Not to get too far away from our LBCs, exhaust systems for V-Twin motorcycles
like the Harley Davidson are a tremendous aftermarket to cater to motorcycle
tuners. There are several manufacturer's that stand out, but I have noticed a
similar concern with low end to mid-range torque loss with open headers (maybe
not legal, but tolerated her in Kalifornia-for now) that a lot of owners convert
to. The answer from some of the major manufacturers is something called a
"torque cone". This is nothing more than a truncated funnel that fits in the
header where it attaches to the cylinder. It applies enough back pressure at
low
speeds to help with the torques loss, but will pass enough air at high rpms to
not effect the torque in the upper bands. It would be interesting if we could
run a high flow exhaust and muffler on our cars and try one of these torque
cones
at the head. Not cheap at around $70 apiece though.
Mike MacLean-60 Sprite
"Robert E. Shlafer" wrote:
> Well-
>
> You can't have it both ways, for sure.
>
> It's all a matter of extent and tuning for
> specific circumstances. I run a street
> Cooper "S" tune. I'd do better at the
> top end by not advancing the cam
> 4 degrees (belt set-up) but I wanted
> street torque so decided to sacrifice
> the top for really strong bottom end
> and solid mid-range by advancing the
> cam. It works. This thing will "chirp"
> in 3rd with a 3.7.
>
> Same with headers....keep up the gas
> speed where you think you'll need it
> the most. And yeah, the dyno will show
> the way, for sure. Keep all the same and
> simply change the header and watch the
> "changes". I tuned my PO'd '74 "Vizardized" Midget this way. Took off
> the medium bore header/system and
> stuck on the large bore stuff (this engine
> had 11.0-1, large valves, VP3 cam, 1.5RR, 45DCOE....the "works" insofar
> as a streetable Spridget goes.
>
> Upper end Horse Power zoomed
> while low end took a beating and to some
> extent, so did the low end of mid-range.
>
> But, man, when this thing got to 3,500
> it absolutely took off and went to 7,000
> in a heartbeat and had no problem going
> down the thruway at a sustained 6,000
> rpm in 4th with a 3.9. Made Stamford
> to Bridgeport Airport in slightly less than
> 20 minutes that morning....not a cop in
> sight at 4:30AM. Only time I've ever done
> this but conditions were right. 'course, that
> was about 20 years ago!!
>
> Today, I'm into low end and mid-range
> torque. Medium bore LCB, 1.75 exhaust
> and RC40 rear box. "Everything" under
> 5,000rpm. Works! Now, if we could just
> come up with a water delivery system to
> "cool" a Judson!
>
> Cap'n. Bob
> '60 :{)
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