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Pontiac - Boost Turbo, supercharged, Nitrous, EFI & other Power Adders discussed here. |
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#1
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OVERBALANCING the parts of the engine
Back in August of 2009, I made a post about Overbalancing the parts of the engine on the forum I moderate on another website.
Because some of the info directly related to Boosted Engines I will start a thread here and welcome any new info on the subject. Here is the post from August of 2009. This is the Advanced Tech Section but sometimes it helps people if they understand the basics of how things work and then can apply that info to other "Advanced Tech" Racing Projects. I found this web site while looking for an answer to a "Dishing" Pistons vs Balance question on another forum. Here is the website: Parts 1,2, & 3 are covered in this link http://www.eatonbalancing.com/blog/2007/11/ Parts 4 & 5 are covered in this link: http://www.eatonbalancing.com/blog/2007/11/page/2/ This info caught my eye: "The use of nitrous oxide, superchargers, or turbo chargers typically also requires a certain amount of overbalance. Using nitro methane in conjunction with a blower is likely the worse case scenario as cylinder pressures are extremely high under detonation which artificially increases the piston weight by a more than a normal amount. Any form of blown engine will benefit from a given amount of overbalance simply due to the weight of the piston averaging artificially heavier not only from the increase in cylinder pressure at ignition, but the increase in cylinder pressure taking place while the cylinder is also filling during the intake stroke. In this instance, the piston is averaging an overall heavier weight when running at speed. A normally aspirated engine has a given amount of pressure counterbalance in that the piston is subjected to negative pressure when the cylinder is filling but is under increased pressure during compression and ignition. If an aspirated engine is working with an extremely well designed induction system and is benefiting from a ramming effect to fill the cylinders at the upper rpm ranges, then overbalancing also helps here. And then there's the rpm factor. Balancing is linear up to a point throughout the rpm range but depending upon the masses at work within your particular assembly, there is a point in which the crankshaft rpm starts to out run the dynamics of the existing state of balance. Overbalance allows these dynamics to stay in tune or 'caught up' to the rpm's of the crankshaft. There are proprietary formulas that calculate these amounts of overbalance for all the different variables and will vary somewhat from shop to shop. Again, talk with your balance shop regarding overbalancing and determine if this would be best applied to your application." Tom Vaught So Mike and Eric, & Jack, any new info out there? Have a great day and be safe out there. TV.
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"Engineers do stuff for reasons" Tom Vaught Despite small distractions, there are those who will go Forward, Learning, Sharing Knowledge, Doing what they can to help others move forward. |
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I use 2% overbalance in my current 421 turbo combo with an AllPontiac Scat 4.00" crank, and previously also used 2% in my previous high-ish 7000 rpm n/a 400 combo with a factory cast iron crank,for the very reasons Tom detailed above, the bearings always looked good. I settled on re-using the 2% figure for my turbo combo after discussing it with Tom a couple of years ago.
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#3
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The links dont work
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My Half AN Injun..... |
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Link
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" Darksiders Rule "
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#5
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Quote:
Thanks for finding it.misterp266 So hopefully you will not get bashed for posting a Ford Link. Tom V.
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"Engineers do stuff for reasons" Tom Vaught Despite small distractions, there are those who will go Forward, Learning, Sharing Knowledge, Doing what they can to help others move forward. |
#6
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We ran 2% overbalance on the Grocery Gettet engine 541 nitrous oxide. That was the advice of my engine shop from day 1. We had excellent bearing life with those engines. The nitro engines were 4% overbalance from advice of Bill Miller, Pat Dakin (top fuel) and the Zombies. We had tons of main bearing issues due to oiling system problems not related to balance. Once the main bearings received plenty of oil at proper pressure, the overbalance was probably fine. These results are completely anecdotal though. It’s hard to produce hard data on what is the perfect balance for a race v-8.
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#7
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Is there any conclusive data that really indicates overbalance helps with reliability and/or bearing life?
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#8
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Quote:
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When Bill Miller and Pat Dakin, along with Smokey Yunick (and our own Crankshaft Technical Specialist in Ford Research) says it works, then I will not argue with them on the subject. Post up who you think is qualified to dispute their knowledge. Tom V.
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"Engineers do stuff for reasons" Tom Vaught Despite small distractions, there are those who will go Forward, Learning, Sharing Knowledge, Doing what they can to help others move forward. |
#9
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I’m not arguing or disputing the claim that it could be beneficial for some applications. I’m Just trying to understand if it would provide a benefit to my engine as we’ll be balancing in the next few weeks. I did mention overbalancing to my local shop to get their take. They had never seen any big performance gains. I the past, they had spoken with Crower who mentioned that they had not seen any benefits from it either. Once we got the bearing clearance right with the 4.5 stroke we were running for the last 1.5 seasons we haven't had bearing issues either. I have no big names to reference. I did reach out to Bill M. to get his take on my specific application though. Ed
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2023 Best ET Slip 60’ 1.224 330 3.186 1/8 4.784 MPH 152.07 1000 6.175 ET 7.347 MPH 189.92 Weight 3650 YouTube Channel --> https://www.youtube.com/channel/UC21...rWwgFdfTRqShGQ FaceBook Group --> https://www.facebook.com/groups/220092308823847/ |
#10
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Eric and Mike are very good customers of Bill Miller, so my opinion is:
If Bill Miller tells Eric and Mike that it works, and Mike posts up that it has worked on their race car for many, many passes, then why would I need to waste Mr Miller's time having him tell me exactly the same thing again. Explain that one to me. Tom V. I also believe that somethings that you do for the durability of the engine, have very little effect on the engine making more horsepower. If you are asking Crower if adding the 2% gets you some hp increase I would say that you are asking the wrong question.
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"Engineers do stuff for reasons" Tom Vaught Despite small distractions, there are those who will go Forward, Learning, Sharing Knowledge, Doing what they can to help others move forward. |
#11
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I hate to see Tom and Ed argue over this one. Hard data, that I can quantify and look at on a spread sheet or something, I just don't have. Ed, I don't know if you read the six part article Tom posted but there was some good info in there and very similar to what I read in the Sunnen engine rebuilding text book by John G Edwards, 1998. General "rule of thumb" for the past 30-40 years is high stress, high RPM V-8 engines without support for the main caps will benefit from some overbalance. BBC, and Pontiac fit that category. The question that is never really answered is how much? I have never heard of an overbalance greater than 5%. Seems like 1-2% is typical and the 4% we used I just tried because we were killing main bearings. Turns out that was not the issue but I never went back to 2%. We just left it when the bearing issue was corrected. I can't say I have ever heard of a situation where a slight overbalance hurt anything. The gains are all in bearing life, not HP IMO. So if you have zero bearing issues, I would keep doing what your doing or maybe try 1, 1.5%. Engine balance even in 2020, is still a bit of black magic I guess.
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#12
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Not really arguing with Ed, as I consider him a friend, but hate to see very busy people bothered with questions. Now if Ed bought the number of Bill Miller Rods that you guys have bought from him over the years, then maybe you should get a bit more phone time with an expert on that stuff like Mr Miller or Richard Bachelor (the Connecting Rod Expert at Carrillo Rods. I have bought several sets of his rods over the years so he will take a few minutes of his time to explain stuff to me.
Not sure what rods Ed is using in his stuff. No hard feelings with Ed at all, just hate to see busy people bothered. I apologize Ed. Tom V.
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"Engineers do stuff for reasons" Tom Vaught Despite small distractions, there are those who will go Forward, Learning, Sharing Knowledge, Doing what they can to help others move forward. |
#13
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On this year’s refresh, I am switching to BME rods and a shorter stroke. BME shipped the rods out mid-last week. I did end up talking to Bill today about balancing/overbalancing, he did have a few comments which led me to stick with zero balancing.
No apologies needed Tom.
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#14
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Not sure what all you and Bill talked about, but I thought I would mention the tightening technique he wants used on his rods. It was different from anything I was used to, so that's why I mention. Also not sure if you are using the 396 or 426 forgings. But his big deal is dousing the serrations of the rods, and the fasteners completely in the engine oil your going to run. No assembly lube! Then snug the caps with feeler gauges between the rod pair to perfectly align them. Snug would be 20-25 ft. lbs. Then go to the final torque in one smooth single pull on the torque wrench. None of this 3-4 step stuff. I found it pretty difficult under the car with the 426 forgings going to 100 ft. lbs. Much easier on the engine stand for sure. How long are the new rods? 6.7? Best of luck with them.
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#15
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Some very good info there Mike, Thanks very much.
Tom V.
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"Engineers do stuff for reasons" Tom Vaught Despite small distractions, there are those who will go Forward, Learning, Sharing Knowledge, Doing what they can to help others move forward. |
#16
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Yes, we're using a 6.7 rod, Bill recommended the 396. I have used a few sets in a couple of other builds and did follow the assembly instructions from their site. Only difference with the new set is the torque, 100ft/lb instead of 75. (1) Disassemble each rod. Blow the parts clean of contaminants with shop air. Pay special attention to the serrated mating surfaces and rod bolt holes. If the connecting rod or bolts must be cleaned, use only a solvent bath. DO NOT use any aqueous cleaning process, aerosol "brake clean" products, MEK, acetone, lacquer thinner or any caustic cleaning process, such as "hot tanking", as all of these will cause the connecting rod bolts to corrode which may lead to stress-corrosion cracking and bolt failure. (2) If serrated surfaces are slightly damaged during installation or usage they may be dressed with a small, jeweler's file. (3) Apply lubricant to all serrated surfaces, all bolt threads, all washer seats in rod caps, all threads in the rod's big end and both sides of washers (4) Install washers on the bolts with the chamfered, inside-diameter toward the bolt head. (5) Assemble the rod cap to the beam and lightly snug the bolts making sure that large chamfer on the rod faces the crankshaft cheek. (6) As an aid for cap alignment and bolt tightening, two feeler gauges of the proper thickness should be inserted between the pair of rods at the parting lines. (7) Tighten all rod bolts to the torque specifications listed below in one smooth pull. Do not tighten in steps or increments. Doing so will produce improper bolt elongation and reduce clamping force.
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2023 Best ET Slip 60’ 1.224 330 3.186 1/8 4.784 MPH 152.07 1000 6.175 ET 7.347 MPH 189.92 Weight 3650 YouTube Channel --> https://www.youtube.com/channel/UC21...rWwgFdfTRqShGQ FaceBook Group --> https://www.facebook.com/groups/220092308823847/ |
#17
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Pretty much identical procedure for my Brooks B2 ali rods. These are MUCH thicker/bigger than the 396 rods I had, but the surface finish and 'feel' wasn't close to the BME's.
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#19
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So what was your issue with killing the bearings if I might ask. Thanks GT. |
#20
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I don't want to derail the thread. Very briefly, The 90% nitro engine needed huge main clearances, .0065-.007", and 200 PSI down track oil pressure to survive. Also internal main oil galleries had to be gun drilled larger. 42 GPM oil pump Stock Pontiac, is around 7 GPM.
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