Chevy Nova Forum banner

1 - 15 of 15 Posts

·
Registered
Joined
·
19 Posts
Discussion Starter #1 (Edited)
Hi guys
Looking for some direction in what rear gear is best for my car...I have a built BBC 396(500 + hp) turbo 350 trans 3200 stall, and the current gear is a 5 13..We are mostly street driving this car,but like to tear it up sometimes.I would like to drive to a car show with lower rpms instead of driving at 45 mph at just about 3000 rpms..My rear tires are mickey thompson sportsman 33x19.50x15..would like to be able to drive 60-70mph and would like to stay under 3000 rpms,any help would be much appreciated...
 

·
Registered
Joined
·
19 Posts
Discussion Starter #3
Hi guys
Looking for some direction in what rear gear is best for my car...I have a built BBC 396(500 + hp) turbo 350 trans 3200 stall, and the current gear is a 5 13..We are mostly street driving this car,but like to tear it up sometimes.I would like to drive to a car show with lower rpms instead of driving at 45 mph at just about 3000 rpms..My rear tires are mickey thompson sportsman 33x19.50x15..would like to be able to drive 60-70mph and still have a strong takeoff from a stop..also keeping it under 3000 rpms would be a plus..thank you..,any help would be much appreciated...
 

·
Registered
Joined
·
19 Posts
Discussion Starter #7
Thanks guys for the info..i was thinking 4:11 because of the rear tire size but maybe the 3:90 will be the way to go..thanks again
 

·
Registered
Joined
·
19 Posts
Discussion Starter #8
Going with a 3.90....what do u think my rpms would be at 65-70? Just a guess? With the 5:13...at 40-45 we r at 3000 rpms..
 

·
Registered
Joined
·
212 Posts
Hi guys
Looking for some direction in what rear gear is best for my car...I have a built BBC 396(500 + hp) turbo 350 trans 3200 stall, and the current gear is a 5 13..We are mostly street driving this car,but like to tear it up sometimes.I would like to drive to a car show with lower rpms instead of driving at 45 mph at just about 3000 rpms..My rear tires are mickey thompson sportsman 33x19.50x15..would like to be able to drive 60-70mph and would like to stay under 3000 rpms,any help would be much appreciated...
You might want to go to a Axle Ratio Calculator site to run your numbers.

http://www.angelfire.com/fl/procrastination/rear.html

This is a link to a very simple one and it also give you alternative ratio choices to choose from.

It's hard to recommend something for someone else not know what they can live with rpm or speed wise. You're running taller tires than I would think most here would be running, so a recommendation becomes very subjective.

Good luck with your axle ratio choice.
 

·
Registered
Joined
·
3,601 Posts
You might want to go to a Axle Ratio Calculator site to run your numbers.

http://www.angelfire.com/fl/procrastination/rear.html

This is a link to a very simple one and it also give you alternative ratio choices to choose from.

It's hard to recommend something for someone else not know what they can live with rpm or speed wise. You're running taller tires than I would think most here would be running, so a recommendation becomes very subjective.

Good luck with your axle ratio choice.
X2 what he said! Also, you cant forget about the converter slippage as you move away from the 5.13's.
 

·
Registered
Joined
·
19 Posts
Discussion Starter #11
Not exa tly sure how convertor slippage works wht73..can you explain in simple man
Terms...
 

·
Registered
Joined
·
58 Posts
New gears

I have a 78 with a 496bbc/400 thm. I just put in a posi unit and 3.42 gears. I'm right at 2500rpm at 60mph.
 

·
Registered
Joined
·
212 Posts
Not exa tly sure how convertor slippage works wht73..can you explain in simple man
Terms...
Torque converters, non lockup, are not a true solid coupling between the motor crank and the input shaft of the transmission.

The converter is nothing more than a simple water wheel, but with trans fluid being flung from one set of turbine blades into another one making a coupling of sorts between the two turbine, which are inside the converter.

There are not a 100% coupling though. The amount of slippage to some extent will depend on the stall speed of the torque converter. The stall speed will be the rpm that for all practical purposes the converter couples up. If you brake torque your car, the rpm that starts to spin the rear tires is "close" to the stall speed. The lower the stall speed the positive the coupling is due to the straighter angle of the turbine fins inside the converter.

As an example in my '40 Willys couple with a blown 392 hemi, I ran a 4:11 rear and a Chrysler 518 31% O/D.

With a 3500 rpm stall converter I could cruise down the road in O/D 70 mph at 2700 rpms. I had numerous R&R's of the trans due to more hp than it could handle and the converter going out a few times.

The trans guy gave me a stock 6cyl converter while he was fighting to get one made for me. I used that one and drove to Indy Good Guys and it would pop rubber on every shift and I could cruise at around 2500 rpms at 70 mph. So this converter was more efficient than the stall converter.

When the trans guy got me another stall converter he said this is the one now to use. I took it out and was blown away with its performance, but it was VERY impractical for the street. I hit the go pedal and it went to the MSD rev limiter at 6000 rpms and never left the rev limiter the full time until I was over 100 mph and let up on it. With this converter I was at 3200 rpm at 55 mph. WOW!

So the very high stall converter was so inefficient that I was loosing all that speed at cruise. I ended up driving the car down to another Good Guys event in MI with that very high stall converter. I fried my trans fluid because of all the slippage and heat build up. That was good for the go quick and stop, but not great for cruising.

Again, sorry for the rambling, but sometimes I might be able to share experiences that are appropriate for the thread.

Anyway, a stock converter will slip about 3 to 5% and the higher the stall speed the more it will slip. As was said above, the ratio you pick will also depend on your converter efficiency; low or high stall speed.

If you're running a 10" or smaller converter you're going to be slipping on the high side and you should allow for the extra rpms when you pick your ratio.

Sorry again, but I just had another memory that I thought of earlier and forgot to say. Cut me some slack as my grey hair causes my memory to fade from time to time.

I mentioned about chirping the tires on every shift. When I finally got the right converter, about a 3500 stall, even though I had a stage II trans kit setup, the shifts did not produce any shift tire chirp. The reason is that the converter is slippery inside and when the trans would shift the converter would slip and not provide enough coupling to produce a rear tire spin. The stock 6cyl converter was amazing on how HARD is shifted in each gear and on the 5000 stall converter I could not feel one shift at any time on full throttle.

Power was not an issue. I could light the tires up at 45 mph just by nailing mashing the treadle to the floor; although the tires were not that grippy, BF T/A's, 285/70-15's 29" tall.

I hope I have not bored you with my ramblings.

Hope my explanation makes sense to you.
 

·
Registered
Joined
·
19 Posts
Discussion Starter #14
Thanku dan
I actually like the illustrations...they help alot! Im kind of new to these parts of the car and i appreciate the great info...i ha e large 33 inch tires on the rear with a 350 trans..not exactly sure of the stall on my convertor but the rear gear is a 5:13 and just to cruise around town at 40mph im near 3000 rpms...its mostly a street driven car but we like to s.oke them up time to time so i still want some takeoff power and be able to drive the car somewhere without driving so slo and being at 3000 rpms...was thinking of a 3.90 or 4.11 because of tbe rear tire size..thAnks for any direction dan
Tony:
 

·
Registered
Joined
·
212 Posts
Thanku dan
I actually like the illustrations...they help alot! Im kind of new to these parts of the car and i appreciate the great info...i ha e large 33 inch tires on the rear with a 350 trans..not exactly sure of the stall on my convertor but the rear gear is a 5:13 and just to cruise around town at 40mph im near 3000 rpms...its mostly a street driven car but we like to s.oke them up time to time so i still want some takeoff power and be able to drive the car somewhere without driving so slo and being at 3000 rpms...was thinking of a 3.90 or 4.11 because of tbe rear tire size..thAnks for any direction dan
Tony:
My gut says that with 33" tall tires, if you're looking at in town to short highway hops, 4:11 would be doable for a short hops. If you are going to be cruising to shows or taking more than 40 to 50 mile hops on the highway I would look more toward the 3:50 range.

That being said I'm sure lots of guys here have run 4:11 gears for long hauls etc, but at my age I'm favoring the lower rpms and less noise of the lower gears.

This is almost as subjective of a question as to what is your favorite color.

It's going to boil down to what you think you want and what you can live with. Maybe there is someone in your area you can contact and ride shotgun in his car just to see if it's going to work for you.

Using the chart link I posted above will give you some guide lines that you can begin to use to get some idea of rpms versus mph with your setup.

Good luck with our choice.
 
1 - 15 of 15 Posts
Top