2.8 P/C's
 

Hi
who provides a nice set of 2.8L P. and C. ?
regards
Philippe

Philippe:

Do you want the original Mahle 92mm RSR P/C's or some custom cylinders with JE pistons?

I've been curious about this too. Can a 2.7 90mm cylinder be bored effectively, or does the sealing ring make it less than desirable? Short of LN Nickies + JEs, what are the options?

90mm (2.7) cylinders can be bored and replated to work. You'd use a set of JE's with these. These should be bored and honed using torque plates so they will stay more concentric when torqued up in the motor and at operating temperatures. Since these have CE rings, one is left with a VERY narrow inner lip next to the bore and these have given some trouble.

The Mahle 92mm RSR P/C set is the most durable, but these are now out of production and availability is very scarce. The current sets dispensed with the CE ring grooves for a much more durable cylinder.

Hi
I'd like to have an idea of the price...

Big differences,............

You'd have approximately $ 2300 in a set of rebored, replated 92's with JE pistons and about $ 4500 for a set of Mahle 92mm RSR P/C's.

The final choice lies with your budget and how long you expect everything to last.

LN cylinders are 2750 plus approx 900 for pistons (from the LN website, http://www.lnengineering.com/911.html ). Seems like a viable option price wise, not to mention that they could be superior to the Mahle counterparts.

(edit: I have experience or affiliation w/ LN)

You could even go a little bigger, say 93 or 93.5mm with a set of Nickies, as long as you aren't also planning to put a turbo on there :-)

ouch !!!
I was told it's a bit expensive..
I have a nice set of stock 2.7RS pistons and cylinders (10000kms)
i was thinking about this option during rebuilt, may you give me an idea of the changes it should give me to install 2.8 P/C's.? (what about 019 pump recalibration....)
Steve, would you do that ? (rebore... ?)
best regards from France
Philippe

Philipe:

Indeed, its not cheap to do (properly).

92's are a slip-in so the only other thing you would need is MFI pump recalibration. Bear in mind that the compression ratios are different between the Mahle RSR P/C's and a JE setup. One can get JE's in any CR you want that will be compatible with the gasolines you will use, but the Mahle RSR pistons yield 10.7-11:1 with 2.7 heads.

Personally, I'm not a fan of boring 90mm cylinders since too little material remains between the bores and CE ring grooves for reliability. JE's are great for race applications where CR flexibility is very important, but they do not last anywhere near as long as Mahles.

Really,...its all about how long you expect the engine to last before needing some work. :)

Hope this helps,

What reliability problems have you seen with the JE pistons??

Steve

Prematurely worn top ring lands, worn skirts, and in race engines that see over 7800 RPM, cracked wrist pin bosses.

JE's are OK as long as one bears in mind that they should be be replaced once in awhile* as they do NOT last anywhere near as long as Mahle's. Given the cost differences, thats an acceptable tradeoff in a competition engine,...:)


*Replacement intervals depend on many things; operating RPM's, compression ratio, bore size, rod ratio, etc. No hard & fast rules apply here.

But would JE's fare ok in a hot high compression street engine?? Assuming they are treated like any other street car with ocasional high rpm use should they see over 100K miles??

Steve

Steve:

I've never seen ANY JE approach 100K miles before needing replacement. They are fine racing pistons but they simply lack the longevity of the Mahles.

Steve...what would you surmise the longevity to be in a street engine? 50K?? less?

Yessir, thats about right.

I like to perform semi-annual leakdown tests to monitor the condition of rings and valves and given the reasonable cost of new JE's, I'd replace them at the 50K level to keep the motor at peak performance and control oil consumption.

Mahle has 2.8 and 2.9 slip in p/c sets , made to update the 2.7
9.25-1 and 10.5 -1. flat top cylinder no CE rings
just bought a set 2.9- 10.5-1 4200.00 Pure Mahle

These mahle sets are new?? The compression ratios listed are for the 2.7 heads? Where would they be purchased?? Through andial or are host maybe?? I'm doing a 2.8 build but dont have the rsr heads. Thanks for the help!

Steve

Andial carries the 2.9's (93mm) but I'd warn you that these cylinders are VERY thin and the rings do not seal well when hot.

92's (2.8) are, practically, speaking the largest useful bore size you can use with a case of this stud spacing.

You can use the 92mm Mahles (if you can find a set) with 2.7 heads but you'll need twin-ignition and some creative machine work to get the CR down to pump gas compatible levels.

FWIW, I have one new set of Mahle 92's left.

Hey Steve...thanks for the info. What in the way of machine work would be necessary to the heads or deck height etc... Could modified 2.4 heads work? Whats realy the max for 93 octane pump gas with twin plug 10:5 to 1? Thanks for info again, and let me know your price for your 2.8 p/c set.

Thanks,
Steve

Not bad! That is in the realm of Nickies w/ JEs.

My pleasure. :)

Your heads will need some creative machine work and modified for double plugs for this to work. One must cc the chambers to see what the volumes are before proceeding as that determines what needs to be done. 2.4 heads can work just fine.

Deck heights are NOT a variable. that must be held to spec; .040 to help prevent detonation.

I shoot for 10.25:1 for pump gas as detonation thresholds are not static; they change with outside air temps and engine loads.

E-mail me directly for pricing. :)

I have a 2.8 using (I believe) the Mahle 2.8 slip ins. The p/o (mechanic) said it was a 2.8 and had flat top pistons (he didn't build the motor). Runs fine on pump gas, runs a little better on 100 octane. Not sure of the cam profile. Comes alive at 4500 rpm pulls strong to 7500, shift point is 7,000. Twin plug, Electromotive ignition, 46mm Webers w/36mm chockes, 1 5/8" o.d. headers, custom muffler. 224 h.p. @ the wheels. This was in a street car now converted to track car. As long as the leak down #'s and compression #'s are good is there any reason to tear the motor apart. This is the second season used as a race motor. I'm not sure how often the motor should be torn down and inspected, or the longevity of a motor like this is.
Thanks,
Harold
'74 rsr w/2.8

Mahle has 2.8 and 2.9 slip in p/c sets , made to update the 2.7
9.25-1 and 10.5 -1. flat top cylinder no CE rings
just bought a set 2.9- 10.5-1 4200.00 Pure Mahle

914/6 sent you a pm. I'm looking for a source for the 2.8 Mahle slip ins.
Thanks,
Harold

Harold:

FWIW,......I have 1 more set of new Mahle 92mm RSR P/C's if that helps. Mahle Motorsports in German tell me that there will be no more after this.