Topic: daytona 1970, did you know?

[Old Scrambler]

A few more notes and comments: Yosh supplied Ti cylinder studs but Billy Denby decided to use Heavy Duty steel units later shared with Russ Collins.

Factory-supplied electronic ignitions were tossed in favor of a custom unit made by Denby........then retarded from recommended 38-degrees advance to 30 or 31-degrees.

The Denby-Mann bike actually idled because Billy trimmed a very small part of the CR29 slides to allow air to pass......The Japanese team thought he was cheating but later realized the carbs were simply 'adjusted'.

Compression was measured at just about 15 to 1

The crank was used as supplied with the base racing motor.

Dyno RPM was 10,000 but peak power declined after 9,100.

Not sure of sprocket sizes but the motor sprocket was one-tooth larger than what came with the motor.

Denby removed the inner-tube valve-stem lock-nuts because he noticed air-loss after only a few laps......the valve-springs were weak at that time. The Japanese team questioned this but did not alter their bikes.

He built another CB750 for the 1971 Daytona races but only entered the 100-mile event......AND WON....with Dave Parkside???

Mr. Denby was a well known motor builder. His 60's-era record setting Triumph double-motor dragster is in the British Museum. He really thinks the CB1100F was one of Honda's best. He was very happy to have worked with Dick Mann. Bugsy only did what you told him to do.......nothing more.......he knows that you have to finish to win.

We will talk again, but no promise as to when.........

[bwaller]

Awesome Dennis, thanks man. I'm interested, but not surprised, about retarding ignition lead especially at Daytona. We've seen the same proof of this on a dyno. All of his recollection is appreciated. The healthy compression ratio and how they handled the head gasket is cool. I wonder how oil tight it was afterward?!!

[livefast_dieold]

Thanks Dennis! Super interesting.

It has always been an head-scratcher the high advance on the stock bike and even the increase recommended with high-performance camshaft (up to 42°).

CR 15:1 is really high, I thought it was 12.5:1.
It's a bit strange as he was saying: "Machined chambers to make round.......then custom valve pockets in moderately domed pistons similar to F2". How did he get to 15:1 with this setup?

[livefast_dieold]

Some more food for thoughts on the advance.
I've seen this webinar on EFI tuning (it's for cars but applies to our bikes too):

https://www.hpacademy.com/free-live-lesson/recording?utm_source=webinar-follow-up&utm_medium=email&utm_campaign=tuning-webinar&utm_content=follow-up-2
(interesting part starts at minute 40)

Basically, they are saying that with a fully open throttle at high rpm (8000/9000) advance should be REDUCED at around 10° to 15° as the air-fuel mixture is rich and takes less time to travel once lighten up, a bit counterintuitive on what we are doing.
On the other hand, with high rpm but close throttle, that's when you need the 40° advance.
At low rpm and close throttle you get the usual 10 ° advance, but at low rpm and open throttle, advance gets negative (spark past TDC) at -4°.

Considering that throttle sensors are banned for our bikes in any organization, we can still make some adjustments with the advance keeping the above in mind.
For example, I will be at full throttle at high rpm most of the time (and if I am at high rpm with the close throttle it means I'm hard braking), thus no need to keep advance at 40° there...

[gschuld]

Thanks Dennis! Super interesting.

It has always been an head-scratcher the high advance on the stock bike and even the increase recommended with high-performance camshaft (up to 42°).

CR 15:1 is really high, I thought it was 12.5:1.
It's a bit strange as he was saying: "Machined chambers to make round.......then custom valve pockets in moderately domed pistons similar to F2". How did he get to 15:1 with this setup?

I had to dig this up from the way back machine, but (reportedly) the genuine Works heads had a different chamber shape (more hemi like) than a factory k head.

That said, 15:1 static compression would require a massive chamber filling dome.  I have a set of RSC 61.5mm (749cc) 2ring slipper race pistons.  The dome is constant and low.  Less dome than late F model factory pistons.  10.5-11:1 would be tops for those pistons with a tight 23-24cc k chamber.

The Works Daytona bikes may well have used custom pistons and left the RSC race pistons for the kit racers.  Dunno.


George

[livefast_dieold]

on the other hand, a 15:1 doesn't require special fuel?

[gschuld]

on the other hand, a 15:1 doesn't require special fuel?

I’m sure the octane requirement would be very high.

I’m having a hard time thinking anything over 12.5-13:1 was functionally feasible. 

This was an engine that needed to survive 200 brutal endurance miles in a high heat environment.

I can somewhat imagine an extra high compression engine used JUST for qualifying for maximizing bragging rights, grid position.

But for an engine needing to survive the attrition that plagues these events, 15:1 is hard to imagine.

George

[MRieck]

on the other hand, a 15:1 doesn't require special fuel?

I’m sure the octane requirement would be very high.

I’m having a hard time thinking anything over 12.5-13:1 was functionally feasible. 

This was an engine that needed to survive 200 brutal endurance miles in a high heat environment.

I can somewhat imagine an extra high compression engine used JUST for qualifying for maximizing bragging rights, grid position.

But for an engine needing to survive the attrition that plagues these events, 15:1 is hard to imagine.

George

I agree. A person I know well running that kind of compression in a 750 head was using much larger diameter pistons and a positive deck height of about .100 which required counter-boring the head. It was always a struggle to get really high compression these engines. That head was used for dragracing. Extremely high compression ratios hurt top end too and it is safe to say Daytona was a top end track especially during that time.
 No disrespect intended just my experience and the experience of some other people I know that I consider pretty smart fellas.

[turboguzzi]

no surprises for me at least, muzzy publicly claimed that best power for the 750 kawi was at 28 degrees, but you need turbulence generating squish to run such low numbers. can vary from engine to engine but thats what both my 500/4 and 750/810 gpz liked.   

[MRieck]

 Sure.....low advance #s = efficient burn. Throw huge domes, large bores etc in the mix and things change quickly.

[gschuld]

I REALLY appreciate Bill Denby’s openness and offering his memories from 50 years ago.

I didn’t mean suggest Bill was misleading about compression ratios or anything.  Perhaps his memory has faded 🤔. That’s totally reasonable given his age.

Regarding timing, creating a good controlled squish band with a k heads non symmetrical shaped chamber and a 62mm bore is all but impossible without either extremely complicated 3D crown milling or welding up the chambers and creating a machined tapered squish band and having pistons made to match.  I’m not sure about the specifics of the reportedly special cast Works heads though.

George

[Old Scrambler]

Clarification.........While Mr. Denby stated the compression was NEAR 15:1.......certainly greater than 12.5:1. Removing the head gasket was his proven method of eliminating a weak-spot in a race motor and gaining compression. He said he took the head and machined the chambers to be round vs the factory egg-shape, and then ground a 'clearance'-band (squish-band?) around the chamber perimeter. I interpret the initial chamber machining to 'shaving' the head which would further increase compression. Mr. Denby did state that both the cylinder and head were machined to his spec and the pistons cleared the deck by 'a few thousands'.

The pistons were made with one valve-pocket. He machined the 2nd pocket to provide sufficient valve clearance.........remember, he had installed 2mm larger valves on both intake and exhaust from what the race-spec head had when sent from Japan.  In practice laps he noted that  the oil-temp went to 400-degrees........hence the break-down of the roller material on the cam-tension units. On the evening before the race they noticed bake-lite material in the oil-filter. A complete motor tear-down and cleaning lasted well into the night as confirmed in an earlier post on the Daytona thread by Mark McGrew. That is when the Teflon-coated rollers were installed. 

[Old Scrambler]

George: regarding octane..........That is a question for our next visit. I don't know what was allowed 50-years ago, but the AMA has long-approved racing fuels that were superior to 110-spec aviation gas........which is usually at 101-octane.

[Old Scrambler]

Big Questions............So how did Billy Denby and this exotic motor get into the Mann #2 bike when the race-bikes were first delivered only a week before the event?.........and why have we not heard of Mr. Denby before?

To be continued...........

[livefast_dieold]

Regarding timing, creating my a good controlled squish band with a k heads non symmetrical shaped chamber and a 62mm bore is all but impossible without either extremely complicated 3D crown milling or welding up the chambers and creating a machines tapered squish band and having pistons made to match.  I’m not sure about the specifics of the reportedly special cast Works heads though.

George

Exactly! I had the same conversation with Yossef a few weeks ago. Using stock bore sizes it's quite a challenge!
The valves are right at the edge of the chambers, so even by welding up them I don't think it's feasible to obtain a correct squish area

[johno]

Traditionally rather than focus on the squish on 750 heads, I got more benefit from the valves being so close to the edge of the bore I got good results by grinding a scallop on the edge of the bore next to the inlet and exhaust valves, down to about 1mm above top ring. This improved the flow right through the lift.
Two things that wasted my time on the 750 was looking for squish gains and and crankcase vacuum systems, very theoretical and minuscule.

Re the 15 :1 comp........ooooo that's out there man BUT I learnt to never say something is impossible , the modern Nascars all run 15:1 , it can only work on constant full throttle , no off on, Fuel would be a challenge , anything Ive done in the old days over 13:1 or 14:1 I had to use Methanol to get away with it, BUT I never had any involvement with constant full throttle with so who knows ?
Johno

[johno]

Just a note to add to the previous post was : the Nascar 15:1 comp ratios only worked when they had the restrictor plates under the carbs for compliance, so may the old fella was using smaller carbs ie maybe 29mm carbs was small enough to get away with it ??
Ah the mysteries of life 

[MRieck]

Clarification.........While Mr. Denby stated the compression was NEAR 15:1.......certainly greater than 12.5:1. Removing the head gasket was his proven method of eliminating a weak-spot in a race motor and gaining compression. He said he took the head and machined the chambers to be round vs the factory egg-shape, and then ground a 'clearance'-band (squish-band?) around the chamber perimeter. I interpret the initial chamber machining to 'shaving' the head which would further increase compression. Mr. Denby did state that both the cylinder and head were machined to his spec and the pistons cleared the deck by 'a few thousands'.

The pistons were made with one valve-pocket. He machined the 2nd pocket to provide sufficient valve clearance.........remember, he had installed 2mm larger valves on both intake and exhaust from what the race-spec head had when sent from Japan.  In practice laps he noted that  the oil-temp went to 400-degrees........hence the break-down of the roller material on the cam-tension units. On the evening before the race they noticed bake-lite material in the oil-filter. A complete motor tear-down and cleaning lasted well into the night as confirmed in an earlier post on the Daytona thread by Mark McGrew. That is when the Teflon-coated rollers were installed.

He basically counterbored the head to compensate for the positive deck height. Would be interesting to know if it was a straight plunge counterbore or angled/radiused 5 degrees, 10 degrees etc. I can't remember if you said he machined a flat around the perimeter of the pistons or not.

[bwaller]

Probably right Mike, also considering the lack of gasket. Regarding the no gasket, what's the thought?  Grooved sleeve flanges using aluminum wire knowing how much it would compress under torque? Dennis said regular o-rings for oil delivery so that's easily managed.

[MRieck]

 I don't know....they use copper head gaskets in top fuel (bikes and cars).

[gschuld]

So if Bill Denby supplied the race winning engine for Dick Mann’s bike, and it was an entirely different animal than the Works engines that came with the bikes mere days(week or so) before the Daytona race, was it and everything else Denby supplied sold to Bob Hensen and/or Honda?  Bill likely didn’t get the engine back or anything. 

Wouldn’t that be a huge embarrassment for Honda that the no expense spared Honda Works magnesium cased, special custom cast head, close ratio trans engines dripping with unobtanium and GP racing engineer scrutiny were TOTAL failures at Daytona, yet the race winning engine was developed by one guy in a private shop in Florida in the 3 months before the race with little to no access to the factory race parts...🤔. 
 

George

[Old Scrambler]

A small amount of historical insight.........Mr. Denby worked for Duane Taylor at a Triumph dealership in Georgia back in the late '50s. Billy and Duane, along with others, were well known in the drag-racing world and built a record-setting double-motor bike known as The Duece in 1959. Billy was the only rider into the early '60s when the bike was retired. Apparently the T&M dealership took on the Honda brand and Bob Hansen became familiar with Billy Denby. I will try and get more info...........

Duane used 'wired' heads on the Triumphs so Billy knew it was somewhat reliable. He has commented to me that Nortons were 'damned fast' and he recalls my acquaintance T.C.Christianson and his double Norton.....The Hog Slayer.....(watch movie on Amazon). Harley-Davidson and others were still using fiber head gaskets on some in the '50s.........so motor-builders resorted to wire or copper for improvement. I learned on my AMA landspeed record-holding Triumph Cub to keep as much gasket material as possible between the fire-ring and the stud-holes....especially at the exhaust.

[Old Scrambler]

George.......already on my question list...........according to Billy, at the conclusion of the race the torn-down motor and chassis were shipped to American Honda and eventually to Japan. I believe Bob Jamieson could confirm this. Remember, that motor contained a special out-put 5th-gear that reduced the final ratio and helped the motor stay in its comfort-zone between 8000 & 9000 rpms rather than over-revving in 4th.

We know that the original Ti-cases (covers?) did not work and all.....or most.....were replaced with standard units. Did Billy bring his custom gear, pistons, and aluminum wire and use a milling machine at the track to accomplish the build? We have a reported Bugsy quote that following the late-night motor clean-up, the bike ran better than ever!

Billy was busy today.........I'll get more info............   

[gschuld]

From a popular book on Honda motorcycle history(forgot which one sorry)

No mention of Bill Denby.  Was this guy in the federal Witness Protection Program or something?

George

[Old Scrambler]

George.........no one knows at this point...............but 3 days (+2 nights) and 're-engineered' is about the same amount of time it took for Dave Murre and me to final machine, assemble, and get my CBR motor running.