Upper RPM harmonic problems for 170 and 200?

[my way]

Am getting into a serious inline build plan and have heard of upper?? rpm destructive harmonic band for in line 6 cyl. What RPM range are we talking for the 170 and 200 engines? Does this go away above a certain rpm? The classic inline high performance balancer is rated for 6500. What happens above that? What is that 170 XK Falcon turning? Shorter stroke 170 have less problems?
Any info or experience will be appreciated-THANKS
My way

 

[CNC-Dude]

Try to limit your RPM to the range that it makes power in, above that, its only making noise. Several things affect the harmonic frequencies at the points they occur, and most cranks have more than one or two RPM ranges that they occur in. Stroke, RPM, crank length and # of main journals that support the crank, and power output. There are formulas to help determine where they occur in a stock engine, but once you begin altering the power output, they can change based on how many of the factors above get changed ie, RPM, power output, etc....

 

[my way]

One more time. As this is not for daily transportation it will go in either a 71 or 72 Maverick to be drag raced to see how far we can go. Have been window shopping at classic inlines and reading every tech and build article old and new I can find. At this point I am under the impression that 6 to 6500 has been done. If there is a band that one can get through and survive I'd like to know. Gonna find out one way or another so any experience will be helpful and appreciated. Don't really want a metal oil and water mix, but if that is what it takes so be it.
Started racing 6's against flatheads in the 60's( think we were in the 5+ area by the gearing-no tach) and participated in the claimer deal of the 80's, so have experienced success and failure before. Just that I don't have as much time to waste as I used to. So any help will be appreciated . Thanks in advance.
My way

 

[xctasy]

There are no major points in the Ford 200, either four bearing or seven. People race the 170 to 280 hp, and 7500 rpm without failure.

The Argentina Ford racers run seven bearing short stroke 183 cube engines to 9500 rpm and 380 hp.

Mathematically, there are small vibration periods in the working rpm range, but in practice, the engine isn't afflicted due to its large 2.124" crank pins and low reciprocating weight. The 10 counterweight crank isn't wonderful, but with a better than stock 1993 EF Falcon balancer, you wont have any issues.

In Australia, our same bore spacing, and smaller crank journal. larger main bearing 3.625" bore, 3.25" stroke, 5.25" rod and 1.61:1 rod ratio 202 General Motors Holden engines had two torsional vibration periods, one at 4500 and another at 5300, and with a standard vibration dampener, it shock everything loose.


The early solution for the early 179 and 186 engines with 3" stroke and the short stroke engines an 1.75:1 rod to stroke ratio was to go for the 13 pound heavier 149 steel crankshaft over the later nodular iron one. When the engine got stroked to 202 cubes, it got a more pronounced vibration, much more noticeable, at the same rpm points. It was then that Holden went to a fully counter weighted 12 counterweight nodular iron crank, which was 13 pound heavier, and pushed the torsional vibration period up above 7500 rpm, where most racers wouldn't run into it. Adding an inserted down to Holden 202 size 1.25" spigot 350 Chevy balancer was the early solution before the advent of the 12 counterweight crank.


On the big 250, the US engineers just went to a small block Ford/Big Six style 1.375 spigot balancer. In Australian 200/250 9.38"tall deck and 9.22" medium deck 3.2/3.9/4.0 OHC sixes, they stayed with the 1.245" spigot, and played around with balancer, the counterweights went to 12 for some models, then they downgraded back to a 10 counterweight crank, but with bigger main bearing and longer rods. So Ford Oz was working the cost benefit of engineering changes.

I'd personally not even bother, but an EF Falcon balancer should help pull out any vibrations from the crank.

 

[my way]

Thank you
This is very helpful as the 7500 number was tempting me with the hope of something around 1.5 HP per C.I. on carbs and this sounds attainable with the right parts---at least for a little while.
You mention an Argentine 183 C.I. 7 main Engine. A seven main short stroke 2.8 X 3.71 motor to compete or at least participate in the 3 L category is a lurking fantasy :roll: Is a crank like this that would go in our 200 or 250 block available down there?
A lot of stretchy thinking, but for the time being have a 7 main 200 on the engine stand, and a C8DE 170 short block out in the back shed and two old mavericks -71 and 72 that I hope to get enough time to experiment with.
Thanks again-Any more info would be great!!
My way

 

[powerband]

... $ .02 more:

... consensus is a well built bottom end on US 200/250 7 main will keep together with breathing being power limiting factor.. Generally the 4 main 170's out for race build vs 7 main 200/250's, if you want a high RPM screamer - go heavily modified 200 there's lots of help available ... , if you want to build engine / drivetrain geared toward torquey' US 250 {Stroked 200}, longer stroke 250 may limit RPM somewhat and 'don't think any performance rated balancers availble any longer for US 250.

have fun

it's an advantage building a six specifically for Drag Racing not dual purpose street/strip compromises. Lately set the 250/T5 tach shift light @ 5K- but easily runs 5500-6K if I'm excited. 8)