[jesusm3]

[quote author=pinkcheese link=topic=136400.msg2939371#msg2939371 date=1234754169]
with 9 pounds of boost what would the safest compression ratio be on pump gas 91 octaine?
[/quote]
when you go forced induction it is extremely important to lower the compression for a good reason. the highest compression you would really want to run would be a 9:1:1 compression.(somewhere in this area. i personally am running a 9:1:1 compression and i would not go any higher than that.) you really do not want to go much higher with that. anywhere in the 8s are good as well. just do not run a higher compression or you can and will go boom boom :boom:[quote author=HIm link=topic=136400.msg2939385#msg2939385 date=1234754483]
man you need to get a book called maximum boost..... if you read it you will understand why no one is going to give you an answer to this question........ There is a lot of math/experience/information needed to determine the answer to this question. If you want a simple version of the answer it is the lower the compression ratio the better on an FI engine.
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get all of your information by reading. read some books. we got some people on the forums who will help you out. ive been learning and studying about force induction for about 3 years. i ve got still alot to learn but i also know somewhat about it.

 

[jesusm3]

[quote author=classicaddict link=topic=136400.msg2940754#msg2940754 date=1234819554]
i have seen MANY smal to mid sized turbo setups running 7 to 13psi with 10:1 compression. 9psi in an engine with 10:1 compression will make more than 10psi in an engine with 9:1 psi. assuming you take the proper steps and use the proper heat range plugs, the car is being cooled correctly, and you keep tabs on EGT and water temps with after market gauges i see no reason at all to lower compression unless the car is higher than 10:1 and you plan on a large turbo.


a t-25 or t-28 sized turbo will absolutly LOVE 10:1.
[/quote]
have you even seen what happens to a motor that melts because of high compression? i am not talking about throwing a rod either! you will need a near perfect tune out of hell to get it to run and not blow. the size of the turbo has nothin to do with if you will blow the motor or not. when you are talking 10:1 compresssion you may be referring to big block v8s. my buddy ran his 5.0 with a 9:5 compression

 

[jesusm3]

[quote author=classicaddict link=topic=136400.msg2940841#msg2940841 date=1234822165]
[quote author=jesusm3 link=topic=136400.msg2940811#msg2940811 date=1234821403]
[quote author=classicaddict link=topic=136400.msg2940754#msg2940754 date=1234819554]
i have seen MANY smal to mid sized turbo setups running 7 to 13psi with 10:1 compression. 9psi in an engine with 10:1 compression will make more than 10psi in an engine with 9:1 psi. assuming you take the proper steps and use the proper heat range plugs, the car is being cooled correctly, and you keep tabs on EGT and water temps with after market gauges i see no reason at all to lower compression unless the car is higher than 10:1 and you plan on a large turbo.


a t-25 or t-28 sized turbo will absolutly LOVE 10:1.
[/quote]
have you even seen what happens to a motor that melts because of high compression? i am not talking about throwing a rod either! you will need a near perfect tune out of hell to get it to run and not blow. the size of the turbo has nothin to do with if you will blow the motor or not. when you are talking 10:1 compresssion you may be referring to big block v8s. my buddy ran his 5.0 with a 9:5 compression
[/quote]

i have a buddy running a t4 on a FWD sr20 with 9.5:1 compression at 13psi.

i have another good friend running an SC61 turbo on a nearly bone stock internal ed FWD sr20de at 9.5:1

turboing an engine with 10:1 compression has been done so many times its not even funny. and yes i have seen plenty of blown engines from turbo, normally caused by not monitering the engine properly or not taking the proper steps to keep it cool.

i stick by my origonal statement. i see absolutly no reason to mess with compression ratio unless it is over 10:1 and you plan on running high boost levels.

also, the size of the turbo has everything to do with it. that is a very uninformed statement. 10psi from t25 is much much less volume then 10psi from an SC61.......MUCH less. there for there will be alot more piston melting heat from a 10psi SC61 setup than a 10psi t25 setup. and oh yea.........many of the 10:1 setup tunes are a basic ecu daughter board install with an average base tune not much more.
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what throws a rod is not the fact of the bigger turbo. it part of it that is put into the equation but it is in fact of the tune ( you run a car that is set up @ 8psi and you go 12 or 14 psi you will spike and risk the chance of blowing the motor.) If your motor is running lean then there you go. boom boom is a very high chance. i am not saying it is not possible but it isnt very safe. you are right about the volume on a turbo but for our cars there is not reason to run a t25 or t28 really. there are guys on this forum who will back me up on this. ask jake about the t25 or t28.
but back on subject. anything is possible for us to do with compression but on a daily driven setup i would think twice about it. you are right with a 10:1 compression will make more power at 10 psi than 9:1 compression but you are also limiting the amount of boost you can run