[MeltMan]

*** Removed by user at Jul 21 2009 2:45PM (Server Time) ***

Ignore my rambling

 

[cheezthis]

Bottom line here, if you recall Tuan's old stuff too, both cranks in proper form will handle that rpm range perfectly fine.

 

[RacerZook]

Yeah it seems the GSR crank is the way to go. I'm all about less rotating mass. Anyone know an for sure number on the weight of each? only thing I've found on other web sites was that the GSR crank is 4lbs lighter than the ITR. But as far as I'm concerned, that's uncomfirmed.

 

[madrrio]

4lbs seems about right, i had both once upon a time, i have sold the itr since so i couldnt go out an messure it for you.

i have read howver that the rods, though stronger, were the same weight.

 

[SniperX]

if someone has both, and you have an electric salce to weight yourself wiht
take your weight, step off, grab one con rod and step back on, do amth thnen repeat for the others.

i did this wiht a rim and it was off by .1 lb.

 

[RacerZook]

Not true. The entire thing has to be balanced. Why would they add weight to one side of the rotating assembly without it COUNTER WEIGHTING the other side. I have a set of GSR and ITR pistons and they are in fact heavier. Different casting, higher dome, different material on the skirts.

This makes sense also. If you think of the whole assembley as a wheel, if the wheel is unbalanced, you get vibration, a "heavy spot" that will always move to the bottom. I wonder if a perfectly balanced assembly would yield better results than less weight?

 

[dyingwish]

Chris: In terms of durability, a fully balanced rotating assembly will in fact outlast anything else. It would have a marginal effect on power though if it was heavier overall. Marginal being the key word, balance is key to having a durable motor, especially if high revs are desirable. Honda motors are known for high frequency vibrations, so minimizing that is nothing but helpful.

As for the weight difference, IIRC the GSR crank is 3.45lbs lighter than the ITR crank. Pistons are roughly 80 grams apieces heavier in the ITR, from memory. Honda balances all thier cranks to the gram, machine shops will further balance to the tenth, or hundredth of a gram provided they have the mean of measuring such small weights. In order to "blueprint" an engine the entire rotating assembly must be balanced fully assembled.

 

[rocketsauce]

After reading all of this, I'm not seeing what the benefit of having a heavier crankshaft would be for use with heavier pistons and possibly rods. once the fists, wrists, and rods are all bolted to their respective spots on the crank, shouldn't "balanced" just be "balanced?"

I would guess that the heavier rotating mass was a calculated reduction in the throttle response so revs were easier to handle for the average driver during rev matching etc.

I mean 3.45 lbs is pretty dramatic! one pound being about 450 grams, the extra weight from the pistons would only add about three quarters of a pound.

While I would also guess that the ITR cranks are balanced to a tighter spec, I would imagine the GSR cranks also have a very quality balance.

 

[RacerZook]

Found this picture:
ITR on the left, GSR on the right.

 

[dyingwish]

After reading all of this, I'm not seeing what the benefit of having a heavier crankshaft would be for use with heavier pistons and possibly rods. once the fists, wrists, and rods are all bolted to their respective spots on the crank, shouldn't "balanced" just be "balanced?"


I mean 3.45 lbs is pretty dramatic! one pound being about 450 grams, the extra weight from the pistons would only add about three quarters of a pound.

Heavier means a bit more inertia so when the clutch is in the revs don't fall so quickly.

As said, take the weights with a grain of salt, The actual numbers are simply hearsay and innerweb fiction. I never had all three pieces from both motors in the same place to determine and actual weight difference. I agree that the piston weight alone (since the wrist pins are the same) doesn't account for the the *supposed* extra weight of the ITR crank. There is no way the rods are almost a pound each heavier..... We need to get real numbers for future reference.

 

[rocketsauce]

The revs wouldn't fall or rise as quickly due to inertia, thus the decreased throttle response. Well Zook, good luck with the balance, that's a sweet find of a photo, and you'll have to post up how it works out.

I'm especially interested in the cost of balancing.

 

[dyingwish]

My local machine shop / engine builder charged me 75 for a quick journal polish and balance to the hundredth of a gram on just the crank, FWIW.

 

[SniperX]

now that ive seen pics of the 2 cranks side by side the extra weight makes more sense for the ITR crank, if the pistons are 80g heavier.

 

[00g3teg]

also keep in mind the ITR uses a lighter flywheel to compensate for the heavier crank

 

[snm95ls]

Stumbled across this thread via google looking for ITR crankshaft pics, and I apologize for bumping such an old thread.

I have to say that there seem to be a lot of misconceptions in this thread.

The added mass works to quell high order harmonics at high RPM, and has very little to do with the added mass of the pistons. With the ITR, it was all about adding stability to the entire engine at higher RPM.

I doubt there would be much difference in bob-weights between an ITR crankshaft and a GSR crankshaft. Also a single plane inline 4 crankshaft is inherently balanced by design, and as long as the masses of each component are equal between the 4 assemblies, then it will be as dynamically balanced as it can be. You cannot balance out the second order vibrations on an inline 4 engine within the reciprocating assembly. This is why balance shafts have been used in many inline 4 cylinder engines.

I could be way off base here, but this is my semi educated view on the matter.