Who's running a 340 intake on a 318?

[71Challenger318]

My 71 is equipped with the stock 2bbl carb currently. The engine is stock other then a .030 overbore. I have a set of full length tube headers and a pypes dual exhaust system coming from Summit Racing. It has the mopar electronic ignition conversion.

My question- I keep reading (and hearing my father's bitching) that the 340 intake and thermoquad that was GIVEN to me (I love free stuff!) will not work on the engine. I understand the intake's ports to be much larger then the 318's stock heads. It would seem to me that generally speaking this isn't a huge big deal and for a cruiser would work just fine. Anyone agree? Disagree? Let me know what you guys know. Should I gasket port the heads myself? I have done some mild work on aluminum before but never iron.

 

[burntorange70]

The 340 intake on a 318 will work but is not the ideal set up. With the bigger runners of the 340 intake velocity will be hurt. Gasket matching will help some but I think some thing like an Eddy performer with it's smaler runners would be a better intake.

 

[71Challenger318]

We are going to gasket match intake and exhaust before bolting it all together...I thought that would help a lot.

 

[Rob C]

It will, but like he said.... It's really not a huge deal. You'll like the Performer better.

 

[71Challenger318]

Ok, in my line of thinking the factory wanted bigger ports on the 340/360 for a reason. More air and fuel into the engine to make more power obviously. Now it seems that people running eddy intakes on 340/360 (part number is same for 318 and 273) have the reverse port mismatch. Which isn't a problem for flow...but it would seem that it would hurt volume of air. Thus, if you port the head on a 318 to match the larger port size of the 340, you get good flow characteristics AND more volume then the smaller port intake would provide. "But Jeff, what about loss of velocity?" The port on the head would simply be a mild taper, you would pick the velocity back up there. Am I crazy?

 

[Rob C]

Theres no real loss of velocity at this point. If you wish to port match the head to the intake, go for it. To worry about it here is like splitting a hair on a fleas butt with a cannon at 1,000 yards, no sight glass.

The Performers smaller runners into the larger head port isn't a bad thing. But you wondered about the bigger port window of the factory head and compared them.
Well, the performer flows equally as well as the OE 340 intake for the most part. The smaller runners would be a hinderance if they followed the same path as the OE intake, but they don't. They follow a smoother path that allows the velocity to stay up, mixture to be fine and the abilty to flow enuff to make power due to the smoother bends in the runners.

 

[71Challenger318]

The weight advantage is another point worth mentioning. That 340 intake is HEAVY! I am going to stick with the 340 for now...answer my own question with a little much needed experience. I will likely go aluminum later, maybe when I do a cam. I should do a cam now but I just want to get the car back on the road. I might want to go big block or 5.7L.

 

[Rob C]

Form a plan and stick with it. It'll save you tons-o-money up front and in the long run.

If the intake is off now and you want to upgrade the engines performance with a cam, NOW..... is the time. Besides the gaskets, sealent, cam, lifter and spring purchase, theres also 2 oil changes and filter along with it and any machine work needed for the head. (Valve spring fitment.)

 

[burntorange70]

Let us know how it works for you.

 

[71Challenger318]

Form a plan and stick with it. It'll save you tons-o-money up front and in the long run.

That has been a problem during this whole project. Looks like it is finally starting to get figured out though.

If the intake is off now and you want to upgrade the engines performance with a cam, NOW..... is the time.

It had a drag/comp purple cam in it after the first rebuild and without consulting me that cam was removed and a stock cam was installed. This was my father's doing. The cam was to wild for what we wanted but why he didn't use a 340 cam I have no idea. So it has a brand new stock 318 cam in it...hate to tear that out. See, mine is a problem of to many cooks in the kitchen. Luckley I have cleared it out now.

There are also 2 oil changes and filter along with it and any machine work needed for the head. (Valve spring fitment.)

You wouldn't need that for a stock cam would you? Like a 340 cam.

Let us know how it works for you.

I will. I hope it works out well.

 

[74ChAARger]

I used a SP-2P Edelbrock on my 318. The port match is good and runner velocity will be great with the stock cam. The thermoquad will fit. I used an AFB, 500 CFM, and it worked very well.
These intakes are no longer made, but I had no trouble finding one on the internet.
You should be fine with the 340 intake, and 340 exhaust manifolds would help out, too.