1.7 Ratio Rockers

OCCI · #1 (**permalink**) 05-12-2005, 12:11 AM

HAS ANYONE MADE THE SWITCH TO HIGHER RATO ROCKERS ON A SMALL BLOCK? IF SO WAT WERE YOUR RESULTS?

coosawjack · #2 (**permalink**) 05-12-2005, 04:45 AM

I did it years ago on a SB Chevy boat motor and saw absolutely nothing from the conversion??

You may get a few more HP but you may also get some spring bind depending on your cam??

Coosawjack

427sharpe · #3 (**permalink**) 05-12-2005, 08:39 AM

All it will do is give you slightly higher lift and a ton of headaches redoing all the math/tests for valvetrain binding and interference. If Comp Cams or Crane saw a great advantage to using a different rocker, they'd sell you one. Stick to mfg reccd's and you will have a much easier life.

SuperHart · #4 (**permalink**) 05-12-2005, 11:20 AM

When I built my 351W based on a '69 block I went with the Crane 1.7 ratio roller rockers that were offered by Ford Racing and have had absolutely no difficulty with them. My bottom end is box stock, heads are GT-40P iron heads. As long as you are not using 2.02 intake valves AND are keeping the total valve lift WITH 1.7 rockers below .510 according to the techies at Ford Racing there should be no interference problems. I can't say if there was any increase in performance since I never used the 1.6 rockers but I figured a little extra valve lift couldn't hurt anything.

Of course, it is always best to be able to check them out when the motor is on the stand and you can check valve clearance with some clay but I do believe the above information should serve you well. In order to figure out the actual valve lift with the 1.7 rockers you will need to know the advertised valve lift of your cam (usually assumes 1.6 rockers). Set up a ratio consisting of the following: 1.7/1.6 = X/advertised valve lift. Another way to set it up is "advertised lift" x 1.7/1.6 = X. Solve for X which is your valve lift with 1.7 rockers. Therefore, if your advertised valve lift with 1.6 rockers is .442 , it should be .470 with 1.7s. Have fun.

What'saCobra? · #5 (**permalink**) 05-12-2005, 12:29 PM

We switched to 1.7's on a stock FORD 385hp 351W Crate and it seriously brightened up the engine. No dyno #'s, but i would guess 15-20hp. A few thousand miles or so and they are just fine. Same springs, no stacking. i've got nice 2 into 2 headers, so that helps also.

Not sure about the cam/spring/piston clearance on a newer 392 FORD stroker 351.

To be cautious, i index the plug tang to the top (or between the valves) position and limit it to 35thou, even though the MSD will fire 40 (or 50) with ease. i shift hard at 6500-6600, quite regularly. Nice motor.

Nice mod, but with a bigger cam lift, who knows? Better measure, if not stock. Same with revised springs. The 750 Holley HP certainly likes to feed the deeper opening valves.

Got the trick from a 'Stang Drager.

Works fine for me.

OCCI · #6 (**permalink**) 05-26-2005, 09:55 PM

WELL I PUT THE 1.7'S IN MY 260 & PICKED UP @28 HP.@6000.. NOT BAD FOR THE $$$$$$$$$$

What'saCobra? · #7 (**permalink**) 05-26-2005, 10:09 PM

Nice to hear your results and your measurements. i was trying to be conservative about the hp gain. i am not surprised at 28hp. That's what it feels like, but my butt is not calibrated.

Got an MSD installed? If not, get it.

Got a new Holley HP series carb, if not, get it.

They also added lots of power, starting ease and all around smoothness.

i'm having no trouble with double-pumper and mechanical secondaries on the street. But, if you live in a cold place, maybe you need a choke. This rig works just great without one and it comes off the line just fine, thank you.

Good luck. Keep us informed.

racinjason2316 · #8 (**permalink**) 02-21-2006, 12:39 AM

There is no universal formula for figuring out wether your engine will benefit from the increased rocker ratio. Switching to the higher ratio does two main things- #1. lifts the valve faster (effectivly increasing seat to seat duration)#2. lifts the valve higher. If your cylinder head flows well enough to benefit from the increased lift, there is a good chance you will see gains. A lot of it is cam/head combination. Larger ratio's do tend to exaggerate any valve train geometry problems that you already have. Every engine is different. Some engines benefit from the higher ratio on the exhaust side, and some on the intake side. Even more some on both. The best way to find out is to test them on the intake side first, and if that gains power add the exhaust. I have seen engines gain 20 HP from the bigger rockers on one side or the other and then loose a few or gain nothing from the other side. Heck some Chevy's like to have a little more ratio on just the center exhaust ports. 1.5's on all intake valves and the four corner exhaust valves, and 1.6's on the center exhaust ports. The only way to know is to dyno before and after after every change. Usually the gain is not enough to feel "seat of the pants".
As for piston to valve clearance, with any aftermarket camshaft and rocker package the clearance should be checked initially. If you document how much clearance you had with the previous set of rockers, you can subtract the increased valve lift provided and generally figure the clearance. If it's close, dissasembe it and check it properly. Sure beats a bent or dropped valve. And figuring the gross lift is best done by multiplying the camshafts actual lobe lift (printed on every cam card) by the rocker arm ratio.