850 Commando vs 998 Vincent Rapide on Dyno Hill

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worntorn

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I've always thought the Commando would win this one fairly easily.
The Vincent is tuned at stock Black Shadow level, 8 to 1 and small carbs, 928s, straight thru silencer.
The Norton is a nearly stock 850, Boyer ignition and open peashooters. The CR measures 8.5 to one.
Overall gear ratio on the Norton is 4.60 to 1. That is with standard primary and a 20 tooth gearbox sprocket.

The Rapide has standard Vincent gearing of 3.5 to 1, very high.

The Norton wins if top gear is used on both, however if third gear is used on the Rapide then things change.
Third on the Rapide is still a higher gear than the Commando top. It is about the equivalent of the Commando with a 22 tooth sprocket. The Rapide can be taken well past 100 mph in third if required, so third is a good hill gear on that bike.
In third on the 14% grad of Dyno Hill the Rapide hits the same 113 kmh as the Commando does in top. If the Commando was packing the same ratio as the Rapide in 3rd, it wouldn't manage 113 at top of hill. That would be a 22 tooth on the Commando which would net somewhere around 107-108 kmh.
Also, the Rapide lives with a fairly hefty rack and top box full of supplies, so it is about 30 lbs heavier than the Commando .
So at 4000-4500 rpm the Rapide engine provides a fair bit more oomph than the Commando.
The butt dyno was wrong on that one too.

Glen
 
worntorn said:
I've always thought the Commando would win this one fairly easily.
The Vincent is tuned at stock Black Shadow level, 8 to 1 and small carbs, 928s, straight thru silencer.
The Norton is a nearly stock 850, Boyer ignition and open peashooters. The CR measures 8.5 to one.
Overall gear ratio on the Norton is 4.60 to 1. That is with standard primary and a 20 tooth gearbox sprocket.

The Rapide has standard Vincent gearing of 3.5 to 1, very high.

The Norton wins if top gear is used on both, however if third gear is used on the Rapide then things change.
Third on the Rapide is still a higher gear than the Commando top. It is about the equivalent of the Commando with a 22 tooth sprocket. The Rapide can be taken well past 100 mph in third if required, so third is a good hill gear on that bike.
In third on the 14% grad of Dyno Hill the Rapide hits the same 113 kmh as the Commando does in top. If the Commando was packing the same ratio as the Rapide in 3rd, it wouldn't manage 113 at top of hill. That would be a 22 tooth on the Commando which would net somewhere around 107-108 kmh.
Also, the Rapide lives with a fairly hefty rack and top box full of supplies, so it is about 30 lbs heavier than the Commando .
So at 4000-4500 rpm the Rapide engine provides a fair bit more oomph than the Commando.
The butt dyno was wrong on that one too.

Glen
Click to expand...
Very interesting stuff
 
998 ccs vs 828. As the old saying goes, you can't beat cubic inches! ;) PLUS the Boyer hurt the Norton due to its retarded timing compared to the OEM setup. Install Points/AAU in the Commando and try it again!
 
At 4000 the Boyer is giving 31-32 degrees of advance, no power loss there.

Glen
 
"At 4000 the Boyer is giving 31-32 degrees of advance, no power loss there."

I agree IF you are starting all your runs at 4k+ RPM. If you are starting below that the OEM ignition will get you off to an initial lead and you will keep that lead until the end of the test track, no matter how long it is.
 
MexicoMike said:
"At 4000 the Boyer is giving 31-32 degrees of advance, no power loss there."

I agree IF you are starting all your runs at 4k+ RPM. If you are starting below that the OEM ignition will get you off to an initial lead and you will keep that lead until the end of the test track, no matter how long it is.
Click to expand...
Tri Spark has the closest curve to stock doesn’t it?

Do I detect another back to back test on the horizon Glen ?!
 
It would be interesting.
When I recently timed analog Boyer on the 920 it strobed 31-33 degrees at 3000 and stayed there up to 5500. I didn't check above 5500.
So it had full advance by 3,000, which is about the lowest rpm the bike sees other than when putting around in slow traffic.

Glen
 
If the Boyer does have full advance at 3k then it is very close to the OEM. There were curves published here some years ago that showed the Boyer didn't achieve full advance until nearly 5k. In that thread, the Trispark was among the closest to the points/AAU.
 
Yes, I just had a look at that.
It appears that the Boyer actually gives earlier advance than the stock Points ATD does, other than in one small space, from 2800 to 3400+-. Even there the difference isn't huge, a couple of degrees.
I'm not sure if that is good or bad, but it definitely gets going early on the advance.

Glen
 
850 Commando vs 998 Vincent Rapide on Dyno Hill
 
If one wanted to replicate the AAU, Pazon Altair comes closest.
I suspect there is nothing in it between any of these advance curves/ramps.
These old motors aren't that fussy on ignition timing , as Nigel found on the dyno and I've witnessed on Dyno Hill.
850 Commando vs 998 Vincent Rapide on Dyno Hill
 
Look at the shape of the curve, not the maximum advance shown on the tables. The max advance is simply a setting that can be changed with any of the systems. IOW, if the max advance is set at say, 31 degrees, note that the OEM pointas/AAU system curve would hit the 31 degrees advance at around 3k RPM whereas the Boyer curve wouldn't achieve 31 degrees until at least 6k RPM. That's a large range of 'less than optimum advance.' ;)
 
On those charts the AAU never hits 31, it stays at 28 forever. An even longer range with suboptimal advance!
So if you want 31 at 3000 with the Boyer you just adjust it a bit, same as any ignition.
I have the Commando Boyer set for 31 at 3000 rpm.
The bike starts easily, no kick back.

Glen
 
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It will hit 31 if you adjust the timing for it to hit 31 - or any other setting. I set my points/AAU at 32 degrees for the altitude the bike operated at (7600 ft) when it was in Mexico City. When it was in NY I set it for 28 (sea level). Now there is a trispark on the bike, set for 31. (6500 ft).

The reason the points in the chart hit 'only' 28 is because that's where the owner/operator /mechanic set the timing.
 
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Exactly.
Same with any of those ignitions plotted. Set them where you want them, they'll all work fine as far as advance curve/ramp.

My wife read the timing disc as I ran the bike. She tells me that it was 31 at 3000 climbing to 33 at 5500. The bike doesn't seem to mind a bit more advance at a higher rpm, in fact it likes it!

This fellow was unbeatable on his Trident sidecar rig at Westwood. He is a great tuner and was an avowed believer in points ignition for racing.
He told me that his Sidecar Monkey convinced him to try the new Boyer EI ( late 70s) on the racebike.
With the Boyer in place the bike pulled 500 rpm higher up the mountain and was also faster on the straight. He never went back to using points.

Dave Wildman - Class of 2010 | Canadian Motorcycle Hall of Fame | Temple de la Renommée de la Moto du Canada

canadianmotorcyclehalloffame.ca canadianmotorcyclehalloffame.ca
 
Since where I live is mostly sea level or couple hundred meters up , the older gent who helped time my 750 , said 28 degree at 2800-3000 so since he knew 40yrs worth more than me that where it was set , afaik still set there for new owner , was a newer version of Boyer …. Bike pulled hard in all gears ….
 
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