Fullauto head vs combat head vs standard head

If you apply any type of epoxy more than a couple of mm thick, then failure is certainly possible due to different rates of expansion/contraction of the alloy head and the epoxy. Its also crucially important to key the port surface properly first, and a scuff over with P40 grit sand paper is simply not good enough.

I would advise against using any type of epoxy filler. Any thickness will eventually flake off, no matter how good the preparation. We used devcon on many types of aircraft, for several purposes, and all failed regularly. Manufactures called out for the stuff, but it never worked as it should. I have some abladable liner material I got when I worked at cessna. It was used to surround the fan blades on the engines. It's a 2 part putty epoxy, light blue when mixed. I wonder how well that would work on reshaping inlets. It's light, strong, won't hurt if it comes loose. I have a gallon of it in the basment, an experiment might be in order.

Jim,
I know this is just plain greedy on my part. Is there any chance at seeing numbers on an RH10 head?

Carbonfibre said:

If you apply any type of epoxy more than a couple of mm thick, then failure is certainly possible due to different rates of expansion/contraction of the alloy head and the epoxy. Its also crucially important to key the port surface properly first, and a scuff over with P40 grit sand paper is simply not good enough.

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Yep, key it. In the early '80's I built a Yamaha SR500 head per a Gordon Jennings/Cycle magazine hop up article. To raise the floor to fix the short turn, he used JB Weld but first drilled and tapped a mess of holes for machine screws to come up from the bottom side of the head/port. I followed the article, using aluminum machine screws. Where I could get an angle, I also used a sharp punch to lift barbs from the port floor. Although it has not run in years, that head is still on the bike. It has I don't know how much time/miles and the last time I had to change out a cylinder (being an excessive overbore it cracks cylinders parallel to the deck) I checked and 95% of the JB Weld was still there, the feathered edges - leading and trailing had lifted and the engine had swallowed those chips but the main portion is still solid.

That said, it's not something I'd recommend. OK if your eyes are open to the risk.

Yeah, I had installed screws in the bottom of my racebike intake and like yours the thick part of the TI epoxy putty was still there. The edges where the material was thin had broken away. The thickest part that was missing was about 1/8 inch thick. It just got caught in the wrong place at the wrong time. It had been in the port for 3 weekends of racing and practice over about 6 months.
I had JB weld in my streetbike for a couple years over studs and when I took it out it was full of cracks and the edges were gone but they had obviously passed without harm. Jim

rvich said:

Jim,
I know this is just plain greedy on my part. Is there any chance at seeing numbers on an RH10 head?

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I don't have an RH10 head in condition to test right now but I have tested them before. They flow just like the standard 750 head up to around .300 lift and then drop off a couple cfm due to the big guide.

The RH4 head flows just like the combat head with drop above .300 lift because of the big guide.

As I have time I would like to do some more tests with velocity numbers included. I [and many others] have found that keeping the port velocity high is more important than the actual flow numbers. Jim

ludwig said:

interesting article(s) :
http://www.mototuneusa.com/homework.htm

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Yes, I have followed his work for years and came up with similar results. Jim

Yes that fella's use of JBWeld in heads gave me the courage to fill in head surface the significant hot jet cuts leading from chambers to the push rod tunnels on the most kick ass head tested on Peel. It held up clamped in place for many on and offs but noticed it losing some integrity last I looked. Can he really get away with intake JBW on air cooled heads?

There is not only too big but also too small. When super sonic speeds reached the mach one, shock-pressure waves jam up in the smallest section and interfere with much further flow even if more vacuum pulling or more pressure pushing is added.
IIRC to shot for ~.70-80 mach speed number.

Alas flow in not constant and head not bare when installed so flow bench can mislead. Some benches chop the flow to help compensate. Wish I knew more.

Rather more important than numbers from a flow bench or dyno, are how well a bike actually works on the road or track. I know someone with a GSXR race bike who a few years back managed to obtain 195bhp at the rear wheel, but found the bike extremely difficult to ride. Alterations were made to the motor, which resulted in less power, but a much easier bike to ride, which resulted in faster lap times.

In general most quoting flow bench numbers will not be the people who are winning races, as these types tend to keep information on what works and what doesnt very much to themselves. On poorly designed old hemi style heads as used on the old Brit bikes there is a great deal of room for improvement, but seems to be little understanding of the relationship between port and valve sizes, and that in many cases smaller ports will mean improved performance.