Rear ratio difference

SadbutTrue

Founding Member

May 1, 2002

2,390

4

49

Granada Hills, California

Jul 2, 2004

#1

• Jul 2, 2004

• #1

I already asked this question once, but is there a significant difference between a 3.50 ratio third member and a 3.25? I would go 3.50 but I'm afraid I could see driveability problems, excessive gas consumption and it being too aggressive for my engine. Any comments? The car will be daily driven and probably won't receive serious engine upgrades until at least next summer, but I'd like to get the car into the 14s by taking what I have below and adding a posi rear with some gears.

 

M

mak6363

New Member

Jun 17, 2004

21

0

0

Jul 2, 2004

#2

• Jul 2, 2004

• #2

I did some calculations to figure engine RPMs for you.I don't know what the diameter of your rear tires are so I did the calculations using a 26" tall tire.

At 55mph with 3.25 ratio engine RPMs are 2310
At 55mph with 3.50 ratio engine RPMs are 2487

At 65 mph with 3.25 ratio engine RPMs are 2730
At 65mph with 3.50 ratio engine RPMs are 2940

Using a 27" tall tire drops rpms about a 100rpms
using a 25" tall tire raises rpms about 100rpms

If you want to figure other ratios and tire sizes the formula is:

(Gear Ratio X MPH X 336) / Tire Diameter = Engine RPMs

This formula is for non-overdrive transmissions.

Hope this helps out.

 

ratio411

Founding Member

Apr 21, 2002

3,870

73

109

Pensacola FL

Jul 2, 2004

#3

• Jul 2, 2004

• #3

3.25 IMO

There is little difference.
You have a fairly light car.
You should have gobs of torque.
Your intake does best at very low revs.
You daily drive.
It all adds up to 3.25s by my calculations.

Do you have an aftermarket cam?
If so, duration @ .050"?
Dave

 

SadbutTrue

Founding Member

May 1, 2002

2,390

4

49

Granada Hills, California

Jul 3, 2004

#4

• Jul 3, 2004

• #4

yeah, my cars always been pretty torquey. The cam is stock.

 

ZStanger

Founding Member

Mar 10, 2002

311

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0

Pity City

Jul 3, 2004

#5

• Jul 3, 2004

• #5

3.25's Should be sufficient. Best of both worlds. Relaxed highway cruising, yet crisp acceleration.

 

ratio411

Founding Member

Apr 21, 2002

3,870

73

109

Pensacola FL

Jul 4, 2004

#6

• Jul 4, 2004

• #6

Okay, stock cam just makes me more certain on the 3.25s.
You can actually lose useable power with a short gear and stock cam combo. Add the Performer intake and you would hate any gear much lower than 3.25.

 

SadbutTrue

Founding Member

May 1, 2002

2,390

4

49

Granada Hills, California

Jul 5, 2004

#7

• Jul 5, 2004

• #7

yeah, im bidding on a rebuilt 3.25 third member as we speak, should work out nicely.

 

1

1969mach1351

Member

Apr 18, 2003

285

0

16

Sacramento, CA

Jul 5, 2004

#8

• Jul 5, 2004

• #8

I recently went from an open 3.25 to a locked 3.50 and the only difference I notice is the higher RPM on the freeway. My 1/4 mile time is exactly the same at 13.2 @108.

 

F

Fostang

Founding Member

May 8, 2002

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36

Stockton, Ca

Jul 6, 2004

#9

• Jul 6, 2004

• #9

SadbutTrue said:

yeah, im bidding on a rebuilt 3.25 third member as we speak, should work out nicely.

Click to expand...

Careful on those ebay pumpkins.

Some are not even rebuilt units just cleaned up and some have that crappy lock right(wrong) units.

 

Max Power

Active Member

Jul 31, 2003

1,774

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36

St Paul

Jul 6, 2004

#10

• Jul 6, 2004

• #10

http://www.drivetrainsuperstores.com/calculate.asp

Here is a handy calculator......