Your absolutely right Mr. Larrowe, the more counterweights the better. The fully counterweighted are more desireable for that fact. The bad thing is that everything we do to an engine normally for performance gains(more RPM, more compression,etc...)in an inline, worsens the harmonic issues. So we just have to deal with them the best we can.
Many people confuse harmonics and engine balancing, as they are two totally seperate things. Balancing you can fix, harmonics not so much.
Ok, well i have the fully counterweighted cast crank i think so thats good. And definately invest in a top of the line harmonic balancer so that should help. In leo's book it says something about using aluminium rods to dampen the vibration/force put on the crank journals, also using rod length of 7.250 in aluminum can help aswell? Is that what your talking about when you mention harmonics?
I'm bolting together a 292 for a tow rig right now and I've found a lot of useful information and help at the Inliner International forum., http://www.inliners.org/
Harmonics are vibrations created by the crankshaft twisting and flexing out of its natural shape. At low engine speeds,the crank is fine and undistorted. But as the RPM and/or load on the crank increases, it will bend, flex and twist along its axis' causing it to shake your teeth out at certain RPM points known as Orders. All crankshafts have a certain number of First Order, Second Order, etc. of harmonics. The design of the crankshaft has a lot to do with how it acts in terms of this. Long strokes and poor bearing overlap on long crankshafts make for a flimsy combination, especially if they only have 4 main journals like a GMC Jimmy engine. While shorter length cranks with shorter strokes and better bearing journal overlap tend to be more ridgid and not as prone to the effects of harmonics as bad, even though they still have them. Overall, it is what it is, people have raced these engines for close to 60 years and they had to deal with those issues then as well, you can only try to avoid operating the engine at those points where the harmonics seem to appear, and either stay just below those RPM points or go slightly higher, as a lot of Bonneville guys do where they have a sustained throttle type of racing. And yes, aluminum rods can help absorb some of the vibrations, but it doesn't eliminate them or make them stop.
CNC-Dude aren't you using a 292 in your Camaro?? Which crank, rod, damper works best for you. I've heard the cast cranks outlast the forged cranks and shake a lot less for the strip. Didn't Jim Headrick and Cotton Perry also run a 292 in their H/MP car?? What combo did they run?
Gary, im actually building several different engine combos for that to fit the multiple classes I am going to race in, but yes im doing a 292 as well. The fully counterweighted 250 and 292 cranks are what i'll use in my engines. As for rods, I also am going to use aluminum rods in both the 250 and 292 engines, and am going to duplicate the same procedures for engine prep as was done in all of Cotton's engines, even down to the lightening of the cranks. Cotton's engines were all 292's, and used the cast TF casting fully counterweighted cranks(lightened and knife-edged). Back in the time of the H/MP days, balancer technology is not what it is today, and Jim always used a solid aluminum hub on all of the 6's he did, not only for Cotton's engines, but all of the ones he did for other top inline racers. To make a comparison, Bruce Sizemore, who raced the Ford inline 6's, used a steel production Ford crank and a Boss Cleveland style balancer....his cranks lasted only about 12-15 1/4 mile passes at 9000 RPM. Cotton used a cast 292 truck crank with an aluminum hub, made about 100 more HP than Bruce did and left the starting line between 10,500 and 11,200 RPM and his cranks lasted 20 1/4 mile passes. Did the aluminum hub help or not? Jim felt that for the time, balancer technology was just not as developed for these engines for the HP level they were at. This is by far an extreme case of how these engines have been used and abused, but made awesome HP for the time period. After Cotton moved on up into Comp Eliminator, he used the same engine from the H/MP car, and only left the line at 5500-6000 RPM(the difference being going from a 3300 lb .Doorslammer to a 1700 lb. Rear Engine Dragster) and the cranks lived forever it seemed. The 250's we did for other Comp guys never had any crank breaking issues like the 292 has, and they even used aluminum hubs on their enignes, and some even used the ATI dampers with no problems either.
So i got a email from Venoila today saying the pistons are $81.30 each (piston alone). Just waiting on the spec sheet from GRP. My auto teacher is extremmely excited for this engine build.
Get ahold of that guy, Bruce? From St. Louis. The guy who had the 37 chevy coupe at the HAMB drags. He is a member here. Lippy
I will start looking for him then, should test my hide and seek abilities. I was probably going to run the stock SBC i think something like 1.94 and 1.60. Can i go bigger without the risk of cracking the chamber?
Where these engines really seem to shine is with the addition of a turbo, http://www.youtube.com/watch?v=gex-uUio8Dc&feature=related
haha yeah that is an insane pickup (ute here in australia) I plan on adding a turbo later on when I finish my automotive course, my main idea was a setup like the 2JZ's, teh sequential turbo deal. But for my license over here you can only drive 6 cylinders and under, no turbo or supercharger. But this build shall provide enough kick to kill some serious competition. Hopefully.
Hulk, your combo is going to be a real strong runner and you will be very satisfied. You can easily go to 2.02" and larger, but 1.94" is plenty for what you are doing. There are several guys on Inliners that are making over 800 HP with these 292 engines with a turbo and even nitrous, and a couple are over 700 HP with 250's, so they have as much potential as any other engine to make some big HP numbers, and most of the time in a much lighter engine package.
I havent driven anything over 300hp before so this shall be a treat Well thank you all very much for your info and suggestions (especially CNC-dude) Greatly appreciated! You shall be updated with photos of machining when I get started in around March, till then I will be doing ALOT of measuring, quoting and thinking!
A little bit of modifying and it does a 202 fits pretty good so Im guessing a 292 will just fit. If it doesnt I can always put it in my WB ute, which has the biggest engine bay I have seen. Fits a big block with ease.
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