Ashley Southgate wrote:
[... snip ...]
> Degrees duration ; " 264" " 264"
> lift inlet at cam 292" at valve 438"
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> inlet open 26btdc closes 58abdc
> ex open 62 bbdc closes 22 atdc
ok, that's 48 degrees of overlap.
> can see that lift at cam 292 X 1.5 rocker = 438
> at valve,question can a 1.61 rocker ratio be of any
> value.
I'm not familiar with the TR4 engine, but is seems that
a lift of 438 would be substantial enough. How much
more lift is that over stock? You might get into trouble
of valve springs binding with any more additional lift.
Be sure to check that none of the spring coils touch when
the valve is full open.
> Question is this grind suitable for a
> fast road TR3b & suitable for getting away at traffic
> lights & town running.
I'm basing my comments on my research on TR6 grinds, but
the key to getting a good idle is not too much overlap
(having the intake and exhaust open at the same time).
Based on talking to racers, a cam grind which has over
60 degrees of overlap is difficult to get a nice idle.
Personally, I would stay around 50 or less for a street
car, but I really like my car to idle, and not lope.
The other thing to consider WRT idle is duration, but
that reflects back to overlap. (More duration means
more overlap, in most cam grinds.)
The addtional lift will help your car breath, however,
remember that everything in your engine is a system. You
might want to consider a free flow exhaust, or some intake
modifications to get full advantage of your cam. On
the other hand, if you plan to keep the RPMs low you'll be
fine. I find that many people are interested in High
Performance, however they tend to drive their cars in a
lower RPM range anyway, like myself. I rarely take my
car over 5000 rpm, which is where many HP cams make
power.
Anyway, it sounds like you have a nice street cam in your
hand, and it'll perform just fine for you.
Good Luck,
-Scotty '75 TR6
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