whos running an iacv on 16v with itb's... need opinions

[levincoupe]

Im in the process of converting from carbs to efi with itb's. I have a vipec v88 ecu and the plan is to hopefully have a really good cold start idle operating in closed loop. Coming off my t3 manifold i have 4mm pneumatic push on fittings which i intent on running equal length hoses to a small manifold which has a 6 wire 1jz stepper type iacv mounted onto it. Also coming off the vacuum manifold will be my vacuum source for my booster. I would like this setup to only be used for cold starts and be closed when the engine is warm idling via the bleed screws on the throttles. I am not going to be using a map sensor for tuning. This setup seems to work in my head but any feedback, opinions or criticism would be greatly appreciated. Cheers, Trent

[ill-minded]

Sounds fine to me. Not being familiar with the Vipecs, I've got no idea on how the ISCV would be wired, but given it's a high-end ECU, it should handle it without issue. Not using the MAP sensor for fuel load eliminates any of the issues that you would have had. It'll just take a bit of fiddling with the idle speed control settings when you get it up and running to get it to idle nicely when cold. The issue there is that you can only do that when it's cold, so every day, just fiddle with the settings until you get something you're happy with.

[Javal]

One concern i would have, and i may be interpreting your proposed setup wrong, is that if you have an iscv bleeding air into a common chamber to bring the idle up - the same place where you're taking your brake booster vacuum from - is that when the iscv is open, you will have very poor vacuum in that chamber to provide the booster, as opening the iscv will bring the chambers' pressue back to near atmospheric.

What i would do - ditch the iscv and just run a coldstart on your ecu. Low coolant temp = small increase in injection time.

Edit: why don't you look in to retaining whatever method is used to bring the idle up on a normal st20v? Or is the elaborate vacuum distribution / control setup deleted when fitting quads to the t3 adaptor? Because if it's just an electronically controlled vacuum solenoid to a idle-up diaphragm (it probably isn't, but wouldn't it be nice?) then you might as well retain it.

After i've said all of that, i know of multiple cars running bt20v quads which have a fuel-only coldstart enrichment setup.

And you should definitely run a MAP sensor, you will be able to achieve massive drivability improvements if you can tune it knowing manifold pressure. RPMxTPS is great for racing, but as you stated you want it to idle well so i assume drivability is on the cards.

[levincoupe]

Thanks for your input. Thats exactly what i was looking for. Javal the factory vacuum distribution manifold thing is deleted by using the t3 manifold. The reason i was looking into running the iscv is because i was unsure how it would idle with just fuel enrichment when cold as ive never had itb's before and im not real keen on sitting in my car with my foot on the throttle until its warm and idles by itself. I should of added that i am running 272 degree toda cams on a ported smallport so unsure if it will produce enough vacuum to tune with a map. I dont think the lift is massive because its still got shim over bucket setup but i can try with map. I will be also running an iat sensor. Javal i understand your comment about not having enough vacuum for the brake boosted thats why im proposing to just use iacv for cold starts. Im not familiar with tuning ecu's but with the idle control running in closed loop i would imagine the ecu would have a target rpm and actual rpm and just adjust the stepper automatically. Thanks again for your help and if you can think of anything else please keep the comments coming. Cheers, Trent

[SamsTA22]

I'm not sure if there is an option that will turn off idle control after the engine has warmed up. You may have to set it up as an open loop control where it just has the stepper motor location mapped against coolant temperature, with it set to fully closed after it's warm.

[ill-minded]

I don't think you'll lose an appreciable amount of vacuum in the balance tank for the brake booster, but honestly, it'll vary between setups so you'll probably just have to test it. For example, whereas the brake booster on my Daihatsu runs off a single runner (which isn't linked to the other two at all) and has no issues, you may find otherwise with your setup. Another simple setup you could use would be a solenoid type on-off valve.

Also, a mate of mine has an NA6 MX-5 with silvertop throttles on a T3 manifold with hoses from each runner going into a balance tank and used as the brake booster source and the MAP sensor hose. It also has cams and has had porting done. I've driven his car and it felt fine to drive. From what I gather, the brake booster will "charge" under decel when there's more vacuum in the intake most of the times, but even at idle, I think there was enough vacuum to maintain booster function. On a side note, his car does run alpha-N (TPS only for fuel load) and it felt better to drive than my Celica, haha. Not saying that the MAP sensor is useless, but you can still get a decent streetable tune in certain applications. You may be able to have a blended fuel map which incorporates both MAP for lower load sections and TPS for higher load, but once again, I'm not too well versed in ViPecs.