The value of ITB's...

[BCBirk]

I'm starting to plan a few winter projects and was hoping to get some of your valued input to justify (or not) an upgrade to ITB's.

 

My ZX-3 zetec is managed by an SDS ECU and has a few mods including:

- stage II cams + gears

- mild porting

- mild shave (don't know amount nor compression ratio)

 

After spending way too much time tweeking FI maps, the powerband is now very smooth and tractable on the street and pulls well to about 6800 rpm on the track. I can't, however, quite keep up with the 'big boys' on the relatively short back straights of my local track --my ultimate goal...

 

Any ideas as to how much additional power a set of Jenvy's or AT Power ITB's would produce on the zetec?

 

I'm currently using manifold pressure as my tuning base which has been effective and I'm assuming that I'd need to change over to throttle position tuning. Any comments on drivablility using TP sensing?

 

Cheers, -Paul

[rzempel]

Which throttle body are you using now? If you are still running that little stock throttle body, you may simply be running out of air at 6800. I changed mine from the tiny Ford one to a 65mm C-F-M unit (I have a 72mm Ford Racing TB, but it's too big to fit the stock manifold) mounted to a lightly modified Contour plastic manifold. I have 174 hp at the rear wheels, and pull hard to 8,000. I wouldn't expect to see much (if any) improvement over that with ITBs.

[BCBirk]

I think I'd be happy (for now) with 174 wheel HP. I've not had mine on a dyno, but a g-tech unit estimated 156 HP, for what it's worth.

 

A bigger TB would be an easy upgrade, and the only reason I havn't gone that route yet was a test (below) I came across on the SDS site.

 

" Rev the engine out at full throttle and note the MAP. If the TB is too small, you will see the vacuum start to increase at higher rpm. Ideally, you should not see any higher vacuum at high rpm as what the MAP sensor reads with the engine not running. If you see -2 inches with the engine stopped and -4 inches at full throttle and 5000+ rpm, the throttle body is restricting airflow and hp."

[SkinnyG]

I converted my 4AGE Locost from "factory" EFI (I had made my own plenum manifold, deleting the TVIS) to ITB's using GSXR600's, Megasquirt and EDIS-4.

 

The ITB's were noticeably more torquey in the mid range. Top-end felt about the same, but this is my butt-dyno talking.

 

In datalogging, there are numerous points where my MAP reading with the ITB's (I never measured the stock system) were reading ~higher~ than atmospheric.

 

ITB's must be tuned off the TPS, not the MAP sensor. It will also be fueled completely different than what you have now, so you will be completely re-mapping the engine. ITB's can be made to work very well and very driveable, but wee movements of the throttle can give you BIG changes in RPM. I find it harder to drive smooth, but you get used to it.

 

Also, at full throttle, the ITB's are louder than my exhaust - something you may have to shield for track days with a dB limit.

[BCBirk]

ITB's louder than exhaust? Now I'm really interested!