PV question - 67 L79

[Chris E.]

Ok guys, so my engine is basically done getting a rebuild. In the interest of long term reliability (I'm 33 and intend to keep the car forever), I went with roller rockers.

I was just reading in the PV judging guide that as part of the PV judging, the judges listen to the sound of the engine. At the same time, my engine builder is telling me that there will be a slight "whooshing" sound due to the rollers. Will this be a problem when I go to judge the car?

Has anyone here with a roller rocker setup gone through PV judging? Just curious what your experience was.

[Duke W.]

Re: PV question - 67 L79

Where did you get the idea that aftermarket hot rod rocker arms are more reliable than the OE rocker arms?

Have you ever heard of an OE rocker failing or "wearing out" on a high mileage vintage small block before the valve guides wore out or the bore wear was excessive? The OE valvetrain parts are inexpensive and have proved to be dead-on reliable over the past 50+ years on over 10 million examples.

I've heard about plenty of hot rod rocker arms that disintegrated - aftermarket cam lobes that went flat - aftermarket valve springs that broke... the list goes on...

OE and OE equivalent parts made by Federal Mogul and Dana Corp. are the most reliable parts you can use. I'd rather cop of set of OE rocker arms off a worn out old truck engine than use overhyped aftermarket junk.

And I hope you installed a real L-79 cam and '67-up OE 3911068 or equivalent Sealed Power or Clevite valve springs. If you installed a set of aftermarket gorilla valve springs, you're asking for a wiped cam lobe.

Duke

[Joe L.]

Re: PV question - 67 L79

Duke-----

I agree that stock-type rocker arms used on most small and big block Chevrolet engines are extremely durable and "bullet-proof". However, I wouldn't use any of these off of a "worn-out, old truck engine", though. These rocker arms do wear out. In fact, I'll bet a lot of them on engines today are really beyond their service life. Any grooving or wear WHATSOEVER on the valve stem contact pad renders them not fit for continued use. Also, any wear or spalling in the rocker ball contact area also renders them unfit for continued use. You'll find these problems on many rockers removed from higher mileage engines.

As far as roller rockers go, I used to think that they were a a lot of "overkill". However, my thinking on this one started to change in 1996. That's when GM PRODUCTION-validated the first use of roller rockers on a GM engine. That engine was the Corvette LT4. When aftermarket manufacturers try to sell one roller rocker arms, that's one thing; when GM PRODUCTION-validates and installs them on PRODUCTION engines, that's another thing. That makes me "stand up and take notice".

With the release of the Gen III small blocks in 1997 came continued use of roller rocker arms, albeit of a different design than those used on the LT4. The LT4 used cast aluminum roller rockers with roller tips as well as roller fulcrum. The Gen III V-8 uses investment cast steel roller rockers with roller fulcrum but no roller tip. Actually, I don't think that the roller tips used for the LT4 and virtually all aftermarket roller rocker arms do a lot of good, but I don't think they hurt anything, either. The roller fulcrums are another matter.

GM has now PRODUCTION-validated and installed roller rocker arms on PRODUCTION 4.3L V-6 engines (the 90 degree V-6 that is derived from Gen I small block V-8's). So, that represents further credibility for roller rockers. I wouldn't be surprised to see some form of them show up on GM's "bread-and-butter" 60 degree OHV V-6's soon (3500, 3900).

The way I see it, there's no way that GM would have started using roller rocker arms if the old stamped steel type were just as good. The added cost factor must be significant, so they'd have to be a real benefit for them to use them. Also, they need to be pretty reliable, especially if GM is now warranting the engines for 100,000 miles.

I'm not a big fan of aluminum roller rocker arms, though (even though GM did use them on the LT4). However, I am a fan of steel roller rockers. I regard them as exporting Gen III and Gen IV V-8 technology to earlier Chevrolet V-8 engines, both big blocks and small blocks alike.

[Mike M.]

Fail

If the Judge can tell there roller rockers it is a fail as far as I know.

[Chris E.]

Re: Fail

Ok, that's what I was afraid of. Thanks for the reply Mike.

[Jack H.]

Add-on...

I agree with Mike's assessment. But, if we're simply talking about roller tipped rockers vs. a complete roller motor build AND the original engine was hydraulic vs. solid lifter based, there's little in the way of telltale sound from the engine....

[Chris E.]

Re: PV question - 67 L79

Duke,

I went with the advice of my engine builder on the roller rockers. He has been working on engines for a long time, and recommended them. I didn't do a full roller setup, just the rockers.

I stuck with a stock replacement cam and I can't tell you about the valve springs. I'm hoping that for the thousands of dollars I'm spending with this shop that they will properly match the valve spring tensions for this setup.

Can you give me an idea of what spring tension is too much or not enough? I haven't done much with that part of the engine, so I'm wondering what the range of tensions are, etc. For example, if the range was from 80-240, and I posted back here that I got a spring rate that was 225 (e.g. near the top), what would that tell you? Anything else beyond excessive wear against the cam lobe? Are higher tension springs more likely to break?

[Chris E.]

Re: Add-on...

Ok, so far, one vote for Fail, one vote for Pass.

Any other takers?

[Duke W.]

Re: PV question - 67 L79

My post was a bit embellished, however, on rebuilds, I have absolutely no qualms about reusing the existing rocker arms/balls as long as they pass a thorough inspection (which doesn't take long) and show no signs of excess wear or galling, which is easy to see.

The GM roller rocker arms have roller trunnions and solid tips, The motivation for installing them was lower friction. When combined with several other internal friction reduction techniques better EPA fuel economy numbers can be claimed in an environment where the manufacturers are pushing CAFE limits before they have to pay big fines.

I think the typical aftermarket roller tip rocker arms are a crock.

Duke

[John H.]

Re: PV question - 67 L79

Chris -

The stock springs are 80# closed, and 200# open @ 1.25".

[Duke W.]

Re: PV question - 67 L79

One of the things I've observed about "engine builders" is that they have a habit of replacing well engineered OE parts with a vast history of proven reliability with aftermarket hot rod parts. Yet they are not experienced engineers and have no technical justification for their actions. I've never met one that had an engineering level understanding of what's going on inside an engine from a fluid mechanics, thermodynamics, or structual engineering point of view.

It's up to their customers to have enough savvy to manage these guys. You're the customer. You're paying for the work, and what you should insist on is OE or OE equivalent replacement parts.

The OE springs I referenced have a rate of 267 lbs/in with a nominal seat force of 80 lbs at 1.70" installed height. These springs went into production in 1967 (replacing an earlier spring with slightly less rate), and they were used on all production SBs including the Z-28 and LT-1 engines. These springs, properly installed, will allow the L-79 cam to rev to at least 6000 before false motion sets in, and the Sealed Power VS677 equivalents can be bought at Internet sites for about a buck a piece.

However, I would not be surprised if aftermarker springs are installed that are 350 lbs/in with over 100 lbs seat force. All these will do is load up the valvetrain and potentially cause problems.

You're paying thousands of dollars for this job. You have a right to specify what parts you want installed, and if you don't know, you owe it to yourself to ask.

If you use an aftermarket cam (which I don't recommend) other than an aftermarket exact reproduction of an OE cam - use the cam manufacturer's recommended spring. If you use an OE cam, use OE springs.

With careful attention to setup these springs will allow OE hydraulic lifter cams to rev to about 6500 and 7200 for OE mechanical lifter cams. Now, whether the engine will produce useable power to these levels is a function of head massaging. With just a valve reseat and no pocket porting/port matching/chamber relieving, they won't make useable power to these levels no matter what cam you use.

Duke

[Chris E.]

Re: PV question - 67 L79

John and Duke,
Thanks for the additional commentary. I'll check with the engine builder this week, but at this point, the valve train is installed, so if I wanted something different, I'd have to pay to replace it.

Given that this same engine builder just worked on another customer's 435 horse 1967 427 and got more than 435 hp using completely stock components, I think I'll be OK. All throughout the build, I've been telling the engine guy "reliability, reliability, and reliability, that's what I want". This car will probably never see the drag strip, won't ever be autocrossed, but rather just driven with some spirit now and again. It'll probably have 3-5K miles per year put on it (if I'm lucky).

Duke, two more questions.

1. On the after market seat force comment you made, can I assume that 350 lbs/in would not create valve recessing given that I have hardened valve seats? (this assumes that the springs I'm getting are 300 lbs/in)

2. Given that I'm using all stock profile replacement components except for the roller rockers, what additional information would you need to make a judgement call on what the actual redline of this engine would be?

[Joe L.]

Re: PV question - 67 L79

Duke-----

Yes, there's no doubt that roller rocker arms reduce friction and the fuel economy implications of that may well be a major reason that they are finding increasing favor in PRODUCTION engines. However, reduced friction has all sorts of other benefits. Reducing friction is an area that benefits street and racing engines alike. Folks have been working towards that end for years.

I don't favor ball fulcrum type roller tip rockers (e.g. Comp Cams Magnum). One is still left with a high friction, ball fulcrum and the roller tip, itself, provides very little, if any, real advantage. However, these rocker arms do provide one benefit. They are investment cast and, consequently, provide a much more precise and constant ratio than the stamped steel type rockers.

[Joe L.]

Re: Add-on...

Chris-----

Any judge that could tell the difference between the running sound of an engine with roller rocker arms and one with stock-type rocker arms would have to have the hearing acuity of Superman.

[Duke W.]

Re: PV question - 67 L79

A 350 lb/in valve spring will not likely damage the seat, but there is a significant risk that excess loading at the lobe-lifter interface will cause excess lobe/lifter wear. But beyond that they are absolutely, totally unnecessary with the L-79 cam.

If you want OE valvetrain reliability, use OE or exact OE replacement valvetrain parts. The OE valvetrain is essentially bulletproof when you stick with proper OE matching parts.

My recommendation is to use your original rocker arms/balls/pushrods if you still have them and they pass inspection (and a new set of 3911068 springs or equivalent like Sealed Power VS677 installed at 1.67-1.70" height, minimum preferred using .030" and .015" shims as required). If not, just buy a set of Sealed Power or Clevite replacements. These will be of the "self aligning" type, which are fine for hydraulic lifter cams, but CANNOT be used for mechanical lifter cams.

The first Special 300 HP engine is running and going through testing. The special camshaft in this engine has a L-79 lobe on the inlet side and a '67 up base cam (3896929) exhaust lobe on the exhaust side. The exhaust lobe has five percent greater negative acceleration over the top than the L-79 lobe, but this is somewhat offset by the slightly lighter exhaust valve.

My instructions for the 3911068 valve spring installed height are very specific for this configuration, and because exhaust valve lift is about .030" less than inlet valve lift, my recommended installed height range on the exhaust side is .030" less. These ranges will result in equal compression of the valve spring on each side, so restoring force on each is the same at peak lift while retaining about .090" coil bind margin.

Expectations are that this configuration will provide useable power bandwidth to about 6500 RPM, IF the valves don't float before that rev level, and the above careful attention to valve spring installed height will yield the highest valvetrain limiting speed while retaining OE valvetrain loading/reliability since the lobes and all valvetrain components are exact OE replacement parts.

But unless the heads are massaged, a L-79 typically will not make useable power much beyond the 6000 OE redline. Much over 6000 and it's wheezing because the inlet tract is essentillay choked.

The valvetrain limiting speed on first Special 300 HP prototype has not been found yet. I have instructed the owner to "sneak up on it" by increasing maximum revs in small increments with each WOT test run until the power "lays down", which is likely the initiation of valve false motion (light float) It could be as high as 7000, but I'll be happy if it makes 6500.

Some initial test results should available in about two weeks.

Duke