First time posting, but a long time visitor

I have a 07 SCREW roush IC SC f-150, its lifted 6" with 35s, was wondering what the increase of rwhp would be from swapping my gears from the stock 3.73 to a 4.56?

Any perdictions?

 

probably no increase in power, it just corrects the power band and the way it is put down to the pavement

Have any mods done to the kit? tune, exhaust, pulley upgrade?

 

I hava a custom tune done by Mike Troyer, dynatech long tube headers, and MBRP SIDO exhaust...

I appreciate the info though

 

I have same tires and lift and also went to 4.56 from 3.73 but I wished I had went to 4.88. The 4.56 brought the truck to life so it was a good move for me. At 70mph I tach around 2100.

 

What HP do you have now with the Roush?

 

X2


But i also have a blower like OP, but im running the magancharger

 

I'm at 360 rwhp / 430 ft/lbs tq running at 8.5psi, I have a feeling I could make more, but Troyer does put heavy emphasis on engine saftey when tuning.

 

Thanks

 

Dont the larger/heavier 4.56 gears actually lower RWHP numbers vs. a smaller 3.73 R&P?

 

they wil help spare the transmission and help the truck get out of it's own way

 

Those heavy tires are costing you power at the wheels, in addition to a less than optimal RPM to speed ratio on the pavement. The gears will help with the latter, but not the former. My truck is putting down north of 400 RWHP when the weather is co-operative.

 

believe it or not going to a lower gear ratio like 373 to 488 you will lose RWHP. and no i'm not gonna explain the physics involved cause i'm lazy!

 

I do believe the wheel and tire weight alone from a 35" tire is killing RWHP, but gears i am not to sure. i make close to 400 rwhp with 35" muds, 20's and 4.56 gears on about 9 lbs..

I know there are others making more with same boost levels but they arnt rolling on a wheel and tire combo of 130lbs.. So thats what i would account the HP lose from.

 

I don't believe you will get more horsepower, only more torque and more quickly. I believe if I remember right you will actually lose about 10% in horsepower, but don't quote me on that.

 

yes you are right since i can't find the post i'll try to give the basics.... your engine HP is rated from the crankshaft, which is a 1 to 1 ratio, following me, your trans changes this ratio from 1st-3rd, 3rd gear is a 1-1 (in 4r70w at least) then you come to the final drive ratio or rear end. (lets use mine as an example)
3.55 to 1 ratio. it's a much lower ratio than 1-1. this is where most of the power loss do to drivetrain comes from, in theory if you had a 1-1 ratio throwout the entire drive train (including tire size) you would have the same RWHP as you do at the crank. this is one reason when you go to the dyno they do the run in third gear. it's 1-1.

to the OP since you have massive tire yes gears i will help, big time however you won't see any HP the only to gain power is by adding air or fuel.

hope this helps.