sams'66

Or even a roller cam? Do they work better? i.e. more efficient?
The car and engine is ALL stock...but in need of a rebuild. Any opinions?
I have heard that the engine will just plain run better with less wear.

:confused:
Sam

SWCDuke

No - they're just aftermarket hype - benefits are marginal at best on a street engine.

Spend the money on pocketporting/port matching the heads/manifold and a street three angle valve job with .040" inlet seat width and .060" on the exhaust.

For the L-79 I recommend OEM or OEM equivalent rebuild parts including the cam. Resist the urge to waste a lot of money on aftermarket stuff. Don't read hot rod magazines or at least don't look at the ads. Buy "How to Rebuild your SB Chevy". A good pocket port, port match, and three angle valve job will improve peak torque about 3 percent and top end power about 8 percent without loosing any low end torque.

Duke

Rogs65

Thanks for the insight Duke...I just pulled out my engine this past weekend
and was contemplating the same...will do what you suggest.
Engine has never been pulled apart on mine...completely stock and orig except water pump and carb...Had 3 broken rings when I pulled the pistons out. Very minimal scoring on one cylinder wall.
Have any other good advice? :smash:

SWCDuke

Well, you already took it apart, but I always recommend measuring piston to deck clearance prior to disassembly. That way you have the dimension data you need to calculate the actual compression ratio of the rebuilt engine. With a typical composition head gasket and typical OE machined deck height the actual compression ratio with OEM pistons will be about 1/2 point below the OE advertised ratio so both medium performance (300 HP) and SHP/FI engines will operate satisfactorily on unleaded pump premium.

I had one or two broken top rings come out of my '63 L-76. They were on the cylinders with the greatest bore taper - about .005". I don't know if they broke pulling them past the taper or from the fatigue of expanding by the taper during operation. The engine ran great prior to teardown and sure didn't feel like it had a broken top ring.

Measure bore taper. Assuming it needs to be bored contract with a shop that has boring equipment that indexes off the crankshaft. If they index off the deck they will want to deck it. DON'T LET THIS HAPPEN!!! Get it in writing and make sure the shop understands that they are RESTORING A NUMBERS MATCHING CORVETTE ENGINE, not building a hot rod engine. The deck can be measured for parallelism to the crank. If it's parallel, and most are, deck indexing boring equipment can be used. Most shops just "take a cut to be sure". If your shop has this attitude run like hell somewhere else!

Buy "How to Hotrod your SB Chevy" for info on pocket porting. The old Chevy Power Manuals also have guidance. Pocket porting will yield similar percent torque and power increases on a 300 HP engine without affecting the stump pulling off-idle torque.

If you have a pre-'67 engine throw away the rods and buy the later small bearing rods - the ones that have the little hump of metal adjacent to the bolt seats. Magnflux late small bearing rods. For mechanical lifter engines consider buying a set of Crower Sportsman rods for a bullet proof bottom end you'll never have to worry about - as long as the bearings don't get oil starved.

If you can find a correct coolant pump casting, have it rebuilt with a 5/8" ball-roller bearing. This is an upgraded bearing that replaces the front set of ***** with rollers, and it will live longer.

Duke

Rogs65

I'm a new participant to the Forum only because I finally picked up my 65 L79 "dreamcar" about a month ago BUT I have been following the forum for quite some time now.
You (Duke) and many other highly knowledgable people never cease to amaze me. I and many others have learned so much from you guys.
Thanks!!! :flag :seeya :steering:

Dave McDufford

Duke,

Your response surprised me a bit. On July 15th & 16th on another board you and Joe Lucia were providing your normal great insight (I mean that sincerely) and both of you seemed to recommend roller lifters.

I am going to rebuild a 1965 L79 this winter as part of a complete restoration project. Per the previous owners (I have talked to the owners back to the mid 1970’s) the engine is the original engine but has been re-stamped. It currently has what was described by the owner who rebuilt it as a “Duntov 30-30” solid lifter cam in it. I liked the idle and performance (the hole in the exhaust pipe probably helped in this perception).

As a starting point, based on your and Joe’s comments, and I was considering an LT-1 cam, the pocket porting and intake/head matching you recommend and Keith Black pistons with the appropriate head gasket (per Joe). In addition, I was planning on using Comp Cams Magnum Roller Rocker arms (reduce side load on valve and friction). What to do next becomes fuzzy. I have not rebuilt an engine since the early 1970’s and do not know what part of today’s technology is worth using.

I was thinking of using the LT-1 cam with either solid rollers or hydraulic rollers (if they can handle the acceleration) – then my thinking gets stuck.

That is on odd days. On even days I think I want to just build a stock L79 because it was a pretty good street engine. I do not plan to race the car but I want a noticeable idle. Any comments?

Thanks.

Dave

:cheers:

Kid_Again

hmmmm.....what's the harm in reducing valve train friction with roller rockers if you can get a decent price on the rockers?...if there's no harm and potential benefit at higher revs i would urge you to consider the rr's if you can (i did and think it's a worthwhile investment BUT you need to factor in the cost of tall valve covers - this ain't cheap :nono: )...and follow the advice of ensuring you can get the air efficiently in and out of the heads!

SWCDuke

I recall Joe advocating a modern roller cam, but I always recommend OE or equivalent cams and valve train parts. If you want an hydraulic lifter cam the L-79 is excellent. If you want a mechanical lifter cam the LT-1 is the way to go. The LT-1 cam makes about the same low end torque as the L-79 with greater peak torque and power. The 30-30 cam makes marginally more power at 6000-6500 than the LT-1, but loses below 6000 and big time below 3000.

Cam lobes are designed for the specfic lifter type. The LT-1 cam is designed for flat mechanical tappets and you cannot just install a roller lifter. Lobes designed for roller lifters have very different profiles due to the way the fulcrum point changes as the cam works the roller. Also, a lobe will have different clearacne ramp and acceleration characteristics depending on the type of lifter it is designed for.

Always use the proper lifter type that the cam is designed for. If not, your asking for BIG trouble.

Rollers allow more rapid valve acceleration, so a roller can have less duration than a mechanical lifter cam and make the same peak power, but because timing is shorter, torque bandwidth is usually improved. Most mechanical roller lifter cams are designed for racing and valvetrain life is short compared to OE valvetrain components. There may now be some street oriented mechanical or hydraulic roller cams for vintage SBs, but will probably require some block machining. It appears Joe has researched the issue of street oriented roller cams in vintage SBs, so he would be the guy to talk too.

Regarding roller rockers(either the "semi-roller rockers" with roller tips or full roller rockers that replace the pivot ***** with needle bearings) I don't think they are of much value in a street high performance engine. Valve guide wear in Chevy V-8s is not excessive with OEM lobe lifts, so valve less valve guide wear with roller rockers is debatable, and there are occassional reports of aftermaket rocker failures. Full roller rockers are of benefit in a racing engine that will operate consistently over 5-6000 RPM because they do exhibit less friction at high revs and less oil heating. Plus, they need less oil than the OE rockers, so you can reduce overhead oiling.

I like OE components because they are inexpensive and proven in tens of millions of engines over the last 45+ years, and Chevrolet spent a lot of R&D developing cam lobes that provide excellent torque bandwidth with full OE valvetrain reliability. They are also optimized for the OEM exhaust manifolds. Using the LT-1 as an example, I have never seen an aftermarket cam with the clever lobe design characteristics of the LT-1 cam. To this day it is unique!

The best investment you can make in a vintage SB is to work the heads regardless or whether you have a medium performance (300HP) engine or a SHP engine. For a given cam, good head work will pay noticeable dividends in the upper third of the rev range, without affecting low end torque, idle quality, or driveability. Completely hogging out the ports is not necessary, nor desireable, but working the port pockets to remove the ridge from the cutter tool that was first used to rough form the pocket, cleaning up any casting flash in the port ("polishing" is neither necessary nor desireable), matching the head/manifold joint on both inlet and exhaust, and careful attention to valve seat geometry with entrance and departure angles (the proverbial "three angle valve job") will pay dividends with no negative effects, and if you are handy and like to do your own work you can do most of this yourself.

My philosophy on rebuilding engines is to do it once, so it lasts a lifetime in collector car service. Careful attention to detail such as clearances and the dimensions that determine actual compression ratio is a must as is qualifying all critical bottom end components such as the rods and crank by magnaflux inspection. The only really weak internal parts in vintage SBs are the early (pre-'67) small bearing rods. They can be qualified and reworked, but nowadays, it's cheaper and better to replace them, apriori, with the last design small bearing rod design that went into production in '67. OE valvetrain parts are usable as is, and you pick the cam based on the engine operating characteristics you want - 929 for a smooth idling torque monster, L-79 for high performance characteristics, and the LT-1 if you want a little "edgier" SHP characteristics and want to maximize average power across the entire operating range.

Duke




[Modified by SWCDuke, 10:40 AM 9/11/2003]

Crazyhorse

Duke, what about replacing the rockers with some true 1.52's. Didn't you mention once that the stock stamped rockers actually spec out to about 1.43 ?

I agree that the roller cam conversion is not cost effective for our street motors. I think it's around $600 just for the parts.

chris ritchie

"A priori"

All right!

Crazyhorse

OK I found this.
Although this article is analyzing the effects of a change to a 1.6 ratio they have included a test of stock stamped units.

From the article……….
“First of all, rocker arms rarely maintain the same ratio throughout the entire valve-lift curve because the rocker arm moves in an arc as it generates lift. Roller rockers do a good job of maintaining their stated rocker ratio throughout the entire lift curve, but the same is not always true of stock-stamped factory or budget stock replacement rocker arms. These pieces often test far short of their rated rocker ratio. To prove this point, we tested several supposedly 1.5:1 small-block rocker arms and discovered rocker ratios between 1.30:1 and 1.49:1. We also found that the ratios changed throughout the lift curve, increasing the ratio as lift increased. This reduced ratio means lost valve lift and potentially lost torque and horsepower. “
http://www.chevyhiperformance.com/te...ock/index.html

SWCDuke

I've measured the OEM SB rockers. The ratio starts out at 1.37:1 at the lash point and increases to 1.44:1 at max lift with an OE SHP cam. I've never measured any aftermarket rockers, but they are all going to very somewhat from the claimed ratio.

I just can't get excited about rocker arms. I DO "factor" the OE specified valve lash since the specs assume a 1.5:1 ratio, so my timing points are true and the valves aren't dropped onto the seats at higher than ramp velocity, but beyond "fixing" the lash specs, the variation in rocker ratio from the nominal number is not anything to worry about.

My two favorite engines are vintage mechanical lifter Corvette engines and the Cosworth Vega engine. I've run hundreds of simulations on each and have pretty well characterized what is worthwhile and what isn't and have proved out some changes on the actual hardware.

The bottom line is always the same - OE cams/valvetrains are great. If you want broad torque bandwidth, combined with good driveability and maximum top end power in a streetable high performance engine - spare no expense on the heads. With what you save buying OEM or equivalent replacement parts instead of hot rod parts you should have plenty of budget to build a bullet proof bottom end topped with killer heads, and it will last forever.

Duke

Rogs65

Duke,

I noticed that you are in southern Ca like me...Know someone who does top notch jobs on heads? I have the L79 350 hp with the 2.02 heads.
Rog

SWCDuke

No, I've always done my own head work, so I don't know of any So Cal shops that one can trust. I'm sure they're out there. I just don't know of them.

Duke