low cr?

[tuner student]

so i've been doing my f/i homework for a while so that when the time comes i hopefully don't have many or at least big problems. i've heard from some people that in the case of my car planning to be a daily driver that i would be wise to lower my compression ratio when i boost for relaibility. is it true that a lower cr than the stock 11:1 for 8th gen si would bring more relaibility with the price of having to use more boost to acheive the same amount of power that a high cr would have? And if it is recommened that you lower cr, whats some of the best ways to achieve it and how hard would it be?

[sgtpruitt]

depending on the amount of boost you're pushing you may or may not want to lower it. I'd say anything more than 12 psi that you'd want to drop it for sure. That means new pistons. Then all you got to worry about is the increased lag.........

[Highrev1]

From the FAQ

"Just a quick note on engine wear and boost pressure. The key in all this is the combustion pressure and it's timing...which is why boost pressure isn't the end all for power or wear.
An engine makes power as a function of how much pressure you create in the cylinder and when that peak pressure occurs. Best power comes from peak cylinder pressure around 14 deg ATDC (after top dead center)....not to be confused with BTDC (before top dead center) which is when the spark occurs.... you see, if you spark at 30 deg BTDC and peak pressure is at 14 deg ATDC, then you know that it took 44 deg for the spark and subsequent combustion to create peak pressure in the cylinder. And 14 deg ATDC is a good number for most engines, but it depends on the pressure available under the curve to the piston (like a horsepower graph). If measurable pressure starts at 25 deg BTDC, then you actually get some of that combustion pressure acting the wrong way on the piston.
OK, peak pressure is based on a number of things including the amount of oxygen in the cylinder, the fuel (and how well it atomizes and disperses), and finally when the combustion process is begun with the spark. If you start it too early, then peak pressure can occur closer to TDC, and the combustion pressure has no where to expand to....whereas when it occurs at 14 deg ATDC, the combustion can push the cylinder away and your car goes forward.
Anyway, so it's easy to run 10 psi and retard timing to make internal cylinder pressure (combustion pressure) less than a 9 psi setup with more advanced timing. The key for good tuning is to balance the boost pressure with the spark timing in a way that doesn't create too much cylinder pressure.
There is one other component in all this.... and that is heat. Heat is not your friend. If you are getting too much heat buildup in the the cylinder, you can start to have increased detonation. That's why EGT parameters are important.
The key is to control EGT, knock, and optimize cylinder pressures with fuel tuning and spark timing. And btw.... a/f ratio affects how fast combustion happens... so changing fueling will change peak pressure timing as well... a little bit anyway."

[Excalibur]

Originally Posted by Highrev1

From the FAQ

"Just a quick note on engine wear and boost pressure. The key in all this is the combustion pressure and it's timing...which is why boost pressure isn't the end all for power or wear.
An engine makes power as a function of how much pressure you create in the cylinder and when that peak pressure occurs. Best power comes from peak cylinder pressure around 14 deg ATDC (after top dead center)....not to be confused with BTDC (before top dead center) which is when the spark occurs.... you see, if you spark at 30 deg BTDC and peak pressure is at 14 deg ATDC, then you know that it took 44 deg for the spark and subsequent combustion to create peak pressure in the cylinder. And 14 deg ATDC is a good number for most engines, but it depends on the pressure available under the curve to the piston (like a horsepower graph). If measurable pressure starts at 25 deg BTDC, then you actually get some of that combustion pressure acting the wrong way on the piston.
OK, peak pressure is based on a number of things including the amount of oxygen in the cylinder, the fuel (and how well it atomizes and disperses), and finally when the combustion process is begun with the spark. If you start it too early, then peak pressure can occur closer to TDC, and the combustion pressure has no where to expand to....whereas when it occurs at 14 deg ATDC, the combustion can push the cylinder away and your car goes forward.
Anyway, so it's easy to run 10 psi and retard timing to make internal cylinder pressure (combustion pressure) less than a 9 psi setup with more advanced timing. The key for good tuning is to balance the boost pressure with the spark timing in a way that doesn't create too much cylinder pressure.
There is one other component in all this.... and that is heat. Heat is not your friend. If you are getting too much heat buildup in the the cylinder, you can start to have increased detonation. That's why EGT parameters are important.
The key is to control EGT, knock, and optimize cylinder pressures with fuel tuning and spark timing. And btw.... a/f ratio affects how fast combustion happens... so changing fueling will change peak pressure timing as well... a little bit anyway."

Always full of good explainations.

[losorio]

Pretty well said, almost anything can be solved with a decent tune and my take on it is if you can yield the same amount of power with less boost on a high compression set up, the your set. Problem is that boost, like most drugs and college girls, is higly addictive.

Starting at 6-7 psi and having to stop at 9 psi is setting my self up for desperation from the get go, specially knowing that you can yield an incredible amount of power from a little more boost with a k20 engine. What i don't get is how rsx owners push their engines with 17-18 psi and reach 500 whp like it's nothing, must be on a built engine right ? If so i'll drop my $750 and buy low comp pistons and forged rods.

I myself hate this about my 06 FG, on my evo VIII i started at 19 psi and when i changed to my 35 R set up i pushed it close to 34 psi yielding close to 475 whp, i have a long way to go, can't believe i sold it

[tuner student]

i looked at the FAQs before i started this thread. unlink some i usually try to read FAQs cause like they say i've answered most ?s from just reading them. but the one you guys quoted i didn't quite understand when i read it. can someone break it down even futher. like i said in the intro thread, i'm pretty new at cars. i can fix turboprop engs on a c-130 all day long but cars i still am just a tadpole in the pond.

[Highrev1]

Basically you can change the combution pressure by adjusting when the spark plug ignites the fuel. The saftey of the car is all in the tune...

[tuner student]

so if i'm aim for 300 whp should i stay with a high cr motor and add a little boost for should i lower the cr and that way i can push more boost. like i said just aiming for that 300 mark. once i hit that i'll prob not go high since this will be a dd.

[kenny rogers]

(The following numbers are completely made up)

2 motors - 1 using 9.0:1 static CR pistons & 1 using 11.0:1
- 14 PSI to reach 300 HP using the lower CR motor
- 8 PSI to reach 300 HP using the High CR motor

If the motors are the same except for the pistons, both motors are experiencing the same amount of combustion pressure to hit the 300 HP goal. However, you cannot use the same amount of timing for both motors. When using a high static CR motor there is less "room for error" in the tune.

With good standalone units (IE: Hondata K-pro) the tune can be dialed in very precisely, which is one of the reasons why you see HIGH hp RSX's. The difference between a beast and a blown motor is the tune.

[tuner student]

ok so now i just gotta to A: find a tune shop that knows what there doing as to not blow up my DD. cause i don't know crap about tuning and not gonna do it my self. B: time to take leave so i can just sit around without a car to get to work without havign to steal the girl's all the time.

[LoverOfCivics]

Originally Posted by tuner student

ok so now i just gotta to A: find a tune shop that knows what there doing as to not blow up my DD. cause i don't know crap about tuning and not gonna do it my self. B: time to take leave so i can just sit around without a car to get to work without havign to steal the girl's all the time.

, no tuning options are available like that just yet, but were still waiting and hoping

[loves to speed]

Originally Posted by LoverOfCivics

, no tuning options are available like that just yet, but were still waiting and hoping

i pray to the car gods every night that our savior comes
Hondata K Pro.....
As soon as that (or something similar) comes out
The boosting will really begin
i can't wait.

[LoverOfCivics]

Originally Posted by loves to speed

i pray to the car gods every night that our savior comes
Hondata K Pro.....
As soon as that (or something similar) comes out
The boosting will really begin
i can't wait.

Exactly!!!! We have a Beast, Its just waiting to be unleashed

[tuner student]

can't u self tune the e-manage in the greddy kit?

[LoverOfCivics]

Originally Posted by tuner student

can't u self tune the e-manage in the greddy kit?

Its just a piggy back, Its like Trying to Drive a Car withreally Long Oval Tires , It will work but no where near as good as a standalone AKA Circle Tires

[tuner student]

hmmm guess i'll just wait for a stand alone setup to come out. i plan to boost without lowering the cr and i've been told the tuning has to be spot on.

[LoverOfCivics]

Originally Posted by tuner student

hmmm guess i'll just wait for a stand alone setup to come out. i plan to boost without lowering the cr and i've been told the tuning has to be spot on.

yes thats what where all waiting for, then and only then will you see the true potential of our cars...

[kenny rogers]

Welcome to the conclusion of 99% of Forced Induction threads...

[nothingfancy]

LoL

Hondata..K-Pro..please D:

[kamue]

i got a question for you guys, since you know allot more abut this stuff than i do. i have a custom boost intake system on an 03 civic ex that feeds a constant psi of boost into my engine at all rpm ranges, i just have no clue what boost pressure i should set it at. it has a stock engine so at what psi will i be compromising the safety my engine?