77 carb CFM?

[Ken A.]

Re: 77 carb CFM?

Duke,
OK, going from everything, I'll try this on for size and see what you think. The engine has 140k + on it, so it will need to be bored, so get new pistons that will boost the CR to what, 10:1? Maybe a little less?. Next, heads. I just talked to a friend an hour ago and he suggested maybe put in some bigger valves, .194's if the heads can be machined that far. He has headers, but they go into a single free flowing cat, so I'm telling him to get a second cat. Is the L-48 carb a 750? I thought the L-82 had a different carb than the L-48. Keep the same intake, but put on an open element air cleaner like is on my 69. He lives in Phoenix, so cold weather is not a problem. I have the 350/350 cam in my 69, but I know that is old school. Is there a new equivilant cam? Now what about smog? I don't know how stringent they are in AZ, but he does have to get it smogged. It is a CA car, what can he take off and get away with?

Thanks for your help,
Ken

[Duke W.]

Re: 77 carb CFM?

Lot's of questions. For a full rebuild I recommend domed pistons and a head gasket that will yield a true 9.75:1 with the 76 cc heads, which is typically what '69-'70 base engines were when they left Flint with flattop pistons and 62 cc heads. I listed the carb CFM in my first response to this thread. All Chevrolet Q-jets, including BBs, have the same flow. The primary difference between them is calibration. The engine doesn't need a bigger carb!

Pocket port/port match/chamber relieve the heads. Do not install larger valves. Head mods are covered in How to Hot Rod SB Chevys, David Vizards books, and other sources.

Ditch the headers and go back to the OE manifolds.

With an auto trans I do not recommend the L-82 cam or any other. Just retard a new OE equivalent cam 4 degrees from OE indexing. The L-82 cam is an excellent piece, but more suited to manual transmissions. There is no such thing as "old school" cams. Many aftermarket cams have more aggressive dynamics, which loads up the valvetrain and reduces reliability, but they only produce marginal, if any, power improvement. They also almost always have too much overlap. It's all marketing hype. The key to power is cylinder head flow.

As far as what can be done vis-a-vis emissions, that's a local/personal issue for the owner.

I've made many posts about this approach to improving power, so searching the archives should yield more details.

Nothing beats thorough up front planning, and you will save a lot of money by sticking with OE equivalent name brand parts. What you save can be invested in head work.

Duke

[Clem Z.]

Re: 77 carb CFM?

I don't think so. These 3-speed TH transmissions don't have lock up converters. If you add throttle below stall speed the converter will allow revs to approach stall speed. The more converter slippage, the less efficient the transmission, so a high stall converter will consume a lot of fuel on a tall geared, low revving engine. The basic operating range of a L-48 is off-idle to about 4000 and the gearing keeps it in this range at normal road speeds. A high stall converter on a base engine will cause more problems than it will solve. I doesn't make any sense to have a 3000 stall converter on a 4000 RPM engine.

Did you ever install one on a base engine?

Duke

i had one installed in the black and silver indy pace car corv ette which i think was a 78 and it had the std engine for that year. the car was a slug from a standing start at full throttle but the converter made a BIG difference.the 6 cylinder converter will up the stall about 400 RPM which makes a difference. if we wanted to really up the stall speed we used a 4 cylinder vega converter.

[Clem Z.]

Re: 77 carb CFM?

Duke,
OK, going from everything, I'll try this on for size and see what you think. The engine has 140k + on it, so it will need to be bored, so get new pistons that will boost the CR to what, 10:1? Maybe a little less?. Next, heads. I just talked to a friend an hour ago and he suggested maybe put in some bigger valves, .194's if the heads can be machined that far. He has headers, but they go into a single free flowing cat, so I'm telling him to get a second cat. Is the L-48 carb a 750? I thought the L-82 had a different carb than the L-48. Keep the same intake, but put on an open element air cleaner like is on my 69. He lives in Phoenix, so cold weather is not a problem. I have the 350/350 cam in my 69, but I know that is old school. Is there a new equivilant cam? Now what about smog? I don't know how stringent they are in AZ, but he does have to get it smogged. It is a CA car, what can he take off and get away with?

Thanks for your help,
Ken

i would buy a GM crate engine and just store the original. you will get a engine with all new parts and a warranty. they have them in any HP and $$$ range you can afford.