JE Pistons, 11.5 cr into a 3.2 flat 6?

[wadsworthi]

I understand that you are unlikely to see 11.5 to 1 on JE Pistons or indeed Mahle. I don’t think that either 3 litre or 3.2 heads will give maximum compression as they are unlike the RSR heads which should.

Clewett do a knock sensor kit that requires drilling, it does not fit into the temperature sensor drilling as far as I can see. My engine has temperature and cam sensor, but no knock sensor.

[PeterK]

My last 3 rebuilds I've fitted them dry, but clean, no leaks.
It is a last resort if clearances get too tight.

I can only find 0.25 and 0.5 mm thick gaskets.
Are thicker available?

Porsche only list 0.25 & 0.5mm.

I have 2 complete sets (6 in each) of 0.25mm in the garage.(Victor Reinz)

[911hillclimber]

Thought as much on the thickness as couldn't spot thicker elsewhere.
Too think and I guess they get too soft as a gasket under such stress.
Think I will build with 0.5mm and not the thin ones I have in the Elring gasket set I have for this rebuild.

[Cortina]

Thought as much on the thickness as couldn't spot thicker elsewhere.
Too think and I guess they get too soft as a gasket under such stress.
Think I will build with 0.5mm and not the thin ones I have in the Elring gasket set I have for this rebuild.

Do people ever read what they type these days ............. (sorry , it's a bug bear of mine) ??

in reply to an earlier comment ............ I would hope that the CR would be measured and calculated , and NOT Assumed (we should all know the rules of assuming by now !) , THEN decide what CR you want , THEN build accordingly

............. carry on

PS: in the lab at university , we had a lovely set up on the test bed / dyno , where we could alter the CR (?? as engine was running ... I can't remember !, not relevant ) but the graph of peak HP vs CR told a very clear message which has always stuck with me. You know what it is , so yes ..... as high as possible , but as you know ............. there are no free lunches !

PPS I don't think the gasket will be under much stress at all ....think about it.

[911hillclimber]

The 11.5cr is a well known spec (I've read) and I will trial fit the lot dry build with plasticine pads on the piston points to see how close it all is.

80 thou or more clear anywhere seems good.

As to the base gasket, my comment was on there being two, a 0.25 + a 0.5 if I need some more space in the combustion chamber to get to 80 thou.

Obviously well clamped, but it was a conversation yesterday with a Porsche engine builder that made me thing about shuffle between the soft surfaces over time.

We shall see when I get to fitting the piston/barrel/head/cam combo together with the plasticine to see what I have for clearances.

My new ring piston ring compressor came today, what an easy why to do the assembly!

I can't see any red lines under any words, so this might read ok!

[PeterK]

You could have used way instead of why in the second to last sentence



I should be the last to throw stones - my e-mail signature is ‘typos by fat fingers’

[911hillclimber]

Well spotted, a deliberate mistake of course...

[Cortina]

....and what about "made me thing" ??? Have we digressed (clearly spell checking is NOT going to help you) ? I'll go for coat now ..............

[911hillclimber]

It's Christmas!

Just remembered to draw 2 Xmas cards tomorrow, so rod assembly delayed for an hour or so.
Just been reading about CR's on the JE web site and feel positive about 11.5:1

Have to get weighing before the rods go on, so heavy rod has a light piston etc to try to get a split of balance so to speak.
My new Chinese fine jewellers balances are remarkably repeatable to 0.1 gram. All for £7.

I need to have a clear head for this stuff at my age, and that is also my excuse for poor English.

[PeterK]

The pistons will be fairly precise, although there may be a slight difference in rod bolts. If rods are different, then a slight fettling will see them right.

If you're doing it properly, balance the little ends so that they're all the same, then the whole rods by 'adjusting' the big ends. IIRC though, Porsche specify quite a large permissible variance - an inherent benefit of the boxer engine I suppose.




I had my complete bottom end balanced, so rods, pistons, crank, flywheel, clutch and front pulley. Will I ever be able to notice a difference - no chance, but the £2-300 was a drop in the ocean of total rebuild cost, and I can brag about having a balanced engine in the pub now

[911hillclimber]

Carrillo and the UK supplier are quite adamant:
The roads are weighted and balanced, and you cannot see any witness of that as the surface is shot peened after. They claim +/- 2 grams on weight.
If of course if I took a grinder to them, warrantee is gone if there is one for a racing engine.

All are CNC machined so I would expect the rod lengths to be 'exactly' the same to a thou or 2 at most.

The pistons I would believe will be the same condition of manufacture, but I'm sure I've read that on the flat 6 you can put a light rod/piston on one journal and put a similar weight combo on another to give a better balance, so the one is coming down while the other is coming up, but this is a WOT hillclimb engine where the thing runs hard for about 40 seconds on average then back to tick over for a few mins.

The rest of the car moves about a bit (!) and you feel a lot more than the engine ….

I'm trusting I've bought quality and have certainly paid for it and expect they know far far far better than I.

[neilbardsley]

Interesting balancing video

https://youtu.be/1Bqa3v5AfoA

Sent from my M2004J19C using Tapatalk

[911hillclimber]

Yes, an interesting video.
I have a few thoughts on it though.
1
Crank balancing including the clutch cover. It implies that when you change the clutch down the line, the crank assembly could be out of balance?
2
Few have a die grinder at home. You need a lot of air and the grinder is not cheap.
3
The rods will loose their warrantee if you touch them. Just weighed my Carrillo rods and all are within 0.5 gram. They state 2 grams.
4
Any set of scales need to be very good down at this level, a 0.1 of a gram is tight, and just because they are digital does not mean they are accurate, but can display such and increment, so doing
all this fine balancing on cheap scales can be iffy.

I have some cheap scales, 2,000 gram x 0.1 grams (displayed).
I did rough quick weighing of the rods as an item and little end weight, all were within 0.5gram displayed, importantly, they were well within the tolerances of 2 grams per rod.
5
Don't have my pistons yet, so when they arrive will see if they need heavy pin to light piston to get a tighter indicated weight.

[Bruce M]

1) the idea is to balance the crank first. Then add each additional part & only balance that, in turn. In theory each part is balanced independently but there is likely to be some stacking or offsetting of tolerances but hopefully not much.

[coomo]

Have on order 10.5 cr Pistons for my 3.2 engine.
Cannot get them anytime soon.supplier has a set of 11.5 cr Pistons instead in stock.

Hillclimb engine, ge60 Cams and 99 octane petrol.

Any comments if 11.5 will be ok?

I had exact same build spec as this.Depending on your source (ie USA uk) You might likely end up with various opinions, regarding neccssity ot twin plug for anything approaching 10.5.Most USA builders assume our fuel is as crap as theirs is.I see no issues.
I eventually went with 10.5 but changed from JE to Mahle,as the deal Don at EBS Offered was a no brainer.The Mahles are all perfectly balanced too,out of the box.JE tend to be no so much.Apparently they can be a tad "clattery" on startup, which can cause some indignation amongst those in the know etc.From what I can accertain,its merely an anaomolie (?) of the metalurgy of the piston.