15lbs on a stock motor bro

wicked long edit, but thats 15lbs on a stock gsr motor, ya know, 15lbs on a motor thats already 10:1 compression. that'd make the compression like 13 or 14:1 which is like f1's and shit.


/e ? thought i edited my last post instead of posting a new one....my b

This post was edited by Avoid on Sep 20 2010 02:01pm

Boost has no bearing on compression. Static compression ratio is determined by the bore, stroke, piston volume, compressed head gasket thickness, and combustion chamber size. It is fixed. Dynamic compression is calculated with static compression and valve events, specifically IVC and EVC (Intake valve closing point and exhaust valve closing point) which is determined by the camshaft specs. Compression ratio is a fixed measurement that will not change by adding pressure (boost), nitrous, or anything.


A 10:1 engine on 15lbs of boost is still a 10:1 engine.




In the non-toy fuel injected engine world 10:1 is mild compression. 10.5:1-12:1 are pump gas N/A numbers, 9.5:1 - 10:1 is supercharger territory, and 8.8:1-9.5:1 makes for a good turbo engine (all assuming pump gas). The big boys, people you see making big power, are running lots of boost AND high compression. Honda guys are the only people I talk to that insist on having an 8:1-8.5:1 compression ratio to keep the engine alive under boost. The lower you go with compression the less power you will make. You also make exponentially lower amounts of torque off boost. An 8:1 engine that was already low on torque in the first place will be completely gutless and no fun to drive off boost (where you spend most of your time on the street).

i see.

so why do people say its bad to boost stock gsr's? almost like boosting a stock vvtl-i

Many reasons. The parts in the engine were not designed for boost. A 10:1 engine with pistons and rods designed with Natural aspiration in mind will not hold up to the increased cylinder pressure of boost or nitrous (cylinder pressure IS torque and torque IS power). Cylinder pressure causes heat during combustion. The more pressure the higher the heat. Most N/A engines do not have forged pistons. They use cast or Hyperutectic pistons which do not like the extra heat caused by the extra cylinder pressure. They will literally melt or crack (usually at the ringland area). The optimal design for an N/A piston and rod is as lightweight as possible. At 10:1 compression even a super thin and light piston would barely be stressed in an N/A setup. That same piston would instantly shatter when placed under a lot of pressure. They also need to expand when heated to seal against the cylinder walls as much as possible. A little bit of blow by in a N/A engine can really hurt performance. Forged pistons do not expand well. Most forged pistons have a taller and thicker ringland (area above the compression ring). This holds up better but it is also heavier.


That is a good explanation as to why much bigger engines have similar power limits as smaller engines in stock form once boost or nitrous is introduced. It's not because it's a bad design. It's actually because it's a good N/A design. It's a give and take thing.


I don't know much about specific honda engines but in general the higher powered N/A engines are going to have an optimal N/A setup which in turn is not an optimal boost setup.



The lower you go on compression the less chance you have of getting detonation. Tuning an engine that still has a relatively high CR for pump fuel and boost is not easy. From my experience most honda "Tuners" would have trouble with basic algebra. It's much easier to put a small (IE too small) of a turbo on an engine with really low compression and max out the boost to make your power. Your limit is the turbo. To properly tune a higher CR engine with a proper size turbo (fuel octane is the limit instead of turbo flow) is not so easy. You have to be able to adjust hundreds of parameters correctly. Most of my experience with turbo honda guys has gone something like this:

"How did you tune it?"

"I put in the injectors someone on the forum told me to use and adjusted my fuel pressure regulator until my WOT A/F ratio was close on my eebay wideband"

"Wow"



There is a reason you pay $500-$800 just for a competent tune on a "real" performance car like a Corvette (therefore anything LS1 powered), Viper, etc. Even the people that are supposed to be good at it know that there is always someone better.

people run 15 lbs on stock gsr's all the time... I for one would'nt do it, but people do it all the time without any problems.

Well the tune shop we had gone to down in Mass at the time when my buddy was going to turbo his Celica GTS, wouldnt turbo it without upgrading pistons, rods, etc because of the 11:1 compression of the vvtl-i

You also need to keep in mind that that is a shop that probably doesnt want to buy someone a new motor, should something go wrong.

I dont know much about toyota motors, but from my experience, celica's dont have the most stout motor around.

I do know that it is the same motor that you will find in the scion tc and also the toyota corrola, all three cars i see having a lot of trouble with their motors.

What do you drive might I ask

eg hatch.
no its not fast
no its not super clean like omg
its just lowered on some blades.