Thread: V8 Exhaust Port Matching Expert Help Please

How much difference between the port and extractors?, you won't have much to play with , wouldn't be opening more than the id of the extractor tube.

I think I might be ok discovery; the measurements are:

Ports = 37x27mm
Gaskets = 37x22mm
Extractors = 33x24mm
Pipes = 40mmOD

So I might be able to open up the extractors to 37x27mm and the same for the gaskets.

What do you think? And would it be worth doing (I'm thinking yes for flow)?

Cheers

According to theory, you should have a step between the size of the port (smaller) than the exhaust manifold (larger) . This is to help prevent gas reversion .

But really with RV8 ports the difference is minimal as the exhaust ports are so poor in design and execution.

You would be much better off cleaning up the core flash half way down the port between the valve seat and valve stem and smoothing and widening the port cross section around the valve guide.

If you are grinding ports you should only raise the port opening as this is where the majority of the gas flows. I would grind the gaskets if they overlap the ports and maybe take a bit out of the top of the extractors.

BTW extractors for RV8s usually have quite small primaries to give good low down torque. A lot of work has been done over the years to work out the optimal size. BUT 3.9 iron manifolds flow just a well as most extractors.
Regards Philip A

Thanks Philip A,

I had the headwork done a while ago and apparently according to the guy who did them, they are fully gas flowed and as far as you should go.

The top of the extractors look like they only need about a mm taken out. See pic below showing the mismatch:
http://efq.com.au/Extractor.jpg

Looking at the pic and the measurements you'll be able to do that no problem battler .

Each time i had the heads off any of my previous V8's ( and any motor infact) i matched the ports to the manifolds both inlet and exhaust.
You will notice the dark area's where the ports dont line up properly.

Originally Posted by Battler

Thanks Philip A,

I had the headwork done a while ago and apparently according to the guy who did them, they are fully gas flowed and as far as you should go.

The top of the extractors look like they only need about a mm taken out. See pic below showing the mismatch:
http://efq.com.au/Extractor.jpg

G`day ,

if you go off the carbon , that would be to take the extractors to the size of the gaskets not the ports .


From your figs the exhaust ports are larger than std the gaskets are std 10 bolt head size , ( 3.9 to 4.6 ) and the extractor port size are 3.5 figs but the pipe size is larger than usual .

You could if you wanted delete the gaskets and use silicone instead , you may also want to check how the fastener thickness and placement affect the line up .

The heads are actually off a 3.5l and they are on a 4.6l

I've nearly finished one side and it's going well. Now I need more of those little grinding stones; off to Bunnings.