Why Does Close Ratio Feel Better?

[James B.]

I have two mid-years that I drive frequently- 1964 L-84 with close ratio and 3.70 and 1967 L-79 with wide ratio and 3.55. Both cars have 205/75s.

When shifting the '67 it feels like I am dropping a lot in RPM vs the '64 (I am talking about the 1/2 and 2/3 shifts). However, when I calculate the gear splits they are almost the same. Also, if I calculate rev difference- say I shift from 1st to 2nd at 4,000 RPM it is essentially the same at 1016 RPM for both configurations- the only difference is road speed; the '67 would be at 34.8 MPH vs the '64 at 38.3 MPH. I have had several other mid-years and always the same sense that I dropped more RPM at shift points with wide ratio transmissions.

I have checked both cars and know the differentials and transmissions are correct. Also, I know there is a significant difference in clutch engagement torque and torque/HP through the operating range in these two cars. The situation I am trying to describe is mild acceleration and shifting at 4000 as the example. I realize the ratios on the '67 are 10% deeper but the splits are the same.

Can anyone explain why I feel such a difference or am I delusional (or the aging process catching up).

[Wayne P.]

Re: Why Does Close Ratio Feel Better?

James I wish I had your problem two great cars to chose from. Do they both have the same exhaust size ? good luck

[William C.]

Re: Why Does Close Ratio Feel Better?

Delusion, as the gears inside the trans are the same and don't know that box they are in, the 3-4 shift is the only place where the actual gears are different, but then you already know that, so what elsle is left?

[Duke W.]

Re: Why Does Close Ratio Feel Better?

Good and correct analysis. The difference in feel is probably due to differences in the shape of the torque/power curves.

The L-79 should actually feel stronger due to both shorter overall gearing and better torque up through the top of the mid range. The L-79's peak rated SAE gross torque is 360 lb-ft @ 3600 versus the '74 L-84's 350 @ 4600. Of course, these advertised SAE gross ratings are highly suspect, but maybe the engines have been modified from their OE form, like different camshafts or spark advance curves.

You should give each a good tuneup, including a compression check. Also, determine if the spark advance maps are modified.

The only real definitive test is a chassis dyno. Start the pulls at 1000 revs and see how they compare.

Duke

[James B.]

Re: Why Does Close Ratio Feel Better?

Thank-you all for the responses,
Wayne- Thanks and yes, they are both neat cars. '67 has new CCentral off road exhaust (as it originally had, per tank sticker). Of course the '67 is 2" XMs into 2 1/2 pipes instead of 2 1/2" on 64.

Bill- You are probably right re delusion! I have always believed close ratio meant narrow splits and maybe that belief and the differences in torque @RPM have given me the wrong impression.

Duke- '67 is 3 owner (I talk to the other two and have all receipts) car with 52,000 miles and heads have never been off. '64 has been rebuilt w/ LT-1 cam replacing the 30-30. I've borescoped both cars and they still have high compression pistons (of course I don't know what they did for head gaskets on the '64). Jerry Bramlett recently did my fuel unit and distributor so I suspect that advance curve is correct. Both recently tuned but I have never done compression checks. Anyway, I don't think state of tune is significant in this- I think you have highlighted the problem (the driver).
The 1000 RPM difference in torque peaks is interesting; I've never focused on that. I will say the '67 feels like a stump puller off the line vs the '64. If I ever get the opportunity I will chassis dyno both, I would love to see what the complete torque/hp curves look like.

[Kenneth B.]

Re: Why Does Close Ratio Feel Better?

Delusion, as the gears inside the trans are the same and don't know that box they are in, the 3-4 shift is the only place where the actual gears are different, but then you already know that, so what elsle is left?

OK Please tell me then why did GM offer wide & close ratio if there was no difference exect 3/4. Was it a marketing thing. Seems to me that there had to be a reason other than smoke & mirrors. Why were most HP Corvettes ordered with close ratio then?
KEN

[Michael J.]

Re: Why Does Close Ratio Feel Better?

Interesting comments. I have a '67 with an M21 and 3.55 rear, and a '66 with an M20 and a 3.36 rear. I don't really sense much difference in accel and gearing, but it seems the M20 has a closer gate shifting pattern, as I seem to miss 2nd and get to 4th too easy after driving the M21 which seems to have a wider shift gate pattern. Is this my imagination or are they different too?

[Kenneth B.]

Re: Why Does Close Ratio Feel Better?

Interesting comments. I have a '67 with an M21 and 3.55 rear, and a '66 with an M20 and a 3.36 rear. I don't really sense much difference in accel and gearing, but it seems the M20 has a closer gate shifting pattern, as I seem to miss 2nd and get to 4th too easy after driving the M21 which seems to have a wider shift gate pattern. Is this my imagination or are they different too?

The linkage has 2 holes one for a long shift & a other for a short shift. the factory set it for the long shift.
KEN

[Duke W.]

Re: Why Does Close Ratio Feel Better?

Thank-you all for the responses,

Duke- '67 is 3 owner (I talk to the other two and have all receipts) car with 52,000 miles and heads have never been off. '64 has been rebuilt w/ LT-1 cam replacing the 30-30. I've borescoped both cars and they still have high compression pistons (of course I don't know what they did for head gaskets on the '64). Jerry Bramlett recently did my fuel unit and distributor so I suspect that advance curve is correct. Both recently tuned but I have never done compression checks. Anyway, I don't think state of tune is significant in this- I think you have highlighted the problem (the driver).
The 1000 RPM difference in torque peaks is interesting; I've never focused on that. I will say the '67 feels like a stump puller off the line vs the '64. If I ever get the opportunity I will chassis dyno both, I would love to see what the complete torque/hp curves look like.

The LT-1 cam goes a along way to recover low end torque relative to the 30-30, but is not quite as strong down low as the L-79 cam. You should verify the spark advance maps, and the L-79 map can probably be quickened without detonation. The centrifugal curves are very different and the specs are in the service manuals and AMA specs.

You don't know what the spark advance map is unless you get a sheet from whoever worked on the distributor or you map it yourself. Everyone has their own ideas of what it should be.

It's easy to measure head gasket thickness. Just use feeler gages at the corners of the head/block interface.

The original four-speed was designed for road racing in a relatively light weight, high torque car - the 1957 Corvette.

As it migrated to heavier cars, shorter gearing was required for good street performance. So GM just changed the countershaft ratio with a different clutch gear and countershaft to shorten the first three gears. Everything else inside both is the same for a given year except the M22, which had lower helix angle gears and other detail differences.

It would have been better to put the big gap between first and second gear, where it would have been less noticeble, but that would have required more parts changes.

They finally did this with the Super T-10 when it replaced the Muncie in the seventies.

Duke