Rear gears ??
Thread Starter
Burning Brakes
Joined: Jan 2006
Posts: 957
Likes: 6
From: Burlington wisconsin
Rear gears ??
OK, there must be someone on here that has this set up...
[*]350 motor[*]TH350 trans[*]P235 60 / 15 tires[*]3:55 gears
How many RPM's are you turning @ 70 mph?
I've been to numerous rpm calculators and keep getting different numbers. I have spoken to others with a close set up, but never apples for apples. I now have 3:08's & want to go as high as I can, but I do 70mph on the highways quite often, as we live in the country & to get anywhere most streets are 55 mph highways (find it hard to go that slow, not many troopers) now with the 3:08's I do 2700 rpm's @70 mph. Can I go 3:55's and keep it at or about 3K?
I know I'm going to hear "go 4 speed" & all that, but it's not in the cards right now & my diff is out & is going to be rebuilt now.
Jimbo
[*]350 motor[*]TH350 trans[*]P235 60 / 15 tires[*]3:55 gears
How many RPM's are you turning @ 70 mph?
I've been to numerous rpm calculators and keep getting different numbers. I have spoken to others with a close set up, but never apples for apples. I now have 3:08's & want to go as high as I can, but I do 70mph on the highways quite often, as we live in the country & to get anywhere most streets are 55 mph highways (find it hard to go that slow, not many troopers) now with the 3:08's I do 2700 rpm's @70 mph. Can I go 3:55's and keep it at or about 3K?
I know I'm going to hear "go 4 speed" & all that, but it's not in the cards right now & my diff is out & is going to be rebuilt now.
Jimbo
Thread Starter
Burning Brakes
Joined: Jan 2006
Posts: 957
Likes: 6
From: Burlington wisconsin
how detrimental to a strong motor is 3200 rpm for any lengths of time. It takes me an hour to get just about anywhere and 70 is the norm.
Jimbo
Le Mans Master
Joined: Oct 2005
Posts: 9,429
Likes: 44
From: Macon, GA
With a good cooling system and a good functioning ignition system you'll have no problem. I drive mine that far regularly for regional car shows and have yet to have a problem. Gas mileage is another issue though. 
Thread Starter
Burning Brakes
Joined: Jan 2006
Posts: 957
Likes: 6
From: Burlington wisconsin
Thanks for the input. Gas mileage was never a concern, unless I hear otherwise, I think I'm going 3:55's. I don't think 3:36"s would be enough of a jump to get a thrill at all??
Le Mans Master
Joined: Dec 2006
Posts: 8,837
Likes: 1,028
OK, there must be someone on here that has this set up...
[*]350 motor[*]TH350 trans[*]P235 60 / 15 tires[*]3:55 gears
How many RPM's are you turning @ 70 mph?
I've been to numerous rpm calculators and keep getting different numbers. I have spoken to others with a close set up, but never apples for apples. I now have 3:08's & want to go as high as I can, but I do 70mph on the highways quite often, as we live in the country & to get anywhere most streets are 55 mph highways (find it hard to go that slow, not many troopers) now with the 3:08's I do 2700 rpm's @70 mph. Can I go 3:55's and keep it at or about 3K?
I know I'm going to hear "go 4 speed" & all that, but it's not in the cards right now & my diff is out & is going to be rebuilt now.
Jimbo
[*]350 motor[*]TH350 trans[*]P235 60 / 15 tires[*]3:55 gears
How many RPM's are you turning @ 70 mph?
I've been to numerous rpm calculators and keep getting different numbers. I have spoken to others with a close set up, but never apples for apples. I now have 3:08's & want to go as high as I can, but I do 70mph on the highways quite often, as we live in the country & to get anywhere most streets are 55 mph highways (find it hard to go that slow, not many troopers) now with the 3:08's I do 2700 rpm's @70 mph. Can I go 3:55's and keep it at or about 3K?
I know I'm going to hear "go 4 speed" & all that, but it's not in the cards right now & my diff is out & is going to be rebuilt now.
Jimbo
http://www.gounitrax.com/default.htm
Race Director
Joined: Jan 2003
Posts: 15,176
Likes: 88
From: State of Confusion
Assuming your Tach reading is accurate, I plugged in your results. If you are turning 2700 RPM with 3.08 your tire diameter is 25.25. Your new RPM at 70 with 3.55 would then be 3112RPM
http://www.gounitrax.com/default.htm
http://www.gounitrax.com/default.htm
RPM x .9 (slippage for non-locking torque-converter ) x .006 x 1/2 TH (tire height ) divided-by GR (gear-ratio ) = MPH
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Burning Brakes
Joined: Mar 2004
Posts: 816
Likes: 1
From: Finland
Last year I changes from 308 to 411 and gained ONLY 0.2s on 1/4 mile. Later I realised the reason...my stall had of cource changed due to different gearing...
Race Director
Joined: Jan 2003
Posts: 15,176
Likes: 88
From: State of Confusion
When you move from 308 to 355 your flash stall will drop lower a bit and that hurts performance! You should change converter also to get full advantage...
Last year I changes from 308 to 411 and gained ONLY 0.2s on 1/4 mile. Later I realised the reason...my stall had of cource changed due to different gearing...
Last year I changes from 308 to 411 and gained ONLY 0.2s on 1/4 mile. Later I realised the reason...my stall had of cource changed due to different gearing...
Safety Car
Joined: Nov 2004
Posts: 4,359
Likes: 57
From: Mundelein Illinois
OK, there must be someone on here that has this set up...
[*]350 motor[*]TH350 trans[*]P235 60 / 15 tires[*]3:55 gears
How many RPM's are you turning @ 70 mph?
I've been to numerous rpm calculators and keep getting different numbers. I have spoken to others with a close set up, but never apples for apples. I now have 3:08's & want to go as high as I can, but I do 70mph on the highways quite often, as we live in the country & to get anywhere most streets are 55 mph highways (find it hard to go that slow, not many troopers) now with the 3:08's I do 2700 rpm's @70 mph. Can I go 3:55's and keep it at or about 3K?
I know I'm going to hear "go 4 speed" & all that, but it's not in the cards right now & my diff is out & is going to be rebuilt now.
Jimbo
[*]350 motor[*]TH350 trans[*]P235 60 / 15 tires[*]3:55 gears
How many RPM's are you turning @ 70 mph?
I've been to numerous rpm calculators and keep getting different numbers. I have spoken to others with a close set up, but never apples for apples. I now have 3:08's & want to go as high as I can, but I do 70mph on the highways quite often, as we live in the country & to get anywhere most streets are 55 mph highways (find it hard to go that slow, not many troopers) now with the 3:08's I do 2700 rpm's @70 mph. Can I go 3:55's and keep it at or about 3K?
I know I'm going to hear "go 4 speed" & all that, but it's not in the cards right now & my diff is out & is going to be rebuilt now.
Jimbo
With the 3.55 at 70mph you should be at 3200 RPM
Le Mans Master
Joined: Dec 2006
Posts: 8,837
Likes: 1,028
I used his RPM to supply a constant, and used this for the new RPM. This allowed for the margin of error of his tach. The actual tire diameter is not as important as using the same for both calculations.
Race Director
Joined: Jan 2003
Posts: 15,176
Likes: 88
From: State of Confusion
Le Mans Master
Joined: Dec 2006
Posts: 8,837
Likes: 1,028
I figured using this formula, with the actual tire-diameter, eliminates all errors the tach may show (the only variable remaining would be converter-slippage, generally-acknowledged as 10% in THM350/THM400s ), and produce the actual RPM, at any given MPH, knowing tire-height and gear-ratio.
Race Director
Joined: Jan 2003
Posts: 15,176
Likes: 88
From: State of Confusion
70 MPH x 3.08 div/by .9 div/by .006 div/by 13.5 = 2957 RPM
and about 64 MPH @ 2700 RPM 'if' the above (tire-height/rear-gearing ) is true
2700 RPM x .9 x .006 x 13.5 div/by 3.08 = 63.9 MPH
Le Mans Master
Joined: Dec 2006
Posts: 8,837
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I am figuring he 'should' be turning about 2950 RPM at 70 MPH, 'if' he has 27" tall rear-tires, and 'if' the rear-gear is currently3.08
70 MPH x 3.08 div/by .9 div/by .006 div/by 13.5 = 2957 RPM
and about 64 MPH @ 2700 RPM 'if' the above (tire-height/rear-gearing ) is true
2700 RPM x .9 x .006 x 13.5 div/by 3.08 = 63.9 MPH
70 MPH x 3.08 div/by .9 div/by .006 div/by 13.5 = 2957 RPM
and about 64 MPH @ 2700 RPM 'if' the above (tire-height/rear-gearing ) is true
2700 RPM x .9 x .006 x 13.5 div/by 3.08 = 63.9 MPH
Thread Starter
Burning Brakes
Joined: Jan 2006
Posts: 957
Likes: 6
From: Burlington wisconsin
Sorry Guys, My bad, I re-did the tire height calculations & they are 26.1 (235-60-15's), with my 3:08's at 70 I was 2700 rpm.
I went to Randys ring & pinion website and it came out pretty close to my findings.
It also claims that with 3:55's using the same 26.1 tire height and a 3 speed (1.00 3rd gear ratio) I would be turning 3285 rpm's at 70 mph.
At 60 I'd be turning 2816 rpm's. I think I'll be ok. As for the converter deal, that will also be changed soon when the motors out.
Thanks for all the input.
Jimbo