I shouldn't do this but I cant help myself. Someone just posted a vid on youtube explaining why small blocks are so good. Folks this is the most inaccurate vid I have seen in a long time. Small block 340 and 360 head have poor exhaust ports and good intake ports. The intake port is a large reason for 340 domination on factory street engines. Because of the poor exhaust port headers make a big difference in performance. This vid claims that the only reasons small blocks run like they do is a accident by Chrysler engineers. And only this genius figured it out and then goes on to show early 426 hemi heads and big blocks heads as prof to the reason for small block performance. NOOOOT
Small block chevys have excellent exhaust port and bad intake port. This is why the 340 beats the lt1 all day long. If it was about exhaust flow chevy would dominate the world but they don't, look back in the day of nascar when they were running. ford and mopar were the big dominators when big block power was being used chevy then had a Superior exhaust port.
Ford 351 c engine are killer on the street and the track at that time and there exhaust port sucks bad.
Here's the truth about exhaust, better exhaust on a mopar picks them up a bunch. early chevy engines like fuelie head engines the builder had be careful not to make the exhaust to effective cause the result was over scavenge causing poor fuel consumption and poor mid range response. This is why it was common practice to put a split pattern cam in a chevy with lower number on the exhaust side. it was also common to put a 1.6 rocker on the intake and a 1.5 on the exhaust to balance them out.
One more point, the struggle isn't getting exhaust out....its getting intake in. If it was the exhaust you are worried about then you put in a smaller intake valve and put in a larger exhaust valve. The intake is larger cause we live in about 14lbs of atmosphere that's all the push we have to get oxygen into the engine.(unless you use a turbo, blower or nitrous). The exhaust on the other hand has many pounds if needed to get it out and that's why using a turbo witch plugs the hell out of exhaust flow works. Remember when the piston is on it way up it can make a heck of a lot of pressure. Check it with a compression gauge you will see it.
Now 340 exhaust is bad but it is not terrible and there is a advantage to fixing the exhaust for sure. W2 heads have awesome exhaust in them and the have very good intakes so that makes it hard to compare at least factory to factory parts are concerned. And ford Cleveland exhaust ports are terrible and fixing them is a nice pick up.
340 engines advantages are big bore short stroke. long rod stroke ratio; strong factory parts and good intake ports' large diameter lifters. large diameter valve springs to name a few.
Alright long enough rant here bottom line if your using factyory parts don't give up on the exhaust it important and there is big improvement to be had. so header up it works good on LA heads, GOOD LUCK ALL
