Piston Specifications and Extras

[Billman]

Hi,

i know that various of these subjects where discussed in different threads but i could not find some clear statements or experiences.

So, i was searching to pistons extras like gas ports, coatings ect and the opinions are very different. In order to have the best from both worlds between reliability on High BHP and also longevity (not needing to rebore the engine every 10-20 tkms).

It is possible to have with custom pistons the 150000 kms that the stock piston configuration gives you (with the small clearance (so no piston slap at start uo), the nice skirts ect)
With the custom piston extras some say the coatings come off, other say the lateras gas ports seal better but give excesive cyl wall wear.

What shout someone choose in order to have such a piston? CP i.e. that i am considering offers the following:

1. Accumulator Groove
2. Lateral gas ports
3. Anti detonation grooves
4. Skirt coating
5. Anti Detonatio Grooves

If the mods think this thread is unnecessary feel free to erase it.

Cheers,

Vasilis

[Jamo]

Hasn't your question been answered here? http://www.s2forum.com/forum/showthr...t=16684&page=6

[Billman]

Actually not completely. Although Marks answer was very extensive i would like to hear also other opinions/experiences. Like i said if it is unnecessary DELETE.

[Billman]

In order to help, here is Marks post:

Gas ports allow combustion pressure to get behind the top compression ring and force the ring out against the bore wall resulting in better ring seal on the compression / power strokes. This gas pressure still gets behind the ring to a lesser degree with normal pistons but the gas ports allow more pressure to get behind the ring and give a more aggressive seal, the down side of this though is accelerated ring and bore wear, (not something I was particularly concerned about with this build).

Piston gas ports come in two flavours vertical or lateral, vertical are used in drag race applications as these engines are usually rebuilt often and carbon doesn't get a chance to block the ports significantly between builds. Lateral ports are usually used in circle track motors.

I am experimenting in using these and so far I am happy with them, although to be fair my lack of time and progress with other areas of the car have prevented me from really giving them some stick.......so far.

Edit
Here is something cut and pasted from the Wiseco site:

Vertical gas ports are primarily used in drag race applications. Lateral gas ports are more often used in circle-track and road-race applications where carbon build up can occur. When gas ports are used, pressure is directed to build up behind the compression ring and seal it against the cylinder wall. This helps prevent ring flutter and extends the power curve upward in the RPM range. Vertical gas ports have the holes drilled from the deck of the piston into the top ring groove and behind the ring. Lateral gas ports are drilled through the bottom side of the top land and extend to the back wall of the ring groove.


And something from JE showing them with other custom piston machining options

http://www.racetep.com/carpics/jeoptions.jpg


Other questions that arise are:

CP says that the lateral gas ports should be used with back cut rings with low friction (does it decrease wear)?
Accumulator grooves also increase wear?

What about the Anti Det grooves and coating?

[Jamo]

Coating - http://www.s2forum.com/forum/showthread.php?t=25140

Lateral gas ports do increase wear Mark has said as such on the fourm.

[BRY]

Grant is having a few sets of pistons made based on his Dubweiser Golf pistons with a few tweaks. They are proven to 750hp.
I think they will be around £175 each piston.
I can get details if people are interested.

[Billman]

Here also Marks post on Coatings:

Regarding skirt coating

I am sure that you have already thought of it, but remember when you measure pistons with skirt coating prior to block machining and bore sizing you will also be measuring the thickness of the coating in addition to the actual piston diameter.

This coating will wear after not too long and alter your piston to wall clearance if your machinist measures the pistons in this way, without taking account of the coating and its subsequant wear.

Shouldn't be a problem if the pistons are supplied with accurate dimensions on the job sheet and you work to these (I have found JE's to be very accurate), however I prefer to measure the pistons myself to be on the safe side, something that can't be accurately done with the skirt coating applied, even if you have a ballpark figure for the coating thickness.

Another option would be to order your pistons naked and measure and set up the machining before getting them coated.

I have actual experience of this coating wear causing the the pistons to slap like fook even when hot after only a few k miles. I still have these pistons and can take pictures that show this wear in the skirt coating well. Let me know if and I'll dig them out....

Mind you, having said all of that skirt coating cuts down on friction and that has to be good, if you have a good machinist who knows what he is doing you should not have any problems.

@Bry
What pistons are these? I need them for a stroker project: 95.5 stroke, 158mm Rods with 23mm Pin diam.

[Jamo]

I've had mine made by JE as all the power peers I have talked to are running them.

Jeffer, Mark Halligan, Doug_RS2, Audiman, Volcano RS, Sal S2, Andy P, TerryBullwon

My piston options are Contact Reduction Grooves & Accumulator Groove no coatings.

End of the day Piston companies want you to buy the extra option especially coatings as it makes them money.

[BRY]

Have they all got 750hp?

[Jamo]

Have they all got 750hp?

Nope never said they did

[BRY]

I'm getting mine from Grant, because he has.



I won't have 750hp, not yet anyway.

[Billman]

I've had mine made by JE as all the power peers I have talked to are running them.

Jeffer, Mark Halligan, Doug_RS2, Audiman, Volcano RS, Sal S2, Andy P, TerryBullwon

My piston options are Contact Reduction Grooves & Accumulator Groove no coatings.

End of the day Piston companies want you to buy the extra option especially coatings as it makes them money.

How does CP call this contact reduction grooves?

What was with Marcos last pistons? I thought the engine was OK when you bought it.

[Jamo]

How does CP call this contact reduction grooves?

What was with Marcos last pistons? I thought the engine was OK when you bought it.

You need to speak to Darius at CP what their Piston options mean in relation to other Piston makers.

JE options are as this website http://www.racetep.com/jecustom.html#custopt

[Billman]

I spoke with Darius, i think they call it Anti Det grooves.

Problem with Darius is that yo uask 3 questions youget only 1 of them answered.

He also said Piston/Wall clearance should be 0.09mm

So, i would say for Stroker RPM Limits and smaller bore and ring wear:

Pistons with:

-Anti Det Grooves (Contact red grooves)
-Double pin oilers

And what about the Accumulator grooves? Does it increase wear?



cheers,

Vasilis

[Billman]

When i asked about a set that will last longer in time i got this answer, what do you think?

"For the longest life between rebuilds I would suggest you use a 4032 alloy. It is not as strong as the normal 2618 we use, but expands much less and the ring grooves don’t wear as fast. However, it is much stronger than the factory piston."