Head flow testing.

lcrken said:

The RH7 head starts with the same casting as the standard 850, but has the intake guide at a steeper angle (26.5 instead of 28 degrees off vertical) and has a fully sphered combustion chamber with no squish band. ...

Ken

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The fully sphered RH7 combustion chamber could use fully domed piston as below.

Comnoz, thanks for pointing out that patent.

The more I read about the MC4S engine of the subject patent the more impressed I am with it. Appears Ole Dan has brought together all of the best in this design. Large bore, generous squish area, short stroke, Nikasil coated Al cylinders, cylinders offset to crank centerline to improve rod geometry thereby reducing piston thrust, high angle tapered port design, very generous guide support with a proper caliber guide fit, counter rotating crankshafts to reduce vibration and the list goes on. They even call out the multi-layered steel head gaskets offered by Cometic (the ones we need in our Nortons as the Al head squirms while the cast iron cylinder is better behaved). And the ultimate proof might be in the performance quoted. The patent cites one preferred bore/stroke embodiment of 5”and 2.8” respectively, that as Kvinnhering points out has a displacement of 1800 cc. If this engine size is employed in all the examples, they suggest 189 HP without the novel porting system when mean piston speed is under 4200 ft/min, with the novel porting system 262 HP with mean piston speed of 4200 ft/min, and 309 HP with the novel porting system and a mean piston speed of greater than 4200 ft/min. Holy shit, that is 2.8 HP/cu in from a relatively low compression engine capable of running pump gas! A very nice package. Now, back to our favorite dinosaurs.

Fast Eddies RH10 head before and after a street port job with 3mm oversized intake valves.

comnoz said:

Fast Eddies RH10 head before and after a street port job with 3mm oversized intake valves.

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Thanks Jim!

I'll have to change my name to 'Even Faster Eddie' ...!

That's lookin' really good for you bike "Even Faster Eddie" :mrgreen:

comnoz said:

Fast Eddies RH10 head before and after a street port job with 3mm oversized intake valves.

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Congratulations Fast Eddie! Will be interesting to get feedback how this works.

Jim, can you show us the graph of air velocity as well. It had been very interesting!

Here are the velocity numbers

Thanks again Jim.

So, in summary, we have more gas entering the combustion chamber... and its travelling faster...!

For the benefit of the viewers, can you explain what has been done to achieve this?

It will certainly be very interesting to see the dyno results and correlate this with the known increases in flow and velocity.

Can't wait to get it nailed back together !!

I have long wondered what a flow bench really demonstrates. If the gas in the inlet port is in the form of a standing wave, aren't we looking at sonic effects and mass transfer of inlet charge, rather than gas flow characteristics ? If you have a look at the fuselage shapes of jet fighter aircraft, the best shape for sonic speeds is not what you would expect. With a commando engine, surely the mechanical limitations prescribe efforts should be directed at improving mid-range torque rather than top end power ? The best 350cc single cylinder fourstroke racer was the Ala D Oro Aermacchi which has tapered inlet ports. The Linto 500 was almost a competitive GP bike.

acotrel said:

I have long wondered what a flow bench really demonstrates. If the gas in the inlet port is in the form of a standing wave, aren't we looking at sonic effects and mass transfer of inlet charge, rather than gas flow characteristics ? If you have a look at the fuselage shapes of jet fighter aircraft, the best shape for sonic speeds is not what you would expect. With a commando engine, surely the mechanical limitations prescribe efforts should be directed at improving mid-range torque rather than top end power ? The best 350cc single cylinder fourstroke racer was the Ala D Oro Aermacchi which has tapered inlet ports. The Linto 500 was almost a competitive GP bike.

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As has been stated, we shall see what we shall see on the dyno.

Jim has put a tremendous amount of info on the entire topic of head porting on here. Please do not upset the collective learning by throwing abstract comments about.

And please do not turn this into a thread about how all Commando's should have 6 speed close ratio gearboxes, low CR, never rev above 7,000 and be fitted with E3134 cams ...

Fast Eddie said:

Thanks again Jim.

So, in summary, we have more gas entering the combustion chamber... and its travelling faster...!

For the benefit of the viewers, can you explain what has been done to achieve this?

It will certainly be very interesting to see the dyno results and correlate this with the known increases in flow and velocity.

Can't wait to get it nailed back together !!

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The main thing done was just increasing the area of the valve opening by using a larger valve. The valve open area is the circumference of the valve times the lift of the valve.

The port size was not changed from it's 30mm diameter. The bowl and guide area was reshaped to help get the air to the seat without causing separation.

Installing a larger valve is just like installing a higher lift cam without increasing the duration of the cam.

Increasing the lift of a cam without increasing the duration is difficult to do when using a pushrod valve train without causing problems with valve bounce and/or broken parts.. Jim

PS, the numbers generated by a flowbench have nothing to do with the airflow on an actual engine. They are simply used to help design a port that will flow at an increased velocity.

Many people use flow numbers to compare one cylinder head with another cylinder head. Actually the flow numbers do not usually equate to the horsepower developed. Moving air into a cylinder and then keeping it there until the valve has closed is what we want to do.
Making a port that is the correct shape to support air at a high velocity so the pressure wave in the port that is created after the piston reaches BDC is strong enough to keep the charge in the cylinder until the valve closes -and maybe even push a little extra air into the cylinder between BDC and valve closing is what we want. Jim

Eddie - flow benches and dynos are not the same as riding the bike. To me a horsepower figure is only about bragging rights, where is the correlation between that and on-circuit performance ? When I was racing regularly, two stroke bikes were very difficult to beat. These days in Australian historic racing the four stroke bikes are faster. The power characteristics and handling of the two types of bike are vastly different.

Eddie would you possibly please post a side-on photo of your bike without fairing and details of the type of gearbox you are using, and also about the types of circuit on which you mainly race ? When I'm reading about your motor, I feel I'm only getting half the story. I look at those dyno curves and I realise that an increase in horsepower probably represents an improvement, however I can't put together what it means on-circuit.

Eddie
this reply has nothing to do with gearboxes, but all to do with flow potential through a port!

Jim's flow tests indicate that there is promise of a performance improvement for your engine with the valving and porting modifications he has carried out.

Another view of this is to examine the situation when the valve is lifted by 25% of the inner seat dianeter, which by and large can be considered to give a curtain area equivalent to that of the inner seat diameter, (referred hereafter as LD).

For the standard valve in conjunction with the PW3 cam, the duration through which the valve is lifted to the LD value is equivalent to the flow aperture being at optimum area for 31.25% of total duration.

Changing to a 3 mm larger valve, flow at the LD value is significantly reduced to only 15.45% of total duration.

Losses on swings outweighs gains on the roundabout (or vice-versa!).

As a matter of interest to some, of all the Commando cams I have data for, most have a LD flow potential with the 38 mm intake valve, of 30% or better, except one - the Norris RX which lags slightly at 29%.

To really maximise on the larger valve, a different cam would be required with increased duration above the LD value, but as Jim has stated, with the pushrod engine this becomes increasingly difficult to manage as a number of things begin to stack up against it. As it is, the increase in curtain area is sufficient to provide an increase in the flow potential, so the overall result is still coming out on the right side.

All will inevitably depend on how well you configure the rest of your engine to get what you want. If you are at Donnington for the Easter meeting, I will look forward to seeing you there, meantime let us all know via this forum the results of your testing.

Snotzo,

As is so often the case, thank you for allowing us to see what we always see but think what some of us (me) have never thought. With respect to your comments about the fifth lift point (valve lift = 25% of the valve seat ID which you referred to as the “LD value”), you mention that for all the CDO cams you have data for, all but one provide LD flow potential of ~ 30%, does this include the stock CDO cam. I ask because just eyeballing the lift curve of a stock cam makes this observer think the LD flow potential would be far below 30%. In arriving at this conclusion I was thinking the valve seat ID might be ~ 1.40” and the LD lift point would therefore be 0.350” (1.40 * 0.25 = 0.350”) as I looked over the lift curve. Are these values reasonable datums for examining stock and other lift curves?

One final question on your following statement.

Losses on swings outweighs gains on the roundabout (or vice-versa!)

I realize the foregoing was directed to Eddie, thus a Commonwealth to Commonwealth communication. However, this dumb Yank is in need of a translation, so perhaps you might try it one more time for my edification. I know that swinging can result in large losses, e.g., a relationship, wife, children, etc, and roundabouts are a sort of new traffic control device over here that are being installed with some regularity this century, whereas I suspect you’ve been employing roundabouts since medieval times. Anyway, if you might be so generous as to restate the above passage I would appreciate it.

PS – all Yanks are not as stupid as me so don’t assume that my inability to understand the above quote exists throughout the general population.

(also it's swings and roundabouts) UK saying› said to ​mean that the ​positive and ​negative ​results of a ​situation or ​action ​balance each other: "The ​route through ​town would be ​shorter, but there'll be more ​traffic." "Well, it's just ​swings and ​roundabouts."
(Definition of what you lose on the swings you gain on the roundabouts from the Cambridge Advanced Learner’s Dictionary & Thesaurus © Cambridge University Press)

comnoz said:

(also it's swings and roundabouts) UK saying› said to ​mean that the ​positive and ​negative ​results of a ​situation or ​action ​balance each other: "The ​route through ​town would be ​shorter, but there'll be more ​traffic." "Well, it's just ​swings and ​roundabouts."
(Definition of what you lose on the swings you gain on the roundabouts from the Cambridge Advanced Learner’s Dictionary & Thesaurus © Cambridge University Press)

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See, I told you all Yanks were not as stupid as me!

Jim

sorry you had trouble with 'swings and roundabouts', I thought it was a universal saying, but obviously not. Perhaps I could have put it better as 'you gain some, you lose some, and as often as not you find that the gains balance out the losses'.

I didn't include the stock CDO cam because I have never had an opportunity to measure one, but if you have an S96 file for one that you can send over, I'll do the necessary and report back

Snotzo said:

Jim

sorry you had trouble with 'swings and roundabouts', I thought it was a universal saying, but obviously not. Perhaps I could have put it better as 'you gain some, you lose some, and as often as not you find that the gains balance out the losses'.

I didn't include the stock CDO cam because I have never had an opportunity to measure one, but if you have an S96 file for one that you can send over, I'll do the necessary and report back

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Oh, I didn't have trouble with swings and roundabouts. I always equated it to "no free lunch"

I do have a file but it's in my PC with the dead motherboard. I will have to spend some time recovering them. Jim

Perhaps our trans continental friends understand the term "6 of one half a dozen" of the other" ?? Used more widely in the UK prior to joining Europe and "metrification" :?