3.2 pistons and barrels in 3.0L?

[davidppp]

Hello all.

The piston pin is of course bigger..

Has anyone done this..reamed the bush of the 3.0L to fit ?

Thanks
David

[Henry Schmidt]

Yes we do it all the time. But it's not that easy.
Some back ground.
The 3.2 has a longer stroke but a shorter rod. To make it all fit and maintain the same overall engine dimension Porsche raised the pin location. (pin height).
The stroke is 4mm more, but the rod is only .8 mm shorter.
That means they raised the pin height 1.2 mm because the stoke made a 2 mm difference at each end.
Here's what you do.
Remove the old pin bushing.
Off set bore the 3.0 rod end to fit the 3.2 bushing. Remembering that we are trying to make up for the different wrist pin location, set the bottom of the new hole at the bottom of your existing hole.
This will give you almost 1/2 of the rod length you need.
If you want all the the deck height back you will need to make a bushing that has a 3 mm larger OD with a 20 mm id and install that bushing in the 3.0 rod. Now you must off set cut this bushing .5 mm. This will give you the proper deck for normal installation. When you're all done your rod length should be 2mm longer. On most Porsches longer rods are better.
Higher compression pistons, no CE rings and longer rods, all good.

I have also seen people install a solid 2.7 bushing and just off set cut that solid bushing and the results are ugly but it works.
"Ugly but it works", where on this board have I seen that?

[914timo]

Interesting, but have to ask why ?? Why you do this all the time ?? Why someone want to use 3,2 pistons in 3,0 engine ?? New JE pistons are about $900. The machining of the rods can not be cheap. Maybe not $900, but new pistons are new and you get new piston rings too. Is there something else I donīt see ?

[Henry Schmidt]

Originally posted by 914timo
Interesting, but have to ask why ?? Why you do this all the time ?? Why someone want to use 3,2 pistons in 3,0 engine ?? New JE pistons are about $900. The machining of the rods can not be cheap. Maybe not $900, but new pistons are new and you get new piston rings too. Is there something else I donīt see ?

There apparently is a plethora of things you don't see.
First, the additional machine work is about $200. I assume that if the rods are out they are being rebuilt anyway. If your machine shop wants to charge much more perhaps someone more proficient with Porsche should be doing your machine work.
Second, JE does not make a squish a chamber piston.(they may on request but I dought it) There are some who theorize that squish chamber pistons may help prevent detonation and CIS engines are notorious for detonation.
Third, as much as I like JE pistons, Mahles are better.
It is far easier to fit Mahle pistons in Mahle cylinders than JEs. Unless you sent JE your cylinders, proper fitment is a crap shoot. Mahle on the other hand makes 4 different sized piston for each size group.
Forth, If there is nothing wrong with your 3.0 cylinders why are the pistons being replaced in the first place?
Fifth, 3.2 cylinders are a better design than a 3.0.
Six, New 3.0 high compression Ps&Cs are not always available. It seems that 3.2 are (available) and generally at a better price.
Seven, Because they built more 3.2s than 3.0s good used 3.2 Ps&Cs are readily available sometimes at a great price.
You will also find that 3.2 cylinders are used to make 98mm cylinders leaving 3.2 pistons in great supply. The same (98mm conversion) is not true of 3.0 cylinders.
Eigth, when this process is complete you end up with a rod that is 2mm longer and rod length to stroke ratio is improved making the engine run better (more hp, higher rpm, less friction do to piston side loading)
I could go on and on but I think you get the picture.
Cheers

[ChrisBennet]

Great post Henry!
-Chris

[davidppp]

Sincere thanks, once more, Henry, for a generous and helpful post...

I my case, to the rod machining I will be adding some piston crown work to provide valve clearance for the G80 cams...

This will be a post-Historic rally motor on 46 PMO's..

I'm very interested that the small ends are strong enough to take the big overbore....

I'd actually planned to just get the 0.5mm offset, and machine the barrels to get the deck height back..

But since you have proven the rod has the needed strength, I'll do that instead..much better all round.

We will need the bottom end to be safe to 7,600 or so to allow some margin on corner exits...do you think the modified rods will hold that?

Thanks again..
David

[KobaltBlau]

Originally posted by Henry Schmidt
Second, JE does not make a squish a chamber piston.

Henry, what do you mean by "squish chamber" ? I am familiar with the squish band concept. For example, would you consider a 3.0 RSR piston "squish chamber" or just something like a CIS piston?

[Henry Schmidt]

Originally posted by KobaltBlau
Henry, what do you mean by "squish chamber" ?

It is just how I refer to CIS piston domes.

[Henry Schmidt]

Originally posted by davidppp
.....
We will need the bottom end to be safe to 7,600 or so to allow some margin on corner exits...do you think the modified rods will hold that?.........

We here built 600+ horse power engines with this modification and have experienced no small end rod
failures.

[kenikh]

Couldn't you CNC a forged JE piston blank into a "squish" profile?

[Henry Schmidt]

I believe you could. Now my question is why?

Mahle makes a better product and they are available at a reasonable price. Why would you want to go through all that hassle.

The original post asked if you could put 3.2 pistons on a 3.0 crank.
Lets assume he had a reason.

Now your question:
Couldn't you CNC a forged JE piston blank into a "squish" profile?
Where are we going with this?

[kenikh]

Originally posted by Henry Schmidt
I believe you could. Now my question is why?

Now your question:
Couldn't you CNC a forged JE piston blank into a "squish" profile?
Where are we going with this?

Is it theoretically possible to create a squish type piston with higher CR than an off-the-shelf Mahle with enough clearance for a high lift cam? If they do indeed mitigate detonation better than a conventional piston, it could be useful.

[914timo]

Thanks Henry. I bought 3,2 cylinders and pistons couple of months ago to my 3,0 engine. I was going to use a set of JEs with those cylinders, but bought the original pistons too. Thanks for convincing me it was a good idea then buy those pistons too.

There apparently is a plethora of things you don't see.

Thats why I ask. Sorry, if you donīt like my questions.....

[davidppp]

Great thread...

The reason I want to use the OE 3.2 pistons and cylinders is exactly what Henry said..

They are an excellent quality, forged piston with tight clearances in the also excellent nikasil cylinders...and cheap!

That said, once I have worked out a set up to make the cuts to the valve pockets (I have an existing set up which works on the early heads) I'll have some time invested..so if anyone in UK wants this done, let me know...

Kind regards
David

[Henry Schmidt]

Originally posted by kenikh
Is it theoretically possible to create a squish type piston with higher CR than an off-the-shelf Mahle with enough clearance for a high lift cam? If they do indeed mitigate detonation better than a conventional piston, it could be useful.

Theoretically, yes. Why not?
The detonation we are trying to control with this type of piston is caused by lean mixture necessary for emission requirement.
Lets hope that in a high compression engine with more aggressive cams that lean fuel mixture is not an issue.

[KobaltBlau]

Thank you, Henry. I see what you are saying.