Ross Racing Piston - Group Buy!

[Mark Halligan]

Doug,

I've got five spare but they are in good nick so I dont really want to butcher them, if you dont mind it would be useful to know how thick the crown is.

Cheers,

Mark.

[Pisobiker]

I see you don't pay attention to my posts, guys......
Blame on you

Just kidding. I took some mesurement some time ago without cutting the piston in a half, so might be interesting to see if I did some mistake when measuring....

http://www.s2forum.com/forum/showthread.php?s=&threadid=1517

Marco

[Mark Halligan]

Thanks Marco

Mark.

[Mark Halligan]

Does anyone know how much can safely be taken off of the crown of the piston in the bowl/dish area?

Mark.

[Doug_RS2]

Marcos drawings look right - I fancied chopping one up anyway.

I can't find my calipers to take accurate measurements (it's a pain having half my tools at another garage) but 7 mm in the centre looks correct - measured on a wooden ruler

I think we need to flatten the top surface AND take it, very slightly, below the dish point to get 8.7:1. Marco did some calculations elsewhere I think

[Pisobiker]

Should be ~8mm Doug (min dome thickness, written on bottom of drawing).
7mm should instead be distance from piston crown to first ring groove.

[Doug_RS2]

It's definitely less than 8mm, maybe more than 7.5mm but a wooden ruler is not a good way to measure

[timucin]

ok bros ; pls decide something and tell me how much do i have to cut?

[Pisobiker]

Originally posted by Doug_RS2

........I think we need to flatten the top surface AND take it, very slightly, below the dish point to get 8.7:1. Marco did some calculations elsewhere I think........

I made some rough calculations on how much to take off the piston crown to lower CR but cannot remember where it was posted.
Let's try to figure out indicatively.
Some approssimation must although be made because of the 0.7mm protruding area between the intake valve pockets and the valve pockets themselves, unless some empirical measuring method is used (burette and fluid).

1) Piston total area @ 81.5 mm bore = 52.14 cm^2;
2) OEM dish area = 27.33 (Ø 59 mm);
3) OEM protruding squish volume = ~ 0.4 cc

This means taking piston top flat where OEM dish is, will reduce volume ~ 3.36 cc.

Going to the 4.2 cc will need cutting away another ~ 0.16 mm from top of piston so if OEM min thickness is 8mm it will be reduced to 7.84 mm ....... Which doesn't look so scary to me.

I would rather be carefull about lowering piston hight related to block deck. This way you're actually increasing squish hight at TDC of ~1.36 mm which could not be the right way to go. You lower CR to raise knock limits and use more boost, but reducing squish effect could actually even make things worse.

Before going this route I would suggest you get some feedback from credible people who has experimented this, or just think on going the originary route.
I mean you're putting a lot of money and effort on your project, so two or three weeks and a hundred of bucks (but are you sure OEM pistons are cheaper?) shouldn't be your primary concern.


Just my thoughts



Marco

[timucin]

well as i said at the beginning thats why i wanted to buy anew set of pistons. but waiting time is too long.otherwise they are worth the value in my opinion.i dont know the term in english but difference between top of block and piston top aint good.

[Doug_RS2]

I am still undecided.

What gaps are the wiseco and JE pistons required to run at cold? This was the main reason for staying with standard pistons - no piston slap at cold.

[timucin]

do you mean piston to wall clearance?

[Doug_RS2]

Yes timucin - the Ross pistons require a very large gap due to the amount of expansion at higher temperatures. So it is critical you know what temeratures they will run at - I presume (maybe wrongly) this will be different if you decide to use NOS?

[Pisobiker]

Doug,

High perf. pistons manufacturers usually ask how much power / boost and which use the engine will be put at, providing consequently the right product with the right clearance specs (you actually tell them your precise final bore size, and they do the rest).
If your concern is piston's behaviour at warm up, I think you can be pretty safe with both Wiseco or JE which really have a great consideration worldwide with high performance applications not only for track or competition vehicles.
Of course you might need to be a little carefull not to blast full load when warming the engine up (but it should be a good habit on stock engines as well).
And I think you should of course agree to keep some little drawbacks in exchange with having a 200+ hp per liter engine with over 600 hp potential on it.

Anyway I would like to point out I'm just having the same problems and doubts as you do. I'm trying to get the best I can out of my engine and belive me, I really don't have money to waste.
Sharing infos and talking to each other hopefully will allow each of us to make the right choices......or the wrong ones, but with consciousness


Marco

[Doug_RS2]

I was just wondering about timucins situation though - what happens if you are running crap octane fuel most of the time but also occasionally run NOS? Would the occasional times he runs NOS cause problems with pistons being cooler and maybe larger gaps?

I have no experience of this and just learning as I go along - maybe there is nothing to worry about.

The conversations we have on here help though.

I am waiting on a response from JE.

Out of interest Marco - are you using gapless rings?