What Cam do I NEED

Hi what cam do I need ?
I have been Breaking rocker gear left right & centre
I think it is coil binding
heads have just been serviced.
Installed height 2.065 from spring to under neath the retainer.
Coil bind @ 1.195
Spring pressure seat 470 lb @ .500 830 lb

Motor is 511 KB Hemi 14/71 Bae fat heads 6.6 @ 205mph

Cam I have 66912 Crane grind 296/500-16
intake @ cam 500 @ valve 785
Lift :
Exhaust @ cam 500 @ valve 760

Is this cam too big or what is my problem?
Beside I need help

Thanks

 

Why are you guessing just check the coil bind?

 

Where are you getting the lift numbers from? On a cam card they're usually figured with a std. ratio rocker system and aren't accurate for your application. You need to take the lobe diamater and multiply it by your intake and exhaust ratio respectively. I'd say .060" from coil bind is fine for the spring. The best way to measure lift is to put a dot on the retainer and a dot on the cylinder head. Measure the distance (with backside of dial caliper - you can also make a fixture with a dial indicator that bolts to the rocker gear and touches the retainer <- that's the best but not the simplest) with the valve closed and with lash, then run the valve down to fully open and measure the two dots. The distance between the two measurements is the lift the motor is actually seeing. It's not going to take into account all the deflection the motor sees at high rpm but it's far more accurate than the cam card. Take the accurate lift number and add .060 for distance from coil bind, 1.195 for the spring coil bind, and that'll be your installed height. If at that point you're still breaking stuff something else is going wrong, but I suspect something in the aforementioned is inaccurate. If you need any help you can contact me and I can lend what knowledge I have, also Noel Manton is an expert in this area...you may contact him as well.

Regards,
Brandon Booher
NHRA TAD #34

 

Cam

Brandon Thanks for your reply,
Read the lift straight from the cam card.
how do I or do I find the lobe diameter & then my rocker ratio ?
these head are Bae 3 fat heads

I tryed the dot measurement came up with
intake 2.200 closed 1.380 open with 25 thou lash
Exhaust 2.185 closed 1.480 open with 25 thou lash
Need more help
It would be good to here from Noel as well
Thanks

 

The lobe diameter is listed on the cam card, since it's a 296/500 - 296 is the duration and .500 is the lobe diameter..but you need to make sure that it's .500 on both intake and exhaust. It very well could be .500 and .510 or something of that nature. The rocker ratio is going to be based on your stands, I'm guessing they're BAE Rockers....perhaps give Jeremy at BAE a call and he'll know for sure. Based on your calculations your lift is the following

Intake - .820
Exhaust - .705

If we assume you have a .500/.510 cam Then I'd say you have a high ratio setup, perhaps a 1.75 and 1.6.... Regardless given the info on the intake you're .050 away from coil bind and on the exhaust your way safe. .050 is closer than I like to run them but unless you're revving the piss out of the car it should be fine. If you have the time, I'd back the intakes up .030 or so. It could also be that the rockers are worn out or you have a bent shaft or cracked stand. Take the back side of the dial caliper and measure from the locator shim (shim closest to spring bottom) to the bottom side of the retainer; make sure in fact they're in at 2.065". Once you check that if it's different backtrack the numbers and see if you have a problem. Take the installed height you find with the calipers, take away .820 on intakes and .705 on on exhaust, take away .060" on both and see where you're at in relation to the 1.195 coil bind figure. I'd say that cam is just fine for your application, let us know what you find.

Brandon Booher
NHRA TAD #34

 

Rocker Gear

You say the Heads are BAE 3 fat heads. Are the rocker arms made of aluminum or are they steel.
This will help in solving the problem.

Noel

 

Cam

Good to here from you Noel. I need some push rods etc
Intake are bae aluminum Exhaust are steel

Dave