Balancing necessary?

Posted By: FarDarter

Balancing necessary? - 09/09/08 09:34 PM

I'm planning on doing a hone and re-ring of my 318 shortblock that is totally mid-seventies Dart stock. I'm going to top it with some 302 heads and as I understand it, that will lower the compression a small amount beyond how low it already is. So, if I were to go ahead and get some new pistons to bring it up to around 9.0:1 is there any chance I could get away with runnning it without balancing? Since every car build seems to have a name these days, you can go ahead and call this one "Cheap."

Posted By: dogdays

Re: Balancing necessary? - 09/09/08 09:50 PM

302 heads have smaller chambers than the '68-and-up 318 open chamber heads. As you will most likely be replacing a steel shim gasket with a composition gasket twice as thick, gaining about 4 cc of volume, your net compression will remain the same as stock.

Replacing stock LA 318 pistons with KB167s will make necessary rebalancing the rotating assembly as the 167s weigh about 84 grams less than the stockers.

R.

Posted By: Baxter61

Re: Balancing necessary? - 09/09/08 10:20 PM

You dont "have to" have it balanced. But your going as far as you are with boring and new pistons, its only like $180 extra to have it done and it will in theory run smoother.

Posted By: 340727dart

Re: Balancing necessary? - 09/09/08 10:50 PM

Quote:

You dont "have to" have it balanced. But your going as far as you are with boring and new pistons, its only like $180 extra to have it done and it will in theory run smoother.

IMHO, there is no "theory" about it. I won't ever build another engine without having it balanced.
Besides, since he is changing to lighter pistons, that almost requires having the engine balanced.

Posted By: marklock

Re: Balancing necessary? - 09/10/08 02:10 AM

Have it balanced, money well spent. my

Posted By: BADBEE

Re: Balancing necessary? - 09/10/08 02:43 AM

I agree, its no theory, its fact. An engine will perform better, live longer and have less stress on all internal components when its balanced.

Posted By: Ryan_340

Re: Balancing necessary? - 09/10/08 03:01 AM

Posted By: solidcam

Re: Balancing necessary? - 09/10/08 03:10 AM

From the factory a lot of engines weren't balanced that good.You will really appreciate a good balance job and so will your engine.You may even pick up a few ponies in the process.

Posted By: Baxter61

Re: Balancing necessary? - 09/10/08 04:20 AM

Quote:

I agree, its no theory, its fact. An engine will perform better, live longer and have less stress on all internal components when its balanced.

Ive read articles and spoke with an engine builder who was a long time endurance racer and they used to run motors in 24 hour races and do dyno testing on motors that werent balanced and they concluded there was no evidence that not-balancing as no ill effects on on engine life. I dont disagree that its money well spent, but Ive run motors that werent balanced and I had 0 issues with it. Plus, you really think factory motors from that era were balanced all that well? My buddy used to race 340's in the early 90's and he said he would pull motors apart where 1 cylinder was already bored .010 over from the factory, go figure that one out!

Posted By: FarDarter

Re: Balancing necessary? - 09/10/08 04:56 AM

Well the question has now become moot, as I have been corrected in my understanding of what my compression ratio is going to do. Somehow I had come to believe the 302s had larger chambers than earlier 318 heads despite the quench pads. I'm not sure how that happened but now that I know the truth, I'll be keeping my same pistons. Project Cheap just got cheaper! Thanks for the input, fellas.

Posted By: DaytonaTurbo

Re: Balancing necessary? - 09/10/08 04:58 AM

Quote:

My buddy used to race 340's in the early 90's and he said he would pull motors apart where 1 cylinder was already bored .010 over from the factory, go figure that one out!

That makes no difference to balance. Piston A is standard bore size and the same piston in a .03 will weigh the same. They make them like that just so you can avoid the rebalance issues if you kill an individual piston/cylinder.

Posted By: Baxter61

Re: Balancing necessary? - 09/10/08 05:19 AM

Quote:

Quote:

My buddy used to race 340's in the early 90's and he said he would pull motors apart where 1 cylinder was already bored .010 over from the factory, go figure that one out!

That makes no difference to balance. Piston A is standard bore size and the same piston in a .03 will weigh the same. They make them like that just so you can avoid the rebalance issues if you kill an individual piston/cylinder.

I never knew that

Posted By: dOoC

Re: Balancing necessary? - 09/10/08 05:44 AM

Factory OEM "balancing" ? ..... some I have heard from people I know are as much off as 50 grams ! ...and from a Bud in FL ...as much as 90 grams !!! ......... And a 300$ balancing job OFF as much as 30 grams !!!!

It ALL depends on who is doing the balancing job. I did a 383 some years ago with a grams scale and did EACH to within 2 grams. And that did not take that much work to do.