulator, the turbo one did not. 5 PSI is 5 PSI regardless. I know that his rising rate pressure regulator is way out of spec, so why not remove it AND the boost retard device, and regain all that lost power and mileage?! THOSE MIATAS ARE INJECTED, CORRECT? I WOULD THINK THAT IF THE FUEL MAP CALLS FOR X AFR AT LOAD POINT Y THEN THE INJECTOR DUTY CYCLE WILL BE ADJUSTED ACCORDINGLY BY THE ECU. I WOULD GUESS THE REGULATOR TYPE DEPENDS ON WHETHER THE ECU CAN CORRECT FOR THE CHANGE IN RELATIVE DELIVERY PRESSURE.. I SOMEHOW DOUBT THAT THE ECU WOULD HAVE TROUBLE WITH A 5PSI CHANGE ON PERHAPS 50PSI DELIVERY PRESSURE. I WOULD EXPECT THAT STEADY FUEL PRESSURE DELIVERY WOULD BE EASIER TO MANAGE AT THE INJECTOR THO... SO I SAY LOOSE THE RISING RATE FPR AND ADD ADVANCE TIL THE POWER RETURNS

My reason for rambling on is to illustrate the fact that factory settings can sometimes be very close to what we need to get the job done, the exception being the short trumpets! I wonder if they are there merely for the purpose of emissions control here in the states?? WHO KNOWS?? Are they the same size in the DOM/ROW cars?? Let us know! CURIOUS WHAT LENGTH THE ROW USES. MIND YOU THEY ARE ON DHLA40 AREN'T THEY? MAYBE LOTUS COULD ONLY GET 45MM LONG TRUMPETS FOR THE 45DHLA, SO SIMPLY USED THEM WITHOUT CONSIDERATION TO POWER LOSS AS LONG AS THEY PASSED EMISSIONS TESTING.

Off now to search for those trumpets!

Edited by f1karting

If you set no goals you shall surely reach them..

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The Cosworth Sierra plenum was similar in that the trumpets were close to the plenum wall. Looking at the photos of the Lotus, I would say that the area around the trumpet and out to the plenum, the curtain area, is about the same as the trumpet cross-section so shouldn't be a restriction. The wave reflection is usually just outside the trumpet but it may actually be at the plenum wall in this case and so the tuning peaks don't move as much as you would expect when the trumpet lengths change.

S4 Elan, Elan +2S, Federal-spec, World Championship Edition S2 Esprit #42, S1 Elise, Excel SE

 

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The Cosworth Sierra plenum was similar in that the trumpets were close to the plenum wall. Looking at the photos of the Lotus, I would say that the area around the trumpet and out to the plenum, the curtain area, is about the same as the trumpet cross-section so shouldn't be a restriction. The wave reflection is usually just outside the trumpet but it may actually be at the plenum wall in this case and so the tuning peaks don't move as much as you would expect when the trumpet lengths change.

The rule of thumb I have always believed is that the distance from a trumpet to any airbox face or other should be at least the diameter of the trumpet.. therefore 45mm not 16mm in this case. Perhaps the curtain area does set the minimum, however if you look at the relationship of the OE trumpets to each other and to the sides of the plenum, there is very little clearance all around.

I never thought the OE lotus S3T setup was well thought out... it seems to bear out.

As to reflections and harmonics in the intake system, I think OE intake length is too short to make good use of anything within the rpm range of the engine. Shortening the trumpets 30mm may move any harmonic up perhaps 500 rpm. Such harmonic, as far as I can figure, would be up around 6K rpm and pretty weak.

If you set no goals you shall surely reach them..

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The Cosworth Sierra plenum was similar in that the trumpets were close to the plenum wall. Looking at the photos of the Lotus, I would say that the area around the trumpet and out to the plenum, the curtain area, is about the same as the trumpet cross-section so shouldn't be a restriction. The wave reflection is usually just outside the trumpet but it may actually be at the plenum wall in this case and so the tuning peaks don't move as much as you would expect when the trumpet lengths change.

I would say that the distance is sufficient too, but what is not so good is the airflow path into the trumpets because of their relatively sharp edges causing turbulence as I tried to explain badly in my last post - here is a marked up photo of what I meant, I believe this would give similar results - done on all 4 trumpets of course!

post-191-1193328015.jpg

Phil

98GT3

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I would say that the distance is sufficient too, but what is not so good is the airflow path into the trumpets because of their relatively sharp edges causing turbulence as I tried to explain badly in my last post - here is a marked up photo of what I meant, I believe this would give similar results - done on all 4 trumpets of course!

Phil

98GT3

This is what Richard Jenvey at Jenvey Dynamics writes:

"The air horn serves three main purposes; 1) To convert the pressure difference between bore and entrance into air velocity with the minimum of energy loss. 2) To act as the interface between the induction system and the atmosphere, i.e. the point at which pressure waves change sign and direction. 3) To complete the system to the required overall length.

For ease of description the air horn may be considered in two parts; the 'flare' and the 'tube';

The main job of the flare is to spread the low pressure zone over the largest possible area - to reduce local pressure reduction - whilst guiding incoming air into the tube with minimum disruption or induced vortices. The flare should be shaped to encourage air to enter from the sides, but not from the rear, of the mouth. This is achieved by either finishing the mouth with a sharp edge when the arc is a little beyond 90 degrees from the air horn axis or by folding material back, parallel to the axis, when the arc is at, or just below, 90 degrees to the axis.

The main job of the tube is to accelerate the airflow smoothly and progressively. This is best achieved by an exponential shape - i.e. one where the radius of curvature is increasing constantly until the angle of the sides matches the next part of the system, usually the throttle body. At the intake end this should blend smoothly with the flare. "

Maybe in our situation a full radius would help... but remember our trumpets are in a small box and the masking extends around the trumpet curtain area as well!

Does anyone have any supporting evidence for what constitutes "sufficient distance"? As far as my current testing shows, there isn't in our application. It would be interesting to see what a full radius would do.. but to be honest, who cares.. the short trumpets work!

BTW.. The 16mm trumpets I used were selected because that was all that were available to me without fabricating ones from scratch. If anyone wants to provide me alternative trumpets, in whatever shape and size, I will arrange to test them at my expense.

Jan,

...If you had to venture a guess, would you deduct from your HP vs AFR graph that the power jet is coming online @ approx 4500 RPM?? That is where you really start to go rich...

I also believe that the emulsion tubes need to be factored into this equation. The richness could well be changes in the mixture strength discharged through the emulsion tube as it reaches its upper limits.

Edited by f1karting

If you set no goals you shall surely reach them..

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There is a lot of good stuff in there Jan, defo worth a read if anyone is interested in engine design.

Of all the bits of info in there,this graph probably tells the biggest story.

inletresonance.jpg

You can quite clearly see how changing the inlet length alters the engine output.

Interestingly, the NA 9XX inlet length is about 16" which is 406mm (0.4m) so you can see why Lotus chose that length as it give the best overall performane

Seeing as the Esprit is a road car where you spend the majority of the time below 5000rpm, longer inlets would be good to improve the engine in the mid range, variable would be even better.

If you could change the inlet length from 500mm to 350mm @5800rpm you can get some really good gains.

Variable inlet was going to be my next project on my old 912 until I did the V8 conversion which already has it.

Hilly

1981 S3 4.2 V8 6 speed (The Mutant)

Mutant V8 Conversion Thread

Knowledge is power .................... apparently.

 

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Quoting Jan...........(I must have screwed up the quote thingy)

"As to reflections and harmonics in the intake system, I think OE intake length is too short to make good use of anything within the rpm range of the engine. Shortening the trumpets 30mm may move any harmonic up perhaps 500 rpm. Such harmonic, as far as I can figure, would be up around 6K rpm and pretty weak."

Edited by Esprit Aviation
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Inlet tuning is less important with forced induction than NA, but it doesn't mean you can just ignore it.

The air still has to move through the runner and with the turbo you are just increasing the pressure differential.

Hilly

1981 S3 4.2 V8 6 speed (The Mutant)

Mutant V8 Conversion Thread

Knowledge is power .................... apparently.

 

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Doesn't the mere fact that we are turbocharged negate much of the tuning for ram effect etc? We're just jamming the air/fuel mixture in there! NO ITS MORE LIKE RUNNING AN ENGINE IN A VERY DENSE ATMOSPHERE.. THE PHYSICS ARE THE SAME.

Also wondering if the dyno runs were done after you had changed those restrictors where the carbs mount, or whatever you did to them. NEVER RAN THE CAR ON THE DYNO WITH THE RESTRICTORS ALL TESTS WERE WITH ONLY THE STACKS BEING CHANGED.

Interestingly, the NA 9XX inlet length is about 16" which is 406mm (0.4m) so...

Hilly

ahhh.. good to know that.. 16" or more does seem ideal .. I had it in my mind somehow that our engines were about 13" ( never actually measured it) in which case my comments about the lack of and weak harmonics may be full of holes. Curious.. is the NA engine intake length the same as the turbo? J

Edited by f1karting

If you set no goals you shall surely reach them..

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The turbo inlet is a bit shorter as the inlet manifold isn't as long, I would guess the length to be about 14" looking at photos as I have never actually measured it.

Hilly

1981 S3 4.2 V8 6 speed (The Mutant)

Mutant V8 Conversion Thread

Knowledge is power .................... apparently.

 

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Some stuff concerning air horns on sidedraught carbs from my old Weber book.

"Air horns are fitted to carburettors mainly to prevent turbulence at the air inlet, which would otherwise cause varying mixtures and uneven charging of the combustion chambers. Their purpose is also to reduce the effect of blow back through the carburettor and in fact ,some air horns house a flame trap. On racing applications the air horns also help contain fuel mist spraying from the mouth of the carburettor. This phenomenon is sometimes reffered to as stand off and may be attributed to a harmonic sffect within the inlet manifold, although where air horns are mounted externally on the vehicle, the effect can be due to air passing across the mouth of the air horn. A number of different shapes and sizes of air horns are available for the Weber range of carburettors and the choice will in most cases depend on the fitting space available. angled air horns can be obtained for the more popular sidedraught DCOE carburettors. Where an air cleaner is fitted, there is normally no need for an air horn, consequently the usual application is on sports engines where maximum air supply is important"

Of course this doesnt take into account that we have been talking about the air horns use on a blow through turbo application , but the engine does also run in a naturally asperated state in the lower RPM range (up to about 2,500) rpm, so maybe the Lotus engineers were taking this fact into account when setting the lenth of the air horns.

SUNP0003-1.jpg
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perfect.. I originally looked for something about 25mm.. who makes those? Would they fit the 45DHLA?

Pippercross makes them. Here is a dealer in England but I am sure someone state side would be able to order. A good variety of lengths as well.

https://www.burtonpower.com/product_main.as...p;sTxt=dellorto

Good luck,

Jeff

www.espritturbo.com

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  • 2 weeks later...
If the proximity of the stacks to the edge of the plenum is causing such high flow restrictions, why didn't Lotus make the plenum deeper ????

Hilly

I can't say, but my '87 has 16mm lips cast into the backing plate to replace the trumpets (although injected cars don't rely on intake velocity to draw fuel like carbs do.

I also added a 1" spacer to the plenum which allows one to open up the diffuser as well. Adding the spacer opens the radius of the charge path and looks to be a lot less restrictive

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