looong intake runners for HP

Esmerela said:

Long intakes fine for top end power, but getting it sharp coming off the bottom to mid range, will be a challenge.

Best Regards

Esme

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I read a story about Leo Goff years ago that kinda flies in the face of that. Some guys were roadracing a Norton at Daytona and couldn't get it to run coming onto the banking. They called Leo and he told them they had the "typical Norton midrange miss" and that full power would come with the addition of some velocity stacks to lengthen the intakes.

Long story short, nobody in Daytona had any Amal velocity stacks, so they cut the ends out of some beer cans and the midrange power returned.

I don't believe much in Paul Dunstall. Back in the day and lot was about commercial imperatives. Gus Kuhn and Peter Williams might be better sources of information. If you think back to the 1960s, there was not much after-market stuff around and Paul Dunstall got in at the right time when you could sell anything.

It is interesting that when Peter Inchley was playing with piston-port Villiers two strokes, he could not get them to rev high at first. Then the long bell-mouth fell off the carburettor and the motor revved right out.

acotrel said:

I don't believe much in Paul Dunstall. Back in the day and lot was about commercial imperatives. Gus Kuhn and Peter Williams might be better sources of information. If you think back to the 1960s, there was not much after-market stuff around and Paul Dunstall got in at the right time when you could sell anything.

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I think you have a point there, but back in the day Norman White was ferried over to the US for NVT were getting flack from a dealership that did not believe the factory claims for standing quarter times . He had run a sub 13 ec time on a standard bike in the UK , presumably at Thruxton.So in front of the American trades sceptical finest , on a stock bike of their chosing he ran a quarter in 12 .24 I think. The lesson is that the inlet length as standard must be near as damn it right. But it certainly is not around the near thirteen inches cited here but half of that . In terms of waves that makes sense , so going outwards the next length would be 26inches for an optimal ram effect .

My '68 P!! Ranger dragster lesions tells hobot that what the 12.24 sec 750 really showed - was that Greatest generation were better men than afterwards. so bold=brave enough to do what it actually takes to make the factory short intakes come into their own from clutch drop release on. Spectacular display of intense skill not to spin out or wheelie vertical nor blow AMC guts out on track.

BTW flat track is similar to drags in sense engine is essentially all WOT top end rpm tire spin power band too. One the winning-est is Kelly George's factory 850 ran a single 38 carb on normal length manififolds. Seen it win but out dragging a National Level 1000 cc Harley XR which eat up a few elite Norton 920's of famous devoted builders. I was forced to ride it, but on hard rough surface not the loose stuff naked. Could not get much past mid range before front lifted by roll on in 1st 2nd about 80ish mph so never felt its full power hits just roll on to mid range. Whiplash response w/o long tracks. go figure.

Both my Combats felt like a 3rd piston hit after 6800 stretching wrists pressing butt more as front lifted a few inches in 1st 2nd. So if not always over torque peak rpm longer throats help. On flat drag slick built for it 750 P!! did mid 10 sec 1/4m with dual Amals factory short manifolds.

Norman was on last of 750's model which weighs ~430 lbs if had turn signals. Assume Norman weighed 180 suited up for a total 611 lbs then HP is 65.85 computed from your vehicle weight of 611 pounds and ET of 12.24 seconds. Norton told truth in advertisements that provided 9.25 lb per hp w Norman on a 6.5 lb/hp Combat.

In 1973 a privateer Combat spec 850 did 12.1s 1/4m w/o long intakes.
In 1973, Cycle World also did an article "Turn your 850 Commando into an 11 second terror" It involved bigger carbs, head work and a cam.

acotrel said:

I don't believe much in Paul Dunstall. Back in the day and lot was about commercial imperatives. Gus Kuhn and Peter Williams might be better sources of information. If you think back to the 1960s, there was not much after-market stuff around and Paul Dunstall got in at the right time when you could sell anything.

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Cycle World tested the Dunstall 810 and ran an 11.9 second 1/4 mile with it. This was the fastest time of any production motorcycle they had tested. It was also faster than any other production bike tested by others.
As such, the Dunstall 810 is listed as the first production motorcycle to 1/4 in under 12 seconds.
Fair accomplishment.