Author Topic: SOHC CB750 top speed. (Read 7629 times)

Sam Green Racing · « **on:** August 11, 2019, 02:44:31 AM »

With the modern day parts and know how available, would it be possible for a true 750 bike to top the speed of the 1970 Daytona bikes ?
I know from people with first hand experience that the speed of the works Daytona bikes that they topped 160mph.
Can anyone today claim to have topped this speed with just 750cc on tap and in similar trim ?

Sam.

gschuld · « **Reply #1 on:** August 11, 2019, 04:29:06 AM »

I believe Mark Mcgrew’s M3 racer at its peak had modestly more power and better relative speed numbers on the Daytona track than the original 1970 factory Works racers.

George

Sam Green Racing · « **Reply #2 on:** August 11, 2019, 07:17:55 AM »

Yes George but do we know what speed it clocked ?

gschuld · « **Reply #3 on:** August 11, 2019, 08:46:32 AM »

I believe this is what I was referring to from Mark McGrew regarding relative speed.

George

HondaMan · « **Reply #4 on:** August 11, 2019, 09:32:44 AM »

Do I sense a Bonneville run?
The original engine in the Lakester I used to work on was the CB750K3 engine in my garage now. It was replaced with a KZ1000 to break 140 MPH, but that is pushing a whole car. It last ran 168 MPH with a Hyabusa, stagger-bored to 1500cc and drinking nitrous.

Jerry Rxman Griffin aka MuthaF'er · « **Reply #5 on:** August 11, 2019, 09:39:32 AM »

Old Scrambler is currently the AMA Bonneville record holder. He has gone 148+ on salt which I hear has a 15% slip factor. Shooting to top 150 this year in 2 weeks. Stay tuned. I'd love to see what it would do on a solid surface. I believe his pistons are 61.5mm which I also believe were the size the Daytona bikes ran??

gschuld · « **Reply #6 on:** August 11, 2019, 10:46:42 AM »

Salt flats racing is a very unique animal.

Altitude and the reduced traction of salt(which in itself varies greatly from day to day, year to year) makes anything more than a casual comparison to sea level on a hard surface nearly impossible.

Regardless, I wish Dennis all the best luck in breaking 150 on the salt👍 That would be a cool benchmark.

Aero drag becomes the all dominant speed limiting factor at such high speeds. A high strung 750cc cb750 engine in a tiny streamliner chassis should be capable of 200mph plus on a hard surface with ease.

George

Sam Green Racing · « **Reply #7 on:** August 11, 2019, 12:14:22 PM »

Quote from: Jerry Rxman Griffin aka MuthaF'er on August 11, 2019, 09:39:32 AM

Old Scrambler is currently the AMA Bonneville record holder. He has gone 148+ on salt which I hear has a 15% slip factor. Shooting to top 150 this year in 2 weeks. Stay tuned. I'd love to see what it would do on a solid surface. I believe his pistons are 61.5mm which I also believe were the size the Daytona bikes ran??

Thanks Jerry and George and I to hope Dennis manages to top his 150mph target in the coming weeks.
I to would like to see what Dennis could do on a hard surface with no salt and altitude problems.
I think the ECTA now have a venue over the standing mile in Arkansas. I think the airfield runway is just over 2 miles so there's plenty of time to get up to top speed and stop again safely.

Sam.

scottly · « **Reply #8 on:** August 11, 2019, 10:33:24 PM »

Coincidentally, I was recently re-reading the June 1970 edition of Hot Rod magazine, which included coverage of Daytona.

The fastest qualifier was Gene Romero on a Triumph triple @ 157.342 mph, followed by Mike Hailwood's BSA triple @ 152.905 and Gary Nixon's Triumph @ 152.827. Dick Mann's Honda was forth, @ 152.671.

Sam Green Racing · « **Reply #9 on:** August 12, 2019, 01:54:45 AM »

Quote from: scottly on August 11, 2019, 10:33:24 PM

Coincidentally, I was recently re-reading the June 1970 edition of Hot Rod magazine, which included coverage of Daytona.
The fastest qualifier was Gene Romero on a Triumph triple @ 157.342 mph, followed by Mike Hailwood's BSA triple @ 152.905 and Gary Nixon's Triumph @ 152.827. Dick Mann's Honda was forth, @ 152.671.

Thanks Scott, I'm not 100% sure but were these not just average speeds around the banked track in qualifying.
I think the infield part of the track was only used during the race itself, but like I said, I'm not 100% sure.
All three of the three British riders who were all good friends of mine told me they were all hitting over 160 with Ralph Bryans close to 170 on the straightaway.

Sam.

andy750 · « **Reply #10 on:** August 12, 2019, 03:03:54 AM »

How were they measuring speed Sam? I wouldnt trust an analog speedo to record accurately.

thanks
Andy

Sam Green Racing · « **Reply #11 on:** August 12, 2019, 05:35:05 AM »

Quote from: andy750 on August 12, 2019, 03:03:54 AM

How were they measuring speed Sam? I wouldnt trust an analog speedo to record accurately.

thanks
Andy

Hi Andy, how are you ?

Analog Speedo, hahaha, no such thing on these bikes mate.
The speed would have been calculated from the gearing and what rpm they were pulling on the longest straightaway.

Sam.

bwaller · « **Reply #12 on:** August 12, 2019, 08:30:14 AM »

They timed with a sun dial in 1970 Sam!

MRieck · « **Reply #13 on:** August 12, 2019, 02:29:34 PM »

Quote from: bwaller on August 12, 2019, 08:30:14 AM

They timed with a sun dial in 1970 Sam!

.....and they used their feet for brakes too.

Old Scrambler · « **Reply #14 on:** August 12, 2019, 05:17:55 PM »

Thanks for the kind wishes...........I'm told by a few of the Bonneville Boys that 150-mph on the salt equates to 165+ on pavement near sea-level. The primary consideration for an oval-track speed on a straight-a-way is the bike and rider did not have to maintain that speed for the entire mile as required on the salt. I have thought about going to Loring, Maine, but adding front-brakes alone are not enough to negotiate the run.........my feet and the shifter-touch touch the track on mild turns........but could be adjusted.

The calculated speeds are just that........the tracks have been using 'radar-guns' since the late 60s.

andy750 · « **Reply #15 on:** August 12, 2019, 05:37:30 PM »

Hey Sam all good here thanks and thanks for the insight - I had no idea!

Sam Green Racing · « **Reply #16 on:** August 13, 2019, 08:50:08 AM »

Thanks for all the replies guys and good luck Dennis, I hope the weather stays favourable.
Great speaking with you again Andy, brings back great memories of my times at Mike's.

H2Eric · « **Reply #17 on:** August 14, 2019, 03:58:42 AM »

Hi Sam

I would love to give my CR750 a good ol' thrash at an Elvington top speed event, but I suspect the anti-noise brigade would prevent it.

Eric

MRieck · « **Reply #18 on:** August 14, 2019, 04:20:21 AM »

Quote from: H2Eric on August 14, 2019, 03:58:42 AM

Hi Sam

I would love to give my CR750 a good ol' thrash at an Elvington top speed event, but I suspect the anti-noise brigade would prevent it.

Eric

Are you kidding me Eric. For Christ sake.....will the BS ever stop or just keep getting worse?

bwaller · « **Reply #19 on:** August 14, 2019, 06:24:50 AM »

Mind if I answer part of that Mike? Certainly here residential sprawl threatens many tracks, the closest track for us will shut down at the end of this season. The owners have been harassed by the city for years. Noise restrictions have been in place everywhere although not always enforced, but that too is changing. Another beautiful track only a couple hours away, is restricted to four events a year, and none of them are motorcycles.

The absolute shame of a track closing not only affects race events, but trackdays that scratch the itch of so many squids who would otherwise terrorize the streets! It's a bad deal.

gschuld · « **Reply #20 on:** August 14, 2019, 07:16:52 AM »

I’ve been told that at least USCRA and AHRMA have been under increased pressure to reign in the high decibel offenders.

George

slikwilli420 · « **Reply #21 on:** August 14, 2019, 07:20:04 AM »

Quote from: gschuld on August 14, 2019, 07:16:52 AM

I’ve been told that at least USCRA and AHRMA have been under increased pressure to reign in the high decibel offenders.

George

That is true. I remember last year someone clocked 120+ decibels at Road America. Many tracks have pretty stiff requirements and we are starting to police it a bit more. A few of the loudest guys found a few more ponies with some added back pressure, and are now within the limits.

gschuld · « **Reply #22 on:** August 14, 2019, 10:02:33 AM »

Though it doesn’t exactly enhance the aesthetics of the bikes, some have resorted to add ons after the exhaust in an effort to modify(reduce) the exhaust sound with minimal intended effect on power. This pair for a cb350 racer is made from perforated steel tubing(wrapped sheet material and welded) with perforated steel angled baffles inside. I suspect things like this will be more common looking fwd.

Small airports and race tracks have been dealing with similar noise based “quality of life” pressures for many years.

George

simon#42 · « **Reply #23 on:** August 14, 2019, 01:03:16 PM »

unfortunately there are people out there that confuse sounding good with stupid loud , no idea why but it gives the anti noise people plenty of ammo .

bwaller · « **Reply #24 on:** August 14, 2019, 02:25:42 PM »

I can think of 4 or 5 cases of stupid loud in all of the VRRA. It would be a great midnight special adding some baffling! LOL

The fast guys are rarely ever confused on the subject.

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Author Topic: SOHC CB750 top speed. (Read 7629 times)