[dnbsi]

i know we have a high compression ratio, 11:1 right? what exactly does this mean in terms of the car though?

 

[schield]

Higher compression = more power. This is the justice for premium fuel. Premium fuel is needed to stop premignition which can cause pinging.

Diesel engines range from 14:1 all the way up to 24:1. This as you know, requires Diesel fuel. Diesel fuel cannot even be ignited with a match, it only ignites at extremely high pressure. This is why diesels do not have spark plugs. Diesel engines are know for their torque.
(Most commercial diesel engines also have one or more turbochargers)

In the case of the Si, the engineers went the route of higher compression and a naturally aspirated engine versus a turbo or supercharger. Force-fed engines do make their power because of a higher compression since more air is fed into the cylinders creating a greater gas volume, and therefore higher compression in the compression stroke of the engine.

There are many thermodynamic prinnciples that characterize combustion in an engine known as conjugate variables. These include pressure-volume, chemical potential-particle number, and temperature-entropy.

Hope this helps.

 

[brdhouse]

^ nice answer. I feel smarter now. :thumb:

 

[Riverak21]

Not to get too technical but, compression ratio is how close the piston head comes to the head of your motor.

 

[GeezerSi]

It is the ratio between the volume of the cylinder, when the piston is at the bottom of its stroke, and the volume when the piston is at the top of its stroke.

 

[Incubus]

It is the ratio between the volume of the cylinder, when the piston is at the bottom of its stroke, and the volume when the piston is at the top of its stroke.

That's more like it.

 

[Riverak21]

It is the ratio between the volume of the cylinder, when the piston is at the bottom of its stroke, and the volume when the piston is at the top of its stroke.

Thank you. + Rep

 

[CanyonDriver]

i know we have a high compression ratio, 11:1 right? what exactly does this mean in terms of the car though?

basically high compression means with aftermarket forced induction our engines will blow like a overfilled baloon poked with a needle. This is why successful FI requires a huge rebuild with low comp. pistons, stronger connecting rods, and stronger block sleeving. Kinda off topic but a bit of a warning to anyone thinking of the greddy or other turbo kits. Unless you prep your block for a FI set up for thousands of dollars before the kit your gonna need a new engine within 10K miles of high rev. driving.

 

[klk15]

basically high compression means with aftermarket forced induction our engines will blow like a overfilled baloon poked with a needle. This is why successful FI requires a huge rebuild with low comp. pistons, stronger connecting rods, and stronger block sleeving. Kinda off topic but a bit of a warning to anyone thinking of the greddy or other turbo kits. Unless you prep your block for a FI set up for thousands of dollars before the kit your gonna need a new engine within 10K miles of high rev. driving.

wut about a supercharger?

 

[trickyazn]

basically high compression means with aftermarket forced induction our engines will blow like a overfilled baloon poked with a needle. This is why successful FI requires a huge rebuild with low comp. pistons, stronger connecting rods, and stronger block sleeving. Kinda off topic but a bit of a warning to anyone thinking of the greddy or other turbo kits. Unless you prep your block for a FI set up for thousands of dollars before the kit your gonna need a new engine within 10K miles of high rev. driving.

wow really.. balloon popped huh.. i guess all those Greddy Turbo guys obviously dont know what their doing.

 

[solidust]

basically high compression means with aftermarket forced induction our engines will blow like a overfilled baloon poked with a needle. This is why successful FI requires a huge rebuild with low comp. pistons, stronger connecting rods, and stronger block sleeving. Kinda off topic but a bit of a warning to anyone thinking of the greddy or other turbo kits. Unless you prep your block for a FI set up for thousands of dollars before the kit your gonna need a new engine within 10K miles of high rev. driving.

hmm i coulda sworn you needed high compression with F/I opcorn:

 

[Firestrife]

hmm i coulda sworn you needed high compression with F/I opcorn:

Nope lower the compression is better for F/I, in fact if i recall the Evo is like 9.5:1 or something like that, this is also the reason why tC's with turbos do so well.

As for threads with such simple general questions please use wikipedia or google, theres tons of information there that can be tapped without having to make a thread and wait for responses.

 

[Mitch]

Nope lower the compression is better for F/I, in fact if i recall the Evo is like 9.5:1 or something like that, this is also the reason why tC's with turbos do so well.

As for threads with such simple general questions please use wikipedia or google, theres tons of information there that can be tapped without having to make a thread and wait for responses.

The reason lower compression is "better" with FI is because it leaves a larger margin for error. There really isn't a problem with boosting 10-11:1 compression engines, so long as they are tuned properly. If the tuning isn't "perfect" or if there is any unforseen situation that causes a lean condition, then the engine could grenade. The margin of error in tuning gets smaller and smaller as the compression of the engine goes up.

This is why there are successful turbo kits for the k20 with no internal modification. The key to these kits is slightly conservative tuning.

 

[CanyonDriver]

only problem with the kits offered for our car is they only add about 40 hp to the crank at 8 psi. Thats a decent amount to add but not for what greddy wants for their kit. If I were to do FI id rebuild the block with CP pistons, pauter rods, and cast iron sleeve it that way when i bolted the turbo kit on I could already start running 20psi to make 350hp. Expensive but way more reliable that trying to tune the engine with stock internals. But i'm pretty fiscal when it comes to buying auto parts, and dont need that kind of power so sticking with NA sounds more appealing to me.:vtec:

 

[CanyonDriver]

wow really.. balloon popped huh.. i guess all those Greddy Turbo guys obviously dont know what their doing.

they know what theyre doing as long as they dont alter the boost. But if you have a turbo set up maxing out your boost seems to be an obsession. Why pay $3400 on a set up thats only gonna add 40hp to the crank? Watch someone with the greddy kit on a track trying to dial up big boost on stock internals. Theyll be pissed when they hear a big boom and figure out they blew their block. Supercharging is a safer way to go on stock internals and adds pretty equal amount of hp for the same price. Also 10x easier to install. And the comptech CF cover looks pretty snazzy under the hood :thumb:

 

[rbsjnh]

Supercharging is a safer way to go on stock internals and adds pretty equal amount of hp for the same price. And the comptech CF cover looks pretty snazzy under the hood :thumb:

boost levels being the same --a turbo will always make more hp...it doesn't have to drive the pulley

boost levels being the same --a supercharger is no more reliable than a turbo, if you got proof, than thats one thing...boost is boost and the motor does not understand the diff between turbo boost and s/c boost

boost level is what decides when things will brake, as well as the tune itself...

as for the snazzy cover...it only adds weight, because it does not NEED to be there...besides there are nice c/f ones on the market it you want it on your turbo car...

 

[Izzy]

they know what theyre doing as long as they dont alter the boost. But if you have a turbo set up maxing out your boost seems to be an obsession.

Amen! And completely agreed.

 

[CanyonDriver]

boost is boost ur absolutely right. however people with turbos usually crank up the psi meanwhile supercharging has a set boost level. on a high compression motor ur fine boosting as long as u leave the psi where the manufacturer intended it to be. greddy is either 8 or 8.5 which is b/s. if im gonna spend over 3.5 grand i wanna be able to crank the psi well above 15 and have the peace of mind knowing that my motor wont blow. only way to do that is to have a motor FI from the factory or rebuild for FI.