Top Speed with 3.91s?

[miller]

I am switching my rear end from a 8 1/4 to 8 3/4, and from 2.77 open to 3.91 sure grip. However when using the rpm calculator it seems that with my tire size 255/60/15 and a torque converter efficiency of 98%, the car won't top 100 before it hits redline. I normally cruise at 60, but if I take it to the drag strip, will I run out of gear before the 1/4 mile is done?

http://vexer.com/automotive-tools/speed-rpm-calculator

Thank you,
Miller

[Chryco Psycho]

it is hard to say exactly , it depends how fast the car is / how much power you have , if you are running 15 seconds in the 1/4 90 MPH should cover it , the faster you go the sooner you run out of RPM , I can tell you 391 is really no fun on the highway for long

[miller]

it is hard to say exactly , it depends how fast the car is / how much power you have , if you are running 15 seconds in the 1/4 90 MPH should cover it , the faster you go the sooner you run out of RPM , I can tell you 391 is really no fun on the highway for long

Right now it has a mildly built 440 thats in dire need of a performer RPM intake and bigger carb. After that is done and everything is tuned properly... I was hoping for around 400 horsepower.

[Purple68]

Maybe think about running some taller tires. I ran 3.91s with 275/60s and was quite happy. I'm now running 295 /65/15s with 4.10 gears. I'm turning about 3300 rpm at 70mph.

[Troy]

I had 3.91s in the Challenger last year for the Nats and with 275/60-15s in back I had to drive 61 mph and I still lost 4-5 mpg. I'm used to driving at least 75 mph on the highway and I never go to the track so I yanked them back out within a week. They were a lot of fun stoplight to stoplight but useless otherwise (for me).

Troy

[Paul G]

You have options. You can go with the 3.91's and use an A518 overdrive trans. You get great street and track performance, same as a 727, plus it will cruise at 70 turning 2300 rpm. You get the best of both worlds.

An A518 overdrive won't help top speed at the track. Won't engage at full throttle.   

[John_Kunkel]

the car won't top 100 before it hits redline.

What's your red line? With 27" tires and 3.91 gears 100 mph is around 5000 rpm.

[miller]

the car won't top 100 before it hits redline.

What's your red line? With 27" tires and 3.91 gears 100 mph is around 5000 rpm.

I thought a 440s stock redline was 5000, my could probably rev higher, but still being in college.... I don't feel like have picking up the insides of my motor with a bucket.

[mauve66]

most stock lifters will float around 5200-5500

with 3.23's i could do around 120-125 fairly easily so i doubt 3.91's would do more than 110 or so

[Musicman]

You have the right on line calculator, but you'll want to set your TQ Converter efficiency at 90% for greater accuracy... some will do better of course, but then again some are much worse.

[miller]

most stock lifters will float around 5200-5500

with 3.23's i could do around 120-125 fairly easily so i doubt 3.91's would do more than 110 or so

The springs are Crane Cams 99839-16 , cam is  COMP Cams 21-222-4, and the lifters are ht2011b. Where would that put me for potential to float the valves/lifters?

Also what happens if you get to that point?

[John_Kunkel]

You can theorize all you want but you'll never know the actual valve float rpm of your motor until you take it there.

[BSB67]

most stock lifters will float around 5200-5500

with 3.23's i could do around 120-125 fairly easily so i doubt 3.91's would do more than 110 or so

The springs are Crane Cams 99839-16 , cam is  COMP Cams 21-222-4, and the lifters are ht2011b. Where would that put me for potential to float the valves/lifters?

Also what happens if you get to that point?

You will run out of camshaft before you get to valve float.  I would guess that cam will have nothing left after 5600 rpm in a 440, and that is if you have a decent intake.

[Schlabuster]

Last year i run a 3.91 and had the problem that i had not enough power for this setup.  I got good starts from the line but after the 1/8 mile the engine stays on 4600 rpm and wont go faster. Now i switched to a 3.23 and a bigger carb and it feels much better.
The other thing is that a 3.91 is not much fun on normal streets or the autobahn, engine had too much rpm and top speed is bad.