[Tom Vaught]

Originally Posted by PontiacJim1959

Hmmm. How did our engines ever last when speeds were 55MPH, tire size was 26.5, and we had rear gear ratio's that were 2.56, 2.73, and 2.93?

Maybe the 2.56 posi in my brother's '68 Bonneville w/400CI should have destroyed his engine because he was lugging it doing 55MPH on the interstate. What did those factory engineers know anyway?

I guess I better tear down the 360 in my Fury with its 2.73 gearing just to make sure I haven't beat the bearings out of it by lugging it around town. On the highway I cruise at 75MPH, so I guess I am good there, right?

Never heard of such BS, guys. 1,200 RPM in 4th gear would be lugging it. 2,300 RPM is not lugging an engine unless you have such a radical cam the engine didn't come alive until 2,500-3,000 RPM's.

And as pointed out, the factory advance curve generally did not reach total advance to near 4,000 RPM's. Did all those engines suffer from carbon build up on the pistons & heads? Of course they did because that was a normal expectation of the old leaded gas. I don't recall anyone adjusting timing to prevent this as most mechanics/garages simply told you to blow the carbon out of it by hard accelerations a couple times - and you could literally see the black smoke pour out the exhaust and when it cleared up, you were done and the engine ran great again.

There must be a really young crowd on this forum.

I think other issues are at play here.

X2 on the above post.

I used to swap from a 4.33 gear Rear Axle to a 2.56 Rear Axle if I knew I was going on a long trip. About a 2 hour job to do the Axle swap.

I could cruise at 70 mph all day long with that 2.56 gear and my Muncie 4 speed in 4th gear. So like I said above, I agree with PontiacJim1959.
A lot of miss-information being posted on in this thread when it comes to higher gear ratios.

PontiacJim1959 has it right, Tom S has it right, just saying.

Tom V.

[ponjohn]

With all of this said, I do believe that cam selection becomes important when considering locking up the convertor from 1800-2200 rpm. I would guess ( no expert by any stretch) that you'd want a wider LSA.

[Formulajones]

Here's what I do Footjoy, and it works well for me on several cars.

A good example is our 69 Z/28. Little 302 with a 254 @ .050 cam. I'm running 3.55's in it with a .64 overdrive (TKO600 5 speed)

It's 11:1 compression with the original iron 186 heads. With that cam it's very happy on 91 pump gas and is daily driven with over 30k miles on the setup now over a 3 year period.

It likes 36 degrees of timing and it's all in by 2600 rpm. That rpm is where it wound up with the spring assortment I was playing with so I left it with intention of maybe going back in and slowing it down a pinch, just never found the need to. The vacuum advance adds 10 degrees.

I lug this thing around town all the time at 30-35 mph, barely 1,000 rpm in 5th gear and it doesn't buck or kick or complain the least bit. Drives very smooth and is actually a pleasure around town without the need to constantly look for gears. Had to get in depth with the carb circuits to make it really happy at those low rpms, but worth the effort. Wife drives it to work, the car behaves like a Cadillac.
On the highway 1800-1900 rpm is 65 mph and it will climb the Bradshaw mountains from sea level to 7,000 feet elevation without the need to downshift and will actually pick up speed in 5th gear while doing it. It cruises 75 mph at 21-2200 rpm all day and returns 22 mpg.

I have not found the need to mess with the timing since the overdrive was installed. I'm guessing it's likely around 28 to maybe 30 degrees mechanical advance at those low rpm cruise speeds, and has the full 10 degrees of vacuum on top of that with the light throttle at cruise so I'm lucky to be seeing maybe 38-40 degrees at light throttle cruise in overdrive. Which is fine, it doesn't complain and still returns very good MPG. Went from 17 with the 4 speed manual to 22 mpg with the 5 speed.

Technically you would want to see as much as 45-48 degrees and sometimes maybe 50 degrees at your light throttle cruise speeds for maximum MPG return and efficiency but that's really not doable with overdrive and mechanical distributors with the low rpm they will cruise at.
Now if you had a Holley Sniper with timing control and full control of digital timing on a graph, it's doable. Mechanical distributor, not so much.

[Formulajones]

As another example I'm getting ready to do, and I don't foresee any issue, is my 454 Chevelle. 242/248 @ .050 cam. It's getting a 4L80E with a lockup stall converter. So in overdrive with the lockup it'll act exactly like the manual trans example I posted above.
It has timing all in at 2800, 38 degrees mechanical. I have another 10 degrees of vacuum advance on top of that.
The great thing about the electronic auto overdrives is that I can program that converter to lock anywhere I want with what ever throttle position I want. So it's much easier to dial in a comfortable lockup speed and tailor it to the engine combo.
I've been down this road before, when doing an auto overdrive the electronic versions have a big advantage in this department. The TV cable mechanical style overdrive autos are finicky with lockup and not as adjustable, using a vacuum switch that has a very small window for any adjustment that most times isn't enough for some engine combos, which is why you see a lot of those transmissions built without a lockup converter to just eliminate the hassle. But you then need a very well built converter that is efficient and couples very well in high gear to avoid the mushy feel in OD you sometimes get with a stall converter.

[footjoy]

I was looking through my old 1971 auto repair manual and found these pages.

It appears we have come along way from factory recomendations.












Sorry I am not good with pictures

[PontiacJim1959]

Originally Posted by footjoy

I was looking through my old 1971 auto repair manual and found these pages.

It appears we have come along way from factory recomendations.


Attachment 546617




Attachment 546618




Sorry I am not good with pictures

You are comparing apples to oranges - then and now, 100 octane leaded gas vs non-leaded ethanol gas, and the factory installed components vs the modified builds most of us have.

If you mechanic is not between the ages of 55-70, then he does not have the knowledge, experience, & skill to work on an "older" car. This is one reason why most all Pontiac powered Pontiacs will go the way of the LS because today's mechanics rely on electronics to monitor, diagnose, adjust/repair an engine problem via a plug in computer port, a screen, and corresponding fault codes. Those of us who actually grew-up and worked on these cars could listen, yes, listen, or take the car on a road test, and tell you what was wrong with it. Try that with today's "auto technician." It ain't gonna happen. LOL

[Navy Horn 16]

The best thing you can do is get a wideband AFR gauge and make sure you are running the proper mixture through the RPM range. If you weren't burning all the fuel and having carbon build up, it wasn't your timing it was rich.

[Tom Vaught]

Originally Posted by PontiacJim1959

You are comparing apples to oranges - then and now, 100 octane leaded gas vs non-leaded ethanol gas, and the factory installed components vs the modified builds most of us have.

If you mechanic is not between the ages of 55-70, then he does not have the knowledge, experience, & skill to work on an "older" car. This is one reason why most all Pontiac powered Pontiacs will go the way of the LS because today's mechanics rely on electronics to monitor, diagnose, adjust/repair an engine problem via a plug in computer port, a screen, and corresponding fault codes. Those of us who actually grew-up and worked on these cars could listen, yes, listen, or take the car on a road test, and tell you what was wrong with it. Try that with today's "auto technician." It ain't gonna happen. LOL

Can't disagree on the statements above.

Even in the early 70s Holley used Electronic instrumentation to help diagnose issues. Mostly these issues were with the engine and not with the basic carb calibration. They would figure out what the engine liked for a given calibration and then passed on that information to the engine calibrators.
Example: "For this altitude and HP level this is what we recommend with this specific engine calibration (when used with this carburetor and engine configuration)."

Not saying over time that the older mechanics could not have figured out exactly the same solution but we needed to do the work quickly so we used Instrumentation as well as KNOWLEDGE. Our instrumentation cost several thousand dollars per wide band unit. You can buy very good instrumentation for a lot less today but you just have INFORMATION. You need to know WHAT that information is trying to tell you. A lot of people do not understand that requirement.

Tom V.

[Formulabruce]

Keep in mind that today's fuel (talking 10% ethanol) is less dense. This requires more fuel than in 1970 to do the same work, even if its the same or higher octane. This means richer idle circuits and different set up than factory. Setting a Pontiac to modern A/F may not be optimal. I'm still a big fan of test drives.

[pastry_chef]

Originally Posted by PontiacJim1959

If you mechanic is not between the ages of 55-70, then he does not have the knowledge, experience, & skill to work on an "older" car.

Strongly disagree.
I have several friends younger than this who are experts with old V8 / muscle car stuff. And 15 to 20 years ago was prime time for us. Hundreds of hours tuning ignition and fuel curves. One buddy worked as a professional mechanic for 20 years, I helped him build his 502 but his own hands were totally capable. It really depends on where you live and the person.

[Formulajones]

Originally Posted by Formulabruce

Keep in mind that today's fuel (talking 10% ethanol) is less dense. This requires more fuel than in 1970 to do the same work, even if its the same or higher octane. This means richer idle circuits and different set up than factory. Setting a Pontiac to modern A/F may not be optimal. I'm still a big fan of test drives.

Correct. I've said that many times on here but it still seems people are fixated on that magic 14.7:1 AFR.

Stoich for 10% ethanol is 14:1, basically 3/4 of a point richer. You can certainly tune a car and run the idle and part throttle leaner, but more often than not the idle quality suffers a bit, vacuum levels drop, and all around drivability suffers to some degree.

So in a nut shell, these factory carbs are actually a bit lean for todays fuels and they do take some fiddling in the idle circuits to restore some idle quality and drivability. Just how much and what depends on the carb and engine in question. Ethanol also varies at the pump, throwing a curve ball in the mix.

[Mr Anonymous]

An 80's G-body car was commonly equipped with 2.56 gears and the 200-4R overdrive. Probably do 300 mph in space. I had two of those cars. Just dumb. And all done that way for the "grams per mile" emissions testing. Yep, if the damn engine hardly spins in one mile, its gonna make less grams, according to their logic.

[Formulajones]

Originally Posted by Mr Anonymous

An 80's G-body car was commonly equipped with 2.56 gears and the 200-4R overdrive. Probably do 300 mph in space. I had two of those cars. Just dumb. And all done that way for the "grams per mile" emissions testing. Yep, if the damn engine hardly spins in one mile, its gonna make less grams, according to their logic.

Those were some pretty dismal years, lol. They were even doing that in the GM F-bodies. Had an 88 Iroc 350 TPI with 2.77 gears out back. Thankfully the 700r helped a bit with a 3.06 first gear, but the .70 overdrive would just loaf down the highway. Even the 4th gen Fbodies (had 4 of those) with 6 speeds and .50 overdrive were loafers on the highway with 3.42's. 1500 rpm was almost 70 mph lol. So GM was still following that logic even in the early 2000's but they were getting better with the 1-4 transmission gear ratios.
I was okay with it, those cars returned fantastic MPG and still ran like stink.
It's why I always liked the fox body mustangs better during the 80's era. With the 5 speed and 3.08's out back, and 3.35 first gear, they were still pretty snappy, but the .64 overdrive put it to sleep on the highway. A great mix of both.

[Tom Vaught]

Originally Posted by Formulajones

I was okay with it, those cars returned fantastic MPG and still ran like stink. It's why I always liked the fox body mustangs better during the 80's era. With the 5 speed and 3.08's out back, and 3.35 first gear, they were still pretty snappy, but the .64 overdrive put it to sleep on the highway. A great mix of both.

I drove a lot of those cars, as a Drive Evaluator, for both them and the CHP Police Mustangs. You had to have very good low speed acceleration and still have the ability to run 140 mph+ speeds on I-40 out west.

Most owners seem to gear for one mode or the other but the later generation drivelines were able to do both and better. Example a 10 speed Corvette Transmission.

Tom V.

[Formulajones]

Originally Posted by Tom Vaught

I drove a lot of those cars, as a Drive Evaluator, for both them and the CHP Police Mustangs. You had to have very good low speed acceleration and still have the ability to run 140 mph+ speeds on I-40 out west.

Most owners seem to gear for one mode or the other but the later generation drivelines were able to do both and better. Example a 10 speed Corvette Transmission.

Tom V.

Yep, The foxes were a pretty solid little package for their time.

I especially liked the 6 speed 4th gens, with a 2.66 first gear and .50 overdrive. With 3.42's they were a good mix, but I liked them even better after swapping to 3.73's. Still gave a good highway cruise rpm and helped the low end at the same time.

I actually swapped my sons fox body to a 2.95 first gear cobra spec T-5, so I could utilize a little more rear gear effectively. The 3.35 first gear is a bit extreme when you start changing rear gears. I put 3.73's out back and has a .63 overdrive in this trans. It's a perfect setup on both ends.

[Tom Vaught]

I have a 3.27 1st gear (5 speed Nash) and a Ford 2.73 Soft Locker so I am inside the window on both ends of your perfect set-up. 5th is 1 to 1.

Tom V.

[Formulajones]

Those kinda work as long as you don't care so much about rpm and MPG. You can't quite get all the way to both ends of the spectrum with the nash 5 speed approach, you give up something on one end or the other, but it's decent for not much money spent.

The final with the current 5th gear T-5 with an actual overdrive ratio and 3.73's out back is a 2.34 vs the 2.73 you're working with.

But I can still enjoy snappy acceleration with a first gear effective ratio of 11.0 You have 8.92 with that setup.

It's hard to beat an actual overdrive transmission.

I've always viewed the Nash as being good fit for doing this.....
Little 302 with 5.13's 3.27 first gear

https://youtu.be/__Ne0sF4IA0

Another buddy of mine used a Nash for his high strung 427 Nova and a bunch of gear out back. Worked really well.

[The Champ]

Originally Posted by Formulajones

Those kinda work as long as you don't care so much about rpm and MPG. You can't quite get all the way to both ends of the spectrum with the nash 5 speed approach, you give up something on one end or the other, but it's decent for not much money spent.

The final with the current 5th gear T-5 with an actual overdrive ratio and 3.73's out back is a 2.34 vs the 2.73 you're working with.

But I can still enjoy snappy acceleration with a first gear effective ratio of 11.0 You have 8.92 with that setup.

I understand that you like a very low (high numerically) effective first gear ratio.

My '64 came with 3.23's and a 4 spd and had an effective 1st gear ratio of 8.27. I had no trouble lighting the tires at will when I was still running that OE setup.

Tom's 8.97 is better than that and with 2.73's in the rear his RPM's are quite reasonable on the highway.

I'm currently running 3.08's with my M20, but will ultimately replace that with an M23Z with that will give me an effective 1st gear of 9.21. I'll be happy with that because I don't have to hack my tunnel and I can retain a stock appearance with my original Hurst shifter.

Not everyone wants or needs to have an effective first gear ratio of 11 or more. To me, that basically makes 1st gear relatively useless.

Your results may vary...

[Tom Vaught]

Originally Posted by The Champ

I understand that you like a very low (high numerically) effective first gear ratio.

My '64 came with 3.23's and a 4 spd and had an effective 1st gear ratio of 8.27. I had no trouble lighting the tires at will when I was still running that OE setup.

Tom's 8.97 is better than that and with 2.73's in the rear his RPM's are quite reasonable on the highway.

I'm currently running 3.08's with my M20, but will ultimately replace that with an M23Z with that will give me an effective 1st gear of 9.21. I'll be happy with that because I don't have to hack my tunnel and I can retain a stock appearance with my original Hurst shifter.

Not everyone wants or needs to have an effective first gear ratio of 11 or more. To me, that basically makes 1st gear relatively useless.

Your results may vary...

I think you are spot-on with your post Champ.
Another thing, The engine in the car will be a 455 engine with aluminum heads, etc. The last thing I need on that Convertible is more torque multiplication in 1st gear. That is the reason why I went with the 2.75 gear vs the typical 3.08 gears some run in their vehicles.

So "Not everyone wants or needs to have an effective first gear ratio of 11 or more" is again hitting right in the center of the bullseye for my performance needs.

Tom V.

[Formulajones]

It's never been a matter of an engine needing it. It's really a matter of clutches and ease of drivability with me. I've had plenty of stick cars with 1st gear multiplication in the 8's and even low 9's and it doesn't matter how much torque an engine makes, you still have a certain amount of clutch slippage needed to get going and in stop and go traffic that gets a little worse for wear. Parades, LA traffic etc... isn't fun when you have a setup like that. Reverse is even worse.

We daily drive one of our stick cars. It had 8.94 1st gear multiplication. I can tell you that after about 20k miles of daily use, clutch chatter starts to set in. It's not bad but it's there, and that's just a 3400 lbs. car. I find that torque multiplication right around 10 to be a sweet spot for any combination. Torque has nothing to do with it.

If I had a Pontiac stick car, with a 455, I wouldn't set it up any different than anything else. I'd shoot for something in the low 10's for first gear. Managing tire spin is a matter of setting up the suspension properly so that's not even a concern.

While I understand people don't want to spend the money on overdrives, and some are perfectly happy with their 2.73 rear gears, it's still not going to return excellent gear multiplication and low rpm cruising at the same time. You have to sacrifice one end or the other, or find a happy medium and live with so so results. If that is what makes you happy, then there is nothing wrong with that.