Rear gear question
 

3400#
440”. 1.80 1st gear 4.10 rear 28? tire.
Car isn”t performing to expectations.
Only running low tens @ 133. 1.45 60?
Think it needs a lower gear?

Re: Rear gear question
 

Well, that would depend on your finish-line RPM. Just looking at your dyno numbers and not knowing much else, I would probably gear it to hit the FL at 7000/7200. But that's a Stocker guy talking. That would to me be conservative. Not knowing what's in your stuff.

Re: Rear gear question
 

Can’t read the graph. At what RPM, does it make peak HP and peak torque. What does your converter flash to and fall back on the gear change and what RPM are you shifting at?

Re: Rear gear question
 

Peak HP, 6700
Peak TQ, 5300
1.80 1st, it's gotta be a PG.

Re: Rear gear question
 

For optimum ET, If it was mine, it would have a converter that flashes to 5800, I’d be shifting at 7200 and gear it so it’s crossing the stripe at 7700. I would also get a 30” tire under it if you can not go wider.

Re: Rear gear question
 

It?s 7100 at the finish line now.
Convertor is around 5800 I believe.

Re: Rear gear question
 

If you don’t have a data recorder get one or at least a playback tach so you have real data. That said, definitely needs more gear

Re: Rear gear question
 

And more tire.

Re: Rear gear question
 

Rarely does more gear hurt! Depends on what your wallet can stand.

Re: Rear gear question
 

As I stated in post #5

Re: Rear gear question
 

My handy dream wheel says 133 is 10 flat horse power, 600 - 620 HP or so.

1.45 60' isn't hateful. Probably has mid 1.30 in it anyhow. A 3 speed, with the extra SLR should make it 60' a little better. A lightweight 3 speed would be even better.

Depends on your goals. More rear gear, as was said, will help. Agree with a 5800 converter. Beyond that, if it's consistency on marginal tracks, you're probably best with that low gear. Want to go fast, need the low gear a 3 speed would offer. And more tire.

Re: Rear gear question
 

Need a neutral or negative converter to get it to pull off line & the gear change.
5800 stall OK, but there is more to the converter than stall speed.
I agree with tire and rear gear change.
1.96 low might wake it up too, but shift it at higher RPM with a lower low gear PG.
You are carrying quite a lot of weight for a 7.38 starting line ratio...2.52 low gear 3 speed puts the SLR at around 10.33. With the right 3 speed converter it would pick up a bunch. Probably on the + side of .15..

Re: Rear gear question
 

oops!

Re: Rear gear question
 

I have to think the converter is real tight.

My Nova is 3600#, 1.80 glide, 4.10 gear, 28" tire and has 660 HP. I can't go 133; 128 is about the best it'll do but it's usually a 1.40 60'.

So, same running gear setup but heavier and less power.

Re: Rear gear question
 

or heads are too big

Re: Rear gear question
 

or cam

Re: Rear gear question
 

3400# car, 28" tire, 739 HP, Auto trans

I would want to see somewhere around an 11.5 SLR

NOTE this is ONLY a recommendation for what might be a good STARTING POINT

Stan

Re: Rear gear question
 

5.14 and a 3 speed might get him there...

Re: Rear gear question
 

A 2.74:1 first gear 3 speed and his present 4.1:1 would give him a 11.234 SLR. Not a bad starting point.



Stan

Re: Rear gear question
 

SLR is internet forum bs like dynamic compression ratio.

My SLR is 8.748, what am I doing wrong? :D

https://i.imgur.com/bkXk8Q4l.jpg

Meanwhile, I have a data recorder, download every pass and KNOW at what RPM exactly my converter flashes to and falls back to on the gear change as well what RPM I'm shifting at and crossing the stripe at in addition to all the other data I record and plot every pass.

Re: Rear gear question
 

Maybe if you really understood dynamic compression ratio, I would take you seriously! :eek:


Without knowing anything about your car. How would anyone know what you might need for a SLR?


I will need even touch this. :D


Stan

Re: Rear gear question
 

keep spewing your misinformation and myth Stan no one with a clue takes you seriously

Re: Rear gear question
 

I laughed so hard at this I almost spit my tea out!!!! LOL!!! Yeah, Stan doesn't know anything about cars/engines/head flow/LOL!!!!!

Re: Rear gear question
 

Clearly not but you think he does, no surprise.

Re: Rear gear question
 

Lets look at Dynamic Compression Ratio a little closer. It is based on engine parameters and IVC. So unless you have done something to have these change once the engine is running it is really now static. People look at Cranking Compression PSI and running cylinder pressure and say see see the DCR has changed. No what has changed is the engines VE / mass air flow. There have been OEM manufactures that actually call this trapped CR and listed it as an engine spec.

Stan

Re: Rear gear question
 

Let’s not! Start another thread about meaningless DCR. Meanwhile this thread is about rear gear, more of which the OP needs.

Re: Rear gear question
 

So peak HP is @ 6700 RPM and he said he is crossing the strip @ 7100 RPM. So just how much rear gear would you like him to run?



As I, and other have said he needs a 3 speed trans.


Stan

Re: Rear gear question
 

800 rpm fallback.
Mast m311 Cyl head 273 runner

Re: Rear gear question
 

He does not NEED a 3 speed trans, he NEEDS more gear!

from what RPM/shift point?

Re: Rear gear question
 

7000

Re: Rear gear question
 

As I stated in post #5

Re: Rear gear question
 

So...
Stupid me is going to throw this out there...

Peak torque is at 5300...
It makes plenty good torque for a 3.75" stroke...
If it falls to 6200 at the gear change I'm going to say you're leaving some power on the table...
I would think if you send dyno sheets to someone like Coan, they could dial you in...
May find you can tighten it a bit?

I think maybe play with the shift point...
As in higher... 7200? maybe more...
See where it slows down...

More gear would help, as would a 3 speed...
If it crosses 72+ it really doesn't matter if the motor doesn't self disassemble...
(don't know the parts or build)
I see things I might try if it were mine...

Depends on your budget really, converters/transmissions aren't cheap these days...

Any way just a few thoughts from a dumb ol' Texas boy...
Maybe some of this helps...
Maybe it don't...
As they say... "Your mileage may vary"

Re: Rear gear question
 

Its a 440” LS with 4.125 stroke

Re: Rear gear question
 

Sorry... Thinking Chrysler...

So...Yeah, Think I'd experiment with shift point, doesn't cost anything, just time...
Still think more gear...
Converter...
There's stuff to try before springing for a trans...
Haven't tinkered with LS stuff...

Re: Rear gear question
 

There?s no question, more gear, higher shift, maybe a converter but not before real data via a data logged but not a 3 speed trans.

Re: Rear gear question
 

:rolleyes: :rolleyes: :rolleyes:
Stan

Re: Rear gear question
 

Stan, what part of the TRUTH and the FACTS don't you like?:D

Re: Rear gear question
 

I am still waiting for you to post something other than a vague generalized statement.

I don't know you, but from reading some of your other posts here, this does seem to be the way you roll.

Stan

Re: Rear gear question
 

and I'm still waiting for you to post photos and time slips of your car, rather than your theory and formulas.

Re: Rear gear question
 

In almost ever thread I have seen you post in, you have had a different opinion than everyone else posting. I will just let the readers of this thread decide which of us is shoveling s h i t.


Stan