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Improving throttle response in a Sport 350. - Sport 350 Technical - The Lotus Forums Jump to content
Bibs

Improving throttle response in a Sport 350.

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Suggestions please? Would Sports Cats help, less restrictive air filters, bespoke exhaust?

What would you do for a quicker and more responsive throttle?

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Hi Bibs,

The easy ones:

check throttle adjustment is correct

SportCATs or cat-free (dare I say that?)...

K&Ns or equivalent non-paper filter elements

Sports exhaust

Not so easy:

Lightened flywheel

My 0.02p

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Hi Bibs

I'm not sure if this thread is "out of use by date" but I try a small input:

Supposing that everything with the engine and its controls is working as intended (and that you don't want to throw out a lot of weight from the car), this kind of changing the "behaviour" of the engine is normally down to the maps of the ECU. They have been programmed by the factory to make the best possible compromise of low emissions, quick responses and power.

There are several functions that the factory programmers use to better the emissions, that take some of the edge away from the engine at the same time.

When you blip the throttle on an old carburettor engine, the sudden wash of petrol from the accelerator pumps sends the revs up immediately, and when you back off, the closed throttle ports cuts the revs. Of course the lighter the moving parts of the engine - including and especially the flywheel - the quicker it will react to input.

When it comes to more modern engines with managements, it's no problem to "mimic" these reactions, but the factories have chosen not to. On the contrary, there are specific parts of the programming that sends the acceleration of the engine through a smoother curve, because this is creating less emissions. The old carb engines reacted quickly, but didn't manage to burn all the petrol in the process, so pushed lots of un- and half burnt petrol out with the exhaust making a high emission.

This is maybe most noticeable on a modern car when listening to the engine note/revs as you first rev up to let's say 3k and then immediately let go the right pedal. You will often hear that the engine keeps the revs high for an instant before slowly lowering again. I have this with my "civilian car" a normal BMW E39, and the first time I wondered if the wire was sticking and started to investigate. The answer was that this is much nicer to the environment, and won't make much of a difference to the normal car driver.

Us hotheads have a different approach of course, and as you may be know I'm starting with blank sheets in my project and will have this particular item available in the back of my head when I set up the new engine and the free standing (non factory) ECU.

As I mentioned it's not difficult for a programmer / rolling road expert to set up an ECU to behave like the old carbs in this matter (and still keep the driveability / tractability of a managed engine) but he has to balance it towards the MOT and emissions control. In my case the car is from 1979 so it's an easier matter with emissions :-)

Geir

Edited by saggitarius

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Bibs,

Sports cats will give BHP but not always better throttle response. I've put original CATs back on mine as low down the back pressure must make a difference. Yes the Sports cats breath easier but to get the turbo to spool up quicker, I've found the standard cats better low down. Oh, I have a Blitz boost controller on mine which may on may not help the equation. The Blitz boost controller, you can program how quick you want the boost to come on and how long. So car feels a lot quicker without increasing top end BHP. Good for insurance too!

K&N's or Green cotton filters will help things out at intake end. I thinks this makes a little difference.

As for chips, I supply PUK to a lot of UK customers. They like dealing with somene from UK and sometimes even drop off their ECU with me. This way there's less risk of ECU going missing. As they are obsolete, most people would consider this as a big risk.

Also check your TPS using laptop and make sure your throttle cable is adjusted right and there's not a load of slack left i.e your foot is on the floor but you are only opening the throttle say 80%.

You can also strip or just lubricate the throttle linkages. On the V8, there's quite a lot of linkages and springs, all of which get stiff and clogged up over the years. After about a year of ownership on my V8, I discovered that my throttle pedal was gradually getting heavier. So I decided to spray the linkages with WD40 first then wipe the old grease of and spray some more then spray with spray grease to protect the linkage. I also tweeked the main spring a bit to make it a tad lighter.

Hope some of thie helps,

David

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Hope I'm not sounding to big headed here, but having spent 9 years creating my version of what the Sport 350 could have been. Here is my 5p worth

6 speed dog box, lsd of course geared for over 200 mph, inter-cooled & SBO valves, forged pistons, flowed, hybrid Turbo's, ecu done, 200 cell metal cats, custom silencer,  apexi boost controller, the list goes on and on

So turbo lag not really but at 3000, you have to be ready for a massive wave of trust that is with 18psi .. throttle response err yeah scary comes to mind, I just wish I was 20 years younger now.

I WILL BE AT CASTLE COMBE FOR CLUB LOTUS DAY MAY 27TH, i HOPE AS MANY OF YOU GUYS CAN BE THERE, 

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Hi Rob,

Just seen your post, only about a year after you posted it, not too bad for me. :-)

How is the car running after all the mods? In isolation which do you think have made the biggest improvement or is that not really a fair question? Mine has been off the road for a couple of years now, I need to refit the injectors but lost enthusiasm half way through. I am looking for inspiration to get moving on it again. :-)

If you have any pictures of the work in progress or the finished article I would be interested to see those and any dyno graphs for good measure.

I plan on getting her back on the road soon and am bracing myself for a whole bunch of new problems to sort out, however if they don't materialise too quickly I have always fancied investigating an after market ECU and having it mapped properly. I have a Red ECU from Marcus but feel this is often a bit rich (it used to get though cats - including metal ones - fairly regularly). Any thoughts on that? I am pretty sure it will be prohibitively expensive but there might be a market for an alternative ECU and map?? All pie in the sky at the moment, as I say I am looking for something to get excited about.

cheers

-Chris

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Hi Chris,

Long time no contact.  Glad to hear that you still have the S350 and plan to get her back to full warp-drive.

If you are prepared for going intercooled/chargecooled or even water/methanol inj.  then there is a lot more power to be had from the existing ECU. Attached is the dyno plot from an engine running optimised Lotus/EFI ECU.  This one is a forged piston, chargecooled engine with hybrid turbos and slightly larger injectors.

If not, then I would really suggest going back to the 'stock'  high torque calibration.  Unless you are looking for significantly more power, there would be no benefit is going aftermarket on the ECU.

One thing to consider in the case of the power hike, will be your clutch.  AP used to offer a custom clutch solution that could cope with over 450 ft/lb torque. Unfortunately, this service (and the parts necessary) is not longer available.  Just be cautious about creating bigger problems or failures elsewhere.

Good luck finding the motivation to get your V8 back on the road.

Cheers,

Mike S

507_BHP_dyno_run.JPG

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Hi Mike,

How are things with you? Any Esprits for you to play with?

I'm not seriously looking to modify anything in the short term, up and running is the aim at the moment. I was looking at the injectors today (I need to test them before popping them back in) and I have a question about the secondary injectors. How many O-rings should each secondary injector have. Both of mine are on the bench with just one at the fat end near the connector but I am sure they should have another one below the smaller inlet filter to stop fuel leaking past the base of the injector into the plenum. Is that correct? Don't suppose you have O-ring dimensions and specs stored in your head do you? :-D

cheers

-Chris

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Now if you would just move your hand I could see where you ordered them from.... :-)

 

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