3.2L to 3.5L questions

[quint22cp]

I'm looking at rebuilding my 1988 euro 3.2L this winter and the inevitable question arises, should I increase the capacity.

I have been looking at these parts "PS100-001-M362" on Pelican's web site and I'm slightly confused with the description.

"Mahle Motorsport Piston and Cylinder Set (set of 6) (100mm bore, 10.5:1 comp), Carb/MFI only, 3.2 to 3.5 Liter, 911 (1984-89)"

Questions:-
Will PS100-001-M362 fit without machining of the crankcase ?
If these do require machining, what has to be machined (and don't reply the spigots), "what's a spigot ?" please post picture if possible.
Why must it be used with MFI or carbs ?
I want to fit a set of these to my euro 3.2L (10.2 comp) modified for dual plugs, will they work ?

many thanks for taking the time to reply to my questions. I have done a tech search for PS100-001-M362 and asked the question direct to Pelican but they where unable to answer this

[JeremyD]

3.2 to 3.5 - Part II
This is a great thread - Ralph is like the local rockstar when it comes to increases in displacement -

No you will need machining - to the holes where the jugs reside -


Why must they be used with MFI or carbs? Because of the quench - pistons shapes work better in different environment.

They will work, but better to find some DME pistons and cylinders that are better suited.

[Carrera3.5L]

Originally posted by quint22cp
I'm looking at rebuilding my 1988 euro 3.2L this winter and the inevitable question arises, should I increase the capacity.

I have been looking at these parts "PS100-001-M362" on Pelican's web site and I'm slightly confused with the description.

"Mahle Motorsport Piston and Cylinder Set (set of 6) (100mm bore, 10.5:1 comp), Carb/MFI only, 3.2 to 3.5 Liter, 911 (1984-89)"

Questions:-
Will PS100-001-M362 fit without machining of the crankcase ?
If these do require machining, what has to be machined (and don't reply the spigots), "what's a spigot ?" please post picture if possible.
Why must it be used with MFI or carbs ?
I want to fit a set of these to my euro 3.2L (10.2 comp) modified for dual plugs, will they work ?

many thanks for taking the time to reply to my questions. I have done a tech search for PS100-001-M362 and asked the question direct to Pelican but they where unable to answer this

You have many options to increase the displacement on your Euro 3.2L, ranging from a simple 98mm piston/cylinder "slip fit" to a 3.7L monster motor using Mahle's 102mm piston/cylinders with your stock crank and Carillo rods, it all depends on what your goals with the car are and how much money you wish to spend.

To use the Mahle Motorsport 100mm pistons/cylinders that you reference, which increases the capacity to 3506cc from 3164cc, you will have to enlarge the engine case spigots from the stock 103mm to 105mm just as Jeremy indicated. Here is another picture of the case "spigots" that are freshly opened up



A Porsche specific machine shop can perform this service for you for under $200 USD, not a big deal in the grand scheme of an engine build that costs thousands and thousands.

The description on Pelican (and others) is misleading, this set is sometimes referred to as the "RSR" style and they work just fine on Motronic engines that are being twin-plugged. This is the same set that I used for my engine build, don't let anyone tell you that they won't work. One advantage that they offer is deep valve pockets which allow for use of aggressive cam profiles should the need ever arise. In the event that you tire of Motronic and wish to "backdate" to carbs/mfi or "update" to Motec or some other sort of engine management, you wouldn't have to tear down most of the motor to change pistons again, just install the more radical cam profile of your choice and you're off and running. You will have proper piston-to-valve clearance where you will not using the Motronic style pistons.

Here is a pic of a piston/cylinder from the set you are interested in:



I don't have pic of the 100mm Motronic version that I can post (I don't have a scanner handy), but I can tell you that the valve pockets are much less pronounced and the piston shape is pretty flat versus the high-dome on the RSR style sets.

Bear in mind that the advertised compression ratio of 10.5:1 may not be accurate, there are lots of variables involved when calculating compression ratio but I ended up at 9.5:1 with this set. This is what Andial says this set is really at on a 3.2L motor.

If you will be twin-plugging the motor (which I think you indicated you will), this is the set to buy. If you are staying with single-plug, the Motronic version (where the pistons have a different shape) probably is the better choice. Most of the 962 air-cooled engines were twin-plugged and used a version of Motronic (albeit more advanced) with the RSR piston style, but there also was a single plug 962 engine that used a piston dome similar in appearance to the Motronic versions.

The same thoughts would apply to 98mm 3.4L versions should you not wish to go through the gyrations of machining the case, use the carb/mfi piston when twin-plugging and the Motronic style if staying single-plug.

Of course, you could always do a 3.6L transplant and have a entirely different set of problems to worry about.

Ralph

[JeremyD]

So Ralph, there is no set of Motronic 3.5 pistons? I swear I almost bought a set of these...

[Carrera3.5L]

Originally posted by JeremyD
So Ralph, there is no set of Motronic 3.5 pistons? I swear I almost bought a set of these...

Yes, there is. I thought I clarified that in the post, but I guess not very clearly. Sorry.

Ralph

[JeremyD]

I see now - my reading comprehension sucks.......

[Wayne 962]

These pistons are specifically designed to work with the high-lift cams of carbs / MFI, not necessarily the Motronic or CIS systems. However, if the engine is built properly, they will indeed work.

However, if you do use these with the Motronic system, then you'll have to run a custom chip, and perhaps larger injectors to avoid running lean...

-Wayne

[Carrera3.5L]

Originally posted by Wayne at Pelican Parts
These pistons are specifically designed to work with the high-lift cams of carbs / MFI, not necessarily the Motronic or CIS systems. However, if the engine is built properly, they will indeed work.

However, if you do use these with the Motronic system, then you'll have to run a custom chip, and perhaps larger injectors to avoid running lean...

-Wayne

Wayne,

My belief (and other sources that I have spoke with agree) is that you can use the 100mm Mahle Motronic style piston for single or twin ignition but should only use the carb/mfi/RSR/insert name here piston if twin-plugging due to the high dome shape of the RSR piston. I think this piston is chosen so that more aggressive cam profiles can be used (which you need carbs/mfi/efi for) and not because it HAS to be used with carbs/mfi/efi.

You would have to run a custom chip regardless of the piston shape you choose, because the motor is being twin-plugged and you run much less ignition advance. Besides, I don't think many would build a "stock" 3.4L or 3.5L motor where the displacement increase is the only modification and not change other variables like cams, intake & exhaust components, etc where a custom chip would be highly beneficial (and necessary) to optimize output.

Not counting my personal motor, we built dozens of 3.4L/3.5L/3.6L motors at Andial and never once needed or changed Motronic injectors. For a street set-up, stock injectors work perfectly fine and do not need to be replaced, although a cleaning to make sure fuel is properly atomized (and not dripping) would be a great idea as many 3.2L motors are now getting up there in mileage.

Ralph

[quint22cp]

Thanks for all of the replies, I have a much better idea now.

I was intending to re-chipped the Motronic or swap it out for another ECU system. I wanted to keep the compression ratio up to around 10.5 as we have 98 octane here in the UK.

With regard to the 3.6L transplant, this is also something I have considered but I would have to rebuild the 3.6L anyhow and when you get in there it would probably need new bores so I would be right back here with the added cost of a whole engine.

[Wayne 962]

Originally posted by Carrera3.5L
Wayne,

My belief (and other sources that I have spoke with agree) is that you can use the 100mm Mahle Motronic style piston for single or twin ignition but should only use the carb/mfi/RSR/insert name here piston if twin-plugging due to the high dome shape of the RSR piston. I think this piston is chosen so that more aggressive cam profiles can be used (which you need carbs/mfi/efi for) and not because it HAS to be used with carbs/mfi/efi.

That's exactly what I was trying to say, getting lazy with my typing...

-Wayne