compression ratio & turbo

[00toyogts]

can anyone explain why a high compression ratio engine such as the scion fr-s'
12.5:1 or our celica gt-s (not sure what the ratio is).....why is it frowned upon to turbo high compression cars? i read its a "nightmare" to turbo them, why is this? and also read getting thinner gaskets can lower the ratio a bit? thanks

[hughesjasonk]

because there is less room to squeeze air into the chamber the higher the CR is.

[smart_rocket]

^^ there are also guys running high compression with turbo producing even more hp... it's more because of detonation.

[evilthorne]

No, high compression pistons build more heat and increases the chance for pre-detonation of the fuel (knock)

Mazda defeated this by going to direct injection which sprays fuel directly into the cylinder cooling the charge enough to prevent it.

[Boosted2.0]

High compression N/A cars generally don't have rings and ring lands strong enough to hold up under the detonation you are likely to get when you cram a bunch of boost on top of them. Direct injection engines can get around this because they don't spray the fuel until late in the game and hence it is not in the cylinder to detonate until it is needed.

[Smaay]

the thing with compression is this. the higher the compression the less space in the combustion chamber at TDC. so when you are boosting, you are pushing more air and fuel into the same amount of space. so that causes a chance detonation. good tuning will help prevent all of this.

[marc]

what Smaay said - its all in the tune. A good, safe tune will actually see far less turbo lag and you'll need less boost to make power.

I have seen switching to E85 for gasoline and meth injection both as effective solutions when turbocharging a high compression car.

[Smaay]

i have been thinking of running E85 in the new race car. only problem is you need twice the fuel, 2000cc injectors and multiple pumps

[the ronin]

You also need E85 gas stations to run E85.... I have never seen one so far..
Or you can do a setup like mine that creates E85 on demand...

[7th Degenerate]

can anyone explain why a high compression ratio engine such as the scion fr-s'
12.5:1 or our celica gt-s (not sure what the ratio is).....why is it frowned upon to turbo high compression cars? i read its a "nightmare" to turbo them, why is this? and also read getting thinner gaskets can lower the ratio a bit? thanks

You would actually want to install a THICKER gasket to lower the CR..As a rule of thumb for every 3-4 psi of boost you add, add +1 to the current CR..So, for example your 12.5 CR running 7-8 psi is now a 14.5 CR..Imagine running more then this, it would cause excessive heat and multitude of other things to happen that the stock engine was not built to handle.

[Smaay]

^^^ that is the worst thing that you can do. unless you deck your head and block and you use a thicker gasket to make up for the lost space. by increasing the space, you can actually change the timing of the cams.

[7th Degenerate]

can anyone explain why a high compression ratio engine such as the scion fr-s'
12.5:1 or our celica gt-s (not sure what the ratio is).....why is it frowned upon to turbo high compression cars? i read its a "nightmare" to turbo them, why is this? and also read getting thinner gaskets can lower the ratio a bit? thanks


Yeah, throw a THINNER gasket on it, that'll lower your c/r (sarcasm)

chek this out: http://www.monkeywrenchracing.com/product_info.php?cPath=21_36&products_id=305

Sammy, thats why you would use a little know device as a FIC, when adding boost to a non boosted car..the lower your c/r the safer you will be from detonation.

[Smaay]

Yeah, throw a THINNER gasket on it, that'll lower your c/r (sarcasm)

chek this out: http://www.monkeywrenchracing.com/pr...roducts_id=305

Sammy, thats why you would use a little know device as a FIC, when adding boost to a non boosted car..the lower your c/r the safer you will be from detonation.

what does that link have to do with anything. its for a big bore 1ZZ. so its a few thou. thicker than stock, big deal. i have been in this business a long time and your 36 posts holds no water with me.

lower c/r is a safeguard from detonation, thats turbo 101.

[Muirner]

I have never seen one so far..

Go to the mid west, like in Iowa. It's there.