318 mods

[72_318]

Im looking to upgrade my 72 challenger with a 318. I've got a set of 340 heads that im rebuilding. Anyone else have a 318, and if so what performance upgrades do you recommend. I already have hooker headers and 2 1/2 dual exhaust. My plan so far is a 4-barrel and an aluminum intake, any suggestions or recommendations. I have no idea what to do for a new cam, would a stock 340 cam do the trick?

Thanks

 

[burntorange70]

Have you raised the CR? With the big chamber heads on a low CR 318 it will not run very well unless you have.

This a cruzer fun car? If so I would go with a 650 cfm carb and an Eddy performer RPM intake. For a cam some thing like a 340 grind cam would be good like a Comp 268. Should work well with a stock converter and still make good vacume.

 

[72_318]

Thanks for the advice. Yes this is just a cruzer fun car im not looking to win any drag races, I just want more than the stock 150 hp, im hoping to eventually get around 350 hp. The engine isn't the stock 318 its actually from a 70 fury so if I'm not mistaken it has slightly higher compression (9.2-1) as opposed to the later 318's (8.6-1).

 

[Challenger340]

The 340 heads will work, but careful not to overcam the small engine ?

Compression will be lower from the bigger head chamber, thats what kills the bottom end characteristic, and too big a bumpstick further depletes the compression down low.
If you aren't racing, the 340 resto Cam from Comp Cams, wakes the Wee-18 up pretty good from a Roll ? Will put a smile on yer yap !

 

[72_318]

thanks for the tips, anyone have any tips as far as a carb goes?

 

[burntorange70]

Thanks for the advice. Yes this is just a cruzer fun car im not looking to win any drag races, I just want more than the stock 150 hp, im hoping to eventually get around 350 hp. The engine isn't the stock 318 its actually from a 70 fury so if I'm not mistaken it has slightly higher compression (9.2-1) as opposed to the later 318's (8.6-1).

CR is not going to be very good with them large CC 340 heads. I would check and see what the final CR would be with them heads first. Then do every thing you can to raise it. IE thin head gasket maybe mill the heads a little if it needs valves get ones that stick out some to take up some CC's in the heads.


I would go with a vacuum secondarie 650 Holley.

 

[moper]

Pretty much all 318s are the same. There were no special ones until the cop car engines which really weren't any better in terms of power. But, it's not hopeless. Definately use the Mopar Performance thin head gaskets, and definately have the heads milled .030 during the rebuild. You'll have to have the intake sealing surface cut .030 too. For a cam, instead of the factory 340, the Summit brand smaller cam would be good, another choice that would have a little thump to it would be the Comp High Energy 268H. As far a carb, I like Edelbrocks on milder street cars, and I'd use the Thunder AVS 650.

 

[bad440]

Also depends on how much you want to spend. a set of Edelbrock or Indy heads will make that 318 scream. It's basically a smaller bore 340, all 340 parts are interchangeable. If it was me a modern set of heads along with the other mods mentioned and you will make over 300 HP no problem.

 

[btceng]

I too have a 71 318 that I want to wake up a bit. I have a four barrel manifold froma a 360 and 600 cfm Edelbrock carb. I installed a 284 Mo Perf cam that is too much for the 318. Very rough idle and will not stay running at idle with the stock converter. I am going to polish the stock heads and try the thin gasket. I also plan on adding a set of Hookers and 2 1/2" exhausts. I have stock manifolds and 2" pipes now. The engine runs good but has poor low end and a very pronounced chop as mentioned before.

I pulled my engine and transmission (904) this week to do work on my firewall and get ready for paint. I'm interested in this thread as I look for that "magical 318" that runs like a 340.

Also, I have the stock 2.73 gears and think that a set of 3.55 or 3.91 would help more than almost anything else.

Good luck.

 

[Cranky]

A 70 381 is listed as having 8.8-1 in my book but a 69 318 is listed as a 9.2-1. Yeah, a 340 is pretty close to a teen but the bore is much larger which lends itself to larger valves more readily not to mention they had a lot more compression. Larger bores help unshroud the valves which allows better breathing but a teen can still be made to run well. Small engines don't have much low end torque so some gearing helps them a lot, especially with heavier cars and Challengers are not exactly light. Also the smaller cams that produce some low rpm cylinder pressure help too and cams that produce lumpy idle usually don't do that....

 

[shadango]

I have a 318 in my 72 fish....either a 76 or 78 block...cant remember now....anyways, it was messed with before I got it......J heads, double roller tc, deep sump milodon oil pan, eddy performer manifold, 600cfm eddy (it came to me with a 750), dougs headers.....and a purple cam....but no idea what grind....its pretty lumpy at idle and I have low vacuum... Using a 3400 stall (Breakaway from TCI) and just put a 3.55/true-track in. The gears made a huge difference in power......really a lot of fun to drive now....the 2.76s made it a real dog off the line. She isnt a hemi, but she gets going ok for cruising and a little fun.

 

[LXguy]

Yeah, those book numbers are typically nowhere close. They heads have bigger combustion chambers than typically listed (plus valve sink), and the pistons are usually way down in the hole.

Actual compression ratio on my 71 was 7.5:1. Pistons were .100 in the hole! Can't imagine what it would have been with valve reliefs.

Err on the small side for camshaft. Dynamic compression losses will make a bad situation worse. Hughes supposedly sells camshafts to crutch the low compression problem.

For heads, I'd go straight to the RHS X heads. They have a low 60s CC out of the box (lower than any Mopar heads you are going to find), and flow a ton better than the factory iron. They cost more, but only a little after you get into milling and valve springs and crap. Plus they'll bolt right on to whatever you "graduate" to.

Gear and converter are big improvements. E-body is a heavy beast.

My 318 really responded to a LD4B intake and a Holley 670 street avenger carb. With the bigger heads, I'd get a performer RPM or LD 340.

 

[LXguy]

Also, 318 have really thin head gaskets to start with. You have to use the thinnest one Mopar or Mr Gasket offers, or you end up giving up CR.

 

[72_318]

http://www.popularhotrodding.com/enginemasters/articles/mopar/0667em_mopar_318_engine/index.html

this is a really good article on a good 318 build that makes 400 hp fairly easily.

 

[btceng]

Thanks for the link. I had read it before but forgot how to find it. I've been thinking seriously about finding a 360 and building a stroker. Many of the upgrades that I have on my 318 would bolt right on. I've heard a lot of good things about the 408.

 

[burntorange70]

http://www.popularhotrodding.com/enginemasters/articles/mopar/0667em_mopar_318_engine/index.html

this is a really good article on a good 318 build that makes 400 hp fairly easily.

Thats a good combo of parts that I have seen on a lot of SB. Works well and still very drivable.