CamaroX84

I understand that a larger ratio will net you more lift, but does it change your effective RPM range? I'm just wondering if my motor would benefit from them over the stock ratio. Thanks.

AlkyIROC

You'll gain about 5 HP with just a straight rocker swap. Slightly more when going from stamped rockers to roller rockers.

Using 1.6 rockers is just a poor man's cam swap. Sometimes the extra rocker ratio is needed to get a bit more valve lift when the cam pattern is at the limits of what can be done with a lobe grind.

Depending on your cam specs, going to 1.6 rockers may decrease performance if the valve train isn't designed for the increased lift. Springs can bind, the underside of the retainer can hit the top of the valve stem etc.

Some people also just play with half the rockers. 1.6 rockers on the intake, 1.5 rockers on the exhaust.

CamaroX84

The cam I'm currently running is 230/236 dur at .050 and the lift is .510/.520. The springs are pretty good (AFR). I just don't think my cam right now has quite enough lift/duration to take advantage of my 195cc heads. The biggest concern I have is valve/piston clearance. The heads were milled to 64cc chambers, and the block was zero-decked. It's been a while since I put my current cam in, but I seem to remember it being pretty close as it was. Is there a way to check it without removing the heads?

formulafastfoot

i was also wondering what kinda gain would doing a 1.6 push on a stock do ? my friend at work says it frees alot up ... thanks for the info ..

Sonix

iTrader: (1)

1.6 rockers on a stock motor gives the same 5HP stephen mentioned, as it would on an aftermarket cam.


valve-piston clearance is usually a non issue. F-bird has described this a few times, but basically, when your valve is open, your piston should be nowhere near the top, so you shouldn't have any interference issues, until you have a GIANT duration cam and/or domed pistons. You have neither, so I wouldn't sweat it.

CamaroX84

The only thing is that when I installed the cam with the rockers I have now, clearance was an issue. I had to shave off a little extra on the valve reliefs on the pistons to get .050" clearance. The 1.6 rockers will give more lift at all times, right? I don't really see how it won't be an issue again.

Sonix

iTrader: (1)

it wasn't an issue then, and it isn't an issue now.
well, let me clarify, how did you test for clearance? force your valves to stay open to max lift, then turn the motor over, moving the pistons up? (then it's not an issue)

or just rotate the motor over, with putty on the pistons? This would be an accurate test. Usually though, unless you have tons of duration, which would keep the valves open when the pistons rising, then it won't matter.

CamaroX84

I did the putty method and another method (can't remember what I did...this was 3 years ago), but I do remember that both methods resulted in having only about .010" clearance, so it was an issue. That's when I cut the valve reliefs on the pistons a little more to get .050" clearance. By the way the specs on the cam are 230/236 dur at .050, and .510/.520 lift. Thanks.

irocalot

another side effect of the 1.6 rockers is that it will give you about 3 degrees of extra duration on your camshaft.

Sonix

iTrader: (1)

ok, if you forced the valves open when the piston was up, ie, not keeping the valves moving in respect to the pistons, then yea, you'll show very little clearance. This means your motor is now interference fit, so that if your timinig chain snaps, you're screwed. (Factory motors are built this way nowadays.) However, if all runs well, you're ok.

stephen87 or f-bird could tell you more on this, i've never actually done the putty method on the pistons, but from what i've *heard*, only if you've got upwards of 245* intake duration @ .050, and a very decked block, would you have an issue.

anyway, grinding deeping valve reliefs in the piston isn't the end of the world so...

in short; you probably won't gain enough HP going to 1.6 rockers to justify replacing your perfectly good 1.5s. If you had no rockers, then i'd say go for the 1.6's. I did.

85z28iroc

iTrader: (1)

This is all very interesting. Why doesn't everyone change to 1.6 for the extra cheap HP? What are the cons?

pizza_guy

My thoughts----> Swapping 1.5 for 1.6 is just like bumping up the cam:

cam x 1.5 = total lift and dur.
cam x 1.6 = more total lift and dur.

Basic math there. So, just like a bigger cam, it puts more force just about everywhere on your valvetrain. If you got push-in studs/stock(I hope not) they start to work themselves out of their holes when the forces get too great.

1991CamaroRslow

iTrader: (3)

cons: Increased load on the lifters, possible interference with the guide holes in the heads. Chevy used modified Crane 1.6 roller rockers in there LT4 engines and I've heard 1.6 roller rockers recommended for the LT1 engines several times. I would say the pro's outweigh the cons. I'll be able to tell you how mine worked out when I finally install this set that's been collecting dust for a month.

CamaroX84

Can I check the clearance after installing new rockers without pulling the heads?

1991CamaroRslow

iTrader: (3)

Install a pair of them and slowly turn the engine over by hand to check the clearance on the guide holes. You can check the valve to piston clearance that way but it would be scary in my opinion.

AlkyIROC

Using the putty method means pulling the heads. You get some modeling clay from a local hobby shop. A small amount is placed in the valve pockets in the pistons. You only need about .100" - .200" thick. Once the putty is on the piston, the head is reinstalled and torqued down as a normal assembly with rockers installed. Normally it's best to use a solid lifter to eliminate any leakdown from a hydraulic lifter. The engine is then turned over by hand 2 full revolutions. The head is then removed and the thickness of the clay is measured. I don't have the exact specs handy but I think intake is a minimum of .060" and exhaust is a minimum of .100".

You could do it without clay but you may not have an exact measurment. Set the head up as normal using solid lifters (you only need 2) as I just mentioned. Install a dial indicator on top of the spring retainer. Rotate the engine 5-10* at a time then push down on the rocker, pushing open the valve. Even when the valve is partially open, you need to push it down to check clearance. If at any time the valve movement is less than the minimum requirement, you're going to have interference problems since it's hitting the piston. This can be very time consuming since you need to turn the engine over 2 full revolutions 5-10* at a time. You can cheat a bit since you know the piston isn't going to touch the valves when it's at the bottom of the hole. You only really need to check it once the piston is within the top half of the cylinder and the valves are still open. Once the piston reaches the top, the valves are closed. If you can push the valves open past the minimum limits, then there's no chance of having a piston to valve clearance problem at that point in the rotation and you don't need to push them down any more.

As for why not everyone change to 1.6 rockers? If you get a proper grind cam, you don't need them. As mentioned above, they can add more stress to the valve train. The distance from the rocker stud to the valve tip stays the same so to increase the ratio, the pushrod distance is changed moving the pushrod closer towards the rocker stud. Some heads need to have the pushrod hole modified slightly to relocate the pushrod that little bit.

I think the SB2.2 engines or possibly the LS1 use 1.8 rocker ratio. It's just a way to get more lift without having a small base circle cam to increase the lobe lift. A camshaft lobe can only be as tall as the came bearings or else you could never get the cam into the engine. To increase lift, you take material off the base of the lobe. If the base circle gets too small, the cam becomes weak. By adding a higher ratio rocker, you keep the larger base circle cam and increase lift.

My BBC uses 1.7 rockers but the distance between the rocker stud and the valve tip is also greater. BBC have an option to use 1.8 rockers for those who need a bit more lift.

racereno

I've always stuck to the 0.100 exhaust and 0.080 intake clearance rule. Any lift you can do inside of that will be cool.