Built fsde compression ratios
- Thread starter quatelate
- Start date
Metallic36
Member
- :
- 2003 Mazda6 3.0L Speed Yellow
JDM Sam would know the answer to this.. I'm guessing that if you're not going to go with extreme boost or whatever, that 9.0:1 is the choice.. I have 8.5:1 just because I have the thought that it will allow me to build my car more than if it was at 9.0:1. I figure you might as well go with 8.5:1 if you're going forged. 9.0:1 is too close to stock imo.
SeR_Cyclops
Member
- :
- Mazdaspeed Protege
you can run more boost with less risk of it pinging.
yeah but when building your motor id assume people would be upgrading the fuel system and intercooler greatly reducing your chances of pinging... i mean the reason i even brought this up is that i have friends in the honda world making 400whp+ with almost 12:1 compression and no pinging... so is there something wrong with our motor making it more prone to pinging that we need to compensate with lower compression
My motor is 8.1:1.......But once everything runs again I plan on running 30-35 PSI
Rob
is that what u plan to run on the street daily? what turbo do you plan on running? sounds bad ass
Last edited:
you have to take into account what kind of fuel you want the car to run on. If you only want to put 91 in and run high boost go with lower compression. If you have access to 93+ and have a well setup system you can go with 9:1.
a fsde combustion chamber is not as good at thwarting detonation as a honda combustion chamber. The honda design is excellent for resisting detonation and flows more cfm.
a fsde combustion chamber is not as good at thwarting detonation as a honda combustion chamber. The honda design is excellent for resisting detonation and flows more cfm.
2.0t03speed
Member
- :
- 08.5 CWP Speed 3
im going to be running 9.0 w/ a thicker hg to bring it down to around 8.8 and im gonna run about 22 psi w/ meth i dont really see any problems with it
2.0t03speed
Member
- :
- 08.5 CWP Speed 3
im going to be running a mam msp exhaust mani. 3" dp and full 3" exhaust
thanks that is pretty much the answer i was looking for... r there any ways to improve the combustion chamber?
The ideal comp ratios are 8.5 to 9:0. It depends on what you plan on doing and the setup you plan on running.
9.0 makes more hp and tq per psi compared to 8.5.
Depending on your tune and octane 9:0 will support 16-19 psi and
8.5 is tuneable to 20-25 psi. All depends on your EMS and octane. If you get headwork as well you will be able to run more boost efficiently at a higher comp.
Pick a compression based on your turbo sizing efficiency and what you plan on running.This is for general reference to give you an idea on what the turbos are good for.
Stock 16-18 psi
GT28RS 18-21 psi
GT2871R 20-23 psi
GT3071R 23-26 psi
9:0 can get you in the 275-350 hp range on pump gas
8.5 can get you in the 350-450 hp range on pump gas
FYI, you are already past the transmission's power/torque capacity @ 275. It's just time on how long your 3rd gear will last.
9.0 makes more hp and tq per psi compared to 8.5.
Depending on your tune and octane 9:0 will support 16-19 psi and
8.5 is tuneable to 20-25 psi. All depends on your EMS and octane. If you get headwork as well you will be able to run more boost efficiently at a higher comp.
Pick a compression based on your turbo sizing efficiency and what you plan on running.This is for general reference to give you an idea on what the turbos are good for.
Stock 16-18 psi
GT28RS 18-21 psi
GT2871R 20-23 psi
GT3071R 23-26 psi
9:0 can get you in the 275-350 hp range on pump gas
8.5 can get you in the 350-450 hp range on pump gas
FYI, you are already past the transmission's power/torque capacity @ 275. It's just time on how long your 3rd gear will last.
Last edited:
So lower compression means more air and fuel into the chamber. Wouldnt that create a bigger combustion? With lower compression you have more room too play with (horse power wise), than with a high compression? Cause obviously your able to put more air into lower combustion. Or would they both cancel each other out and would be the same hp gains?
No and no, low compression pistons allows you to run timing advance @ higher boost b/c its not as prone to detonation as higher compression is. It is about tuning and knock thresholds of each setup.
Read the top paragraph.
http://en.wikipedia.org/wiki/Compression_ratio
MSP2003.5_Nick
Member
- :
- 2003.5 Mazdaspeed Protege - Dark Silver
So if you're aiming for large horsepower sticking to the highest octane pump gas available then 8.5 is the way to go? I have T3/T4 turbo on my fs and was wondering was was the best option when the time to forge comes.
Lots of good info so far, can anyone go into a bit more detail possibly? I have a lot of honda friends and they are all about crazy high compression, after listening to them its hard to know whats right for me haha.
Lots of good info so far, can anyone go into a bit more detail possibly? I have a lot of honda friends and they are all about crazy high compression, after listening to them its hard to know whats right for me haha.
If you have a race motor, you want to run the highest possible comp ratio and highest octane gas. Higher comp motors make more power per psi of boost. The knock threshold of higher comp ratio motors is what holds people back when they use pump gas, so they resort to lowering the comp ratio to run more boost. Lower comp will give you more room when tuning for more boost, but too low a comp (less than 8.5), you will have to run a lot of boost to make up for it.
If I wanted to make 300-350hp. 9:0 @ 18 psi or 8.5:1 @ 25 psi. Which would I do? The 9:0 because it is more efficient. The powerband on the 9:0 will come on sooner in the low end and will have less stress as it is running less boost.
You'll need more than just rods and pistons to make high hp. Rods and pistons alone, do not make power. They are heavier than stock and will rob power due to the added weight in the reciprocating assembly or if you go lower compression you will lose power. If you gain any power, it'll be due to improved ring sealing and from balancing the assembly. Besides a larger turbo, headwork will free up a lot of HP. A set of turbo grind cams will produce big midrange to top end power. Then you will need a standalone to tune the whole thing, along with the correct size fuel injectors.
A lot of you guys say you want big power, but many of you forget the tranny doesn't hold big power. Are you prepared to spend $2000 and up on beefed up transmission parts after you dropped around $5000 in engine parts and labor?
If I wanted to make 300-350hp. 9:0 @ 18 psi or 8.5:1 @ 25 psi. Which would I do? The 9:0 because it is more efficient. The powerband on the 9:0 will come on sooner in the low end and will have less stress as it is running less boost.
You'll need more than just rods and pistons to make high hp. Rods and pistons alone, do not make power. They are heavier than stock and will rob power due to the added weight in the reciprocating assembly or if you go lower compression you will lose power. If you gain any power, it'll be due to improved ring sealing and from balancing the assembly. Besides a larger turbo, headwork will free up a lot of HP. A set of turbo grind cams will produce big midrange to top end power. Then you will need a standalone to tune the whole thing, along with the correct size fuel injectors.
A lot of you guys say you want big power, but many of you forget the tranny doesn't hold big power. Are you prepared to spend $2000 and up on beefed up transmission parts after you dropped around $5000 in engine parts and labor?
Last edited:
