what gear ratio

[stella16]

need some help guys
I'm debating on putting chevy's LS3 430 horse in my old truck . It's a connect and cruise package with the 4L65E transmission. Overdrive of .70

I can't seem to find the power band specs for this engine

I'm trying to decide what the optimal highway rpm would be. 60, 65, 70 mph

I have 30" tall tires, .70 final drive

anybody?

[Mr Twisty]

Are you asking what rear gear ratio you need to run a specific RPM at a specific speed?

What is your rear gear ratio now?

Optimal RPM would be close to the same as the 5th gen Camaro, your truck is probably close in weight. ~1500-1600 @60mph in high gear would be a fine engine speed to shoot for with the LS3...

[CamaroFred]

I believe the dyno chart in the Wiki here on Camaro5 would be good for that crate motor. I know it is rated 430 instead of the Camaro 426 but I think that is due to the exhaust manifolds. The same motor in a Corvette is rated 430.
http://www.camaro5.com/forums/wiki.p...ns#Dyno_Charts

You can use this program to help determine a final drive. I'm not sure what gears you have available on your old truck.
If you have euro-metric size tires enter what you have. Or put in a tire size of 315/40X20 for a 30" diameter.
http://fredricksensoftware.us/EngineSpeeds/index.htm
As a starting point a 3.56 with 30" tires is about the same as a Camaro SS with a 3.45 and 28.5" tires. Your 0.70 is in between the Camaro's 5th and 6th.

[stella16]

thanks. My gears are so "tall" now, that I can't use the OD on the 700r4. I'm going to change the gears out in both axles and am planning ahead for the LS swap.

I used and online calculator, went for a drive, and am pretty sure that I've got 2.76's or maybe 3.07's......but certainly nothing bigger.

what I'm finding, is 3.42's, 70mph would be 1877rpm and 60 would be 1609rpm
and
3.73's, 70 would spin at 2047 rpm and 60 would be 1755rpm

also, I'm running 15" wheels. It looks like every inch added to how tall the tire is, drops the rpm by 500

I'm thinking 3.73 gives me just over 2000 at 70mph and gives me room to put bigger wheels on it down the road

I'm just brain storming

thanks for the input

[Mr Twisty]

I let my pickup go to OD at 1200 to 1400 all the time cruising. It's a big block, but I'd do the same with a 6.2 as long as It's flat road.

[stella16]

I guess I have to big of a stall converter in the 383/700r4. I can't remember what's in it, but it currently won't lock out the stall when it hits OD.

At least that's what I'm told is happening

[CamaroFred]

I'm with Mr Twisty.
2000 is too much, IMHO. There is a lot of torque in the 376.

I don't know what the trans ratios are in the 4L65 but kicking down to 3rd (or even 2nd) for passing should give you some decent acceleration even if you use a taller screw.

If you have 2.52/1.52/1.00/0.70 a 3.73 will take you to triple digits in 2nd.

[stella16]

so, CamaroFred, you are saying go with the 3.42's?

[CamaroFred]

Thinking about it more today. How much highway are you planning to drive?
If not a lot, go for the 3.73s.

I found the gear ratios for the 4L65-E
With 3.73:



With 3.45:


There is only ~150RPMs difference @70MPH.

[stella16]

It's my daily driver. I drive 40 miles a day , at least, of mostly highway between Arlington and Irving

[CamaroFred]

Up to you, then. There is ~8% difference in acceleration/RPMs/fuel consumption between the 3.45 and 3.73.

What stall are you going to use?

[stella16]

spec sheet says it's a 2400-2800 stall

[CamaroFred]

3.73, as you first thought.

[stella16]

thanks. I appreciate your input