Dont mill them and run larger cam as why said stay 11.0

 

Noted. Please don't be insulted by my questioning, I'm only trying to learn how to build a well matched combo. I'm very green here.

So the consensus is not to mill so that I don't decrease PTV clearance so much that I won't have room for a big enough cam? Considering I'm not willing to have the heads ported, doesn't that limit the amount of lift I should run? If I'm correct here, wouldn't that leave me with more than plenty of PTV? If so, wouldn't it make sense to mill for the highest CR possible if the valve lift that makes sense for my heads leaves plenty of PTV on the table?

It's my understanding that the tighter the PTV (based on every contributing factor), the higher the VE? Without getting close enough for collision of course.

If I'm thinking straight, could it make sense to have the cam spec'd first based on displacement, head flow rate, and desired power band, THEN measure PTV and if there's room left mill to achieve max CR? I hope what I'm asking makes sense.

Thanks for your input guys!

 

Makes sense, yes but as far as ptv, youve already stated you have no desire to flycut the pistons, with flat tops youre linited as far as how much lift you can get away with, ve is affected my how much and and how long the valves are open, as previously stated youre talking about 11:1 ish cr with your set up, these ls engines are far mire effeicient than older sbc, where for any sort of hp etc you had to increase conpression to ridiculous amounts, not so with ls engines..... And the 1-2 hp gain if youre lucky really arent worth it for what youre looking to do with it, you need more lower end torque thana high hp high revving engine, i would suggest getting a cam speced and go from there, build around the cam youll need rather than build an engine and be limited by cam choices, does that make sense???

 

Having heads ported has nothing to do with lift of a cam jusT how the heads flow.... Most gm heads flow well enough that porting is another 1-2 hp deals that if you were looking for et increases and trying to increase and squeeze out every 10th in qtr then yeah,but for what youre doingnot really worth the expensive....

 

my understanding is duration and lsa is what effects PTV, not lift

 

They all play a factor but lift is how far the valves open, which is the biggest factor in ptv

 

Thanks guys. So regarding valve lift vs head porting, I was under the impression that beyond a certain point, extra valve lift is a waste if the heads don't flow enough to support that lift. Wouldn't that mean that porting (increasing flow rates) would increase the amount of optimum lift. If so, the opposite would have to be true right? Ie, a stock flow rate wouldn't require a lot of lift?

 

but duration and lsa control the valve events more which can make or break ptv.
tighter lsa would be worse for ptv then wider
I am not 100% sure I am right, just what I have read.
as far as how much lift, if your head doesn't flow much over .600 then no point in going with a cam over .600

 

You can cheat a low flowing head by duration and lift

Alot of the Y2k era of max effort cams were like this

You had 610/615 lift cams with 240s duration on 110-112lsa with heads that flowed 220-250 cfm making huge numbers and setting records

 

I have to agree with GREENSIERRA here,

Duration directly affects PTV clearance more than lift. Duration is how long the valve stays open and the crank is still spinning the pistons, hence why you see some cams with notes "check/verify PTV clearance".

Example:

212/218 .650/.650 lift 112 lsa

This cam would be perfectly fine in a stock 5.3 or 6.0 motor without PTV issues. Take the same lift and add duration and you get PTV issues.

Example:

232/242 .650/.650 112 lsa

This cam would have PTV issues.