# Should I bore my 2004 GTO?



## Dan81 (Jan 22, 2009)

My dad had a 1966 GTO when he was younger and was talking about how he had it bored out 60 over with a 13 1/2 :1 compression ratio. When he past he left me his stock 2004 5.7 Pontiac GTO. My questions are 1st, what did he mean by saying it was bored 60 over. Second, is it something that helps out a lot when trying to get a stock car to the drag strip? Third what did he mean by saying it had a 13 1/2:1 compression ratio? Thanks in advance for all your help.


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## TR GTO (Mar 17, 2007)

Bored 60 over is actually written as bored .060 over. It's a measurement of how far the cylinder walls have been bored out to allow larger pistons to fit, effectively increasing the displacement of the engine. Someone else will probably be able to fill in what actual unit of measure goes with bored .060 over as I'm not too familiar it, but I do understand how it is done. I've just never done it with a vehicle.

Edit - I just looked it up. The LS1s stock cylinder bore is 3.90 inch, so a bore of .060 over would equal out to 3.96 inch bore. Someone please fill me in if my logic isn't quite on.


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## jetstang (Nov 5, 2008)

No, you shouldn't bore your motor.

You bore the motor to get fresh metal for the new pistons. After boring, the engine is larger displacement, 350 stock, 355 at .030 over, 361 for .060 over. You can only bore an engine so much before the cylinder walls get to thin. You bore an engine out of need, not for the cubic inches.
Your engine is nothing more than an air pump with gas in it. An air compressor compresses air and captures it in the tank, your engine does the same thing, but adds gas for ignition.
Compression is the amount of times the air in the cylinder is compressed. A 13-1 motor is a race gas only motor at $9 a gallon. Compression will raise your cylinder pressure. An 8-1 motor may be 100 PSI, while a 13-1 motor may have 200 PSI. Compression is power.
The max compression for pump gas is about 10 1/2 to 1.


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## Rukee (Feb 8, 2007)

No, you should keep it fun and exciting for it!   :cheers


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## svede1212 (Nov 1, 2005)

Dan81 said:


> My dad had a 1966 GTO when he was younger and was talking about how he had it bored out 60 over with a 13 1/2 :1 compression ratio. When he past he left me his stock 2004 5.7 Pontiac GTO. My questions are 1st, what did he mean by saying it was bored 60 over. Second, is it something that helps out a lot when trying to get a stock car to the drag strip? Third what did he mean by saying it had a 13 1/2:1 compression ratio? Thanks in advance for all your help.


increases in how many cubic inches do help give more HP and torque as well as compression increases do also. the old engines were solid iron blocks that could be bored out quite a bit. our 5.7 is an aluminum block with fairly thin sleeves that can't really be bored out to give any significant increase in cubic inches. if you wanted bigger C.I. you could make it a stroker which means you replace the crankshaft with one that makes it go up and down a little more but that's a lot of money and work. the best mod you can do to increase HP thru flow and compression is to bolt on some new heads. ARP and Trickflow are some of the better heads but they are pricey


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## Aramz06 (Mar 2, 2008)

Rukee said:


> No, you should keep it fun and exciting for it!   :cheers


Ah it was only a matter of time..


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## GM4life (Mar 18, 2007)

Dan81 said:


> My dad had a 1966 GTO when he was younger and was talking about how he had it bored out 60 over with a 13 1/2 :1 compression ratio. When he past he left me his stock 2004 5.7 Pontiac GTO. My questions are 1st, what did he mean by saying it was bored 60 over. Second, is it something that helps out a lot when trying to get a stock car to the drag strip? Third what did he mean by saying it had a 13 1/2:1 compression ratio? Thanks in advance for all your help.


You can't bore a LSx aluminum blocks, they have thin iron sleeves. The most you can do with our stock bore is hone/bore maybe .010 per GM. The only way to increase your displacement is to do larger stroke crank and larger sleeves installed. Larger crank is the cheapest, reliable way to go, few people do the larger sleeves and its more expensive. Some people go the iron block LQ4/LQ9 truck block route to get more cubes and power. The most popular iron block strokers are 402 and 408ci. These blocks can be bored also.

Do a nice set of head and cam on that stock LS1 and you'll be happy.


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## devinsgn (Apr 6, 2007)

The amount of machining to get the extra cubes is not worth it. Just get a heads and cam package or if you want to have a stock feel get a blower and call it a day.


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