340 intake on a 318?

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Garethw

Mopar. Because rocket science is too easy.
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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.
 
Port size on the 340 intake is likely larger than the 318 heads. What heads you got on the motor? If they’re J heads, you should be OK
 
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They put 360 intakes on the 4bbl 318's...port mismatch and all. Probably OK.
 
Good points, I forgot about the large port mismatch. It’s not an amazing deal anyway so I may just keep looking.
 
Thanks guys. Part number is 3462848. I’ll see if he still has it.
 
Chrysler did it to millions of them. I don't even know why anybody even brings up the port mismatch like the world's gonna stop spinnin or somethin. Evidently, Chrysler thought it was a non issue. ....and it is. Go for it.
 
Why not just get the correct one so you don't have to guess whether it will work correctly or not? Most times you will have no problem with the differences in port size, but, I have personally seen a couple where it caused a bog. These were on the earlier heads though, so, that might not be a problem with the 302's since their intake ports are kind of in between the old 920/675 castings and the 694/915/596/ castings. Cam choice and rear end gearing can play a part here too.
 
I haven’t picked a cam yet but probably something like the 340 cam. Nothing wild. Rear gearing is a Ford 8.8 with 3.73 locker. Trans is a 42RH.
 
With those gears, I don't think you will have a problem, but, no guarantees from me. I'm not a fan of mismatched parts.
 
I haven’t picked a cam yet but probably something like the 340 cam. Nothing wild. Rear gearing is a Ford 8.8 with 3.73 locker. Trans is a 42RH.
I had the 340 " radical resto" mp cam in a 318, with that intake, a small Holley and headers, in a truck with the pig that's in my car now (4:10) then pulled it and put in a Ramcharger. It was a ripper! I've had a few, still have one.
 
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Back in the day, I had a couple different 340 manifolds on my stock 318. It was a big improvement in power. Probably would have ran better with the correct manifold, but didn’t have any money back then, poor people have poor ways…..l
 
Mid 70s means Low-compression 318LA. right? What will the 302 heads get you?
With a hi-stall it will be fine.

Had you chosen a Regular A833 manual trans;
in a Low-compression 318LA, the bottom end with the 340 cam would be soft to about 2400, then slowly start to wake up to about 3500, after which things get moving. But the heads will be done before the cam is, so..................
So the trans and gears you chose will be fine with a stall of 2800 or more. I've combo'd a few like that. I wouldn't call them rippers until you get into 4-series gears, but with 3.73s they're fun in first gear at least. And passing gear works pretty good.
The hard part is getting back up on the cam after the 1-2 shift. With heads done at ~5000, if you shift there, the Rs will fall to 56% or 2800rpm, way off the cam. So you will want to stretch it out a lil. Shifting at 5600 will get you 3150, still pretty low. By 6000 you're way down the choke-line but on the shift, she will come in at 3370 ........ see what I mean........
On a good note, the 340 cam has a long flat power curve; just what that trans wants.
Rear gears cannot help with this. They only change at what road-speed this happens. If you make the 1-2 shift happen at a low-enough roadspeed, before wind-resistance starts to get up, Second gear will work better.Hence the 4 series gears.
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I have run a low-compression 318LA with 4.30s and a 2800. Not a ripper, but fun none the less. Yes with Headers and a 4bbl, but with the stock heads and cam, on account of I knew about the choke-point. For which I just ran 5500rpm springs and short shifted the 904.
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The most fun I had with my 318 combo was actually with 2.76 gears, manually shifting up into third gear ASAP, and then letting the 2800TC/Thermoquad do their magic, moooooaning all the way to like 80 mph, still at ~2800 rpm,lol.
2.76s are like 4.30s except everything happens one gear later. What I mean is ;
2.76 x 2.45 (low gear)= 6.76 and
4.30 x 1.45(Second gr)=6.23.
So, First gear with 2.76s is just a tad better gear than 4.30s in Second. So then at 3500=40mph, or thereabout, they are a draw. (The big gears, in this case, only help get off the line). But of course take-off sucked, lol. I didn't care because at this time this was my winter engine and a DD, so the 60mph =2100 mattered more to me.
Eventually my son ended up with this combo and my 3.55s, which he soon swapped for 3.23s. ( I had a lotta lotta gears for a while back then.)
 
With those gears, I don't think you will have a problem, but, no guarantees from me. I'm not a fan of mismatched parts.
It's not a mismatch. Chrysler built millions of 318s with four barrel intakes. To my knowledge, not one single one ever had small ports. I'll put it like this. I've never seen one and I've torn down a LOT of virgin engines in the junkyard. If Chrysler engineers didn't see an issue with it, then there was none.
 
A big port intake on a small port head is a mismatch in my book. The first factory LA 318 4bbl's started in 1978. By then you had lots of smog equipment, different castings, but still, ports that matched. Mild cams, lean burn, thermoquads, mild compression ratios and cams, restrictive exhausts, etc. Totally different animals. Some combos work fine, some don't.
 
A big port intake on a small port head is a mismatch in my book. The first factory LA 318 4bbl's started in 1978. By then you had lots of smog equipment, different castings, but still, ports that matched. Mild cams, lean burn, thermoquads, mild compression ratios and cams, restrictive exhausts, etc. Totally different animals. Some combos work fine, some don't.
You can throw up all the excuses you want, the fact remains, Chrysler did it and didn't think anything of it. With a 318 built for performance with a good ignition curve, decent gears, and in a light A body It'll never be noticed.....and wasn't in much milder and much higher geared heavier vehicles. It's just a non issue. If you had a bog with the "mismatch" as you call it, I can promise you it was somewhere else.
 
A big port intake on a small port head is a mismatch in my book. The first factory LA 318 4bbl's started in 1978. By then you had lots of smog equipment, different castings, but still, ports that matched. Mild cams, lean burn, thermoquads, mild compression ratios and cams, restrictive exhausts, etc. Totally different animals. Some combos work fine, some don't.
Now, I can tell you WHEN it would be an issue. Lets say for instance, we had another application.....one that maybe wasn't even an engine. A large "hole" mated up with a smaller "hole". Lets say air was being pushed under pressure, no negative force from "in front". Then, I could see an issue with turbulence around the perimeter of the smaller opening. Considering the negative pressure surrounding an intake port in an internal combustion engine, I just don't see it as a problem. Although it can be argued (and correctly) that the air and fuel ARE being pushed into the engine, it is because of negative pressure "in front" of that air fuel charge. Were that not present, then I could see an issue.

Help me understand your position on this. It's a good discussion, let's keep it going.
 
You can throw up all the excuses you want, the fact remains, Chrysler did it and didn't think anything of it. With a 318 built for performance with a good ignition curve, decent gears, and in a light A body It'll never be noticed.....and wasn't in much milder and much higher geared heavier vehicles. It's just a non issue. If you had a bog with the "mismatch" as you call it, I can promise you it was somewhere else.
I had a 77 D-200 4 Door, with a 318 ( not the same one mentioned in a different post) in o6 till o8. Daily driver. Same Lil intake, ran an eddy and then Holley. 4:30 Dana, 727., stock mannys on the out, That Truck HANDLED just like my Bros tricked out Dak R/T. And, it LOVED PAIN! No BS She Pulled HARD! I didn't build the mill ( got her from a redneck dude who's Grandpa built it, 500 bucks, sitting on the Last Farm in Carrollwood, and got it running) picked it's Sis outta there too. 700 for a club cab 400 . Lost my *** on that one. Rotted up. BAD. Should have never traded her. Gas was over 4 bucks a gallon, that's to obozo. The real estate/ building market SHOTOUT in FL. So I traded Her ( and a Lil $) for an 01 Dak sport 4.7 5 spd w ac. Cool truck, but.....
 
Now, I can tell you WHEN it would be an issue. Lets say for instance, we had another application.....one that maybe wasn't even an engine. A large "hole" mated up with a smaller "hole". Lets say air was being pushed under pressure, no negative force from "in front". Then, I could see an issue with turbulence around the perimeter of the smaller opening. Considering the negative pressure surrounding an intake port in an internal combustion engine, I just don't see it as a problem. Although it can be argued (and correctly) that the air and fuel ARE being pushed into the engine, it is because of negative pressure "in front" of that air fuel charge. Were that not present, then I could see an issue.

Help me understand your position on this. It's a good discussion, let's keep it going.
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.
 
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.
In all of my cases, headers and duals were used. Except the D200, it had factory mannys, but a customized pipe set up. Big stuff, was on there when I got her. Thing Growled!
 
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