Hello all, I was wondering at what kind of flow or horsepower levels do you advanced guys feel an unported head is a choke point?

I was also wondering if anyone has pictures of a head cut apart to see how thick the port walls are amongst other things.

Thanks.

 

The port limitations cannot be expressed in terms of hp so long as a turbo is involved, simply because increasing the turbo pressure increases hp for any given volumetric flow rate through the port. A better way to understand this is to realize that maximizing flow potential through the port enables more power to be generated at less indicated boost. Reducing restriction at the port while improving compressor efficiency as a result of a lower PR (pressure ratio) increases power.

The thickness of the port walls in an EVO VIII head vary, which makes extensive porting tricky.

 

just figure, boost is a measurement of restriction, porting can improve flow somewhat on a boosted application but more so on a Naturally aspirated application. You want to increase flow while maintaining velocity if you increase flow but lose velocity it won't help anything, in fact you will probably loose bottom end power. Thats why porting can be pretty touchy, and the reason bench flow is important because it tests both factors. But i wouldn't be very worried bout a choking point there are plenty of guys making a lot of power on a stock port head. There are even guys making a ton of power on stock valve train

 

I understand more is involved, I don't want to sound arrogant. I am just new to the evo world. I figured someone out there has an opinion on what level a stock head starts to choke. Say for example maybe they might say once you crest the 500whp mark you are usually leaving alot left on the table. Or maybe once you start flowing 70lb/min the stock ports really hold you back. ETC ETC. I understand its sort of a blanket statement. Thanks for your input though, I was hoping someone had a cutaway of the head, I really do not have the funds to buy one just to cutup on the band saw.

 

It just can't be simplified in such a neat and tidy way, especially when so many other factors influence the outcome.

Here is a back-to-back test of a hand-ported head vs. a CNC ported head. Needless to say, the difference between the CNC head and a factory head will be significantly greater.

https://www.evolutionm.net/forums/ev...head-test.html

 

The problem with a turbo motor is once you reach the limits of the turbo, there isn't a ton you can do to pick up extra power from airflow because the turbo is still the choke point.

For example, say a GT35R on 25 PSI is making 500 WHP on the stock heads. The turbo has plenty of flow left. Improving the head might pick up 75 WHP because the turbo has the capacity to put out that extra flow.

Now crank the boost up on the two setups. The stock head takes 40 PSI to make 650 WHP, but it maxes out the compressor at that point. The ported head makes 675 WHP at 35 psi, but the turbo can't make 40 PSI now because it is maxed out. The 25 HP gain is from efficiency improvements more so then airflow improvements because the turbo is pretty much choked out at ~65 pounds/min.

Same theoretical setup and in one situation, it seems pretty obvious to toss on the ported head for a 75 WHP gain. At high boost though, that $2500 for 25HP doesn't look as good. A blanket statement of "over 500 HP needs a ported head" doesn't really work.

As a friend once said years ago, "that little 2.0L motor is just there to get the turbo to spool, the turbo is where business happens."

 

porting is always going to help, because the motor will flow more and you will make more power on less boost, but there isnt really a choking point, like your looking for. There is a guy here in idaho runnin low 10's on a stock evo head with 280 cams making probably in the nieborhood of 800whp? The car isn't stripped, it is his dd and makes big power. This is the reason i dont really think there is a "choking point" maybe if your shooting for 1000awhp it might be tought after that but not very many people are shooting for that, nor have the money to do that.