BBC weak points

General engine tech -- Drag Racing to Circle Track

Moderator: Team

User avatar
Alan Roehrich
Guru
Guru
Posts: 3069
Joined: Tue Jul 04, 2006 5:58 pm
Location: Murfreesboro TN
Contact:

Re: BBC weak points

Post by Alan Roehrich »

In some 40 years, I can count on the fingers of one hand the times that I've seen the roll pin or distributor gear fail on its own. Of course, there are situations where people have jacked up pressure or volume, or both, and worn out the gear. It's not ideal, but it's not terrible, either. It's plenty good enough for a truck engine.

The only problem with OE chain drive for the camshaft is the cheap parts used. They use cheap metal for gears and don't heat treat. If they were to use heat treated steel, they'd last the life of the engine and still be tight on tear down.

One thing that I did leave out on the old 8.1L with regard short comings is the oil pan. For a truck engine that sees heavy use, it should hold 8-9 quarts by itself. I use a PF-932 two quart filter on mine, but unless you go with a remote (and you should), you can't do that on a 4x4.

Now, I do despise the net lash rocker system used on the late model big block. However, such valvetrain is common these days, the OE's prefer non adjustable valvetrain.

The current hot setup for the old 8.1L is a set of decent headers, pulling the intake to modify it and adapt a much larger throttle body, improving the air duct from the filter box, pulling the screens from the MAF, dumping the catalytic converters, and tuning. The factory tune is way short on timing and has seriously delayed enrichment, but then runs rich at heavy throttle, as well as serious torque limiting. There are people using up to 228 degrees @ 0.050", and around 0.520" lift, on a 114 LSA. I'm actually working on a shaft rocker system that will allow a bolt in setup with full adjustment. I have an 8.1L sitting in the shop, I bought as an extra to work on and do R&D with. At some point, when I have time, I'll have some packages for the 8.1L.

The only way I'd even consider another truck is if GM reintroduced the 8.1L Vortec modernized, with maybe an 8 speed Allison. Otherwise, old faithful is getting serious upgrades, including conversion from 5 speed Allison to 6 speed. As well as a full header and dual exhaust system, the intake, MAF, air duct, and throttle body upgrade, and a cam and shaft rocker setup. No reason to expect less than 450HP at the flywheel, without pulling the heads.
Walter R. Malik
Guru
Guru
Posts: 6353
Joined: Tue Jul 24, 2012 11:15 am
Location: Roseville, Michigan (just north of Detroit)
Contact:

Re: BBC weak points

Post by Walter R. Malik »

Alan Roehrich wrote: Sat Mar 02, 2019 10:43 pm In some 40 years, I can count on the fingers of one hand the times that I've seen the roll pin or distributor gear fail on its own. Of course, there are situations where people have jacked up pressure or volume, or both, and worn out the gear. It's not ideal, but it's not terrible, either. It's plenty good enough for a truck engine.

The only problem with OE chain drive for the camshaft is the cheap parts used. They use cheap metal for gears and don't heat treat. If they were to use heat treated steel, they'd last the life of the engine and still be tight on tear down.

One thing that I did leave out on the old 8.1L with regard short comings is the oil pan. For a truck engine that sees heavy use, it should hold 8-9 quarts by itself. I use a PF-932 two quart filter on mine, but unless you go with a remote (and you should), you can't do that on a 4x4.

Now, I do despise the net lash rocker system used on the late model big block. However, such valvetrain is common these days, the OE's prefer non adjustable valvetrain.

The current hot setup for the old 8.1L is a set of decent headers, pulling the intake to modify it and adapt a much larger throttle body, improving the air duct from the filter box, pulling the screens from the MAF, dumping the catalytic converters, and tuning. The factory tune is way short on timing and has seriously delayed enrichment, but then runs rich at heavy throttle, as well as serious torque limiting. There are people using up to 228 degrees @ 0.050", and around 0.520" lift, on a 114 LSA. I'm actually working on a shaft rocker system that will allow a bolt in setup with full adjustment. I have an 8.1L sitting in the shop, I bought as an extra to work on and do R&D with. At some point, when I have time, I'll have some packages for the 8.1L.

The only way I'd even consider another truck is if GM reintroduced the 8.1L Vortec modernized, with maybe an 8 speed Allison. Otherwise, old faithful is getting serious upgrades, including conversion from 5 speed Allison to 6 speed. As well as a full header and dual exhaust system, the intake, MAF, air duct, and throttle body upgrade, and a cam and shaft rocker setup. No reason to expect less than 450HP at the flywheel, without pulling the heads.
My brother only has a 4 speed automatic in his truck with the 8.1 Liter engine.
Except for the fuel mileage, he is very happy with how it runs.

DART does offer a carbureted, 2 plane intake manifold for it and I wonder if injector bungs were added and an aftermarket throttle body, if it would be an improvement to the mileage aspect.
http://www.rmcompetition.com
Specialty engine building at its finest.
User avatar
Alan Roehrich
Guru
Guru
Posts: 3069
Joined: Tue Jul 04, 2006 5:58 pm
Location: Murfreesboro TN
Contact:

Re: BBC weak points

Post by Alan Roehrich »

Walter, do a search in the 8.1L intake, you'll find people modify it, there are a ton of pics. There's a guy who will modify it for you for $800, which is probably cheaper than you could do the full Dart deal.

I doubt the Dart would do anything for fuel economy. He'd probably get a lot more out of a good tune, and headers with a good exhaust. You can get the tune cheap, maybe $300.

My buddy at Hedman says the 2nd generation Camaro headers work well, according to his customers.
Schurkey
HotPass
HotPass
Posts: 1858
Joined: Sun Mar 01, 2009 2:42 am
Location: The Seasonally Frozen Wastelands

Re: BBC weak points

Post by Schurkey »

Shortcomings of the MK IV--Gen 5/6 engines:

Smokey Yunick talks about the '63 "Mystery Engine" that set records at Daytona in qualifying in his book set.
https://shop.carbonpressonline.com/prod ... tegoryId=2

Seemed to have much respect for Dick Keneith who was the main design guy. Then he says the "Mystery Engine" design was degraded for production, the result was the Mark IV of 1965.

I don't know enough about the "Mystery" engine to understand what was compromised. Anyone else with Mystery Engine experience? I've seen a few photos of the Mystery Engine on-line, and I have the Hot Rod article from '63, but no real details about what was changed to produce the Mark IV.
Post Reply