920 Dyno result

Matchless · Oct 12, 2014

Last Thursday I spent a couple of hours on the Dyno playing with the 33mm CRs. The jetting was pretty close. Ended up lifting the needles to the richest position. Just needs a slightly smaller slow air jet to improve the off idle setting. but ran out of time & jets.
At this point I have to say it doesn't seem to run any better than I remember with the Amals. This just proves what basically sound carbs Amals are.
The Dyno showed 63.35 rwhp @5900 & 58ft/lb. I had guessed 64 ish. There is probably a little more to come but the main thing is, the bike is a joy to ride, & just as importantly, bombproof.
The spec. is:
Fullauto head with 3mm o/s inlets modified by Jim Comstock
920 Maney barrels
JS rods & pistons
Maney crank & cases
PW 3 cam
Trispark ignition
Keihin 33mm CRS carbs.
Unbalanced pipes
Fluted baffle Peashooters.

Martyn.

Fast Eddie · Oct 12, 2014

Matchless said:
Last Thursday I spent a couple of hours on the Dyno playing with the 33mm CRs. The jetting was pretty close. Ended up lifting the needles to the richest position. Just needs a slightly smaller slow air jet to improve the off idle setting. but ran out of time & jets.
At this point I have to say it doesn't seem to run any better than I remember with the Amals. This just proves what basically sound carbs Amals are.
The Dyno showed 63.35 rwhp @5900 & 58ft/lb. I had guessed 64 ish. There is probably a little more to come but the main thing is, the bike is a joy to ride, & just as importantly, bombproof.
The spec. is:
Fullauto head with 3mm o/s inlets modified by Jim Comstock
920 Maney barrels
JS rods & pistons
Maney crank & cases
PW 3 cam
Trispark ignition
Keihin 33mm CRS carbs.
Unbalanced pipes
Fluted baffle Peashooters.

Martyn.

Nice one Martyn. That does sound like it would be a very nice road engine indeed.

At what revs was your 58ft/lbs peak torque?

But the most important question of all has to be: what yer gonna do next ??!

Matchless · Oct 12, 2014

Hi Eddie,
The Dyno blokes printer wasn't working so the figures are from memory. I can't remember the revs for torque or any of the lower revs measurements. And as for whats next, ride the nuts off it of course. I am more than happy with the way it rides & consider it all worthwhile.
I have just read your post. Are you going to rework the RH10 or splash out on a Comstock Fullauto. Having said that yours sounds good to me. If you want to make the thing quicker & more useable on the road, buy a TTI 5 speed. Best money you will spend!
Regards,
Martyn.

Reggie · Oct 12, 2014

Martyn, You've got a very nice build there, and assuming all things being equal, 2 more horse power than me with my 920 and half a lb/ft.

I am quite interested in the TTI 5 speed g/box. Do you know if you can have it modified to fit the Mk3 arrangement with left sided gear change? I suspect not, and if this is the case it would mean modifying the rear brake arrangement. :cry:

worntorn · Oct 12, 2014

Would these two results happen to be from the same dyno? If not, it seems common to see 10-15% or more variation between dynos. So , though useful numbers to have for tuning the bikes, if done on different dynos, it won't really give any indication as to what the relative output of the two engines is.

Glen

cjandme · Oct 12, 2014

Reggie said:
........I am quite interested in the TTI 5 speed g/box. Do you know if you can have it modified to fit the Mk3 arrangement with left sided gear change? .........

+1 since I'm a MkIII guy too, just no money at the moment so I haven't looked in to it much, but still curious. Thanks for taking the time to post your dyno reaults & my hats off to you on your build, happy trails

Reggie · Oct 12, 2014

worntorn wrote;

Would these two results happen to be from the same dyno?

No. But they could suggest that we're in the same area :?:

worntorn · Oct 12, 2014

Yes and both making a lot more HP than a stock 850. I don't think any dyno tests posted here to date have shown over 50 HP from a stock bike on any dyno, including dynojet numbers.

SteveA · Oct 12, 2014

Reggie said:
Martyn, You've got a very nice build there, and assuming all things being equal, 2 more horse power than me with my 920 and half a lb/ft.

I am quite interested in the TTI 5 speed g/box. Do you know if you can have it modified to fit the Mk3 arrangement with left sided gear change? I suspect not, and if this is the case it would mean modifying the rear brake arrangement. :cry:

Bruce Verdon does supply TTi boxes with left foot gearchange. It works in much the same way as the MkIII by taking the selector shaft left out of the inner cover.

You would need to check with TTi to see if it lines up with a MkII primary case....

Bruce does these boxes to accomodate racers who grew up left foot changing and who may ride more than one bike in a day.

Matchless · Oct 12, 2014

I have to say the comments about figures being different from one Dyno. to another are correct. The numbers are no more than a guide. I would be interested to know what a stock 850 makes on the Dyno. I am using. Does any one know the rear wheel HP? The main thing for me is my bike is better to ride in every way.

worntorn · Oct 12, 2014

From reading here and on the NOC site, seems 45-50 is pretty much as high as the stockers show.

Glen

Kvinnhering · Oct 13, 2014

worntorn said:
From reading here and on the NOC site, seems 45-50 is pretty much as high as the stockers show.

Glen

Can you please told us the torque
figurer also.

Jan-Egil

worntorn · Oct 13, 2014

I can't recall all of the Max torque figures posted, but a search yielded this post of Mick Duckworth's chart. You can see why 850s can be a lot of fun without revving to near destruction.

Glen

Hobot · Oct 13, 2014

63 hp from 55 cid = 1.1454545 per inch cubed.
850's can sure strain my Combat and SV650 and nerves to keep up with in twisties as they just zoom right out of them so smartly. I pity the poor rear tires. Someone else might do the percentage of change math for pecking order fun.

worntorn · Oct 13, 2014

Makes you wonder what was done with the 850 to create that great big old midrange torqueball. It is beyond the increase one would expect from an 85cc displacement increase.
Same basic design, same cam, same basic head configuration, bit lower compression and where did all the torque come from? No big loss at the top, still has couple of horses on a non combat 750.

Glen

Hobot · Oct 13, 2014

Only thing must be the speed of bigger intake mixture slug into chambers at lower rpm than 750s and a cam that traps most the mixture by closing early but gives up some top end hp due to missing out on the over packing of over lap hot rod cams, that need like 6000+ to do their thing. In practice they are so close its more a personal choice of where ya want to feel the pull most and how often to shift to feel it.

worntorn · Oct 14, 2014

Not very close at all at 3200 rpm. The 850 line shows about 60% more torque than the other two. No wonder the 850 strains the trans.
I would have guessed that the same basic engine over bored 12% would make torque and horsepower lines roughly 12% above the smaller engine, but that is not at all what occurred. At bottom the gain is roughly 60% and at top the gain is about 4 %.
Interesting. I wonder what happens to these lines (not just max hp)when all else is left as is and the overbore is to 920?

Glen

Hobot · Oct 14, 2014

Granted Glen that the spiffed up 850 is a low down torquer compared to the others but all Cdo run up toward top speed in similar time. The couple 850's i was on impressed me on first throttle up per gear but tapered off enough I like the Combat character better. I like short shifting as much or more than anyone and 850 do that well. In legal ride style the 850 grunter has the right stuff.

920 Dyno result

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