Hello to everybody. Hope you have all had a good Christmas.
Surfing the web today came across this item.
Being a novice can anybody enlighten me, as it seems to go against all the advice given for engine upgrades:hmmm:
Smaller ports on Harley Davidson
V i e w e r F e e d b a c k
Yo MotoMan:
I've been reading your e-columns for a while with some considerable amusement. I'm finally compelled to write because of the reference in your latest issue to Harley-Davidson motors & the question of whether small ports would work in that application.
I road-race a Buell which, of course, is fitted with a H-D Sportster motor which comes with upgraded heads, cams, pistons. In stock tune it delivers approx. 85 h.p. and 80 ft/lbs of torque at the rear wheel. Virtually ALL Harley race tuners use typical small-block Chevrolet NASCAR-type technology to build race motors on this platform (read: BIG cams, BIG ports, LOTS of squeeze). They then spin the motors at 8,000+ rpm to make it all work. Bearing in mind the H-D V-twin motor is basically an over-sized air compressor, the results are predictable: manifestly unreliable motors which struggle to keep up with Ducs, RC51's, etc., etc. They typically make 110 h.p and 90 ft./lbs. of torque (rear wheel) with very narrow power bands.
After a 2 season alliance with a local Harley dealer (with a lot of racing experience) resulted in nothing but innumerable broken parts (including one spectacular exit of a con rod through the transmission resulting in a lurid rear wheel lockup and slide for a couple hundred ft. but, Hey!, I didn't fall down..) and major expense, I went looking for a different solution. I found it in the person of a Mr. Bob Johnson of J.E.T. in Westerly, Rhode Island. He has a fascinating background in leading edge automotive head design, but currently does only one-off customer engine projects, both bikes and cars.
To make a long story short, Bob built a new race motor for my Buell based on his research and applied mathematics to produce the best port velocity and cylinder-fill characteristics, i.e. small ports. In fact, his research, and empirical testing reveals that the most powerful cylinder head Harley makes (regardless of engine size) is their "little" 883 head. He has made 100 h.p. in testing by simply bolting (with some minor modification for fitment) a set of 883 heads on a big twin (1340) motor with appropriate cams.
And now the BIG QUESTION: how does my motor work???? At 10.1:1 compression, Red shift 567 cams, 44CV carb, modified intake manifold (to straighten the runners out), the puppy makes (rear wheel) 108 h.p, @ 6800, 100 ft./lbs. of torque @ 4500. 86% of max torque is available between 3,000 and 6800; the acceleration curve of the motor is nearly vertical, oil temp never exceeds 150 degrees, it runs on pump gas. Not a single mechanical failure. The bike pulls like Jack-The-Bear, blowing off Ducati's, Hondas, Suzuki's, everything in the class. We have so much torque available (and THAT'S what moves the bike, not h.p.), we're considering replacing the 5 spd. Trans with a 4 spd. I really only need 3 race gears and a low for the pits/start line. The bike is much easier to ride fast because the torque is available everywhere and is smoothly predictable, unlike the typical H-D race motor which is tuned to produce h.p. waaay up in the corner of the power curve.
Bob calculates there's another 10 rear-wheel h.p. in the motor by going to even smaller ports (I presently am running 1203 'Thunderstorm' heads modified by Bob to shrink the ports) with 883 heads and more cam, but the power delivery would be more radical and would probably require a slipper-type clutch to be rideable (due to deceleration compression). I haven't gone that extra step simply because I don't need any more power!! (Imagine that!).
Sooooooo MotoMan ???
The answer is, YES small port technology works on two valve motors, and specifically H-D motors !!!
Hope you find this interesting
Cheers !!
~ Robin
---------------------------------------------------------
Hi Robin !!
Thanks for the incredibly encouraging info, I'm suddenly starting to turn "orange and black" !!! I want to work on some Harleys !! Look for more info in upcoming Power News issues about the mighty V Twins from Milwaukee !!
~MotoMan
Surfing the web today came across this item.
Being a novice can anybody enlighten me, as it seems to go against all the advice given for engine upgrades:hmmm:
Smaller ports on Harley Davidson
V i e w e r F e e d b a c k
Yo MotoMan:
I've been reading your e-columns for a while with some considerable amusement. I'm finally compelled to write because of the reference in your latest issue to Harley-Davidson motors & the question of whether small ports would work in that application.
I road-race a Buell which, of course, is fitted with a H-D Sportster motor which comes with upgraded heads, cams, pistons. In stock tune it delivers approx. 85 h.p. and 80 ft/lbs of torque at the rear wheel. Virtually ALL Harley race tuners use typical small-block Chevrolet NASCAR-type technology to build race motors on this platform (read: BIG cams, BIG ports, LOTS of squeeze). They then spin the motors at 8,000+ rpm to make it all work. Bearing in mind the H-D V-twin motor is basically an over-sized air compressor, the results are predictable: manifestly unreliable motors which struggle to keep up with Ducs, RC51's, etc., etc. They typically make 110 h.p and 90 ft./lbs. of torque (rear wheel) with very narrow power bands.
After a 2 season alliance with a local Harley dealer (with a lot of racing experience) resulted in nothing but innumerable broken parts (including one spectacular exit of a con rod through the transmission resulting in a lurid rear wheel lockup and slide for a couple hundred ft. but, Hey!, I didn't fall down..) and major expense, I went looking for a different solution. I found it in the person of a Mr. Bob Johnson of J.E.T. in Westerly, Rhode Island. He has a fascinating background in leading edge automotive head design, but currently does only one-off customer engine projects, both bikes and cars.
To make a long story short, Bob built a new race motor for my Buell based on his research and applied mathematics to produce the best port velocity and cylinder-fill characteristics, i.e. small ports. In fact, his research, and empirical testing reveals that the most powerful cylinder head Harley makes (regardless of engine size) is their "little" 883 head. He has made 100 h.p. in testing by simply bolting (with some minor modification for fitment) a set of 883 heads on a big twin (1340) motor with appropriate cams.
And now the BIG QUESTION: how does my motor work???? At 10.1:1 compression, Red shift 567 cams, 44CV carb, modified intake manifold (to straighten the runners out), the puppy makes (rear wheel) 108 h.p, @ 6800, 100 ft./lbs. of torque @ 4500. 86% of max torque is available between 3,000 and 6800; the acceleration curve of the motor is nearly vertical, oil temp never exceeds 150 degrees, it runs on pump gas. Not a single mechanical failure. The bike pulls like Jack-The-Bear, blowing off Ducati's, Hondas, Suzuki's, everything in the class. We have so much torque available (and THAT'S what moves the bike, not h.p.), we're considering replacing the 5 spd. Trans with a 4 spd. I really only need 3 race gears and a low for the pits/start line. The bike is much easier to ride fast because the torque is available everywhere and is smoothly predictable, unlike the typical H-D race motor which is tuned to produce h.p. waaay up in the corner of the power curve.
Bob calculates there's another 10 rear-wheel h.p. in the motor by going to even smaller ports (I presently am running 1203 'Thunderstorm' heads modified by Bob to shrink the ports) with 883 heads and more cam, but the power delivery would be more radical and would probably require a slipper-type clutch to be rideable (due to deceleration compression). I haven't gone that extra step simply because I don't need any more power!! (Imagine that!).
Sooooooo MotoMan ???
The answer is, YES small port technology works on two valve motors, and specifically H-D motors !!!
Hope you find this interesting
Cheers !!
~ Robin
---------------------------------------------------------
Hi Robin !!
Thanks for the incredibly encouraging info, I'm suddenly starting to turn "orange and black" !!! I want to work on some Harleys !! Look for more info in upcoming Power News issues about the mighty V Twins from Milwaukee !!
~MotoMan
