slate blue

Interesting stuff, there is a few things that I would like to say, if you use beryrilium copper seats you must use leaded fuel, the valves must be treated for longevity as the Del West coating is only meant to be very short lived. The coatings required are very expensive and for very long life you may want to use two different coatings or surface treatments.

I don't think I would use a Ti exhaust valve if you are using on the street, I will use a nimonic/inconel valve as the Ti at elevated temperatures doesn't heat cycle very well, also it is a smaller valve less need to be Ti and the ramp on the cam tends to be smaller less mass to control.

There is a few websites out there that you can plug your cross sectional area of your port into to work out what is required. Depending on what revs and capacity of the engine the CSA will change, the 968 head does have a reasonably large port but it looks bigger than it is. You need to measure at 90 degrees from the port as the gasket area is angled as such it looks bigger than what it is in terms of CSA. The 968 port btw is the same size as the Carrera GT port and that has 10 cylinders and is current technology.

As to wet flow benches, there is or will be out soon an adaptor for most Superflow benches to be converted at a cost of $2000 to a wetflow bench.
The flow numbers that Carl posted are O.K the one concerning factor and we will find out when the heads are tested on an engine is that the flow really starts to back up in the upper lifts, even though the cam wont lift that high it is not a good sign, at least the numbers are not going backwards, that would be a terrible sign, you also need to flow the heads with no valves in them. This gives a baseline to come off. If you are within I think 85% of the no valve flow, this is normally as good as you can achieve.

Greg

GregBBRD

Carl:

Great that you are throughly "up to speed" regarding the titanium valve issues. Your initial pictures and descriptions concerned me. I certainly did not realize that these pictures were old and that you had moved "past" this point. Your stainless valves look nice...they should work fine. (I called Carl today and he told me that the beryrilium seats had also been removed, for the stainless valve application.)

Glad you cleared up that these ports were for a supercharged application. That changes most the "requirements" for port shape and volume. The supercharger, will indeed, blow through almost anything. So, with a supercharger, problems with intake port shape and volume are certainly going to be masked. Not sure what happens with the fuel mixing issues, when using a supercharger, but I'd guess that it is less of an issue than when doing naturally aspirated engines. The supercharger might even push hard enough to help with the exhaust side.

Keep up your efforts...

Greg Gray:

If you set a 968 intake gasket onto a 928 head, you really get an idea of how large these ports actually are. We certainly have not had the need to make the ports this large, which is a good thing. There is enough "core shift" in most 928 heads that make getting anywhere near the size of the 968 port is impossible, without finding "water". When our intake manifold (we've been working on this for over a year...with dozens of changes) for these engines is done, increased port size might become more desireable.

Gretch

Fascinating stuff!

Stromius

(Noobie question)

If I understand correctly I can send in my heads, basically get a valve job plus updating my heads with bigger valves. It seems most will spend this $$ on SC or Turbo'ing their engine but what about us knuckle draggers that will keep stock intake/exhaust for now.

What gains will someone like me (88 S4 5 speed) get with $2800 (porting valve, gasket)? Would this be a waste without new headers, )( pipe, high flow cats?

Further if I run my stock cams for now, can I safely update to the GT or S3 cams down the road?

Mrmerlin

Carl are there any modification needed for the pistons so the valves dont hit from an over rev.
If these new larger valves are used??

Carl Fausett

MrMerlin - we always recommend you check the Piston-to-Valve clearance on any change in deck height, camshaft, or valve diameter. This can be done before the head is removed from the block, which will give you a P2V clearance number that even includes head gasket crush.

Then you can know, and not guess. P2V clearance is too important to guess at.

In the case of increasing the valve diameter where pocketed pistons are used, the piston valve pocket must be at least as large as the valve + .010", and in the right location.

Alan

Concours

Alan

dprantl

Maybe those shows were at an airport

Dan
'91 928GT S/C 475hp/460lb.ft

GregBBRD

I would venture to say...and I'm sure that Carl would agree, that these heads are not designed for your naturally aspirated engine and might even "hurt" the performance.

GregBBRD

Carl:

I know the answer to this one.

Yes, the valve reliefs in the pistons will need to be enlarged on a stock application. The bigger intake valve will "touch " on the eyebrow of the stock valve relief.

Stromius

Thanks Greg...kinda thought there would be more $$ involved. Thanks also Colin.

Still learning....

Carl Fausett

Often times head work is the LAST item looked at by the hot rodder, not the first. And yet, very significant gains are not uncommon when the head work is done correctly on all sorts of Ott-cycle motors from acrossed the spectrum.

I think the reason for this is that the tuner (hot rodder) often begins their search for HP with bolt-ons. That suggests headers, exhaust upgrades, maybe a SC unit - all bolt-ons.

Although this thread is about maxed-out heads for supercharged race car, MANY have completely missed that point and pointed out "flaws" based on the application in their mind.

Yes - for a performance street application, we would not recommend Ti valves and thats why we have already developed the SS valves. (Greg - your valves are on their way).

And, for street, the port profiles would be adjusted and not as agressive as shown here. For us, the port profiles are matched to the camshafts selected by the customer. Then we can compute the CFM and velocities that would put the cams in their sweet spot and go from there.

However - I have only one CNC head porting program at this time (they are expensive) and I did this one first because I needed it for my race car. Your heads would be ported the traditional way, which we describe and offer here:
http://www.928motorsports.com/servic...alve_heads.php
(yes, I know that page is all 16v, but the process is the same)

I am pretty excited about Mark Anderson's posted flow/velocity numbers and his measured HP output. If you compare his flow numbers to mine, his heads flow even more than mine do. The camshaft he and I are using are very similar (not identical, but damn close).

My engine, after we finish assembly, will be broken in on a engine dyno, so I will get good dyno info from it. But for the moment, I now am beginning work on the matching intake manifold to supply these heads.

With my present workload and racing schedule, it may take 6 months before I have the intake manifold done.

The process will be similar to this one I recently did:
https://rennlist.com/forums/928-foru...prototype.html

If you haven't looked at this intake manifold development thread, you will find it very informative.

ptuomov

"Often times head work is the LAST item looked at by the hot rodder, not the first. And yet, very significant gains are not uncommon when the head work is done correctly on all sorts of Ott-cycle motors from acrossed the spectrum. "

So what's you're saying is heads first and cams last when designing an engine? That makes sense to me.

Almost everyone who's hot rodding his car as a hobby seems to go the other way around: Cams first and the heads last. I think the only reason why the 928 crowd has been saved from the cams first curse is that until recently there really weren't many cam options!

EDIT: I was able to do it even dumberer than cams first. I got the valve springs first! ;-)

Stromius

Thank you Carl. I appreciate taking the time to answer. Like I said...still learning but at least I am asking questions instead of lerking.

Cheers !

Carl Fausett

Good questions are always a pleasure. I love to educate, and to be educated.
Thanks for your post and good luck with your project.
Email me at carl@928motorsports.com if I can help.