Fastest production pushrod 750 at Bonneville

I got a call today from Steve Adkins of preservation motorcycles. He's rebuilding a Kenny Dreer 880 and was looking for pistons when we strayed over to another bike he built for Randy Johnson. According to Steve its a production 750 Norton with a few trick JS internals and Axtell style porting that holds the SCTA 750cc production pushrod record on gasoline (126mph at Bonneville in 2012 with a best one way speed of 128 mph). He's trying to push the record up to 130 mph. To supply enough fuel at sustained WOT it required Alk type Amal carburator bowls and huge 340 main jets (not far off from the 325 mains I used to race with). This is a bike that looks stock on the outside (to clear the rules). Mufflers are gutted and air filter element removed. Remember that the high altitude and less than ideal salt softness can cost you 5 to 10 mph compared to ideal sea level conditions on asphalt. The amazing thing is that after running wide open at Bonneville - he took off the number plates and now uses the same bike on the street for transportation and will probably put the plates back on it and go for another run come next season's Bonneville speed week. That's a testament to the versatility of Nortons and it reminds me of the days I used to road race and test my racer on country roads.



Note the hot rod pickup in the back.

Congratulations !
A testament to its durability then that its a street bike in between times.

Any idea what cam is in it ?

Very impressive what the hidden upgrades can do, but where's the oil cooler?

128 MPH. - Wide Open - On Salt
I can only imagine but I bet it was one thrilling ride.

Good for him !!!!

Cool, thanks for that, Jim.

Impressive work.

xbacksideslider said:

Cool, thanks for that, Jim.

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+1

Ya Hoo, just think what it could do if he put it on a diet & lost the weight of all those stock parts.

gtsun said:

Ya Hoo, just think what it could do if he put it on a diet & lost the weight of all those stock parts.

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It wouldn't make any difference, indeed it might make it slower. Going fast on the salt is all about grip, or lack of it. Many vehicles add weight (lots of it!) to increase grip.

hobot said:

...but where's the oil cooler?

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Steve!

Stop that!

all I can think of is "Rollie Free" position.

congrats. Ive had my 750 commando up to 99ish m.p.h. on the san mateo bridge. tucked in of course.

126mph at Bonneville in 2012 with a best one way speed of 128 mph). He's trying to push the record up to 130 mph.

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Makes the claimed top speed of one of our forum members rather dubious.

When comparing speeds at Bonneville with speeds on pavement at sea level, you need to keep in mind the difference in density altitude and traction between the two locations. When I ran my Norton at Bonneville this year at the AMA meet, the density altitude recorded on my timing slip was 5964 ft. That makes a significant difference in horsepower. And the salt was so slippery that my tach showed an rpm that would have given me another 20 mph if the rear wheel hadn't been slipping so badly. My speeds at Bonneville in previous years with a 750 Commando race engine were in the high 120s and low 130s under good conditions, so the 126 mph average for Randy's bike seems about right to me. He would probably get at least another 10 mph at something like the Texas Mile event.

Ken

jseng1 said:

According to Steve its a production 750 Norton with a few trick JS internals and Axtell style porting that holds the SCTA 750cc production pushrod record on gasoline (126mph at Bonneville in 2012 with a best one way speed of 128 mph). He's trying to push the record up to 130 mph. To supply enough fuel at sustained WOT it required Alk type Amal carburator bowls and huge 340 main jets (not far off from the 325 mains I used to race with). This is a bike that looks stock on the outside (to clear the rules). Mufflers are gutted and air filter element removed. Remember that the high altitude and less than ideal salt softness can cost you 5 to 10 mph compared to ideal sea level conditions on asphalt. Note the hot rod pickup in the back.

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Isn't this like cheating. Isn't it sort of a modified unit rather than a "production" unit. Just how far do the rules allow for when it come to tweaking the internals?
When records are broken isn't there some sort of an inspection to validate these class claims?

pete.v said:

jseng1 said:

According to Steve its a production 750 Norton with a few trick JS internals and Axtell style porting that holds the SCTA 750cc production pushrod record on gasoline (126mph at Bonneville in 2012 with a best one way speed of 128 mph). He's trying to push the record up to 130 mph. To supply enough fuel at sustained WOT it required Alk type Amal carburator bowls and huge 340 main jets (not far off from the 325 mains I used to race with). This is a bike that looks stock on the outside (to clear the rules). Mufflers are gutted and air filter element removed. Remember that the high altitude and less than ideal salt softness can cost you 5 to 10 mph compared to ideal sea level conditions on asphalt. Note the hot rod pickup in the back.

Click to expand...

Isn't this like cheating. Isn't it sort of a modified unit rather than a "production" unit. Just how far do the rules allow for when it come to tweaking the internals?
When records are broken isn't there some sort of an inspection to validate these class claims?

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The officials are actually pretty tight about cheating and yes there are inspections. For example - they tried removing the aluminium plate on the rear wheel hub but it wouldn't pass tech so they had to replace it. They wanted to put an air scoop on the fuel tank vent to pressurize the tank and supplied more fuel to the carbs (as some do) but that is not allowed is production class. Their closest competitor was a Guzzi but it was disqualified because it was running twin spark plugs per cylinder. Apparently you can change things like pistons, rods, cams, valve springs - Those parts have been swapped out for off the shelf lightweight JS domed pistons, longer rods, JS2 cam with radiused lifters and beehive springs. Not all that much really and not much hotter than an original 750 Combat - just more efficient and reliable with less energy wasted starting and stopping the reciprocating parts and higher compression which is allowed. But those things together with the Axtell head port copy were enough to claim the record. Gutted mufflers, missing air filter element, and handlebars are the only differences you can see on close inspection from the outside. You have to pay attention to bore & stroke etc, (displacement is checked by officials) and anyone can protest and prevent a competitor from going too far. What they consider a production class is not an exact off the showroom model, but it has to look the same. You just have to know what will pass and what won't. As in all racing - competitors will usually do everything they can to go faster just short of the point where they are disqualified. Some internal modifications are allowed. But its nothing like the extreme modifications you see in "stock car" racing when hardly anything in the vehicle is original.

To get it over 130 may be tough. Options are a stage 3 cam, ceramic type bearings to reduce friction. And short stroke if that is allowed (I'm not sure it is). You start pushing against a brick wall where small gains become harder and harder to achieve.

The SCTA rules for production class bikes allow you to do pretty much anything you want inside the engine, as long as you meet the displacement limits and keep OEM heads, cylinders, crankcases, carbs, air cleaners, etc. The exhaust must look stock from the outside, and from the end, i.e. is has to have the same size exit hole in the muffler. You can do what you want to the inside of the muffler. The rules specifically require that the bike and engine have stock external appearance. Paint and such do not have to be original colors. The rules do allow different handlebars, as long as they mount in the original mounts, and are no more than 15" above, 4" in front of, and 4" below the original mounts. Basically it has to look like a stock bike, but you can add flat or slightly dropped bars. You can do a lot inside the Commando 750 engine, but the 32 mm carbs will probably be the limiting factor.

Ken

I've never run SCTA, so this is a real question.
Do the carbs have to be original, or just LOOK original (bored out etc). Back in my Superbike racing days the rule was anything goes, as long as it "looks stock from 50 feet".

The rules just say you must use OEM carbs. You might get by with boring them out. Then again, you might not. If I recall correctly, the most I ever managed with the original 32 mm Amals was 33.5 mm. And that was legal at the time ('70s) for the class.

Ken

lcrken said:

The rules just say you must use OEM carbs. You might get by with boring them out. Then again, you might not. If I recall correctly, the most I ever managed with the original 32 mm Amals was 33.5 mm. And that was legal at the time ('70s) for the class.

Ken

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What about a short stroke in this class?

jseng1 said:

What about a short stroke in this class?

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I don't think so, Jim. The rules read "This class is limited to production, street-legal motorcycles of which 500 or more have been produced and which are available to the general public through retail motorcycle dealers."

I don't think Norton ever delivered any Commandos to the public with the short stroke engines. They sold a lot of short stroke engines to racers, and others, and some may have been installed by dealers, but I've never seen any evidence that any were delivered that way from the factory. I could be wrong, but even so, they certainly never made 500 of them available through dealers. According to Brian Slark, during a discussion Rob Tuluie and I had with the AHRMA officials way back when, Norton did not sell any production street bikes with the short stroke engine. They did build at leas a few of the "Thruxton Club" production racers with the short stroke engine, but they weren't street legal, and I've only ever seen reference to two of them, so there couldn't have been many built.

So the short stroke is clearly not legal for the Production class, but that doesn't mean you might not sneak one past the officials, particularly if you had a copy of the advertising brochure that said they were available in Commandos! I don't think I'd try it. It's pretty expensive to run a bike now at Bonneville, and it would be a shame to get there and be declared illegal for the class. I have run a short stroke 750 at Bonneville in the Modified Production class, where it is legal, and even held some records with it, for a while.

Ken