Welcome to the forum. Lots of great information contained here. Since the car has 5K miles on the the rebuilt engine, consider asking the previous owner what fuel grade was used. Good luck with the car and we need some pictures. Jerry

 

Two big maintenance items to avoid in a vintage Chevy small block...

Excessive detonation and lack of ZDDP in the oil...

You've found about at the first -- and any CI-4 rated oil addresses the second...

 

ZDDP or CJ-4 rated oil is new not me. What is this?

Butch

 

John, here's something I discovered many years ago when I owned a very early 70's Harley, Sportster.

Because the octane rating was dropping then, along with compression, I became concerned about detonation. However it was difficult to hear the engine over the sound of the exhaust on that Sportster.

I was also flying reciprocating airplanes at that time while attending flight training. In order to hear our radios over the sound of the large radial engine right in front of us, we wore ear plugs under our helmets. I decided to wear them under my motorcycle helmet and noticed the ear plugs muffled the exhaust enough that I could now hear the engine. I added some octane boost and noticed immediately that the engine ran even quieter. I have continued to wear earplugs under my helmet while riding to this day.

One other thing I noticed many years ago (in the early 80's), was that when leaving the drive through of a fast food restaurant with the window down, I happened to notice our carbureted Honda seemed to be pinging a bit. It was summer and the A/C was on, so I turned it off and drove through again to see if there was a difference. Sure enough the pinging was gone. Something about the close proximity to the wall of the building (and the window being down) amplified the engine noise that I had not otherwise noticed. A slight tweak of the timing seemed to eliminate the problem.

I believe that the widespread use of electronic fuel management and knock sensors has pretty much eliminated this as an issue on most modern cars, but techniques such as this may prove useful in diagnosing our older classics.

Good luck... GUSTO

 

Yup that's what it was, but mixed correctly it added about 2 points to the octane. It is a product used in making tires, but was used by the Germans in WWII to add to the refined coal they made into gasoline.

 

I suggest you start by testing the spark advance map to determine if it is OE or modified. Low end torque can be significantly improved by installing lighter centrifugal springs in the distributor to bring full advance in earlier than the OE 24 @ 4600. Then set total WOT advance in the range of 36-40 a few hundred revs above the point where the centrifugal is all in.

Search for threads started by me and download and study the tuning seminar pdf for a more thorough discussion.

Also measure head gasket thickness at the corners of the head-block interface. Chances are it will be much thicker than the OE .018"steel shim gasket.

Start with the highest octane available, then let the tank get close to empty and add about three gallons of 87. Then test for detonation by loading up the engine at low revs, like half throttle or more at 1500 in top gear, especially going up a mild grade.

If no detonation run the test again, or if it does detonate run the test with mid-grade. Over the years most OE engines have been rebuilt with lower compression than OE, so I figure you have at least a 50/50 chance of being able to run detonation free on 87 or 89 even with a more aggressive than OE spark advance map.

Duke

 

Flat tappet motors require specific levels of Zinc-Phosphorus to avoid excessive cam and other mechanical wear. Many (most) modern oils have eliminated this (it was bad for catalytic convertors). So, you'll want an oil with the proper amounts of ZDDP in it. Typically those are modern diesel oils (CI-4 rated). There are others if you prefer some Rotella brands, Mobil One 15W-50W.

There is a forum 'sticky' thread at the top of the web page somewhere that discusses this in detail... Here it is:

https://www.corvetteforum.com/forums...in-please.html

Don't want to hijack the thread but, as a new owner, this is critical info...

 

Zinc and phosphorous have NOT been "eliminated", but current S-category oil has a P limit of 800 PPM and current C-category is 1200, which is about the same as before any limitations were established. The Zn concentration is usually in the range of 100 to 150 ppm more than the P concentration.

To the OP - along with downloading the tuning seminar download and read my oil article, and I think many others may need a refresher on this subject, too.

Duke

 

That is true of course... I got carried away...
This chart shows typical levels in the Mobil One product line.
I use the 15W-50W (red rectangle) product....some say I'm foolish for spending the money for synthetic...some say not.
My annual oil change in one classic car is hardly breaking the bank and NAPA has this oil on the shelf...

 

Thanks Frankie, I've printed it off. Excellent information!

Butch

 

You may find this helpful..................

http://nicoclub.com/archives/detonat...on-tuning.html

 

In my experience, the camshafts that are going flat are new-ish or recently manufactured camshafts that are not hardened properly, combined with poor quality newer lifters. I have only seen new cams and lifters fail, not ones installed decades ago. That said, the old stuff was run with plenty of ZDDP in the older oils. Most cams that are still running in these cars and that are old will be ok on most newer oils, if they are running the milder stock profiles. A stock GM camshaft in a 250-350 HP engine should be just fine with minimal ZDDP. I have old fashioned flat-tapped cams in all of my old cars, as I've seen too many roller cam failures take out expensive engines. The key is to have good quality parts. Personally, I have been running Rotella for about the past 18 years. Before that, it was Kendall GT with the high ZDDP count. I have had no oil related failures in multiple vehicles over 100's of thousands of miles. Good luck with your 'new' Corvette. They are a real blast to drive!!

 

The oil did change and camshaft failures did start at that point. I think I first saw this in the early 90's.
Camshafts are hardened 3/8 of an inch deep on the nose. All lobes are hardened the same. That is why re ground cams were possible. It is not a surface hardening.
Lifters did change and that probably contributed. Remember the old days GM lifters had the hard plate, the last 1/8 inch that touched the cam lobe was different material.
Sealed Power Lifters had the ping mark where they were all tested for hardness prior to sell. That was the old days and in 1970 you paid more for those lifters than you pay today 40+ years later. The oil used today is more important to protect your cam and lifters. I still run Rotella or Delo Diesel oil 15-40W and it has worked so far.

Detonation, if you jab the gas and the engine starts to wind up and then feels like it is dragging a heavy load and the sound of the exhaust kind of goes flat. That could be heavy detonation. Get out of the throttle and hope no damage was done.
This type is silent except for the exhaust note change.
Pinging although bad is not nearly as dangerous as heavy detonation.

 

Bought my '61 in Jan '71. Now I'm 71 and still enjoying driving the classic auto. Don't worry about comfort because the fun factor takes over