question

[aubry588]

i want someone to explane to me why low compression pistons and better than high compression pistons in a turbo car. i just realy dont know how all that works and what the difference is..

[SLow_POke]

**again info i found hope it helps*

TURBOCHARGERS & COMPRESSION: THE MYTH!!!
There has been a long-standing myth with turbocharged Honda cars. For as long as I can remember, people have been quite concerned about having too high of a compression ratio, on their turbocharged Honda. The myth is: the lower the compression...the better. Well, this is not entirely true.
Why is a low compression motor good to turbocharge?

In essence, a low compression motor is good to turbocharge, because it is just easier to do so...and not worry about it. But is that what we really want to do as enthusiasts? Do we want to just slap a turbocharger on a car, and call it a day? Absolutely not. With turbocharging, comes the responsibility of tuning and care. If you are just going to turbocharge your car, and call it a day, then frankly, you don't deserve the luxery of boost! As well, might I add...that simply because it is easy to slap a turbocharger on a low compression motor and not worry about it, does not mean that it is right. I can guarantee you, that if you turbocharge a low compression motor, and fail to tune it correctly, you will end up on the side of the road, with blue smoke coming from your exhaust pipe.

Generally, a lower compression motor affords you more margin of error, when tuning. A slightly imperfect a:f ratio probably won't lead to the demise of your motor...unless you drive like a total jerk.

Why should I consider a higher compression motor, while making my decision of what motor will suit my needs?

Different from a low compression motor, a higher compression motor will not give you a large margin of error, when tuning. As stated before, if you expect to slap on a turbocharger, and call it a day, well then stay away from the higher compression motors all together. A higher compression motor demands slightly more TLC than a lower compression motor. But oh, the rewards are plenty.

Bottom line...a higher compression motor, pound for pound, will make more power, than a low compression motor. This works along the same lines as naturally aspirated Honda motors. You never see an NA enthusiasts spouting off about low compression do you? No, one of the keys to NA performance is high compression. So, why should it be any differnt for turbocharged applications? Of course, the routes to high compression are different (NA uses lightweight rods and pistons, that a turbocharged application would simply tear to shreds), but the end goal is the same.

Let's make an observation here. I am going to throw a scenerio for you...

Car A:
B18B (stock 9.2:1 CR)
Rev Hard Stage II
Thermal 3" exhaust
MSD 6AL
MSD Pro Cap
MSD Blaster 3 Coil
Holley 255lph in-tank fuel pump
AEM fuel rail
RC440cc injectors
A'pex S-AFC

Car B:
B18B (JE pistons, 10.5:1 CR)
Rev Hard Stage II
Thermal 3" exhaust
MSD 6AL
MSD Pro Cap
MSD Blaster 3 Coil
Holley 255lph in-tank fuel pump
AEM fuel rail
RC440cc injectors
A'pex S-AFC

Now for the sake of argument, let's say that both cars are well tuned, by the same tuner, both have an identical weight, both have the same slicks, both are boosting 1.0bar, and both are being driven by the same guy...at the same time (yeah, yeah, yeah...just roll with me here)! Now, which one do you think is going to come across the finish line first? Mythological thinking says that the guy with the low compression is best suited to win...right? Wrong. The guy with the 10.5:1 compression ratio is going to smoke the guy with the low compression.

Another point I would like to bring up is the misuse of the term "high compression" when it comes to Honda motors, and turbocharging them. In all honesty...10.6:1, 11.0:1, etc...aren't even really that high. Most NA monsters utilize 12.5:1 or higher...and some even as high as 14.0:1, in cases of extreme race. If you do some snooping around, you will realize that most of the really fast Hondas, and I'm talking sub-10 second monsters, utilize high compression setups, to achieve enourmous horsepower goals. Most of these guys won't openly discuss it though, so you are likely to come across terms such as "undisclosed compression", or something along that line. As I stated before, the myth is that low compression is key...so these guys want to stay on top, and the way to do it is hide the fact that they are using high compression, turbocharged motors...to propel themselves into sub-10's.

Reliability, and compression...

This is a regular question that pops up, and is quite valid. Frankly, as soon as you modify a Honda at all...reliability becomes an issue. A lot of us can testify that the proverbial "can of worms" sprung open as soon as we made our first modification. Many times, Honda enthusiasts will spout off the reliability factor, in Import vs. Domestic wars, when in actuality, they fail to realize that we are in just as much danger as those old pushrod V8's are, as soon as we modify our Honda engines.

Now, what is the solution? I have been saying it for a long time, as have several others such as Tuan, neouser, texan, and st00pid...TUNING IS KEY! That's the bottom line.

A well tuned higher compression motor will last just as long as any low compression motor. Tuning is not a factor that can afford to be sacraficed. You will not survive with an untuned higher compression motor, just as you will not survive with an untuned low compression motor.

So, with all of that said, it basically boils down to your own personal choice. Do not fear the B16A, the B18C1, or the H22A...etc. If you have the monitary requirement to turbocharge a higher compression VTEC motor, I would say, do not hesitate to do so.

You can have either Cheap, Reliable, or Fast

Cheap and Fast can't be Reliable

Fast and Reliable can't be Cheap

Cheap and Reliable can't be Fast

Tuning is not necessarily cheap when you have to do it every month on a turboed honda, but the above statement says it all.

[aubry588]

ok i read all that and understand another question what do the ratio numbers such as 10.5:1 mean?

[SLow_POke]

compression ratio .. in simpler term ..

10 lbs of shit made to fit a 1 lb bag .


look bellow

[SLow_POke]

sorry im really abd at explaining things but if your mechanically incline . you figure this out .. heres what i have


The compression ratio is a single number that can be used to predict the performance of any internal-combustion engine. It is a ratio between the volume of a combustion chamber and cylinder when the piston is at the bottom of its stroke, and the volume when the piston is at the top of its stroke. The higher the compression ratio, the more mechanical energy an engine can squeeze from its air-fuel mixture. Higher compression ratios, however, also make detonation more likely.

The ratio is calculated by the following formula:

, where b = cylinder bore (diameter)
s = piston stroke length
Vc = volume of the combustion chamber (including head gasket). This is the minimum volume of the space into which the fuel and air is compressed prior to ignition. Because of the complex shape of this space, it usually is measured directly rather than calculated. Due to pinging (detonation), the CR in a gasoline/petrol or LPG or CNG-powered engine will usually not be much higher than 10:1.
In engines with a ping or knock sensor and an electronic control unit, the CR can be as high as 13:1 (2005 BMW K1200S)
In a turbo charged or super charged engine the CR will be around 8.5:1
In a diesel engine the CR will be 14:1 and higher.

[SLow_POke]

LOL sry if i confused u ill some else give it a hot

[aubry588]

ya i kinda understand but i would like a little more info if anyone elese has any..

[SLow_POke]

What Is Compression Ratio?

Remember what happens during the compression stroke of the four-stroke cycle: Both the intake and exhaust valves are closed so no air can escape, and the piston moves upward from bottom dead center (BDC) to top dead center (TDC) so that the air/fuel mixture in the cylinder is compressed into the combustion chamber. Compression ratio is the relationship of cylinder volume (or displacement) with the piston at BDC to cylinder volume with the piston at TDC. If the volume of the cylinder with the piston at BDC is 10 times greater than the volume of the combustion area with the piston at TDC, then 10 units of volume get squeezed into 1 unit of space, and the compression ratio is 10.0:1. There are five factors that affect compression ratio: cylinder swept volume, clearance volume, piston dome or dish, head-gasket volume, and chamber volume.

[Vteckidd]

Lower compression means less risk of detonation. Usually in a turbo car you keep it 10:1 an under. although with tuning you can go higher.

ALl Motor cars usually run 11:1+

[3kgtdrvr]

we just finished a 73 chevy at work with about 14.5:1 its also got about 1,000hp so yeah lol

[SLow_POke]

we just finished a 73 chevy at work with about 14.5:1 its also got about 1,000hp so yeah lol

14.5 that really high on a v8

[3kgtdrvr]

whats even more impressive is that itll rev to 8500 rpm!!! lol

[SLow_POke]

whats even more impressive is that itll rev to 8500 rpm!!! lol

nice my 302 wouldnt go pass 6k 8500 is like a 11000 rpm honda lol

[SLow_POke]

Lower compression means less risk of detonation. Usually in a turbo car you keep it 10:1 an under. although with tuning you can go higher.

ALl Motor cars usually run 11:1+

told you i wasnt great at explaing

[3kgtdrvr]

...its also got a 400hp shot of nitrous

[IntegraXTR]

+1 smoke em for a good write up

[scttydb411]

[QUOTE=smoke_Em]
Let's make an observation here. I am going to throw a scenerio for you...

Car A:
B18B (stock 9.2:1 CR)
Rev Hard Stage II
Thermal 3" exhaust
MSD 6AL
MSD Pro Cap
MSD Blaster 3 Coil
Holley 255lph in-tank fuel pump
AEM fuel rail
RC440cc injectors
A'pex S-AFC

Car B:
B18B (JE pistons, 10.5:1 CR)
Rev Hard Stage II
Thermal 3" exhaust
MSD 6AL
MSD Pro Cap
MSD Blaster 3 Coil
Holley 255lph in-tank fuel pump
AEM fuel rail
RC440cc injectors
A'pex S-AFC

Now for the sake of argument, let's say that both cars are well tuned, by the same tuner, both have an identical weight, both have the same slicks, both are boosting 1.0bar, and both are being driven by the same guy...at the same time (yeah, yeah, yeah...just roll with me here)! Now, which one do you think is going to come across the finish line first? Mythological thinking says that the guy with the low compression is best suited to win...right? Wrong. The guy with the 10.5:1 compression ratio is going to smoke the guy with the low compression.
QUOTE]

actually neither will finish without making windows in the block. safc for tuning as the hack and no other management specified is going to jack up timing curves to the point of detonation and 440cc inj won't handle 1 bar of boost without being maxed out.

just busting your balls...good write up and it's true regarding higher compression turbo'd hondas. you will get more hp/lb of boost, but your buffer zone is far smaller in terms of detonation and timing advance. extra fuel/richer mixtures merely become a thermal protection to help aid in keeping detonation at bay as well as good tuning. det cans and a good pair of ears are key.

[SLow_POke]

[QUOTE]

u did bring up excellent points