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Re: Cam LSA - Vizard

September 9 2011 at 11:39 AM
Dan Jones  (Login 74Pantera)
Member
from IP address 130.76.96.146


Response to Cam LSA - Vizard

> Its interesting, if you look at Dave Vizards writings he uses a higher LSA for
> cams than what he recommends in his LSA charts

His charts are a simplification of the cam selection software he uses.
The cam selection software has much more detailed information including
head flow data, port and runner dimensions, even things like desired idle
vacuum levels. I use his simplified rules as a starting point for Dynomation
simulations. Dynomation will iterate on cam specs

> If we take the same approach as above for a 355 CID Cleveland we end up
> with a recommended LSA of 109.25. Interesting.

That's the same number I got when I went to design the cam for the 351C
dyno mule and where I made the mistake. I went 2 degrees narrower when
the suggestion was to go 2 degrees wider, based upon the canted valves.
That was before I had Dynomation. Now I model the engine in Dynomation
and use the iterator to optimize the cam specs for the maximum average
(not peak) power over a specified RPM. I'll further iterate on LSA to
determine the sensitivity to the LSA. In something like a stroker
Cleveland in a Pantera, I don't typical add the 2 degrees to the LSA
as it is not generally needed. In a heavier vehicle with automatic
transmission, I generally do but I check the sensitivity first. For
best average power, it's best to be too tight than to be too wide.

> I think this makes the 107 LSA in the 351 test mule seem severely tight,
> and perhaps this explains the lower output.

Yes. When I optimized the cam using Dynomation, the peak power went
up by approximately 40 HP. With the flow numbers from the heads we
did for Glen Hartog's 408C (closed chamber 4V with short side radius
work), the simulation predicts 476 HP @ 6000 RPM. The prediction
for the same engine with ported C302B heads is 531 HP @ 6000 RPM
(assumed a bit more aggressive ramp rate). Optimal LSA's for the
two engines are in the 109 to 111 degrees range with similar intake
duration but shorter exhaust duration on the high port heads.
I've toyed with purchasing a new cam for the dyno mule but I'd have
to re-baseline the 4V results for comparison against the other head
types. I've got a 403C (4.005" bore x 4" stroke) with high port heads
going together soon (block, heads, intakes and other bits at the dyno
with stroker kit on order with Brent Lykins). I'm waiting on the
flow bench numbers for the A3 heads but it'll get a custom roller
cam designed using Dynomation. We've used it recently with good results
on both a 408C with CHI-4V heads and a 393C with ported Aussie 2V heads.

Dan Jones

 
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