Rear end ratio

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i have a '69 mustang fastback and i am putting a 408ci small block stroker. it puts out 525 horsepower and 500 foot pound of torque. it is attached to a tremmec t-56 6-speed manual transmition. should i keep the rear-end the stock 3.70 or change it to a 4.11 or 4.54 rear end

posted by  markman

Would help if you could tell us what the cars main purpose would be. Is it a driver, a drag car, track car, built for top speeds ? Is it a 9inch ear ? I think that realistic choice for evryday use would be the ratio you haven't mentioned the 3.89's. For track use the steeper the better, with that tremec 6-spd you can pretty much run that 4.54 and still have a decent rpm at highway speeds. Sounds like this stang's going to be a beast !!!!! :thumbs: :thumbs:

posted by  ode94

it is going to be a driver, and a drag car. not full blown but something that i can go to the strip with and run some decent times. it is not going to be on the freeway much so top end isnt much of a concern but i would still like it to hit in the 150s if not higher

posted by  markman

Alot of guy's with tremec t56's in newer cars are running the 411's with great highway manners/gas mileage. The 6 gears make all the differnce for your application in my opinion. Go with the 411's cause with a 6spd tranny you should get highway compatibility and still get good launches at the track. :wink2:

posted by  ode94

Shouldn't you be looking at your max torque rpms and work from there?

posted by  Wally

the engine has roller rockers and roller lifters
the redline it somewhere around 10,000 rpm!!

posted by  markman

How nice, but redline is not your max torque. I take it you have read a site somewhere that says you should select gears based on redline? In which case the gear ratios are all evenly spaced?

posted by  Wally

Max tourqe is at 7200 rpms

posted by  markman

I'll still stick with the 4.11's, as far as the stereo, just put enough so you can listen to some tunes. Your gonna be too busy listening to that lumpy exhaust note to care about loud music !!!!!!!!! :mrgreen: :mrgreen:

posted by  ode94

I wanna see a dyno plot of a Ford small block with a stroker kit that makes max torque at 7200 rpm! That's gotta be one magic engine!


:banghead:

posted by  ChrisV

I was thinking the same thing. :roll:

posted by  fc7gtx

I am so amazed at some of the 'so called specs' of said motor that I had to run a dyno test on my computer to see if I could duplicate any of this info.

Here's my 'test bed engine'

406CID
compression 13.1:1
fully ported race heads
single plane intake with 780 holley
large tube open headers
cam: .733/.696 lift 320/320duration

This is just an example but for comparison I ran up the compression and it has a 'full' race cam, nothing that would work on the street. Here's the #'s

Max Torque: 533ftlbs@5500RPM
Max HP: 669HP @ 7500rpm

Now I wonder how you build an engine with the max torque up at 7200rpm and only have 525Hp and still spin it at 10,000RPM Redline.

Please tell us how this is done. Bragging about one's own car is fine but none of your numbers add up.

posted by  fc7gtx

markman, I think you must have underestimated your peak power, because at 500 ft lbs-force @ 7500rpm I get a higher figure than you quoted and power wouldn't have peaked by then. Did you mean to say that peak power was 930hp?

The engine would be a stroker? I can't imagine the work that has been done to get a 10000 rpm redline with the subsequent piston speeds/acceleration involved. And to avoid the pushrod flex, valve bounce, cam flex etc you must have had an extraordinary engineer help you.

posted by  Wally

He's full of shit. A 408 can be made to turn 8500-9000rpm but that requires that one be a rocket scientist and fall ass first into a large pile of money.

Hey guys, I have roller lifters in my 302...based on that 408, that means that with the reduced rotating mass, I should be able to redline at about 15,000rpm and make peak torque at about 9,700rpm! (note-sarcasm)

posted by  Sick88Tbird

[QUOTE=Sick88Tbird]He's full of shit. A 408 can be made to turn 8500-9000rpm but that requires that one be a rocket scientist and fall ass first into a large pile of money.

Hey guys, I have roller lifters in my 302...based on that 408, that means that with the reduced rotating mass, I should be able to redline at about 15,000rpm and make peak torque at about 9,700rpm! (note-sarcasm)[/QUO

ha ha i have a 89 chevy cavalier that won't hold coolant i shoulde be able to hit 125 in the 1/4 mile with a redline of 3mil :screwy: :banghead: :cussing:

posted by  antiJDM

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