I ordered a 3" pulley today for my Whipple S/C. I dynoed the truck at 365/395 with the 3 7/8" pulley pushing 8psi and the stock exhuast. Anybody got an idea of what I should be getting with the new pulley with the Dynatech LT's and 3" duals? Of course, I'll have it custom tuned again when the pulley is on it and I'll post the results.

 

Probably close to 400rwhp

 

For my sake, I hope you are wrong. That's only a 36hp increase with the addition of LT headers, 3" dual exhuast, and 3 more lbs. of boost. That's a lot of money invested for that little of a gain.

 

I think youll be higher w/o a doubt.Post up how it goes

 

I'd bet more than a 36 hp increase with new exhaust and tuning on a 3 valve. How do you know that it will be 11 psi? Simple math says 25% more revolutions to the blower, which would be 10 psi if you start at 8 psi. Is the increase actually linear? just curiosity

 

According to Whipple, 1/8" decrease in diameter equals 1 lb. of boost increase. The new pulley is supposedly good for 3 lbs. Now, I don't think I'll be getting near 11psi because I lost boost pressure when the headers and exhaust went on. So, I'm guessing that it will be around 9-10 lbs. I'm hoping with the efans, headers, exhaust, smaller pulley, and the new tune, I'll be getting a minimum of 425 rwhp. The only thing I know for sure is, first of next week, I'll have the hard data.

 

Sorry, I think the 1/8" = 1 psi is BS. I recently changed from a 3.75 to 4.25 on my Paxton (the only change), and saw 11 psi go down to 9 psi on the gauge. If that formula worked I would have seen 5 psi?
I know , different blower different truck. Good luck.

 

edit

 

All I know is what I was told, but next week I'll do a baseline run, get a boost reading, put the smaller pulley on, then tune it. Then we'll all know.

 

It's different for each blower kit based off the characteristics of the blower and the drive ratio (crank pulley size to SC pulley size). Magnuson kits for the GM stuff (Truck, Corvette, GTO CTS-V, etc) usually give you ~0.75lbs for each 0.1" change in pulley on a completely stock vehicle. Headers, cats and ported heads will also effect the boost gains seen.

TG

 

If you aim low and hit high, you are happy. If you aim high and it is hot or bad weather and the power is lower than expected you are disappointed. Just trying to help with happiness.

 

I agree. I think I'm being conservative looking for 425 hp. I'm guessing with the efans, headers, and exhuast, I probably at 400hp now. When I add 3 more psi, I would hope that would be worth another 25 or so hp. Seems like I read that 1 lb. is equal to about 10 hp. I maybe wrong.

 

After watching Whipple work on my truck, here are a few thoughts...

I went from the stock 3&7/8" pully to a 3&1/8" pully and saw about 2 extra pounds of boost. This is without headers. On the dyno I was around 9.5lbs of boost, and when we tossed on the 3" pully, I was right at 10. This is a bit lower than street running because of the lack of air flow into the engine while sitting on the dyno. So you can probably expect with 3/4" smaller to gain 2 pounds of boost, so for you with 7/8" smaller pully, you might see 2 and change. With the headers, you might lose a pound of boost, so you will probably be around 9lbs plus change.

As for your horse power numbers, you should be in the 400 range, but I saw how those numbers are affected by the quality of the tune. Getting you those extra horses will solely be up to the tuner, and how much fuel he can deliver while keeping your engine safe. Whipple worked on my tune for hours upon hours, datalogging and sending the information to Ford Racing on the east coast. They would compile the data, send a new tune, and he would tell us before we dyno'd with the new tune the horsepower and torque we would expect. He was usually within 5 horsepower and torque with his estimates. We would run a touch lean or rich, send him the info and he would clean it up. Throughout the day it got hotter and hotter, as did the truck, and we got our highest numbers at the end of the day with a worked out truck running miles on the dyno and 99 degree smoggy heat.

We opted to go with the 3&1/8" pully because we drew so many horses with it. In cooler temps, I'm easily closer to the 450/500 range, which is plenty high unless I plan to start rebuilding the lower end. We did run a dyno run with the 3" pully and it was sick, but I just wouldn't trust it in the long term. I might order one to throw on for a drag race or two though.

Good luck with it. I hope your tuner gives you a good, safe tune. Make sure to stop by the computer between burnouts and post the numbers for us.

 

Thanks for the insight. I definately post the results next week.

 

Are you talking about your upper or lower pulley? Your boost pressure is the ratio of the crank pulley to the pulley on your Vortech. If you want bigger numbers, get a bigger pulley on your crank, but do it safely. You also might want to look into a heads/cam setup along with a fuel system before you start upping your boost, so you give your motor some insurance that it can supply your new found power just fine with out hurting it.