V8 Head home porting

[350matt]

I found some good gains on my Sd1 heads by de-shrouding the inlet back to the gasket line in the combustion chamber.
Also worth cc'ing the combustion chambers as mine were about 3cc different down each head where the casting hadn't been picked up true before machining.

Also you can use stones on ally but you have to keep flooding the job with Wd40 or similar, the clogged stone then de-clogs.

Matt

[Darkspeed]

Cheers Guy's

Doing some measuring at the moment to map the port to see how far off ideal the original port is and exactly how much needs to be modified to get the most from the standard valve size. This may take some time as I cannot find my bore gauges.

From all the reading it is amazing how critical the port size is - 0.8 0.82 0.84 of valve diameter are the numbers from Vizard for slighlty different port shapes having considerable effects on flow.

0.8 = 32mm
0.82 = 32.8mm
0.84 = 33.6mm

Less than 0.5mm on the diameter.

However this is for an ideal port - nice and straight and not what we find in practice with lumps bumps and port shape transistions - what this has really shown me is that development without a flow bench is pretty hit and miss and a flowbench would move things along far quicker.

However cleaning up the ports in line with some recognised guidelines will be worthwhile.

If he neighbours thought that compressor going all ady was loud - have you heared a flowbench at full bore - 6 or more vacuum cleaner motors

Cheers

Andrew

[katanaman]

A flow bench only tells part of the story as well. You can open out the ports for max flow but if you don't have any velocity in there the engine will run like a dog, then take off when you get up the revs enough to get the inlet velocity up. If it was easy everyone would be able to do it but it isn't and there is still a fair amount of mystique in the whole process. Unfortunately no two designs are the same either so what will work on a Ford could be poor on a Rover.

[Darkspeed]

I appreciate that its not the whole story but its regarded as about the best method of gauging a heads power producing potential and thats good enough me.

What has been clearly established by the benches is that opening ports out over 0.8 of the valve diameter reduces flow - and that in the main is due to port velocity - opening them to 0.9 reduces the flow so much that you may as well have not bothered.

Your right its not easy and not everyone can do it - but unless you take those initial steps to try you certainly never will.

I am willing to put some faith in what I have read to build a bench and have a good play.

Andrew

[CastleMGBV8]

Andrew,

Heres an album of pictures of mods to both Rover and Buick heads from a Guy called Dan Jones in the states which may be of interest.

Kevin.


http://www.bacomatic.org/gallery/album12?page=1

[Darkspeed]

Boy oh boy is old noggin spinning from all the info its trying to take in on gas flow techniques.

Some useful info I have found.

It's well worth matching the inlet manifold(s) as best you can to reduce any steps at this junction however the real restriction to flow is at the push rod tube area not the manifold face so no need to go really mad.

On one website regarding a G33 with rover V8 there was some detail of matching the exhaust ports with the gasket on the port and the manifold - This may well be a very good way of adding power on the inlet but its the best way of losing power if done on the exhaust - There must always be a step at the manifold port interface - manifold being larger - Have a google at exhaust reversion for details.

Seems to be why there is a favour for D shaped ports with the step at the floor to give anti reversion - for exhaust port matching, only match the top 3/4 of the gasket on the head and the full gasket on the exhaust to make sure you have this step.

Just making up my jig now for grinding the valve backs.

And found this place for long shank carbides - Just need to get brave enough to ring them for prices Tekmat

Cheers

Andrew