What is it? Why does it happen? What are the effects? Hopefully our guest/featured speaker will be none other than ... you guessed it ... Cam from Crank This! Performance. Cam's a very busy man working 24/7 to bring you the fine, innovative, quality products from Crank This! Performance (and he's old) but has agreed to try to lead the discussion with a bit of a tutorial followed by a Q&A session in between naps. So big round of applause folks and we'll get this started. (first couple of posts are what prompted this and have been transplanted from another thread. and some quotes from... Cam)
maybe this can help as well.. http://www.chevyhiperformance.com/techarticles/95298_camshaft_lobe_phasing/index.html
Overlap is the period of time when both the intake and exhaust valves are "open". Technically the exhaust valve closing while the intake valve is opening, but they're both off their seats. It's main benefit is scavaging. The exhaust valve remains open while fresh air is vacuumed in. Scavenging utilizes the vacuum force that the exiting exhaust gas creates to fully evacuate the spent gases (and a little clean). Too much overlap for the RPM band and you lose air volume, then decreased cylinder pressure = decreased torque. This why blower cams usually have a wider LSA and less overlap. They don't need much scavenging because their intake charge is pushed in instead of being pulled. The goal with a blower cam is decrease overlap and pack that cylinder full. Too much overlap and you loose boost pressure. Who needs Cam?
How about a short glossary of the main cam specs? Like LSA Seems like the effect of overlap is going to be highly dependent on flow, which would change significantly with RPM? and load? and throttle blade position? If so, what are the tradeoffs? Do you target a narrow rpm band for optimum performance? If you do so does it barely run the rest of the time? What prompted this was related to "tuning by afr". What are the considerations there?
Gezzz Dave, can't a guy ever sleep around here, haha. Adam, what I was discussing was not overlap per say, but the effects of overlap and the injector pulse timing and how it can effect AFr's with misleading information. Anyhow, Dave buddy. I'll gladly join in on this in a couple weeks. I have two major projects to pump out before next Tuesday and than I'm gone for a week. So hold tight and we can have a nice long conversation down the road.
Sorry, earlier the qoutes didn't show up here at work for some reason. I'll check it out when I get home.
In translation, Cam has to buy Hooked on Fonix so he can learn to read. :censored: lol Dave put the quotes in the OP after your first reply.
That's 'cause it took me about an hour to put the thread together... I tried to move individual posts out of the other thread to this one, then tried to copy the whole thread over here and copy posts out of it or merge it (twice... puts them chronological order which I didn't want), and then I finally gave up and just cut'n'pasted into quotes...
LOL I was just trying to stimulate conversation and discussion sorry to cause you so much hassle quick.
Well... I'm interested. Stuff about the EGT too. So it looks like overlap will effect your afr. I would assume that, depending on the timing or fuel, you might be lighting off that charge in the headers or an incomplete burn might still be going on as it gets sucked/blown into the headers. That's got to effect EGTs too. Who knew friggin Cam was goin on vacation for 2 weeks? Maybe Adam will help us out.
Sorry, but I fly out tomorrow for my vacation. Mine is only 1 week though. I don't own a performance shop like Cam does. He's rolling in his driveshaft loop fortune.
