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Esprit V8 Modifications

Esprit V8 Modifications



Original Poster:

16 posts

188 months

Friday 3rd May 2002
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3,035 posts

188 months


267 posts

190 months

Friday 3rd May 2002
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Have you e-mailed Johan directly?

I've been curious about the cat issue myself. My mechanic had a US Sport 350 (which is really just the wheels, brakes, and front bar I believe - no special bodywork) with no cats in his shop. He said the check engine light was on all the time. That can't be good.


179 posts

189 months

Saturday 4th May 2002
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Mike, what modifications have you made to your v8?


179 posts

189 months

Saturday 4th May 2002
quotequote all
Mike, what modifications have you made to your v8?


490 posts

195 months

Saturday 4th May 2002
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Well, I'll take a shot at the questions... I'm only doing minor stuff on my V8, but have at least looked through the Lotus shop manual which explains and details the 918 engine quite well. So, not claiming to be an expert.....:

1) Why would you want to use two seperate dump valves, when a single shared one would allow the boost pressures to equalize?

- According the manual, the turbos are plumbed cross-fed from the exahust drive and the intake pump from one bank driving the opposite bank and vica-versa. The dual butterfly throttle has a bore between them specifically for balancing of the intake pressures between banks. When you consider the cross-feed setup, they are isolated from each other, hence you are better off using seperate BOVs.

2) If you remove the cat's, how do you get around the ECU safety features. I think that the ECU is programmed to 'return to default value' if the sensor reading is the same either side of the cat?

- IMHO, if you plan to remove the CATs, then I would "assume" (hate to use that word, but sometimes it just fits) you want to go racing. For street use, I'd prefer to keep it legal in the sense of emissions, etc. The Race ECU from Lotus may allow this without turning on the MIL. Maybe someone who has the Race ECU sans CATs can comment. But to each his/her own.

3) At what point do you need to consider larger injectors? If the duty cycle of the existing ones is <80% on maximum boost (1.2 bar), why would you go to bigger ones?

- Logically, if you increase boost, you increase fuel quantity to maintain the proper mixture, mainly NOT too lean. Lotus seem to think that the stock injectors are fine with the Race ECU which increases the boost and puts you somewhere around 425BHP.

Now, adding Intercoolers changes this. As the V8 is NOT intercooled as supplied by Lotus, intake air temperatures are going to be a fair amount higher as you increase boost pressure. So, it's still hot (and hotter) air, and as a result it is lower density despite the boost pressure. Adding intercoolers drops the intake air temperature so now at the same boot pressure you have a denser charge of air. As a result, you "may" need larger fuel injectors to compensate and be able to satisfy the increased need for fuel to maintain the proper mixture. As for the duty-cycle of the injectors, there is probably a limit built-in to the ECU hardware (and programming) which could also nessecitate the need for higher flow injectors.

4) What about transmission oil cooling?

- Yea, that would be nice. I read on a forum that someone else was either looking for one or had/was making one. Can't help here, but changing the gearbox lube more frequently will help. Right now my plan is to change it along with the engine oil.

5) How do you seal off the ECU and boost solenoid area when fitting cone type air filters?

- I think the website mentioned has some more details on that. However, I opted for a set of ITG Profilters. These are oiled-foam and have a nice stainless wire mesh section to prevent "suck-in". They are not as "musical" as the K&Ns but easy to install and they make a difference. I also reset the ECU (yank fuse 5 for 30 minutes) to force a new map.

Hope this helps a little....

Regards, KM
2000 V8


23 posts

204 months

Wednesday 8th May 2002
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Your answer was very good. Here are some added info:

1. On the GT1 esprit there where another plendum made out of sheet aluminum. The reason for this is that the stock plendum is a little restrictive, but it also fits nicely. The made plendum is much taller. Also the made plendum does not separate the cylinder sides. You also have to consider that lotus used only 1 large turbo in the beginning. At later stages I don't know if they used a twin setup. Today the GT1 cars are GT2 cars and are for sale.

You can proof that you need both dump valves by just disabling one intake side. With an analyzer you will see that one engine 1/2 would suffer more than the other It will not be balanced!!!. So unless you want to remake your plendum use 2 dump valves.

2. If you remove both cats and if you reinstall all 4 O2 sensors. Your MIL will not turn on. I drove my car 6 month w/o cats and no MIL light with a standard ECU. I have done 2 other cars like mine and they have no MIL light turn on. But maybe I am special or my secondary O2 sensors where off to begin with . If you have a problem, a couple of resistors could perform some magic for you.

3. To begin with, the Lotus injectors are cheap crap. (bad patterns, plugs easily ETC ETC ETC). You would need them only after reflowing your turbos if you want max performance (The ECU will balance itself to the injectors). After some testing my injector duty cycle where much higher than 80% at 1 bar. Besides maximum boost is .65 bar with the stock ECU. Now you add reflowed turbos, cams, intercooling, exhaust, porting, ECU (modified race), and more fuel is necessary.

4. Transmission cooling is definitely necessary if you are racing the renault. However, the biggest trouble with the transmission is its design. It has very long shafts. If you put a lot of power on the 2nd gear, the shaft would bend and you will wear the gears on the edges, which in terms will strip. I have friends racing Trophys with renault 21 transmissions and they have to rebuild them after every race. I am in the process to install a G50 transmission instead.
Lew installed a transmission cooler onto his car. I will publish the installation on my website this month. Also the cooler is VERY loud.

5. You just make a box for it. Its not on the website yet.

Another couple of things to consider. After you do any major mods to your engine, change your main bearings. They are way to thin to handle much power and will fail quickly. The stock bearing are using a VP1A ("A" denotes a 14 micron lead indium overlay) bearing and the racing lotuses are using a VP2C bearing ("C" denotes a 20 micron lead indium overlay)

Also you may want to relocate your knock sensor.

Regarding body panels: Where did you find them. The only place I knew about is in Belgium and they are not making them anymore.

If you are interested in performance mods join:


it a very lotus heavy group.

The racing ECU "red" has only slightly modified boost and fuel mapping. We are presently rewriting some of its code.