Exahuast porting (valve guides )

XR8TED · Post by **XR8TED** » Fri Mar 25, 2005 2:49 am

I have asked on several of the mustang boards and nobody seems to help with this question. I am doing a set of 4v heads for a 98 cobra I have done a few sets of these heads and only tapered the valve guides. I have seen a few pics of cnc heads where they cut the guides completely so I tried to see what I could come up with. Do you think it will improve flow? These heads are going on an all out low mileage streetcar where performance if number 1 priority see a lot of track time. Sorry I have only been doing this for 2 years and am 21 and have not been able to save up to get a flow bench yet but I hope to get one/build one soon.

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cboggs · Post by **cboggs** » Fri Mar 25, 2005 1:08 pm

I do a bunch of these heads, I've never seen a huge benifit
to cutting the guide down. The down side is not supporting
the valve properly, I don't cut them down, ever.

I always remove the guides in a 2V or 4V head, .. port, then install
a guide with a taper on top.

It's much more important to support the valve stem, in my $0.02 worth.

Keep at it, .. but a flow bench will really help to open your eyes.
Read the stuff here on CSA or Crass sectional area, .. very important.

Curtis

XR8TED · Post by **XR8TED** » Fri Mar 25, 2005 2:29 pm

Thanks C... I have read several threads on here and have asked several head porters around town, but nobody can seem to explain the term cross sectional. Kind of embarrassed to say but after 2 years I still do not no what it means.

So with the heads do you think it's best to replace this one guide or cut the other 15? Keep in mind I would have to send them out for that kind of work. I do not have the tooling to do it, but if it is something I can do I my backyard shop point me in a direction in where to buy the tooling.

Sorry for all the questions but like I said I am young and inexperienced with a lot of will and I apply what other’s teach me very well. I just wish wyotech wasn’t 22,000 could have bought a lot of tools vs. very little knowledge gained. On top of trying to build a 12,000 dollar race motor.

Walline · Post by **Walline** » Fri Mar 25, 2005 3:27 pm

Thanks C... I have read several threads on here and have asked several head porters around town, but nobody can seem to explain the term cross sectional. Kind of embarrassed to say but after 2 years I still do not no what it means.

CA = cross section area, or the cross section of a port. Take and slice the port and the area you see is a cross section of the port. If the port is say square (to keep it simple) say 2"x2" multiply 2x2 or 4 square inches CA. It is ussually much more compicated to figure then that.

I hope that helps some!

68corvette · Post by **68corvette** » Fri Mar 25, 2005 4:22 pm

i dont think that cutting down those guides will make harm as much as in some older desings where bowl is made mush swallower.
If you compare quide lenghts to older 8v desings ill bet they have much more support to valve and even after cut down valve comes closer to quide because of smaller runner size.
viewtopic.php?t=621&highlight=

I dont have opportunity to test how much flow can be cained with cutting down the quide, but after looking your pictures i'd say that you should rather concentrate to widen the shortside than cutting valvequides.

someone can straighten this out, but all that bias in your pictures is not necessary with 4-valve heads..

cboggs · Post by **cboggs** » Fri Mar 25, 2005 5:15 pm

Cutting down the guide in this head isn't a good thing to do, ..
trust me. It doesn't really gain much and with the little
stem on that valve it needs the support at 10,000 rpm.

Also be carefull of that short side radius, .. avoid the temptation to
round it over and "smooth" it, .. it'll hurt high lift flow if it's cut
down too much.

CSA is Cross sectional area, .. the #1 thing you should be paying
attention to as a cylinder head porter.
If your local head porters couldn't explain cross sectional area they
likely are not the best source for porting advice.

There are several in depth threads on this site regarding CSA.

Curtis

Darin Morgan · Post by **Darin Morgan** » Fri Mar 25, 2005 6:41 pm

cboggs wrote:Cutting down the guide in this head isn't a good thing to do, ..
trust me. It doesn't really gain much and with the little
stem on that valve it needs the support at 10,000 rpm.

Also be carefull of that short side radius, .. avoid the temptation to
round it over and "smooth" it, .. it'll hurt high lift flow if it's cut
down too much.

CSA is Cross sectional area, .. the #1 thing you should be paying
attention to as a cylinder head porter.
If your local head porters couldn't explain cross sectional area they
likely are not the best source for porting advice.

There are several in depth threads on this site regarding CSA.

Curtis

I agree. I have never seen the benefits to cutting the guide out of the head for one or two cfm on the bench. Supporting the valve is more important.

ADR · Post by **ADR** » Fri Mar 25, 2005 10:31 pm

In the past I have tried cutting down the guides on one set of heads and I didn't run them long enough too be able to tell you good or bad on the longevity or wear but one thing I did notice was the oil tracking away from the valve guide. It looked to me like the cut away guide was at such an angle that the exiting exhuast was ripping the oil out of the valve guides. Just an observation.
Dale