I have a question...Why our engines can not handle boost over 1,6bar?There are other cars operate over 2 or over 3 bars...(Evo)is it something with the boxer design?

 

I'm sure Chad (CJV) will come in with a detailed reason why we are not able to do so.

From what I gather is because we are an all aluminum motor so we have problems with expansion due to heat, plus factor in a lot of cylinder pressure, etc. It's just a recipe for disaster. At least this is how it is for the LS1 guys. They actually have had blocks made now that utilize an extra cyl. head bolt to help hold the heads down so they do not lift.

 

Why mitsubishi Evo engines(4G63) are so bullet proof in high boost?i think it is very interesting to see why our engines do not hold high boost...

 

Aren't the EVO's engines iron blocks. I cannot remember. I just know the aluminum blocks have problems shifting at extreme temperature and high amounts of cylinder pressure.

 

I thing they are alloy...(but not sure)

 

cryogenic alum.
Also check the % of elements in each case(e.g. copper,magnesium,silicon,manganese)

 

Limits on boost are dictated by fuel octane and compression ratio. If you stay with the 9.4-1 compression ratio you need to use higher octane as the boost increases.

As for the 996tt motor, the weak link is the sealing of the heads. The stock 9 mm studs simply are not big enough. The supra's use 12 mm studs. Second is the type of thread used on the studs along with not bottoming out the studs. In addition, stock Porsche studs simply do not have enough tensil strength. Third, the type of cut washer being used. The Porsche washers just do not help the heads from moving. Finally, the head gasket needs to be stronger and the head needs to be double o-ringed.

If the above is done the heads will safely stay in place to 2.5 bar or 35 psi. If you want to go above 2.5 bar, you must lower the compression ratio to 8.6-1, mainly due to the fuel's octane and resulting detonation.

 

I see...so i suppose Mitsu took under consideration all above factors when 4G63 was engineered?

 

Probably. Plus the compression is lower. 8-8.5:1 I think. My MKIV Supra was 8.5:1 and I could run 22PSI all day long on pump with single conversion (60mm turbo) on STOCK fuel with great A/F.

 

hmmmm...so finally our engines are not so bullet proof as i thought...or to be more realistic,they do not override 1,6bar...i start thinking that i run too much boost(1,35)now...

 

Boost Pressure in and of itself has nothing to do with cylinder pressure.... (banging my head against the wall here).

If these engines can make 700 whp stock, it doesn't matter if you do it at 1.3 bar, or 2.0 bar. If all of the other incidental items are up to the task(fuel, MAF - if so equipped, intercoolers, turbos, tuning, valve springs, etc), the car does not care what the boost pressure is.... especially on a MAF car.


Justin

 

Ok...so based upon your knowledge what boost pressure is safe on a 996TT car?(with proper tuning of course...)

 

In my opinion, after 1.2 bar you are looking for maintaince issues unless you have built your motor for more.

 

Aaaarrggggghhhhh.

1.2 bar on K16/16g turbos, or 1.2 bar on GT35R turbos?

One will make 450 wheel horsepower, and the other will make 650 wheel horsepower at the same boost level. So please, can you elaborate on the increased maintenance that you would experience by running the K16/16g setup at 1.4 bar?

Justin

 

Every setup is different, and that is a trick question. Boost Pressure has absolutely nothing to do with it. Turbo size(airflow), cams, torque at the engine at a given rpm, octane, elevation, tuning... those things all affect how much boost pressure you can run.

I can tune a car to run 1.6 bar on pump gas, but it doesn't mean it's efficient at that level. At that point, I have pulled so much timing that it's not worth the added .2 or .3 bar, so we back it back down. However, increase the octane and we are back up to 1.6 or 1.7 bar with the appropriate timing, making the appropriate torque.

Justin