Greg,
I think what he is actually refering to is relieving the top inside edge
of the cylinder block to enhance valve flow inside the cylinder.
If the duration is increased for the same lift, the valve opening &
closing rates will be quicker, not slower. The valves have to open
quicker to get to the same lift in a shorter time to give more duration.
Thus stiffer springs may be required.
Dave Russell
BN2
Greg Wilkinson wrote:
> Hi Steve, Something is definitely missing in that equation. If only
> the duration is increased, why would you need to port the block? Same
> holds for the stronger springs. If the lift is the same over a
> longer duration, the valves would probably open and close slower than
> stock for a given RPM. Sure it's not necessary to put headers on, but
> I don't think a cast exhaust manifold can breath as well. Isky
> reground my BJ8 cam to a slightly longer duration and higher lift,
> the base circle of the lobe is almost flush with the shaft now.
>
> Best, Greg
>
> -----Original Message-----
>
> Hiall,
>
> Saturday I heard from someone who should know (Kurt Tanner) that a Mk
> 1 3000 cam in good shape can be ground to 290 degrees with all other
> specs per stock and that that, in combination with strong valve
> springs (and relieving the block) will "transform" a Mk 1 to BJ8 plus
> performance while keeping the stock 1-3/4" carbs. He said it's not
> necessary to add steel tube headers but using a Monza exhaust adds
> horsepower as well. He showed us one--all the pipes are larger--I
> didn't measure it but the tailpipe looks like 1-3/4 or 2" and one
> could improve on the wussified sound of the Monza by welding straight
> pipes on the end in place of the muffled tips. Tanner says the Monza
> fits through the roadster frame cutouts as well.
>
> He said using the smaller carbs with these cams works better than the
> 2 inchers because they'll "almost" idle due to better velocity than
> the large pots.
>
> He has some old unused race engines he's acquired with these cams and
> believes they were originally either reground by Isky or Sig Erson.
> He has installed one of these cams in a roadster purchased by a
> knowledgeable customer who, he said, was amazed at the power and said
> it was the fastest Healey he'd driven.
>
> I notice Denis Welch's hot street cam is 278 degrees--Tanner said the
> BJ8 cam is 265 degrees.
>
> Discuss.
>
> -- Steve Gerow Pasadena CA 59 BN6
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