#56739 - 04/11/10 05:07 PM
Re: Dyno day for a 250
[Re: Mean buzzen half dozen A.K.A. Hank]
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panic
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Registered: 01/11/05
Posts: 1341
Loc: Hempstead, Long Island, NY
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the charistics of a given crank can be used to predict at what rpm harmonics will cause problems
Yah, but the analysis is really complicated even using ex$pensive software. The point is not to detect some metaphysical, sub-atomic internal property, but to find out when a given piece of metal will ring in sympathy to an external shock. It's just a big, weird-shaped tuning fork (no power or compression forces apply here) and it "rings" at a certain frequency - long and thin makes a deeper tone (lower Hertz frequency) than short and thick (higher). Big bearings raise the tone, long stroke lowers it. Depending on the firing order, number of cylinders, bank angle etc. there are specific "orders" that will stress the crank, and frequency determines the RPM at which these occur. Where “O” is the number of the order, and Hz is the frequency RPM = Hz × 60 ÷ O Hz = RPM ÷ 60 × O For an L6, the critical orders are (strongest harmonic first) the 3rd, then 2-1/2th, 2nd, and 6th (the 9th is smaller, 1st is outside the normal RPM range). I made a stab at how it might be estimated by suspending the surgically-clean, undamaged crankshaft in a soundless environment, and either: A. striking it smartly with a brass hammer, and using a microphone to record the sound, then reading the oscilloscope trace to get the frequency, or B. using a tone generator to excite the crank by slowly passing through the suspect period (200-250 Hz for an L6) while intently watching an attached .010" wire for vibration?
No one thought it will work, but they couldn't say why.
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#56748 - 04/11/10 08:39 PM
Re: Dyno day for a 250
[Re: Mean buzzen half dozen A.K.A. Hank]
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CNC-Dude #5585
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Registered: 09/27/08
Posts: 1743
Loc: N. Georgia
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I would think cranks can also be balanced so it will run smoother @ high RPM & run a little rough in the lower RPM range. I'll ask Dave @ "The Balance Shop"
When I used to road race a two stroke GP bike & other 2 stroke engines,I keep on breaking cranks because the class made us use the stock heavy flywheel.
I had my friend Dave @ The Balance Shop ,balance the crank so it would run smoother @ high RPM ,,& it did just that,a lot smoother & just pulled cleaner all the way up to 13,000 RPM,eventually the crank still broke,but it did last longer than w/a stock crank & with stock/original balance.
Originally the engine turned to 8500 RPM,& the crank would last a full season.
MBHD
Hank, thats called "over balance", we did it. Winston Cup and many race classes that have engines that run in the high RPM range like that also have done it for 20 years or so. It definately helps. Its easier to do on engines that use bobweights to balance them, because you just cheat the bobweights by the amount you want to "over balance" it. On an inline that doesn't use bobweights, its a little more difficult, but it can be done.
_________________________
There's no such thing as too much cam....only not enough engine!
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#56757 - 04/12/10 06:11 AM
Re: Dyno day for a 250
[Re: panic]
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panic
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Registered: 01/11/05
Posts: 1341
Loc: Hempstead, Long Island, NY
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If you examine the crank, there are huge counterweights to both provide inertia and oppose the dead weight of the rod throw 180° away. I've read many articles on L6 balancing, and have yet to see a specific recco as to what mass the individual counterweights carry, or even the total imbalance. Obviously, 100% of the rotating weight is included (pin, arm, bearings, rod big end), but what (if any) opposes the reciprocating weight? Why are some counterweights heavier? The only definition is what it's not: it isn't a percentage of the reciprocating weight (which is what V8s require).
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#56758 - 04/12/10 06:30 AM
Re: Dyno day for a 250
[Re: panic]
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panic
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Registered: 01/11/05
Posts: 1341
Loc: Hempstead, Long Island, NY
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An example of a very complex analysis of crankshaft design, with almost nothing on exactly what determines counterweight mass: http://www.bacomatic.org/~dw/library/angle/angle.htm
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#56759 - 04/12/10 06:46 AM
Re: Dyno day for a 250
[Re: panic]
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panic
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Registered: 01/11/05
Posts: 1341
Loc: Hempstead, Long Island, NY
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Just a thought: the well-known "perfect inertial balance" of an L6 is not a physical analysis, but theoretical. In practice, each pin and its components is opposed by another cylinder on an opposing stroke (unlike L4, V8, etc.). Where's the difference? The other cylinder is (at best) next to it (not exactly opposite) such as the #3 & 4 (the balanced #1 & 6 are at opposite ends, duh), and the forces between them bend the crank at the web connecting them. The counterweight provides opposing weight as close as possible to the actual pin (on both sides). But, again, what does it weigh, and why?
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#56763 - 04/12/10 08:43 AM
Re: Dyno day for a 250
[Re: panic]
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tlowe #1716
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Registered: 04/01/04
Posts: 2334
Loc: Dysart, Iowa
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Here are pics of a few things. bad balancer/ crank Langdon cast headers 3 side draft OER carb setup.










Edited by tlowe #1716 (04/12/10 08:48 AM)
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#56773 - 04/12/10 04:14 PM
Re: Dyno day for a 250
[Re: CNC-Dude #5585]
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68falconohio
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Registered: 11/30/09
Posts: 30
Loc: Cowtown, Ohio
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Panic, you may give the people at http://www.bonal.com a call. Their equipment is meant for stress relief but finding the first harmonic frequency is a required step to using the equipment properly. Very knowledgeable folks on harmonics.
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#56787 - 04/12/10 08:53 PM
Re: Dyno day for a 250
[Re: CNC-Dude #5585]
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tlowe #1716
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Registered: 04/01/04
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Loc: Dysart, Iowa
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Had the 250 running again this evening. Sounded good , again. Idle is a little different with the heavier balancer and 5 lb heavier crank. Oil pressure was also good. While warming it up found a oil leak from one of those removed timing cover bolts. Blah! Thought the bolt hole was blind on the back side. Cleaned it and sealed with silicon. Let sit overnight to dry. Hit it again on tues. Tom
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#56792 - 04/13/10 01:59 AM
Re: Dyno day for a 250
[Re: Winter]
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ACH57
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Registered: 05/21/07
Posts: 42
Loc: Clarkdale, AZ
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Any info on what size and style the side draft carbs were?
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#56794 - 04/13/10 05:55 AM
Re: Dyno day for a 250
[Re: strokersix]
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tlowe #1716
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Registered: 04/01/04
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ACH57, The side drafts are 45's, fitted with 36mm chokes, also have 40 mm and 32mm chokes available.
The balancer had a nice fit for both the 292 and the 250. Who knows what could have went wrong. Tom
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#56821 - 04/14/10 05:26 AM
Re: Dyno day for a 250
[Re: Mean buzzen half dozen A.K.A. Hank]
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tlowe #1716
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Registered: 04/01/04
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Loc: Dysart, Iowa
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May do that yet.
On tues night, the motor was back up to snuff making 285 hp. Tonight, bolt on the turbo stuff, turn down the timing and see what happens. Might not run tonight, but will try. Tom
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#56829 - 04/14/10 07:49 PM
Re: Dyno day for a 250
[Re: tlowe #1716]
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tlowe #1716
12 PORT ADVERTISER
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Registered: 04/01/04
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Loc: Dysart, Iowa
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All the turbo stuff is bolted on. Thurs after work, will fire it up with out the turbo charge tube and get carb setup, make a few light pulls. Then turn down the timingand get the boost dialed in and nail it. When You see the pics (none taken yet) it is a throw down turbo setup, yet funtional. Tom
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#56859 - 04/15/10 07:09 PM
Re: Dyno day for a 250
[Re: tlowe #1716]
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tlowe #1716
12 PORT ADVERTISER
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Registered: 04/01/04
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I'm back from the shop! Got a few trophy burns this time too. Turbo motors have more hot parts!
Used a SPA turbo manifold, turbonetics wastegate, a old Air Research T04 and a holley 500 2 bbl carb in blow thru mode.
Wastegate held the boost perfectly at 5 psi and we saw a 33% gain in tq! 87 Ft lbs to be exact. This little 250 thought it was a good running 350 chevy. Also saw the 345 hp in the #'s. But the tq was king for the runs.
It was a crude setup and put together from scrouged parts. This was done mainly to show how easy it is and some of the power gains that can be seen. We had hoses blow apart because there was no blow off valve. So when coming back down in rpm from a pull the throttle had to go slow to not build up excess boost and blow the hoses.
All in all, it was a success and definately more power can be had from this turbo setup. Boost was almost instant and the engine never missed a lick. What a fun night. Got plenty of vid, I think my hands were shaking from the excitement. Plenty of tuning needed to be done. Tom


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#56913 - 04/17/10 03:00 PM
Re: Dyno day for a 250
[Re: Mean buzzen half dozen A.K.A. Hank]
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tlowe #1716
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Registered: 04/01/04
Posts: 2334
Loc: Dysart, Iowa
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Sorry, it is a .96, get mixed up with all the #'s. Tq in the 340's were seen, it was always above 320 ish.
Add a intercooler, adjustable fuel pressure reg ,10 psi and look out.
The timing was run low to be conservative with the DIY setup, mixture was also rich and the fuel also conservative with 110 sunoco. No need to damage the motor for simple tests. So more power can be rung out of even a 5 psi setup. Tom
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