big block chevy question for med duty trucks
 

what are these tubes for on the deep side of the factory intake manifold ?

this intake is from a early 80's . the intake off the 88 truck don't have them but the intake was machined for them to index in . both were 366 engines and same part # carb . early intake non-egr later intake has egr .

read a few guys on other forums say ditch the factory dist and carb and use a reg old hei with a vac advance and simple carb like a 600 cfm edelbrock and there running fine for years with better performance .

any input would be great guys thanks .

Re: big block chevy question for med duty trucks
 

Not sure about the tubes. I have a 1970 366 with 20k miles. I swapped to an HEI and edlebrock 600 cfm, best thing I've done to the truck. I just cranked it for the first time in 2 weeks and it ran perfectly. I only run ethanol free gas and it makes a world of difference.

Re: big block chevy question for med duty trucks
 

got my hei with vac advance dug out . and looking for a edelbrock carb now .

any good tips or pointers ?

Re: big block chevy question for med duty trucks
 

Make sure the HEI is long enough for the 366 you are putting it in. Regular hei's wont mesh with the oil pump and will run the engine dry quickly. Itll fit in, just make sure the collar is the same distance on the replacement distributor.
As for the carb, just give it a good cleaning rebuild if needed and you should be all set. May want to replace the plugs while you are doing the wires. The hei plug gap is .045 not the .035 for points distributor.
That's about it. Pretty easy

Re: big block chevy question for med duty trucks
 

my intake is cast deep for the dist hole so it should be fine . i think this hei was from the first or 2nd engine . . . long story on them in my other thread here .

yes i have new wires and plugs so we should be good to go this way .

got my eye on a few good clean carbs . 1 600 cfm and a few 750 cfm . looking for mech choke to keep it more orignalish . trying to stay with the 600 cfm since its only a 366 and no more than 4k ish rpm . got a new 50k volt coil and mod with built in adjustable rev limiter i will set at 4,500 rpm .

Re: big block chevy question for med duty trucks
 

600 should be plenty. My 366 taps out at around 3200 rpm, but shes strong to that point.

Re: big block chevy question for med duty trucks
 

I am an expert at nothing....
Post one, if the intake has EGR, the tubes are to allow EGR gases to be pulled into the intake, without getting back into the carb. THere would be holes in the intake below the carb mounting pad.
If the carb is non EGR, I'd say the tubes are to keep the velocity of the air/gas mixture high as it hits the bottom of the intake on that side.

THere's nothing wrong with a 750 carb. You may need to open up those holes on top of the intake. I considered doing that on a 366 intake, once, got rid of the engine. It takes a lot make a 366 work in a pickup...

I have several old distributors out of 366's. They all interchange with regular small block and big block distrbutors...have never heard of one that did not interchange...???

Re: big block chevy question for med duty trucks
 

I have several old distributors out of 366's. They all interchange with regular small block and big block distrbutors...have never heard of one that did not interchange...???[/QUOTE]

A 366 requires a longer shaft distributor to reach the oil pump when using the stock intake manifold. DUI performance distributors makes one that has an adjustable collar that will work with the stock manifold. It doesnt have to run long with the distributor not keyed to the oil pump to run dry. Ask me how I know...

Re: big block chevy question for med duty trucks
 

egr intake = no tubes in the 1 half
non egr intake had tubes in the 1 half

found a brand new in the box 1405 edelbrock carb 600cfm rated for power and towing over the reg versions and had man choke so its a vitual drop in .

got a pertronix hei module with built in rev limiter and will be setting this to 4k -4,500 rpm range not sure yet . and a 50k volt coil .

Re: big block chevy question for med duty trucks
 

Beware the throttle blades may not line up with the hole in the intake. Some grinding can make it good, though!!!

Re: big block chevy question for med duty trucks
 

I bolted a 1405 manual choke to my stock manifold in my 1970 with no clearance issues. I did go back and add a heat insulator diaphragm to cut down on heating my fuel on long hauls. I've had zero issues.

Re: big block chevy question for med duty trucks
 

yep forgot to say i got a 1/2" thick phenolic spacer for heat separation .

i even did a banjo bolt hard fuel line kit to bring it down and out the front so i can make a hard line from the pump up to the carb .