when it comes to internal mods, i am pretty clueless... however, i was wondering what hp/tq numbers i'd come across if i bumped up my compression ratio (12.5:1 or a little lower)

what octane would i need to run
how much would it cost
what numbers would result from it

 

man, that's like asking how many tic tacs it'll take so that your mouth doesn't smell like the underside of a dead goat... i dunno.


basically, you have to look at engine theory... that is to say, how they run. the accepted method here is to run as much compression as you think is safe and call it good enough. my thinking would be that you'd spend at least 4 Gs for a good engine builder to put something together. you may look around on line and see if anyone is running some sick all motor ecos.

and octane? well... i'm guessing high test. i can't see building a street car to run on race gas... that would be silly.

 

Hey do any of you know where I can get the gmpp headers from? I've looked online and not finding anything. I even went to the saturn and chevy dealership, but nothing from them. There kinda slow around there when it comes to anything about our cars.

 

hp gain:
the rule of thumb is 4%HP per every point of compression.

how much will it cost?
a lot more then turbo/SC kit, and alot less power then a turbo/sc

what octane:
depends completely on your tune. you can run any octane as long as your knock sensor isnt throwing... that is the only reason to increase octane, it doesnt "give" you more power, it stops timing retard

pros rarely go this route because F/I is
1. easier
2. less expesive
3. more powerful.

another issue is theres few internal parts available right now.

 

but you gotta admit... high compression, high RPM engines are just freaking nasty

 

goto the supported vendors forums or search for "GMPP" and find where others have bought them.

 

What he said. If you raise the compression ratio any appreciable amount, you'll definitly require 93 or more or the knock sensor will be pulling timing out like crazy.

The easiest way to raise the compression ratio would be to weld up the combustion chamber (cylinder head). If you get someone who really knows what they're doing welding, they can probably find you some extra power then just what the compression ratio increase will give you too.

But in the long run, for the little bit of power this will gain you its not worth it. Throw a 50 shot of spray on it or wait for the Hahn turbo kit.

 

nasty like the underside of a dead goat?

combo of F/I into high compression, now thats nasty! If your turbo setup is giving you 290hp at the wheels, you add two points of compression, those 4%'s start seeing some light of day... but your increasing the chances of blowing your hard work to ****... you've really got to know what your doing to make it work safely...

 

has anybody ever even heard of someone who has done this, i am actually considering a lighter compression increase, maybe 10.5 - 11 : 1. I have a 2.2L though, so i would hope to see some good gains.

 

your only examples of this will be outside this forum. cobalts are too new to really have this kinda of thought put into them, most people are still buying CAI and changing tires.

look at some v6 or v8 forums, theres tons of examples.

 

easiest way to increase compression: Smaller head gasket=Higher compression

 

thinner-- but thats what you meant. Likewise to lower a comp ratio a thicker headgasket works too.

 

Im surprised NJHK has not chimed in yet

 

I think a high compression N/A 2.4 with a 100 shot of nitrous would be pretty tough.

the only question is what compression would you be able to run and still use 91/93 octane? Is 12:1 compression too high?

I don't think it'd be that expensive for the build up, throw in some higher compression pistons, forged rods, throw in some aggressive cams and you'd have a tough engine with the addition of bolt ons + the 100 shot.

 

+1 (Thinner, not smaller, you still want it to fit, lol.)

If you want to blow the motor, yeah! A stock motor would be lucky to handle that much NOS with it's compression. Try around 8:1 for a 100 shot on these motors... I would assume anyways.

Stock bikes run that high compression and run on premium, but nohing less than 91 octane. Example: my 10 has 12.7:1 comp stock, and I run premium. They have a thin head gasket for them that raises it to 13.5:1, and that's pretty much the limit on my bike till I would need to run race gas. It also depends on the air flow.

 

The 300hp LSJ build book uses 10:1 compression with a 73mm (2.87") pulley. I'm sure they were also using race gas.

 

for sure they used race gas, but you can still run 91, you just need to retard timing, knock off 2 degrees overall and you should be fine (of course pros and cons)

water/meth injection could be a solution as well.

 

I don't think compression is going to be an issue with nitrous, if anything nitrous is more partial to higher compression, imagine how shitty a shot would be on 8:1 compression.

Plus, the bottom end would be forged, my question is more geared at whether you could still go everyday on 91 octane and still have a great performing engine.

 

Like I said, it depends on the motor. But so far, I haven't heard of any 4 cyl. shoot more than a 70 shot and not blow the motor after very long of using it.

Back before slapping turbo's on 4's were popular, my buddy built his '95 Civic with a turbo with a lot of R&D. Then he dropped in a 1.8 LS motor with a 100 shot, dropped the comp. to 8:1, and it ran just as good on the bottle as the turbo car did. Problem was, you needed the bottle to run like the turbo did all the time. With the lower compression, he never had problems with that motor. Never blew at all.

And sorry man, compression is a big thing with nitrous. Especially on a stock car.

 

The problem with putting a thinner head gasket on is twofold. For one it probably wouldn't raise the compression any significant amount, and for two.....getting one would probably be a problem. With all this talk about high compression and a 100 shot of nitrous, I think a third problem would be keeping the head gasket actually between the head and block!!

 

I would never up the comp. on my car, AND put a 100shot on it. That's just a recipe for disaester. NOS likes compression, but it also likes to blow your motor. As long as you're getting enough fuel, I guess it'd be alright, then yer at the limit of your motor again. It's all in the tuning.

If I remember right, every .2mm smaller adds .25 of a point to comp. And yer right, getting one is the trick. To thin, and your pistons could potentially hit the valves.

 

lets take a hint from the celica gts. 11.5:1 compression on 91/93.

how to get there, mill the head down. if that wont bump the compression ratio enough then you need new pistons.

i wouldnt go more then 11.5:1 for street

 

LOL.....isn't that the truth, well said.

 

if I'm gonna be upping the compression its gonna be with forged internals bro...100 shot is a piece of cake.

these cars are already good for a 75 shot on a stock bottom end.

also nitrous doesn't like to blow your motor, people using nitrous like to blow their motor.

 

100 shot isn't a piece of cake on any 4 cyl. engine. If you really think that it is I suspect your engine will end up in pieces.......