techinspector1 said:
Posted by xntrik:
"The best thing you could do for your "street" driver power is tighten the lobe separation. Ideal is 108*"
I've been doing some reading and happened on the article in which David Vizard did testing on a 350. He made best power with a 108* LSA. The same article (Popular Hot Rodding) shows a graph that substantiates Vizard's findings and uses cylinder displacement divided by intake valve diameter to find the best LSA for a particular motor. Using that chart with a 383 and 1.94" valve, the best LSA for the motor would be 104*.
xntrik, I'd like to have your input on this please.
Sure, :welcome:
I follow Viz. Viz is correct.... he invented the graph. So I don't assume to know more than the teacher.
First that CC circle track cam fiscus has is not cataloged... but it looks like close to 100* overlap on 104-5? LSA.
Big valve, 406.
Note that when you browse a CC catalog using the 383 cube, when you see the specs, read the cam characteristics for the next smaller cam..... remember you have another 30 cubes over the 350, so the cam seems 6* tamer in a 383, like firestone said. (their commentary is for 305-400 engines :mwink: )
Viz says 1) LSA, 2)overlap which determines 3) duration, 4) always all the lift you can get.
104.5* ideal on Viz's chart, .8* wider for 2.02 valves. (fiscus never said)
Remember
Using higher lift 1.6 rockers for more lift, you can add 1*, so I did 105.3 + 1 = 106.3. A 107 ? If you use small 1.94 valves knock off 1* of LSA. (longer rockers open valves .005 farther at .050 tappet lift, IS a bigger overlap triangle)
My incorrect 108 would be much better than the 112 he was looking at. 8* more overlap, but more torque too.
Viz says about 55-60* overlap for regular street use 383.
Comp is recommending the XE262H split duration 110 LSA (462 lift 1.5, 493 lift 1.6) to smooth the idle that gives tame 0 overlap at .050, 46* overlap at advertised. If we use 1.6 rockers this makes it seem 1* shorter.
XE262H spreads the longer exhaust lobe, opening the ex valve 8* sooner and closing it at the same point as a single pattern 262/106 cam.
This shortens the power stroke 8*, lessening torque slightly, but allows a better blow out at higher rpms. That might answer PatM's question
Trade off is less torque, but better hp above 5200, and a straighter torque curve, though less peak.
If we look at firestone's split pattern XE268 on 110* (477 lift 1.5, 509 lift 1.6) it has a 54 overlap, and 7* overlap at .050 (right in Viz's range, but on a wider than ideal LSA).
A single pattern 218/218 (262 adv) special on 106* (454 lift 1.5, 484 lift 1.6) we would have 50* overlap/ 6* overlap at .050,
Will our young man be able to live with that overlap with his stock stall converter, even though it will make more torque from 1800 on up? I think he needs an actual 1800-2000 converter with a tighter cam. Remember too, he has a
dual plane intake :thumbup:
Since fiscus's 383 is underheaded and undervalved.... it should make gut busting torque (probably 380 from 2400-4500, 440 peak) and pull well giving up some at 5400 or so, being great with 3.08-3.23 gears, and getting decent mileage at fiscus's 3200 running weight, I personally would go to true 2000 stall.
Now throw a wrench in this...
....
The dynamic compression might stand a single pattern 224*/106*(270 adv) cam 477 lift w/1.5, 509 w/1.6, 12* overlap .050, 56 overlap
Since CC would be custom grinding the cam anyway, a different flat tappet lobe from the catalog could be used, and the lift could be increased slightly to about 530 w/1.6 .....
And you thought this would be simple. :mwink:
Added= Since CC cannot assume nor control the variables of exhaust systems, etc..... they made a good recommendation in the XE262H cam.
Me. I think either firestone's XE268H or my 224/106 single pattern with a 2000 stall would be :thumbup:
