Was The XR750 Engine At Its Displacement Limit?

General engine tech -- Drag Racing to Circle Track

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Tom68
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Re: Was The XR750 Engine At Its Displacement Limit?

Post by Tom68 »

hoodeng wrote: Sat May 21, 2022 9:47 pm
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A.I.R. Did you know Johnno Stepancic ?
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Re: Was The XR750 Engine At Its Displacement Limit?

Post by rebelyell »

PackardV8 wrote: Sat May 21, 2022 1:14 pm
SchmidtMotorWorks wrote: Sat May 21, 2022 11:23 am The thing that surprised me the most was the speed accomplished with the low power level.
The unsurprising result of making power in air-cooled iron heads and barrels was it was only good for a couple of laps at those speeds before melting down. That's the reason the V.1 XR750 H-Ds are so rare today.

The other thing to which our friend truckedup can attest, the H-D racers were little bikes with minimal frontal area. The H-D Racing Department spent fifty years honing a stone ax to a keen edge.
Well said.
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Re: Was The XR750 Engine At Its Displacement Limit?

Post by hoodeng »

Well spotted Tom, a quiet days testing some other bikes. I knew Johns name around the track but not personally. I was involves with fuel Harley's at the time,,, a well remembered team..
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Re: Was The XR750 Engine At Its Displacement Limit?

Post by Tom68 »

I fixed his Oldsmobile at Sawkas in Main North Road, he put it on pole at A.I.R. when he hit he track next.
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Re: Was The XR750 Engine At Its Displacement Limit?

Post by Geoff2 »

There was a Sportster in the 60s that was in the 200 mph club.....with one gear. From memory the rider's name was Warner Riley & the bike used 4th gear only. Had to slip the clutch to 110 mph...

The SuperSportster was taken to England where it broke lap records using only 3rd & 4th gear....
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Re: Was The XR750 Engine At Its Displacement Limit?

Post by hoffman900 »

Good aero will make up for a lack of power for sure, this is how a bicycle has gotten to 183mph (with a major draft).
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Re: Was The XR750 Engine At Its Displacement Limit?

Post by Truckedup »

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Geoff2 wrote: Sun May 22, 2022 3:17 am There was a Sportster in the 60s that was in the 200 mph club.....with one gear. From memory the rider's name was Warner Riley & the bike used 4th gear only. Had to slip the clutch to 110 mph...

The SuperSportster was taken to England where it broke lap records using only 3rd & 4th gear....
Riley's bike looked somwhat stock,in the naked frame class, 1200 cc's on nitro he ran about 197 mph. I beleve he ran around 205 with a fairing.
The first naked frame bike to set a record at Bonneville was a Royal Enfield double 750 engine machine..Then just a short time late a double 750 Triumph ran about one MPH faster. Both bikes N/A on nitromethane, two engines making about 220 total HP..
Stradding engines running flat out for several miles , five times the original power well beyond the limit of reliabilty...
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Re: Was The XR750 Engine At Its Displacement Limit?

Post by Geoff2 »

A mate of mine actually built a dual Triumph, got it registered & rode it on the street. late 1960s. 650 engines, rear was unit construction, front was pre-unit. Lengthened a std Triumph frame about 14" from memory. It was a pig to ride...
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Re: Was The XR750 Engine At Its Displacement Limit?

Post by Truckedup »

I built this one 5 years ago for land speed racing. My 6 foot height shows how compactness of the build. Two 1956 650 engines on gas making a total of 110 rwhp, Harley 5 speed. The bike made several trial runs about 150 mph on the Maine track...My yonger frind who rides and paid for much of the build keeps talking about more racing but the bike just sits collecting dust
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Re: Was The XR750 Engine At Its Displacement Limit?

Post by rebelyell »

truckedup:
did y'all ever run at the (now closed) ECTA old army airfield runway at Maxton NC ?
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Re: Was The XR750 Engine At Its Displacement Limit?

Post by Truckedup »

rebelyell wrote: Tue May 24, 2022 1:27 am truckedup:
did y'all ever run at the (now closed) ECTA old army airfield runway at Maxton NC ?
No, I ran at the ECTA Ohio track, now closed....Still have the modified production 650 pushrod record there ...
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Re: Was The XR750 Engine At Its Displacement Limit?

Post by rebelyell »

thanks. Not as LS competitor but I attended ECTA events at Maxton NC a few times. Thoroughly enjoyed the laid back open vibe in pits. Saw so many cool bikes & cars ... owners/crew/drivers as well. Vast majority of folk were Yankees who hauled down to hot, sticky flat swampy Maxton; this local native was also favorably impressed w/ how all those Yankees behaved so dang decently. I've been involved as buiIder/owner & occasional driver/rider in other motorsports and seen plenty of attitude; didn't get that at Maxton LS. understand the gubmint took the runway back years ago; sad no more Maxton Mile LS. IIRC, LS event went to Ohio after leaving Maxton. Screaming bikes; everything from some non-descript fifties Italian tiny two stroke to 300+ HP turbo Hayabusa and all else in between. Even a stupid fast streetable Smart car w/ 'Busa in the back; they put on a heck of show one evening in nearby Laurinburg cruise-in. Fond memories of friendly folk. Not unlike that time a gaggle of touring Jersey Speed Skiffs churned up glassy Lake Juniper at Cheraw SC.
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Re: Was The XR750 Engine At Its Displacement Limit?

Post by Truckedup »

Ecta now is in Arkansas on an unused military runway, one mile
I think the 1-1/2 mile track in Limestone Maine is the best paved track. There are east coast Bonneville racers there. Very low key but strict tech inspection.You will see moose in the distance..... There are no engine displacement checks, your word is good..Some cars run 250 mph ,bikes around 230... The late Bill Warner went 310 mph on a partially stream lined bike ,as in a bike you sit on , not inside bodywork..A long boring ride to get there but worth it for racing.
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