Is that a stock bore or 105/105.5 @ 400 grams ???

Seems kind of heavy still if it's a 105 superlight !

 

that's lighter than either weight I got for the two I weighed, but as I mentioned I do not put much faith in the accuracy of the scale I used, although comparing the two I can conclude if one is lighter than the other.

so what's this "gas ported" that xr650 mentions? I have no knowledge of that, what does it mean? now you got me wondering if this is the right move for me or not.

 

I was just curious on the weights, as my xr engine is compared similar to the ds in bore/stroke and H/P #'s available to be derived from these big-block beasts.
The past 105 pistons I have had made are similar in weight but still think I have boat-anchors,
one was at 423 grams, another at 406 grams, and current one is 383 grams ; and one lighter in the works as we speak for my next build. Just wondering what's out there and what is the latest people are working with on our big-block motors.

As for as the gas-ported piston, I have yet to have one done, and have very little feedback on ones that have.
As I understand, holes are drilled all above the top ring land resulting in a lot more load on the rings, thus having a bit more bang for the buck , but at a price of re-ringing on a regular basis to keep going between rebuilds.
I am open to all discussion to correct me or fill me in as well.
I pull mine down enough as it is, much less don't want to do extra maintenance if the H/p is not worth it ??

 

would the lighter piston effect the stock engine balance in a negative way??

 

I have often wondered the weight diff from stock to aftermarket. I do know that when an engine is designed and built, the rotating assembly is balanced to + or - so many grams. So if you install a piston that is either + or - 10 grams or so I would think that it would need rebalanced. I know for a fact that a car or truck engine needs rebalance after a rebuild if changing size of pistons, type of pistons, rods, and crank etc, if you want it to be right. I remember that one of my engine rebuilds was goin back into my camaro with a 4 speed manual and when they balanced the rotating assembly I decided to have the flywheel balanced as well because the old engine had a bad vibration at higher rpms and when I tore the engine down it was also rebuilt and balanced "not by me-I bought it this way", so I figured the vibration was comming from the flywheel. Anyways the flywheel ended up being 100grams out of balance. So just from experience with the engine building that I have done, it would seem that a change in weight anywhere would affect vibration, and performance. I do know also that vibration will effect valvetrain performance. I asked a shop one time about piston changes and if the weights were diff, "because I know about balancing" and that shop told me that aftermarket pistons are usually designed to be about the same weight. But with what little experience I do have now with building the little single 4 strokes, I know this is untrue. SO I as well am wondering if shops are rebalancing engine rebuilds, especially big bores, and what there thoughts are about balancing. I know a lighter piston wont affect vibration as bad as a heavier piston. SO are we building these incorrect if they are not rebalanced or are these pistons that may be heavier being weight releived or if lighter is the cranks being releived. This is a great question and would like to hear answere's as well. Thanks for you all being considerate in reading these kind of replies. RUSS

 

was that a mis type on the stock piston weight or is the scale that far off? the stock piston weighs about 1.1 lb with rings, clips, and pin. A 2lb piston would be disastrous!!

Also, it does look like you were you weighing rings, clips and pin with it??

222

 

Really? that would be alot more than 3g heavier than the standard non lightened HPR 14:1 back in 2003.... It would really be heavy compared to today's superlight.....In fact, that would be comparable to the 105.5 big bore weight.....I've heard 3g and a few grams several times....without doing a search- who's been putting that info out??

222

 

I did!!

I have the piston you sold me as a 14 or 16 to one. (What ever you were telling people at the time). I weighed it next to the RW's 14 to 1 and there was about 3 grams + or - different.( I didn't read into the tenths) This was on a NOS scale that weight in grams and ounces .

 

222 I said twice in my last two posts to not count on the weight because the stupid scale I used is for big stuff, I was merely mentioning that regardless of accuracy it seemed to indicate a difference in weight between the two I weighed. I should not have posted it at all.

EDIT - OOPS - yes 222 that was a typo, very silly of me, good catch, sorry, I sit here now and see my notes on my desk and realize I typed a 2 instead of a 1!! [img]i/expressions/face-icon-small-confused.gif[/img][img]i/expressions/face-icon-small-blush.gif[/img]
1.225 stock, 1.090 pami 11.2:1, may not be accurate but i.d. of the lighter one holds true.

 

Our sartorious smart scale that we use at work for mixing paint says stock piston, no rings, wristpin or circlips is 413.7 grams. My old 14-1 weighed the same way was 403 grams.