-8cc pistons v's -25cc pistons...
03-31-2009, 06:50 AM
#21
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so does anyone else have info regarding this setup, -25cc pistons with standard 241 heads over the -8cc pistons with 317 heads????
03-31-2009, 07:40 AM
#22
Hold on fellas... Compression can affect driveability if you lower it too much. Lower compression motor makes less HP but can handle more boost.... Detonation will destroy your motor.... so you dont want that. A street driven boosted motor that you are going to run pumpgas into... (IN MY OPINION) should be below 9:1 Compression ratio... So...
To help you answe these questions you have you have to give us more info... What size motor? How do you drive it? Daily? Semi-Street? Track only? What are your HP goals? What fuel are you going to run?
To help you answe these questions you have you have to give us more info... What size motor? How do you drive it? Daily? Semi-Street? Track only? What are your HP goals? What fuel are you going to run?
03-31-2009, 09:24 AM
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03-31-2009, 10:55 AM
#25
-25cc is good but you have to understand that you should have a good combination with the heads to lower compression. plus the size of the motor counts. a 418 and up that would be a good piston to use with some 72 chamber heads to get the compression down. but what I am trying to say is don't rely too much on just the piston to lower you compression it will cost a lot of money if it isn't set up right like previously stated. but who knows they have -33cc's out there
03-31-2009, 08:54 PM
#26
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-25cc piston IS NOT GOOD WITH 72CC combustion chamber. you will be in the 7.5:1 compression ratio range. if you are aiming for 1000whp on pump gas maybe but i am sure you are not.
the best way to lower or raise the compression ratio is to do it with the piston. you want a big combustion chamber, it will prevent knock to a point. why do you think diesel engine have pretty much no combustion chamber at all ?
the best way to lower or raise the compression ratio is to do it with the piston. you want a big combustion chamber, it will prevent knock to a point. why do you think diesel engine have pretty much no combustion chamber at all ?
03-31-2009, 09:20 PM
#27
im gonna forge the bottom end to aim for 800+rwhp by adding a MPT78 or a TC78...
whats the better choice? im not going to be running 20 psi or anything ( so i guess? )
but i want to hit 800+rwhp....
can someone explain the pros cons etc... or anything else i should expect etc?
03-31-2009, 10:05 PM
#28
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diesels use compression to detonate fuel and the lack of a combustion chamber makes it easier to explode under compression, something you do not want happening on you gasoline engine without a spark. i was just trying to show him benefits of using a bigger combustion chamber, no need to be an ******* man.
04-01-2009, 09:19 AM
#29
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-25cc piston IS NOT GOOD WITH 72CC combustion chamber. you will be in the 7.5:1 compression ratio range. if you are aiming for 1000whp on pump gas maybe but i am sure you are not.
the best way to lower or raise the compression ratio is to do it with the piston. you want a big combustion chamber, it will prevent knock to a point. why do you think diesel engine have pretty much no combustion chamber at all ?
the best way to lower or raise the compression ratio is to do it with the piston. you want a big combustion chamber, it will prevent knock to a point. why do you think diesel engine have pretty much no combustion chamber at all ?
She runs fine... likes timming though! 
04-01-2009, 10:01 AM
#31
Lower compression doesnt automatically mean less detonation, if you have a smaller turbo/blower and have to crank it up to move more air to make up for the less compression the extra heat is just as bad as the heat geberated by higher compression. You dont get something for nothing with engines, not to mention chamber design, dome/dish design and even the size of bore itself can affect detonation.
IMO anything between 8.5-9.5:1 is workable on pump fuel. 98 research octane in australia is the same a 92 R+M/2 here.
04-01-2009, 10:13 AM
#32
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Cant compare a 346 to a 408 when using dish/dome volumes, that same combo you use would be about 1 point of compression less on a 346. Plenty of calculators out there to figure it out, you come out with 8.2:1, that same combo on a 346 = 7.33:1
Lower compression doesnt automatically mean less detonation, if you have a smaller turbo/blower and have to crank it up to move more air to make up for the less compression the extra heat is just as bad as the heat geberated by higher compression. You dont get something for nothing with engines, not to mention chamber design, dome/dish design and even the size of bore itself can affect detonation.
IMO anything between 8.5-9.5:1 is workable on pump fuel. 98 research octane in australia is the same a 92 R+M/2 here.
Lower compression doesnt automatically mean less detonation, if you have a smaller turbo/blower and have to crank it up to move more air to make up for the less compression the extra heat is just as bad as the heat geberated by higher compression. You dont get something for nothing with engines, not to mention chamber design, dome/dish design and even the size of bore itself can affect detonation.
IMO anything between 8.5-9.5:1 is workable on pump fuel. 98 research octane in australia is the same a 92 R+M/2 here.
04-26-2009, 08:33 AM
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i was basicly asking, -8cc pistons + 72cc heads or -23cc pistons + 243 heads...
was a interesting one, but think im gonna head towards the -8cc pistons + 72cc heads + mp78 or similar...
will be interesting..
was a interesting one, but think im gonna head towards the -8cc pistons + 72cc heads + mp78 or similar...
will be interesting..
04-26-2009, 03:23 PM
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What are the spec's on the MP78, will it make your goals ?
04-27-2009, 01:38 AM
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the mp78 i will have to find the specs on, as for turbo selection, ive been told tc78 mpt78 etc...i might even try another garrett if it will work for me.
also whos a good parts suplyer to go through for the rotating assembly anyone? i been dealing with texas speed, is anyone else recomended?
04-27-2009, 05:58 AM
#39
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317 heads are better because of the thicker deck which is better for higher boost. It all depends on final CR that you want. Assuming all equal, go with -8cc pistons + 72cc heads.
