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Boring 318 for more power?

  
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Boring 318 for more power?

 
johnsch8 johnsch8
New User | Posts: 14 | Joined: 02/09
Posted: 03/09/09
03:37 PM

Hi all,

I've got a 318 at the machine shop and need some advice. I've been following the 400hp 318 build article for a while. I plan on following this to a T. Just need to know if over boring would bring more power. I'm asking because the shop says boring it 30 over or even 40 over won't be noticeable as far power goes. I assumed that bigger bores=more compression=more power but looks like I was wrong. Is this true or did I assume wrong?

Any help is welcome...

CJ
Confused  

batman43 batman43
User | Posts: 55 | Joined: 06/08
Posted: 03/09/09
07:25 PM

Boring any engine out increases the displacement..030 will normaly give you around 4.5 to 5 cubic inch gain. larger piston = more area = more volume. The increase in HP will be minimal but it will increase.If this car is going to be a cruiser do not bore .040 unless absolutely necessary.This will drastically decrease the wall thickness of the cylinder wall and can cause the engine to run hotter. Drag cars typicaly bore on up to .060 but these engines only run a short runs down the track and are shut off after each run.  

RBolig RBolig
Moderator | Posts: 948 | Joined: 12/03
Posted: 03/10/09
06:48 AM

Oversizing the bore will not affect compression. So simply increasing the bore will not yeild a noticable power improvement. Since you are boring the cylinders, you'll need new pistons, and if you are wanting to up the compression, you can do so now. Talk to your engine builder, and get his suggestions.  
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Some people are like Slinkys; they're not very useful, but fun to watch when pushed down the stairs.

johnsch8 johnsch8
New User | Posts: 14 | Joined: 02/09
Posted: 03/10/09
04:23 PM

Thanks for the replies. I am going with bigger pistons and a few more upgrades like cam and lifters, porting the heads, and carb rather than throttle body. I was told by a different shop that the heads are where the power is made so I'll focus more on those. Thanks again

Grin  

neelhaq neelhaq
New User | Posts: 10 | Joined: 12/08
Posted: 03/10/09
08:36 PM

I've also just recently got my hands on a 318. Though I know the 340 is more fun this is my first "muscle car" and I'd like to not ditch a nice underdog 318.  I noticed the post regarding  40 boring over heating and have found the same on my research.  I'm guessing bore to 30 would tend to the same problem.  I'm just trying to rebuild for street cruises and the occassional peel outs ... not the track.  So would you say it's best to simply rebuild stock (with respect to everything like rings etc) go for a bigger cam and some nicer heads, intake and carb?

Has anyone seen summits intake and carb package for like 500bux comes with a holley and edle  

RBolig RBolig
Moderator | Posts: 948 | Joined: 12/03
Posted: 03/11/09
07:59 AM

John: YES, the heads are where power is found and lost. good heads and/or porting is a must for performance.

Neel: If you bore the engine .030 over, you should not have aproblem.  
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Some people are like Slinkys; they're not very useful, but fun to watch when pushed down the stairs.

johnsch8 johnsch8
New User | Posts: 14 | Joined: 02/09
Posted: 03/11/09
03:13 PM

RBolig

Would piston choice matter? I mean I was gonna go with a set of KB, which a friend recommended, but was told by the shop that it really doesn't matter- the name brands just tend to last longer.  They've already bored 40 over, I was just trying to get better compression out of this sb since that was a major downfall of this engine. Any experience here?  

RBolig RBolig
Moderator | Posts: 948 | Joined: 12/03
Posted: 03/12/09
05:34 AM

Keith Black Hypereutectic pistons are a decent and more economical choice than a Forged piston, and I have never heard of anyone having an issue with them--IF used within their relm of usage. Adding a bunch of juice or forced induction will shorten their lifespan. Since it sounds like you are just planning a decent overhaul, I see no problem. I would however be alittle concerned if the shop already bored the block before you have the pistons. I always like to have the block bored for each piston that will be filling a particuliar cylinder. There are production variances in EVERYTHING, and I just like to remove a possible variable. By doing this, you can keep the piston to sidewall clearances at a constant.  
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Some people are like Slinkys; they're not very useful, but fun to watch when pushed down the stairs.

johnsch8 johnsch8
New User | Posts: 14 | Joined: 02/09
Posted: 03/12/09
03:49 PM

Thanks RBolig,

I won't be adding any power adders at all. Just want to make sure the bottom end holds together for a while to come since this truck is 20 years old and has never been opened up. The shop actually told me they would have to bore it first then get the pistons/rods. Not sure why. I did notice some deep gashes on the bottom end of a few of the rods where it bolts on to the crank. So it looks like it wouldn't have been long before something dropped out the pan. I look at it this way- if it's worth doing, do it right. Hopefully I won't have any issues with it. Thanks for your comments.  

johnsch8 johnsch8
New User | Posts: 14 | Joined: 02/09
Posted: 03/14/09
02:07 PM

Anyone used 360 heads on a 318 bloc? I hear one person saying it'll kill power and another saying it adds a lot of HP. The 318 heads I pulled off are cracked, so reworking those is a no go.  

neelhaq neelhaq
New User | Posts: 10 | Joined: 12/08
Posted: 04/19/09
09:00 PM

Icon QuoteRBolig:
John: YES, the heads are where power is found and lost. good heads and/or porting is a must for performance.

Neel: If you bore the engine .030 over, you should not have aproblem.


There's a local selling an already magnafluxed 318 but bored 0.40 over.  If I'm not draggins so much as just city cruising do you think it would be a poor choice and I'd just overheat? I mean does 0.40 bore run that hot?  

marcohotrod340 marcohotrod340
Enthusiast | Posts: 470 | Joined: 09/08
Posted: 04/20/09
03:12 PM

A used block with worn out cylinders must be bored to make good power. .030 is not much different than .040 , always bore the least needed to get the cylinders to clean up. some shops prefer to bore befor ordering pistons to be sure of what size all cylinders clean up at, then the new pistons are measured to make sure they are correct. a set of 8 modern pistons should all measure identical and the proper average clearance is built into the piston. in the old days a set of pistons had a much wider tolerance range and the oversize pistons needed to be measured befor boring so each cylinder could be bored to each new piston for the proper clearance. math says a 400hp 318  at +.030 is 406hp 323  at +.040 is 409hp 325 . 360 heads are fine on a built 318 offering bigger valves and bigger ports = more flow , and bigger combustion chambers = less compression -- cut heads .020" and all is fine (this minor of a cut usually does not reqire the intake to be cut to bolt on) with a decent fan and radiator, correct ignition timing and fuel ratio and spark plugs , mopars do not run hot.  

neelhaq neelhaq
New User | Posts: 10 | Joined: 12/08
Posted: 04/20/09
07:14 PM

Wow nice details thank you.  Anyone know of a trustable shop in NY?  

vanjr1 vanjr1
New User | Posts: 1 | Joined: 09/08
Posted: 11/19/09
11:08 AM

I have 360 heads and 340 exhaust manifolds on my 318. 600cfm Edelbrock Carb 340 grind cam. Here is a link that shows it. I think it has some decent power.
http://www.youtube.com/watch?v=0EBEvNxtUUk  

Plypar68 Plypar68
New User | Posts: 33 | Joined: 11/09
Posted: 11/19/09
12:48 PM

As far as running hot goes....heres my experience. 68 318 block, bored 060, trw forged pistons, Hot Arizona weather. Never had any problems, still runs cool. Rebuilt in 1993. In 1998 installed 360 heads (milled 020) significant HP gain, never had to re-ring the pistons, and ....still runs cool in the summer. Ive always used hotter thermostats (185-190) it seems to keep the fluids in the radiator for a longer duration.