I just came across this auction for a set of GT Cams. As to how to verify that they are GT cams... good luck

Regards,
Abdul

 

Hmmmmmm....

 

I'm sure they are. Phil Threshie from 928 Developments is selling them.

 

GT cams could be the cool ticket for an in car S4 upgrade: Do cams alone distinguish the GT engine, or are there other head/ECU/etc. pieces required to achieve a signifigant improvement in the S4 eng.? -can anyone quantify the performance of this as an upgrade?
Secondly, would any benifit achieved be usable in auto vs. manuel trans cars - or were the benifits of the GT tailored uniquely for the 5-sp?

 

There is different engine management for the GT compared to the S4. The GT cams may offer a slight increase in performance on an S4, but don't think the full potential would be there without the GT ECUs.

 

MikeN

I believe that to be not true at least with respect to the LH, the EZK may have some differences, havn't checked. Fuel maps are the same for all 87-91 MY's.

Chris

 

If I'm not mistaken the LH mapping and EZK are booth different then the stock S4, with the '89 GT and '88 Club Sport being different still. Looking at the part numbers the manual trans versions of LH/EZK are different part numbers then the S4 auto trans cars.

 

My '88 S4 A/T had a GT LH brain in it when I got it. No difference in performance between it and the S4 brain that it now has.

 

Interesting.......so is it a case of same unit, different part numbers......or are there real differences inside for the manual trans vs. auto trans versions?

 

Yes there are differences, like rpm limit and idle.

http://www.928s4.com/lh/lh_homepage.htm

I added some graphs recently showing the fuel maps.

Chris

 

Thanks Chris, again interesting. Brings up a point then.......the GT has a higher idle for use with the more "wild" cams. So if you stick GT cams in an S4 with lower idle speed......would there be (if any) side effects? Most likely just some low vacuum problems......but I wonder if any other driveability issues would crop up......

 

Even though the GT cams are considered 'performance' camshafts for the 928, they nonetheless have extremely mild timing and lift numbers partly for emission considerations one would think.

However, since the GT cams do have a slightly more aggressive grind than the S4's, maybe at worse, the idle may not be as smooth as the S4 at the S4's lower idle speed.

 

It's been said in other threads in the past that the GT has a real 10:1 compression ratio, where the S4 compression ratio that's usually a little lower, but may go up to 10:1. The GT is also supposed to have different heads, with some minor porting or something. Those factors may very well have something to do with that extra 10hp that the GT is rated at too, and not just the different cams.

 

From what I have seen in dyno results and seat of the pants experience, the "10hp" difference is a bunch of crap........to me it feels more in the 20 - 25 range when at full boil.........

 

Garth

I think John Speake JDSporsche has a full set of chips now '87-'95 for all models, so can supply the chips to convert your ECU's to any model, eg.CS/SE, GT etc

MikeN

The CS/SE actually had 2 (early & late) different ECU's (which do perform differently in the same car) & the '89 CS had a '89 GT ECU

SteveM928

The '88 CS/SE engine (hand built by the motorsport division) had the same pistons as a '87 S4 when we had the 2 engines apart at the same time, The GT heads had no porting, just the intake port slightly machined at the intake face, the '90/'91 S4's also had this machining, so the heads were the same as the GT's, but with no advertised bhp increase.