64 engine cam

[Steve Pettit]

Re: What can I say?

What a shame that this type of rancor gets an airing in this great forum. Nobody is forced to take Duke's advice, and in this case I might not take it either if I had the mouse, but a sense of respect for each other is the sign of professionalism and expertise that I, for one, value on this board. I have learned much from this board, and from the participants in this squabble, and think that it is too bad to have this personal animosity shown. If you don't agree, just lay out your premises, state your facts and explain your conclusions.

Regards to all,
Steve

[Mike McKown]

Nothing personal here.

I just stated my opinion. It's the same opinion I've had since the LT-1 cam cam out.

What's your opinion, other than trying to "make it personal"?

[G B.]

A word of caution.

Since you said 375 hp rather than 365, I assume you're going to run a 7380 injection unit. If you're going to run a 7375R unit, this advice still applies.

Make sure you run enough valve lash to get a steady vacuum gauge reading of at least 12 inches at an 850 rpm idle speed. That will require a minimum of .030" lash on both the intake and exhaust when adjusted cold at TDC. Some owners have found they have to run even more lash than this (up to .035"!) to get enough idle vacuum for the FI unit to perform well.

Also, make sure that your distributor has a low vacuum canister such as an original GM 236 or an aftermarket B-28 hooked up to work full time. No, the reproduction 236 canister doesn't work right. Yes, it does look pretty. But if you were just building a trailer potato, you wouldn't have come here to ask about the cam, would you?

[Steve Pettit]

Re: Nothing personal here.

Mike,
My opinion regarding the merit of either of these cams wouldn't be worth the time it took to write or read. One of the reasons that I admire this board and guys like you that are the backbone of it is that you explain things that I just had a very cursory knowledge of. I'm strictly a learner here and the only thing that I have to offer is a pretty stock 66 427 that I've been around since it was delivered.

Steve

[Duke W.]

Re: A word of caution.

The proper cold lash to ensure the valve seats at clearance ramp velocity is .023". The 30-30 cam drawing says .025" based on the "theoretical" rocker ratio of 1.5" (but it's really 1.37:1 at the lash point). The top of the clearance ramp is .017" above the base circle (based on analysing the lobe data on the drawing), and .017 x 1.37 = .02325, but all the service literature says .030" - probably to "shorten" the effective duration to get the FI system to idle acceptably. This loose cleance is going to cause more rapid valve seat recession because the valves are slammed into the seat at greater than clearance ramp velocity, and more clearance will make it worse.

A friend with a 327/365 recently cold lashed his valves at .023" - down from my previous recommendation of .026", which was based on a dial indicator analysis of the 30-30 lobe that indicated the top of the ramp was .020", but the drawing data is much more granular and accurate than the dial dial indicator data.

He reports no change in idle quality (other than virtually no lifter clatter) and about 10-11" vacuum at 900 - the same as before.

FI system idle quality has always been probabmatic, and IMO the best solution is to raise the idle speed, and with a 30-30 cam I recommend about 1100 as a starting point. IMO the Chevrolet recommended idle speeds for both carbureted and especially FI mechanical lifter engines are WAY to low.

The correct replacement vacuum can for the OE "236-16" is marked "B28" The NAPA /Echlin part number is VC1810, and it is available in other "brands", but, of course, different part numbers. Even if you order a Delco can under the original part number you will probably get a can marked "B28" since Delco no longer manufactures them. They just buy them from Dana Controls like everyone else.

The "B28" can matches the OE specs (0@4", 16@8") and should be used on ALL mechanical lifter cam engines. It was also OE on L-79s.

Duke

[mike cobine]

Re: Look Up RESTORE.....

Where are you all when guys paint their cars with BC/CC or enamel, whether or not they try to "disguise" the enamel as lacquer, which is not easy to do and is usually easily detectable.


I have to agree with Duke on this point, however, Michael has his points also on the "restore" part.

It seems that the Corvette hobby is fast to be critical on "restore" if it is something they wouldn't do (stamp an engine, use the LT1 cam, etc.) but very lenient on something they would (BC/CC, Radial "reproduction" tires, etc.)

How is using non-original, not-even-available-back-then BC/CC more correct or permissible than using a non-original, not-even-available-back-then camshaft?

But then we step pretty close to when is a reproduction acceptable and when is it not?

[G B.]

Why stop there?

Just run .005" lash, 1.6 rockers, 200 lb. valve springs, and a 2,500 rpm idle speed. Think of the theoretical duration and lift! And the top end! I'm talking 8,000 rpm! For a little while, anyway.

Seriously, I haven't intentionally spun an engine over 6,000 rpm in thirty years. However, I still let them run at idle speed on a fairly regular basis.

I think I'll stick with the low end power and strong 850 rpm idle I get using .030".

[Joe C.]

Re: What can I say?

Steve:

I have no animosity toward any of the fine people who frequent this forum. Duke, in particular, is one of the more astute contributors, IMHO. His advice has helped me in the past.
I am not alone in that opinion, and with that said, I believe that I can safely say that Duke's "recommendation" carries more than a little weight around here. I will not say who the recipient of my letter, posted above, was. I merely posted it as a source of logic, to reason out the opposing viewpoint. If you crunch the numbers, you will see that the LT1 camshaft is not all that it is cracked up to be.

Joe

[Duke W.]

Re: Why stop there?

The .023" 30-30 cam valve clearance is based on the maximum running clearance that will allow the valves to seat at no greater than clearance ramp velocity. Hard running will likely tighten the clearance, especially on the exhaust valve, and that's why mechanical lifter cams have generous clearance ramps - so the clearance never closes up completely, which will hang the valve open and cause it to burn very rapidly.

On the other hand, if the valve clearance is too loose, the valve is slammed into the seat at greater than clearance ramp velocity, which will acclerate seat recession.

There is some myth surrounding valve clearances. For example, tightening clearance "will make for more effective duration" is a myth as long as the clearance is in the range where the valve is lifted and seated at clearance ramp velocity. For typical mechanical lifter cams that have constant velocity clearance ramps, the increase in "effective duration" by running tight lash is miniscule, however, if the clearance is loosened so that the valve is lifted/seated at greater than ramp velocity - the beginning of the opening flank/end of the closing flank - where there is significant acceleration, "effective duration" WILL be reduced a measureable amount. And for this reason some racing cams are designed with constant acceleration clearance ramps, which allows for "lash tuning", but they are not intended for street use because the cam and valve seats may have shorter life than what is expected for a street engine.

My interest is in determining the "optimum setting clearance" that will ensure the valve opens and closes at ramp velocity between lash checks under all operating conditions, so I've measured (SB) actual rocker ratio behavior and determined that is starts at 1.37:1 at the lash point and peaks at about 1.44:1 at max lift with a cam lobe of about .03" lift. (I am trying to obtain BB rocker ratio behavior, but don't have one I can measure myself.)

I've never found a signficant difference between hot lash (either measuring immediately after shutdown or hot and running) and cold readings after the engine cools down, so I recommend cold lashing with the engine off since it is the easiest and least messy procedure.

I have researched available literature on valve heat transfer and valve temperature characteristics under various operating temperatures, and though I cannot determine how much, if any, valve clearance closes up with hard running, the available data indicates that hard running (WOT) will close up exhaust valve clearance a few thou.

I've also determined that a "special procedure" is required to lash all but the Duntov cam because all other mechannical lifter lobes on "on the ramp" at TDC.

I've done all this research and experimentation to satisfy my own curiosity and have made it available in bits and pieces to others. At our last chapter meeting I presented an overview of my research looking for feedback on whether I should write it up for The Corvette Restorer, and although it went over the heads of many, there seemed to be enough interest to pursue the idea.

If its met with cynicism, if not outright rancor, by most of the membership, then maybe the whole idea needs to be rethought. It does get down to a very esoteric and low level of engineeering detail, which may only be understood and appreciated by a very few.

Terry also has to decide whether such an article would be of sufficient interest to the membership to devote the considerable space it will consume as opposed to more "found in the barn" stories and other general interest, non-technical articles.

Duke

[Bill Stephenson]

Re: Look Up RESTORE.....

Mike,

-------The correct cam is readily available. The lacquer paint is difficult if not more than difficult to obtain anymore. And I keep harping on the fact that the little bit of lacquer that is available is not as good as lacquer used to be because of a lack of all the ingrediants that gave lacquer even the short life it used to have back in the day. This arguement doesnt hold water as far as I am concerned. This paint versus cam thing is not apples to apples...........Bill S

[Mark H.]

Your article should be printed. *NM*

[mike cobine]

Re: Look Up RESTORE.....

You can always argue the other way. A Crane cam cut to the specs of the 30-30 cam or the L88 cam is still not the original Chevy cam. It may act the same, but it isn't the same. It has a CRANE number on it, not Chevy!

Still, that is MUCH closer than the BC/CC vs lacquer.

BC/CC is not even close to the old lacquer. At least the new acrylic lacquer is still lacquer, even if it is different in many ways.

- New lacquer is to old lacquer as new Crane cam is to old Chevy cam.

- BC/CC is to old lacqer as is 350 crate engine is to a dated and numbered 327 engine.

As to available, contact PPG and get all you want, except in California and possibly NJ due to their own state EPA requirements. Maybe places like NYC, Chicago and Cook County, etc. are also banning it.

And it also goes back to the a couple of old sayings:

"If it was easy, anyone could do it."

"If it is worth doing, it is worth doing right."

Otherwise, why not just restore Corvettes with any available 350 crate engine as it is too difficult to get a correct engine and restore it correctly. Why not have Maaco paint it as it is too difficult to get lacquer and paint it myself. Heck, around here, I can't get anyone to shot lacquer, as it is too easy and fast for them to shoot BC/CC and be done in a day, as opposed to sanding it out and buffing it out.

Now that said, I am not opposed to people putting LT1 cams in any small block, not opposed to painting it BC, BC/CC, flames, candy, whatever, updating to Wilwood disc brakes, dropping in an LT1, LS1, etc., and basically doing whatever you want.

But restored means a certain thing and should be used only when a car is "restored" and not refurbished or renewed or rebuilt.

[Thomas H.]

Re: Your article should be printed. *NM*

[Bill Stephenson]

Re: Look Up RESTORE.....

Mike,

-----I can appreciate what you are getting at, but a cam manufacturer can duplicate the correct grind exactly and an engine builder can build an engine with manners and performance so close to the original that no NCRS member could tell the difference. While by your definition this imaginary motor is not correctly restored, by mine it is.
-----Base coat/clear coat or even single stage enamel paint is fairly easily discernable to any one who spends a bit of time learning the differences. As far as new lacquer, sure, go ahead and use it. I did, and it turned out well, but it is difficult to take care of and will not have the life of lacquer shot by the factory or aftermarket back in the day. If continued use of your Corvette is one of your goals then bc/cc is probably your wisest choice. I wish I had gone that direction now!
-----Please dont be offended but I find your analogies about 350 crate motors and Maaco completely off the beam. Any restoration of any car right up thru the Duesenbergs you see on the lawn at Pebble Beach use newer, better quality materials. None use 100% original internals that cant be seen. In the context of automobile restoration I just dont think your ridgid interpretation of "doing it right" serves anyone well. Geez, the restorations are costly enough as it is. Theres more than one way to do things right in the restoration business.
-----Personally, I will use original parts when available for anywhere near a reasonable price. I just rebuilt (restored) a 69 Z/28 motor. The original pistons were plain worn out. I found a set of GM part# stamped TRW 20 over pistons and felt lucky to get them for a nickel ($500). Now, by your rules my motor is incorrectly restored because the pistons arent quite the right size, while I think I did the best I could and am pleased. I would have substituted close approximations of those pistons had they been exorbitantly priced and felt satisfied with the outcome.
-----Hope you dont take any of the above as a slam, as it isnt. We just have somewhat different viewpoints............Bill S

[mike cobine]

Re: Look Up RESTORE.....

Actually, Bill, I think we line up more than you think.

My point really is more about the unequal treatment of some items by those in the restoration hobby/business.

On item "A", the slight imperfection costs you all your points and all your dollars.

On item "B", being the same color is usually enough to nearly max out the points and have zero impact on the dollars.

On item "C", it may not be correct to this car, but it is what many think is correct, so you max out the points again.

Item A gets killed with B and C cruise through with no hassle.

The problem I believe is that years ago, NCRS was about "restoration and preservatio of Corvettes and their history." Today, it is about restoration. With very few exceptions, the history of many of these cars do not matter. Joe's '57 is an example. Joe knew what it was, and worked hard to get it and preserve it. However, the pressure on most who would not be nearly as strong willed would be to restore it, destroying the real value of this car.

Another case here in the last couple of days is a 1960 that matches a Bow Tie car but not the JG, yet he is pressured to match the JG for judging purposes.

Do I really feel you need lacquer paint? Only if you insisted that all other items be 100% correct or even 90% correct. If you permit someone that is zero percent correct, but looks right (BC/CC with a lot of work), then why not allow other items that are not correct but look right?

As to your .020 over pistons, they should fairly easy to find, at least compared to other 302 parts. The reason is that .020 was all you could legally take the engine out to or you would cross the 5 liter limit for the cars. A .030 piston was over and illegal in competition. As such, the .020 piston had to be readily available back then, more so than the .030.

Now as to how many survived sitting on a shelf...