Inliners International Forums General Discussion Hi Performance Dyno day for a 250

Does this damper require any machine work to fit a L6 Chevy and being 8" cause any interference with the water pump pulley and belt alignment..??

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Scrapiron: My small block Streetdampr I shortened the damper hub to tuck the damper in as close as possible to the timing cover. Next time I'll counterbore the timing gear instead for a more robust damper connection.

If you don't mind the damper sticking out a bit then I think it's a bolt on deal without modification. Can't say for sure on the GM damper but it's probably similar.

Panic, is thet stuff always going on in your head? It must hurt sometimes. No wonder you used to be so cranky! Wow, That is a lot of thinking. So you are saying that the charistics of a given crank can be used to predict at what rpm harmonics will cause problems and then a dampener can be built to even them out at several different rpms? I thiought they just kind of deadened them as they came by. Beater

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

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.

Measure the torsional stiffness by torque versus deflection. Then measure the polar moment (correct term for rotating inertia?) by hanging from a soft spring, twist and release, and measure oscillation period. Combine the two and you should be able to calculate natural frequencies.

I think so anyway.

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.

So how exactly do you overbalance in inline? Add 100g bobweight to each crankpin? I'n not sure what that will accomplish. Please explain.

Measure the torsional stiffness by torque versus deflection

But... that's not something I can do. The crank flexes in normal service perhaps 1/4 to 1/2°; I can't make an accurate measurement that small, and I'd need a fixture sunk into the ground to anchor the crank (my lathe only weighs a few hundred pounds, and will lift right off the floor).

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).

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

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?

Here are pics of a few things.
bad balancer/ crank
Langdon cast headers
3 side draft OER carb setup.

By my understanding:

Inline six counterwieghts are there to reduce crank bending loads and bearing loads. They do not contribute to a smooth running engine in terms of externally felt vibration.

Not true on other engine configurations such as v8. v8 has unbalanced forces and will vibrate externally. The externaly felt vibrations can be altered by changing the recip factor or under/over balance.

For example, balance factors on motorcycle engines are chosen so the engine vibrates fore/aft instead of up/down for rider comfort.

A torque wrench, dial indicator, and a little creativity will get you torque/deflection.

Polar moment of inertia (not sure if this is correct term?) is a little tougher but also obtainable with a stopwatch and some more creativity.

Combine the two and you should be able to calculate first order natural frequency of the crank, damper, flywheel assembly. Don't ask me to do it though, my math is rusty.

Im surprised to see this in a 250. You usually have these type of issues in a 292, with loose flywheel bolts and balancers.

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.

But, again, what does it weigh, and why?

Panic,
When I built my 321 inch Jimmy I used a 308 Hudson rod, Pontiac pin and a custom JE piston. I saved more than 1.25 pounds per cylinder. I tried to find out how much weight to remove from the crank counterweights to compensate for the reduced weight but was unable to find anything.

Any thoughts/formulas,etc?.

Ron

I believe,what ever you remove from recipricating (SP) weight ,should be the same amount of weight you should remove on the counter weights,,,but that's just a guess.

At least that's what I remembered that was removed from when I ran a lighter or heavier piston,on a single cylinder MC engine.

MBHD

Single cylinder engines like that and the Briggs 5 HP engines are balanced with a bobweight, and probably don't follow the same principles as a "neutral" crank that doesn't use bobweights for balancing.

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

Wow,,that damper took a beating. Looks worse than any of mine that went bad & in much less time.

Are you going to retest the Langdon headers again?
I am thinking the damper was loose on those tests & caused a loss in HP @ the upper RPM range (due to vibration) where you stated they held there own until the upper RPM's.

MBHD

Hmm

Looks like the fluidamper was loose on the crank. To work effectively the need like 0.001-0.002" interference fit.

Comparing the Langdon headers verses the long tube headers dyno data, surprisingly, the big difference was in the low 2500 to 2800 rpm range where the long tube headers delivered 13 to 20 ft.lbs more torque. The 1500 to 2500 rpm torque readings would have been interesting, if they had been available.

Any info on what size and style the side draft carbs were?

Panic:

Inline six counterwieghts are there to reduce crank bending loads and bearing loads. I don't know but suspect this is the reason GM changed form 6 to 12 weight cranks for 250/292 engines. Weights opposite each crankpin should result in less crankshaft bending and lower bearing loads.

As to how much, I expect that is a compromise of cost, manufacturability, crank fatigue durability, and bearing life.

As mentioned above, removing counterweight proportional to reduced recip mass is probably a safe bet.

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

Should use the 40 MM chokes.

My 48's had paper thin chokes, like 46 MM.

It's take a lot of time & lots of jets to get them dialed in,not to mention the correct emultion tubes.

MBHD

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

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

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

Very nice!

If I had know then what I know now, I would have turboed a long time ago.


MBHD

Thats awesome Tom!

I'm stoked to see those kind of numbers from very limited boost. It seriusley makes me consider a hairdryer for my car. Curse that shock tower on the Chevy II front subframe...

Can't wait to hear some more of your opinions from this set of dyno day. Awesome work as always.

-Sam.

Sam, for inner fender well clearance issues, theres always a Paxton or Vortech....I'd like to see what 15-16 psi will do with one of these on a 292 for the street.

Oh I've considered retro-fitting a centifugal blower. The boost would be a joy! However, the initial start up of buying a blower keeps detering me. After I get the car on the road though, then I can start saving pennys for some compressed air..Who knows how many years that'll be, haha.

If that 250 took to making that much hp and torque with only 5 lbs of boost...15-16 with a 292 would be a terror. I like the idea...:D

-Sam.

There are many aftermarket front subframes for the early Novas.
You get way better suspension, brakes etc, then the SPA manifold should work.
You guys that dont want to go that route,just run a stock or SPA exhaust manifold & run the exhaust pipe to the turbo on the passenger side.
Or , run the exhaust pipe to the front on the drivers side in the same location as Bosanovas.
Tlowe, what are the specs on that old turbo? T4 .96 Turbine side?

MBHD

Thanks guy's!
It was alot of fun. That little 250 would hunker down and pull. With 10 psi, bigger carb, intercoller and timing control it would scream.

The turbo is a .94 exhaust housing , it boosts great. Originally came on a Old Accel V8 turbo kit. Imagine that turbo on a 350 SBC. Way too small.

Here are the vids. and more. I have a bunch

http://www.youtube.com/watch?v=PLmUO-fJtH0
http://www.youtube.com/watch?v=9QOdLPA7N68&feature=email

Cool,
your video says it's a .96 housing. No biggie.
What kind of torque did it get up to?

Are all the tests using pump gas,91,93 octane?


MBHD

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