RH4 or RH10 ?

Status
Not open for further replies.
"With an identical stroke and valve train, mechanically, the 850 can rev as high as a 750. So where does this "lower rev range" come from?"

Per Norton, oem max HP RPM for the 850 is 5800; 750 is 6500. Clearly they tuned the 850 "down" in comparison to the 750, the idea being that the increased displacement would make up for it and enable better midrange and longer life. I'm sure it does both but per roadtests, the 850 was never as quick as the 750. In a race I believe all my current 850 would see of my old 750 is tailights... ;)
 
Hi what modifications could we do to a standart RH10, to make it better , or just let it alone..........??
Fit black diamond valves and Kibble white guides , then.........? Obviously I am not able to do a proper porting job !
 
marinatlas said:
Hi what modifications could we do to a standart RH10, to make it better , or just let it alone..........??
Fit black diamond valves and Kibble white guides , then.........? Obviously I am not able to do a proper porting job !
Click to expand...

Personally, having an 850 RH10, I would leave it alone. For performance increase, I would prefer to change the stock cam (and if neccesary matching valve springs) increase the cylinder bore to .040" oversize (which will increase compression ratio), lenghten the inlet manifolds and fit well tuned carburettors. The only modification in the head would be solid spacers on the rocker shafts and lighten the rocker arms, just a little.

Mick
 
Does the stock rh10 30mm with 30mm carbs make more peak hp than the stock rh4 32 mm with 32 mm carbs?
Seems like the 32 mm setup ought to give a little more at top at least, unless port shape is quite different between the two?

Compared with the stock 30 mm ports on my 650 ss, 32 mm for 828cc does not seem overly large, but of course this is not a simple subject.
sorry, I see the same question asked and answered above, missed it somehow! :oops:

Glen
 
When them hopped up 850's can pull low 12 sec 1/4 miles then you've arrived into Factory Combat zone, but not if Combat limited to 6500.

Am I right to think the list implies that the RH3 in same things as CHO stamped on Combats? Ie: shaved ~.040" with 32 mm openings and over big tubes with rather acute bends?
 
Didn`t the factory intend to sell a hi-po 850 variant to replace the Combat 750, but were constrained by emissions/durability issues, so they released that factory tuning supplement for 850 owners to do the hop-up themselves - & thereby avoid potential warranty dramas..?
 
worntorn said:
Does the stock rh10 30mm with 30mm carbs make more peak hp than the stock rh4 32 mm with 32 mm carbs?
Seems like the 32 mm setup ought to give a little more at top at least, unless port shape is quite different between the two?
Glen
Click to expand...

The stock 850 RH10 has 32mm carbs, the manifold reduces down to 30mm at the head and then a little less into the port. The idea was to increase low RPM gas velocity and improve the idle. The added benefit was superb torque low down. I don't know if the RH4 made more power, I suspect it would higher up the RPM scale but the trade off may be in a less flexible lower end.

Mick
 
This is what I saw on my dyno on a stock MK3 motor with a K&N and peashooters. Same 32mm Amal carbs but I went to the tapered manifolds with the RH10.

With nothing but a change from a RH4 to an RH10 I got the same peak horsepower.

The RH10 had more power from 3500 to 5500 and the bike felt noticeably stronger on the road.

The best way to get a little more from an RH10 is to widen the port a couple MM in the area from just upstream of the valve guide to the seat and then do a good 3 angle valve job with KW valves. That will increase the power from 4500 up. 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..
 
Great thread. Here's a link to the dyno run I did with my basically stock '74 850 with RH10. If anybody in SoCal has a Norton they'd like to dyno, shoot me a PM and we can set up a time. Shop is in the Orange County area. Would be nice to get a database of runs with various specs, although I suspect that Jim has a pretty good database of such things!

post178549.html?hilit=stock%20dyno#p178549
 
This little jem showed up today, been waiting since June for it (FullAuto).
RH4 or RH10 ?

RH4 or RH10 ?
 
Wow, very impressive...I see where the money goes now... I `d reckon 1 of the 3 wise men would`ve been proud to present that to the baby Jesus..
Is that D-type exhaust port fully finished?
Or is there a tongue fairing to slip up inside the header pipe at the mount?
 
I just looked it up and yes the wisest of the three was on a Norton. He brought the first FullAuto head and gave it to Joseph so that he could put the crown jewel on the motor he had built for the baby Jesus's first Commando. The 'D' shaped ports are the way it came and the only thing that came with it were seals for the guides. Maybe Jim can chime in explain the design. Here is a pic of the combustion chambers.
RH4 or RH10 ?
 
The ports are from molds made of my best running longstroke race 750. They came out slightly undersized just due to the sand casting technique. The race motor had 3mm over-sized intakes.
The intake ports are capable of sustaining flow close to 450 FPS. There is extra metal in the casting both for port work and thermal mass. Jim
 
The d exhaust ports look a lot like those on my Terry Prince big port squish heads for the Vincent. The latest Corvette LS engine also uses d exhaust ports. Ive read that Pontiac first came up with the design for use in it's "hot" 6 cylinder engine used in stock car racing, early fifties.


Glen
 
D port exh are very common on massaged cyl heads in the (US V8) auto world. You used to have to make them, now you can just buy them that way from all sorts of aftermarket suppliers like Edelebrock, etc. We used to D-port all the SB chevy heads as a standard thing on a performance eng rebuild. Some engines worked better with Ds; some didn't and some liked a more extreme "D" shape than others. It's not a universal thing - Mopars in general didn't gain anything with D ports and they are still not considered a worthwhile mod for Mopar motors.
 
How does that saying go....."A thing of beauty is a joy forever".....I think it applies here ;) ....that should wake up your bike a little doug, thanks for the foto's
 
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............
 
Status
Not open for further replies.

Similar threads

jseng1
The problem with RH4 heads
Replies
10
Views
1,616
jseng1
jseng1
maaseyracer
RH4 To Narley Port Conversion Tubes
2 3 4 5 6 7
Replies
125
Views
11,828
maaseyracer
maaseyracer
B
Head gasket question for Jim Schmidt or others
2
Replies
22
Views
1,386
jseng1
jseng1
Jonez69
Can worn isolastics increase engine wear or even damage?
Replies
12
Views
1,297
Jonez69
Jonez69
maaseyracer
RH4 to RH10 JS Intake Port Sleeves
2 3 4 5
Replies
90
Views
10,065
mark parker
M
Back
Top