what is the benefits of switching from 1.5 rocker arms to 1.6 and is there anything that needs to be done. also, on roller rockers, self-aligning or not?

there are both self aligning and non- self aligning roller rockers in the 1.6 ratio available,they reduce friction and lower oil temps slightly in most sbc engines through a reduction in friction due to the roller bearings not haveing as much resistance to movement under the spring presures the valve springs exert on a stock rocker ball piviot points. now as far as the advantage of the slightly higher ratio that increases the rate of valve lift and the total lift that is reached that is a two edge sword, in every case I have seen so far the slight additional rate the valve lifts due to the 1.6 ratio rockers and the increased rate that the valve opens comes at the cost of slightly more stress to the valve train and a slightly lower valve float rpm at the engines redline, now its true that at lower rpms this does not mean much (in fact thats why I run 1.6 rockers on most TPI ,EFI engines because they seldom see 6000rpm and the shorter duration/higher lift combo cams work better in them) but if your trying for max power a well matched cam and 1.5 ratio rockers tend to work better,look at it this way a slight lift advantage is more important in the mid and lower rpm ranges than at 6000 plus rpm where valve train stability and slightly longer duration in cam timeing tend to make a bigger differance in total power due to increased time the valve remains open and a more gentile ramp speed thats easier on the valve train. the 1.5 ratio rockers matched to the correct cam, all else being equal allow the cam/lifter combo a little more rpm potential than the faster ramp speeds the 1.6 ratio rockers permit because those faster ramp speeds also overcome the valve trains ability to keep up with the harmonics generated by those 1.6 ratio rockers at a lower rpm. now of course you can always ad a rev kit, rocker stud stabilizers and heavier springs but thats alot of extra expense to get a few extra hundred rpm that the correct cam and 1.5 rocker could have most likely given you.
example lets say the correctly matched cam and 1.5 ratio rockers lets the engine pull the same torque curve 300 rpm higher due to a little less lift and just a little more duration with the more gentile ramp speeds and more stable valve train harmonics(not at all uncommon) and the engine we are dealing with is a hot 383 the formula for hp is (tq x rpm /5252= hp) so if we have 450 ftlbs of torque at 6100rpm with the 1.6 ratio and the same torque 300 rpm higher with the 1.5 ratio an new cam of about 7 degs more duration @ .050 lift we get

450 x 6100/ 5252=522hp
450 x 6400/5252=548 hp
remember thats with very simular torque curves and only a 300rpm differance in where it places the peak

Thanks Grumpy I had posted I similar question in the chevelle forum. Your explanation cleared up what I was missing http://www.camaros.net/forum/smile.gif

I have a friend with a stock 69 Z/28, he put on roller rockers 1.6 ratio. He promptly broke three valve springs! He's not too happy about it!
On a stock or mild cam you can probably play with them, but on an aggressive cam, you'd better be sure the cam profile and springs are compatable with that ratio.
I once talked to David Crower at a trade show about 1.6 rockers. He had a whole sheet of SB cams that were compatable with the 1.6 rocker, he was very positive on them BUT-.
He said the cam needs to be designed for 1.6. Many of his standard 1.5 rocker race cams would not tolerate the 1.6.
David

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67 RS 327 original owner. 69 Camaro Vintage Racer, 65 Lola T-70 Chev SB Can-Am Vintage Racer

thanks grumpy, that really cleared up alot. have a good one!

They're wasted money and effort on a street engine, and usually require clearancing the pushrod holes to prevent interferences. Stick with a matched combination - valvetrain dynamics and spring harmonics are complex, and the cam manufacturers already know what works and what doesn't.

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JohnZ
CRG
'69 Z28 Fathom Green

if your exaust flows more than 70% of your intake is there not an advanage to using 1.6 on the intakes only? thats my understanding of this anyway.

1.6 ratio increases lift approximately .030 (over 1.5) and doesn't effect duration. So, if your cam has .480 lift with 1.5's, then your lift would be approximately .510 with 1.6's. I personally like useing 1.6 rockers on street engines, because I can use less duration to improve low RPM torque and throttle response, but get more lift for a few more horsepower. Like anything else, you need to make sure your valve train components can handle the extra lift.

Ive read in car craft, and just watched hot rodding this morning and they say that when you increase rocker arm ratio that it DOES increase duration. Im not saying I know for sure, but hey, if car craft and hot rodding say it I believe it. Car craft said that going from 1.5 to 1.6 will make the engine sound and act like it has about 20 degrees more duration. Ill try to find the article again and post what month it was.

here read
http://www.dapa.org/tech/Jhandracing/jhandracing13.htm
http://www.cranecams.com/master/radiarc.htm
http://www.n2performance.com/lectures/lect1/lecture001.asp

The n2performance website has been redesigned and the link in the above post is no longer working. To download lecture one go to http://www.n2performance.com/cgi-bin/axs/ax.pl?http://www.n2performance.com/lectures/airflow.pdf

Thanks.
-John

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www.n2performance.com (http://www.n2performance.com)

David,

I'd be interested to know if the 140 service package cam was compatible. I installed a good used 140 solid cam that my brother ran for one summer into my 12:1 331. After about an hour of time on the engine I have two lobes bad. Cam was in great shape when I installed it. My springs were new and designed for .580 valve lift, with the 1.6 I was at .539 lift. I'm a little reluctant to run the 1.6 rockers again, but I want to run the service package cam again.

[This message has been edited by SY1 (edited 12-19-2002).]

I've been watching things in regards to valvetrain components as I plan my 350 build and one thing I've noticed only recently about rockers is that a cheaper or 'stock' set of 1.5's is really only rated at about 1.46 or 1.48.
A good aftermarket set of 1.5's is a lot closer to or even rated at more than 1.5. More in the 1.52 range. That's much closer to what the manufacturer of cams and the rest of the valvetrain makers had in mind when they designed their parts.
So I agree that 1.6 rockers can be overkill in most cases. I've seen where they can improve performance somewhat if used on the exhaust side, and leave 1.5's on the intake side.

My .02



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Joe
WCA Member
1969 Wallet Crusher
- HwyStar@Rochester.rr.com

HwyStar's Garage! (http://www.geocities.com/hwystarjoe/index.html)

If your cylinder heads flow more at higher lift the 1.6 rockers will probably help 10-15 HP IF the valvetrain can handle it. You need the correct valvesprings for the new rockers (usually more spring pressure is required to control the more radical lift rates) and the correct geometry (pushrod length, pushrod holes clearanced, etc). My engine picked up a few hundred more RPM when I went from 1.5 to 1.6 rockers.

Based on the detailed crank angle/cam lift/valve lift data we've measured (one degree at a time) during our research on the "30-30" cam project, we've found that stock rockers (the "good" ones with the "o" stamped in them) are 1.37:1 at initial lift, and only max out at 1.44:1 at full lift.

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JohnZ
CRG
'69 Z28 Fathom Green