I have a stock motor with a comptech s/c and stock pulley. I have an ap1 by the way. I want to upgrade my pulley to a smaller one but need to know if i can do so without changing the injectors or needing some type of engine management. The science of speed recommends different injectors and ems for even the 4" pulley which is suppose to be 8psi on the ap1 but a couple of people said it would be fine with my stock setup. What do you guys think. Do you think ill be fine?

 

Best bet is to check around the F/I forum. I believe with the comptech you can go to a 7psi pulley without having to get injectors or management. Anythign higher than that you need injectors and some sort of management. I would also suggest upgrading you oil jet bolts as well if you have not already done so.

 

Thanks for the info!!

 

I'm running an AP2 pulley, it's somewhere around 6-6.5psi. I picked up 24whp between the pulley swap and a testpipe. You'll need to raise the fuel pressure on the fuel pressure regulator and get it dyno'd or install a wideband to make sure your fuel pressures are safe. I found that in order to run safe AFR's up top that I had to run the car really rich down low. I ended up buying a VAFC to lean out the car a below 6000rpms, just to keep the stock drivability.

 

But the stock Ap1 pully makes 7psi stock, I'm confused why would you switch to a Ap2 pully? Didn't know they were different either.

 

An AP2 doesn't rev as high as an AP1, in order for them to generate similar boost the AP2 must use a smaller pulley. Putting that smaller pulley on a motor that spins faster will generate more boost. A stock comptech kit + aftercooler on an AP1 will make about 5psi. With the AP2 pulley on an AP1 it will make about 6.5psi.

These are the numbers I got, on my car, with a comptech kit, with each respective pulley on the car. I made 301hp, 190tq with the AP1 pulley and 325hp, 201tq with the AP2 pulley. I took the pulleys off and looked at them next to eachother and saw that the AP2 was smaller, even took some pictures, guess I'll have to dig them up. I'm not sure where you're getting your info, but I'm pretty sure I'm right on this one...

 

[QUOTE=scottrunsxc,May 13 2008, 03:19 PM]I'm not sure where you're getting your info, but I'm pretty sure I'm right on this one...

 

[QUOTE=scottrunsxc,May 13 2008, 12:19 PM] An AP2 doesn't rev as high as an AP1, in order for them to generate similar boost the AP2 must use a smaller pulley.

 

So in order to stay stock as far as EMS and Fuel injectors i should just go with the ap2 pulley and not the 4" is that what im hearing or seeing i guess

 

How do you raise the fuel pressure on the fpr? Do you adjust it on top by loosnening the nut and turning that shaft? Looks like an allen bolt if I remember correctly. Thankfully I have a wideband so I should get some feedback as to what my adjustments have done.

I read that the after cooler was only suppose to drop the psilevel .5 to 6.5 and that the colder air more then well made up for the .5 loss. Is this just not true? Are some Ap1 guys experiencing 6-6.5 psi on the stock 7psi pulley? Maybe I will get lucky. If some of the fittings aren't titened properly couldn't you lose some? I noticed some of these durring instalation were a pita to get on and on properly. I was also told that belt tention needs to be very tight and that it is easly to lose some boost this way as well.