What Gear ratio to run ???

[madsupra88]

sup guys,

i'm trying to figure out what gear ratio to run with my new setup, dont care much about freeway driving , the car is setup for 1/4 mile passes.

the car has forged lower end with all ARP studs.
fully CNC ported heads
Fully ported FFIM
264 cams with .345 lift
cam gears
t67 with .71 ar hot side
th350 3speed auto
4000 stall
26 inch tall tire

not sure where my powerband is going to be but i would guess past 7000 with the head/intake/cams ??

think the car now has a 3.90.

thanks :1zhelp:

 

[turbojuiced]

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Its up to you now. Most people go with the w58 off the mk4 but on some models you will have to get a different bell housing.

 

[madsupra88]

no , i run a th350 gm trans. i was asking about the rearend gear ratio not the trans ..... thanks for the input ... :icon_bigg

 

[Sawbladz]

With a tall tire and the 3 speed auto, wouldn't it be preferable to have the highest gear ratio possible? That would be the LSD 4.30.

 

[madsupra88]

thats what im thinking, 4.30s ...that should put me @ around 135 MPH in 7500, which is about the right MPH for a low 10 sec pass

 

[turbojuiced]

no , i run a th350 gm trans. i was asking about the rearend gear ratio not the trans ..... thanks for the input ... :icon_bigg

Ooops haha totally didnt read the bottom of your post. Thought you were talking about trannys. My bad. Well to be honest with you the diff you have right now is fine imho. Its a decent gear ratio to give you good quickness out from a dig and good gearing for high speed quickness as well.

From the tsrm it states that there are 3 different types the 2 and 4 pinion and the LSD the LSD would be optimal out fo those 3 which is a 430 gear

 

[Sawbladz]

What are the gear ratio's for the tranny you are running?

 

[turbojuiced]

thats what im thinking, 4.30s ...that should put me @ around 135 MPH in 7500, which is about the right MPH for a low 10 sec pass

You will need to be alot faster than 135 for a low 10sec pass. Most mid to high 11sec passes are done at mid to high 120's.

 

[madsupra88]

You will need to be alot faster than 135 for a low 10sec pass. Most mid to high 11sec passes are done at mid to high 120's.

135 for auto car should put me in the 10 sec range ???

 

[madsupra88]

What are the gear ratio's for the tranny you are running?

1st- 2.52
2nd-1.52
3rd-1.00

 

[turbojuiced]

135 for auto car should put me in the 10 sec range ???

Unless you cut a 1.4 60ft or lower you may just may hit 10's but still very doubtful. Now I have seen very few hit 10's in mid 130's but their 60fts were pretty low like in the 1.6-1.5 range. I highly doubt you will hit a 1.5 in an auto even with the stall but it could happen. Most 10sec cars are in the 140's. I said most being that there are some that were in the mid to high 130's so it is possible.

However, I guess we will see when you run the car. So keep us posted.

 

[Sawbladz]

With the 3.91 ratio and the 7000 RPM redline you would top out at ~138 MPH.

With the 4.10 ratio and the 7000 RPM redline you would top out at ~132 MPH.

With the 4.30 ratio and the 7000 RPM redline you would top out at ~126 MPH.

 

[turbojuiced]

With the 3.91 ratio and the 7000 RPM redline you would top out at ~138 MPH.

With the 4.10 ratio and the 7000 RPM redline you would top out at ~132 MPH.

With the 4.30 ratio and the 7000 RPM redline you would top out at ~126 MPH.

Yes I knew the 390's would be optimal for higher speeds but I think its more important for him to get out fo the hole since hes auto. So the LSD would be more optimal for your particular use for drag racing. In drag racing its very imperative to get going as fast as possible obviously. Just my opinion :icon_razz

 

[Sawbladz]

This is true. However, if he has a powerful enough car, he may run out of gear and hit the rev limiter before the traps. That's bad MmmmKay.

 

[Nick M]

The only 10 second cars that run in the 140's are high horsepower cars with tall gearing, heavy, no stall converter, or too big of a turbo.

If he runs a brake on the THM with 4.30s and has a broad powerband, he might hit mid 10s at 135. If he doesn't break anything.

 

[turbojuiced]

This is true. However, if he has a powerful enough car, he may run out of gear and hit the rev limiter before the traps. That's bad MmmmKay.

not really cause he has another gear:naughty:

 

[madsupra88]

whats the stock rev limit set @ ? and how can i increase it ?

 

[gofastgeorge]

Well, if your stuck with a 7000 rpm red line, then 4.30s.

But if you have a really built lower end,
and are willing to either get your stock rev limit bumped up,
(there is a guy in Florida that did mine),
or go to a stand alone that you can program the rev limiter,
then there are also 4.56 gears (I have a set of these in my NA)
and 4.88s (there is a set on eBay right now).

I turn my NA to 8500 (264-272 split duration cams),
with a 3000 stall (not enough) converter,
but I have one of the small dia. 4000 stall converters headed my way.

 

[buldozr]

Gm slush box with a 3500-4k stall... tell you what, run the 3.90's, see where your at, if your no where near redline, swap the rear, trial and error. GL and have fun! :icon_surp

 

[madsupra88]

Gm slush box with a 3500-4k stall... tell you what, run the 3.90's, see where your at, if your no where near redline, swap the rear, trial and error. GL and have fun! :icon_surp

lol not sure if i would call it a slush box... my brother car been it the 8s with the trans im running.