Topic: Interesting Old Bike Barn blog on RC chopper

[Tintop]

https://oldbikebarn.com/blogs/blog/1975-russ-collins-1000tt-cb750-chopper?utm_source=Old+Bike+Barn&utm_campaign=5424eb2549-EMAIL_CAMPAIGN_2019_12_09_06_06&utm_medium=email&utm_term=0_ad402bfd86-5424eb2549-21681085&mc_cid=5424eb2549&mc_eid=a0fe6d029e

[PeWe]

Very interesting!
An old CB750 chopper equipped with an RC 1000cc  engine, (Cobra?) used as a daily rider since 1975.

[turboguzzi]

super cool, but with the front engine mounts not even attached to the down tubes and that geometry, no wonder it's a death trap! nice reminder from the un politically correct 70's

[754]

Thousands of them were built without the front mounts, and they worked pretty good.  I don't think many were roadraced.. I ran mine on the ice with studded tires..

[Medyo Bastos]

I would ride it!


Sent from my iPhone using Tapatalk

[scottly]

It has a "stock" cylinder block, not the "distinct" RC block.

[754]

Yeah what I am thinking is he may be talking about the 736 cc pad ground flat, then restamped, as RC did..

[scottly]

I'm thinking it's pure BS.

[Tintop]

It has a "stock" cylinder block, not the "distinct" RC block.

So does the A/T & SF Scottly, and I think we're all pretty certain those engines were RC.

[gschuld]

FWIW, the “Turnpike Terror” package was standard with a factory cylinder, the RC cast big block was an option.

George

[NitroHunter]

Remember, 150mph back then was absolute OMG territory. And I'm here to tell you the TT did what they said, with Smoothbores, Dyna, Racers Supply gearing and PZ2 tires it would easily pull the needle past ALL the numbers on both the tach and speedo. Mine also had the factory cylinder with big sleeves and was my daily rider for years.

[Jerry Rxman Griffin aka MuthaF'er]

From the options list I'd say they left a lot on the table for that rw 150hp

[PeWe]

150 whp, really?
What kind of rods? Not RC Golden rods, other steel rods?

I was sure that 120 whp is max possible without nitro, turbo or compressor.

I guess 100-105whp whith a good exhaust.
See Mikes dyno of his bike with billet block and not perfectly tuned 34mm carbs.  A handful hp left to rhe goal of 110.

My bike (billet block 1005cc, TMR32 carbs) maxed 93whp on dyno due to the restrictive exhaust 4-4 and DP315 cam. Now RC295 profile and Hindle 4-2-1 that gives plenty of more.

I dream about same numbers as Mike's, 1/2 hp more is enough!
That is around 105 hp on the wheel on street gas.

Next step is RPE stroker crank available on eBay?

[gschuld]

Those RC catalog power numbers were pure 70s salesmanship.  I was commonplace during the time period.  Simple as that.

The stated 10.90s @125mph.  That takes roughly 105 RWHP in a reasonably light bike with a modest 60ft time based on the power numbers and 1/4 mile times of others.

105 RWHP is perfectly reasonable for that engine especially if the more race oriented options were chosen(H/C pistons, ported head, big cam)

But 150hp, even crank hp rather than RWHP.  Not a chance.  150 mph, sure.  In a full road race setup with full fairing and rider tucked down to the tank like blasting around the track at Daytona. But on some guys chopper on the interstate, no way.

Regardless, RC built many great performing big bore street engines.  They were far more powerful than  stock, and put huge smiles on the faces of their owners who spent a good deal to have them built.

Mike’s 1005cc street engine was last at 106(?) RWHP and a planned change of cam and some more tuning will probably produce the +/- 110 he was aiming for. 

Aiming for much beyond that with a N/A street gas sohc4 Honda IMHO is going to require more displacement, and likely more cylinder head flow creating more challenges.

George

[PeWe]

Good reading in that old RC catalog! It can be seen as a guide what to do.
Cobra engine also there?

[gschuld]

Sure.

George

[PeWe]

That's the menu to order from!

Only 4:th gear undercutted, 2:nd is a common jumper too.

4:th when slamming it in at 100mph followed by wot,  the foot can just nudge the pedal and make it land in the  false neutral between 4-5.
Happened me countless of times before trans got gears undercutted.

The old style heads look very sexy on those 3 !

[754]

Ok let me add a few things.
There was a handful of dynos, harder to compare, if you want to dispute it, why just bring your dyno.. what don't have one ? Oh well . Every dyno read different , I bet. And still I am sure 150 up on XYZ dyno is still more than 130 up on same dyno.
 And RC was setting records.. and as I said on here many times before,
 No matter what your HP today, no matter what you improved, no matter how much better your build is, you have not beat an old RC record till you beat that time.. and it should be easier today. Better chassis and traction I bet....
 And yet there does not seem to be a lot of people beating the old RC Performance at their game.
 Some people forget , some of their records stood for 10 years.. that is 10 years for everyone in the world,  with all the other bikes in the world  to break their record. That is no small accomplishment.
 Can you tell I sort of like RC Eng ?

I remember a Cobra on the street at Sturgis in a Savior frame , it was not as quick as we expected.. but I get with a bit if tuning it would be..  it had Webers, it would be a Torquay fun beast to ride, I bet..

[cbr954]

My dad built a RC 1000cc back around 74.  All the RC parts minus the block which was stock.  put it in a stock bike, total sleeper on the streets.  Most people underestimated it till he fired it up.  A lot of egos broken on the back country roads in central South Dakota with that bike.  Got to a point no one would run him anymore.

[PeWe]

Russ Collins was the big name of the best tuning parts when I bought my CB750 back in 1979. I was late to the era.

My local tuning shop had same parts and upgrades as the RC catalog. The owner of the shop won all Swedish Pro Stock Bike championships 1979-88 until he quit. (Kawasaki and Suzuki)

They had RC, AF and Yoshimura parts to CB750 and Z1-900/1000 plus Campagnolo wheels, Dellorto, Smoothbore and Keihin carbs.

His mechanic did my engine back in 1983. 
Restored and upgraded the -83 ported head a few years ago.

The good thing is that it is still possible to get that kind of CB750 engine built today with even better rods and pistons. Probably developed valves, guides, chains too.
Mike's billet block lift the ribbon a notch further for reliability.

The question today is "which cam?" I'm proud to use a Russ Collins profile that work fantastic.

All for the old good CB750.

This forum let the RC heritage to live on and develop.

More about dyno references...
Same Dyno my bike has been on, a friends bike, an old non restored (still not smoking) Honda CBR1100XX -1997 had 133whp despite around 100.000km or more, no mods except no fairings. That bike had specified 164 crank hp when new.
He paid for that bike what I've spent on my latest set of carbs!