920

Has anyone here done a dyno test on a 920? Im thinking that modifying an 828cc mk3 850 to 920 ought to work well. The carbs and ports at 32mm are already on the large side and should work well with the larger displacement. According to Dave Comeaus info on Atlantic Green, the 32mm port shapes on these engines is a much better shape the 32 mm Combat ports.A boost in cr from 8.5 to around 9 or 9.5 to one could be done with the change. On paper, at least, this ought to be a pretty potent engine without need for a whole lot of other mods. By increasing the bore to stroke ratio, it is heading the engine toward a sportier top end, though with the considerably larger displacement, I imagine the bottom and midrange do not suffer much.

I have one of the 920 kits from RGM but will wait till top end rebuild time for installation.

Glen

Ok, if there are no dyno reports, how about general observations of power changes by owners who have done the mod?

Glen

How about 920cc/745cc X 52 RWHP = 64 RWHP.

Close enuff?

One test you can do is put the 920 barrel on and do a few dyno pulls :lol:

If so then: (1 007 / 745) x 52 = 70.2872483 rwhp hp. Math is funny fun.

Steve Maney report a few years ago, 920 @ 7200 = 100.4 hp, implies 73 lb ft.

920cc with 64 rwhp @ 5800 implies 58 lb ft.

1007cc/70 hp @ 6000 ~ = 61 lb ft.

Obviously other factors than displacement to consider. More cam needs more CR.

Steve Maney's 100 hp engine must have been a maxed out race engine. It would be interesting to see what the simple change to 920 with a little extra compression added would do to wake things up on an otherwise stock mk3 828ccengine. It would seem to be the ideal candidate for this with strengthened cases and crank.
I think the kit was only about $250 + shipping including forged pistons that were machined to match the standard 850 pistons for weight. The idea behind that is to be a no fuss setup, leave the crank balance factor as is.
Aside from the low cost, the big benefit of this mod should be enhanced power right thru the band, whereas many high performance mods tend to give you more on the top, often at the expense of the middle or bottom end.

The direct proportion as suggested by Schrapnel would be quite a nice boost. There may be even great than proportional gains if Connoz' observations about porting and flow come into play- that the bigger engine will make better use of the 32 mm ports and carbs by producing higher inlet flow speed and greater density of charge.

Glen

nothing technical , but my recent rebuild to 920 , with the addition of Kiehin flat slides , gave me a very noticeable increase in power throughout the range , particularly mid to top end .
I would say go for it .

My only experience with a 920 kit was with a friends bike.He had Maney cases with a 920 kit installed locally,std head (I think) and Keihin Carbs.
He had no end of smoking problems when the engine was running and it was using a bit of oil as well as leaking out of the head gasket.
The bloke who installed the liners warned him no to do it as he might have trouble but he went ahead,as he was told he would have gasket problems.

I was in his garage when we removed the head,you could see the problem.as he was warned about.
There is hardly any gasket material between the cylinder liner and the push rod hole ,I would say about 3 mm at best,there was oil all over the top of the piston on one side and the gasket had blown between the pushrod hole and the liner.There was oil on the fins of the barrel and the head.
Over all not a good look.
From memory he went back to a std barrel.

Maybe it might be able to be solved with a Stainless wire (O ring) in the top of the barrel gasket face ?
Put me off a 920 kit forever,I would put a pair of flat slide carbs,decent ignition system,and a cam. Then go for a ride and enjoy what you have.
Brett

You are on the right track worntorn. Steve Maney's 1,007cc @ 100 hp are full race maxed out. We need to keep apples to apples here and the assumption is you are starting from somewhat stock conditions.

The old saying is there's no replacement for displacement and it seems like the 920 kit is probably the simplest most cost effective and reliable way to go.

There should be little to no issues with keeping a copper head gasket in place. If you have doubts then go with a copper gasket and stainless steel wire in groove.


If you go to the Norvil Motorcycle web site and find their "NEW" bike build offerings you will see a table showing the 920 cc offering at 64 HP at 5,800 rpm.

How do you like those apples

I think that 64 hp and the added torque that goes with it would feel pretty good!

Glen

After many years of looking at engine upgrades, and reading countless accounts fore and against, and making lists of parts and seeing the cost involved, I have come to this conclusion:

If money and reliability are of no concern, go all in. Realize somethings will fail, and if they don't all the better. There are many people successfully doing this.

If you want reliability and budget friendly, stay close to stock and spend your money on Lightening and improving the bike as a whole. Maximizing the effectivity of what HP is available.

I have gone the latter route. So far I have dropped 100 pounds off of the stock weight. And I can see almost another 40 or 50 if I go all in, not happening right now.
With that said, I read somewhere every 7 pounds removed is good for 1 HP. so 100 / 7 = 14.29 HP. I don't know how accurate this is, but it makes sense, it all comes down to power to weight ratio.
Lighter is faster.

I'm sure there will be arguments both ways, but this is what works for me and my wallet. Just my 2¢ worth.

No reason not to do both, really, but strictly from a cost perpective, it seems the 920 mod is hard to beat.
The 920 mod costs about $250 for parts and a local engine borer will do the machining for another $250.
An alloy tank typically costs anywhere from $600 to as much as 2k (Evan Wilcox)

If you happen to be in need of a top end rebuild anyway, the extra cost to go to 920 is just the cost to millout the cases, about $150according to the machinist.

Even the tank I built for my Egli cost a fair bit by the time the sheet stock,alloy Monza cap and Pingel fuel taps were purchased.
An alloy tank is nice and is step one in weight reduction, but it seems to me wont make anywhere near the performance difference that the 920 mod will for less money. In fact removing the steel tank and replacing it with alloy probably would not even make a noticeable difference to performance. It would be there, but it would be tiny.
Having said that, there are other advantages(braking, handling,) to weight saving that can make it worthwhile, even if it is quite costly at times.

Then there is the free weight reduction as well- remove things that arent completely necessary. This is what the original cafe racer builders did, isnt it?
Wolfie, what items did you remove or change to get the 100lb weight reduction?
I think the biggest free weight gain available on my MK3 would be to delete the electric start that I dont use. Im guessing that with internals there could be 20 pounds there.

Glen

Note: I no reports of from Maney on his 1007 long stroke, only his Daytona race engine 920 @ 7200 for 100.4 rwhp. Maney barrels have raised bore sleeves to indent into copper gasket. I guess it takes about 10 hp to over come drive train losses in Cdo. This is a fixed amount, not a percentage of engine power so does not increase with the power applied to the drive train. Norton rods are easy up to street tuned and run big blocks but maybe not for a dragster, road racer on full boil.

I see quotes of 7 lb worth a hp in acceleration help. More so if unsprung mass and even better if spinning mass removed, ie: wheels and tubeless tires pay back the most quickest. I could feel the slight aid of loosing a center stand.

*What I most want to hear is how hard a hi CR 920 is like? Them racers dude cheat to hi heavens w/o lights and starter and mirrors and instruments.

dero said:

nothing technical , but my recent rebuild to 920 , with the addition of Kiehin flat slides , gave me a very noticeable increase in power throughout the range , particularly mid to top end .
I would say go for it .

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Dero, were your cases machined in an empty state? This would be the best for machining, however I have no other need to take the bottom end apart. My machinist feels he can do the job with the rods in the way and keep swarf out of the bottom end.
Im not so sure about the swarf part.

Glen

hobot said:

Note: I no reports of from Maney on his 1007 long stroke, only his Daytona race engine 920 @ 7200 for 100.4 rwhp.

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From my understanding and recollection, Steve Maney raced a 750cc ultra short stroke in the States; never heard about Steve on a 920 in the States. Do you have something credible to back up your assertion? Do you really think a business person such as Steve Maney would risk his reputation, business and livelyhood on running one of his bikes in a race class he did not belong in?

hobot said:

Them racers dude cheat to hi heavens w/o lights and starter and mirrors and instruments.

Click to expand...

Another generalization.

Again, do you have specifics or anything whatsoever even remotely factual to back up your assertion or are you just being facetious because of the lights and starter and mirrors etc......?

Hehe Dances do I detect another smirk wiping to catch ya up to speed...
Note both us Steve's come up with similar 10 hp drive train loss.

from 5/5/2002 2:43 PM SteveManey@aol.com

Hi Steve
All my long stroke motors peak around 7200 rpm in race tune so I don't rev them past 7500 rpm this is way fast enough for a 89mm stroke motor.

I have seen standard 750 road bikes on the dyno they typically produce some 42-45 bhp at the back wheel this equates to 52-55 bhp at the crank, if revved to 7000 rpm for any length time they do come apart,

My 920 race motors typically produce around 100 bhp at the crank (last time at the dyno my own bike showed 100.4 bhp at the crank)

So it doesn't take much to imagine what would happen if I built one of my engines with the standard crank, crankcases, cylinder, etc.

To sum up, the mean piston speed of a 89mm stroke engine is ok up to 7000 rpm, when you use my engine parts you will be able to raise the power output considerably without risking mechanical disaster.
Steve

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I'm not generalizing about racers as cheaters as their bikes are not road legal and can get away with a lot less stuff than the daily commuter I'm brewing to take on anything up to what ever top speed I can attain or shaved tires can take in straights. I've a bar switch with compression release lever to help me get off w/o pits tire rollers. To tease more smirks I'd like to be first to perform sideways barrel rolls on a motorcycle, on purpose instead of accidentally. Red Bull would have to help me on this like they have the acrobatic helicopter project. If not secure enough to practice traction loss into low and hi side antics in public blinds, maybe someone is missing out on something vital.

Steve,

You have failed to present any evidence to support your assertion about cheating.

You have failed to present any evidence to support your assertion (and I quote you) "his Daytona race engine 920".
Steve ran his Seeley with a 750 cc engine in the States.

Wake up! :lol:

I'll give you this, you get a free get out of jail card today since you alluded to a hard night of drinking in the woods and Norton fixing; good for ya!

What we have here is a failure to communicate, comparing street vs race 920's.
A Maney 920 has made 100 hp at the crank and racers get to 'cheat' around many real life issues - in the sense they don't need all the stuff a legal or convenient street bike needs like a starter to lug around or battery charger system etc. A 920 is like 20% more cc's than 750 so one would expect about 20% 1/5th more power on just displacement. Maney and likely yours and other's souped up engines show its possible to ~double the power off 20% more displacement. A related data point I'm also interested in - Ken Canaga said it became a 50/50 affair when he moved up to 920's to kick start at race time, so 'cheated' wisely with roller stater like the rest of ya pit puppies that the rest of us can't lug around.

Hi All,
one of my mates has a 920 conversion on his commando & put it on a mobile dyne last year at a classic bike event in the UK.
It turned out 61 bhp which I assume was at the back wheel.
Some other people were a dissapointed with their results on old dommies & other modified classics.
Having said that, when I follow him on a run with him 2up & me one up I can just about keep up with him on my standard 750.
It must be the quick action throttle that makes mine go quick. (sorry Reggie) His bike does look a lot nicer than mine though.
Cheers all

Worntorn , my cases were empty and opened up with a flap wheel .
No head gasket problems .
I got the norvil kit , not sure now but i think i had to get the small ends bored out .

hobot said:

comparing street vs race 920's.

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Glad you recognized your confusion. Worntorn was clearly referring to a stock engine when "somebody" injected information on an all out 920 race engine.

hobot said:

Maney and likely yours and other's souped up engines show its possible to ~double the power off 20% more displacement.

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The above assertion is missleading at best. I don't own a 920 so engine performance data I have provided to date is all 750cc. Steve's race endeavors in the US of A are on a 750cc.

Focus.