using Dean's "Performance #1" cam

[art11144]

I've replaced the stock R16 cam (orig specs say valve lift = 0.335" valve lift/256 deg duration but Dean's site says "std grind" = 0.350 valve lift/248 deg duration (maybe stock cam and Deans' std cam readings not taken at same initial lift?) with a "Dean's Perf #1 cam" having valve lift = 0.420" valve lift/260 deg duration. So not a major increase, but still a change.

My basic question is: should I be modifying the spec'd initial timing (16deg BTDC @ 600rpm) with new cam? Also, engine idles smoother @ higher rpm (800-1,000 rpm) so I keep at about 1,000 rpm. But timing is set at 16deg BTDC @ 800rpm so mech advance does not kick in when setting timing. And I seem to remember from old "street hot rodding" days that we'd up idle a bit for smoother idle if cam was a bit "hotter".

Any suggestions or experiences from folks who may have changed cams? Should I be looking at modifying any other general specs (points dwell angle, etc...)

Thanx,
Art

[AidanDawn2000]

Usually I think the main thing to do when you swap cams is change fuel jetting. And yah more lift / overlap / duration all result in less vacuum at idle so you end up with a slightly higher idle speed to still get em smooth

[Gregs672000]

A 1000rpm idle is fine. It's not a radical change, but as Aidan noted you may want to monitor the engine performance at higher rpm as more lift and duration may want more fuel since you're taking in more air... hard to know without a wide band A/F meter. If the engine hesitates a bit with additional throttle now at higher rpm, you may want to talk with Keith about what SU needles will richen the mix at higher rpm. If she runs good, just monitor your plugs for a lean condition, listen for any ping and enjoy!
Cam lift is lift, but to calculate total valve lift you have to multiple it by the rocker ratio (1.4 on a U20). However, duration numbers that get advertised can be all over the place, and thus what you want to compare to is "duration at 50 thousands" as that's apples to apples so to speak. For example, my Isky U20 grind is .384 cam lift x 1.4 rocker ratio for a total valve lift of .537 (that's a lot and is close to coil bind on the springs). Duration is 278 degrees (same as a "B" cam listed at 280) but is actually 246 at 50 thousands. The engine makes max torque at 4800rpms. I expect you moved max torque up a few hundred rpm but is probably making more torque at the same rpm as the stock cam so it should be happy and not peeky. Should be good!

[art11144]

Thanx guys. Totally forgot about the needles and nozzles issue! I was having "stumble" issues at 3500 - 4000 rpm that I solved by going with thicker dash pot oil (changed to 30w vs ATF). But back now that I've readjusted valves and reset A/F mix, but did mix at about 2500 rpm. Next test drive on hwy I'll try quick test - pull choke a bit at 60mph/approx 3200rpm and see what happens. If stumble goes away, then yes too lean at higher rev/speed. And ask Keith as you suggest also.