Im wanting to optimize my setup and am curious how overlap effects boost. My current cam has +5* of overlap. The cam pat G spec'd for me has -4* of overlap. so does that mean that the intake and exhaust are both open for 5* with my current cam? what is the ideal overlap for a boosted motor? Specifically a procharged motor.

 

Yea overlap just means the intake valve opens while the exhaust valve is still open. And with the pat g cam, the exaust valve will shut 4* before the intake valve opens.

 

Ok, so since both valves are open at the same time I would bleed off boost, correct?
Would I be better off with a cam with more negitive overlap to keep from bleeding off boost which would net me more power. Is that right?

 

That's the general consensus about it in most cases. Hence the specs you got from Pat G.

 

Too much overlap and it will restrict high rpm power and timing that you can run. Also something to note, if you've got a power adder that can flow the CFM you can get away with more overlap. There are some people that claim you can make more power and some of the top dog setups actually have quite a bit of overlap.

 

Less overlap drives smoother and isn't as tempermental, but isn't as aggressive up top. My turbo cam has -8*

 

Between the high shift points of your current cam, and the pretty big difference in overlap between the 2 I would say the custom cam is a much better option for you at this point. Bleeding off boost will only emphasize the lack of low end you feel now compared to how it will pull up top. The way I see it is with a procharger you want a cam that will help the bottom end and mid range as much as possible because they are great at feeding the maching up top anyway.

 

If you like the manners and operating characteristics of your current cam, boost will only make it better. Run it. You're hp ahead of a milder blower cam. Boost just makes it better. Unless it's a stupid big cam, your power numbers, at the end of the run, will be similar. The business about boost blowing out the exhaust valve for those with higher overlap cams is a little misleading. If you have an engine that breathes better (bigger cam), you're not going to see as much boost.

That being said.....you can make similar power with a well mannered, well chosen blower cam vs a lumpy/higher overlap cam. Most like to have their cake and eat it too. Good power and manners.

 

ok, well my current cam is
227/235 .612/.624 113LSA on comp lsR
Pat G spec'd me
218/234 .58x/.60x 115+2 on LXL lobes
and another one I'm looking at
218/226 .58/.60 114LSA

I'm having to shift my current cam at about 6900. With a procharger I don't really want more than 12# of boost at the shift points. I want to move my shift points to no higher than 6500. that way I can run a smaller pulley and boost will come in sooner. So I would like a cam with better low and mid range and let the procharger work with the top.

 

That thing is gonna be nasty shifting at 6500 with that Procharger LOL

I keep wanting to up my shift point a little more each time but am trying to be somewhat safe and conservative.


Maybe at the track I will take it up a couple hundred more RPM




can't wait to see your truck once that PC is on it