GeorgeB64

Hi all, I want to go thru my engine and set a baseline for driving the car a lot and to set my own maintenance schedule. The engine was rebuilt by a PO a few years back and the story is it has @ 1500 miles.Everything else on the motor matches as far as being "stock"...2.5 center dumps, manifold, Holley, distributor etc.

I'm a little confused as I see in past threads the cam is referred to as the Duntov 30-30? Is it because lash was .030 for both intake & exhaust valves?

The more I read the more confused I get. I also see different numbers posted for the same cam as far as lift duration and adjustment. Sorry if this was asked before I just could not find it or a clear answer.

I have a receipt for the rebuild and it states a new set of solid lifters was installed and the installed cam is CS118R.

What I really need to know is the valve adjustment spec for intake and exhaust for the CS118R?


I'd like to hear from experienced driver/maintainer use the following, if you dont mind taking a few secs:

A.is there a "power band" for this cam....meaning does it "come on" at say 2500rpm and last thru redline but is not real smooth at idle? Just curious.

B. Is the best method or time for adjustment hot or cold running or not or both? I read the manuals but curious what real user experience has been.

C. Out of curiosity: What is the cam grind lift?
What is the cam grind duration?
Who makes this billet?

Thanks in advance for the help.

George

65tripleblack

Buy the Speed Pro CS118R, which is an exact duplicate of the original GM3849346 cam. It was known as the legendary "30-30" cam. The "Duntov" cam was an earlier, much milder cam first used in the 1957 283 Corvette engine, and last used in the 1963 327 Corvette engine. The "30-30" was used on 1964-65 327 365 and 375 engines, as well as the 1967-1969 302 Z28.

The cam comes on rather abruptly, at around 4000 RPM, and keeps pulling up to redline.

The best way to adjust solid lifters, I have found, is to use the "hot" spec. Get the engine to operating temperature, shut it off and let it cool for about 20 minutes until you can touch the hot exhaust manifolds without burning yourself. Set them with the engine off.

Here are accurate specs. In addition, the lobe lift is .323/.323:

http://www.summitracing.com/parts/slp-cs-118r

GeorgeB64

Thanks very much. So the adjustment/lash is then:

Intake.030 and Exhaust .030?

Just wanted to be sure.

Appreciate the help 65tripleblack.

George

larrywalk

The spec duration (approximately 346 degrees) is very long due to the very long ramps, but the valves don't open then because of the .030" of valve lash. A far better measurement is 254 degrees at .050" of lifter rise, but due to the valve lash, the cam is roughly equivalent to at hydraulic cam with a duration of 240 degrees at .050.

Because of the very long ramps, don't try to lash this cam cold at TDC firing because the ramp will give the wrong lash. It works better to use the EO-IC method, lashing the intake when the Exhaust Opens, and lashing the exhaust when the Intake Closes. Once you've determined the amount of change from hot-and-running to off-and-cold, you can lash the valves cold with the change applied.

Further, since the stock stamped rocker arms average only about 1.37 rocker arm ratio, there is good rationale to lash the valves at .024; however, this will slightly hurt idle and low rpm performance compared to the lash of 30-30.

The cam really does come on strong at 3500 rpm and up!

Lastly, the cam is a cast iron cam and does work with stock SBC springs although the stronger off road springs work even better.

65tripleblack

Larry,

Speed Pro rates the advertised duration @ 295/295, and very strangely, at 310 on the exhaust side of the LT1, which as you know is the same as the 30-30 intake and exhaust lobes! Verrrrry interesting. One's correct and the other's not! I believe that 310/310 is more accurate. I never heard of 346/346 for the 30-30, and this sounds much too long. I have the actual, measured cam angle vs lift measurements, and the actual measurements match very well with Speed Pro's 310/310 durations @ .004" valve lift (J604d or seat-to-seat). Even at 310/310, there's a WHOPPING 56 degree difference between .050 lift and seat-to-seat lift!! VERY lazy dynamics, huge pressure bleed-off and horrible efficiency by today's standards. The Duntov, although much milder, is a MUCH more efficient cam.

The Z28 springs are not necessary. I wouldn't install them unless the rocker studs are screw-in or at least pinned. The stock marshmallows are enough for this very lazy cam.

The EO-IC method is the one I use, as well. I also lash this cam at .025/.025, which was the original blueprint spec on this cam before GM "band aided" a drivability issue with the Rochester engine by widening the lash. "The Professor" or "Poindexter" professes that the cam should be lashed at .023/.023, which compensates for the actual rocker ratio at POML. I think that .025/.025 is safer and a better compromise. Lashing at .023/.023 or .025/.025 will decrease engine idle vacuum, make for a much more potent "wow" factor at the cruise-in, will increase the dramatic effect when the engine comes on the cam, and will increase peak power. The drawback to this is a loss of low/midrange torque. The lash debate has gone on for a long time now. Pandora's Box is now open. Have at-it.

MikeM

I had a '69 Z 28 with this same cam in the early '70's. It had a close ratio transmission and 4.11 gear.

One day I decided to adjust the valves on the engine. It was in print even back then that the valves should be adjusted to the original design spec which was around .023-.025. Anyway, I cranked the valves down to that spec. Took it out for a drive and the thing wouldn't even spin the back tires. Wouldn't get out of it's own smoke!

Back in the driveway and re-adjusted to the .030 spec and it ran much, much better. I never tightened the valves down on any other engine that tight again using that cam.

You can try it both ways and see what your engine likes.

I would suggest you make sure the rocker adjustment nuts are in good condition. They are torque prevailing nuts and if they don't have good resistance to turning, you'll be adjusting your valves more than you should have to which isn't very often at all. Maybe every 10K miles if you wind it up quite a bit.

65tripleblack

I agree about smoking the tires, but disagree with what you said about "what the engine likes". Here's what I said about lash adjustment:

"Lashing at .023/.023 or .025/.025 will decrease engine idle vacuum, make for a much more potent "wow" factor at the cruise-in, will increase the dramatic effect when the engine comes on the cam, and will increase peak power. The drawback to this is a loss of low/midrange torque."

And this applies to any cam, as you know. Tighter lash has the effect of making the cam "bigger" because it increases lift and duration (and, consequently, overlap). And, what that does is covered in my quote from the previous post.

Instead of saying "what the engine likes", it's more correct to say "what YOU like" since the engine will run great either way.

MikeM

I said in one sentence what it took you two paragraphs to say. You like/engine likes, almost the same thing to me. The difference is, if you run that engine a lot at low engine speeds with the tight lash, neither you or the engine will like it.

Gears have a lot to do with it too but I didn't want to get too windy.



You probably didn't notice but I was trying to support everything you said with as few words as possible.

65tripleblack

Yes, Mike. I realize that. Are you sick, or something?
Anyway, yer a regular Gary Cooper.

larrywalk

65TripleBlack... I think that the confusion arises with this "30-30" cam between valve events and lifter events. Virtually all the cam companies publish numbers at .050" of lifter rise, but GM, in some of the Chevrolet Power books, published duration at the lash point of the valve, which would be valve open and close - this is, of course, much greater than the duration at .050" lifter rise. At a lifter rise of .050, the valve would be open .075 (with 1.5 ratio rockers) less the lash (.025 or .030) which would be .050 or .045". In actuality, the stamped rockers fall short so it would be even less.

From the NCCC Technically Speaking document, the duration of the GM cam 3849347, it is listed as 346 degrees and 13 minutes on both the intake and exhaust lobes of the cam (not the valve). These are very long ramps and take up the valve lash, be it .024" or .030" before the valve evens starts to open.

I do have a 30-30 cam (in a box under my workbench) which I used to run 40 years ago; I've profiled it years ago with a dial indicator; the lobe rise is .323" on both lobes. It was a fun cam, but the newer cams have much faster lobes and hence higher vacuum and better low/mid range performance. I don't care what people use for lash as it's quite forgiving, so I don't have a dog in the fight.

climbabout

George - I went through a the process of learning how to adjust my 64L76 not long ago - you might read through this thread to see what I learned.

http://forums.corvetteforum.com/c1-a...nt-method.html

Tim

Critter1

These cam discussions (wars) are definitely worth the price of admission.

I agree Mike. If anyone really thinks that setting the 30-30 cam lash at .023-.023 is going to result in anything positive, other than sounding tough, they've been reading too many hot rod magazines.

65tripleblack

Don't take this as confrontational. The so-called "30-30" cam was meant to be lashed at .025 - .025. If you'd rather lash this, or any other solid lifter camshaft wider than design spec, then that means you should have installed a milder camshaft to begin with. If you want to stick with GM vintage cams then pull the 30-30 and use an LT1, or, milder still, an 097.

MikeM

If you choose to drive with this cam with closed exhaust, highway type gears and low speed driving, loosen the lash.

If you choose to open the exhaust, use drag strip type gearing and a lot of aggressive driving you can tighten the lash.

If you choose to use this camshaft with a Rochester fuel injection, leave the lash at 30-30 for all street driving.

I like the OEM GM designed camshafts because they don't need real heavy valve springs, push rods and are very durable. Besides, they seem to run very well in any situation short of the owner wanting maximum power.

Some like to call them obsolete and low tech. They are neither. They just work!

The 097 is an excellent cam for those wanting the rumplety bump idle and power up past 6000 rpm. Not only is it also low tech and obsolete, it also doesn't require the cam killing valve springs, heavy duty push rods, screw in rocker studs, etc. It just works too.

Critter1

I've been looking for some documentation that GM ever recommended setting the lash on the 3849346 30-30 cam at .025". I've never seen any.

I know the original checking clearance specification shown on the print was to be .025" but that wasn't the same as running lash.

GM used "checking clearance" on all mechanical lifter cams of either .020 or .025.

The very first GM new products info manuals for the new 64 model show .030-.030" with no record of a revision. The information was released in July of 1963.

GeorgeB64

Hey guys, thanks to all for the posts. Sorry for stirring this up as it is clearly not a new discussion to those who have been around. I guess I have to use the search better, as I really tried but never came up with Tim's thread on this subject. Thanks Tim.

Appreciate all chiming in as, like a lot of guys, I want to understand what I'm doing on the car, and then do it. Old enough to know I can break more than I can fix real easy if I dont really understand the task and the how & the why. I can get so much from books, but the information gathered from folks with actual practical doing it experience, like many of you have...priceless.

Thanks.
George

MikeM

[QUOTE=Critter1;1583115621


The very first GM new products info manuals for the new 64 model show .030-.030" with no record of a revision. The information was released in July of 1963.[/QUOTE]

The date alone rules out a lot of possible speculations about the valve lash.

65tripleblack

Opening the exhaust with this cam will make minimal difference in the RPM range where this cam is weak. Opening the exhaust will have dramatic benefit when the motor "comes-on-the-cam" because of pulse tuning due to its high overlap. If you have highway gears and use your 30-30 equipped car for low speed driving, then you should have ordered you car with the L79 instead.

The 30-30 cam behaves in the opposite way than all the rest of the Chevrolet factory cams, when driven on the street: it delivers maximum power and behaves less than would be desired at normal loads and engine RPM's. This is true when it is lashed per the design spec. If you didn't want to deal with this, then you should have ordered the "other" SHP cammed engine: the L79.

65tripleblack

What is the purpose of checking clearance and what was the checking clearance of the 097 cam?

MikeM

I just wonder who you are arguing with?

You're just saying again what I've already said except I don't see anyone in this thread thinking they bought the wrong engine except you.