True valve lift with roller rockers

[49-blues]

If i use a cam with a .587 lift and a 1.55 ratio rocker arm what would the true lift really be? is the lift of the cam the true lift if using a 1.50 ratio? also what would the lift of the .587 cam be with a 1.65 ratio rocker?

 

[charlief1]

Take the lobe lift of the cam and multiply it by the rocker arm ratio. This will give you total valve lift.

 

[49-blues]

thanks- i forgot how to do the math. .587 lift x 1.55 ratio gives me .90985? WTF?

 

[charlief1]

The .587 is valve lift, not cam lobe lift. You need to know what the cam lobe lift is. Take the .587 and devide it by 1.55, then multiply by the rocker arm ratio.

 

[Nick Micale]

Cam lift = .378"

1.50 rockers - lift = .567"

1.65 rockers - lift = .638"

 

[UncleDave]

How much lift is too much before we start seeing piston-to-valve clearance issues? I know, depends on duration, cam degree +/-, deck height, etc... (Interested because I think I'm pushing the envelope with my build...)

 

[49-blues]

Cool- thanks, I was told to keep it below .600 for a mostly street motor-stage2.

 

[Phoneguy]

Correct me if I am wrong.
.587 lift cam is measured at 1.50 rocker ratio.

.587 divided by 1.5 = .391 cam lift

.391 times 1.55 = .606 lift with a 1.55 rocker
.391 times 1.65 = .645 lift with a 1.65 rocker

Am I missing something?

Bryan

 

[49-blues]

Sounds right to me- thanks for simplifing that!

 

[Slow91z]

Correct me if I am wrong.
.587 lift cam is measured at 1.50 rocker ratio.

.587 divided by 1.5 = .391 cam lift

.391 times 1.55 = .606 lift with a 1.55 rocker
.391 times 1.65 = .645 lift with a 1.65 rocker

Am I missing something?

Bryan

Since the stock rocker ratio for a Buick V6 is 1.55 my cam card has lift numbers that reflect that, so .587 divided by 1.55 = .379 and .379 x 1.65 = .625

Not saying they all do, but if you have access to the cam card just look for the tappet lift and do your math from there.

 

[turbofabricator]

How much lift is too much before we start seeing piston-to-valve clearance issues? I know, depends on duration, cam degree +/-, deck height, etc... (Interested because I think I'm pushing the envelope with my build...)

Dave there is no way to answer that question with out specifics. You will actually need to place clay on the piston and run the engine through four revolutions and make SURE you use light springs and a solid lifter. A hydraulic lifter will NOT work. Also make sure the rocker geometry is correct prior to checking. After making four revolutions, remove head and measure the thinnest area of the clay. Spray the valves and piston with WD-40 first so the clay doesn't stick. Use the correct head gasket. You can vary cam timing to increase clearance to a point of loosing power, though.
How much lift and duration are you running and what piston, bore size, deck highth, valve size, lobe separation angle, installed C/L, ect.? If all custom, then you MUST check it. You can also use a solid lifter, checking springs, and rotate the engine between 30* BTDC and 30*ATDC and then use a dial indicator on the vavle retainer and then press down on the vavle at max lift and measure the amount the valve moves before making contact with the piston. Do this every 5* of crank at valve over lap event. If you have less than .060" you may need to "fix" it.

 

[UncleDave]

Dave there is no way to answer that question with out specifics. You will actually need to place clay on the piston and run the engine through four revolutions and make SURE you use light springs and a solid lifter. A hydraulic lifter will NOT work. Also make sure the rocker geometry is correct prior to checking. After making four revolutions, remove head and measure the thinnest area of the clay. Spray the valves and piston with WD-40 first so the clay doesn't stick. Use the correct head gasket. You can vary cam timing to increase clearance to a point of loosing power, though.
How much lift and duration are you running and what piston, bore size, deck highth, valve size, lobe separation angle, installed C/L, ect.? If all custom, then you MUST check it. You can also use a solid lifter, checking springs, and rotate the engine between 30* BTDC and 30*ATDC and then use a dial indicator on the vavle retainer and then press down on the vavle at max lift and measure the amount the valve moves before making contact with the piston. Do this every 5* of crank at valve over lap event. If you have less than .060" you may need to "fix" it.

I started a new thread rather than hijack this one, but that's very useful info. Thanks Ken!

 

[49-blues]

This is some good information -thanks guys- feel free to hijack if you like cause i think i got the info i needed!