Dyno runs before and after engine mods

acotrel said:

Nigel's 5 speed gearbox was probably a more significant change than all of his engine improvements. Commando engines have poor throttle response, but deliver massive torque. Most gearboxes have gear ratios which are evenly spaced and first and top are usually in the same place in road bikes. 5 gears mean you are less dependent on throttle response.

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Not sure how a 5 speed box effects dyno numbers…

Fast Eddie said:

14.7 is optimal yes… but that’s too lean for safety with most old air cooled lumps.

Anywhere between 12-13 is good as I understand it.

Below 12 is indeed too rich. So your Dyno man is right IMHO and you are too rich between 2,900 and 5,500… which is where you’ll spend a LOT of time!

But, many Dyno operators don’t understand old carbs, they don’t ‘feed the throttle’ they just whack it open to WOT and hold it there. That makes it difficult (ok, impossible) to estimate which carb circuits to change.

Best to mark the twistgrip at 0, 1/4, 1/2, 3/4, WOT and get him to hold the throttle steady, with the AF probe in place. That’ll give a much better indicator.

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Thats exactly what my Dyno man did. First thing he made marks on the grip with a white marker pen.
The AFR chart I posted was when he remained at different throttle positions for a few seconds.

The choice of what gear to use for the dyno run changes the power reading. A dyno pull in, say 3rd gear will produce a different "power" on the dyno than a pull in 4th gear. Ideally, the selected gearing for a dyno run should be whatever gear produces a 1:1 ratio. You also have the final drive gearing to deal with + whatever transmission/drivetrain friction losses are involved. The only way to get accurate engine power on a dyno is to use an engine dyno, not a chassis dyno. Admittedly, not very practical in a typical situation.

Of course, the relative numbers are accurate as long as you do the pull in the same gear/same day. Dynos are not as consistent as some folks think...10% power variation between two runs on the same engine is not really unusual!

Max power jetting is the same as timing ---adjust for max power. Usually going leaner than stock (to a point) will produce more power. Obviously one has to consider that the difference between the air/fuel ratio for max power and the too-lean point for burning up an engine is not very wide! So especially for air cooled engines, jetting is typically richer than optimum for power.

Joachim said:

Thats exactly what my Dyno man did. First thing he made marks on the grip with a white marker pen.
The AFR chart I posted was when he remained at different throttle positions for a few seconds.

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Cool. You should have a reasonable idea of what to tweak then.

Fast Eddie said:

When I did ’version 1’ rebuild on my 850, although I did a lot to it, the main performance enhancing items were 1) a JS#1 cam (essentially in between a stock cam and a PW3) and 2) a raise in CR to 10.5:1.

So I had a slightly milder cam and a higher CR than Joachim. IIRC that gave circa 56-57 rwhp and the same ‘more of everything above 3k’ summary. So Joachim‘s results do seem to correlate with my own.

My version 2 was as above but with ‘the full monty’ Comnoz head job on the RH10 inc bigger valves. That unleashed another staggering 9 rwhp. And ‘even more of everything above 3 k’.

So, my conclusion is that these Norton lumps have a surprising amount to give in the early stages of tuning which will be VERY noticeable (unless you ride much below 3k rpm). Of course, that will taper off into diminishing returns the more serious one gets, but those early steps of cam, compression and (skilled) cylinder head work, do seem to unlock a lot. Well, that’s my experience at least.

Also, regarding Joachim‘s cam, the PW3 often gets bad press, now, I’ve never used a PW3 myself, but Mick Hemmings swore by the PW3 as does Norman White (who describes it as ‘the only cam to consider’) and it was designed by PW himself… so it really should not be a bad cam. And then we have Joachim‘s evidence, how can anyone argue against his before and after graphs?

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Comnoz info , also from a dyno , his own, was quite different.
He also informed me that Full Auto Ken's PW3 that wore out at 25,000 miles ( remember the thread) and took the engine with it, was the longest lasting PW3 he had ever seen.

I too wish he would post again so I could stop quoting, but there it is.



Glen

Nice results on the dyno. More is better.

I should put mine on a dyno and see if it can turn the rollers. My seat of the pants dyno says 48HP is probably close if the dyno has a downhill simulation mode.

worntorn said:

Comnoz info , also from a dyno , his own, was quite different.
He also informed me that Full Auto Ken's PW3 that wore out at 25,000 miles ( remember the thread) and took the engine with it, was the longest lasting PW3 he had ever seen.

I too wish he would post again so I could stop quoting, but there it is.



Glen

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I can’t recall the context of Jim’s findings. For example, was the CR raised? A big cam without a raised CR is a sure fire way to throw power away! High CR with a mild cam is a sure fire way to detonation!

We often debate cams on here, and CR. Maybe we forget to debate them as a package. What I know as fact is, a bigger cam (less aggressive than a PW3 though) and a boosted CR transformed my bike above 3000rpm beyond any question. I deliberately did that work without the head work to begin with in order to try and see the effect. I’m glad I did too as it not only demonstrated the above, but I was even more staggered by the difference before / after the head work!

I think the chilled iron cam and Norton cam follower wear issue is a big topic, I for one certainly can’t remember where that ended up, but it’s perhaps best left out of this thread.

As I recall, Jim's current iteration road hot rod is running the stock cam along with fancy head , fairly high Cr, fuel injection and so on.
His comment on that was it made the most midrange power of all the cams tried. I think he has tried all, and indexed the data.
He's probably looking at longevity as well .That has been a troublesome issue. It did result in that wonderful oil testing data, which we all use.

I never quite know what to think on dyno data. You can't do more than Joachim has done, same dyno before and after.
I read about the multitude of dyno correction figures available and it occurs that these corrections might confuse things. For example, the most commonly used SAE J1349 includes 15% for friction. All dyno results seem to be posted as RWHP on auto and motorcycle forums, but reality is that if J1349 has been applied, the calculated number is a fairly generous representation of crankshaft bhp.
I guess the best dyno truly is the dragstrip.
We know the stock cam and engine ran at 12.69 with Cook Neilsen and 12.24 sec. with Norman White. Have other profiles bested those times?
I wouldn't be surprised if they have as dragstrip times are representative of top end power.

Glen

The correction factor doesn‘t matter Glen does it, so long as it’s not changed between runs.

If it’s exaggerating the actual rwhp, it also means the stock engine was less.

The relevance of using a dyno is purely to give a comparison. Which in Joachim‘s case is a difference of 13 rwhp. Even more impressive is the increase in the torque curve. Personally, I don’t see what more ‘proof’ could be offered.

So, a stock Commando is the most fun you can have with 40 hp?

One hopes that the same correction factors are always used. I always look for the CF on dyno graphs and it is seldom listed.
Correction factor allows a 62 HP Commando racebike to pass an 80+ HP Commando racebike on a straightaway.


Glen

maylar said:

So, a stock Commando is the most fun you can have with 40 hp?

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Kinda… so long as you ride WOT at over 6,000rpm…

I don't see 40 HP getting 12.69 or 12.24,even with a light rider.
There are many inconsistencies and unexplainables in the Commando World. Nigel feels the stockers are about 35 HP, I feel they are about as advertised, 60 +-bhp at crank.

Glen

"I guess the best dyno truly is the dragstrip."

Absolutely right! And it's the trap speed to compare, NOT the ET. Trap speed tells you engine power, ET is about launch skill.

worntorn said:

I don't see 40 HP getting 12.69 or 12.24,even with a light rider.
There are many inconsistencies and unexplainables in the Commando World. Nigel feels the stockers are about 35 HP, I feel they are about as advertised, 60 +-bhp at crank.

Glen

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You and I do enjoy this repetitive debate it has to be said !

But, let’s make sure we’re talking apples vs apples please.

I have said that a ‘bad‘ fully stock late 850 (black caps, snorkels on the air box, etc) could easily be less than 40rwhp. My own 850 with its 7.6:1 and single Mikuni I do believe would have been comfortably in the mid 30s. Even Joachim‘s graph supports that, with the single Mik mine just flattened off at 5000, at which revs Joachim‘s was doing 38 rwhp.

I might believe a good Combat could be close to 60 at the crank, that would be mid 50s at the wheel, and with the 2S cam, 10:1 CR and open peashooters, that actually sounds about right to me. But not a ’stock’ Commando. I’ve dyno’d lots of Brit twins and triples over the years and would eat my Shoei if a stock, none Combat, Commando was 60+ at the crank. It just doesn’t make sense when you compare it to other Brit stuff.

Regarding Normans 12.25 qtr, I’d add a few points of note: 1) Norman weighs about as much as I did when I was 9 years old. 2) he is far and above an average rider. 3) I have never believed that was a standard bike (unless we mean standard Combat) as that’s only about a second slower than a lighter, much more powerful, streamlined, early Slingshot GSXR 750J/K IIRC.

I‘ve repeated this many times, so once more won’t hurt… when I’d finished my ‘version 1‘ build I road with a mate with a low mileage mk111. Quite stock apart from peashooters and EI (I forget if he’d fitted a ham can or not). My bike left his for dead at every drag start or roll on we tried. This was the same when we swapped bikes (to eliminate rider difference). There was simply no comparison. And that was before the Comnoz head job !

But, all only in my humble experience of course.

It would be interesting to see Joachim's dragstrip result after the mods.
The Wallace et Calculators are remarkably accurate.
For example, I punched in Cook Neilsen's famous run using his then weight of 165 lbs. Using Cycle's scaled weight the 750 Commando and Norton's advertised bhp of 58, the resultant time is 12.65 seconds, within a split hair of the Cycle 12.69.

One day I will dragstrip test my MK3. The Wallace Calculator gives it 13.6 seconds with my 240 lbs on there. That is if it truly makes advertised bhp.
Then when we go thru the 1/4 in 16.8 seconds...I'll never talk about it again

Glen

I can find no fault or shame in a Commando not being the 'bat outta hell' demon it was advertised as. I wish the facts fed my ego, but they are what they are,...... and old too. They've been through the test of time and previous numb-nutted owners abusing them, and still run.... sometimes reliably.

As I keep saying they're plenty fast for me....

worntorn said:

It would be interesting to see Joachim's dragstrip result after the mods.
The Wallace et Calculators are remarkably accurate.
For example, I punched in Cook Neilsen's famous run using his then weight of 165 lbs. Using Cycle's scaled weight the 750 Commando and Norton's advertised bhp of 58, the resultant time is 12.65 seconds, within a split hair of the Cycle 12.69.

One day I will dragstrip test my MK3. The Wallace Calculator gives it 13.6 seconds with my 240 lbs on there. That is if it truly makes advertised bhp.
Then when we go thru the 1/4 in 16.8 seconds...I'll never talk about it again

Glen

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Like I said in an earlier post on 1972 Combat 1/4 mile times thread. " My first time drag racing a stock 1970 S in about 1974 with a bike that had thousands of miles on it by the previous owner and myself . Race 1 = 13.74 @ 101 mph,, Race 2 =12.95 @ 101 mph,, Race 3= 13.04 @ 102,, Race 4 =12.69 @ 103.32 . I can see how a freshly broken in bike could pull off the times in magazine tests and get into the low 12 seconds. with a highly skilled rider and a well tuned bike. The S models had something special in the heads and exhaust systems and I assume about 55 HP at the rear wheel. There was nothing real special about me at the time. It was my first time at the 1/4 mile.

My bike had a longer Cerriani folk on it due to an accident when owned by the previous owner, that made it a little tricky to launch as the front end got rather light. and I was not as skilled at tuning as I am now. When you do a real hard launch on a Commando, It's like taking a ride on a rocket sled and it's a skill and a thrill that few will experience or master.

Really, you can get a throttle response trace when warming the bike up, the tester on mine was pretty impressed with the throttle response when changing through the gears when warming the bike up on the dyno.

very impressive work! Thank you for sharing so many details.