Dyno tuning results

I spent Friday morning at the with the guys at Motorcycle Performance in Madison WI doing multiple runs on their Dyno, looking for some help with jetting my FCR's. We started out very rich and after 5 runs, and still looking a little rich, they decided I ride the bike for a while and see how it feels.
The bike was rebuilt 3 years ago and is my transportation to work, about 60 miles round trip, on good weather days. The engine (880 cc) has JE pistons (78.99 mm) that are copies of TC's 880 pistons that I got in the 70's. I don't know the compression ratio but am guessing 9.5 - 10/1. The cam is a Mega Cycle 5600 00 and the head is a Fullauto with standard valves that Jim Comstock did some mild street porting on.
The blue line on the graphs is from the 1st run and the red is the last run







We did one run with the air filters off and topped 59 hp but power was down everywhere except at the very top end.

Bill G

Dang that was some rip roaring Cdo power noise day! 55 hp is a heffy huffer!
Applying logic with your clues, max air flow resistance occurs at top rpm, so better power lower down with filter implies filter helping en-rich mix, implies still lean over all. I think, unless some how the filter is reducing intake turbulence for more air flow down low. Go back and do it a again please : )

If I understand correctly the mains (now 148's) are possibly still on the rich side and they thought maybe I should go up one size in the pilot jet because the air/fuel ratio looked a little lean around 3 thousand rpms. We did not do another run with smaller mains because they were surprised that the two, 2-step reductions in main jet sizes, going from 158's to 148's had not made more difference than it did. They thought it might tell them something if we did a run without filters to see if that leaned out the air/fuel mixture on the upper end. It did and we got the just over 59 hp reading on that run but the engine was so lean down low that it was stumbling badly. They suggested cleaning the air filters and doing a run with them dry. That was the red line on the graphs, just over 58 hp and about 2.5 hp gain from the first run. The pugs looked perfect so it was their suggestion to ride it as is and see what I thought as they did not want to risk going too lean. That is where I am now. Based on my ride home from the shop I thought it felt pretty good and more perky than when I went in.
I am open to suggestions and would love to see results from other people.
Bill G

That dip in the blue torque curve at about 2500 rpm is a bit disconcerting.

How where they measuring the richness factor ? CO or O2 levels ?

Rohan said:

That dip in the blue torque curve at about 2500 rpm is a bit disconcerting.

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That was why they felt I might want to go up one size on the pilot jet, which is a 58. You can see on the 2nd graph the mixture goes lean at the same rpm's. At this point I am following their advice to ride it and see how it feels. I haven't had it out enough since to come to any conclusions. That said all comments are welcome.

Rohan said:

How where they measuring the richness factor ? CO or O2 levels ?

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I do not know. They ran a sensor into the left muffler. I did not think to check how far in it was or know enough to ask how they were monitoring the air/fuel ratio.

Interesting - thanks for posting.

Hobots right, all those ponies should make it a ripsnorter of a Commando to ride !

Thanks for posting those results Bill. Very interesting to me as Ive got the 35 FCR's for my 920 with 33.5 inlet ports & 41 mm valves. Hopefully will dyno it when the its built!
foxy

Foxy said:

Thanks for posting those results Bill. Very interesting to me as Ive got the 35 FCR's for my 920 with 33.5 inlet ports & 41 mm valves. Hopefully will dyno it when the its built!
foxy

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You will probably want to drop your needles. My clips are now in the second slot from the top. The plugs were very sooty in the stock position.
Jim Comstock is doing another fullauto head for me with larger intake valves. I will be building another 880 with JS pistons and rods.
Bill G

Looking at those graphs again, the calculated hp curve is not quite correctly overlaid onto the torque curve, the dips do not correspond at quite the same rpms ??

Rohan pointed out that there were some errors in the graph. Here is a corrected version supplied by the shop that did the dyno work.



Bill G

Hi Bill, that dip in the curve could well be your exhaust/mufflers, I had the same problem with my new build engine on the first few runs on the dyno, took off the so called replica mufflers, fitted a set of Asian copies that I run on my road bike and presto, better curve and more output!!!
Regards Mike

Thanks for the suggestion. The headers are 1 3/8" from Andover and the mufflers are also from Andover.
I have a new head coming from Jim Comstock and new 880 light weight js pistons and rods I will be fitting this winter. It will be interesting to see the comparison. This engine will probably end up in my '71.

big-valves-fullauto-head-t15646.html

Bill G

Bill for comparison I can post my dyno readout in the next day or so, pretty basic set up i have in my engine but the TQ and RWHP are there
Regards Mike

Brooking 850 said:

Bill for comparison I can post my dyno readout in the next day or so, pretty basic set up i have in my engine but the TQ and RWHP are there
Regards Mike

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I would like to see it, and anyone else's too.

Bill

Looks like a nice-running engine.

Here are a couple I did with my 1974 850. Engine is stock with 15,000 or so miles. Stock airbox with paper filter, Amal Premier carbs and Tri Spark ignition. The headpipes are original with crossover and the silencers are stock type, but new manufacture.

I think is a testament to good ole Brit engineering that we can have so much fun with so little horsepower. Every rocket jockey that rides my Norton is impressed with low end torque and great handling. They lose interest at 100 mph but then so do I for a different reason!
Mike

Hi Bill , first one is with the dud mufflers and wrong jetting. You can see that mid range dip like yours and running rich in the middle and leaning out at higher RPM , not the best result


Second one is the final run with the better jetting and OEM mufflers, unfortunately dyno operator didnt tab the recording until we were over 4000 rpm although after riding it , I know there is stacks of mid range from low down. We quit due to a slight leak in the rocker overhead feed pipe.

Third pic posted is the speed run. Stopped at just ove 7000RPM , new motor and results were encouraging so no need to press it.


1973 motor Std crank and cases, JS rods and pistons 0.040" over, std cast iron barrels ,JS Stage 2 cam , 32 mm Mk1 Concentric Premiers, RH10 head
std Commando manifolds. 21 tooth sprocket on 5 speed TTI box 44 tooth at rear wheel which I found the gearing to tall, so have changed that to 46 tooth at the rear
Regards Mike
Header pipes are upswept std bore with a slight angle change right at the head, I may go to a 4" straight pipe length out of the head next time around.