Joe Lucia-Need Help Please

[Kurt B.]

Joe,
Machine shop is encountering difficulties in assmbling my stock L 79 motor and is asking me for ALL the specifications on the L 79 camshaft. I have only been able to find lift, stem diameter, etc from the GM Service Manual for 68.
Do you have all the specifications that relate to this particular camshaft and can you provide me with same? One of the things they asked is "duration" and I can't find that anywhere. They are telling me if they build this motor to stock specifications it will require 101 octane gas and I don't remember having that problem in 1968 or in 1072 when I first purchased the car. If you can provide me with cam specs I can forward them to the shop as I do not knwo what I am talking about and can't seperate "wheat from chaff" when they speak to me.
Thank you in advance for any help
Kurt 26406

[John H.]

Re: Joe Lucia-Need Help Please

Kurt -

The L-79 cam specs are 221*/221* duration @ .050", .447"/.447" gross lift, 114* lobe separation, 110* intake centerline.

[Joe L.]

Re: Joe Lucia-Need Help Please

Kurt-----

The 1968 L-79 camshaft was the GM #3863151. This same camshaft was used on all 65-68 L-79 engines. Unfortunately, there are various "specs" that are often reported on Chevrolet camshafts. The major discrepency usually involves the "duration". I believe that a lot of this has to do with the particular definition of "duration" that is being used by the reporting source. The following are the GM-sourced specs:

duration at lash point:

intake---320 degrees; exhaust---320 degrees

duration at .050" lift:

intake---221 degrees; exhaust---221 degrees

lift with 1.5:1 rocker ratio:

intake---0.447"; exhaust---0.447"

lobe centerline:

114 degrees

Some sources report intake and exhaust "duration" on this camshaft as "342 degrees". I believe this to be the result of some other definition of "duration"; as I mentioned previously, there are many.

Personally, I would not build an engine today with any compression that exceeded 10.0:1. Your 68 L-79 originally used 11.0:1 compression. However, many folks with original 65-68 L-79s report no operating problems using 92 or 93 octane pump gas. Empirical evidence is always the best evidence; it always supercedes "theories".

[Kurt B.]

Re: Joe Lucia-Need Help Please

Thank you Joe and John for your very detailed and extremely helpful input.
Once again I am stressing out over this restoration because I seem to be at odds with the machine shop who wants to do one thing while I (who am paying) want the motor done the way GM did it. I spent years and many dollars accumulating parts that I once had and foolishly discarded so I could rebuild the original motor and now it is turning into a nightmare. Since I do not have motor building expertise, I am baffled how I can see Corvettes with exotic high horsepower motors running around on pump gas but I can't have a stock 1968 L79 motor. I have a friend with a blower Corvette in my town who claims to be pushing over 500 horsepower and he runs 87 octane pump gas with no problems.
It seems at every turn of the road on this restoration I am having to fight for what I want (stock, original) and it is taking the luster off of this project which seems to have become my own personal "Holy Grail".
Thanks again for your input. It is sincerely appreciated.
Kurt

[Shannon Burgess]

Re: Joe Lucia-Need Help Please

Kurt, I know exactly what you mean. I called a few engine shops in my area about rebuilding the engine in my '69. Each shop was recommended to me by people I know. In every case, they first started talking about the need to deck the block, and it went downhill from there. They were incredulous that I wanted a stock rebuild to L-46 specs. I think it's primarily due to the fact that most of these guys are used to building race motors, or as dale calls them, "Harry HotRod" specials. When I informed them that I wanted the stock cam, with the cast iron intake, Quadrajet, and rams horn manifolds, they immediately lost interest.

Shannon

[Gary B.]

Kurt, my L79 runs fine on pump gas

Kurt,

I agree with Joe in the sense that stock 65-67 L79 cars can run well on pump gas. My '66 L79 with 82K miles does anyway. Now my car has no power steering, no power brakes, no A/C, no A.I.R., so maybe that helps some. Optimal ignition timing is also one key and not lugging the engine and stomping on it is another. I just removed my engine for a future rebuild and I'm sure I will be told the same stories down the road that you were. I think that one can cheat a bit during the rebuild with a slightly thicker head gasket, but other than that I think empirical evidence does suggest that running a stock L79 without excessive pinging on today's pump gas is achievable.

Gary

[Mike McKown]

Somebody's pullin' your leg

I'm not a chemist, engineer nor am I am expert. I have run a l-79 in a Chevy 11 (same as your Corvette) since 1966. It still has the 11-1 pistons and the stock cam. No (audible) detonation or preignition on 93 octane gas. Same thing with a 396/375 engine in my '70 Nova. Same thing with the 350/350 engine in my Corvair. Same thing in my 10-1 compression engines in my '63 and '65 Corvettes. All these engines run with healthy timing and have not caused any problems that I have detected. I would think the 10-1 engines would cause problems before the others because of the cam. But, they don't. Another thing, none of my engines uses hardened valve seats. Don't seem to be a problem. Of course, these cars are not driven every day, day in and out. I know of many propane fueled vehicles that ran way over 100,000 miles back in the '60's that did not have valve problems. Propane has no lead in it. That was my benchmark for not installing hardened seats when "no lead" came along.

If it were mine, I'd go back stock. 11-1 and all.

Mike

[Mark Ring]

Re: Joe Lucia-Need Help Please

"151" cam valve opening points I:40*BTC, E:92*BBC Valve closing points I:100*ABC, E:48*ATC. 221* duration @ .050 tappet lift, Lobe centerlines I:110* ATC, E:118*BTC 88* overlap @ zero tappet lift. 35* overlap @ .010 tappet lift.

I know what you mean about being frustrated by the available machinists. You are among friends here. The struggle will make the sucess even more sweeter when you are finished.

-Mark.

P.S.- I built an 11:1 motor a few months ago using the 327/365 SHP cam. It runs well on pump premium with a little race fuel added. I have not tried to run straight pump fuel but I bet it will run. Good luck.

[Clem Z.]

Re: Joe Lucia-Need Help Please

as a builder of blower motors that run on "pump gas",93 octane they only run 28 degrees of total timing. a 8.5:1 static compression engine with a blower at 6# of boost is equal to 11:1 engine.the blower engines i build also have intercoolers to drop the temp of the fuel charge to prevent detonation. also the pistons and head chambers are deburred,polished and equalized to make sure the CR is equal in all cly. the carbs are also jetted 20% rich. the LS-1/LS-6 engines now in the new C-5 corvettes are 10:1/10.5:1 static CR but they also have knock sensors that take timing out to prevent damage and fuel injection to make sure of equal fuel distribution. with a carb and intake manifold the big problem is unequal fuel distribution which causes detonation in some cly. and not in others. because of this i would never build a street engine over 9.5:1 if you intend to get max power by running full 36/38 degrees of total timing.

[Clem Z.]

PS

i am talking about real CR not stated CR because factory engines are lower than their stated CR. you will have a bigger chance of detonation if you just use a thicker head gasket because once the deck clearance gets greater than .040 you get fuel mixture trapped between the piston and the head that does not burn efficiently.

[Mark Ring]

Re: Joe Lucia-Need Help Please

I do need to qualify that 11:1 street engine I am running. It does have a very tight .035" quench which is difficult to duplicate without decking the block. The chambers were all carefully matched and the "30-30" cam is very long so the duration will bleed off some cylinder pressure. I did not mean to suggest a 327 with the "151" cam would run well on pump gas at 11:1 C/R. If you do build it that way, some special fuel may be required.

I did build a 327 with a "151" cam that did run well on pump gas but it had roughly 9.5 C/R and variable duration lifters.

-Mark.

[Mike McKown]

Re: Joe Lucia-Need Help Please

Kurt:

So tell us. What's it going to be? Domed or dished?

Mike

PS. This discussion makes me wonder how many "original" 11-1 big and small block engines there are out there. Could it possibly be true that an "original" 11-1 engine that has been castrated with dished pistons is more "original" than a restamped but otherwise correct block? Just a thought.

[Joe L.]

Re: Joe Lucia-Need Help Please

Mike-----

Manageable compression ratios for small blocks don't usually require dished pistons. For most 63-70 Corvette small blocks with 63-65 cc combustion chambers, flat top pistons (with "eyebrows") will provide about 10:1 which is a "safe" compression ratio with current fuels. Dished pistons with these engines will produce about a 9:1 ratio. Flat top pistons will provide the best combustion efficiency and flame propagation characteristics for the small block engine, anyway. That's why GM uses this type piston in virtually all "modern" small block engines.

Big blocks are different. For even a 9:1 compression ratio, "domed" pistons are usually required. It's just that the "dome" height for a 9:1 piston is lower than that for, say, an 11:1 piston. The dome heights of the latter type pistons can produce more problems than just those associated with the compression ratio.

[Mike McKown]

Re: Joe Lucia-Need Help Please

Joe:

Thank you very much for all your technical information about "domed versus dished". I knew all this but it's good knowledge for those that didn't.

Maybe I mis-interpreted what Kurt was talking about. He said (or so I read) that he wanted to re-build his engine to a "stock, original configuration" and can't understand why his machine shop doesn't want to do it. And I presume, stand behind the rebuild for some period of time or miles. Well, I didn't see anyone addressing that concern and that's why I jumped in with my recommendation to go ahead with the 11-1 rebuild. As you pointed out in your first message, there have been reports of owners of 11-1 engines being run successfully on the street on pump gas. I happen to be one of them.

Now then, I believe that "most" owners of restored Corvettes (I don't know all of them) would probably like to make a quick punch on the throttle from one stoplight to the next, say first and second gear. No power shift so you get a little cooling between gears. Or just out cruising on part throttle. Or running down the highway at 60-70 mph on a long trip. In my experience, easily done with that compression ratio and a few degrees ignition retard from 36-38 degrees theoretical ideal.

Dropping that one point compresion out of a bumpity-bump Chevy just kills the throttle response and sound of the engine. I'll take my 11-1 engine on pump gas with a few degrees ignition retard against a 10-1 engine from stoplight to stoplight any day. Probably same goes for gas milage

I need to hedge a little on my original statement. If I was in business to build engines, I wouldn't build an 11-1 for the street either if I had to guarantee it. Too many people out there that don't know an engine ping from an engine pong.

Also, I believe Kurt wanted his engine to be "original". In other words, "do you have the real McCoy or don't you? I happen to be an engine kinda guy and get really distressd when I overhear someone making sport of my halogen headlight bulbs. Little do they know, I still have my original pistons and I wouldn't have it any other way.

I'm really suprised that more of the "dome heads" didn"t respond to this post. Or, are flat top pistons all the rage for now.

Thanks for listening to my point of view.
Mike

[Joe L.]

Re: Joe Lucia-Need Help Please

Mike-----

No, I don't think that flat-top pistons are necessarily what anyone would call "the rage". However, GM does use them in just about all of their engines for at least the past 10 years, or so.

The reason that I don't usually recommend that folks go higher than 10:1 is not because I consider you can't go higher than 10:1 without experiencing detonation or pre-ignition. I know that there are many folks that do run higher than 10:1 and don't have problems using pump gas. However, if you build an engine with higher than 10:1 compression then your CHANCES of having detonation/pre-ignition problems is much greater. And, if it turns out that you do end up with such problems and a few degrees of initial timing retard DOESN'T solve the problem, then what? Run aviation gasoline? Run high octane racing gasoline? Add large quantities of expensive octane boost every time you fill the tank and carry a case of it around with you if you go on a long trip? Tear the engine down and install new pistons? All of these are not acceptable options, in my opinion. So, I recommend that one be safe and use a compression ratio that will give one a high chance of not having problems to begin with.

Personally, I don't think that higher compression ratios (i.e. in the 11:1 range) really offer much real advantage as far as throttle response, engine sound, etc. There may be a little, but I really think that it's minor. In my opinion, one of the best sounding Corvette engines ever built was a 1971 LS-6 and that engine had 9:1 compression.