Shrink Porting

[richwrench]

Recently somebody posted a link to MOTOTUNEUSA about engine break-in ? ( Gary was that you ?) Well I found it very interesting so I subscribed to the link & started reading all the other racing secrets. One that really caught my eye was shrink-porting the intake ports of cylinder heads to increase charge velocity. Goes against everything I've ever read - "bigger is better". I understand that PEAK horsepower may be smaller, but the gains will be over a much broader powerband spectrum & therefore much more useful than a narrow horsepower gain. Sean, Jeff, Lank - all you racers out there - have you ever played around with shrink porting ? I'm not a racer myself, but this acually seems like something an average mechanic could do to a spare set of heads with a very minimal investment. I couldn't find any threads when I searched, so I figured I will ask the Big Dawgs ! What do ya'll think ?

 

[one2dmax]

I've looked at it and that's a great idea. I may have to do up a set and have it ready for the dyno day in Topeka.

Sean

 

[RagingMain]

If it works I want some for my bike!!!
Plus if it does work and I throw in some bigger cams maybe I can break the 140 hp barrier. 130 hp is getting a little boring. Maybe time for nitrous???
Cheers

 

[Jeffb]

small ports & high port velocity is perfect. Couple years ago Car Craft mag. built a 383 chevy & put Edelbrock's smallest, small block heads, on it. pretty much for a 283. Thing made like 500 hp with a great torque curve. bigger is better only applies as rpm range goes up. big ports kill bottom end, until it has a supercharger anyway.

 

[DanQuin]

small ports & high port velocity is perfect. Couple years ago Car Craft mag. built a 383 chevy & put Edelbrock's smallest, small block heads, on it. pretty much for a 283. Thing made like 500 hp with a great torque curve. bigger is better only applies as rpm range goes up. big ports kill bottom end, until it has a supercharger anyway.

To a large degree, yes. And the clue is in the last sentence. It's all about V/E. Having a cylinder that can move 150 cfm, and a port that can move 400 cfm will not make big power. Maximizing the shape and overall efficiency of the port is what will do it in most cases. Without some form of forced induction, bigger may not mean better when it comes to porting.

 

[4gasem]

I probably posted it up. I used their method on my max and my G8.

Works great!

I'd like to see the results of the shrinking.

 

[lankeeyankee]

I have never done any shrink porting to any of my bikes. I am a bracket racer so speed isnt really important to me, hell I have proof I race a VMAX.
Porting is a skill and not something you want to do yourself with a tube of epoxy and dremel bits. Leave the custom head work to someone that has 10+ years of expierence and owns the high dollar equipment.

 

[KJShover]

I'd like to see the results of the shrinking.

well, Chris, you could always join the Polar Bear club :biglaugh:
http://www.polarbearclub.org/