Ok so i have every single part I need for an engine build, i'm assembling it this coming Friday. It was brought to my attention today that if i don't have a balanced rotating assembly I will have to rebuild my motor every few years. Now this will be a 80% street car, and i'm worried that the few dollars i saved for the build will end up burning me in the long run. I'm expecting to have the motor for at least a solid five years. So i want the hard facts cleared up now so i can make a decision on this before i put it in my motor.


Here is my combination

1992 350 4 bolt main 1pc rear main
bored .060 over
flat top pistons (speed pro)
Reground crank i bought from savage i think its a federal
Stock Rods
Vortec Heads (valve guides shaved down .010")
stock gm steel rockers
stock pushrods
.017" head gaskets
Comp XR270 cam .503 Exhaust lift
Comp lifters
Edelbrock Performer RPM
Holley 650 cfm manual choke secondaries

Also how much hp should i expect with this setup?
I'm getting my 700r4 build and im running dual strait pipes with turbo mufflers
2200 stall and 3.42 gears.. 12.7s?

Thanks for your input, if im missing something please let me know

 

I don't know about costs at your machine shop but the shop I use in WA is only $165 to balance the motor . If you were using the crank that the rods came from I'd say ,maybe . If it's all kinds of mismatched parts get it balanced you'll be happier in the end .

 

I'm more concerned with engine life than anything. I've heard you can rev higher and faster with a balanced assembly but im not really worried about that, i won't be going past 5800-6k.

 

get it balanced, that is too high to rev it unbalanced

 

Any time you use non factory parts, you should get the rotating assembly balanced. A severe unbalance will cause a noticeable vibration usually seen as the antenna vibrating at an idle and will eventually hammer the bearings out of it.

You're using a turned crankshaft and oversize pistons. The balance will definitely be off. Without getting it balanced, I wouldn't want to take it over 5000.

 

When the guy balances it he makes sure all the parts and pieces weigh the same . I just had a brand new set of pistons balanced and 1 was 11 grams different from all the rest . You can weight match all the pieces to get close but unless you spin it it won't be right . If something is really wrong it will eat up the bearings and keep going down the line . If you really don't want to balance it use a Fluid damper as that will soak up a lot of vibration . The other thing with an out of balance motor is everything in the car will vibrate . I saw a slant six in a Valiant that the guy missed on the balance and every bolt on the engine would loosen up . Had to get it rebalaced to fix .

 

If you dont get the assembly balanced with parts that are mixed and matched, other than a stock assembly. You will eat up your main and rod bearings quite quickly and also have an engine that will not run smooth. You are putting rods and pistons onto a crank that do not match the OE weight specs. Pay the extra cash to get it all balanced correctly and you will have an engine that will run smoothly,rev smoothly and be reliable. As long as its assembled correctly. If you dont you are just looking for problems.

 

Let the flaming begin. If it isnt going to top 5500 much, Id let it go. I seriously doubt you will see tremendous amounts of quick bearing damage. Lets look at it this way, ever see someone crank kit an engine? At work I do at least 2 a month. Its mainly yodas now, but in the past its been lots of gm 60*V6s and many SBCs. We just use a partstore crank and bearings, reuse the rods if they are close enough and ship it out. The balancing is effectively ruined at that point. I test drive every engine I do, and none of them have ever had a vibration. If I were building an all out endurance engine, then it would be balanced. An endurance engine spends lots of time over 4500 rpms. Odds are, based upon the stockness of parts i would say you are not. It wont spend its time in the range you would notice it most anyway. That being said, if you can afford it balance it, if not, dont freak out and think it will crap on you every 30k, cause it wont.

 

I got mine balancedj ust because that's one of those advantages you have available to you with a custom-build. The factory's parts are balanced to a degree, but if you're building a new combination, getting it balanced right is an easy way to make sure it runs well.

Getting my rotating assembly balanced only cost me around $150 I think. Very reasonable. Just do it.

That said, I've got a friend who has an unbalanced motor that runs noticably rough and runs taht thing to almost 7,000 all the time. It's lasted a few years now...

For whatever that's worth...

With all that said, I'm glad mine is balanced, just one thing I dont have to worry about later.

 

I was quoted $300 to have my engine balanced, so I passed on it. If I was quoted $150 I probably would have done it.
I used my stock crank, turned .010" under, ohio i-beam rods, and speed pro .030 over flat tops.
I didn't have mine balanced. It's generally ok if you stay under 6000RPM.
For your street car, i'd forget it and move on.

 

I'll also get into my flame suit and say that the balancing is not absolutely necessary. You motor isn't going to wear the bearings any more or less beacuse of the balance, but it will be smoother. A v8 slightly out of balance will be smoother than any 4 cylinder without balance shafts. (So says David Vizard). On the other hand, those Speed Pro forged slugs are quite heavy... (600+ grams) Around me a balance job costs $150. I sprung for it on my build since my rotating assembly was all aftermarket.

 

Wow alot of mixed opinions here, so I can call a local shop and give them my current pistons, rods and crankshaft and they can balance everything out for me?

 

And rings & rod bearings.

+3 that it's overemphasized. I've balanced a grand total of one engine in my life.

 

hey a little off topic how much did u pay for your crank? and my vote is with those heavy pistons theyl probably have to add weight to the cranshaft witch is when it gets pricey....id say sence u went so low buck anyways dont worry with it....how much did u pay total for your rotating assembly cause u can buy a scat one for about 900 balanced....

 

I payed $130 for it. The pistons are forged aluminum if i'm not mistaken they dont weigh much of anything, but they dont have the speed pro symbol on the side. I didn't go low buck with the motor either man, everything was honed cleaned and checked. I bought everything besides the rods and crank brand new. The crank is regrinded and the rods were cleaned and off the g20 van.

I spoke to a few mechanics today and they said it wasnt really neccessary and that it wont hurt engine life. They said unless i'm pulling 7000+ rpms i'll be fine. They also said i wont notice any more vibration than usual either.

 

I can't remember what it cost for my balancing but I think it was around $500. If a heavy mallory weight needs to be added to the crank, the cost will go up. With my lightweight pistons, weight had to be added.

Parts required by your engine balancer:

Crankshaft
Rods w/rod bolts, nuts etc
Wrist pins
Pistons
Rings
Rod bearings

Although an internally balanced crank doesn't need it, also supply your harmonic balancer and flexplate. My crank was spun up 10 times to get the balance weight down to .00 grams. The first spinup was without the flexplate. The second was with the flexplate. The neutrally balanced flexplate was off 10.1 grams. The pistons, rods and wrist pins should all be separate.

This is how an engine is balanced
http://www.eddiesvalvegrinding.com/balancing.htm

To give an idea how much weight is in your typical engine, a crank shaft weighs approximately 50 pounds, a connecting rod and piston assembly are 4 to 6 pounds. At any revolutions per minute (RPM) there is a substantial amount of weight reciprocating and rotating inside the engine block. At 4000 RPM, 28 grams (1 ounce) of weight 4 degrees from center of the crankshaft produces 112 pounds of external force on the crankshaft. This causes an overloading of main bearings, which increases bearing wear and significantly reduces the life of the engine. It also takes away usable horsepower caused by the increased friction. At 6000 rpm, that 28 grams produces 252 pounds of force. At 8000 rpm, 448 pounds. And you wonder why an engine vibrates when it's out of balance.

A typical street engine rarely goes above 3000 rpm except for brief spurts. Although factory engines are not perfectly balanced, the amount of imbalance won't be noticed at the lower rpms. The higher an rpm the engine operates in, the greater importance of a proper balance job.

Anyone can assemble an engine but having it built properly will make it last a lot longer.

 

Hmm so with that 252 lbs in mind, how much usable horsepower could we be talking about? .25 hundreds of a second in the 1/4?

 

If it is an engine you care about and want to keep for a long time then have it balanced.

Chances are good that your balance is not horribly off. Chances are poor that the balance is within tolerance. I did happen to have an engine come out under 1/2 a gram off after changing piston type, size, rod type, and grinding the crank down. That is unheard of luck.

I am the only person I know (in person) that has had an engine balanced. I know quite a few people that run 6k+ with their engine and never had the engine balanced. It seems most people won't balance an engine if they are running stock rods and crank, even if they didn't come from the same engine. I won't build engine I expect to run hard or keep for long without balancing it.

 

Depends how much HP the engine loses trying to counteract the friction imbalance.

Take a heavy weight on a string and start spinning around with it. The faster you spin, the heavier the weight feels and the more the center of rotation will go outward from your body along your arm or string depending how fast you're spinning. With a heavy enough weight, you'll start to lean back (olympic hammer throw is a good example) Now take 2 equally heavy weights on string one in each hand. Start spinning. The second weight balances out the first and the center of rotation stays inside your body.

This is the effect of engine balancing. You're keeping the weight of the reciprocating mass at or near the centerline of the crankshaft. If it's imbalanced, the weight moves outward from the centerline and creates friction forces on the bearings.

Personally, I'd say his balance will be off a lot. A reground crank will have slightly less material on the throws. The .060" over aftermarket pistons will be a lot different weight than stock cast pistons. Even identically looking wrist pins can be different weights. I had to custom order 2 new wrist pins to match the other 6 after hurting 2 pistons when I threw a rod.

 

after re reading my post i realize i seemed a little insultive i apologize for that.... i just meant a budget build, witch i didnt mean to imply wasnt a quality build....and why i asked about the crank is simply i notice alot of people like re using stock cranks, i just dont quite understand it when a scat 9000 series crank can be had for about 40 dollars more, but yea like i said b4 dont worry with the balance job....

 

Ask Mwnova66 (the guy with 'arguably the fastest 305 on the boards, and a stout SBC at that) if his hot engine is balanced.
Hint - no, it's not.

 

Well this is good news because i've been putting months of hard work into this. I thought i would only need about $1200 for everything (ha) but at that time my plan was to use more used parts than i did. I was building for 400hp and I'm guessing i should be pretty close. Last week i got a $3000 dollar loan to speed up the process and i used another $700 for the springs carb oil pan retainers... you name it. So with that $2200 i'm having somebody build it and install it for me and hopefully then some. I think im going with a th350 also instead of keeping the 700r4. Its just too damn expensive to build one and theirs too many pieces to blow lol. But damn I cant wait to goto the drag strip and not run 15.5's