Thread: Porting and Polishing Heads

Probably the simplest mod you can do , match the ports and clean up the casting and you will notice the difference.
I wouldnt pay anyone to do it though.

Sent from my GT-I9300 using AULRO mobile app

I agree. Regardless of port size (standard or ported), the efficiency gains are only going to be better with more open ports. Especially for towing or heavy ab/use.

Engines are pumps. Make a pump breathe and expel more efficiently (within limits - too big will reverse the efficiency gains on all but race motors) and you'll be a happy chappy.

Cheers
Keithy

Thought it was just porting. The polishing promotes laminar flow, which you don't want at that stage.

Yeah I'm not sure about polishing. When I used to tinker with old red Holden 6's I only ever ported. I've heard all kinds of rumours about polishing actually being detrimental, then the ones that say it's the only way to go.

Depends upon the engine, the person who's doing the job, & what it is that you want to achieve.
Pickles.

I found it worth the effort on my 92RRC 3.9, as it gained 7% on the dyno as I had before and after runs done.
The heads on RRVs are poorly cast and the later ones seem worse , particularly in the exhaust ports , where I found a large ridge .
There are also ridges in the inlet ports near the valve seats. Just cleaning them up there should be worth several percent.

I shortened the inlet valve guides also.
You should read Tuning Rover V8s by David Hardcastle and How to Power Tune Rover V8 engines by Des Hammill.
A while ago How to Power Tune Rover V8 Engines was available to read on Amazon AFAIR.

These books give cross sections of the heads and where to safely remove material.
Regards Philip A

After I took the heads off a 3.9 I have and found them to be ported to roughly 25% larger in ID than a standard EFI head. Whoever had done it had also cut straight through all of the valve guide that entered the chamber, this was damaging the valve stems and just looked like bad news and the possibility of belt valves in the future.

So I spoke to one of my mates who knows far more about motors than I probably ever will and has built several big HP motors. After I showed him photos of the porting that had been done he said I should use the ported heads but did suggest replacing the valve guides with new ones. I got some bulletted valve guides and new valves from Rimmer Bros and won't be shortening them.

My mate also told me that in most cases, when you have or are going to port heads it is better to leave them not entirely smooth or polished but get them to be as even as possible within your limits of patience, at least on the inlet side. A slightly rough surface can actually help bring more air into the motor and if you have also enlarged the extractors so that there is no ridge to hinder the exhaust gas escaping, you will see/feel gains no matter what engine it is.

But, the time you can spend on porting factory heads to be to such a high standard that polishing and getting the exhaust side perfectly smooth and even just isn't worth it.


This is what I was told and looking at the logic behind it, it makes sense to me.

It was my understanding that you roughened the inlets (promotes turbulence and the air fuel ratio) and match the exhaust to the headers - smoothing the exhaust to promote cleaner / faster exhaust gas exit.

Another thing to consider is adding and X or cross pipe to a dual exhaust system- straight pipe across promotes lower rpm torque where a cross (X) pipe promotes hight RPM horsepower.

As mentioned before - engines are an air pump.