Check out my car and talk to me about 318/340 swap

-
bet you're confused now....
back to your original question."should you swap in the the 340"?
.....Absolutely!
 
If you have a 340 yes, why wouldn't you? unless you have two cars of course...what's even better? 2 340s LOL!
 
I understand the whole “if it ain’t broke don’t fix it” mindset. I do. The car is a really fun cruiser, but the 318 is REALLY slow. Like…the Kia Soul I drive to work every day will run off and leave it easy.
 
Typically people will say leave the 340s to the numbers matching crowd.. if everything is stock in the motor and everything hopefully operates as it should how much does it cost? You do know those extra 22 cubic inches aren't going to light your world on fire or anything like that..
Now a 360 to 408 stroker build will definitely make your eyeballs get wide and impress your friends...
 
I have designed mounts for the swap contact me if interested
 
Dartswinger70 said:
There's more to it than the 22 cu inch difference 318s have lousy heads...low compression etc. Sorry had to chime in saying the only difference is 22 cubes is a misstatement. When talking LA 318 vs 340 stock for stock.
Click to expand...

You don't get it. Try reading and understand. 318, J heads (71-72 340/360 heads), cam, intake, and 4 barrel carb. It is just 22 cu in difference if you have all the good stuff. Actually if you have the same heads and same compression, it will have the same horsepower, just run a little higher rpm.
 
I think you will find a big difference with a well tuned stock 340 in a light A body.They pull extremely hard to well past highway speeds.For strictly street use keep the cam stock or at least short duration and stay with 26" rear tires.
...I can hear all the murmurs !
 
jrjones said:
Hey folks! First post here! My dad and I start rebuilding this when I was 16. We just finished last year. It has the original 318 with 360J heads and an edelbrock 4 barrel carb, bigger cam, original 906, 8 1/4 rear end and discs up front.

After we finished building the engine and tranny and getting it set in place and other stuff built around it, we found a X heads 340. The guy we got it from said the number on the block matched to a 69 charger. He had just pulled it from an 80s ram charger.

So now that I’ve been able to cruise with it for a bit I’m starting to think “what if” about the 340. Assuming everything is good in the engine (or I have it rebuilt) it should bolt right in place on the 904 right?
Click to expand...

It is always nice to have a spare engine. Especially a 340.
 
I have also found i had to add the a rear top ear on a drivers' side 318 mount to bolt to the 340 block. Maybe there are different 318 A body mounts?
 
66fs said:
You don't get it. Try reading and understand. 318, J heads (71-72 340/360 heads), cam, intake, and 4 barrel carb. It is just 22 cu in difference if you have all the good stuff. Actually if you have the same heads and same compression, it will have the same horsepower, just run a little higher rpm.
Click to expand...

A 340 is already torque challenged.Take away 22 cubes and lower the compression, use mismatched heads and cam and the 318 will fall way short. With the 318's smaller size a 360 2 barrel cam at about .410 and shorter duration would perform better but you still have compression in the 7's and smaller pistons
 
I still think the 22 cubes isnt the issue its the heads and the low compression of a stock 318. Ive said it before why take a 318 and try and convert it to a 340 just get a 360 as a foundation.
 
The factory put 727 behind the 340.id say a 904 could hande it on the street. if 1/4 mileing it all out full throttle then yes you'd need more beef. i am thinking these days the auto guys have figured out how to beef up the 904. However traditionally the 727 is the heavy duty unit for sure.
 
Dartswinger70 said:
There's more to it than the 22 cu inch difference 318s have lousy heads...low compression etc. Sorry had to chime in saying the only difference is 22 cubes is a misstatement. When talking LA 318 vs 340 stock for stock.
Click to expand...
I agree, but KB167 zero deck flat tops and 65cc closed chamber heads on a 318 remedy that low compression issue. If your gonna rebuild the teener, that's what you need to do to give it a pump gas friendly 9.7-1 ratio.
 
66fs said:
You don't get it. Try reading and understand. 318, J heads (71-72 340/360 heads), cam, intake, and 4 barrel carb. It is just 22 cu in difference if you have all the good stuff. Actually if you have the same heads and same compression, it will have the same horsepower, just run a little higher rpm.
Click to expand...
Stock teener pistons TDC at .080" to .100" below the deck. Thats a serious loss in compression. This is compounded with heads designed for a bigger bore engine along with the associated valves for a bigger engine. To make a teener run, you need pistons that change direction at the deck, or a couple thousandths below the deck not 80 to 100 thousandths below. The valves , ports, and runners need to be sized for the bore it's got. The whole throw bigger at it does not apply. Putting 340/360 top end on a stockerish 318 bottom end, actually hurts it, not helps it. It slows down port velocity. Bigger valve J heads on a low compression 318 makes it perform worse than if the stockers were left on it. Most engines (street engines) live at off idle to 5,000 rpm max. Rev it higher?? Ok how much higher to get the power back? Will that require better rods, better crank? Etc?
 
Last edited:
jrjones said:
You gonna bolt that up to a 904? I figured anything bigger than a 340 would really need a 727 sitting under it.
Click to expand...
Negative ghost rider! That’s an Old wives tale.
HP level dependent, you Might! ….might have a point. If there dead stock transmissions coupled with a really high HP engine. The 904 can be built up as well as a built up 727.

Perhaps one day this BS (Old Wives Tales) will stop!
Dartswinger70 said:
The factory put 727 behind the 340.id say a 904 could hande it on the street. if 1/4 mileing it all out full throttle then yes you'd need more beef. i am thinking these days the auto guys have figured out how to beef up the 904. However traditionally the 727 is the heavy duty unit for sure.
Click to expand...
When the 904 was introduced, the Pro Stock racing teams of the day had to drag the officials down to the dealerships and physically point out that the 904 was the stock transmission. Running into the 8’s with a 904 can be done when it is properly prepped.
 
Rumble is correct..as usual!
A local ran a 372 in a duster with an early 904 built with the later low 1st and 2nd gears.Shifted at
8000 and et'd at 10.7 (488 gears).
The 340 eventually cracked the block, but the 904 was fine!
 
moparmat2000 said:
Stock teener pistons TDC at .080" to .100" below the deck. Thsts a serious loss in compression. This is compounded with heads designed for a bigger bore engine along with the associated valves for a bigger engine. To make a teener run, you need pistons that change direction at the deck, or a couple thousandths below the deck not 80 to 100 thousandths below. The valves , ports, and runners need to be sized for the bore it's got. The whole throw bigger at it does not apply. Putting 340/360 top end on a stockerish 318 bottom end, actually hurts it, not helps it. It slows down port velocity.
Click to expand...

ir3333 said:
A 340 is already torque challenged.Take away 22 cubes and lower the compression, use mismatched heads and cam and the 318 will fall way short. With the 318's smaller size a 360 2 barrel cam at about .410 and shorter duration would perform better but you still have compression in the 7's and smaller pistons
Click to expand...

Have you actually tried what you say can not work? I have run a 273 with 72 340 J heads. Best it ever ran, and that is with a 3.665 bore and 67 cu in smaller. No valve notches in the block. No port velocity problems. Not sluggish. Not torque limited. What compression loss? 675 heads are about 68 cc per chamber and a .020 milled J head is about 69 cc, at .040 you are about 65 cc. Bore is the smallest adder there is. I used to put 360 heads on 318's all the time. Never a complaint, never a dog. Do you know how to tune an engine and set up a transmission? I would never run a stock 360 cam in anything. Would a low compression 318 beat a 10.5:1 340 with X heads, no, but it will beat the snot out of a 318 2 barrel.
 
Last edited:
66fs said:
Have you actually tried what you say can not work? I have run a 273 with 72 340 J heads. Best it ever ran, and that is with a 3.665 bore and 67 cu in smaller. No valve notches in the block. No port velocity problems. Not sluggish. Not torque limited. What compression loss? 675 heads are about 68 cc per chamber and a .020 milled J head is about 69 cc, at .040 you are about 65 cc. Bore is the smallest adder there is. I used to put 360 heads on 318's all the time. Never a complaint, never a dog. Do you know how to tune an engine and set up a transmission? I would never run a stock 360 cam in anything.
Click to expand...
agreed, i had a 69 d100 with a 318. mild cam, 360 heads and performer inlet with a 600 holley were the only changes and it ran really well.
 
66fs said:
Have you actually tried what you say can not work? I have run a 273 with 72 340 J heads. Best it ever ran, and that is with a 3.665 bore and 67 cu in smaller.

I think we're talking about 2 different things. 273/318 heads are about 60cc and 360 heads are about 72 cc's which just makes very lo compression in a small engine.... and yes I know guys that run this combination.I'll say no more.
We disagree, it's OK, i'll stick with 340's
Click to expand...
 
66fs said:
Have you actually tried what you say can not work? I have run a 273 with 72 340 J heads. Best it ever ran, and that is with a 3.665 bore and 67 cu in smaller. No valve notches in the block. No port velocity problems. Not sluggish. Not torque limited. What compression loss? 675 heads are about 68 cc per chamber and a .020 milled J head is about 69 cc, at .040 you are about 65 cc. Bore is the smallest adder there is. I used to put 360 heads on 318's all the time. Never a complaint, never a dog. Do you know how to tune an engine and set up a transmission? I would never run a stock 360 cam in anything. Would a low compression 318 beat a 10.5:1 340 with X heads, no, but it will beat the snot out of a 318 2 barrel.
Click to expand...

How far in the hole were those 273 pistons at TDC? I am betting they were much much closer to the top of the deck than your run "o" the mill 318. I have 2 of these 318s the 77 one the piston TDC was .080" in the hole the 74 was .100" in the hole at TDC. If his teener pistons TDC at around that, with 72cc 360 heads, your really dropping that CR. Mid 7s on CR.

You would be surprised how much it can change by just changing the head cc. Do you have any numbers to share on that 273? What was the piston depth in the holes at TDC, what were the CCs of the heads you used?
 
Last edited:
Now that I am done at work today and have time to reply, heres for all you smart guys on here talking about running 360 heads on a teener. That performance gain is all in your mind. Heres 3 models for you to look at. Standard bore 318, stock rod ratio, pistons TDC .080" in the hole, and I will give it 5cc valve reliefs from a quickee rebuild. .038" compressed height felpro permatorque headgasket with a 4.03" diameter. Real common autopart store stuff. And the 72CC 360 heads. The first model shows 7.46-1 compression with them 72cc 360 heads on a stock 318 with stock pistons. Hardly an effing hot rod

Second model I changed nothing on the equation but stuck 60cc heads on it. CR jumps to 8.34-1. Better yes, but about a stock 318 running on rat piss.

The 3rd and final model I changed the heads to 62cc, and put the piston at near zero deck height with 5cc valve reliefs. This is typical of the KB167, and some decking. That shows 9.66-1 compression. A nice pump gas hot 318.

In closing are ya gonna get there with a low compression 318 short block and 360 heads. Hardly. You may get closer with zero deck flat tops and them 360 heads, but not on a stock low compression 318 your not. The numbers dont lie

Screenshot_20210919-173731_Samsung Internet.jpg


Screenshot_20210919-173758_Samsung Internet.jpg


Screenshot_20210919-174221_Samsung Internet.jpg
 
Last edited:
You must log in or register to reply here.
-

Back
Top