Wondering if anyone sells back-cut or undercut stock diameter replacement valves.

I tried searching the site first and found the ULTRIK PERFORMANCE OVERSIZD VALVE SET sold by Mini Mania but if I use those I need to install larger valve seats. Possibly I shouldn’t be but I am reluctant to get new valve seats installed.

Does anyone know if stock diameter replacement valves with either of these features exist? I think it would still offer a major improvement in the stock diameter.

 

The ULTIRK valve set does NOT require the installation of new seats. The stock seats can be cut to accept these larger valves.

 

Are there other companies making upgraded valves without having to do new seats?

 

Quote:

Originally Posted by Don Racine

The ULTIRK valve set does NOT require the installation of new seats. The stock seats can be cut to accept these larger valves.

Thanks Don. Could you help me understand this a little better? If the stock seat can be re-cut does that mean the root diameter is still stock size and the seating surface is all that needs to be reworked to accept the larger valve? If the seating surface is re-cut for a larger valve is the valve now at a different height requiring a spring shim and resulting in different rocker contact due to a taller installed height?

I am living in an area where I do not know the local machine shops like I did at home and so I was thinking if I had a set of stock diameter valves I could get away with hand lapping the valves on the original seats without re-cutting. But to be honest although I have worked on heads before I normally let an experienced machine shop fit the valves and so I am not certain what I was proposing would work. If it were possible I would strongly consider a stock diameter valve with the back-cut that the Ultirk valve had because I can see from the photos on your site that there should be a big positive improvement as the stock valves seem rather "fat".

As I believe Clint was getting at...are there any other alternatives?

Thanks again.

 

Root diameter of these new valves are indeed larger and thus in fact will result in higher valve spring pressure unless you cut the valve seats. Cutting the seats will actually return the resulting spring pressure back to close to stock. Shims are the opposite of what is needed.
Increased valve size is one of the steps often used to increase air flow into the head and thus can often lead to increased ultimate HP. One of the critical steps to be able to make use of these larger valves is in fact to port (increase) the size immediately behind the valve seat. If this is not done, the gains will be small. Your consideration of using an experienced machine shop is the best option.
'Other Alternatives'? - If you engine has had many miles of fun use, it is sure to benefit from simply lapping the valves, but bear in mind that the most you can expect from this is a return of a few HP that you have probably lost over the years and no gain over stock.
Bear in mind that the process to 'back-cut' a valve is not even as simply as putting them in a lath to turn down (cut) the back side of the valve. Even the cheapest of the valves are actually very hard and and almost impossible to cut; rather they have to ground back.
Please give me a call at 800 946 2642 if I can help.

 

Don,
Thanks. I was thinking that to fit the larger diameter into the existing seat possibly the seats were being cut deeper resulting in the entire valve sitting deeper. I understand by your response this is not the case.

I believe I may have used the term root diameter incorrectly. I was referring to the seat not the valve; specifically the cylindrical portion of the seat past where the valve rests against the seat conical area. Because the factory seat has only so much thickness I was wondering if your suggestion to use the factory seat meant leaving the cylindrical portion of the seat the same inside diameter as not to take away too much of the seat thickness. If that diameter remains the same I am not convinced a bigger valve will mean much improvement. I can see the need to remove material from the casting past the seat and I will certainly do this. I was asking if your suggestion leaves the non contact portion of the seat the same diameter though.

My perception looking at these heads is that there is not much room between the stock valve diameter and the wall of the combustion chamber. It seems like a lot of the benefit of the Ultrik design must be the back-cut /undercut. I do realize the valves are hardened and so they would need to be ground; back-cut and undercut were terms I was using to describe the shape. I would not change the OEM valve by grinding because I don’t know the strength of the original production valves and I do not want to risk breaking a valve during use.

I will phone to try to catch you live.

Thanks again,
Scott

 

Thumper may be able to help:
http://thumperoforangepark.com/