Hagerty.com

The oil-soaked details behind our big-block 396 Redline Rebuild

Our latest Redline Rebuild is a rapid-fire restoration of a 1969 Chevrolet big-block 396, and there is more to the greasy-to-shiny story of this V-8 than the time-lapse process shows. For an engine that was freshened up just five years ago, this poor workhorse was tired and in need of some love. Fortunately, Davin Reckow was on the case to nurse it back to health.


This is a companion discussion topic for the original entry at https://www.hagerty.com/articles-videos/articles/2019/05/13/oil-soaked-details-behind-our-big-block-396-redline-rebuild

I’m sorry to have to lead off this way, but after investing an hour and a half I am left disappointed. Although I have several thoughts regarding the presentation format, my biggest disappointment was in the discussion around the ‘roller cam’ - I am still just as much in the dark as I was before my investment of time.

What is my complaint, you ask? It is this - where exactly is the needle bearing? With all those parts on display - the cam, the rockers, the lifters, you couldn’t have shown us? I get the concept - instead of ‘something’ having a flat surface, said surface has a needle roller bearing. I had to jump through visual mental hoops to try and figure where said bearing resides. So here’s my stab - the bearing is actually in the lifter. If so, then why this is called a roller cam is beyond me. If I have it wrong, then I am absolutely no closer to understanding what goes into making a ‘roller cam’.

One thing I noticed in this video, and that was the discussion around the air injection tubes at the exhaust manifold. I would like to take this time to help clarify how they work.

By trade, I am an automotive engineer, and like to use my 1970s vintage car for ‘show and tell’ at the local car shows. I keep mine fully emissions equipped, just as it left the factory, in an octopuses mess of vacuum hoses and feedback systems. I like it this way, because of how I can teach even lay-people (even kids!) at shows how simple it actually can be, and can even with proper direction, goad them into ‘designing’ the same type of system on their own, which really surprises them when they realize the mystery is not so mysterious afterall. That is why I sometimes feel a little like a ‘troll’ regarding what could be taken away as misinformation about some of the systems.

The air injection system (called “Secondary Air Injection”), was not just a ‘dilution’ device, meant to ‘water down’ the excess pollutants in the tail-pipe outlet. The secondary air injection system solved a crucial issue of ground level smog. How? As an engine burns its fuel charge, there are inefficiencies of combustion inherent to the design. Combustion chamber geometry, quench zones, poor spark propagation, you name it. Unfortunately, this means that not all gasoline (in this engine’s case) is fully burned. You can smell this at any car show when a car drive’s on by. That classic ‘overly rich’ exhaust smell that you don’t notice with today’s cars. That unburned gasoline? Those are called ‘hydrocarbon’ emissions, or just ‘HCs’ in shorthand lingo. Get those up into the atmosphere, and through the wonders of chemistry, they transform into ground level ozone after being catalyzed by high humidity and elevated temperatures (think ‘ozone action day’). California felt they had enough smog already, so they requested a fix to the tail-pipe-out HCs (a stance later taken up by the EPA-at-large in following emissions years). So, how do you get rid of unburned gasoline vapors in the exhaust? Maybe try to burn it in the exhaust pipe? The auto industry thought it was worth a shot. The fancy term for ‘burning’ fuel is ‘oxidize.’ One problem, there was no longer enough ‘oxygen’ to ‘oxidize’ the HCs in the exhaust. So, the path they chose was secondary air injection (“Thermactors,” “Smog Pumps,” insert hot-rod lingo here). Exhaust is generally already hot when it leaves the cylinder. Hot enough to burn away HCs. By adding a fresh air charge into the exhaust, there is now some oxygen to oxidize, or burn away, the excess HCs. With the unburned tailpipe-out HCs mitigated (it was not 100% efficient, but still felt to be worthwhile), the car could now make California happy[-er]!

As for the power loss? Well, I can’t argue against that. Every accessory or bearing surface contributes a parasitic load. And while I have never seen a dyno result (especially one that I would consider reliable) to clearly indicate the amount of parasitic losses an air pump contributes, I would hazard a guess the air pump is far less than most people think. Probably less than 5 hp, but admit I’m guessing here (based off of heavy duty diesel air compressors running at 90 psi, much higher than a secondary air injection system).

Thank you for reading!

@scott.hoffman - Good question on the roller lifter.

Below is a close up photo of a roller lifter setup. The Redline Rebuild Explained video didn’t dive too far into the details on specific parts.

The anti-friction bearing is placed on the tip of the lifter, so that it rides on the camshaft lobe. You can see they need to stay directional, and that is why they are tied together in pairs to to keep from rotating. This allows for more aggressive lobe profile since the anti-friction bearing can “climb” the ramp of the lobe easier. It also allows for greater valve spring pressure without damaging the cam or lifter.

roller%20lifter

Great run down - I only knew them as air pumps, no clue what they did other than pumping air…well as you point out, that is all they did, but the science behind all that hot air is very interesting.

As for losses, maybe not a lot in terms of percentage on a V8, or 6, but I had an MGB with all that plumbing and boy you knew there was something bad under the hood.

Well that clears that up - a picture is worth more than a few words.