Which Griffin Transaxle Behind a LS376?

I'm still trying to understand the performance powerband and ideal crusing speed of the LS376 or LS7 engines.

Has anyone done an analysis to determine the optimal transaxle gear-ratios for a Griffin 960SS transaxle living behind a General Motors LS376/480 (redline 6,600 rpm) or LS7 (redline 7,000 rpm) engines?

This would be in mostly street-driven Superlite SL-C (maybe 4-5 track type events per year). Assume rear tires are 325/30ZR19 for the sake of argument.

I think the Ricardo uses a 2.611 1st, 0.625 6th, and 3.36 final drive).

I think the '13 Corvette and ZO6 trasmissions use a 2.66 1st, 0.5 6th, and 3.42 final drive.

Of the two standard Griffin 960ss options, I think the one with 2.411 1st, 0.513 6th, and 3.73 final drive would be the better of the two choices (instead of the version with 2.625 1st, 0.553 6th, 3.73 final drive). I know their website also shows some other variations...enough to make my head hurt. :)

-Harold Jones
Dreaming of an SL-C Someday
 

Seymour Snerd

Lifetime Supporter
I'm still trying to understand the performance powerband ...

If you want to really understand that you need the torque curve for the engine(s). I would imagine those are around for the popular crate engines. Given that, you can plot max. rear wheel force vs mph in each gear and end up with a very intuitive visual model of how the gear ratios interact. You'll want to do this in Excel or its equivalent. Here's an example of the kind of chart I'm talking about:

old_vs_speed_01.jpg

(5 gears gets you to 40 mph? It's not my chart....)

OTOH, with that kind of engine torque in that light a car, does it really matter? :)

Cruising speed is mostly a matter of picking your favorite speed and calculating what RPM you'll have in top gear in each case.
 
A guy posted an excel worksheet a while ago, and I added the stock Griffin ratios at the far right. You can change max engine rpm, tire size, final drive, etc. and play with the results.

I don't vouch for all the data on the various Porsche gearboxes; some of the ratio spreads don't look right, such as the 2007-2009 GT2 box with 4th and 5th gears almost identical.

Now I'm trying to figure out how to re-post the worksheet...

JR

Here it is:
 

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Thanks for the replies and tips. I'm going to chew on that information for a bit and try to make better sense of it.

That spreadsheet is intriguing, and I want to spend some time trying to validate the data for the transaxles that I care about and the hidden formulas to understand how it really works.

I also like the idea of trying to plot the plot max. rear wheel force vs mph in each gear, too.

I see how the final drive ratio and tire size are important to the discussion, too. It is interesting to see the vastly different Final Drive (or Ring and Pinion) ratios in that excel spreadsheet for the various transaxles. I'm thinking that Chevrolet surely must have thought about this a lot when they decided to match their motors to the Corvette ZO6 transmissions and rear-ends and that if I can't go wrong if I stay close to those specs???

v/r,
Harold
 
That spreadsheet is intriguing, and I want to spend some time trying to validate the data for the transaxles that I care about and the hidden formulas to understand how it really works.

.....

I see how the final drive ratio and tire size are important to the discussion, too. It is interesting to see the vastly different Final Drive (or Ring and Pinion) ratios in that excel spreadsheet for the various transaxles. I'm thinking that Chevrolet surely must have thought about this a lot when they decided to match their motors to the Corvette ZO6 transmissions and rear-ends and that if I can't go wrong if I stay close to those specs???

It's just arithmetic. The Porsche transaxles were designed for cars with smaller, higher-revving engines. Thus the low first gear to get the car rolling with much less torque than a Chevy V8 has.

Going with Corvette-type ratios is not a bad idea, but remember that GM put a HUGE 5th-to-6th gap in the trans to get best fuel economy on the highway, as did Dodge with the Viper. Some of us would prefer progressively tighter gear spacing, as the standard Griffin gearsets offer (assuming the boxes actually get built.)

To my mind most of the Porsche boxes are too short for street use of an SLC; making the V8 engine in your 2500 pound car turn 3000 RPM or thereabouts in top gear on the interstate seems less than ideal, and First gear is so low (for a 2500 pound car with over 300 ft-lbs of torque just off idle) that it might as well not be there in this application.

JR
 
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If we are talking about a mainly street driven car then I prefer an overdrive 6th gear (if you have a 6th gear). With the torque and the lack of weight of these cars you don't really need 6 gears. It's just shifting for shiftings sake. I'd rather not throw money out the exhaust pipe while reving down 5 to LA just to say I extracted every last bit of ecceleration out of the grearbox. Now a race car? That would be a different story.
 
If you (or anyone) can get torque curves for the various engines I can help with the spreadsheet part.

How is this; I found these torque curves for the LS3, LS376/480, and LS7 motors on the GM Performance site.
 

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  • LS376.480 Dyno Chart.jpg
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It's just arithmetic. The Porsche transaxles were designed for cars with smaller, higher-revving engines. Thus the low first gear to get the car rolling with much less torque than a Chevy V8 has.

Going with Corvette-type ratios is not a bad idea, but remember that GM put a HUGE 5th-to-6th gap in the trans to get best fuel economy on the highway, as did Dodge with the Viper. Some of us would prefer progressively tighter gear spacing, as the standard Griffin gearsets offer (assuming the boxes actually get built.)

To my mind most of the Porsche boxes are too short for street use of an SLC; making the V8 engine in your 2500 pound car turn 3000 RPM or thereabouts in top gear on the interstate seems less than ideal, and First gear is so low (for a 2500 pound car with over 300 ft-lbs of torque just off idle) that it might as well not be there in this application.

JR

Yup, it's just arithmetic. :thumbsup: I'm the original author of it and the original thread is here: http://www.gt40s.com/forum/rcr-foru...earing-your-transmission-right-worksheet.html. There's some explanation in there of how it works, but I'm happy to answer any questions.

I agree that a lot of the Porsche boxes are not well suited for mating to a V8. Likely best candidates are the ones coming off Turbos and GT2 (also a TT engine). Call Stan at GBox to get more info on potentially changing gearing if you feel like you need to.

Tim
 
Yup, it's just arithmetic. :thumbsup: I'm the original author of it and the original thread is here: http://www.gt40s.com/forum/rcr-foru...earing-your-transmission-right-worksheet.html. There's some explanation in there of how it works, but I'm happy to answer any questions.

Tim: Kudos on an awesome spreadsheet and reference tool. I cobbled a much cruder version about 3-years ago when I rebuilt my '88 Fox Mustang for that build, but yours is way more detailed and useful. Job well done, Sir.

-HJ
 

Seymour Snerd

Lifetime Supporter
Here are the promised force vs. mph in gears for the three mentioned gear ratio sets, all behind the LS-376 torque curve:

Z06.jpg

Ricardo.jpg

Griffin.jpg

Also just for fun the three engine torque curves "de-marketinged" on the same axes.
LS Torque.jpg
 
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Here are the promised force vs. mph in gears for the three mentioned gear ratio sets, all behind the LS-376 torque curve:

Nice work, Alan! I am going to study those along side TimT's spreadsheet and try to make sense of it all. It would be too small of a world if so, but I have to ask...do you have/had any family in Roswell, NM?

-HJ
 

Seymour Snerd

Lifetime Supporter
Alan,
Would you do a chart for the G97/50 behind the LS376? Thats what I have and it would be really helpful.

Sure; what are the ratios and tire size or diameter?

BTW the LS376 torque curves stopped at 6,500. Is that the redline for that motor? If not it would make the curves more "realistic" if I had data running all the way to redline.
....

Ooops, ratios right there in the other spread sheet.... back in a bit...
....
OK here are all four charts now including the G97/50; I rescaled them all since the P-box raised the bar on stump-pulling, topping out at almost 6,000 lb in first.
Charts1.jpg Charts2.jpg Charts3.jpg Charts4.jpg
 
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6,600 for ls376 unless your alex and want to take a pushrod engine to F1 rpm's...

<TABLE id=specs_table cellSpacing=0 cellPadding=8 width=525><TBODY><TR><TH align=left colSpan=2>LS376-480 HP - LS3 Gen IV TECH SPECS:</TH></TR><TR><TD style="BACKGROUND-COLOR: #fff">Part Number: </TD><TD style="BACKGROUND-COLOR: #fff">19171224</TD></TR><TR><TD style="BACKGROUND-COLOR: #edf3fe">Block (P/N 12584727): </TD><TD style="BACKGROUND-COLOR: #edf3fe">Cast Aluminum with 6-bolt, cross-bolted main caps</TD></TR><TR><TD style="BACKGROUND-COLOR: #fff">Bore x Stroke (in): </TD><TD style="BACKGROUND-COLOR: #fff">4.06 x 3.62 (103.25 x 92mm)</TD></TR><TR><TD style="BACKGROUND-COLOR: #edf3fe">Camshaft duration (@.050 in): </TD><TD style="BACKGROUND-COLOR: #edf3fe">219 degree intake / 228 degree exhaust</TD></TR><TR><TD style="BACKGROUND-COLOR: #fff">Camshaft type (P/N 88958733):</TD><TD style="BACKGROUND-COLOR: #fff">Hydraulic roller</TD></TR><TR><TD style="BACKGROUND-COLOR: #edf3fe">Compression ratio: </TD><TD style="BACKGROUND-COLOR: #edf3fe">10.7:1</TD></TR><TR><TD style="BACKGROUND-COLOR: #fff">Connecting rods (P/N 12617570):</TD><TD style="BACKGROUND-COLOR: #fff">Powdered metal</TD></TR><TR><TD style="BACKGROUND-COLOR: #edf3fe">Crankshaft (P/N 12597569):</TD><TD style="BACKGROUND-COLOR: #edf3fe">Powdered metal</TD></TR><TR><TD style="BACKGROUND-COLOR: #fff">Cylinder heads (P/N 12598594): </TD><TD style="BACKGROUND-COLOR: #fff">LS3 rectangle port; as cast with 68cc chambers</TD></TR><TR><TD style="BACKGROUND-COLOR: #edf3fe">Displacement (cu in):</TD><TD style="BACKGROUND-COLOR: #edf3fe">376 cu in (6.2L)</TD></TR><TR><TD style="BACKGROUND-COLOR: #fff">Engine type:</TD><TD style="BACKGROUND-COLOR: #fff">LS Series Gen IV small-block V8</TD></TR><TR><TD style="BACKGROUND-COLOR: #edf3fe">Maximum recommended RPM: </TD><TD style="BACKGROUND-COLOR: #edf3fe">6600</TD></TR><TR><TD style="BACKGROUND-COLOR: #fff">Part number:</TD><TD style="BACKGROUND-COLOR: #fff">19171224</TD></TR><TR><TD style="BACKGROUND-COLOR: #edf3fe">Pistons (P/N 19165089): </TD><TD style="BACKGROUND-COLOR: #edf3fe">Hypereutectic aluminum</TD></TR><TR><TD style="BACKGROUND-COLOR: #fff">Recommended fuel: </TD><TD style="BACKGROUND-COLOR: #fff">92 octane</TD></TR><TR><TD style="BACKGROUND-COLOR: #edf3fe">Reluctor wheel:</TD><TD style="BACKGROUND-COLOR: #edf3fe">58x</TD></TR><TR><TD style="BACKGROUND-COLOR: #fff">Rocker arm ratio:</TD><TD style="BACKGROUND-COLOR: #fff">1.7:1</TD></TR><TR><TD style="BACKGROUND-COLOR: #edf3fe">Rocker Arms (P/N 12569167 int):</TD><TD style="BACKGROUND-COLOR: #edf3fe">Investment cast, roller trunnion</TD></TR><TR><TD style="BACKGROUND-COLOR: #fff">Valve lift (in):</TD><TD style="BACKGROUND-COLOR: #fff">.525" intake / .525" exhaust</TD></TR><TR><TD style="BACKGROUND-COLOR: #edf3fe">Balanced:</TD><TD style="BACKGROUND-COLOR: #edf3fe">Internal</TD></TR><TR><TD style="BACKGROUND-COLOR: #fff">Valve size (in):</TD><TD style="BACKGROUND-COLOR: #fff">2.16 int / 1.59 exhaust</TD></TR></TBODY></TABLE>
 
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