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lars49
Larry Barnes
Colorado Springs
(177 posts)

Registered:
06/11/2009 02:12PM

Main British Car:
1980 MGB GM LA1 3400 V6

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Valve to Piston Clearance
Posted by: lars49
Date: June 27, 2013 03:58PM

Does anyone know offhand what the valve to piston clearance is on a '02 GM 3400 V6 engine? I am considering milling the heads to increase the CR.

I could do it with clay but I was hoping that I could find a quick answer instead of trying to track down where to buy modeling clay locally.

Cross posted to MGE


MGBV8
Carl Floyd
Kingsport, TN
(4514 posts)

Registered:
10/23/2007 11:32PM

Main British Car:
1979 MGB Buick 215

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Re: Valve to Piston Clearance
Posted by: MGBV8
Date: June 29, 2013 08:31AM

Larry,

Spend some more time mulling this over. There are other places to get more bang for your buck. Your engine is already rated at 9:1. This is an all iron engine. It's not going to tolerate as much compression as an all aluminum engine. A wee bit more compression is not going to do much, especially for the money & effort involved.

If ya really want to wake up this engine, swap over the late aluminum heads & intake from a FWD engine. This requires a piston change, though. Add a bigger cam, too. ;)


Moderator
Curtis Jacobson
Portland Oregon
(4577 posts)

Registered:
10/12/2007 02:16AM

Main British Car:
71 MGBGT, Buick 215

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Re: Valve to Piston Clearance
Posted by: Moderator
Date: June 29, 2013 05:21PM

If you're swapping heads and/or doing a valve job anyhow, milling heads is actually pretty cheap. But how much bang do you get? Bruce Bowling (of the "Bowling and Grippo" who originated MegaSquirt") has a handy little online calculator for estimating the horsepower benefit of boosting compression ratio. It's an extremely simplified estimator, but it'll give you a ballpark figure. Link: [www.bgsoflex.com]
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MGBV8
Carl Floyd
Kingsport, TN
(4514 posts)

Registered:
10/23/2007 11:32PM

Main British Car:
1979 MGB Buick 215

authors avatar
Re: Valve to Piston Clearance
Posted by: MGBV8
Date: June 29, 2013 06:22PM

Bowling's Compression Ratio -> HP Calculator
Computation Results:
Engine Horsepower (peak) is 160
Old Compression Ratio is 9.0
New Compression Ratio is 10.0
Computation Results:
Computed New Engine HP is 165, a 3 percent change


lars49
Larry Barnes
Colorado Springs
(177 posts)

Registered:
06/11/2009 02:12PM

Main British Car:
1980 MGB GM LA1 3400 V6

authors avatar
Re: Valve to Piston Clearance
Posted by: lars49
Date: June 29, 2013 08:39PM

It is an aluminum head engine with a current CR of 9.6:1 But looking a the numbers and after talking with my machinist, I've come to the conclusion it is not worth it. New pistons would do it but I am not willing to fork out another $1K on parts and $600 to balance the engine. .I'm hoping that a 25% increase on the input flow volume will do something worthwhile.


MGBV8
Carl Floyd
Kingsport, TN
(4514 posts)

Registered:
10/23/2007 11:32PM

Main British Car:
1979 MGB Buick 215

authors avatar
Re: Valve to Piston Clearance
Posted by: MGBV8
Date: June 29, 2013 10:48PM

Is this a FWD engine?

Bowling's Compression Ratio -> HP Calculator
Computation Results:
Engine Horsepower (peak) is 185
Old Compression Ratio is 9.5
New Compression Ratio is 11.0
Computation Results:
Computed New Engine HP is 192, a 4 percent change



Edited 1 time(s). Last edit at 06/29/2013 10:50PM by MGBV8.


lars49
Larry Barnes
Colorado Springs
(177 posts)

Registered:
06/11/2009 02:12PM

Main British Car:
1980 MGB GM LA1 3400 V6

authors avatar
Re: Valve to Piston Clearance
Posted by: lars49
Date: June 30, 2013 09:11AM

Yes it is a FWD. Not much bang for the buck by increasing CR, is there?



Moderator
Curtis Jacobson
Portland Oregon
(4577 posts)

Registered:
10/12/2007 02:16AM

Main British Car:
71 MGBGT, Buick 215

authors avatar
Re: Valve to Piston Clearance
Posted by: Moderator
Date: June 30, 2013 12:12PM

More than fancy valvecovers... and over the whole RPM range too.


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(6470 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: Valve to Piston Clearance
Posted by: BlownMGB-V8
Date: June 30, 2013 12:27PM

Also increases gas mileage.

Jim


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