Diff between 318 and 340

[71SATELITE]

Hey Mopar land big question. For my lack of Mopar literature I have a question on 340's. What is the difference between a 318 and a 340. Is it the bore, stroke or all the above, and how much. The reason I am ask is I have tracked down a stock 340 intake and plan on upgrading to a stock 340 cam. I have heard on this sight that they produce good horsepower on a 318. With these mods I was wondering how far off my engine would be from a 340. One last thing is would a 340 crank bolt up in my exsiting 71 sm block. Thanks.

[6 packin]

The bore is diff..........

318 3.91 Bore X 3.31 stroke

340 4.04 bore X 3.31 stroke!

[skydome]

If you're going to use a 340 cam, put 360 heads(1.88 intake) on it Any scrapyard smogger heads will work. The 318 head has small ports and valves that are not compatible with 340 cam and intake. If you don't want to change the heads, go to a 360 2bbl camshaft . Then you have to find a318 4bbl intake so the ports match. Do not go crazy and get 2.02 heads because the valves will hit the block. I have done this swap many times with good results.
Good luck, kev

[usdart]

Hi: I am no expert , but I just did those very things to my 318.
I got the stock 340 cam from 'Sealed Power' and I also went with an Edelbrock Performer Intake and 600cfm Electric Choke Edelbrock Carbuerator. I went to 2 1/8 Dual Exhaust.I have stock 8.6 to 1 pistons with Sealed power Rings.
I don't think there is a 'Large' gain in Horsepower but there must be some. I was rebuilding it anyway so it wasn't a big expense to upgrade to these items. I get about 18 mpg if I can keep my foot out of it.

Maybe some of these other guys (they are wonderfully gifted in Mopar speak) can tell you some possible HP numbers. I too would like to know mine as well.

I am told that if you also bore .030 and go to 10 to 1 pistons, and a set of 340/360 heads you REALLY wake the little 318 up.

Those are future plans for mine..Since I already have a proven power plant I think I will just upgrade my current block.

Didn't mean to sound like a braggert,just wanted to help; Dave

[skydome]

PS, sorry,I didn't answer the last part. You don't need a 340 crank.340 cranks are so heavy duty 340's don't need them.I have a 318 crank in my 340 for years, rods too! Leave the 340 cranks for the racers. As far as performance goes, I had the 318/360 cyborg in my 3900lb valiant broughamandhere's the facts
15.0 flat @ 90mph
21mpg @ 70mph
(2.94 rearend)

[71SATELITE]

Thanks for the help. I tracked down a 4 barrel intake and bought a thermoquad off e-bay. I plan on sending it to demon sizzler for a work over. I also purchased a MP electronic distibutor, and plan on putting on an orange box. This car runs awesome how it is and it is a daily driver so it has to have good drivability. But, power is important also, I hate driving a slug. Skydome what cam have you had your best results with? This car has duels with glass packs so it breaths pretty good. Thanks.

[skydome]

My set up was as follows
318 short block-.020 over
340 windage tray kit from mopar
340 cam
360 smog heads freshened and milled .020
edelbrock performer intake
thermoquad
low gear lockup 904 tranny
2.94;1 rearend
Good luck, Kev