Roller Rockers 1.5 vs 1.6

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DentalDart said:
Stock steel rockers
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:eek:
I ‘m just about at the point where I almost wouldn’t even run stock stamped rockers in a stock motor. I would go with what you’re considering, it wouldn’t surprise me if you don’t notice an improvement just by installing decent (even factory ductile with the ratios matched) 1.5 ratio rockers with the geometry corrected with the aforementioned B3 kit.
 
I thought we were talking about valve to piston clearance (or lack of) if the OP uses 1.6 rockers instead of the stock 1.5's.
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Exactly.
His concern was the extra lift from the 1.6 rockers would cause a V/P clearance issue.

I kinda want 1.6 for a little "extra" lift from my cam but worry about valves hitting pistons?
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The max valve lift occurs at the cam C/L position.
So, at 106 intake C/L, the max lift occurs at 106* atdc......or, after the piston is past 1/2 way down the bore....... so with a stock stroke SB, the piston is like 1-3/4” inches from TDC.

Max lift in itself is not an indicator for V/P clearance.
 
PRH said:
Peak valve lift has nothing to do with valve to piston clearance.

Where is the piston when the valve is at full lift?
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PRH said:
You’re missing the point completely

I’ll help the thought process.......
The xe268 cam has an lsa of 110.
Let’s say you install it at 106.

Where are the crank/pistons when the valve is at full lift?
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Ummm.... In the Motor... :poke: :lol:

You my friend are talking chinese to me right now. I would love to know the real answer to that but really I have no idea what the answer is and I have no idea how to check it. Hell I have no idea what the tools are to check it either...
 
Thats not to say that changing the rocker ratio won’t have any affect on V/P clearance...... it does.
But minimally.

In the OP’s example.... xe268 cam, in at 106.
The lobe lift at TDC is .070”, so valve lift with a 1.5 would theoretically be .105”.
And with a 1.6 rocker....... .112”.
So...... you lose .007” clearance.
 
PRH said:
Thats not to say that changing the rocker ratio won’t have any affect on V/P clearance...... it does.
But minimally.

In the OP’s example.... xe268 cam, in at 106.
The lobe lift at TDC is .070”, so valve lift with a 1.5 would theoretically be .105”.
And with a 1.6 rocker....... .112”.
So...... you lose .007” clearance.
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Here is some info from when we installed the cam (Tony, 70aarcuda did the smart stuff like degreeing it, I was just the muscle).

Luckily I write everything down.

Screenshot_20220530-143426_Samsung Internet.jpg


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Totally agree with PRH and TT5.9MAG on the whole max lift vs cam position discussion as it pertains to piston to valve clearance.
The directions I gave for measuring piston to valve is only if you’re going to contact comp to run their program. And then it is only to see which of THEIR cams will fit at what ICL and rocker ratio. Their directions is to use TDC clearance because it can be done without needing to set up a degree wheel. Their program does the rest with piston location according to rod length and stroke. So that’s really more appropriate if you’re looking at a “larger” camshaft. It only requires a basic dial indicator and base setup to measure accurately. I would think that most cam grinders would have similar programs they could use for the same end.
 
You seem to have the money to play. Just call Mike at B3 racing. Have a nice conversation with the guy and put in your order.
 
PRH said:
I thought I read where Mike at B3 wasn’t doing kits for the SM aluminum heads anymore??
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SM did have a problem with the rocker shaft pedestals. B3 Racing was refusing to address the issue. Not sure where the stance is now.
 
You'll never notice the difference on your build. I'd stick with 1.5.
 
RustyRatRod said:
No, I told you what I would do.
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You're right you did say what you would do. I am serious though, I really do appreciate when you chime in.

Usually when you or Tony say "do this" or "I would do this," I follow the advice. Problem is you both said different ratio rockers :rofl:

Ill have to get them both (eventually) One for now and one for later...
 
DentalDart said:
You're right you did say what you would do. I am serious though, I really do appreciate when you chime in.

Usually when you or Tony say "do this" or "I would do this," I follow the advice. Problem is you both said different ratio rockers :rofl:

Ill have to get them both (eventually) One for now and one for later...
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For what you're doing, you'll never know the difference. If you just want the 1.6, get them. They'll work good. Just make sure the assembled spring height can take the extra lift at the valve the higher ratio generates. Also another thing to watch out for is the pushrods hitting the heads in the pushrod holes. The increased ratio rockers move the pushrods closer to the rocker shaft to achieve extra lift. Sometimes you can run into clearance issues at the pushrod holes if they are small.
 
Sorry, post #21 is incorrect. Depending on r/s ratio & lobe profile, V to P clearance can be less a few degrees BTDC [ compared to at TDC ] for the exh valve & a few deg ATDC for the int valve.
 
See Garrett's post #2 when he talks about measuring clearance. That is what I was talking about The piston can not come any closer to the valves than at TDC and the valves cannot come any closer to the pistons than at maximum lift regardless of when maximum lift happens. Cam timing, whether ground in or adjusted at the timing set, cannot make either measurement change more than it's maximum. For instance, a cam with .500 lift and .100 P/V clearance at TDC will never get closer than .100 regardless of cam timing. That was my point. Because of valve timing, if the valve opens before or after TDC, the piston will be further away from the open valve because it is either not at TDC or has already passed it and is traveling down. That was my point. Post #2 made the point that v/p clearance should be checked especially when adding lift with a 1.6 rocker.
 
Cam A has .485” lift with a 1.5 rocker

Cam B has .509” lift with a 1.6 rocker

Cam C has .390” lift with a 1.5 rocker

If checked in the same engine, at the same intake C/L, which will have the most, and the least V/P clearance?
 
Doc, Unless you are looking for that last little bit of HP running the 1.6 are not going to benefit you that much (almost unnoticeable). Build your heads with the 1.5 rockers making sure everything it set up correctly & run with it. We tried 1.6 rockers on my 416 stroker but the possibility of valve to piston clearance was WAY too close. I went back to 1.5 rockers & have no problems twisting the engine to 6400-6700 RPMs through the traps. Just keep in mind, my application is race only.
 
You will most likely run into pushrod head clearance problem with the 1.6. I have ran those heads for years on a 340 with right around 500 lift and the push rod is right up against the head clearance hole as it is. my opinion going to a 1.6 would be a waste on your particular build if you want more go with more cam lift eventually unless you want to grind on those heads. 1.5 are a much better fit all around.
 
For instance, a cam with .500 lift and .100 P/V clearance at TDC will never get closer than .100 regardless of cam timing.
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This just isn’t correct.
It’s all about the cam timing.
If it were an intake lobe that had .100” clearance at TDC, and you advanced the cam 10* it will then have noticeably less v/p clearance.
(Advancing the xe268 cam 10* would eat up .052” clearance with a 1.5 rocker)
And the exhaust clearance would grow.
 
PRH said:
This just isn’t correct.
It’s all about the cam timing.
If it were an intake lobe that had .100” clearance at TDC, and you advanced the cam 10* it will then have noticeably less v/p clearance.
(Advancing the xe268 cam 10* would eat up .052” clearance with a 1.5 rocker)
And the exhaust clearance would grow.
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Thanks for making me engage my brain this morning. Took me a while to picture it all in my mind. I’m thinking if all cams were ground with an ICL at TDC engines would be boring and inefficient at best.
 
IMHO, the OP’s setup is okay with the 901 type springs that the cam calls for. But going with upgraded 1.5 rockers (and by that I mean good quality stiff rockers with consistent ratios) and geometry correction won’t hurt anything. There’s some talk about a different engine being built, so if swapping these heads and rockers onto an improved short block are part of the plan, I say to go ahead and upgrade and have that much out of the way. But I would probably be looking at saving up for a little better rocker than the SM/ProComps. So, what are the plans for an upgrade? Oh, thanks @PRH, loving the calculations that show exactly how much extra clearance that they increased ratio rocker will use up. I’ll be needing to use some of those myself for a nice solid cam upgrade. I got a set of used SM steel 1.5 rockers, so I’m going to get find out how those work on some factory 976 casting heads.
 
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As mentioned, call Mike at B3 and talk to him. He did the work for my 340. Edelbrock heads and Comp Cams Xtreme Energy solid flat tappet cam. No problems at all with his pieces, but I did have to clearance the heads for the increased pushrod angles.
 
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