Quote Originally Posted by shwah View Post
I don't know any specific answers, but the Rabbit GTI should make more gains than either Golf in ITB. It has the WORST exhaust manifold ever installed on a VW - swapping from the toilet bowl single outlet to the later dual outlet gives a 5hp bump on the A2. It has a lower stock compression and thus gains a bit more % wise with the .5 bump. I don't think the solid lifter head has any measureable differences from the later hydro. I would be surprised if it all added up to a 1.4 factor, but could see it being .05 more than the A2.
Chris,

I agree that the 'toilet bowl' exhaust manifold is soooo crappy, that it doesn't even make a good boat anchor. However, some differences between the A2 8v hyd. lifter motor and the A1 8v solid lifter motor (both 1.8). The A2 gets two things that help it, over the A1, see more gains when you put a better exhaust system on it. First, the A2 has a larger throttle body, so you can actually get more air into the engine, and second, it's got a higher lift cam (.400" vs. .369" for the A1). The A2 also gets a slightly longer duration (214 deg. vs 212 deg for the A1, both measured @ 0.050".

I know everybody trots out the crappy exhaust manifold, and I agree, it's a POS. But to start seeing real gains on the A1 motors, you've got to start swapping the cam and the throttle body as well.

As far as the gain from the .5 pt bump in compression, I'm not sure exactly how much you're seeing. Look at a stock JH (A1, 8.5:1) vs a stock RD (A2, 10:1). The JH makes 90 hp, and the RD makes 103 hp. The essential differences are compression, cam, and throttle body. Hard to say what makes the most contribution. Back in the day, one of the quick, cheap fixes to get some power out of a JH motor was to swap the exhaust manifold and cam from a 1.6 motor, and the t-body from either an A2 or an Audi 5k. That was said to give somewhere between 7 and 10 more hp. But keep in mind, you went from a .369" lift cam to a .405" lift cam. And again, you're back to a larger t-body, and a higher lift cam, neither of which are legal in IT. How much do you think you'll get out of that .5 pt bump in compression? 3hp? 5hp? 7hp? 10hp?

I'm sorry, but getting 30-35 hp out of a .5 pt bump in compression, a tweaked exhaust system, and a good balance & blueprint just doesn't happen w/ a JH motor. And those are the kinds of gains that are needed to justify the current spec weight.

I'm curious, have you guys ever dyno'd the motors out of the car, and in the car, just to get an idea of drive line loss? I know it's apples and oranges, and the differences are probably lost in the margin of error for the dyno, especially at these low numbers. Just curious as to what you guys think the drive line loss is.