WestJaxVert

First assumption:

Let's say you are making 300hp at 15psi of boost. Your engine is taking in y volume of air. You should still be able to make 300hp at 10psi of boost by increasing y, accordingly (perhaps by changing the size of your ports).

Is this correct?

Second assumption:

Assuming the above to be true, an engine making 300hp at 15psi of boost has less longevity and is more apt to failure than another engine making 300hp at only 10psi of boost.

Is this correct?

Thanks for any info.

Dan

peejay

First assumption:

You should be able to make more power, since the air would be heated less.

As a general rule, the mass of air you flow is how much power you're making. Whether it's 15psi with crappy turbos, 10psi with a good turbo, or N/A with a larger engine or higher RPM.

Second assumption: More or less, yes. All depends on how aggressive the tuning is, of course.

Evil Aviator

1) Yes, porting will increase the volumetric efficiency and move the peak hp to a higher rpm, both of which increase the volume flow rate. Therefore, with a higher volume flow rate (cfm), less boost pressure will be required to maintain the same mass flow rate (lbs/min). Additionally, as mentioned above, 10psi of compression creates less heat than 15psi of compression with everything else being equal, and the lower boost level will allow for a leaner mixture, both of which will increase power. This means that a 10psi boosted engine can create 300hp with a lower mass airflow rate than a 15psi boosted engine, assuming all other factors remain the same.

2) Not necessarily true. While boosting an engine up to a certain point will begin to increase wear, so will aggressive porting and high rpm's. For example, if you compare a 300hp street-ported turbocharged 13B-REW to a 300hp J-ported NA 13B, I would venture to say that the turbocharged engine would last much longer.

peejay

That's because you're introducing a second variable: increased RPM, and RPM stands for Ruins People's Motors.

However if you're comparing turbo engines and you get the better HP/lower boost through a more efficient turbo, only good things can happen.

WestJaxVert

Thanks for the info guys. Very helpful.

I've also sent each of you a pm. I'm hoping that you can give me some application specific advice.

Thanks.

Dan