Here is a question i got from the shortbus. The answer is kinda rough, but its general idea is correct. So, here goes:
Quote:
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Originally Posted by NinjaHampster
hey whats the most boost in psi that the stock engine can safely run? and can we run a boost controller?
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Ill answer your Boost controller first:
No, boost controlers are for Turbos. The Boost controler messes with the wastegate on a turbo, making it think that there is less boost than there really is. Wastegates control how fast the exhaust turbine spins, and keep it from spinning too fast.
Boost:
well when you get into boost, you gotta know about how boost works, its effects on the motor, and octane gas requirements.
short answer: bout 21-22psi tuned VERY WELL on 93octane
Long answer:
boost is a byproduct of restriction in the engine (compression ratio, small ports, small valves, short diration cams, etc.), and the piling up of air being pushed in. Best way to think about boost, if by Cubic Feet per Minute (CFM). You can fit .5L or 31 cubic inches of air (actually less for efficiency reasons) in each cylinder, so when the blower is puting out 1L (62 cubic inches) of air to fill the cyl. then the pressure ratio is 2:1, or 22psi.
Thats why ported blowers, ported heads, and different cams will lower boost, but flow stays the same. Same amount (if not more) air, less cylinder presure, less stress on head bolts/pistons/rings/etc.
So what does that mean for the LSJ...
The head flows really well ont he LSJ, the valves are good size, and the cam duration is pretty long @ 262°. So everything is there for a good boosted motor. The only problem people have been finding on most engines, was blowing head gaskets, due to head flex/gasket failure, at 20psi. Thats why most switch to a better gasket, and ARP head studs instead of bolts. After that, you can put much more boost in the motor. Until the pistons/rings give out from too much cyl. pressure.
NOW...gas is what holds people back.
Normal 91-93 octane can only run safely, up to 22psi, ON AVERAGE, on a 9-9.5:1 compression ratio (CR), or less. Some are able to do 25psi...but thats on lower compression motors. Higher compression motors (11:1) cant usually go over 7psi. Beyond that, youll need somthing to lower intake temperatures.
When air is compressed, it heats up. Too much heat causes knock (when gas ignites before its supposed to), knock can destroy piston rings and/or pistons.
The drag Ecotec, is able to make 1800hp, running 24 psi, 10:1 CR?, on Methanol, with a dedicated water to air Ice-box intake charge temp cooler. They are actually able to run 24psi into the motor, at a colder temperature than whats outside. And the high octane quality of Methanol and power output, make that car's power.
Now, take that same HP and apply it to a 4g63 Evo motor. To get that, they have to run 32 psi, 9:1 CR, on 114 leaded octane gas (C14). Along wih the Air to Air intercooler, AND a Ice box as well.
The higher octane requires MORE heat (bigger hotter spark) in order to ignite the gas mixture, so it is less affected by knock condition. Thus, you are able to run more PSI/CFM into the motor. More Air = more power.
So...lets recap:
most people are able to run 21-22psi on their LSJ with 93 octane, tuned VERY WELL to eliminate knock.
If you plan on going with more PSI, or a Higher compression, plan on spending a LOT of money on:
1) 100 octane
2) Cooling mods
3) Methanol/Water Injection (cooling mod)
4) Nitrous (cooling mod)