Compression ratio dilemma
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Compression ratio dilemma Ok here is my issue. Have a built 355 (everything is listed in my sig) that I am starting to second guess. The car is going to either be getting a ST80 turbo or PT-88, have yet to decide. Currently my combo is right at about 8.5-1 compression wise. The car will be mostly driven on the street but taken to the strip on the weekends when I am off work.
Lately I have heard alot of guys say its going to be a complete turd out of boost. Now of course if this is true I will have to change seveal things on my motor Oh well its only money right! FML! Anyway what has been everyones experience with a turbo LT1 or LS1 for that matter with 8.5-1 compression. I plan to run about 15-20psi to reach my power goals. Thanks
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Lately I have heard alot of guys say its going to be a complete turd out of boost. Now of course if this is true I will have to change seveal things on my motor Oh well its only money right! FML! Anyway what has been everyones experience with a turbo LT1 or LS1 for that matter with 8.5-1 compression. I plan to run about 15-20psi to reach my power goals. Thanks
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the smaller the turbo, the less of a turd it will be, pick a turbo for the amount of horsepower you want to make...i cant see you needing more than a t76 personally. i think the t88 will contribute to more of the turdiness than the 8.5:1
I would think that with the proper intake combo, correct stall selection and a t4 turbo, it should be very responsive for the brief moments that it would take you to get into boost.
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Thanks. Yeah I was trying to get some real world responses back when I posted this with cars that happened to be six speeds and close in cubic inch with a 76mm turbo. I have zero experience with a PT88 on a 355. I realize there is a penalty to be paid when lowering compression. Just went to a stalled 4L80e w/ transbrake, so this changes things a bit. Ordered the PT88 and jose over at forced inductions assured me it will do fine on the 355 I have built, especially with the auto.
Last edited by 355TurboLT1; Feb 4, 2010 at 11:33 PM.
i have a 8.6:1 CR forged 347 with ported 317 heads, i was running 15psi of boost on 94 octane and no meth with no problems, the car was not actually that bad off boost.
the reason why i went with such low CR, is because i am aiming for high hp on pump gas and no meth
it is easy to up or lower the CR in the ls series motors. you just change the heads. 243's have a smaller combustion chamber and that will raise the CR and 317 heave a bigger combustion chamber and that will lower CR.
the reason why i went with such low CR, is because i am aiming for high hp on pump gas and no meth
it is easy to up or lower the CR in the ls series motors. you just change the heads. 243's have a smaller combustion chamber and that will raise the CR and 317 heave a bigger combustion chamber and that will lower CR.
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If it turns out to be a real turd out of boost, just slap on a cheap 35 shot of NAWZ. Trigger it to turn off around 4500rpm and no more turd. I don't think it will be that bad but as mentioned, a lot depends on your gears, cam and turbo choice.
Jim
Jim
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From: Norn Iron
How can anyone call an engine of 355ci a turd off boost ?
its not like its a small engine or anything !!!! And the fact its an auto, the engine will likely always be using higher rpm's etc anyway
its not like its a small engine or anything !!!! And the fact its an auto, the engine will likely always be using higher rpm's etc anyway
Ok here is my issue. Have a built 355 (everything is listed in my sig) that I am starting to second guess. The car is going to either be getting a ST80 turbo or PT-88, have yet to decide. Currently my combo is right at about 8.5-1 compression wise. The car will be mostly driven on the street but taken to the strip on the weekends when I am off work.
Lately I have heard alot of guys say its going to be a complete turd out of boost. Now of course if this is true I will have to change seveal things on my motor Oh well its only money right! FML! Anyway what has been everyones experience with a turbo LT1 or LS1 for that matter with 8.5-1 compression. I plan to run about 15-20psi to reach my power goals. Thanks
__________________
Lately I have heard alot of guys say its going to be a complete turd out of boost. Now of course if this is true I will have to change seveal things on my motor Oh well its only money right! FML! Anyway what has been everyones experience with a turbo LT1 or LS1 for that matter with 8.5-1 compression. I plan to run about 15-20psi to reach my power goals. Thanks
__________________
with that being said why don't you go with t76 and at least a 9.x cr? and a gtx cam?
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The only reason I went with 8.5-1 is that I plan to run above 20psi at some point with the 88. Sounds like it will be more than ok. Like I said, now that the T-56 is gone it shouldnt be an issue. It will never be a daily driver so if it suffers a little on the street its ok with me. I need to get it finished up here and see first hand how it does.
Im running some very nice AI heads (200cc), AI turbo cam 225/225 114+4 LSA .350/.350 lift and AI ported intake with 58mm TB. Should be a pretty mean combo when combined with the PT88 and my stalled auto. Thanks for all of the responses.
Im running some very nice AI heads (200cc), AI turbo cam 225/225 114+4 LSA .350/.350 lift and AI ported intake with 58mm TB. Should be a pretty mean combo when combined with the PT88 and my stalled auto. Thanks for all of the responses.
For a primarily street driven turbo car that sees mostly pump gas I would keep it around 8.5-9.0:1.