Just wondering, how much overlap is actually ok ? From what I can gather zero is best.......correct ?

 

that's a subjective question , and it depends on your personal preference. Overlap is ok.

 

Zero like no overlap? Isn't the purpose of "overlaping" the cams to create the scavenging effect? So zero...not best. Thats why you have adjustable cam gears.

 

Scavenging effect is more important with normaly Aspirated Engines........

Just wondering how much power certain durations of overlap may cost on a 65lbs/min compressor wheel output.......

 

if you're putting on a turbo that big, you better already have a good understanding of what overlap is, and is acceptable, or you're in for a big, big dissappointment.

 

Well, ok to be precise, reversion costs power..........which can be affected by overlap depending on the Exhaust manifold, Turbine size, Turbine A/R & Exhuast..........I think it'll just be easier to stick it on the dyno and see how we go adjusting it via a set of pulleys

 

That doesn't mean its unimportant on turboed cars. You can still use it for a benifit.

And like dubble said about the personal preferance, cars are different, your set up is different from everyone else, you will only find out how much is too much from your own R&D when tuning your car.

 

+1 on just R&Ding it yourself. Just strap it down and start movin the gears around, see how you like it best.

 

Been there, done that. The same trends that apply to other engines apply to the EVO.

Nevertheless, zero overlap is definitely NOT the best arrangement. Turbo cars benefit from overlap until or unless a high PR creates reversion.


Presently, I have HKS 280s set at 0/-2 with a GT35R setup. This gives an LSA of 108 deg, with an advertised overlap of 64 deg, and an overlap of 6 deg @ 1 mm lift. I'm getting ~455whp (DJ) at ~ 23 psi on 93 octane, and ~495whp (DJ) at ~25 psi on 93 + meth. I can't turn the wick up further until I upgrade the clutch. Needless to say, I'm not suffering from a reversion problem.

So long as there isn't a high PR situation caused by a poor choice of turbo, restrictive exhaust manifold, or restrictive turbine housing, overlap is your friend, not your enemy.

 

AFAIK, zero camshaft overlap exists only in the the theoretical design of a 4 cycle Internal Combustion engine (Otto cycle). Very early on, probably 100 yrs ago, they found zero overlap was far from optimum as it does not allow enough time for the intake and exhaust to optimally function so they increased the duration on both. There probably hasn't been a zero overlap automotive IC engine built since?