heres l little thing to also think about the manulal slants which i am blessed with, cant be shifted over 6k unless you dont mind your leg in about as many peices as the clutch would blow in to

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1973 plymouth duster 225 slant six .30 over, erson 270 cam, 9.5 to 1 compression, big valves, headers, and a holley 4 bbl
http://cardomain.com/ride/3135091

hey that thing got a hemi? naw its just a slant six

I blew up my first "warmed-up" 225 at 5,500 RPMs.Stock pistons and rods,ARP rod bolts.Wasting the engine was bad enough,but it sprayed oil on the windshield,and the red-hot headers.I couldn't see where I was going at 80MPH,and I had a campfire going on under the hood as a bonus.

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V8?? We don't need no stink'n V8!!

Whats the safe limit on reused factory rod and main bolts? What about on a factory 9" flywheel?


TopHat

That really depends on many factors. Assuming everything has not been abused and has been checked, 5000-5500 would be my call.

Lou

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Home of Slant6-powered fun machines since 1988

Balancing is KEY! Something I wished I would've invested in when I built my last engine. I would invest in that over rod bolts and such, since you have less parts fighting each other.

Actually balancing makes no difference in the stresses borne by the rods, bolts, pistons, etc. The only way to reduce the stresses on the reciprocating parts it to keep the engine speed down or remove mass.

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Joshua

I agree and diagree. I start to see what your saying and maybe I'm not understanding. The balancing is essentially taking the parts and holding them at a tighter tolerance. So when moving pieces are to work together at higher speeds the tighter the tolerances need to be... concluding that if you have sloppy tolerances the pieces will begin to sporatically move in different directions? Am I off base here? I just know that the balancing we did on the 302's really brought them to life in spinning them to higher rpms.
Going back to higher rpms my uncle always taught me that you need cam and intake. The cam is pretty easily dealt with, but the cross section on the head and therefore the intake seem like they would start to leave the slant winded in higher rpms. Would this have any effect on the higher's on a N/A 170 that would want to spin higher?

My statement did leave out something. A shorter stroke means the piston, rod, rings, etc are moving a shorter distance for a given engine speed so the acceleration is lower and the stresses are lower. This is the primary reason little engines typically will spin faster than a larger engine. I say typically because an engine is a system and it's entirely possible for other parts of the system to limit the speed of a small engine or permit a somewhat larger engine to spin faster. Still, you'll never see even a radically prepared 500 CI big block spin faster than a very pedestrian 50cc engine.

Balancing an engine or adding balance shafts does not reduce the stresses inside the engine. You simple confine the stresses inside the engine instead of transmitting them to the chassis.

A 170 will spin much faster than an equally prepared 225 because the stroke is only 76% as long and the displacement is only 76% of the 225 so the restrictive carburetor, manifolding, cylinder head, etc is suddenly much less restrictive. I think the 170 is also smoother because the reciprocating stresses are lower which flexes the crank less (crank is more rigid too) so the whole unit vibrates less. Did you know that in many years if you bought a Senior Series Packard you got a 9 main bearing engine instead of 5 because it made the engine smoother due to less crank flex and better balance?

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Joshua

I guess that is why my Cox .049 cu in will spin up 15,000 or more rpm's, very short stroke compared to a 225.

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Grandpa's 1974 Dart Custom 4 door 225 auto, Aluminum Radiator, 1920 Holley.

Not true. NHRA 500 ci Pro Stock motors regularly spin 10 grand, and you rarely see an engine failure.

The 632 Donovan we did at the race car shop turned 8000+.

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Official Cookie and Mater Tormentor.

I say ballance anything you would like to see live with RPM's....I have built Big Block Mopars that went 8000 RPM.....and let me say, it wound up fast!! But thats me....I will be balancing this 225 I am building, will be spinning it up in the R's.
Andrew/Kidd

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Wife's: 64 Valiant
My: 70 Road Runner, 67 Barracuda, AND the 62 Valiant drag car!!

It's true they spin Pro Stock engines very fast, but how much do they cost and how long between bearing changes? Valve spring changes? Crank and connecting rod changes? There is an enormous cost in premium parts and maintenance to keep Pro Stock engines from blowing up. The life of many components in a Pro Stock engine is measured in minutes.

You can spin smaller engines faster, for much longer periods of time. A modern sport bike engine spins faster and lasts many times longer.

I'm not saying balancing doesn't have its place or that it isn't of value, but balancing your connecting rods to 1/2 a gram difference between heaviest and lightest instead of 2 grams may or may not be felt in the car. Going to such lengths and expense doesn't help the connecting rod at all. What does make a difference in the stressful life of a connecting rod is a lighter piston and rings, shorter stroke, or slower speed.

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Joshua

I understand what Josh was trying to say is that it doesn't reduce the stress or forces, but will keep them going in the direction they are meant to go. I think the common term is that we assume that we reduce stress force when in reality we simply reduced the stress in a certain location.

so i guess i can grind the balance weights off my crank to reduce the rotating mass and not worry about balancing? why doesnt everybody do that?

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I've been calling it as i see it for my entire life and that's not about to change. Take it or leave it.

Step got me on semantics. I wasn't explicit enough. Having counter weights on the crank does help the crank and block considerably.

Inline cranks are actually neutrally balanced, but have counter weights to confine the stresses. From a crank flex point of view you want the counter weights equal in size and on either side of each rod journal like this:



The counter weighted crank still doesn't help the poor connecting rods though which was the thrust of my argument.

Getting back on target... To raise the RPM limit of an engine's rotating assembly without resorting to destroking one has to loose reciprocating weight or use stronger parts.

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Joshua