Sameer

Ok guys I have the Ti ratainers and race valve springs. Isit an easy swap to switch to better/lighter valves during my next valve adjustment? If yes than which valves are good to go for? Whats needed to do for the swap and how long can it be done in?

Sameer

Anyone?

Geoffrey

You would need to remove the heads and have a new valve job completed in order to install different valves.

Yes, there are better flowing, lighter valves available as well as stronger more durable guides. I have been using them rather than the Porsche valves on all of the heads I've been doing lately. They have been lasting better than the Porsche valves and valve guides in the racing environment, and on a flow bench they flow better.

Sameer

Geoffrey,
Thanks for the advise. Removing the heads would be a big job so I guess I will do it when I drop the engine next time. Hopefully not so soon.

srf506

Geoffrey, guess I'm confused. Did you go oversize on the valve? I'm trying to do the math to understand how the same size hole and displacement of a lighter valve can "flow more" unless you changed duration or lift which is a function of the cam doing the lifting. I guess I could see very marginal improvement if the valve's "cap" was flatter in shape and the shaft thinner. But volume is volume and the piston can only generate so much negative pressure on the intake stroke "suction" given its speed, stroke and volume, and the manifolds only flow so much in stock form. So what other mods did you do to account for the increased flow?

Geoffrey

You can install oversize valves, but what I was talking about is stock size valves. The shape of the valve head, especially where the stem meets the head can dramatically affect the flow. The finish on the back side of the valve can help with swirl and tumble which are two other factors besides flow and velocity that will affect engine performance. So, to answer your quesiton, yes, the shape, finish and profile of a valve of equal size can affect its flow rate. Porsche valves are crude and do not flow as much as aftermarket valves of same size.

srf506

Thanks for the answer Geoffrey. I figured whatever shape change could affect the volume somewhat, and I knew it would definitely impact the swirl. Is the Porsche stock valve too big a fillet from the top of the valve to the shaft in comparison to the aftermarkets or is the angle just wrong?

Win Rice

Geoffrey,

I see several people that use 993TT valves on a modified 930. Under high boost (over 1 bar) on a typical 3.3/3.4 930, are good aftermarket valves available that will be more durable than the Porsche Valves? What head and stem sizes are available? Approximate cost?

Win

Geoffrey

I think what they are talking about is using the 8mm stem size of the 993 rather than the 9mm stem size of the earlier engines. This provides less of a restriction in the port and therefore more flow. I have seen this on a flow bench during my testing. Aftermarket valves come in a variety of material from titanium to inconel so, yes, there are aftermarket valves that are better than Porsche valves. Depending on how creative you want to be, you can come up with virtually any combination to work in a particular application from having custom valves made to using a valve this is very close to Porsche size and profiling the valve to fit. There are a wide variety of valves for American engines in the 5/16 size (7.9mm) that will work or blank 8 or 9mm. I think the guide has more to do with the cooling than the sodium in the exhaust valve.

Costs range from 1/2 of Porsche valves to 2x Porsche valves depending on what you want to do.

Win Rice

Geoffrey,

That's kind of what I thought, the valves are either fully custom, or off the shelf units like Manley or Ferrea, custom machined to fit.

Let's say I'm going to build a 3.4 engine similar to your 89, that will run on the street everyday at 0.8 bar with approximately 550 FWHP, go up to 1.0 bar for a little fun, then fuel up with 100 octane no-lead and go to 1.2 bar. Max RPM around 7000. What would be your recommended valve size and material for both Intake and Exhaust?

Win

Geoffrey

I install stainless valves on both the intake and exhaust with a very good guide. In general, if you have a Serdi style valve machine, you can go up 1 to 1.5mm in size on the valves. I've experiemented with 1mm larger on the exhaust and my initial reaction was that it was better, however, I've now come to think that in a turbo application, it may not be better. I'm not so sure that the Porsche head is exhaust limited as I once thought.

Win Rice

Thanks Geoffrey, good information as always!