Upgrading my 340

I think your main problem is with the ports... You have large port heads, small tube diameter headers, and what looks to be an edelbrock performer or performer RPM intake...

1st thing that I would do is to get the ports matched from the intake to the heads... At least a good gasket match port so the ports on the intake match the ports on the heads...

Then get larger diameter tube headers to let the exhaust flow a little better, either TTI or Dougs headers will work well...

You are loosing too much flow velocity with smaller ports in the intake than the head, it slows down the flow when it enters the head, then you have a restrictive exhaust to choke the flow...

An engine is an air pump, you need to balance the intake flow with the exhaust flow... If one is greater than the other, it becomes the bottle neck/restriction...

I would run an Edelbrock LD340 myself, as they are great street intakes...


Also, why a 1.90" exhaust valve and only 2.02" intake... You've opened up the exhaust valve .030" over the stock size on the exhaust and have the stock 2.02" intake valve....


Another way to increase idle vacuum is to get a set of Rhoades variable duration lifters... They bleed down at idle and make the cam tamer for better idle vacuum and quality, and more low and mid range power without sacrificing top end power... They pump up to full lift and duration by 3500 RPM... I've used them for years on street engines and had great success with them... they will give better idle vacuum, more low and mid range power, and increase MPG slightly - don't expect miracles...

Rhoades lifter main page:

Rhoads Lifters


Part number - you will need the 2018 lifter or the Vmax lifters 20108X - but should run adjustable rocker arms with the Vmax to get their full potential...

Part Numbers


Read the second article here on the "smart lifter" for more info...

Articles


Some people don't like the Rhoades lifters and may give me some crap for recommending them, but I like them and have used them for decades and run them for over 200,000 miles with no trouble... Let them bash away...


My blunt opinion is: you have too much head for a street motor.. A stock 340/360 head with a little porting and a good valve job will be fine for the street...


I would focus more on the ports right now than trying more intake and carb set-ups.... Study a little on fluid dynamics and you will understand what I'm talking about...

Too large of a port will be a sudden expansion and will slow down the air velocity in the port... Velocity is torque...

Port vacuum is determined by the diameter and length of the port... Too big of diameter will slow down the velocity... You have to match the ports for what you are going to do with the engine...