2.8 RSR pistons - opinions?

[kenikh]

I saw these on Ebay; I must admit, they'd be sweet in Nickies or replated and bored 2.7 cylinders:

2.8 RSR pistons...

First, I beleive they are a repost. Second: What the hell are those holes in the top of that one piston? Detonation damage? Some crazy hillbilly with a drill press expressing anger against a German car?

Any thoughts would be appreciated.

[roblav]

I saw those too - and second listing. That guy has had a lot of things for sale that I thought were too high in price / value ratio... Those are detonation holes. I would not use that piston... In fact, I would not use any of them. My time (in building engines) is more valuable to me.

[Steve@Rennsport]

Those are NOT detonation holes; its foreign object damage and given their location above the top ring land, I'd not use those in any engine I cared about.

Using 92's with a 66mm crank yields 2.6 litres and those combinations REALLY go.

The biggest caveat is the mismatch with 2.0 heads, the resulting compression ratio and thats just not doable. 2.2 heads can be made to work with a 92mm bore, but the CR will be over 10.5:1 and you will not run that on pump gas without twin-ignition.

[RandyWebb]

For the future - what do detonation holes look like? How can you recognize them when looking at pistons for sale or just for curiousity?

Is the margin of the crater different? The size or size distribution?

[Steve@Rennsport]

For the future - what do detonation holes look like? How can you recognize them when looking at pistons for sale or just for curiousity?

Is the margin of the crater different? The size or size distribution?

Well sir, the bottom line is that it takes experience to recognize the symptoms/damage from detonation and its cousin, pre-ignition and there is simply no substitute for that.

Pre-ignition makes holes of varying kinds.

Detonation is VERY high pressure shock waves that fracture rings, ring lands, and trigger piston crown erosion that can be seen on spark plug insulators and pistons near the top ring lands.

The size, shape, and location of holes caused by pre-ignition is based on flame travel, plug location(s), any hot spot, and mixture distribution at or near TDC.

I spotted what looks like physical damage to those 92mm pistons from something ratting around in that cylinder but I'd reserve final judgement on a personal inspection.

IMHO, buying used pistons is simply too poor a risk to make unless one can inspect & measure everything for yourself.

[roblav]

Thanks for clarifying that Steve. They still are not worth my time installing.

[Steve@Rennsport]

Thanks for clarifying that Steve. They still are not worth my time installing.

My pleasure, anytime.

I'd agree, new parts (especially Mahle's) are really the only way to go for street cars in terms of longevity.

[Rick Cabell]

Steve, (or anyone)
I have a 2.8 RSR piston and cylinder kit minus one cylinder. Can anyone help?

[Steve@Rennsport]

Hi Rick:

I don't have any singles at this time; only one new 92mm set.

[andrew15]

Actually those are my 92mm pistons on eBay and yes, it is a repost. I can also verify what caused the damage. They came from an engine that had part of the cylinder break away. The cylinder between the bore and the CE ring gets thin when the 90mm cylinders get bored out. In this case part of the cylinder broke away and got tossed around for a bit. I think Steve mentioned this in an earlier post.

When I took the engine apart, the piston was discussed here:
http://forums.pelicanparts.com/showt...ht=92mm+piston

After that, I took it to my machinist and he measured and found it in spec - asked about the damage, he said he would still use it. Like I said in the auction, some may want to locate a replacement.

In terms of value / price relation on auctions - I'll usually do a search for stuff that has previously sold and list at a reasonable price-> if stuff doesn't sell, I'll usually lower the price. That said, you don't have to bid on stuff you think is expensive

Regards,
Andrew M