Could someone tell me approximately how much boost the comptech runs without any upgrades?

 

Mine is showing 6.1 pounds peak boost on a Mustang dyno with the stock pulley. On the same dyno, KAMcDonald got 6.9 with the 4.375" pulley (give or take a .1 of a pound).

-YS

 

So if the stock pulley is running about 6 pound of boost.......could anyone tell me approximately what size pulley i would need to run 8-9 pounds of boost and where i can order it?
thanks

James

 

1RandyC has experimented with a bunch of pulleys, but his boost is through an IC, so unless we know how much the drop is, it is tough to say. If you do very crude math, KAMcDonald's pulley was .2" smaller and it netted him almost a pound. Perhaps another .2" drop from there would be another pound (or more). PM KAMcDonald for the place he got the pulleys. I know he has a 3.875" pulley too, but I would guess that is going to make one heck of a lot of boost. If they made something in the 4.1" range, I would guess that would get you pretty close.

-YS

 

Using a spreadsheet I was calculating from boost levels from a dyno run with the stock pulley, i was looking at the 4.375 giving 6.37 lbs, 3.875 giving 7.5 ang 3.5 giving 8.5.

i purchased the 4.375 and 3.875 and setup a new dyno session, but when using the 4.375 we ended up getting a max boost of 6.78. after some discussion as to why the offset, we decided not to try the 3.875 since i do not have an aftercooler.

the actual run provided a 1 lb increase with a 2/10ths inch reduction in pulley diameter. this indicated that the 3.875 pulley would more likely provide a minimum of 3.5 lbs more boost (7/10ths smaller than stock) and probably more.

check out the end of this thread for more details and a dyno comparison between the pulleys 4.575 and 4.375 pulley. start of thread gives place they were purchased from.

https://www.s2ki.com/forums/showthread.phps...&threadid=58943

if they custom make the sizes, i would say from latest test that a 4.175 would give about 8 lbs, and a 4.0 would be around 9 lbs.

1RandyC has had all kinds of pulleys, last i heard he was at 2.6 inches, not sure if he has been keeping track of boost levels or just keeps going smaller until the engine blows up.

keith

 

Thanks a ton keith. Very helpful information.....i just got my comptech and i want to raise boost, but until they make their intercooler, or i have one custom made, i don't want to go above 8 or 9 psi.
Thanks again

James

 

What? No thanks for me? I feel like a piece of shoe leather

-YS

 

I'm sorry THANK YOU!! you were the first to respond and give some information. it is greatly appreciated

 

[QUOTE]Originally posted by jlangton
[B]I'm sorry

 

Approaching 8psi+ level would mean you need to pump some serious money into making your car run safe.
You are going to run of your stock fuel injectors capacity after Vtec and you will run lean.
My guess on the pulley size to achieve 8psi should be around 3.8-4inches. With simlilar custom intercooler setup as mine would need 3.4-3.5inch pulley to achieve the 8psi.
You can also making the crank pulley bigger but with the S2000 water pump running too closely it isn't possible.

Anything less than 3.4 inch seems to create belt slip. If you are doing anything less than that you would probably need another idler pulley to keep the belt wrap decent around the small pulley. As others have said I have 2.6 inch now and prior to that 3.1 inch and belt slip is just horrible after just short period of initial tightening and I haven't done anything yet to correct that.
Surprisingly the Paxton NOVI 1000 blower is still intact eventhough the maximum impeller speed provided is much further surpassed even when I had 3.4 inch pulley and stock internals still taking like a champ.
Just for the reference with current 2.6 pulley I am pumping about 4psi at mere 4K rpm.

You are always free to experiment like I have but please be careful with the a/f ratio after the pulley swap. Unfortunately my longing to fix my a/f issue has come to a halt. But there are several members working to resolve the fuel modification including management unit affordably and effectively. So hopely those pioneers soon step out and share the information.

Good Luck!

PS: Hey Yellw(Pete) how is it going with your modification on intake?
It would be wise to modify intake to achieve better air pumping and I believe like Pete has that the current Comptech set-up seems bit too restrictive and would benefit greatlyt if we improve the air flow with better filter and intake set-up.