878 ARIAS 12:1 SLIPPER SKIRT PISTONS on offer

[cobbadiggabuddyblooo]

In a couple of weeks time I shall have some 12:1 hi compression ARIAS 878 pistons on offer.
These will be of a slipper skirt design (similar design to the std yamaha trx pistons) .
12:1 compression will still run with no issues on 95/98 Ron fuel and allows you with enough scope to play with slightly higher compression if you choose to alter squish values under 1.25mm (0.048") or use thinner head gaskets.

They will be lighter, and 1.5 points higher compression than the 10.5:1 JE 878 pistons currently the option most have for oversize Pistons for their TRX.
Unlike the JE piston which utilise a full skirt and domed crown, the gains by using the Arias slipper skirt design is not only in the weight savings, but gains in heat and expansion which all sap valuable horsepower from your motor.
Less weight so less heat absorption and expansion so less wear. Also less reciprocating mass so will spin up faster and again less stress on your motor components especially at higher revs compared to the JE pistons.
The overall crown design will also burn more efficiently than the JE pistons so again adding to the gains you will find from the Arias 878.


I am modelling the Arias 878 on the current 12:1 868 pistons I'm running so I've posted the photos of the std Yamaha piston, Ross 868 and the JE 878 piston to give you an idea of what to expect for your money.
I'm offering this first shippment to the forum members before throwing them out to the wolves online.

Send me a PM if interested

THE STD 10.5:1 TRX850 PISTON ON THE LEFT
12:1 868 IN THE CENTRE
AND THE 10.5:1 JE 878 PISTONS ON THE RIGHT

[Killerwhale]

I´m very sure my JE 878 was 11.5:1
Nice one though!

[M.V.]

Oh... my poor wallet.

Are we talking hundreds or thousands?

[cobbadiggabuddyblooo]

Yes I thought they where 11.5:1 too but I questioned TTS around 12 mths ago and noticed on their ebay advertisement they now state 10.5:1..
They use to show a picture of a slipper skirt piston on the ebay site too but they change that after I questioned if they had changed skirt design on the JE 878 when I quizzed them on comp ratio.

I'm still waiting for a final shipping price but I'm pretty sure I can easily match (fingers crossed around $20 cheaper) than the $620 JE pistons price locally here in Australia.

The JE is machined from a blank that just happened to be the size of the 91 mm bore but you will normally find a full skirt piston is used in desiel motors or long stroke low revving motors.
Dome piston also create a slower burning chamber and effect efficiency.

Today just about all automobiles and motorcycle utilise slipper skirts .
Don't get me wrong, the JE 878 is still a well engineered piston to do the job but I am just offering something else more so specifically designed for the task at hand.

http://www.ebay.com.au/itm/331266812994 ... 1438.l2649

[johno440]

Bummer those JE's only 10.5:1, purchased thinking they were 11.5:1. Cobba these ARIA ones, do they come with pins & circlips and are you seeking pre-orders to get a batch made up or will these be available off the shelf for when I have the funds?

[cobbadiggabuddyblooo]

Comes complete with rings, pins and clips.
There's around a 4 week turn around to delivery so when down to the last pair, I'll order once again and try to keep a constant supply on hand.

[misterdimwiddy]

Bummer those JE's only 10.5:1, purchased thinking they were 11.5:1. Cobba these ARIA ones, do they come with pins & circlips and are you seeking pre-orders to get a batch made up or will these be available off the shelf for when I have the funds?

I am almost certain that JE are nominal 11.5:1.

I reshaped the combustion chambers on my head and checked the volumes and was at approx. 11.3:1 before then skimming 15thou off the head which took me to 11.8:1 (measured volumetrically).

[phuk72]

I too though that the JE Pistosn were a nominal 11.5:1 but the real benefit of them is that you CAN use them without balancing the crank.

If the Arias are lighter still, I'd thik very carefully about using without lightening / balancing the crank

[cobbadiggabuddyblooo]

Each of the JE pistons are nearly 40 grams heavier so x that by 2 .
I think I would be doing a little weight saving on each of the JE pistons to save the balancing of the crank.
I'm trying to alleviate this issue and further costs incurred by having something you can just bolt on without having to worry about piston weight.
I'm happy with the Ross pistons coming in within 1 gram of the std OEM Yamaha TRX piston and the balancing done on my crank was to factor in the lighter Carrillo rods and balanced to the flow work done on the head.
Like I said the JE piston is still a quality item, I'm just offering something more suited to the task at hand and as TTS state on the Ebay link and Kedo site 10.5:1.
I can only go by what they state so it comes from the horses mouth.

And piston weights below as I cant find the photos I have of the piston weights.

http://www.trx850.com/phpBB_forum/viewt ... h&start=15

[misterdimwiddy]

Kedo link;

http://www.kedo.com/products/30267.html

Item 30267: BigBore Piston Kit 878ccm, 91.00mm, 11.5:1, 1 Piece (Piston, Rings, Clips and Pin, needed 2x)
Application: TDM850, TRX850

[cobbadiggabuddyblooo]

I'll stand corrected on the Kedo link cheers Dimwitty
So why do TTS state 10.5:1 on their add???
I know why I raised the question a while ago now with 1 stating 11.5 and the other 10.5.
If someone has personal ties with TTS maybe they can find the answer because if they are 11.5 then they are doing them selves a dis service advertising them with a wrong compression ratio on ebay.

[misterdimwiddy]

I agree that it is less than clear from TTS.

Did look into getting Arias pistons made for my TRX soon after I bought it but they would only make 4off as a special order and the cost was pretty high for small numbers.

They do look quality items and the near equal weight cf stock is an appealing feature.

[cobbadiggabuddyblooo]

Pistons arrived today but I'm happy as larry with the finished product.




Here you have the weights of the std TRX piston and wrist pin above.





And here is the weight of the Arias 878 piston and wrist pin.
A saving of 30grams in total on each piston/pin
Compare this to the JE piston, that's 70grams lighter .
I paid a little more to have them lightened in weight so benefits all round.

[cobbadiggabuddyblooo]

Flat top , slipper skirt and, 12:1 as requested and lightened so here is the end result..

[dandywarhol]

They certainly look the part but I'd be a little bit worried about the extra 30 grammes at 9,000 rpm I don't suppose you could use the stock gudgeon pins?