Cam, the rest of the story

Steve Sellers

Steve Sellers

Underconstruction
I am building a mountain road, street use, 1300 with the 231 cam. Yugo head from Bayless, sent through Chris Obert for big valves and porting, Allison`s header and exhaust system and distributorless trigger system with duel 36`s from Vick`s. Running it through a 4 speed with
3.76 gears and aluminum flywheel. So....?
 
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Make sure you run lots of compression.

I personally would not recommend the 3.76.
I had a 4.08 in my 4-speed and then switched to the 3.76.
It killed a lot of the fun. Before, the car felt really quick, both when taking off from a stop and when punching the gas on the freeway. (I run a 1600 with similar mods to yours).
With the 3.76, the car feels like the gears fit the engine, but it also feels much more subdued and normal.

The taller gears still are way too short for comfortable high-speed cruising on the freeway, so you may as well go for more fun on the backroads with the 4.08.

My opinion and experience only.
 
Yes, it sounds like you are building a motor to rev, and the 3.76 is counter-intuitive to that. My guess is your new motor is going to like 4-7000rpm much more than 3-6000rpm which means let the little beast rev. :guitar:
 
I can only say that everyone has a different driving style.

Me, I would rather be slightly slower off the line, but be able to spend more time, and gather more speed, in each gear before needing to shift. Then I can go further into each corner carrying more momentum, and not have to spend so much time shifting.
And when I just have long straights, like on the freeway, I prefer the ability to do that at a lower rpm.

I think Steve's engine will do just fine with the final drive he has chosen. It's what I would choose if building a similar car. My driving style is better with it.

Chris Obert
 
Guys... Steve said a MOUNTAIN ROAD-STREET CAR...

If so... meaning a "mountain road car" that is legal for the street, I think the 4.08's might be better...

If not, if he means a "mountain road AND a street car..." then the 3.76's might be a better "cruising option"...

Mr. Sellers just may become our latest Transmission Expert though switching final drives every week or so...

HA!
 
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Something else not mentioned is tire size... I think that should make a difference on final drive selection as well. a 3.76 ratio is 7.9 percent slower than a 4.08.

For example on a same 13x6 rim, a 205/60-13 installed is 4.3% slower than one with a 185/60-13.

On my '74, I have a 205/50-15 and thats 6.1% slower than a 185/60-13, so just by tire size alone I have nearly matched that 3.76 ratio.
 
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Good catch Rob. I have often changed rear-end ratios...

with just 8 or 10 lug nuts as well!

With my old age, I missed it this time...
 
Black-Tooth said:
with just 8 or 10 lug nuts as well!

With my old age, I missed it this time...
Click to expand...

OK old man (U said it first), the final drive is the second to the last thing that determines how many rpm you are going at a given speed. The tires are the last thing.

So... Talking about changing to a 3.76 from 4.08 is really like talking about going from a small diameter tire to a larger diameter tire.

Using a rpm calculator http://www.ringpinion.com/Calculators/Calc_RPM.aspx lets show some comparisons:

4 speed trans w/ 4.08
Tires: 185/60-13 (21.7" tall)
Trans: 4th gear ( .959 to 1)
Speed: 60mph
RPM: 3635

Changing to 4 speed trans w 3.76
Tires: 185/60-13 (21.7" tall)
Trans: 4th gear ( .959 to 1)
Speed: 60mph
RPM: 3350

Changing tires to 205/60-13 on 4 speed trans w/ 4.08
Tires: 205/60-13 (22.7" tall)
Trans: 4th gear ( .959 to 1)
Speed: 60mph
RPM: 3475

Changing tires to 205/60-13 on 4 speed trans w/ 3.76
Tires: 205/60-13 (22.7" tall)
Trans: 4th gear ( .959 to 1)
Speed: 60mph
RPM: 3202

Make more sense now?

For further comparison, my '74 has 205/50-15 tires on the back and in 4th gear I am spinning 3415 rpm at 60mph. So, with only a tire change, I am close to the same as if I was running a 3.76 ring and pinion and 185/60-13's.
 
Almost right

You meant changing to a 3.76 from 4.08 is really like talking about going from a *larger* diameter tire to a *smaller* diameter tire.

Paul
 
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