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3.8 vs 3.6

 
Old 11-20-2018, 09:24 AM
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Gus
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Default 3.8 vs 3.6

If you left all pretty much the same but only increased the engine size from 3.6 to 3.8 what would be the HP/torque gain. Given piston/cylinder change and machine work for heads. Just wondering what the HP to $$ ratio is and if the change is worth the move??
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Old 11-20-2018, 10:32 AM
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cobalt
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Originally Posted by Gus View Post
If you left all pretty much the same but only increased the engine size from 3.6 to 3.8 what would be the HP/torque gain. Given piston/cylinder change and machine work for heads. Just wondering what the HP to $$ ratio is and if the change is worth the move??
Not much if that is all you do and slip fit IMO is a waste of money.
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Old 11-20-2018, 10:40 AM
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Gus
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Know slip fit is not the route to take, definitely bore. Guessing that new pistons would probably increase compression ratio. Have already up graded to 993 valves, and had heads polished and machine for top gaskets.
But, just doing a rough calculation figure it would cost between $500 to $600 per extra HP.
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Old 11-20-2018, 11:34 AM
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3.6 to 3.8 is only a 5.5% increase in displacement. Without any supporting mods, I wouldn't expect massive gains.
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Old 11-20-2018, 12:07 PM
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Is the argument against slip fit, that it will not be as strong? I've seen people say "slip fit because I'm just going to street drive it".
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Old 11-20-2018, 12:08 PM
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Increase is actually 145cc or 4%. Far better getting some new cams and a whole lot cheaper.
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Old 11-20-2018, 01:03 PM
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Steve Weiner-Rennsport Systems
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Close ratio gears makes a FAR FAR bigger difference than the 3.8 conversion. Its truly night & day.
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Old 11-20-2018, 02:07 PM
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Originally Posted by Steve Weiner-Rennsport Systems View Post
Close ratio gears makes a FAR FAR bigger difference than the 3.8 conversion. Its truly night & day.
How much differens if You fit a G50/21 instead of a G50/20? Is it worth it? Or are a dedicated re gear the way to go?

Edit: The above boxes are 993 six speed ones but maybe Mr Weiner can answer the question regardless of that? 😀

Last edited by Railmaster.; 11-20-2018 at 02:09 PM. Reason: Wrong forum!
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Old 11-20-2018, 03:18 PM
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Why consider the 102mm p&c (3746cc) when 104mm (3894cc) and 106mm (4045cc) are available? Though nobody seems to actually be using any of these bores.
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Old 11-20-2018, 03:49 PM
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Going from stock 3.6 100 to Mahle 3.8 103 w/ a little more compression is worth about 25 lb-ft the flywheel @~5200rpm, a little less at other rpms but nevertheless something that is palpable there at all rpm.

closerer gearing keeps the engine in it's best power range for more of the time but doesn't really change the acceleration positively unless it is also lower(higher numerically)

here is an illustration of the thrust available in a stock 964 w/ 3 different transmissions, g50/03, g50/05 these are stock 964 transmissions and a g50/30 used in 993 Cuop & RSR, Only where the /30 is lower does it improve acceleration, but the extra gear does close the gaps


What would 25 lb-ft extra flywheel torque do to the above curves, well just multiply the overall gear ratio by 25 and add it to the existing curve, of course that is only applicable at 5250rpm, you get less at other rpms
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Old 11-20-2018, 04:00 PM
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Originally Posted by Steve Weiner-Rennsport Systems View Post
Close ratio gears makes a FAR FAR bigger difference than the 3.8 conversion. Its truly night & day.
Ding. Ding. Ding. And we have a winner. By far the best mod I have EVER done in any car. Ever.....
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Old 11-20-2018, 04:07 PM
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Originally Posted by K964 View Post


Ding. Ding. Ding. And we have a winner. By far the best mod I have EVER done in any car. Ever.....
Mike's is a close approximation or clone of a g50/30

Here are some rear wheel torque curves for the various 3.6 & 3.8 engines, the 964 ssi is there only to show what a poor choice of exhaust can do
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Old 11-21-2018, 09:08 AM
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Originally Posted by K964 View Post


Ding. Ding. Ding. And we have a winner. By far the best mod I have EVER done in any car. Ever.....
I have a similar short gear box and it is worth the $$ but not cheap.
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Old 11-21-2018, 10:15 AM
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Every builder ive talked to said just doing 3.8 is not worth the cost as described here. Other things need to be done to make it worth it.


Originally Posted by K964 View Post
Ding. Ding. Ding. And we have a winner. By far the best mod I have EVER done in any car. Ever.....
Is your motor a 3.6 and stockish? What ratios did you go with?

Originally Posted by Steve Weiner-Rennsport Systems View Post
Close ratio gears makes a FAR FAR bigger difference than the 3.8 conversion. Its truly night & day.
Do you have a suggested ratio set for a 5spd strong 3.6?

Im way over analyzing the gear set ratios. Right now Iĺm considering a slight deviation to the rs set and going with a set Matt has been selling for these that changes 1-4
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Old 11-21-2018, 03:20 PM
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Originally Posted by Steve Weiner-Rennsport Systems View Post
Close ratio gears makes a FAR FAR bigger difference than the 3.8 conversion. Its truly night & day.
Steve can you provide a chart or graph that compares this? Like speed vs rpm for each gear? And is an LSD install the right time to do it?
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