I am building a 351c motor for drag racing and some street use. The engine is going into a 65 falcon. It has 10:1 compression and 4 barrel open chamber heads that have new manley valves and triple valve springs. My question is with the 1.7 ratio rocker arms does this increase my lift of the cam? also is the lift of the cam too big for the engine? any help would be great before I get the engine into my car.

These are the rocker arms I am using... Ford: BOSS 302, 351C, 429-460, 1.7 ratio, 7/16 in. stud, Pro Magnum rocker arms
and this is the camshaft

Specifications:
* Advertised duration: 290 intake/300 exhaust
* Duration at .050 in. cam lift: 224 intake/234 exhaust
* Gross valve lift: .536 in. intake/.536 in. exhaust
* Lobe separation: 112 degrees
* RPM range: 2,000 to 6,000
* Decent idle

Any help would be very appreciated.

Josh Peters

Hey Hawkeye,To figure out your lift with 1.7 rockers you need to know the lobe lift.
Then you times it by 1.7 and that gives you your total gross lift
As for clearance the easiest way is with plastersine on the top of your piston,then install your head and cam 2 lifters and poshrods,then spin your motor over by hand and remove head and check if you have .080" clearance on intake and .100" on exhaust

The rocker arms for 351C, Boss 302, 460, 351M, etc are all 1.7 ratio. Therefore the cams that are deisgned for these engine calculate valve lift using 1.7 unless otherwise specified.
As for the clearance issue, I agree with tkmotion. The best way is to measure the clearance using plastiscine, silly putty, or something similar.

I agree with all except the ratio is 1.73 not 1.7. I have used 1.7 bbc rocker arms though as they seem a bit stronger.(don't poke pushrods thru,and less friction with smaller ball).

[David L Gary]

Clevelands love lots of lift and rpm's. 1.73 ratio is standard. Keep overlap at a minim. Very easy to loose compression out the exhaust. To get the compression you are talking about with open chambers you must be running big popups. Feed the beast and watch it run. Best et: '68 mustang 3050 lbs, .030 over (10.7 compression) 850 holley, Holley strip dominator, manual trans, 10.5 slicks, and a solid flat tappet cam (49.99 special) 7.40@93mph in the 1/8. Low budget car that was lots of fun.