whats the better compression?
07-24-2008, 09:45 PM
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whats the better compression?
ok so whats the difference in buying 8:5:1 and 9:0:1 in a boosted car? im not quite sure, all i know is lower is better for boost and helps the tuner. but i also see alot of high HP cars with a slightly higher compression like 9:0:1. someone clear this up for me please .
p.s. i plan on going with boost and fully built engine. and my goals are 400whp, also i want 400 on less than 20 psi.
p.s. i plan on going with boost and fully built engine. and my goals are 400whp, also i want 400 on less than 20 psi.
07-24-2008, 09:54 PM
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Re: whats the better compression?
Figure out who you want to tune the car for you and work with them in building your engine and the specs to help them tune your car for you with what you want out of it.
That way you are not taking the opinions of many different people you dont know and dont care if you blow your engine or if you get what you want. Find a reputable tuner and get their input as to what parts to use to build a motor for them to tune for you.
That way you are not taking the opinions of many different people you dont know and dont care if you blow your engine or if you get what you want. Find a reputable tuner and get their input as to what parts to use to build a motor for them to tune for you.
07-24-2008, 09:58 PM
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Re: whats the better compression?
Figure out who you want to tune the car for you and work with them in building your engine and the specs to help them tune your car for you with what you want out of it.
That way you are not taking the opinions of many different people you dont know and dont care if you blow your engine or if you get what you want. Find a reputable tuner and get their input as to what parts to use to build a motor for them to tune for you.
That way you are not taking the opinions of many different people you dont know and dont care if you blow your engine or if you get what you want. Find a reputable tuner and get their input as to what parts to use to build a motor for them to tune for you.
07-24-2008, 10:00 PM
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Re: whats the better compression?
Static Compression is the ratio of pressure between the cylinder at bottom and the cylinder at TDC. It effects the dynamic compression (the actual PSI after detonation) which is in turn, what the motor needs to be built to 'handle'.
For example, you build a motor to withstand xxx horsepower. That in a way means the motor can handle (lets say) 1000psi of dynamic pressure. Well, when you lower the static ratio, it lowers the dynamic pressure, to say 800 psi. Well, to get back up to that 1000psi, you use boost. So in effect, the less of a compression ratio you use, the more boost the motor can tolerate. That being said, thats where boost lag comes in to play. The more you rely on boost, the more low end you're going to surrender due to lower dynamic pressures at lower RPM's.
To help you out, if you're going to build the motor, you're going to want to find a nice setup that can handle 400+ hp, and run as little boost as possible. The higher the static ratio, the more daily drivable it will be.
For example, you build a motor to withstand xxx horsepower. That in a way means the motor can handle (lets say) 1000psi of dynamic pressure. Well, when you lower the static ratio, it lowers the dynamic pressure, to say 800 psi. Well, to get back up to that 1000psi, you use boost. So in effect, the less of a compression ratio you use, the more boost the motor can tolerate. That being said, thats where boost lag comes in to play. The more you rely on boost, the more low end you're going to surrender due to lower dynamic pressures at lower RPM's.
To help you out, if you're going to build the motor, you're going to want to find a nice setup that can handle 400+ hp, and run as little boost as possible. The higher the static ratio, the more daily drivable it will be.
07-24-2008, 11:24 PM
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Re: whats the better compression?
Static Compression is the ratio of pressure between the cylinder at bottom and the cylinder at TDC. It effects the dynamic compression (the actual PSI after detonation) which is in turn, what the motor needs to be built to 'handle'.
For example, you build a motor to withstand xxx horsepower. That in a way means the motor can handle (lets say) 1000psi of dynamic pressure. Well, when you lower the static ratio, it lowers the dynamic pressure, to say 800 psi. Well, to get back up to that 1000psi, you use boost. So in effect, the less of a compression ratio you use, the more boost the motor can tolerate. That being said, thats where boost lag comes in to play. The more you rely on boost, the more low end you're going to surrender due to lower dynamic pressures at lower RPM's.
To help you out, if you're going to build the motor, you're going to want to find a nice setup that can handle 400+ hp, and run as little boost as possible. The higher the static ratio, the more daily drivable it will be.
For example, you build a motor to withstand xxx horsepower. That in a way means the motor can handle (lets say) 1000psi of dynamic pressure. Well, when you lower the static ratio, it lowers the dynamic pressure, to say 800 psi. Well, to get back up to that 1000psi, you use boost. So in effect, the less of a compression ratio you use, the more boost the motor can tolerate. That being said, thats where boost lag comes in to play. The more you rely on boost, the more low end you're going to surrender due to lower dynamic pressures at lower RPM's.
To help you out, if you're going to build the motor, you're going to want to find a nice setup that can handle 400+ hp, and run as little boost as possible. The higher the static ratio, the more daily drivable it will be.
.....very well put....even I learned something....
07-25-2008, 05:14 AM
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Re: whats the better compression?
Conversly, lower compression results in slower spool times (given examples taken from identical turbos, low vs. higher compression). To find an equal balance of give and take is the goal.
I've built several 10:1 compression (flat-top pistons) 400+whp motors that have had no problems what so ever. I wouldn't reccommend doing so unless you have a nice stand alone, but non-the-less the combination makes for an amazing street machine. We've used turbos that normally wouldn't be applicable for street motor use, on 10:1 motors and have been able to reach full boost at surprisingly low rpms.
On a side note, static compression, dynamic compression, and cranking PSI measures are only a portion of the formula here. Thermal dynamics and volumetric efficiency should be considered in understanding why higher compression can be a better solution (depending on your goal/set-up).
J
I've built several 10:1 compression (flat-top pistons) 400+whp motors that have had no problems what so ever. I wouldn't reccommend doing so unless you have a nice stand alone, but non-the-less the combination makes for an amazing street machine. We've used turbos that normally wouldn't be applicable for street motor use, on 10:1 motors and have been able to reach full boost at surprisingly low rpms.
On a side note, static compression, dynamic compression, and cranking PSI measures are only a portion of the formula here. Thermal dynamics and volumetric efficiency should be considered in understanding why higher compression can be a better solution (depending on your goal/set-up).
J
07-25-2008, 07:09 AM
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Re: whats the better compression?
The more you rely on boost, the more low end you're going to surrender due to lower dynamic pressures at lower RPM's.
To help you out, if you're going to build the motor, you're going to want to find a nice setup that can handle 400+ hp, and run as little boost as possible. The higher the static ratio, the more daily drivable it will be.
To help you out, if you're going to build the motor, you're going to want to find a nice setup that can handle 400+ hp, and run as little boost as possible. The higher the static ratio, the more daily drivable it will be.
Being as how the OP is a fucktard (see his "how do I swap a LS1, SR20, 2JZ into a XXX" threads) that is about all I will go into it.
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