RH4 or RH10 ?

Mark said:

RH4 head owner here!

Other than comnoz's exhaust thread repair a few years ago , 67,000 miles - No Problems.
If it ain't broke............

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Actually the RH4 heads do not crack when in use. The majority of the cracked heads were cracked when the guides were installed at the factory. Sometimes the cracks did not show up until they had slowly grown enough to go all the way into the valve spring seat.

I have also seen some that were cracked when someone replaced the guides with oversized guides without reaming and honing the guide hole first. The intake valve guide fit is very critical on a RH4 head because the metal is very thin there. Jim

'Port/carb sizing is interesting, `70s Ducati sports bikes went from 30mm Amals to 40mm Dellortos, -inlet was still necked down, supposedly for venturi effect - but then they had to put accelerator pumps on `em to get tractabilty..'

I use 34mm carbs on my 850, however the ports are tapered back down to standard after about 15mm. The same type of port is used on Aermacchi 350 singles. I'm using methanol, but I seriously doubt that a 750 commando would be quicker than it even on alcohol. I've found the motor to be extremely torquey, and gearing the bike sensibly is difficult with a 4 speed CR box. I've had t o cook the clutch to get the bike off the line in our clutch start races because the overall gearing has to be so high to cope with the straightaways, and with the close box the acceleration is still extreme, making it difficult to avoid over-revving. I suggest it is very deceptive to get the best gearing when the motor makes a lot of torque. It is difficult to know when to increase the overall gearing. The only indication you have is that when you increase the gearing, the bike goes quicker. But the high first gear keeps you away from that. I'm using a two into one exhaust with silly cam timing, and the motor pulls like a train. When I'm racing a bike , I always feel there should be some lag after each gear change, allowing the revs to build up, with my 850 there is not very much. I'm used to riding a bike with very little torque at low revs, and dropping the gearing to get it to go, because the motor has all top end power, but my Norton 850 is radically different. I would never go in the direction of getting it to make more top end power, by using big overlap cams, and big ports etc. The strength of that ugly motor lies in its pulling power, not in high revs, top end/ small usable rev range stuff.

J.A.W. The 'venturi effect' you mention is about keeping gas speeds high. You can go two ways to improve cylinder filling - increase the gas speed, or increase the crossectional area of the port to get the same mass flow. There have been many examples of guys with the 'big is better' mentality, who have over-ported four stroke motors and made them go slower overall on race tracks with both tight and fast bits. It is possible to tune a bike to a standstill.

comnoz said:

Actually the RH4 heads do not crack when in use. There's the Problem! If guys spent more time riding their bikes than "improving" them.......
The majority of the cracked heads were cracked when the guides were installed at the factory. That doesn't surprise me at all, some bloke pounding them in with a big ol' hammer. Sometimes the cracks did not show up until they had slowly grown enough to go all the way into the valve spring seat.

I have also seen some that were cracked when someone replaced the guides with oversized guides without reaming and honing the guide hole first. Again, hack work. if careful attention was paid to the task.....The intake valve guide fit is very critical on a RH4 head because the metal is very thin there. Jim

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I find the flow stuff interesting. especially that the RH10 has 30mm. intake ports.
The experience here on head design way surpasses mine, so I defer all technical stuff to the experts.

I just wanted to chime in and say that my heads works fine. If it came down to spending the money and then waiting for a Fullauto head to arrive OR bolting on a stock RH4 head and Riding my Bike, I would choose the latter any day of the week.

Mike996, Mopar Hemi aftermarket heads made by Stage V, to uprate the wedge block, utilize the D-port design.
CHI here in Australia do heads for the Hemi 6 Mopar, & Ford Boss/Cleveland in aluminium, they also offer an exhaust port tongue insert to improve the port velocity/flow characteristics,
I wonder if the FullAuto Norton head would benefit from this too.

J.A.W. said:

Mike996, Mopar Hemi aftermarket heads made by Stage V, to uprate the wedge block, utilize the D-port design.
CHI here in Australia do heads for the Hemi 6 Mopar, & Ford Boss/Cleveland in aluminium, they also offer an exhaust port tongue insert to improve the port velocity/flow characteristics,
I wonder if the FullAuto Norton head would benefit from this too.

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If you are talking about a tongue to stick out into the pipe and blend into the floor I have experimented with that and found no more power but an increase in megaphonitis. The floor of the exhaust port being higher than the floor of the pipe seems to help with reversion out of the carb.
Jim

Thanks for the response, good stuff.

'If you are talking about a tongue to stick out into the pipe and blend into the floor I have experimented with that and found no more power but an increase in megaphonitis. The floor of the exhaust port being higher than the floor of the pipe seems to help with reversion out of the carb.
Jim'

Are you talking about the blow-back of fuel you can sometimes see at the carb bellmouth, when you have the bike running and tweak the throttle ? I've never seen a bike with any sort of competition cam which did not do that. Do you get 'reversion' with an extractive two into one pipe ? I've never looked for it, perhaps performance is a better measure of what is right ? Does a Fullauto head give a measurable improvement in torque on the dyno ? I would have thought that the step in the exhaust port would tend to stop the resonation which the pipe is intended to promote ?
I never use megaphones these days because w hen I used to race my 500cc short stroke Triumph the megaphonitis would cause you to crash. When I first raced it with 4 inch megaphones, it turned me into the biggest dud of all time. I then used long tapered megaphones with a reverse cone, and it was just as bad. I fitted a two into one pipe with a big tail pipe - lost 1500 rpm off the top, and started getting decent lap times. After racing it for 12 years, I sold it t o a friend and he fitted straight pipes with silencers. I rode it and it seemed tame enough. But back in the fifties he had actually owned the bike then, and it had crashed him into the guard rail at Skyline Corner at Bathurst and broke his arm and leg. It is the bike I'm riding in my avatar.

About one second after this photo was taken, I was sliding up the bitumen on my back at high speed after the front bake brake locked - the bike was a combination of nastiness :

Presumably at race speed; what the hell were you looking at?

acotrel said:

About one second after this photo was taken, I was sliding up the bitumen on my back at high speed after the front bake brake locked ................

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comnoz said:

J.A.W. said:

Mike996, Mopar Hemi aftermarket heads made by Stage V, to uprate the wedge block, utilize the D-port design.
CHI here in Australia do heads for the Hemi 6 Mopar, & Ford Boss/Cleveland in aluminium, they also offer an exhaust port tongue insert to improve the port velocity/flow characteristics,
I wonder if the FullAuto Norton head would benefit from this too.

Click to expand...

If you are talking about a tongue to stick out into the pipe and blend into the floor I have experimented with that and found no more power but an increase in megaphonitis. The floor of the exhaust port being higher than the floor of the pipe seems to help with reversion out of the carb.
Jim

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For us laymen...does that mean that a sudden drop in pressure helps evacuate the chamber?

Probably looking at the tacho, but I don't know why. All I can remember is that I couldn't stop the thing, and had the brake hard on when it locked and pitched me off. It was a fun bike to ride, it gave a lot of anxiety. I don't know how I survived my first five race meetings. In all I fell off about eight times.
It was funny the other day when I was talking t o my mate about crashing the Triumph at Bathurst. The short stroke motor had all top end, and when the bike got up to speed, it would just go and go. It was pretty useless around the tight stuff unless you used very low gearing. As he flew down Conrod straight , it really got going, and he had big trouble stopping it at Murray's Corner, and started deciding whether he should take the fairly tight right hand bend into the escape road. JUst after that he hung it up on the armco at the top of the mountain. I rode it at Phillip Island and found that it performed that way. From Southern Loop up to Honda Corner , as it approached the end of the curve, it was extremely fast, and I blitzed a lot of guys who all seemed to be backing off. Some of these engine modifications are great in theory, but they can give you a really hard time when you combine them with bad brakes and tyres. I used to have dreams about going down the front straight at Phillip Island looking at the tacho and watching the revs drop instead of increasing ( it is slightly downhill). I can look back and laugh about it now, but at the time....

The volumetric efficiency factor wherein the breathing cycle is overlapping -induction through exhaust -is sometimes regarded as a 5th cycle event [in 4-stroke mills].
http://www.popularhotrodding.com/engine ... to_02.html

Hey Jim how does an RH10 that you've worked your magic on stack up against a new Fullauto out of the box?

The step in the floor of the port helps stop the blow back of fuel and the resulting double carburation [megaphonitis] .

Some pipes produce more blowback than others. Twin megaphones make the most blowback but they will produce the biggest horsepower boost and the narrowest powerband.

Maintaining high velocity both in the exhaust and intake will help considerably with megaphonitis.

The step in the floor does not seem to affect the power at high rpm because at high gas speed the flow is concentrated around the outside of the curve [the top side of the port]. Jim

The Fullauto out of the box will make more power than a conventionally ported RH10.

On Kenny's racebike we replaced a fully ported big valve conversion head from a well known tuner with an off the shelf Fullauto head and made similar peak power.
Then we did a big valve conversion on Kenny's head.