FYI this was in my previous thread.

You want minimal overlap on a forced induction car as you have no need to draw the intake charge by the use of scavenging from the exhaust. There is one big problem that you can't put a good finger on and that is the ramp of the lobe. The other issue is that Crower measured the factory cams using their techniques so you can only use the standard 0.050" and lift rather than Advertised when comparing with other companies like IP and Skunk II.

To Make It Less Confusing I modified their table

AP1..........................Dur@ 0.050......Lift (in).......Adv Dur
Vtec Int..........................226°............0.49 8"..........300°
Vtec Exh.........................222°............0.459 "..........298°

AP2..........................Dur@ 0.050......Lift (in)........Adv Dur
Vtec Int..........................224°............0.48 7"...........296°
Vtec Exh.........................222°............0.475 "...........296°

Crower FI STG II.......Dur@ 0.050......Lift (in).........Adv Dur
Vtec Int..........................230°............0.50 0"............280°
Vtec Exh.........................226°............0.466 "............276°

BTW: There is still one missing variable, in Crowers data, what is the pre Vtec lobe specs (Though they are less important)

If you notice in Crowers info the ratio between the duration at 0.050" and Advertised is much different between their FI cams and the factory. Now this assumes that they used the same procedure for measuring each, which is what they say. So the difference is made in the ramp of the lobe being different.

Lets not forget about the BTDC and ATDC, as the centerlines also make a difference.

I would suggest using software like Desktop Dyno to illustrate differences as you change certain criteria.

Crower Data


Skunk II Data

 

for turbo cars

 

Not true, if you have a higher MAP than EMAP (which a good twin scroll divided turbo setup would) having overlap allows exhaust gasses and combustion byproducts to be "pushed" out during overlap so the cylinder is filled with a better fuel/air mixture. On a log setup you would be absolutely right but you can't use that as a blanket statement...

My previous comment about whichever had more overlap and duration was under the impression they had the same lift which was apparently a bad assumption. Now it's anyone's guess.

 

I agree with lift and duration but do not agree with the a bunch of over lap on turbo cars.

But to each there own.
+ I am not a turbo guy

 

AKA Positive pressure delta.....


Yes in the very small operating range where positive delta is a achieved then yes I would agree with you.

Problem is the turbo does not stay in that range for very long/ is very hard to obtain this positive delta.

I have sen it in VVT and in axial compressors/turbines and very rarely in 99% of the turbo applications out there.

 

Yes this was written with respect to turbos, supercharged cars can still benifit from exhaust scavenging.

 

My MAP is 15% higher than EMAP throughout the whole power band. I'm sure any other equal length sidewinder twin scroll with a decent size turbo would be around the same.

 

MoTec

 

holey sh)! that is nice

 

Oh I guess I forgot to state that my turbo is a GT3582R

If anyone has an AP2 exhaust cam for sale I might be willing to buy it, just PM me a price