L79 & L84 Torque Curves

[James B.]

Just for academic interest does anyone have copies of GM Torque/HP curves for the '67 350 Horse and '64 375 Horse motors (maybe GM never published them?). I have one of each and am surprised at how much more clutch engagement torque the '67 has. Drivetrains are different- '67 has WR w/3.55 and '64 has CR w/3.70 so the '67 has a 10% deeper overall ratio. Engines are both stock/original (except L84 has LT1 cam). Both engines recently tuned and running well so I don't have a problem, i'm just curious. I know the fuelie has less low end torque, it would just be fun to see how the torque curves differ, particularly 900 rpm to 2000 and peak torque values @ rpm.
Also, does anyone have revs/mile for 205X70 radials- I measured this and calculated 4 or 5 years ago and then filed it....somewhere.

[James B.]

Re: L79 & L84 Torque Curves

Forget revs/mile request- I went to tire rack website.

[Duke W.]

Re: L79 & L84 Torque Curves

Full range torque/power curves are tough to come by. WHAT??? You mean there is something more to engine performance than the one-dimensional peak power figure?

Some year AMA specs may have the marketing manipulated SAE gross curves, for what they're worth, and some were published in Corvette News, same comment.

If you really want to know, put them both on a Dynojet chassis dyno and start the pulls at 800 revs. Copy the test files onto a CD and use the free Dynojet WinPEP software to display them on your computer and post them here.

The problem is finding a friggin' chassis dyno operator who realizes that there is life below 3000 revs.

Duke

[George J.]

Re: L79 & L84 Torque Curves

Full range torque/power curves are tough to come by. WHAT??? You mean there is something more to engine performance than the one-dimensional peak power figure?

Some year AMA specs may have the marketing manipulated SAE gross curves, for what they're worth, and some were published in Corvette News, same comment.

If you really want to know, put them both on a Dynojet chassis dyno and start the pulls at 800 revs. Copy the test files onto a CD and use the free Dynojet WinPEP software to display them on your computer and post them here.

The problem is finding a friggin' chassis dyno operator who realizes that there is life below 3000 revs.

Duke

But Duke, if you drive one of them little 4-banger dohc jobs, it doesn't begin until 4000rpm!!!

George

[James B.]

Re: L79 & L84 Torque Curves

Duke, thanks for the reply. Yes, I thought it would be difficult to get curves below 3,000. I do have the dyno run from when Jerry rebuilt my fuel unit but that was on his car- '63, 360 horse w/ Duntov cam and yes that was from 2900 (300 #') to 6100 (199 #')rpm (4th gear, 3.70- acceleration).
If I find a DynoJet and the opporunity I will run them both and post results.

[Duke W.]

Re: L79 & L84 Torque Curves

But Duke, if you drive one of them little 4-banger dohc jobs, it doesn't begin until 4000rpm!!!

George

After remapping the spark advance and reindexing the cams, the Cosworth Vega easily pulls from 1500 in fifth gear (about 30 MPH), and I can drag it down to 200 in first, floor the throttle, and it takes off without protest.

It makes 80 percent of peak torque at 2000, and the upper boundary of the 80 percent peak torque bandwidth is beyond my self-imposed 7000 rev redline.

I have not been able to achieve this broad torque bandwidth in a vintage 327.

A few years ago I did a Dynojet test. After arguing intensely with the dyno operator he finally agreed to start the pulls at 1000 revs, and we did two pulls from 1000 to 7000, so I know the FULL range performance.

Around town fuel economy is up 30 percent. I can run a gear higher in most situations, and highway fuel economy is up about 10 percent. The EPA fuel economy ratings were 16/25. The city rating was low due to the lazy centrifugal curve, no vacuum advance (which I added) and the excess overlap (for NOx control) which conspired with the lazy spark advance map to kill low end torque and fuel economy.

After reindexing the cams for less overlap, NOx doubled, but it was only a quarter of the maximum allowable with the OE cam indexing in the CA ASM emission test.

It's all in the "tuning", which includes valve timing and the spark advance map.

Duke

[Duke W.]

Re: L79 & L84 Torque Curves

Yes, I thought it would be difficult to get curves below 3,000. If I find a DynoJet and the opporunity I will run them both and post results.

The only reason it's "difficult" is because of the damned dyno operators. They all seem to have some inexplicable aversion to starting pulls at low revs. If your engines will pull from 1000 revs in third gear on the road, which they should do with ease if they are running properly, they will pull smoothly from 1000 on the dyno.

You can search for installed Dynojets by zip code on their web site. Make sure the engines are in peak tune in road testing, then put together a test plan, review it with the operator, and get his concurance that he will execute the plan.

But even then you may have to argue with him once the car is on the dyno.

The L-79's low end torque can be enhanced by quickening the lazy OE centrifugal curve. The '64-'65 L-84 curve is aggressive, but you should verify both, and experiment with quickening the L-79 curve with lighter springs. Thorough SOTP road testing will help achieve best results when measured on a dyno.

Also, find an opeator with a wide band O2 sensor to take A/F ratio readings to verify proper fuel flow. The FI system can be easily adjusted between pulls and by running a test at part throttle maintaining manifold vacuum in the typical cruise range, you can verify cruise A/F ratio.

Duke

[George J.]

Re: L79 & L84 Torque Curves

After remapping the spark advance and reindexing the cams, the Cosworth Vega easily pulls from 1500 in fifth gear (about 30 MPH), and I can drag it down to 200 in first, floor the throttle, and it takes off without protest.

It makes 80 percent of peak torque at 2000, and the upper boundary of the 80 percent peak torque bandwidth is beyond my self-imposed 7000 rev redline.

I have not been able to achieve this broad torque bandwidth in a vintage 327.

A few years ago I did a Dynojet test. After arguing intensely with the dyno operator he finally agreed to start the pulls at 1000 revs, and we did two pulls from 1000 to 7000, so I know the FULL range performance.

Around town fuel economy is up 30 percent. I can run a gear higher in most situations, and highway fuel economy is up about 10 percent. The EPA fuel economy ratings were 16/25. The city rating was low due to the lazy centrifugal curve, no vacuum advance (which I added) and the excess overlap (for NOx control) which conspired with the lazy spark advance map to kill low end torque and fuel economy.

After reindexing the cams for less overlap, NOx doubled, but it was only a quarter of the maximum allowable with the OE cam indexing in the CA ASM emission test.

It's all in the "tuning", which includes valve timing and the spark advance map.

Duke

Duke,
I knew you'd have a thorough answer.

George

[Jerry G.]

Re: L79 & L84 Torque Curves

The only reason it's "difficult" is because of the damned dyno operators. They all seem to have some inexplicable aversion to starting pulls at low revs. If your engines will pull from 1000 revs in third gear on the road, which they should do with ease if they are running properly, they will pull smoothly from 1000 on the dyno.

You can search for installed Dynojets by zip code on their web site. Make sure the engines are in peak tune in road testing, then put together a test plan, review it with the operator, and get his concurance that he will execute the plan.

But even then you may have to argue with him once the car is on the dyno.

The L-79's low end torque can be enhanced by quickening the lazy OE centrifugal curve. The '64-'65 L-84 curve is aggressive, but you should verify both, and experiment with quickening the L-79 curve with lighter springs. Thorough SOTP road testing will help achieve best results when measured on a dyno.

Also, find an opeator with a wide band O2 sensor to take A/F ratio readings to verify proper fuel flow. The FI system can be easily adjusted between pulls and by running a test at part throttle maintaining manifold vacuum in the typical cruise range, you can verify cruise A/F ratio.

Duke

Be sure and get A/F from both sides. my unit ran leaner on the drivers side. Haven't figured that one out yet. i'm working on it. Jerry

[Duke W.]

Re: L79 & L84 Torque Curves

With a typical OE dual plane manifold each side has two cylinders drawing air and fuel from each side of the carb, so typically just checking one side gets you the average.

With Fuel Injection, unless you have different nozzle codes on each side, or for some reason the same nozzle code has significant flow rate differences, both sides should be the same.

The other possibility is significantly different air flow in the heads, which could be a case if you have heads that were reworked at a different time and place.

Duke