What should i do next??

Nur_Stang · 07-11-2006

Hey guys I recently purchased a 04 cobra (with 3,500 miles on it!!!) about 2 months ago. Since than I have put on a UPR X-pipe and flowmaster thunder series cat back. Now I am a little confused on what to do next. I know that pulley's are the easiest way to increase the horsepower but i don't know which ones to get. The main thing is I heard that if i do upper pulleys I will end up having belt slip, going through belts, etc.. Than a ex cobra owner buddy of mine told me if i got like a 8lb lower pulley kit with the idler pulley's than i would have the same boost as the 2.8 upper pulleys but without belt slippage, is this correct or am i misunderstanding?? Any help or guide in the direction of how i should pursue modding my cobra would be greatly appreciated.

BlueStreak03 · 07-11-2006

I don't think belt slip really becomes a problem if you only drop down a little bit on pulley size. If you try pushing monster boost then yeah you're going to have slippage. Only jumping up 4psi or so shouldn't give you a problem though.

Nur_Stang · 07-11-2006

Well i have been looking at rpm-outlet.com and I was unsure if i should get the lower crank pulley or upper pulley. They have three different sizes which will produce 2, 4, 6, or 8 additional lbs of boost. There all the same price (Just pully size is different) but i dont know which one to get.

BlueStreak03 · 07-11-2006

Well here's the pros and cons of each. Upper pulley swaps are easier typically, and you're not messing around with the end of your crankshaft (big bonus in my book). Downside of an upper pulley swap is you are reducing the amount of surface area that the belt has to make contact with so if you try to go too far with the boost, you get slip. Lower pulley swaps are harder and more time consuming. Up side is that while you're still reducing the amount of surface area, there's still a lot there, less chance of slip.

What I recommend is that if you are SURE you only want a small amount of extra boost, do a lower pulley for now. If you find in the future that you want still more, do an upper pulley swap. Real danger lies in doing too many swaps on the lower pulley as you can fairly easily strip out the threads on the inside of your crankshaft.

Nur_Stang · 07-12-2006

Well i have two mustangs, so this is not my daily driving car. I would like to make it have as much horspower as possible BUT remain safe. On this mustang I am not going to do the work myself but my plan was, when i figure out what kind whether upper or lower and the lbs of boost i want, i was going to take my car and have J&J motorsports put the pulleys on and also have installed a new tb and cai at the same time. After they install the pulleys, throttle boddy, and cai, i was of course going to have them custom dyno tune it. Their tune package they do there also includes a predator.

9Venom9 · 07-12-2006

Change your idler pulleys to 100mm, there 90mm stock, that will also help, if your worried about belt slip but want to swap out your upper pulley go here, they make some awsome pulleys: http://www.billetflow.com/ grip style to help belt slip. Also look at there IRS brace to help protect your pumpkin from exploding under heavy load.

JD04COBRA · 07-16-2006

I have the 2.8 upper pulley on my 04 cobra. When I did the pulley swap I also went with the 100mm idlers and I also added the aux. idler. I don't have any belt slippage. I also have the 74 inch belt. The belt it a little bit of a pain to get on but, like I said I don't have any belt slip.