Just a guise ,but ,you don't usually see a 60hp difference with 2#s of boost.
I would say the other 30 or 40 is from the tune.

 

I also was surprised, but those were the numbers! The same tuner did both the 8 psi tune and the upgrade, and my 8 psi numbers were typical for a good Whipple tune at that boost (394/445). Perhaps it was the 39# Cobra injectors that went in with that tune, but one would think that would show the most at higher rpm's.... A/F ratios were the same at 11.2/1. Nothing else changed between those two setups. If the previous tune was more "conservative", my tuner didn't mention it.

I'll stress that this increase was in mid-band, with the increase at 5000+ rpm being more what you'd expect (~30HP).

Interesting. I'm just glad it ran a whole lot better!

Lee

 

30-60rwhp/tq isn't at all unlikely. You figure at 3000 rpm a 8 psi setup probably is making 4-5psi. Add bigger injectors which alone can add more torque and power with a better tune and not to mention a 10 psi pulley at 3000 rpm probably makes 7-8 psi its very possible. If you say each psi of boost is 20 rwhp, then 4 psi at 3000 rpm to 7psi at 3000 rpm would be 60 rwhp in itself at that rpm. Now at 5200 rpm a 2 psi increase from 8 to 10 will be 30-40 rwhp. But the huge gap in psi during low rpm boost makes a massive increase in power.

 

Also during a pull on the street the rpms go by so quick it would be hard to map it out, but a 3rd gear pull to 130mph you would see say

8psi set up:
1000 rpm 2psi
2000 rpm 3.5 psi
3000 rpm 4.5 psi
4000 rpm 7 psi
4300 rpm+ 8 psi

Vs 10 psi
1000 rpm 3psi
2000 rpm 5 psi
3000 rpm 7 psi
4000 rpm 9 psi
4300 rpm+ 10psi

If every psi is 20rwhp in theory if you graphed my little example you'd get a huge midrange boost.

 

If you were talking about a centrifugal blower then I would agree.
But a Whipple twin-screw is making full boost by 2000 RPMs.

I can run a 4# difference in boost.(that's 12 up to 16 PSI) with a 4# pulley and the same tune, and it's only a 40RWHP difference on the dyno.

Phil

 

Well that sounds about right Phil. I remember reading about 15 years ago and article on boost in HotRod mag that said each pound of boost adds roughly 10hp. But with that being said a standard 8psi kit should only add around 80hp. However even the weakest numbers on 8psi are still 370rwhp and up to 400rwhp. That's 150-180 more rwhp than stock (figuring an average stock rwhp of 220) and 15-18rwhp per lb of boost.

I too experienced the increased midrange performance. My truck will push you to the seat around 3000rpm up at half to three quarter throttle. I love it to cause it doesn't feel like I'm ragging on the truck. I have a theory about this mid range increase. Leaner is meaner and during these half to three quarter throttle pulls full boost is achieved while the af'a are in the mid to low 12's and tracking toward high 11's not 11.2 as experienced at WOT. This leaner burn could easily account for the power increase.

 

I'm evidence of that!:o