Chrisbsvc

My cylinder head man just finished porting heads for our monster. I knew this guy was good because he has been porting for 17 years (mostly racebikes for AMA etc). Just a thing of beauty. Too bad we have to actually install them.

A couple before and after shots too.

Chris

nathanUK '81 930 G50

Is it OK to shorten the valve guide like that on a 930? Don't worry because I am asking (this is not a sarcastic comment), I have no idea & just find it hard to believe.

Chrisbsvc

Yes. But new guides will be installed and cut down before assembly. Typically porting is done with the old guides in. Or at least thats what he likes to do.

By the way if anyone is interested, he would love to do more headwork like this for an extremely reasonable price.

chris

A930Rocket

I wondered the same thing. I took a look at some pics of my heads that were ported and not as much was taken out. The valve guide was also left stock when replaced. As heat is transferred from the valve head to the valve stem, valve guide, and then the head, it seems a lot of that ability is gone.

But what do I know... LOL

BrianKeithSmith

Here's the way they should look when you get them back from the machine shop

BrianKeithSmith

Chris:

Where are you at in Charlotte man?

Brian

DonE

They look good.

The real question is, "will they perform?" Flow numbers would be interesting. Did you do anything to the intake?

Brian - why didn't you have the air ports welded closed?

JFairman

I worked at Gunnar Porsche Racing for almost 4 years. I did mostly body work but I hung out in the engine room lots.. and saw the insides of many race winning Porsche engines from early 906's to RSR's to 935's and 962's.
Never ever have I seen a valve guide cut back like that.
That looks like an amatuer job from somebody that got carried away with a die grinder thinking bigger is better. If he took anything off the short side radius he is going to create more detrimental turbulance at the valve seat area and actuall reduce air flow through the ports into the combustian chambers.
You want to straighten out the air flow as much as possible before it hits the back of the intake valve and taking away material from the short side radius will do just the opposite of that.
Then there is the possiblity that removing aluminum from the port will leave the port wall thinner so it can not transfer heat as quickly and that part of the head may overheat and warp, or worse.

Porsche knows real well what they are doing in there and if material is removed it should be taken from the top to lift the flow up and sides to let it flow around the valve stem better.

You should only smooth out any casting marks that are in there if you don't have experience and a flow bench to test the heads with the valves installed and open at different lift heights, and leave a nice uniformly rough 80 grit surface to create surface turbulance to keep fuel from wetting out on the port walls and keep it atomized as air tumbles over the rough surface.

Surface turblance cuts down on air drag... it's the same reason golf ***** have dimples.

BrianKeithSmith

I just use the plugs Don. They seem to work for me... A little red loctite...

Chrisbsvc

Short side pretty much left alone besides slight work to D-shape it. Theres really not as much taken out of there as it looks in pictures.

Brian: I actually live in gastonia and work in charlotte at the Honda dealer on Freedom dr. I took the pics of the heads before he even started the "fluff -n- buff". Also the valve job will be done later.

DonE: Air ports are on the short side of exhaust port. But we will likely do it anyway.

A930Rocket: Most heat dissipation from valve to head is going from face to seat.

JFairman: Don't have time to reply to your flaming right now. Obviously you can't see the pictures or you're assuming that you're the only intelligent person alive. By the way, normally when speaking about principles of a golf ball the proper term is surface tension. (you see its irritating when someones purpose in life is to correct you)

attyjeff

Chrisbsvs.......you live in Gastonia...........I have family there......I didnt know more then 1000 people live there.....just kidding. its been years since I have seen gastonia,

Chrisbsvc

Well I grew up a bit north of that in Lincolnton. Imagine that.

JFairman

Sorry to come off the way it sounded...
I've done some porting too, and I went too far in the beginning also.
When I say I've seen the heads and ports (and alot more) of porsche race engines it's the truth.
If taking that much material out would have made those cars faster it would have been done a long time ago.
They should be checked on a flowbench so each port flows the same when that much is removed.
Cleaning up casting marks and streamlining around the valve guide are good things, but those appear to have been taken a little too far.
Shortening the valve guide like that will make it and then the valve seat wear out faster as the valve will have more side play and could possibly lead to a dropped valve if driven in that condition long enough.

I hope they work out well for you.

SGOGT4

Welcome to the world of public boards. Personally I don't see a thing wrong with JFairman's post. If you aren't prepared to hear people tell you that they don't agree with you or the direction your project is going in I would save your time and just not post. There is a lot of knowledge flowing through these posts. But if you don't keep an open mind about things you may miss out.

nathanUK '81 930 G50

Well, I have to agree with the guys here on the following,
Heat being taken away by the valve guide.
The length of the valve guide keeping the valve straighter and reducing wear.
The porting should be rough and not polished.