Whats the best exhaust valve back cut angle?

[TxGSrider]

I'm working on an 1150 head, and while its getting a valve job I was wondering if I should get the stock exhaust valves back cut and what is the best angle to have them cut? Also, would there be any benefit to back cutting the intakes? I'm using stainless APE intake valves and they seem to have a pretty flat back side already. I'm going to be running G-4 cams (.355 lift).

[Steve]

Your best bet is to contact user "rapidray". He does that kind of work all day long, every day.

.

[sharpy]

Best valve job is one from a real motorcycle expert. If u have it at some car "cylinder head specialist" run down there now and get it back

[TxGSrider]

This muzzbe one of those closely held GS porting secrets that people take to the grave with them? LOL!

[rapidray]

I do the back cuts at 30 degrees on STOCK valves.
Ray.

[rapidray]

If you are using stainless, aftermarket, valves you don't have to do anything to them.
Ray.

[jfn2]

I cut my exhaust valves to 30 deg on the backcut. GS 1168. Valves came from Manley, one mm over on both intake and ex. Also had them nitrited and did some reforming of the faces. Port job with unshrouding around the valve seats. G3 cams.

[TxGSrider]

Thank you gentlemen (especially Ray). I thought I had found somewhere where a different angle like 37 degrees or something was being used, but I couldn't find the thread again. As always, this forum is a real wealth of information.

[Chuck78]

I believe I recall 37 degrees being the preferred 8 valve (2 per cylinder) angle for back cutting

[headsbikesmopars]

I use 36-37 degrees for Suzuki's I have tried 36 but 37 works better for me and my customers. While Kawasaki's seem to respond better at 35 degrees. I have found that hemi chambers 'like' 35-37 and wedge heads (auto) like 30 degrees. That is what my flow bench says anyway. I remember John Pearson telling me he likes 37 on Suzuki's also. I know backcutting does help low lift flow it uncovers more valve area sooner in the lift cycle. You can have the same flow @ .100 that you had @.150, same @ .150 as you had @ .200 and so on until around .350 or so at this point the valve is far enough off the seat to not affect the flow. I also believe it does benefit the exhaust side as well for same reasons. Back to back testing on flow bench shows this . Getting the 'moving' column of air moving sooner in the lift cycle helps produce torque sooner in the rpm scale (low end). JMHO.

Terry