Interesting insights into Crank and Cam Harmonics in I6's

[1bolt]

In a thread called:
Inherant critical crankshaft harmonics
http://speedtalk.com/forum/viewtopic.php?t=16279

If you didn't already know about speedtalk, now you do, it's a forum filled with proffesional "big name" race engine builders Guys who've won the Popular Hot Rodding Engine Masters challenge frequent it. It's also where I found out about Engine Analyzer Pro.

[Flash]

Vary interesting, helps me wrap my head around this issue better!

Sounds like the best first step is the best harmonic balancer you can get...or afford........if you eng is going to run long times in that area.

Changing rotating weight to move the harmonic was interesting as well

[George Dickel]

That hurt my head but it is great info. I feel like I stayed at a Holiday Inn Express last night! Thanks also for the site, I wasn't aware of it yet.
GD

[Plechtan]

Great post, This better explains why the 3" stroke statium motor that Hesco use to build did not have a harmonic. Actually it probably does have a harmonic, but it is reduced because of the fully counterweighted billet crank and the short throw. the engine also has smaller pistons and makes it's power up at 7,000 rpm, so torque loads are lower.

So for our Jeep motors, it looks like the best choice is get the most displacment you can and keep it below 5,400 rpm. So a 4" bore and 4" stroke motor making about 325 hp would be about the limit for a street/trail rig.

[SIXPAK]

After 36 years of collective racing between my father and I this harmonic seems to be the only common factor to my main cap failures. I switched to a 4cw at the beginning of the '08 season and at the beginning of the '09 season I have three broken main caps with no evident or definitive cause. My 12cw crank I removed to install the 4cw is going back in a different block that is being bored as we speak.

[gradon]

What rpms did that happen @?

[SIXPAK]

I really have no idea when it broke. Jeep was running fine and running consistant 11.20's. Best was 11.16. Lost my last round and loaded her up in the trailer. Some time that day oil pressure dropped a bit but all else seemed fine. Three days later started it up and pulled it in the garage to inspect. Cold normal pressure was 60 before and pulling in the garage I only had 40psi. Operating range of the motor is 5000-7000.

[lafrad]

looks like you could use some custom billet main caps, keep the 4 Cw crank and get a BIG harmonic balancer.

Should weigh less overall than the 12 CW, rev almost as fast, and work the season for ya

[1bolt]

The gist of it is that the 12cw crank will probably move the harmonic down below 5000 RPM's... if Sixpak is launching at 5000 RPM's (he said operating range is 5000-7000) then the 12cw puts the harmonic where he'll never be bothered by it (well not under load anyway), he'll rev briefly through it with no load on the engine

On the other hand if you're building a mud bogger or something and you plan to peg the stock Rev limiter around 4700 RPM's (or whatever it is) you do not want that 12cw you want the 4cw because it's drastically lighter weight probably puts the Harmonic somewhere closer to 6000 RPM's where you'll never get near it.

A good ATI dampner is on my future ebay score list.

Sixpak do you use the factory crank girdle? What main caps are those from? Those aren't the solid ones are they?

[SIXPAK]

Sixpak do you use the factory crank girdle? What main caps are those from? Those aren't the solid ones are they?

I was using the factory main girdle at the time. The caps are the factory 4.0 and they are not solid. New block MAY get the early solid 258 caps, we'll see tonight. Main studs will be in this time without the main girdle. I may over the winter make my own girdle from billet steel. Over the years I've raced these motors I've never used the girdle and have had no issues. The girdle was in the motor this past time just because I had one laying around.
My balancer is 7 1/4" Fliuidampner. The 12 cw carnk I removed to install the 4 cw had eight years of racing on it and it's going back in. I have no problem improving the motor or trying new ideas. This is the whole reason why I put in the 4cw. BUT, if isn't durable to the point were I can race for several years it's not for me. Frankly, I can't afford issues like the one I experienced on any regular basis. I spent a good deal removing 85 grams off EACH valvetrain assembly and that was money well spent and will serve me well.

[1bolt]

Yeah probably considerably more than a lighter crank will do for you... From what I've read even some of the top ranks in pro stock are debating the actual benefit on the track of extreme lightening of the rotating assembly. There are pros and cons, but the increase in "accelerated horse power" (to use David Vizard's term) from lighter cranks that you can observe in a Dyno test, apparently has debatable effects on the track... I think the ultra light rods and pistons have a much more observable effect.

Not to stray off topic but How much increase in RPM did you see from 85g removed and how did you remove it?

[crustodd]

Hey Sixpac,
Do ya' have pics or vids of your Jeep? I'd love to see some more info on it. I'm not drag racing mine, per say, but I've built it with that all around kind of all-around-performance in mind. I just got my Coolingmist water injection today!!! 2/3 through my 9" rear install Patience, patience I went with the 4wt crank for ease of installation, availability at the time, quick "spool up", and the snout being right for the pulleys. So far, so good.

T~

[SIXPAK]

Not to stray off topic but How much increase in RPM did you see from 85g removed and how did you remove it?

Ceramic lifters, Titanium retainers that I had to modify on a lathe, and going from a 1.460 OD dual spring to a 1.250 OD single spring with damper. The smaller 1.250 spring has more seat and open pressure which of corse has a higher spring rate,205 seat and 505 open. Not sure about RPM increase on the valvetrain weight reduction but we did pick up .1 in the 1/4 mile. Results in the sand are yet to be seen since the main caps gave up before I got back to the sand from playing on the asphalt.

[SIXPAK]

Hey Sixpac,
Do ya' have pics or vids of your Jeep? I'd love to see some more info on it. I'm not drag racing mine, per say, but I've built it with that all around kind of all-around-performance in mind. I just got my Coolingmist water injection today!!! 2/3 through my 9" rear install Patience, patience I went with the 4wt crank for ease of installation, availability at the time, quick "spool up", and the snout being right for the pulleys. So far, so good.

T~

1st run on this vid
http://vids.myspace.com/index.cfm?fusea ... D=49717898
at :48 seconds in this video
http://vids.myspace.com/index.cfm?fusea ... D=50461632
280 ci, ported head, stock valves, fabbed intake, under .500 lift cam

[George Dickel]

Catchy tailgate! Not too many others gave us the same view on that vid. Sweet motor, sounds freakin great