LilJayV10

iTrader: (5)

I am building a 350 for my bird, i am putting a 268xtreme cam in it. all the test's in magazines i have seen and what comp cams says is the cam peaks at about 5800. i can get my engine balanced for 130 bucks. Is it really worth it? i was wondering if anyone has had any experiences or thoughts on it. i understand the concept of balancing it, but is it really worth it for a street engine?

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Wide Open Till You See God...Then Brake

Red Devil

Is it worth it? For that price? YES. Just do it.

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"Perfection is a trifle dull. It is not the least of life’s ironies that this, which we all aim at, is better not quite achieved."

-W. Somerset Maugham

Guest

Definitely worth it. I wont even bother building up an engine anymore without balancing it.

MINN IROC-Z

Yes i would have it balanced at any cost. I have a 62 Nova with a 327 4-speed in it and I run it up to 7000 RPM and i did it before and after rebuilding it. A major diference in the feel of the engine at higher RPM's after it was balanced.

87RS402

I personally feel it adds to the longevity of the engine. It's easier on the bearings and wrist pins not to have the slight imbalance.

$135, Thats money well spent. It cost me $250 to balance my cad.

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'87 RS 402 Big Block
'92 S-10 Blazer 4X4
'77 3/4T Chevy 4X4 P/U with 500 Cadillac
Qsac

Polecat

Man that's a killer price. I paid close to $300, but yes, do it. It will add the longivity to your motor.

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350 4 bolt main, Speed-O-Motive 383 stroker kit, re-sized rods ground for clearance,TRW Forged pistons,10.7:1 compression,HPC Coated RPM intake, Speed Demon 750 cfm carb,World Products Sportsman II heads,2.02/1.60 valves, Comp Cam 1.6 roller rockers, Comp Xtreme 284 cam,240/246@.050 with .540 lift,Crane pushrods,ATI damper,Proform HEI and MSD6A box,HPC coated 1 5/8 headers, 2.5" exhaust with 40 series mufflers,TH350 with B&M 3000 stall, Powertrax NoSlip Locker, 4.11 gears.

The ODB

there is a good argument either way.
An engine builder will tell you that you can't really balance an engine at every RPM. Other builders will say that you cannot really balance a running engine because of unequal combustion & windage.
There really is no balance in a running engine. Harmonics frequency, and amplitude vary with engine speed. Most people will attempt to get all the parts as close in weight as they can and as light as possible. Then the only other thing you can do is try to control harmonics with a quality damper like the Vibratech.

I had to balance my 383 in my living room floor last time. It spins to 7000 rpm and I honestly cannot feel or measure a difference either way.
Most people I know will balance the weights of the parts themselves and then let the machine shop do the spin balance of the rotating assembly.
I can tell you that lighter is always better.

ODB

AlkyIROC

I think any engine that lives above 5000 rpm should be balanced. Factory engines don't see much over 4000 rpm except on full throttle shifts and those engines are designed to run for hundreds of thousands of miles and they're not balanced.

For a daily driver street engine it's not really worth it but for that price, get it done. So your cam peaks at 5800. In a race car your operating range would be 3000-5800. In a street car your operating range is usually 1200-3500 except when shifting at WOT.

If all you're doing is changing the cam then I don't feel you need to have the engine balanced. If you're doing a complete rebuild and using new aftermarket pistons then yes I think you should get it balanced especially for that price.

My 383 wasn't balanced and ran fine until I threw a rod and disintigrated a cast stock piston. The failure had nothing to do with engine balance.

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Follow my racing progress on Stephen's racing page
and check out the race car

87 IROC-Z Pro ET Bracket Race Car
383 stroker (carbed) with double hump cast iron heads and pump gas
461 Big Block installed and ready for the 2001 racing season

Best results before the 383 blew up
Best ET on a time slip: 11.857 altitude corrected to 11.163
Best MPH on a time slip: 117.87 altitude corrected to 126.10
Altitude corrected rear wheel HP based on power to weight ratio: 476.5
Best 60 foot: 1.662

Racing at 3500 feet elevation but most race days it's over 5000 feet density altitude!
Member of the Calgary Drag Racing Association

87 IROC bracket car, 91 454SS daily driver, 95 Homebuilt Harley

[This message has been edited by Stephen 87 IROC (edited February 19, 2001).]

JoelOl75

A 700 horse SB chevy twists more than 1/16" corner to corner at full throttle causing the bearings to not line up but the crank never hits the bearings because of the oil film. Actually using lighter pistons/rods (not aluminum though) and not rebalencing causes the motor to balance higher up in the rpm range. Even an unbalenced v8 will not shake more than a balanced 4 cylinder.

[This message has been edited by JoelOl75 (edited February 19, 2001).]

Ward

iTrader: (1)

Put it this way - you have alot of heavy metal parts spinning at 1000-6000 RPM 3 feet from your face... wouldn't you rather have it balanced? lol come to think of it I would definitely want a motorcycle engine balanced; cruisin with stuff spinning at 9000 RPM under your crotch - yeowtch!

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1983 Pontiac Firebird SE
LG4-Based Chevy 400
700R4 Tansmission
Modified 4 Barrel Q-Jet Carb
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Clarion 45X4 CD/AM/FM Head Unit
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Third Gen Performance
"A four cylinder is only half an engine"

I ROCK

YES. Think of it this way: you could pay 130 for say, better heads (assuming you could sell your current ones) porting job, better cam, you name it and get about the same performance. But your engine won't last as long or be as "tunable" and you'd essentially be opting for a sloppy approach that assumes more expensive parts must work well on any engine - that's a BIG assumption!! Look at GM: could they make a Vette that puts out 700hp and sell it for the same price? Hell yes, but it wouldn't last to 100,000 miles and surely wouldn't get 12 mpg crusing at 150mph!! let alone 18 mpg most of the rest of the time. You can take two identical engines before assembly (let's say run of the mill 350's) mill, get it? lol. and balance one but just throw together the other and I bet you'll see at LEAST 50-100hp difference. Hmmm, GET IT BALANCED!

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"Among so many conflicting ideas and so many different perpectives, the honest man is confused and distressed and the skeptic becomes wicked...Since one must take sides, one might as well choose the side that is victorious, the side which devastates, loots, and burns. Considering the alternative, it is better to eat than to be eaten."

Napoleon I

Box of Rocks

Jay,

My buddy has a 350 with the Comp 268 XE cam, and the 5,800 RPM figure is correct. As far as balancing goes, it's like this:

If you're doing a complete rebuild, including boring, re-sizing the rods, and replacing the pistons, you need to have it balanced. Period.

For $130, it's cheap insurance. Also, a side benefit: there are few sounds in this world more wonderful than a SBC at high-RPM.

(well, a beautiful woman in the heat of passion comes to mind as an exception....but other than that)

A balanced 327 at 7,000 RPM with open headers conjures images of 12-cylinder Ferrari motors and the like. A balanced 350 at 5,800 RPM conjures images of a smart young engine builder who has assembled a short-block platform that will accept nitrous, big cam, and good heads sometime in the future when the budget permits it.

Use forged pistons, nothing less.

BOR

a73camaro

Cranks, harmonic balancers, and flywheels are balanced (mostly) from the factory. All the rods and pistons are close to the same weight.

Stock engines can go 150k to 200k with the above mentioned type of balancing.

If you are building a race motor, get it balanced. If it a daily drive, don't bother, that chunk of carbon that builds up on the piston after 10k miles negates any balance work.

[This message has been edited by a73camaro (edited February 20, 2001).]

JakeJr

It's like the American Express Card, I never leave home without it.

It's a 'Pay Me Now or Pay Me Later' situation, especialy if you've changed any of the rotating or reciprocating parts or plan to rev the engine higher than the stock redline.

Jake

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1986 Corvette Coupe, 415 CID, Edelbrock 6073s, ZZ9

TomP

Here's one of those wild *** questions...

Say I rebuild a motor with new pistons & rings (and other new stuff), but keep the same crank & connecting rods. Say I don't want to dump a ton of cash into the motor.

Could I weigh each piston on some kind of grams scale, and then use a die grinder on the inside of the skirts to remove a bit of metal to make them all the same weight?

Or would removing metal from inside the skirt totally kill the piston? Where do machine shops remove metal from? And how would all of this relate to an externally-balanced engine?

Thanks guys!


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-Tom P (Hot rodded 1986 Firebird 2.8l) from http://www.f-body.net/mailbag/3rd/3rd_mailbag.html message boards
---Think your car could be pic of the week? Visit http://www.f-body.net for details!

The ODB

Tom,
Yes you can balance using a gram scale. Many low buck engines are built this way.

Do not take metal from the skirt as they are already too thin in most pistons.
You usually have a couple of choices.. the bosses that hold the wristpin or under the dome.

It will work fine on a street engine. Many racers even run without balancing at all.

ODB

JoelOl75

Add your piston and pin to your small end weight. Then add this to 2x(big end weight+bearing weight+2)

The 2 is 2 grams for oil retained in the bearing.

If this weight is less than 1900 grams but greater than 1850 grams you can skip balancing. Lighter is better and within this range which is very easy to hit it's not in anyway damaging or harmful. This assumes an unadulterated stock crank. Go for the lighter end. Overbalancing the crank (lighter piston assms) helps at higher rpms because at BDC the forces push the piston up to counter the gas loading. Performance motors are purposly overbalanced. Smoothness has nothing to do with wear or failure within these very forgiving limits. It's more important to match all 8 assms. Save your balance job money on a gram scale and plastiguage/mics and better rod bolts and main studs before worrying about petty balance. Get your bearing clearance right which IS important. Change rod bolts.... which IS important... If you have money left over after this then you could spend it on less important things like line-honing and balancing. Getting the scale and doing your pistons/rods will save you more money here because the machine shop won't have to mess with your pistons/ect. Just give them the bobweight. Some may say i'm usin' my scale to measure more than pistons but I am a machinist and know knowlegable race engine builders who informed me on this. Not only is it written in books and utilized by people who know what they are talking about, true 'performance' balance actually shakes more at idle than an idiots 'cadillac' balance (50%/50%).

Perfect balance is 49% Recipricating 51% rotating.

Avoid going heavier! Cheap forged pistons add weight. Good aftermarket rods add a little or are around the same as stock.

[This message has been edited by JoelOl75 (edited February 23, 2001).]