Head flow testing.

This quote comes from way back up the thread, posted in March.....

I am new and if there is advice on cam selection on here I did not find it yet, so here goes...the quote:

'I spent some time on the flowbench this evening playing with the Fullauto head that is going on my bike. I installed a .070 larger valve in the RH port and did a radius valve job which included tapering the seat up to the larger valve. I also relieved the area around the valve guide boss. I did not increase the area of the port as I did not want to hurt the velocity. This is about as large a valve that I could fit without re-angling the intake guide and it will limit the amount of overlap the cam can have- so no race cams. The main gain is from the improved seat geometry allowed by the larger valve and not because of the slight increase in valve area from the increase in valve size.'

The comment I am interested in applies to ...so no race cams... Well OK, but I want to build a race engine with a FullAuto head, plan is 750 Short Stroke, JS longer rods and flat lightweight pistons (bits I have). I want to develop the motor progressively (meaning I have a whole bike to build, not just an engine so a good engine is better than waiting forever for a full house one I probably could not use).

So am prepared to fit the head initially near stock and look for some flow work later, but cams and valves should be a purchase suitable for a flowed head at a later date. Bike will be for short circuit scratch races in the UK with the CRMC. Good midrange power makes sense but good revs and healthy top end are also desired!, assume box will be 5 speed.

So, what is meant by 'race cam' in this context? and what would be the hottest cam to 'sensibly' use in this combination? To me a minimum would be PW3 or Steve Maney or JS near equivalent? or am I missing the target entirely.

Like I said, if there is another thread I did not find....point and squirt....

SteveA said:

This quote comes from way back up the thread, posted in March.....

I am new and if there is advice on cam selection on here I did not find it yet, so here goes...the quote:

So, what is meant by 'race cam' in this context? and what would be the hottest cam to 'sensibly' use in this combination? To me a minimum would be PW3 or Steve Maney or JS near equivalent? or am I missing the target entirely.

Like I said, if there is another thread I did not find....point and squirt....

Click to expand...

Hi Steve,

I go pretty well with an "off the shelf" Fullauto head (meaning not additional porting or enlarged valves, etc), JS Motorsports' pistons and rods, and a PW3. I will be "increasing the flow" on this head a bit this winter and adding a hotter cam from Jim Schmidt, but that's more about me tinkering than any absolute need for more performance. Midrange is your friend. Good luck, and PM me if I can help.

Thanks Kenny,

We have direct emailed before so I know we are headed in a similar direction....except my build is still a plan with little resources

Wondered what the limitation was, great theoretical information on this thread backed up with practical testing, I am enjoying the read more than any text book.

Steve

I don't know that you will have any great advantage, if any, with a short stroke motor. Kenny uses a long stroke motor and as he says "midrange is your friend".

Fullauto said:

I don't know that you will have any great advantage, if any, with a short stroke motor. Kenny uses a long stroke motor and as he says "midrange is your friend".

Click to expand...

Might be true, but I have the crank and rods so that is what it will be. I have other reasons for choosing to go this way, which are more nostalgia than practicality. :roll:

Any comments on the cam though?

Steve

Steve,
With the OS intake valve in my head I have just enough valve to valve clearance to squeeze in a 2s cam. If one wanted to go with a larger cam you could install a smaller exhaust valve and seat. The stock exhaust valve is quite large in comparison to the intake size. I have had good results doing this on longstroke 750s but I have not tried this combo on a shortstroke.

The other alternative would be re-angling the valves. In many cases re-angling the valves ends up hurting the port velocity and kills the potential power.
There is enough extra metal in the Fullauto head that I think a pretty good port could be done with re-angled valves but as of yet I have not tried it. If you want to send me your head you could be the first. Jim

SteveA said:

Fullauto said:

I don't know that you will have any great advantage, if any, with a short stroke motor. Kenny uses a long stroke motor and as he says "midrange is your friend".

Click to expand...

Might be true, but I have the crank and rods so that is what it will be. I have other reasons for choosing to go this way, which are more nostalgia than practicality. :roll:

Any comments on the cam though?

Steve

Click to expand...

Nope. Ask Jim. He's the man. And fair enough on your reasoning.

comnoz said:

Steve,
With the OS intake valve in my head I have just enough valve to valve clearance to squeeze in a 2s cam. If one wanted to go with a larger cam you could install a smaller exhaust valve and seat. The stock exhaust valve is quite large in comparison to the intake size. I have had good results doing this on longstroke 750s but I have not tried this combo on a shortstroke.

The other alternative would be re-angling the valves. In many cases re-angling the valves ends up hurting the port velocity and kills the potential power.
There is enough extra metal in the Fullauto head that I think a pretty good port could be done with re-angled valves but as of yet I have not tried it. If you want to send me your head you could be the first. Jim

Click to expand...

Would there be any advantage in going to a smaller exhaust valve in say....a new head??

Fullauto said:

comnoz said:

Steve,
With the OS intake valve in my head I have just enough valve to valve clearance to squeeze in a 2s cam. If one wanted to go with a larger cam you could install a smaller exhaust valve and seat. The stock exhaust valve is quite large in comparison to the intake size. I have had good results doing this on longstroke 750s but I have not tried this combo on a shortstroke.

The other alternative would be re-angling the valves. In many cases re-angling the valves ends up hurting the port velocity and kills the potential power.
There is enough extra metal in the Fullauto head that I think a pretty good port could be done with re-angled valves but as of yet I have not tried it. If you want to send me your head you could be the first. Jim

Click to expand...

Would there be any advantage in going to a smaller exhaust valve in say....a new head??

Click to expand...

There is a power advantage to going up about 2mm on the intake and down 1.5mm on the exhaust as long as the seat angles are done to take advantage of it. Custom valves are then necessary. That is what I am currently running on my injected 880.

Just going to a smaller exhaust valve has made no difference that I have seen on longstroke 750s or 850s. Jim

Gday Jim, wondering if there is much if any to gain out of necking down (on a lathe) the inlet valve guides? Also would this weaken Colisbro guides? Thanks in advance!
Foxy

Foxy said:

Gday Jim, wondering if there is much if any to gain out of necking down (on a lathe) the inlet valve guides? Also would this weaken Colisbro guides? Thanks in advance!
Foxy

Click to expand...

With 850 guides I would say there is a gain in cutting them similar to 750 guides. I wouldn't go less than 7/16 diameter in the port. I wouldn't cut any cast iron guide but bronze alloys are pretty safe. Jim

I flow-tested a few more heads this evening.

I flowed this old race-bike head. It has been reworked about as far as a stock casting can go.



It is the dark blue line.
The green line near it is the Maney stage three head I tested some time back. It has turbulence that sets in at .350 lift and sounds like a jet aircraft above that lift. You can see the effect on the flow-graph.
The red line is a Fullauto head with a little cleanup work done around the guides and a radius valve grind.
The yellow line is a fresh stock Combat head. {#084}
The light blue head is a stock RH10 head that is going to get a race port-job.

This is a really interesting thread. It confirms some of my general observations about port size/shape vs type of usage.

I can't add anything on the technical side and don't fully understand the harmonic wave theory discussed here.
On the practical side, I have seen the results of various porting jobs, mostly on Vincents, but I think the same general principles apply to Nortons or any other 4 stroke OHV engine.
The ported out bikes I'm familiar with are all roadbikes and in each case the owners/mechanics/tuners seem to have reduced the actual power available for roadwork, and in one case rendered the bike somewhat useless for my type of riding.

I ride a lot with two fellows who run highly modified Vincents. Steve's bike has high lift cams, 9.5 to one comp. (stock Rapide is 6.8, Shadow 7.3 or in some cases 8 to one) oversized exhausts and ported out intakes, taken from stock 28 mm to about 34 mm. Fitted to this bike are a pair of flat slide 36 MM Mikunis. The owner also has Harley Screaming Eagle ignition on there.
Like most riders of Hotrodded bikes, he is sure this thing is faster than light. .
The other bike is even more highly modified, similar oversized ports and exhaust, shortrodded, and on and on.
It is at 10.5 to one compression. Both bikes have the quaife 5 speed conversion. The shrotrodded bike has had many steel parts replaced with various alloys incuding titanium. The both run Supertrapp exhausts and make a lot of noise. They need premium fuel, my Rapide does great on regular. They get really upset when we are out on the road in some isolated area where only regular is available. On fellow now carries a littl bottle of octane boost, a good idea if needed I suppose and better than a holed piston .

My Rapide is at about stock Black Shadow tuning, stock cams , porting, 28MM Amal carbs, 8 to one pistons. In the 70s someone added state of the art Norton Commando twin point twin coil igniiton to it. This works just fine. It has had no alterations to reduce weight. It has the four speed transmission which it left the factory with in 1947, stock small exhaust, but a fairly open muffler.

The two owners of the hotrodded bikes like to give me a hard time about my stocker, at least they did for awhile . They would often tell me I needed to spend some money on the bike to make some horsepower with it.

Heading home from a Rally in California two years ago we came upon a 6 mile long mountain grade in Idaho called White Bird Hill. We fueled up at a station near the bottom of this hill. There was a large motorhome there and the owner was unhooking the tow car as he said this hill was about the only one he had ever encountered that was too much for the rig with the car in tow. His wife would drive the car up to the top and then rehook.


I mentioned to Steve that now my bike was nicely broken in I would use this hill as a test to see how it pulled compared to his hotrodded bike. Throwing down the gauntlet or what!

When we took off, Steve immediately pulled out and passed, at full bore, the fellow who was leading our group. I took off after him. We were both loaded two up with luggage, but my wife and I probably outweigh them by 40 lbs or so. Third gear was needed, the hill was too steep for fourth. In third a Vincent with stock gearing is good for 110 MPH, so no worries there, we weren't going to hit that speed on that hill with the load. We did pull up and pass the hotrodded bike quite easily and stretched the lead to about a 1/2 mile by the top of the hill. Speed showing on the clock was a steady 90 MPH, not bad for a heavily laden old bike on an 8% grade.

The other modified bike was way back somewhere. The owner of that bike believes in gently pulling up steep hills in top gear. apparently due to the Modification the engine "goes fluffy" if dropped down into 4th at road speed and 3rd is too low on the qauife, too many RPMS for that long run.

Steve claimed he could have caught us had he shifted his quaife down to third, but knowing the competitive ex racer he is, if he had more power available he woud have used it. In any case, a year later out on a ride near Conconully Wa, we got into it again, this time both riding solo, no luggage on board. It was top end that was needed this time. Again there was a large group of riders heading back and it started getting to be real fun as the speeds picked up, then Steve decided to pass the group leader and I gave chase. On a 3 mile straight we found out that my stock bike has about ten mph more top end than his ported/hopped up machine. At home I also have one of these ported out wonders with high compression etc, etc. It has the common Vincent high performance mod of two front heads, the front heads allowing for more port enlargening than the rear.It runs OK but isn't as quick on the road as my 8 to one stock port bike which runs on regular gas.
No wonder there are now fellows in England attempting to fill their Vincent intake ports back in to get the stock performance back.

Glen

That sure goes along with what I have found. "Porting" does have a lot of potential to make more power on a Norton head if it is done correctly. The port needs to be reshaped to increase the speed of the airflow. If the ports size {ie, the cross-section] is increased to make it capable of flowing more air -the power will go down due to the decrease in velocity.

If you look at the flow comparison between the rh10 with it's 30mm port and the Combat head with it's 32 mm port you will see they flow nearly the same. The dyno will always show the RH10 head makes more power than the Combat head [or the rh4] at any RPM if the compression ratio is kept the same. This is due to the higher velocity maintained in the smaller port. This applies to longstroke motors.

The D- shaped port in the old race head has a very small cross section, it is only 24mm high and 38 mm wide. It flows similar to the stage 3 head with it's 38 mm round port but with only 60% of the area the velocity is much higher. To maintain airflow at this velocity the port shape has to be just right. It made very good power. Jim

"To maintain airflow at this velocity the port shape has to be just right. It made very good power. Jim"

I have a 650Ss that Herb Becker did some work on before I owned it. In fact, he made the clutch start to slip when the bike hits 4k rpm, just by modifying the ports. He had the head off to fix a valve guide and decided to change the intake port shape to "the way we do them on the race Commando engines, not so much larger as just a different shape" I guess Herb felt he could do whatever he wanted to the bike, it was he who bought it out of a junk yard and donated it to the Ontario Vintage Motorcycle club as a club resto project to be raffled off to generate club funds. The owner/winner of the restored bike paid $10 for it (ticket price) and had no connection to motorcycles, so Herb went ahead on his own and played with the ports while doing the guide fix.

That is one porting job that seems to have worked out, however the port size at the intake end is unalterred.

Glen

worntorn said:

"To maintain airflow at this velocity the port shape has to be just right. It made very good power. Jim"

I have a 650Ss that Herb Becker did some work on before I owned it. In fact, he made the clutch start to slip when the bike hits 4k rpm, just by modifying the ports. He had the head off to fix a valve guide and decided to change the intake port shape to "the way we do them on the race Commando engines, not so much larger as just a different shape" I guess Herb felt he could do whatever he wanted to the bike, it was he who bought it out of a junk yard and donated it to the Ontario Vintage Motorcycle club as a club resto project to be raffled off to generate club funds. The owner/winner of the restored bike paid $10 for it (ticket price) and had no connection to motorcycles, so Herb went ahead on his own and played with the ports while doing the guide fix.

That is one porting job that seems to have worked out, however the port size at the intake end is unalterred.

Glen

Click to expand...

Mr. Becker undoubtedly knows what he is doing. He has learned it the hard way.

I finished a street performance port job on a 28mm- 750 head today. Here is a graph of the tests.

The blue line is before any work was done. It had stock valves and worn seats. The original guides would only allow .450 lift so that is where the line stops.

The green line is the after picture. All the work was done from just before the guide to the valve. The 28mm section of the port was left untouched. Black diamond valves were installed on three angle seats.

The red line is the fresh 32mm combat head I tested yesterday just for a comparison.

And here is the looser test for the day. It is a freshly rebuilt stock RH4 head with Black Diamond valves and a three angle seat.

It is shown as the green line. It became very noisy starting at about .250 lift and by .400 lift it was ear-splitting.

I re-ran the test with a stock Norton valve thinking maybe it would affect the severe turbulence. It is shown as the blue line slightly below the green line.

The yellow line is the stock Combat head I flowed yesterday.

Facinating.

Two pieces of History, two head, one mine, one belonging to a racer in the '70s called Tony Smith, who (was?) an Oxfordshire farmer and rode for Thruxton Motorcycles, and later the Cosworth Challenge for Norton.

My head was a 750 Short Stroke from the Thruxton race shop, ported by John Baker of the Baker Rawlins drag race team. The head was originally destined for a monocoque, because it had side finning machined away and the port threading removed and it can eto me with short stubs fitted in palce with 3 allen screws. We welded the exhaust downpipes onto these and ran separate pipes with short reverse megas. It was an 850, so a long stroke MkIII crank and cases, but 77mm Omega Pistons that had been machined from the blank with the small gudgeon pin hole (piston or wrist pin!). The valves were 're-angled' in the head form blank and were of course oversize. The ports had been opened to 34mm, and I ran it with 36mm Mk1 Amals, 34mm Mk2 Amals and finally bored the 34s to 36mm, which ran best,and slightly better again when I set the inlet trumpet to valve head distance to 10.25"/10.5" (no more but please forgive my memory?) as advised to me by Peter Williams in '78.

The bike made huge midrange and a load of top end?, possibly helped by the ex Thruxton cam, which however I assume is very close to the modern PW3 item, it was just stamped TX. I ran a 4 Speed, and like Kenny Cummings says, Mid Range is you friend, it helped me out a lot. The bike was never on a dyno, but the late Bob Smith used to offer me cash for the motor on a regular basis, this is a guy who won 50 races in one year at Cadwell Park alone on his Dunstall Norton Lowboy. (When he ran underneath me exiting Charlies on to the straight, I would just use the mid range to get me going and then motor by until it was braking time, then he was gone!)

(Baker is the same guy mentioned in passing on the 8 valve thread, actually I never met him as I got the head from a guy called Dave Sadler who was running the ex drag bike motor in his road race bike and had just been made redundant from Norton, so sold his next project to me!)

I always found the port size counter intuitive, venturis and gas speed and all that. I always wondered if the occasional 'misfire', that could never be traced to ignition, had anything to do with flow disruption in those big ports! I think it was Dave Rawlins who told me that every motor Baker built had an occasional misfire :? I guess it was just drag racer style more than road race. There is a slim possibility that this head still exists, but I have not seen it since '80.

Tony Smith won a lot of races I was in too, and I would have said his bike was faster than mine, but really not a lot, like Bob, he was a hell of a rider. And his workshop was an Aladins cave, with numerous cranks that had been tried, lighweight flywheels, 180 cranks, you name it they tried it, they being Thruxton MCs and I guess Norman White had a hand in that.

Anyway, Tony sold me an ex works Rita ignition and when I was there he showed me an 850 head, possible also a short stroke but with standard exhaust threading, in '76 I think. Sure enough 30mm ports retained, as he said to keep gas velocity up, but inlet manifolds made a real venturi, going out to 36mm to mate with 36mm Amal Mk2s fitted with the widest trumpets, they had to be cutaway on the inside to fit together, trumpets were pretty short though and I reckon the inlet length was under 11". I always assumed that it was the quickest Norton in the UK at the time, post works team and with Thruxton heritage, certainly it was the only one that I 'knew' was faster than mine.

Just a pity that both my bike and so many riders were faster than me...Oh Well!

Steve

Great stuff, Steve. This really is a wonderful website.