impaled

as the title states. what is the lift limit? i want to use the CC306 cam with some 1.7RR's (if i can find some) that would put the exhaust valve lift at .612" and the heads will be ported with bigger valves.

RamAir95TA

iTrader: (2)

There really isn't a mathematical formula to calculate p/v clearance, without mocking everything up first.

What heads are you using, and why did you pick the 306? There are better cams available.

impaled

i was thinking that or the XE230/236 which would work for sure with some 1.7RR's being a 5.89 lift which would work with the crane spring/shim/lock kit (10308-1)

RamAir95TA

iTrader: (2)

The thing is that maximum lift isn't achieved at TDC (most engines are around 15 degrees before/after TDC). That's why you need to mock it up and use a tootsie roll.

FlamingChicken

iTrader: (2)

i would imagine duration would have a greater affect but either way clay your pistons and find out if you have ptv issues.

7.0 camaro

bingo! lift aint got **** to do with anything. i dont know why people care so much about lift. its a useless number.

TABBED 5.3

iTrader: (1)

Could you please explain this statement? Trying to figure out how lift numbers are useless. thank you

96capricemgr

iTrader: (1)

Cam timing is the important thing.
As said peak lift is NOT while the piston is at TDC. The intake valve chases the piston down at the start of the intake stroke and the piston chases exhaust valve closed at the end of the exhaust stroke(intake is opening at this time too). That is generally where interference is a concern.

Should have taken a little video of my friend's gen 1 motor, on the stand you could see through the exhaust ports and watch this happening. BIG solid roller so the lift during overlap was BIG.

I only know of one person having PTV clearance issues on a "stock shortblock" but it was not HONESTLY stock.

7.0 camaro

the reason some of the lifts are as high as they are is for the lobe profile of the cam. you dont pick a cam looking at the valve lift. therefore they are useless and not important.

GIZMO

iTrader: (8)

I have had issues at less than .500" lift when running LT4 heads and thin gaskets. Lot's of duration.

GIZMO

iTrader: (8)

I would think that matching cam lift to the flow bench info. on the heads might be a good idea?

96capricemgr

iTrader: (1)

I believe that. Thank you for posting that as it really backs up the statement several of us are making about peak lift not being the important info.

The engine I am talking about was "blueprinted" and at the very least I know had gapless rings. I suspect things like zero decking and such were done as well.

GIZMO

iTrader: (8)

My point is that you should be looking at both. Choosing the right parts makes the difference betwean a good and a GREAT motor. If you need more valve lift/duration pistons with big valve notches figure next into the equation.

7.0 camaro

most people want cams before headwork. thats why i say that. of course lift means something. but most cams are made to have the right lift for the duration and power range it needs to have. i wouldnt think you can gain alot of horsepower due to 20-30 thous more lift. but if the ramp is steeper and that lift comes in quicker then i can. but when i pick out a cam lift is the last thing i look at. usually its when i machine the heads and choose springs when i look at lift. thats all i was saying.

impaled

i understand duration is an importiant number, but higher duration cams usually happen to have higher redlines. i still want usable power, that is why i was thinking of running 1.7RR's you get the air in without your powerband being in the sky.

Puck

iTrader: (17)

I strongly disagree that lift is not important, especially on LT1s. Stock shortblock LT1s that do not have the strength needed to turn the rpms that big duration cams need often perform great with high lift/lower duration cams. High compression, high lift, and modest duration cams with a nice head is a recipe for a very fun street car that may not peak as high as a huge duration lazy lobe cam but will ET just as good or better while maintaining more tunability and manners. Plus you can keep it under 6200rpm in the "safe zone" for stock block safety on a daily driver.

There is more then one way to get air into an engine - you can either keep the valve open longer, or lift the valve farther off its seat.

I leave the cam spec'ing to the professionals, but I always have a duration range in mind for the rpm range I will be spinning the block to, then squeeze as much lift that the heads can support(both physical contact and flow wise). Sure its tough on your valvetrain, but I do not mind having to spend the extra money on higher end springs and checking them every couple of throusand miles.

You gotta pay to play.

7.0 camaro

i would agree with that. very good post. sometimes its hard for me to type what my head is thinking