This was just something that I was wondering about the other day. How are the stock parts for performance from an LG4 engine. I dont plan on keeping them I already bought an aftermarket intake carb and dist to put on my 350, but I was just wondering. Is the stock intake, carb, exhaust manifolds and dist really that restrictive. I know the hp ratings from those engines were dismal, but was that mostly due to the upper engine stuff or the very low compression ratios and and lower engine stuff such as the pistons and cam. Any thoughts?

Matt

 

I would at least get a different intake. If you wanted to retain the smog equipment and ECM, a Performer EGR, or a Wieand Action Plus EGR would be better, however I have read that the factory aluminum four barrel intakes were not that bad for a mild build.

The LG-4's low power was largley due to the swizzle stick/straw sized exhaust system. But the peanut cam didn't help either.

 

If your LG4 has the factory aluminum intake, then you have something good right there. There are better intakes out there, but its definitely not whats holding your LG4 back.

The heads too, are pretty decent heads. Better than almost anything that came on a 350 in the '70s and most of the 350s in the '80s.

The exhaust parts all suck. All of them. Keep none of it. The manifolds, Y-pipe, cat, pipes, muffler... they all suck.

The cam is pretty pathetic too. Throw it out with the exhaust system.

 

Yea I was just wondering about it. I have a 350 in the car that was rebuilt, but due to lack of money at the time I put all the stock LG4 stuff on the motor. I have accumulated aftermarket stuff over the last year so I will be swapping over.

Matt

 

Just out of pure curiosity, was the car all that much quicker with the 350 vs. the LG-4 even though you retained all the stock parts?

 

The stock LG4 exhaust chokes a stock LG4, as does the single-snorkel air cleaner. A 350 might have a little more power, but its potential is definately being limited.

Depending upon the 350, the heads on it may actually be worse than the LG4 heads. The heads respond really well to larger valves and basic porting work.

The stock intake manifold is helped by port matching and general clean-up. The EGR passages are often plugged, so just taking it off and cleaning it up is going to help.

An aftermarket carb isn't going to improve power, although a double pumper carb is arguably better with a manual transmission for WOT shifting. But, that's about the limit to improvement over the stock carb.

 

I got to drive the LG4 once before a connecting rod broke and the car was pretty slugish. I bought a rebuilt 355 long block from a reputable engine builder and he said the long block as he built it would be good for about 300 Hp. He rocomended headers, exhaust, a torquer 2 intake since it is a manual transmission car. The block is a 74 4 bolt main with 9.5 to 1 compression. The heads were polished and mildly ported. I noticed the car being substantially quicker then it was with the LG4. The car is not that great out of the hole, but it has substantial power in 2nd and 3rd gear around 3000 - 5000 RPMs. I am not really looking to put any serious money into this car because I only paid 250 dollars for the car and I am restoring 73 cuda. This is more for a fun daily driver.

 

300 horse 350 and Torker II just don't jive. Manual transmission is irrelevant.

Stick with a dual plane intake.

 

Do you recomend some thing like a performer or a performer rpm?

 

Depends upon which carb you intend to run and whether or not you need to retain the EGR valve for emissions purposes.

I wouldn't recommend the Performer in either case. Go for a Weiand Action+ or GM Performance Parts q-jet/EGR (the one that comes on the ZZ4 crate engine) if you need the EGR. A Holley square-bore or q-jet spread bore will both fit on any of those manifolds.

If you're going for the double pumper carb and don't have to worry about emissions, the RPM can be justified. But, on a 300 horse 350, it probably isn't necessary.

 

Emissions testing isnt an issue. The air pump and injectors are gone. The EGR isnt connected to anything and it is just bolted to the manifold. I pretty much want to make it like a 60s car with very little in the engine bay for ease of maintenence. For carbs I am not going to buy anything new. I have a few laying around that might need a rebuild. I have a 600 cfm edelbrock that needs to be rebuild, a 600 holley vacum secondary that needs to be rebuilt, a 625 AFB that is in running condition, and a 750 holley vacum secondary that was just pulled off a 5.0 Mustang that was running well on the 5.0. Any thoughts as to carb selection?

 

If those are your choices, keep the q-jet.

 

At 300hp you definately arent in the ballpark for a single plane manifold, like Five7 said. Get a dual plane and you will be a lot better off.