3.55 vs 3.91 track time differences?

All else being equal, would there be a change in 1/4 mile times going from 3.91 to 3.55?

3900lb b body, large cube stroker, same PTC 9.5 converter (built for car with 3.91's)

Just a guess, you may not lose much ET, maybe .05, but will probably pick up a little MPH.

Can't really say without looking at the data log or some numbers. If the car is on the rev limiter going down the track then it might pick up time. If it is traction limited it might go quicker and faster with less gear. If the 3.91 gears are perfect for the engine and car then it will slow down.

Taller gear should raise the converter's stall speed a bit.
Whether the car wants that is hard to tell from here with the info so far.

If the 3.91 gears are perfect for the engine and car then it will slow down.



I'm not really sure. The engine made 601 horsepower at 5500 and 633 torque at 4500

I know that's a vague answer, but I never really picked a gear to build on.

With that kind of torque, I doubt you'll see much difference

What's the car running now with the 3.91?

I haven't ran it with the new motor yet. Old motor went mid 11's with the 3.91's.

Flash rpm yes, stall no. Rear gear has no effect on stall and it really only changes flash rpm because of how flash rpm is defined, not a “real” change to the actual flash rpm. The change is the car just moves easier/sooner. So yes the rpm will be lower when the car first moves, but you can still get to the power band quicker during the run. (The reason we play with flash in the first place)I went with a low gear set 904 which would “lower” my flash rpm, but because the car is moving, I would get to peak torque .5 second quicker in the run, even with the “reduced” flash rpm.

Nothing with that combo.

We run a 3.54 gear with a 505" stroker and rear ratio seems to matter very little with the torque it makes.

It's been 1.36 60 ft. with an 11" converter.

[quote=GY3]Nothing with that combo.

We run a 3.54 gear with a 505" stroker and rear ratio seems to matter very little with the torque it makes.: I ran 4 different rear gear ratios in my old pump gas stroker motor in my Duster, 3:73, 3,91, 4.10 and 4.30 with no other changes, other than running at different tracks. It ran within.08 and 1.0 MPH as long as it didn't spin
I did have a Mopar brand low gear drive set (2.77 I think) in the 727, best 60 ft was 1.42 I think

Well, I may look out for a 3.55 third member then. It does drive well with the 3.91's. Just want a little more on the freeway for some longer trips. I also really like the new PTC 9.5.

If that's[/i] the goal (or the consideration), there are calculators that will tell you how much your RPM's will be affected. I think [i]the track will be the only way to truly figure out the affect at the track.

If you want a higher gear for the freeway then go with the 3.55 gears. Sounds like the car is more of a driver than an all out drag car so make it work for what you want it to do. It isn't going to slow down much at the track. In fact, if it is traction limited then it might actually leave the line better with the taller gear.

http://www.wallaceracing.com/Calculators.htm

You say "third member".

If you're planning on hooking this combo at the track with slicks, you're going to need to upgrade to something stouter than an 8 3/4.

That is a little deceiving. Unless you are saying you went 1.36 N/A.

On my 389 small block, I run a 3.55 gear and have gone 1.37 60ft.... but... there is more to that statement...

1.54 60 ft. N/A

There, how's that?

LOL, much more applicable!

Well, I did do a 1.58 60 with the old motor and 3.91's

Just for info, rear gear changes did have an effect on stall speed on my combo, verified by the racepak.

Likely not much change, and its mostly going to be in the first 60' times. Think it will depend on how hard you can launch the car.

It will definitely show a change, but from the car moving sooner. When I heard that with the low gear set 904 I would “lose” flash rpm I got nervous. In reality you lose flash rpm, but you actually get to power band quicker during the run and while moving faster. I reach peak torque 1/2 sec quicker. Flash being stomp on the pedal off idle and how high the rpm’s climb BEFORE the car moves. Not really the same as if you actually took some flash rpm out of the converter.

Thanks guys. If I can find a decent price on a 3.55 member, I'll probably get one. Otherwise I'll stick with the 3.91's. Drove 130 mile round trip on the highway last week. And at 65-70 it wasn't that bad