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Balancing question for engine builders in here? #244364 03/05/09 08:15 PM 03/05/09 08:15 PM
Joined: Dec 2005 Posts: 541 South Carolina A a408swinger OP mopar addict
a408swinger OP mopar addict A Joined: Dec 2005 Posts: 541 South Carolina	I freshened up my motor this winter and bought 8 new pistons. I also went from a set of hand ported 360-1's to a set of 245cc CNC 360-1's which have a 2.15 intake valve instead of a 2.10 so the only changes I had them make in the pistons was to make them for a 4.045 bore instead of a 4.040 bore and to cut the valve relief for the bigger 2.15 intake valve. The pistons are Ross and they also made my last set. I also had them make the pistons the same weight as my old ones so I didn't have to re-balance my rotating assembly. After getting the new pistons and assembling my motor I had piston to valve clearance problems. After calling Ross they realized they cut the valve reliefs too small and I had to pull the motor back apart and send them the pistons back so they could fly cut the reliefs the right size. Now the pistons are 9 grams lighter than my old ones. They are telling me its no problem and I dont need to re-balance my motor. Is this true? Is 9-10 grams not too light? They are telling me its not a problem for the pistons to be lighter. I turn this motor over 7500 rpm's. What should I do?

Re: Balancing question for engine builders in here? [Re: a408swinger] #244365 03/05/09 08:58 PM 03/05/09 08:58 PM
Joined: Mar 2007 Posts: 572 Shelbyville, TN USA 4 40ford mopar addict
40ford mopar addict 4 Joined: Mar 2007 Posts: 572 Shelbyville, TN USA	They are correct! All you have is a very slight "overbalance" due to the lighter pistons. You didn't say what your bobweight is---probably in the 1600-1700 gram range. This 9 grams would be only 1/2% overbalance. Many high RPM engines use 1,2 or even 2 1/2% overbalance. Some shops overbalance 1% for everything but street engines. What you don't want is an "underbalance" situation.

Re: Balancing question for engine builders in here? [Re: 40ford] #244366 03/05/09 09:18 PM 03/05/09 09:18 PM
Joined: Jan 2003 Posts: 6,591 Canton, Ohio S Sport440 master
Sport440 master S Joined: Jan 2003 Posts: 6,591 Canton, Ohio	Quote: They are correct! All you have is a very slight "overbalance" due to the lighter pistons. You didn't say what your bobweight is---probably in the 1600-1700 gram range. This 9 grams would be only 1/2% overbalance. Many high RPM engines use 1,2 or even 2 1/2% overbalance. Some shops overbalance 1% for everything but street engines. What you don't want is an "underbalance" situation. I dont remember the exact numbers but engine builder/tester David Vizard did some testing with overbalancing and found out there was free HP to be had. I think he found like 15 free HP by adding a slight overbalance on a 350 chevy. So like stated above mike

Re: Balancing question for engine builders in here? [Re: a408swinger] #244367 03/06/09 05:15 AM 03/06/09 05:15 AM
Joined: Jul 2008 Posts: 30,424 Florida STAYcation dOc ! The village idiot's idiot
dOc ! The village idiot's idiot Joined: Jul 2008 Posts: 30,424 Florida STAYcation	Has anyone actually checked weights of the pistons to see how close the shop has actually balanced them to "0" ? ....or whatever the shop claimes ? A Bud of mine checked a well-known shop in the Detroit area ..... they claimed they balanced to 2 tenths. He weighed the pistons and some were off by almost 5 grams. But some people claim that with all the oil flying around and on the rotating-assembly ....up to 10 grams off really does not matter.

Re: Balancing question for engine builders in here? [Re: dOc !] #244368 03/06/09 06:13 AM 03/06/09 06:13 AM
Joined: Jun 2003 Posts: 52,972 Romeo MI MR_P_BODY Master
MR_P_BODY Master Joined: Jun 2003 Posts: 52,972 Romeo MI	Quote: Has anyone actually checked weights of the pistons to see how close the shop has actually balanced them to "0" ? ....or whatever the shop claimes ? A Bud of mine checked a well-known shop in the Detroit area ..... they claimed they balanced to 2 tenths. He weighed the pistons and some were off by almost 5 grams. But some people claim that with all the oil flying around and on the rotating-assembly ....up to 10 grams off really does not matter. Chrysler was the worst of the big 3 when it came to balance on the factory stock engines. Sure they will stay together but I'm a big believer in a good balance specially if you take it up in the revs. For you to feel it in the seat of your pants... its got to be BAD

Re: Balancing question for engine builders in here? [Re: Sport440] #244369 08/16/09 12:43 AM 08/16/09 12:43 AM
Joined: Jan 2003 Posts: 6,591 Canton, Ohio S Sport440 master
Sport440 master S Joined: Jan 2003 Posts: 6,591 Canton, Ohio	Quote: Quote: They are correct! All you have is a very slight "overbalance" due to the lighter pistons. You didn't say what your bobweight is---probably in the 1600-1700 gram range. This 9 grams would be only 1/2% overbalance. Many high RPM engines use 1,2 or even 2 1/2% overbalance. Some shops overbalance 1% for everything but street engines. What you don't want is an "underbalance" situation. I dont remember the exact numbers but engine builder/tester David Vizard did some testing with overbalancing and found out there was free HP to be had. I think he found like 15 free HP by adding a slight overbalance on a 350 chevy. So like stated above mike Found it for you RP, mike

Re: Balancing question for engine builders in here? [Re: Sport440] #244370 08/16/09 10:27 AM 08/16/09 10:27 AM
Joined: Feb 2005 Posts: 5,207 Menomonee Falls DemonDust master
DemonDust master Joined: Feb 2005 Posts: 5,207 Menomonee Falls	Thanks Mike My engine is only 2% overbalance. 1528 g assembly and 1567 bobweight on my crank. SDG Motorsports Hellcat Demon and Redeye Supercharger CNC Porting https://www.sdgmotorsports.com/

Re: Balancing question for engine builders in here? [Re: a408swinger] #244371 08/16/09 10:52 AM 08/16/09 10:52 AM
Joined: Jan 2003 Posts: 16,923 NC 440Jim I Live Here
440Jim I Live Here Joined: Jan 2003 Posts: 16,923 NC	Don't stick those pistons in your engine, tell Ross to stick them... You ordered a certain weight and valve relief size, don't pay for anything less. If it is "OK" or not is not the right question. You didn't get what you ordered. Plain and simple. If you are thinking of accepting the pistons, ask for the cost of rebalancing the crank, plus shipping and handling... LOL

Re: Balancing question for engine builders in here? [Re: dOc !] #244372 08/16/09 10:56 AM 08/16/09 10:56 AM
Joined: Jan 2003 Posts: 16,923 NC 440Jim I Live Here
440Jim I Live Here Joined: Jan 2003 Posts: 16,923 NC	Quote: Has anyone actually checked weights of the pistons to see how close the shop has actually balanced them to "0" ? ....or whatever the shop claimes ? I check them before and after they balance them. My scale isn't as good as a good balance shop, but my measurements showed they all matched within the amount I can "read" on my scale (not claiming 1g accuracy). 1993 Daytona, 5.50 at 130mph (1/8) 1.19 sixty ft (PG). Link to 572 B1 - Part 1

Re: Balancing question for engine builders in here? [Re: 440Jim] #244373 08/16/09 08:15 PM 08/16/09 08:15 PM
Joined: Jan 2003 Posts: 6,591 Canton, Ohio S Sport440 master
Sport440 master S Joined: Jan 2003 Posts: 6,591 Canton, Ohio	Jim , what does the shop that you use, "as a rule of thumb" balance thier cranks to or otherwise thier accepted standard perimeters in reguards to 50%/even or 50%+ overbalance. 51% being equal to a 1% over balance. mike Last edited by Sport440; 08/16/09 09:31 PM.

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