Probe Forged Pistons: You want 'em? GB!

[Merlyn]

I would be so in except as I imagine many people are...

I am noob to engine building...

I don't mind dropping $300 for something but what I think we should at least have a post about is just what exactly is going to be needed to get these working...

I have a GTE and I want something to replace my used ones (hell I would even go stock spec) but if I have to spend $1000 at a machine shop to bore and stroke my motor I dont have the money for that

I guess what I am getting at, and yes their is a search feature, but to enhance this GB to all the members... I don't care what # you go with as you all know more then I, but at least keep the noobs in on the loop as to what has to happen for these to work. I can almost guarantee you you stop using tech talk you will sell these like water... I just don't want to commit without an idea of what is required (more money) to get these in, also what each persons idea of "specs" means in terms of power, boost, longevity ect. Simply the more people that jump in the less we ALL have to pay, so why not make it easier for morons like myself to get stoked about this and jump on the band wagon...

my 2 cents...

to lazy to search since this is something that needs to be decided asap.

I am not trying to seem lazy for not researching... but simply this is a GB... the more people we have the more we all benefit... I work in the service industry selling to customers who are dumb like I am to engines, the more you use tech talk the less sales you have... I buy a set, you save $2 or so... you take 5 min to explain in english what these numbers mean in terms of power, cost to install, ect .... you will save yourself some money

 

[Doward]

I think the JEs get that light weight from sacrificing the skirts, though... we'd be looking more into a ~320ish weight (in grams) in order to keep a long skirt.

 

[Doward]

These will be forged pistons, designed to work with stock rods.

If those that know more than I think the increased friction from the stock rings (how about a 1.5/1.5/3.0 pack?) is worth the increased longetivity, I have no problems going that way.

Long skirts are a must, then?

 

[CRE]

Any chance of a set with a stock N/A compression? I'm assuming not.

 

[TobyCat]

Well so far from what I gather:

Longer skirt = increased longevity/resilience but they will weigh more

Ring size = the thicker the rings are, they nicer they are to you cylinder walls but the higher friction they will cause. Friction means higher heat and energy loss. Too thin of a ring and you wear away the cylinder walls but reduce friction.

Diameter - 17 over, 20 over etc. This means that the piston is 20 thousands of an inch larger than stock pistons. If you plan on running over sized pistons, then you will definitely need to get your block bored out to match. The only reason for boring out cylinders is if you have wear ridges or scrapes on the cylinder wall. How much you bore depends on how deep they are. There is a limit to how much you can bore though, and I *think* most manufacturers make a 40 over piston but stop there. As I've learned from one of IJ's posts, no block is the same and some can be bored more than others (correct me if I'm wrong Ian!)

Compression - stock pistons are 8.4:1 for turbo cars and 9.1:1 on NA cars (ref wikipedia for those #s). The higher compression the more power, but at a cost. A forced induction car (aka turbo/super charger) will see high compression as the turbo spools up...to much compression and *pop* goes your head. Too low and you're a slug.

Piston head - Reading Probe's website it looks like they come in a flat top (with valve tapering) and concave topped (semi spherical tops). I really couldn't tell you why to choose one way or the other. My *guess* here from a thermodynamics standpoint is that a cupped piston will aid in the flow from intake/fuel -> combustion -> exhaust/exhaust . But...anybody know for sure?

This is the info I've gathered from reading here and wikipedia. If any of it is incorrect please tell me and I'll edit this post accordingly!

-Chris

 

[Halsupramk3]

i dont think having a CR of 9:1 on these pistons would be a good idea. If you have to shave a bit off the block and head that would make the CR even higher. A CR of 8:6 or 8:7 or so would allow us to shave some off the deck and still keep it around or below 9:1. yes you can use a thicker MHG but the thinner the better on HG. but after you cut the block/head the only way to change CR is to custom piston or HG size.

i have 9:1 on my ross pistons and about 45 tho clearence with a 2mm mhg. my pistons are coated top and sides and the engine rattles just about all the time until i make repeatative boost pulls. then it will not rattle for a while. i should have had a little closer clearance. 9:1 off boost is really nice tho.

i assume these will be non interference pistons.

 

[bustedknuckle]

1) Doward
2) S turbo 87
3) zachm611
4) TobyCat
5) mark3monster
6)MassSupra89
7)Born2drv
8)90T04
9)woodytsi
10)bmoss85
11)LilMissMkIII - pending shipping price to Aus
12)screaminglemon
13)bustedknuckle
I'm in for a standard bore.

 

[JZ_killa_t68]

What about doing custom cranks and rods as well, what would those run, and what aboot an option for 2j/1j pistons/cranks/rods-or even a complete kit?

also I see they've got a TBA on 2j pistons, see if we can get a gb going on those too.

 

[Mrbaboon]

i dont think having a CR of 9:1 on these pistons would be a good idea. If you have to shave a bit off the block and head that would make the CR even higher. A CR of 8:6 or 8:7 or so would allow us to shave some off the deck and still keep it around or below 9:1. yes you can use a thicker MHG but the thinner the better on HG. but after you cut the block/head the only way to change CR is to custom piston or HG size.

i have 9:1 on my ross pistons and about 45 tho clearence with a 2mm mhg. my pistons are coated top and sides and the engine rattles just about all the time until i make repeatative boost pulls. then it will not rattle for a while. i should have had a little closer clearance. 9:1 off boost is really nice tho.

i assume these will be non interference pistons.

I am running 9:1 on my Wiseco's. No slap on cold startup, no problems boosting (you'll have to run higher than the stock turbo can allow to have to worry), and a 1.8mm HG.

If these pistons are close to the Wiseco spec for skirt length and dish volume then they should be niceeeeee.


Tobycat: Dish/Flat top = change in combustion chamber volume = change in compression.

 

[starscream5000]

Here's what I'm looking for, someone help me find these figures so we can post them in here for comparisons, "WE NEED THE SKIRT LENGTHS OF THE OTHER BRAND PISTONS FOR COMPARISSON!" Sorry for yelling .

I'm good for: Longer skirt (I will gladly make the sacrifice of a heavier piston for this), no matter what we do, these pistons will not be heavier than the stockers, so don't get your panties all twisted up about it people, if you want light, get a JE, thicker piston rings for longetivity (this is my theme for the piston. BTW, how good is the alloy being used for these? Someone fill us in who is knowledgable on this alloy), available in overbores up to at least .020", and a compression of about 8.5 (anyone who is smart when putting these in will have the head and block machined, so that in it'self will raise compression, which will be compensated by the correct head gasket used if you do your research).

Good catch on the CP piston, I forgot about that brand . I'll research it and post up the figures on those from their website.

 

[starscream5000]

In case you all haven't realized it yet:

1) Doward
2) S turbo 87
3) zachm611
4) TobyCat
5) mark3monster
6)MassSupra89
7)Born2drv
8)90T04
9)woodytsi
10)bmoss85
11)LilMissMkIII - pending shipping price to Aus
12)screaminglemon
13)bustedknuckle
14)starscream5000

 

[starscream5000]

CP's website does not dislose the weight of their piston... Let's go with born2drv's post for now unless other info says differently:

CP 301 Grams @ 84mm bore. and 8.4 compression

 

[Doward]

You know guys... all the pistons currently are advertised as 8.4:1 compression - but that's assuming no machine work. We all know we have to get machine work done - why don't we actually set up a -19cc dome, just to bring that compression back around where it should be, after machining?

So what's the verdict on the rings? My vote is a 1.2/1.2/2.8 - a second runner up would be 1.2/1.2/3.0 (almost stock 2JZ thickness)

Also, by going with a thinner ring, it allows more meat in the top of the piston - strengthening it a little more.

Looking at the piston head design, I can't help but think that there has to be something we can do to optimize the quench a little better in there (oh snap, there I go with that again )

 

[TobyCat]

I don't know what quench is

 

[starscream5000]

I would prefer the 1.2/1.2/3.0 John.
Anyone got a file saved on the skirt lengths of these pistons since the suppliers conveniently do not disclose this info.

Thicker piston rings FTW!

 

[Doward]

I'd be happy with 1.2/1.2/3.0s for a daily driver The JZ, as an example, run 1.2/1.5/3.0s

The stock skirt length is 70.95mm from my measurements (from the piston head top to the end of the skirt) - I'd recommend we stay about 70mm, and just taper it slightly to save some weight.

 

[starscream5000]

That's fine as the stock ones are good for +200K miles.

Any idea of what the stock dome is?

 

[Doward]

Stock is a -18.5cc, IIRC. I supposed I could CC one here and find out exactly

 

[starscream5000]

Yes, a little larger would be great to compensate for material taken off the head and block during prep. Can probe give you a good estimate of the compression if the dome was -18.75 or -19?

 

[Doward]

-19 would be about a tenth off.