..........On an 85 z28 lg4 I need non self aligning rockers from what I understand. Are there any push rod clearance issues with going to 1.6 ratio? What kind of gains can I expect with the lg4? Thanks.....Zapr.

 

Push rod clearance issues - probably. But you may get lucky.

Gains on a stock LG4 - probably not. But you may get lucky.

 

......Anyone else with an 85 lg4 with 1.6 rockers? Problems, gains? Anyone? Thanks........Zapr.

 

In my experience, roughly half of all SBC heads will have interference with 1.6 rockers. What a higher ratio rocker does, is to move the push rod seat closer to the stud; so what happens, is that the push rod hits the inboard end of the guide slot.

So I'd say you have 50% odds on each head that they will work. Roughly 25% odds that they will work on both heads.

Most of the gains from replacing the rockers on a stock motor, is from getting the rubber stock ones off, and putting something rigid on there instead of sheet metal. Not from the increased ratio. 1.6 rockers made of sheet metal will do basically no good at all. On the other hand, 1.5 rockers made of solid steel, will probably give you more actual valve lift, than sheet metal "1.6" rockers.

I would not run aluminum rockers on a street-driven motor. I'd suggest Comp 1412 for a 1.5 or 1416 for a 1.6 (roller tip, ball fulcrum) if you want the best bang for the $$$; or their 1300 series if you want full roller ones.

But if you just really want the higher ratio for some reason, and you want to be certain of them fitting, buy a "Louis tool" from Comp. It's a drill guide for drilling the guide slot out on the end.

 

The gains from using a higher-numerical ratio rocker arm come entirely from the extra flow potential and slightly longer effective durations. 1.6 rockers give 6.6% more lift than a 1.5, so if you look at the flow of any particular head (even a stock one), the extra lift results in more cfm flow --- and it doesn't matter whether you look at peak flow or at the flow at the rms lift height (roughly 0.3" lift at the valve), you still get more flow into the cylinders and so you get more torque and power.

As far as the "rubber" or "sheet metal" compound-curve stamped stock rockers are concerned, their stiffness and low-mass is a lot better than you might think as compared to an brick-type aftermarket aluminum rocker arm.



That's what aftermarket mfgs would like the consumer to believe. But you never see a fair comparo test of stamped steel rockers against the aftermarket alternatives, nor does anyone ever publish the bending stiffness and effective added rotary mass (which affects the rpm for valve float) of the stamped vs aftermarket, which can be determined from FEA analysis, or careful mechanical load-deflection testing.

The reduction of friction is always the reason offered for roller-tip and roller-fulcrum aftermarket rockers, but I have yet to see any worthwhile performance gains from those at street rpms, on anything except very high duration/lift cams. So on a primarily street driven car, stamped 1.6 rockers are fine, they're much less expensive, they will provide a performance gain on the order of 4 to 5% (a derating of the 6.6% extra lift).

I do agree with everything you said about interference at the pushrod slot though.



I don't agree.... except under the unlikely circumstance when a very high lift cam is used (and therefore stressing the rocker significantly). In that case, rockers like the stainless Comp Cams double roller rocker will not deform as much as an equivalent 1.6 ratio stamped rocker. But on a near-stock LG4, the difference is trivial, and the stamped 1.6s are fine, mindful of the pushrod interference.



I couldn't agree more. Steel or titanium for rockers, never aluminum.

 

You completely missed the entire point of RB's post. Sure 6.6% more lift. Thats great and all. Course you are still looking at virtually the same duration, but alas, that is not the point either. The point is the stock rockers flex. Bad, Like play doh. You may gain numerically 6.6% more flow, but in the upper RPM's you will probably see a more significant gain not because of the increase in lift (6.6%),, but in the decrease in flex (which will make a more predictable valve event, and provide more lift).

If you buy a set of 1.6 rockers, stamped, you may very well run into the same problem. Will you see an improvement over stock, probably. But that doesnt mean that the overlying issue is resolved.

 

1. All rockers flex, or more precisely, deform due to Hooke's law for elastic springs (something you learn in a Mech Engr class).

2. How much they flex/deform depends on the load they're subjected to, what they're made of, and the design of each rocker (compound 3D stamping, solid beam, or hollowed beam for example).

I also previously wrote "... can be determined from FEA analysis, or careful mechanical load-deflection testing." That's how you prove, or disprove, how much each flexes. Testing on a dyno before/after a rocker swap can also work, but the results are often blurred by the other changes in the test (swaps of springs, cams, ... or the desires of the manufacturer). You, OTOH, stated that stock stamped rockers flex like Play Doh --- what evidence do you have for this, and under what loads?

3. zapr had the original post in this thread, and the answers boil down to (a) possible interference of the pushrods, (b) coil spring bind, (c) stamped rockers are no good. I disagreed with item (c), largely from some of RB83L69's comments, so I don't think I missed anything.



I agree that the goal is to make the valve motion predictable from the profiles of the cam lobes; the matter of flex of the stock rockers again depends on the end use and the load applied. "Upper rpm performance" is hand waving --- being specific, if you change a cam, or springs, or rockers you will almost certainly alter the rpm for valve float (when the valve train inertia overcomes the static valve spring preload force) and/or incur a resonance of the valve springs (erroneously called surge, or spring harmonics). Either of these cause valve motion that is different from the one on each cam lobe. And BTW, the change in rotary inertia from a rocker swap will also change the rpm for valve float.

On a near-stock cam and on a street-driven car (like zapr's LG4), with fairly low preload forces, then flex isn't going to matter much and the 1.6 upgrade is a very inexpensive choice.

If you have evidence to support the claim of the "play doh" theory of rocker flex (elastic deformation), please provide it.

 

I dont need to support evidence. Stock rockers do it, everyone knows it. Play doh is a term applied to describe (with embellishment) the problems with the rockers. Yes it does happen, no its not worth arguing about. If you read through here I agree with almost everything you are saying, I just dont agree on the stock rockers. 1.6 stamped rockers are not necessarily stock, some are better than others. But if they are of the quality of OEM parts, they are crap.

 

........So then drilling the guide slots out on the heads would require removal of the heads? Would I then need S A rockers? Thanks for the info!........Zapr.

 

Yes, drilling out the heads would most likely require removal. Although, with proper precautions, it could conceivably be done on the engine. I wouldn't recomend it though.

No, you would not have to run self-aligning rockers; since you would merely be lengthening the slots toward the studs, not widening them.

Yes, I'm well acquainted with Hooke's law too; I was a math and physics major in college. But since that didn't really give me a marketable skill, I've since been forced to scrounge my pittance as an engineer. Sucks to be me.

It's a helluvalot easier to skip all the FEA and all that other stuff that's almost like work, and just proceed directly to an engine, and observe it. But like I said, I'm just an engineer these days, a practical guy not a theoretical one, so I've adopted a more direct approach to stuff like that.

Have you ever watched sheet metal rockers flapping in the breeze, with a Strobotach? I have. You'll never run another set of them again on anything, if you do.

Have you ever measured the actual ratio of stock rockers? At the time that Comp was developing their 1400 series, I did just that.... we found that in the 3 or 4 motors we had that we could easily measure, the valve lift was anywhere from 1.38 to 1.45 times the push rod lift, with the average at around 1.42 to 1.43. And that was at very low RPMs (turning the engine by hand) with cams like the 929, 151, and an old Comp HE268.

Again, going back with measured actual HP gains on a real-world engine, the bigest difference in power output we obtained, was in going from rubber rockers, to rockers that gave a consistent ratio. The change we obtained on stock and near-stock motors in going from 1.5 to 1.6 rockers, was a fraction of the other. Which is why I don't particularly find the ratio increase, by itself, to be a hugely valuable thing. Now on a motor with ported heads, a good exhaust, short straight intake runners, and too little cam, the difference can be HUGE; but that's alot different situation from some stock LG4. There's numerous other things that are preventing the valve lift from being a significant limit to that particular engine's performance.

 

........I was wanting to avoid a cam swap because of the work involved. Why spend the time and money hopping up a 305 when a swap to a 350 would be the way to go. I figured the 1.6 rockers would give a good bang for the buck with little work involved for now. If pulling the heads is a must than it's more work than it's worth. I guess I'll just run the little 305 until it quits or I can afford a 350. Only problem is, it's a damn good little 305. Or I'll put 1.5 roller tips on it. Thanks guys!.......Zapr.

 

When I switched from stock rockers to 1.52 comp rollers, there was a noticable improvement.
All techno speak aside... Nothing spectacular, but definitely noticable.

 

........Thanks Street! That sounds encouraging.......Zapr.

 

Yeah, I'd go with something like the roller tip Comp 1.52s. I don't think the 305 heads will support enough more flow at lift to compensate for the increased cost/valvetrain stress of the 1.6s.

 

I would not run aluminum rockers on a street-driven motor.

Why not? I have an oppertunity to get a new set for cheap. I don't want to waste my money or my motor, so please explain so I can make a informed choice. Also what are the benefits of roller rockers?

 

Although lightweight, aluminum rockers will fatigue at a much greater rate than steel or titanium. This can result in tiny little shavings of aluminum to get into your motor. It is not uncommon to see this when these types of rockers are used past their lifespan. I think the life span of aluminum rockers is only 20,000 miles or so. I could be wrong but it is around there. The advantage of roller tipped rockers are the reduction of friction and more precise valvetrain motion. Less friction = more power and longer life.

EDIT: Also, most roller rockers are rebuildable.

 

just wondering i have an 89 lo3 305 tbi i have edelbrock performer intake heads are port matched to intake also 2 inch tbi spaced adapter plate ported aswell 350 tbi and police 65# injectors stock cam msd coil/distributer hooker shorties 3 inch y pipe to flowmaster dual 3 inch out no tips custom jet chip heads also have 5 angle valve job and polished bowl enough with mods i was wondering my boss allways gets leftover parts from nascars most only has 1 or 2 races on it and perfect condition well he has a set of 16 Jesel Shaft Rockers and shafts 1.90 and 1.90 set contains, Jesel part number (4) ECDL 90, (4) ECDR 90, (4) E*DL 90, (4) E*DR 90 i bielieve my stock is 1.5 il do machine work if i have to but was wondering what kind of increase i would get? on dyno i am at 317.3hp@5700rpm and 422lb@2600rpm and does anyone know what the formula is to findout the new lift so i know if i have to fly cut the pistons stock lift is .351 int .386 ext wirh 180 int dur 196 ext dur tks in advance and sorry for long post lol and please dont flame me for hopping up a 305 also in my drive way i have a 87 iroc with a tpi 350 and an 87 iroc 305 tpi and sofar i like the way my rs is handeling mods besides whats better beating someone with a stock looking rs with the tbi 305 or the iroc hehe

 

Hmmm...leftover nascar goodies. Where can we reach this boss of yours?

 

hes kinda peticular about what he does with em he sells most on ebay but i kinda get first dibs tell me the type of stuff your lookin for and il post when he gets em lol he usealy gets a pickup full of boxes the 3rd of each month