340 intake on 318

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1974-318

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Brampton, Ontario, Canada
Hi,
Im going to be changing out my 2 barrel carb and intake to a 4 barrel carb and 340 intake. Just wondering should I use a 340 intake gasket or the 318 intake gasket kit? Will it matter?
 
Use the 340 gasket. Upgrade to a 340/360 later. Your 318 will like it.
 
I've used both and never had a failure of either type.Flow doesn't suffer much under .500 lift if using the 318 sized. These days I just take 15 minutes and port match into the head port 3/4 of an inch to the 340 size. I fill the port with modeling clay and use a shop vac when port matching heads on the block.
I'm looking for a head flow chart I did comparing the two different size gaskets on a set of 302 castings and will post it as soon as I can find it.

20190714_204521.jpg
 
It's only a 2-8 cfm loss on untouched stock 302 heads compared to port matched to the 340 size.
 
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Deltatech said:
I've used both and never had a failure of either type.Flow doesn't suffer much under .500 lift if using the 318 sized. These days I just take 15 minutes and port match into the head port 3/4 of an inch to the 340 size. I fill the port with modeling clay and use a shop vac when port matching heads on the block.
I'm looking for a head flow chart I did comparing the two different size gaskets on a set of 302 castings and will post it as soon as I can find it.

View attachment 1716179043
Click to expand...
Deltatech said:
It's only a 2-8 cfm loss on untouched stock 302 heads.

View attachment 1716179062
Click to expand...

Deltatech said:
It's only a 2-8 cfm loss on untouched stock 302 heads.

View attachment 1716179062
Click to expand...
 
What I like about port matching is the quality of the air and fuel going into the head improves. There’s not a lot to be gained HP wise on a low level power output engine. The port matching pays better dividends on the high end high rpm builds. While not a tremendous gain there ether, I figure if you already have the heads off to port you might as well grab everything you can instead of leaving it on the table.

The above 2-8 cfm loss is port dependent FWIW & good to know.
 
I may add, margin of error for flow testing should be taken into account. I flowed 2 ports on each head and took the average. Most stock 318 heads crap out and most performance cams are less than .480 lift anyway.
For future reference and kids that find this later.
It's not worth buying the tools or taking heads off just to port or port match One set, it's only worth it if you already have the tools and shop setup to port and are building a 318 to make more than 300HP.
 
Last edited:
Deltatech said:
I may add, margin of error for flow testing should be taken into account. I flowed 2 ports on each head and took the average. Most stock 318 heads crap out and most performance cams are less than .480 lift anyway.
For future reference and kids that find this later.
It's not worth buying the tools or taking heads off just to port or port match One set, it's only worth it if you already have the tools and shop setup to port.
I just noticed I posted the wrong Jpeg...lol
Click to expand...
You can edit. Nice blower motor but nothing to do with 318 port mismatch. :poke: :lol:
 
Thanks Mike, I'm juggeling my time today, we all know how fun Android is to find older files. I know I have a pic taken of the flow data and in the same folder as the pic I posted but I'll post it when I have time to search for it again later today.
 
rumblefish360 said:
Your 318 will like it.
Click to expand...
Agreed. Yes there is a port match problem but a stock 318 it doesn't matter. Use the 340 gasket as stated above.
Did the swap way back in 1975 when I spun a rod bearing on my 340 Duster .No money to fix the 340 but a year old 8,000 mile 318 only cost a $100 junk yard price back then.Ran fine for 10 years till rust turned the Duster into dust.
 
Deltatech said:
I may add, margin of error for flow testing should be taken into account. I flowed 2 ports on each head and took the average. Most stock 318 heads crap out and most performance cams are less than .480 lift anyway.
Click to expand...
Similar to the bigger heads. Stock ports only go so far and seeing how they were not intended for racing…….
Deltatech said:
For future reference and kids that find this later.
It's not worth buying the tools or taking heads off just to port or port match One set, it's only worth it if you already have the tools and shop setup to port and are building a 318 to make more than 300HP.
Click to expand...
Totally agree. Unless someone just wants to learn how to port an iron head…. That’s on them and I say happy porting to them.
Darter6 said:
Agreed. Yes there is a port match problem but a stock 318 it doesn't matter. Use the 340 gasket as stated above.
Did the swap way back in 1975 when I spun a rod bearing on my 340 Duster .No money to fix the 340 but a year old 8,000 mile 318 only cost a $100 junk yard price back then.Ran fine for 10 years till rust turned the Duster into dust.
Click to expand...
I hear ya there!
 
I have a 72 340 intake on an otherwise stock 69 318. 340 gasket, no porting. port mismatch is not worth worrying about. Runs great
 
A side note: I found that I had to use cork on the china walls instead of just rtv because the gap was too big
 
LOL! That’s a true thing! Sometimes that gap is huge!
 
A better photo of all the linkage including the springs and kickdown is needed to answer.
You should use a dual spring on the return and a spring for the kickdown return.
Nice using the thick base gasket ! Helps with thermal transfer and keeps the fuel from percolating causing hard hot starting.
 
As long as it doesn't bind through the throttle sweep you are good. Sharp edges in the hole can cause wear and breakage. Something to think about.
 
Deltatech said:
I've used both and never had a failure of either type.Flow doesn't suffer much under .500 lift if using the 318 sized. These days I just take 15 minutes and port match into the head port 3/4 of an inch to the 340 size. I fill the port with modeling clay and use a shop vac when port matching heads on the block.
I'm looking for a head flow chart I did comparing the two different size gaskets on a set of 302 castings and will post it as soon as I can find it.

View attachment 1716179043
Click to expand...
15 minutes to port all openings? I doubt it
 
throttle stud between the two halves of the U shaped throttle end
 
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