Topic: Classic Bonneville Racer

[Jerry Rxman Griffin aka MuthaF'er]

How's the Mexican food?! 

[scottly]

I have every sprocket combo calculated for ratio on my clip-board.........then numbered in sequence as to how close they are when compared to a 16 x 45 which gave me the highest speed to date.

Dennis, are you absolutely sure you were running the 16 x 45 when you hit 148 MPH? That figures to 2.81:1. On my street bike, I'm running a 17 x 48, which is 2.82:1, and there is no way I would consider that combination for the salt!!

[Old Scrambler]

Food...........There's always a line waiting to get in I have good salsa and chips in the RV

Scott..... I'm listening........maybe I have a wee-bit of wheelspin? I do remember on my best run the original eratic tach was near 10,000   Several seasoned pros on this board and one other have advised lower rpms for best power........so the 16 x 42 combo should be a good start.

A surprise visitor to the SCTA event is the grand-daughter of Burt Monroe......The Press has been anxious but interviews were only permitted by the SCTA 'AFTER' they watched the movie

 

[scottly]

Dennis, 42/16 sprockets is a ratio of 2.625:1, which isn't that far from a stock 48/18 at 2.66:1.
I would try the 17 front sprocket first with the 42 rear; this will give 2.47:1, and then if the tach is reading over 9500 RPM at the big end try the 18.

Leave the 16 tooth sprocket in the tool box!

[Old Scrambler]

Scott...........OK...........17 x 42 says records will be broken

I will be back in Pokey on Wednesday for Dentist appointment........then will get to the sprockets. Today and tommorrow I am getting all of the gas vs fuel recommendations

[scottly]

Dennis, do you recall what gearing you had when we ran the CBR on my dyno? I can compare your 4th gear MPH/RPM to my 17/48 MPH/RPM with the dyno software. It won't show 5th gear like your old dyno chart, but it might be interesting to see the what it does show?

[Old Scrambler]

16 x 44.................

[Jerry Rxman Griffin aka MuthaF'er]

Thoughts on gears...

Which weighs/has more effect considering inertial energy at the output shaft - 16/44 vs 17/42 ?

Would a 16 have more chain "bind" friction characteristic at the front sprocket vs 17?

Considering, this isn't just a 1/4 mile, it occurs over a 3 mile race where maximum speed/rpm and not just acceleration what effects might these potential issues have? 

[scottly]

Would a 16 have more chain "bind" friction characteristic at the front sprocket vs 17?

YES!! The smaller the sprocket for a given chain size, the lower the "critical RPM", where the friction starts overheating the chain links. I've seen the results when the critical RPM has been exceeded for only a short distance, like maybe 1/8 mile at the most: we are talking about snapped chain links that were heated to the point of pretty colors before they got spat out onto the road. You want to run the largest primary sprocket that will give the desired ratio.
 Dennis, what other rear sprockets do you have that are smaller than 42 teeth?   

[Old Scrambler]

From memory to be confirmed..............37; 39; 41

I had the same concerns about the 16t so I began this quest with an 18..........then made a few runs with the 17..........and very happy to return to 17 x 44 with my almost new chain.........it stretched a bit on my recent road-run.

Water is back on the salt because of strong winds moving it and maybe a sprinkle somewhere near.......They are moving the course-markers and hoping for action on Tuesday. Some racers have left and most of the weekend spectators are gone.

[Jerry Rxman Griffin aka MuthaF'er]

If you have the jetting dialed in top out the tach with the 44 then go down using the 17

You would be WELL served if you an A/F meter setup. No more guessing with seat-of-the-pants jetting

[Old Scrambler]

Jerry, your beginng to sound like a PIT-CREW MEMBER 

Racers are setting up the pits today and will begin racing at 7:30 AM tomorrow. My effort to gather GAS info continues. I have parked my K3 on the edge of the car show and have enjoyed quite a bit of interesting conversation. Hopefully a few new members of the forum!

[BomberMann650]

Would have liked to attend speed week myself.

[scottly]

I compared engine RPM/MPH on the 4th gear dyno runs, my 17/48 (2.82:1) vs the CBR 16/44 (2.75:1). Due to the small O-ring rear tire on the CBR, even with the taller gear ratio, the CBR's MPH was about 8 MPH slower than my bike at 9000 RPM; the CBR was going about 105 at that RPM, while my bike read about 113. At 11,570 RPM, the CBR's road speed, er, I mean salt speed would have been136.89, although at that RPM it wouldn't have made enough HP to pull a sick whore off a piss-pot, much less push a bike through the air at that speed. 

[scottly]

If you have the jetting dialed in top out the tach with the 44 then go down using the 17

You would be WELL served if you an A/F meter setup. No more guessing with seat-of-the-pants jetting

I think a GPS speedo might be of more use, so Dennis can see what his actual revs at a given speed are, in real time.
PS The dyno test report in 2015 noted that the jetting was "right on with 125 mains", and was run with 17/45 gearing. The top speed recorded in 5th gear was 148 at 10,170 RPM, but that was well above the engine's power peak RPM. A dyno run in 2018, after switching to the lower F2 5th gear, showed a top speed of 144 MPH at 10500 RPM, with the same gearing.

[Old Scrambler]

Thanks,Scott

I had a good visit with a mature (vintage) car racer that runs naturally asperated gas.............He suggested I run the 104-octane coctail gas and may have to retard the iginition a small amount.........his nic-name is 'Smokey"

[scottly]

You also mentioned in the 2015 dyno report "timing somewhat retarded and found 5 HP".

[Old Scrambler]

Scott............We found that peak power point and marked it...........then advanced 1-2 degrees for safety

The GAS info from supposedly guys in the know..........Sunoco Maximal @ 15:1 or SR18 @15.1:1 for best A/F.  That tells me I may have to go down one jet-size???

Rear sprockets are 38-45..........right now I'm planning to use 17 x 44 as a naked bike and 17 x 43 with the fairing. 15 Days until I leave. Started packing the trailer today.

[scottly]

What is the GAS info, and who is supposedly in the know? The 15:1 figure is for max efficiency, NOT max power. Leave the 125 jets in place!! We've seen the results of 120 jets on the dyno.
17/42 for the fairing.
What is your target speed for naked?

[Old Scrambler]

15:1 A/F is from the Sunoco spec sheet.

Naked target is 143++..............MPS is 150++

[Jerry Rxman Griffin aka MuthaF'er]

15:1 on hot salt for 3 miles WFO on an air cooled engine??

haven't realized we're only 2 weeks out!! 

[scottly]

15:1 is the "stoichiometric"(it hurts my head to use big words ), or "perfect" AFR for that fuel. Gasoline is 14.7:1, so in any case its only a 2% difference. This would be the AFR you would want if you were competing in the Craig Vetter mileage contests, but not for getting the maximum power out of the engine like you need to go very fast.
For max power, you want 12.8-13.2. Your bike was something like 14:1 with 120 mains, and 13:1 with 125 mains, right in the sweet spot.
I think your target for naked of 143 is a bit on the optimistic side?
I would concentrate your efforts on breaking 150 in PS. After all, where else but Bonneville can you do that on a CB? (Well, there is El Mirage, but you've already decided it's not for you. )
You need to use the tach for whichever class you are running. Your motor has it's peak HP around 9200 RPM, and by 9500 is starting to drop. (Your new cam may alter this peak RPM, but it probably won't be by much, and may even be lower than your custom cam?)
If the bike will pull to 10K in 5th, or higher , your gearing is too low. Don't over-rev the motor trying to go faster, lest you spit out lash caps again. Take it back to the pits and adjust your gearing and try again.

If the bike can't pull over 8500 or so in 5th, the gearing is too high. Down shifting to 4th may over-rev the motor, so be careful.

[scottly]

Jerry, your beginng to sound like a PIT-CREW MEMBER 

Dennis, you need someone to keep track of your settings for each run, like gear ratios, speed, RPM and such. You will have enough to think about at 150+ MPH. I nominate Jerry! Jerry, got an old fashioned clip-board?  

[Stev-o]

Jerry, your beginng to sound like a PIT-CREW MEMBER 

Dennis, you need someone to keep track of your settings for each run, like gear ratios, speed, RPM and such. You will have enough to think about at 150+ MPH. I nominate Jerry! Jerry, got an old fashioned clip-board?  

I second the nom for Jerry!  Might have to buy more beer, Dennis!!

Good luck and keep us updated.

[Jerry Rxman Griffin aka MuthaF'er]

You guys mean become "organized" haha. Guess I better get my clipboard ready. The forum has spoken.

Godzilla is looking for my special clipboard.

AND, I'm bringing along an excellent photographer plus a cooler.