Thread: Cams question

here is the long and short of it and after this im done

low intake velocity and timing are the two things that easily show these motors were designed around the 16ve

if you can't figure it out from there then we aren't having an intelligent discussion

im done

There are certain design restrictions that are taken into consideration when doing any motor build. Certainly there are a lot of good reasons why a 1.6 is better.

Everyone in the K20 camp is going with 2.4-2.6 engines. They were designed around a 2.0, but that isn't the restriction when considering the aftermarket.

I don't care to hear whether or not you think we are having an intelligent conversation. What I want are facts. Can you provide them?

Don't take this the wrong way, I'm sure internet speak this will come off as me being a prick, but don't take it that way. I'm just being the devil's advocate here and would like a good explaination. There isn't anything about a motor that you can talk about that is out of my league, but if there is a good reason why you believe the way you do I want to hear it. I'm sure others would like to hear it as well.

So you were talking about intake velocity?

yeah it comes with a high flowing head. Your honda's dont exactly have breathtaking velocity either. and timing, well thats irrelevant.

Glad you brought up intake velocity. Again, you got things backward. Low intake velocity is bad and it is more of a problem for the SR16.

The generally accepted optimum Mach number for the inlet velocity is .55 to .6, which is 613 fps to 669 fps. Lets find out the Mach number for SR16 and SR20VE.

Here’s the link to the calculator for inlet valve Mach index/ inlet velocity. Inlet Valve Mach Index Calculator

For both engines, I inputted the peak power to be at 7,800 rpm.

This is what it spat out for the SR16.

"Your bore size is 3.39 inches with a stroke of 2.7 inches and has 2 inlet valves with a diameter of 1.34 inches. Running a valve lift of .476 inches at 7800 RPM, the inlet valve mach index is 0.303 . The mach index for maximum volumetric efficiency is .6 . Beyond .6 the volumetric efficiency falls off. As the mach index rises beyond .6 the volumetric efficiency can be increased by later inlet valve closings (60 to 90 degrees ABDC). "

Results are:

SR16=Mach .303/338 fps

20VE=Mach .380/424 fps

As you can see the SR16 inlet velocity is slower than the SR20VE, therefore not as good. There goes your theory the VE was designed to be a 1.6.

Kelford have actually mentioned before that they reckon a ve head could make more power by decresing the area of the port due to the increase in velocity....

So with all this talk of poor ITM velocities in mind, should we be trying to get a company to make us an ITM rather than larger cams?!?!? If I understand correctly, wouldn't a larger cam be useless if the ITM cannot supply the proper air volume/velocity?

Yes, that why I think the 20V has a superior head. The intake port cross section has been reduced.

You're on the right track. I've been kicking around the idea with some cam grinders. That's all I can say for now.

^This thread is on the right track. Keep the discussion going guys. +Rep

I was reading an article by david vizard and going by his testing, he reckons that velocity is related to a ratio between the valve area and port cross section (or something similar, I may have got that slightly wrong it was a long time ago that I read the article) but basically he was saying that a lot of modern japanese heads have a huge port cross section in relation the valve size

He also says when it comes to out and out performance get the biggest valves in there you can fit