your going the wrong way! 3.31 gears in a 302 powered 69?

[zman1969]

I know, I know    currently has 4.10s in it now and its fine around town but get it up on hwy @4000 rpm and I'm still being run over so I'm going to 3.31s it has a M20 so its worse than 4.10x2.52 that I started with first gear ratio was 9.02 and now will be 8.34:1 (a little better than a 3.73 with a M21 @8.21) will this thing be a pig in the city now? or ? will it be tollerable?  future plans is to sideline the 302 for a 383 and that should be fine with 3.31
thoughts guys? 

[X33RS]

3.31's with the M20 is a nice combo and in my opinion work fine for a 302.  Like you said it's actually slightly better in first gear than the more common M21/3.73 combo, and in actuality, the M20/3.31 combo is better through the first 3 gears.  The car will feel slightly quicker around town.  4th is where you'll see the drop with an M20.  By then you're already rolling pretty good, it's inconsequential.   I like the M20 around town better myself but that's personal preference.  It allows a little more highway friendly gear for those occasional long jaunts.

[BULLITT65]

Not sure I would agree with the car feeling slightly quicker around town. The combo may be better for not winding the motor out, but I thought that was the whole idea. The 302 performs best when doing so.

Just my 2 cents....


The 383 may be a nice change of pace if you tend to do more freeway driving, or don't want to get passed by everyone else and there 6 speeds.

[bcmiller]

I know, I know    currently has 4.10s in it now and its fine around town but get it up on hwy @4000 rpm and I'm still being run over so I'm going to 3.31s it has a M20 so its worse than 4.10x2.52 that I started with first gear ratio was 9.02 and now will be 8.34:1 (a little better than a 3.73 with a M21 @8.21) will this thing be a pig in the city now? or ? will it be tollerable?  future plans is to sideline the 302 for a 383 and that should be fine with 3.31
thoughts guys? 

What is your rear tire size now?  Stock?

Larger tire will help, but only a little.

It is up to you, but I am not sure if I had your setup that I would drop all the way down to 3.31 with a 302 engine. 

[X33RS]

Here's what I meant by that comment.  Sorry I should have explained better.  For some reason I thought the OP had standard 3.73's, that keeps ringing in my head.

3.31 x 2.52 = 8.34
3.31 x 1.88 = 6.22
3.31 x 1.46 = 4.83
3.31 x 1      = 3.31

3.73 x 2.20 = 8.20
3.73 x 1.64 = 6.11
3.73 x 1.28 = 4.77
3.73 x 1      = 3.73

[69Z28-RS]

Here's what I meant by that comment.  Sorry I should have explained better.  For some reason I thought the OP had standard 3.73's, that keeps ringing in my head.

3.31 x 2.52 = 8.34
3.31 x 1.88 = 6.22
3.31 x 1.46 = 4.83
3.31 x 1      = 3.31

3.73 x 2.20 = 8.20
3.73 x 1.64 = 6.11
3.73 x 1.28 = 4.77
3.73 x 1      = 3.73

That seems clear to me....  M20 with 3.31:1 has better gearing thru 1-2-3 gears than M21/M22 with 3.73:1 rear...  AND you get a better highway gear (10% better mileage at 10% less wear on your engine)... 

[X33RS]

Yeah, that's how I meant to come across, lol.  The M21 and 3.73's are pretty common but I've always felt the M20 with less rear gear gives better drivability all the way around.  I run the M20 fairly often because of that, since I tend to want to drive my cars, sometimes long distances.  Even though 3.73's aren't a bad all around gear if you can get a 28" tire under it (28" tire gives 2800 rpm cruise at 65 mph) and I find that pretty comfortable.  Shorter rear tire then I tend to want to knock some rear gear out of it.

[dannystarr]

X33RS, what size tire would that be to get the good mileage without over revving... Danny

[jdv69z]

Mine Z has 3:73 w/ M20. I think it's right for in town driving. Too much gear on the highway. I'm revving 3000 at 60 mph. I also think there's a reason the 3:73 was the base factory gear.

[X33RS]

X33RS, what size tire would that be to get the good mileage without over revving... Danny

If your looking for a 28" tire there are only a couple options that I know of that may or may not fit.
A 275-60-15 is 28" and usually what I'll run on the back of most cars, but it's a tight fit on a 69 camaro and would likely rub unless you got fancy with backspacing and rim width.

Another option would be a 235-70-15 which is 27.9" tall and doesn't have near the width of the 275's, so these would be a much easier fit on the rear with stock wheels.

If you want to go more then BFG makes a 255-70-15 which is 29" tall.   Depending on the car I sometimes mount these tires on extra wheels and can quickly toss them on for a long highway trip.  That way most of the time your regular size tires stay on the car.

Keep in mind an inch added to rear tire height only knocks about ~150-200 rpm off the cruise rpm.  It's not a big change unless you're running 26" tires.

I generally run a 255-60-15 on the back of a 69 camaro which fits snug and fills the wheel wells nicely.  These are 27" tall.  With 3.73's I'll turn 3,000 rpm to go 65 mph.  I've criss crossed the country cruising like this without complaint but could knock that cruise rpm down to 26-2700 with the 255-70's tossed on.

[BULLITT65]

Great number crunching, & Good info brother.

[67L78]

X33RS how tall is a 245-60-15? Good info on the gears and tires, thanks.

[X33RS]

X33RS how tall is a 245-60-15? Good info on the gears and tires, thanks.

Doing the math they are just over 26" tall.

Maybe this will help you guys, here's the formula

Section width x aspect ratio = section height

Section height x 2 = Combined section height

Combined section height / 25.4 = final diameter

Final diameter + wheel diameter = overal diameter.

So a typical 275-60-15 looks like this....

275 x .60 = 165

165 x 2 = 330

330 / 25.4 = 12.992125

12.992125 + 15 = 27.992

Just have to keep in mind the 25.4 number you divide with is a constant number no matter what tire you use.  Also keep in mind this gives you an accurate measurement but different tire manufactures do vary their heights slightly so one brand could be a tenth or two off from another brand.

Hope that helps.

[firstgenaddict]

The GoodYear Wide Tread E70 15's are 26" tall inflated and on the car, I checked all of this and provided it along with multitudes of other specs to Crower when they designed the solid roller for the 302.


If I remember back in the day they would go to a 4.88 and tire height of 30" for many of the drag race tests.