turboal1

my Comp cam is .556/.568 -210/224 i want to install a set of 1.8 rollers,799 heads
it will make it just around + or - .600 lift. i have the Pac beehive's
pro's and con's on doing this ?


sig has all my info

Bilster

iTrader: (17)

Comp already engineers an aggressive ramp rate. It's compounded when you add a 1.8 ratio. PAC makes good springs but even they may not be up to snuff at high rpms.

catman3516

wrong bilster. not all ramp rates and lobes from comp are aggressive. some are lazy and slow. now can his currant spring hold up with a 1.8 ratio, I agree with you he will at the go/no go limits of safety. may need double springs to twist it that high and fast.

turboal1

I forgot to put in it's a VVT cam and only rev's to 6500 rpm

shupe

iTrader: (7)

Are you running the comp 156-401-13?

turboal1

cam is # 189-400-13 springs are good to .625 lift and Comp said
it's ok to use these on my cam. 105 C/L it is 6 deg advanced , but i can move
it again with HPTuners. the question is at.589/.600 do i have enough
piston to valve clearance. in a stock motor.210/224 @.050

LowSilver

iTrader: (1)

210/224 and "aggressive ramp rate" don't go together in my books. the 1.8 will net you .589/.601" lift it looks like. What are the spring specs? Where is crush on the spring? weight at .600" lift?

As for piston to valve, I doubt you will have issues if you aren't close now. When the valves are at full lift, the piston is no where near the valves. Piston to valve is more related to your .050" spec. and going to the 1.8 rocker over a stock 1.7, it is a very minimal change at .050" of lift. I'd guess its no more than a degree or two.

-Kenny

Bilster

iTrader: (17)

"Lazy and slow" compared to what? He's quoting an XFI grind. XFI ramp rates are not as aggressive as XE-R. But they are not "lazy and slow" by any imagination. What I have observed is the XFI lobe has slower acceleration rates on and off the valve seat, but then quickly ramps the acceleration rate starting around .020" lift.

turboal1

coil bind is .625+ if that means crush to you. weight ? since the cam
is advanced the int valve would be closer, but it will have less lift.
Comp said it's ok to use a 1.8 rocker on this cam, just watch
the clearance. there not sure on that point.

LowSilver

iTrader: (1)

Yeah, coil bind, crush, same idea. Weight of the spring would be what the lbs. rating is on the spring when the valve is at full lift. It's not going to be an issue for you since you already are running the spring, just as long as you aren't hitting coil bind. You can check valve clearance a few different ways. Many will use puddy on top of the piston. I never do it this way, but it works. (It would require you to yank a head off the engine.

I personally pull the springs off the valves, , then grab one of my light weight springs off the flow bench, put the retainer and keeper back on, and set up a dial mic on the edge of the retainer. Basically re assemble the valvetrain with a light spring. Then check piston to valve clearance by slowly rolling through and when the piston is close to TDC, you can push the valve down by hand, and tap the piston with the valve head. you can take your reading off the dial mic how far the valve can go until it hits the piston. You are looking for atleast .100" at the closest point on the exhaust, and .080" on the intake. (I am pulling those numbers from Edelbrock's reccomendation on say, a vic junior SBC head) I would bet you have way more than that because really, it ain't that big of a cam. If you check it this way with your 1.7's, you will know for sure if the 1.8's are an issue or not before ordering them. Doing it this way, you will begin to understand why its the .050" spec that dictates your piston to valve clearance and not max lift.

FWIW, I was bored this past Christmas season, and I have an old beater 1978 volare wagon with a 318. Since all my racing thus far has been with small block dodges, I have a lot of spare parts for the small block mopar kicking around. I grabbed the smallest cam I had laying around, which was 234/244 @ .050” and slapped a 4 barrel, single plane intake, freash set of stock heads, headers and 3” exhaust on it. The engine has flat tops, with no valve reliefs in the pistons. I had probably .250” clearance on the valves with that cam (just eye balled it lol) It’s a different engine, but its a bigger cam, and it was fine.

-Kenny