Any improvement noticed by porting etc ?

[QBhoy]

Hi

Im aware that GM engines we all know and love so well, although reliable and robust things...they are perhaps not exactly cutting edge or the finest example of precision engineering. I was recently told from a fella, about how he saw a noticeable difference in his 4.3 motor, after porting and polishing the heads. He said they were very roughly cast as they were and swears that the engine seems to just perform better. Not anything crazy, but certainly enough to notice.
Has anyone known this to be a sure fire and easy way to improve things a little ? Has anyone put any numbers on by how much it might improve the HP on your average 4.3/5.0/5.7 GM ? I’m certainly aware it used to make a difference in the good old days when messing with old car engines etc.
keen to hear !

 

[Bt Doctur]

You would have better results with "gasket matching" or installing rockers from an inline 6 , 1.75 Acts like a cam

 

[Bt Doctur]

http://www.superchevy.com/how-to/engines-drivetrain/sucp-0202-rocker-arm-ratio/

 

[QBhoy]

Thanks bt. She has a cam already. Not perfect to be honest. Especially at idle and low rpm.
just wondering if cleaning up things might make a difference.
I’ll have a read at your link.

 

[fishrdan]

I've port and polished several sets of heads, did it on my 140PH Mercruiser. Not sure much HP it netted, as it's about getting the most out of what you have. Personally, I wouldn't port unless completely rebuilding an engine, and trying to make it perfect, like paying the machine shop the extra $100-200 to balance the rotating assembly.

I didn't hog anything out porting, just cleaned up runner imperfections, gasket matched, blended the valve guides and some bowl work. Intake and exhaust manifolds were also gasket matched. DON'T polish the intake side, but you can polish the exhaust side with sanding rolls.

It takes carbide bits on a die grinder to do this work, and you can easily nick a valve seat if you're not extremely careful. Then it's a trip to the machine shop to have them replace the seat. Oh yeah, your going to have thousands of needle sharp cast iron slivers from the carbide cutters.I use a Bosch die grinder, 5-6 different carbide bit profiles and sanding rolls, also a brand new blue Sharpie to mark gaskets. $200-300 in tools and materials.