340 intake on a 318?

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cudamark said:
The two instances I remember, both had a 340 intake on an otherwise stock 318. In both cases, the ONLY thing we changed was the intake manifold, and the bad hesitation they both had disappeared. IIRC, (this was over 35 years ago, so, some details might be mixed between the two), the 1st setup was a '69 Dart with a '68-70 340 intake and a Holley 600 vacuum secondary. The head castings were the stock 675 castings. The rest of the engine was also stock, including the exhaust manifolds, single pipe system, and camshaft. We reused the carb and air cleaner without changing anything. Same distributor and timing specs too. The second time was basically a repeat of the first, except it was a '68 Barracuda that had a aftermarket dual plane aluminum 340 intake...I think it was a Wiand. Same size Holley, and the rest was also stock '68 single exhaust along with the rest of the engine. Both had aftermarket open element air cleaners with new filters (one of the first things we tried in order to get rid of the bog, including full tuneups). I never ran across that exact situation again, but, I got out of the retail repair business soon afterward, so, I expect I would have run across a few more if I continued in that type of work. No way to know for sure though.
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I wonder though if that could have been tuned out......man. The stuff we tried way back when. LOL
 
We tried, but, nothing seemed to help. Swapped manifolds and the problem disappeared. Like I mentioned, I've seen tons of similar combinations that had no problems, but, these two did for some reason.....and the only change made that cured the problem was a manifold change to where the ports matched. All the intakes involved were dual plane, but, they may not have the same exact internal design. I can't explain it either. I figured that the only flow problem you would have would be at high rpm's. It sure wasn't the case here though. It was right off idle that they fell on their face.
 
It will work fine the port mismatch doesn't matter. When I was younger people always told me it wouldn't work and never ever do it because the fuel will smash into the edge and bla bla bla its all myth. Think of it like the the carb doesn't push the fuel down the intake. The pistons suck it like a vacuum. So even with the lip there the engine is gonna suck it right over the edge. Iv had the same 340 intake on 4 engines 3 of them were 318s 2 of those were 302 heads. On the first one I took a dremal and gasket matched the heads to the 360 gasket the the other 2 I did not and I couldn't tell any difference.
 
dartfreak75 said:
It will work fine the port mismatch doesn't matter. When I was younger people always told me it wouldn't work and never ever do it because the fuel will smash into the edge and bla bla bla its all myth. Think of it like the the carb doesn't push the fuel down the intake. The pistons suck it like a vacuum. So even with the lip there the engine is gonna suck it right over the edge. Iv had the same 340 intake on 4 engines 3 of them were 318s 2 of those were 302 heads. On the first one I took a dremal and gasket matched the heads to the 360 gasket the the other 2 I did not and I couldn't tell any difference.
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May be it helps break the fuel charge up more. Who's to say! :lol:
 
I ran a W2 strip Dominator on 340 heads...worked. Terrible port mismatch (round pin in a square hole) still worked great. I even JB'd a little ramp into the W2 ports to make em more square and they were still there 6 months later when I took them off after I found an LA SD intake. I wouldn't attempt that again; a little older, alot wiser.
 
pishta said:
I ran a W2 strip Dominator on 340 heads...worked. Terrible port mismatch (round pin in a square hole) still worked great. I even JB'd a little ramp into the W2 ports to make em more square and they were still there 6 months later when I took them off after I found an LA SD intake. I wouldn't attempt that again; a little older, alot wiser.
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That sounds like 'what if that JB broke off and got sucked into the engine...?" :)
 
Big Cleveland heads actualy benefit from a raised floor intake port (with epoxy wall flush with gasket) that causes a "port mismatch" on any intake. They sell plates that look to have a flap that bends down into the heads intake port (makes a D shaped port out of an oval port) and covers the low velocity floor. DIY able with thin plate. there is the mismatch again, non issue. look at epoxy modded column
Cleveland Flow Testing
 
Perhaps all for nought. The guy already sold it. Some great discussion though. I still learned something. I’ll keep my options open to a 340 intake should another show up.
 
There are thousands of 318s with with big port intake on them. They run fine. I’ve ran a few that way myself way back in the 70s and 80s. I used the finer/composition gaskets. Kim
 
My two cents.... match exhaust ports or larger heading out are important, but the intake ports not so much, due to the tumbling of the fuel will burn better. Kind of like when you port a head, smoothing the exhaust side and leaving the intake side ruff. I have ported my own heads this way, with good results.
 
Makes me wonder why Chrysler decided to foot the bill to make 318 4 bbl intakes when they already had the 360 4 bbl intakes on the shelf. Same thing with the 2bbl's. There had to be something different that warranted casting a new manifold. Later on of course, they used the same manifold, but, the ports between the two heads were a lot closer in size.
 
Garethw said:
Any reason not to put an original 1970 340 intake on a mid 70s 318? I found one local for not a bad price. Just want to make sure it will work well. My plan is for a mild street 318 (~300hp). I’ve got some 302 heads for it already.
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Ran one on a 273 for years, ran great. Stock heads, except springs, AFB, .060" over 11.5 to 1 Jahns, SIG Erson cam and springs, dual points, Cyclone fender wells. 4.10 SG. and 4 speed.
 
cudamark said:
Makes me wonder why Chrysler decided to foot the bill to make 318 4 bbl intakes when they already had the 360 4 bbl intakes on the shelf. Same thing with the 2bbl's. There had to be something different that warranted casting a new manifold. Later on of course, they used the same manifold, but, the ports between the two heads were a lot closer in size.
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probably emissions EGR...maybe?
 
Most '73's and all '74-up intakes had provision for an EGR valve.
 
comparing replacing a 318 2bbl manifold with a 340 4bbl is comparing apples and rutabagas. Sure the 4 bbl will perform better compared with those tiny 2 barrels. The right comparison is between that mismatched combo with a 4bbl manifold with small ports that match. You should be able to get a used Edelbrock Performer manifold for $100 or less with the small ports. Most Weiand small block manifolds come with the smaller ports (you can enlarge the port to match 340 or 360 ports). The turbulence cause by the charge hitting the lip around the head ports can't help but disrupt the flow. For an extra $50 why not do it right?
 
That's been my point all along. The question everyone is asking is what effect does it have? The benefits might be a better mix.....maybe even better mileage because of that. The flow definitely has to be affected in some ways. Maybe unnoticeable in most applications. I would think high RPM would be affected the most. Depending on all the rest of the components, other areas might see a change also...either good or bad. Why not get the part that it's designed to have. You have to ask yourself, why do the manufacturers (both factory and aftermarket) make both types of manifolds if it doesn't matter?
 
You all must be driving in your sleep! To put a set of 360 340 heads on a 318 without matching the ports is a waste of a lot of time and performance. To start with the ports are large enough the 318 is going to suffer in response and power. If you match the ports in the heads than it would work acceptable but not optimal. I tried it and wound up installing a 273 single plane and the engine came to life. The engine had ported heads with headers and early 340 cam. It ran fair with the 340 intake but I had already done a match up of the ports. Now if you use the 360 heads with the 1.88 intakes and the manifold stuff lines up a lot better and upper rpm perf is a lot better but the low end suffers some. It's the same with any engine accept a BBC which is always under valved no matter what combination is being used until you get up around 2.030. READ up on cylinder heads and port design. Some here are saying just run it but if it's worth doing, do it right and match the heads up to it. You will be glad you did. I ran mine with a TQ at first also and it worked ok but it worked be with the AVS and the small port 273 intake, it was way better off the bottom and the top didn't seem to suffer much, it was noticeable but I dealt with it because I like anyone else isn't in the throttle to the floor all the time, just part of the time and an engine that stumbles off the line is nothing to brag about no matter how hard it runs above 3k, you've already lost the race and playing catch up isn't a winners game.
 
cudamark said:
Makes me wonder why Chrysler decided to foot the bill to make 318 4 bbl intakes when they already had the 360 4 bbl intakes on the shelf. Same thing with the 2bbl's. There had to be something different that warranted casting a new manifold. Later on of course, they used the same manifold, but, the ports between the two heads were a lot closer in size.
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Have you ever SEEN one IN PERSON that had 318 size ports? I've not. That doesn't mean anything, but I've never in my life seen one and I've pull a good many off in junkyards. Always had the 340/360 port size. I've seen some the casting number decoded to "318" but they still had the large port size.
 
Bret Tschacher said:
You all must be driving in your sleep! To put a set of 360 340 heads on a 318 without matching the ports is a waste of a lot of time and performance. To start with the ports are large enough the 318 is going to suffer in response and power. If you match the ports in the heads than it would work acceptable but not optimal. I tried it and wound up installing a 273 single plane and the engine came to life. The engine had ported heads with headers and early 340 cam. It ran fair with the 340 intake but I had already done a match up of the ports. Now if you use the 360 heads with the 1.88 intakes and the manifold stuff lines up a lot better and upper rpm perf is a lot better but the low end suffers some. It's the same with any engine accept a BBC which is always under valved no matter what combination is being used until you get up around 2.030. READ up on cylinder heads and port design. Some here are saying just run it but if it's worth doing, do it right and match the heads up to it. You will be glad you did. I ran mine with a TQ at first also and it worked ok but it worked be with the AVS and the small port 273 intake, it was way better off the bottom and the top didn't seem to suffer much, it was noticeable but I dealt with it because I like anyone else isn't in the throttle to the floor all the time, just part of the time and an engine that stumbles off the line is nothing to brag about no matter how hard it runs above 3k, you've already lost the race and playing catch up isn't a winners game.
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Go tell what's left of Chrysler they're asleep too because they did it with millions of 318s right from the factory.
 
cudamark said:
Most '73's and all '74-up intakes had provision for an EGR valve.
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The 73 340 intakes all had the EGR jets in the bottom of the plenum. There might be some late dated 73 intakes out there with external EGR provision, but they were for the 74 model year.
 
RustyRatRod said:
Have you ever SEEN one IN PERSON that had 318 size ports? I've not. That doesn't mean anything, but I've never in my life seen one and I've pull a good many off in junkyards. Always had the 340/360 port size. I've seen some the casting number decoded to "318" but they still had the large port size.
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I have seen only 2. Came factory on a 78/79 1/2 ton. I did measure the ports which were the small ports. That was in the late 80s or early 90s. Haven’t seen any since. Kim
 
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