Upgrading my 3.2 to a 3.3 P&Cs.

[kamaro]

As the topic says, I'm planning to swap in a 3.3 P&Cs into my turbo 3.2, I'm doing it for the added displacement, but doing it to lower my CR to be able to push more boost (up to 1 bar). I know the 3.3 uses a shim gasket between the head and the cylinder, so do I need to use that shim between the 3.3 cylinder and the 3.2 head? .. also I'm a bit worried about the reduced heat dissipation with less cooling fins in the 3.3 cylinders, is that something I need to be worry about giving that I live in a hot climate? .. that was the only reason that I wish I can afford the Mahle 3.4 cylinders, because they have the fins all around. please let me know your thoughts.

[reclino]

Shim gasket is only stock on later 965 3.3 turbo, or on the RUF 3.4. RUF calls it a thermal break. My best guess is it is designed to slow heat transfer from the cylinder to the head. Head temp is the limiting factor on these engines, this shim will force the cylinder to do a bit more of the heat transfer.
Fred Apgar suggested I install the shim gasket,.my engine is not complete, and I am not a professional engine builder. There are other people with much more experience than I have, and I am sure there are different opinions on these shims.
The fins all the way around are not so much for the cooling, but they serve to keep the cylinder round, the half fins of the 3.3 cylinder causes the bore to go out of round from thermal stress.
In the fully finned 3.4L cylinder you put the block off plates to cover the fins on the top of each cylinder like in a 3.2. the trick cheaper cylinder is to boure out the 3.2L cylinder to 97mm and replate it.
David
Performance EngiNerding

[David]

How about sending your 3.2 cylinders out to have them bored and plated to 98mm and then run JE pistons?

[kamaro]

Originally Posted by reclino

Shim gasket is only stock on later 965 3.3 turbo, or on the RUF 3.4. RUF calls it a thermal break. My best guess is it is designed to slow heat transfer from the cylinder to the head. Head temp is the limiting factor on these engines, this shim will force the cylinder to do a bit more of the heat transfer.
Fred Apgar suggested I install the shim gasket,.my engine is not complete, and I am not a professional engine builder. There are other people with much more experience than I have, and I am sure there are different opinions on these shims.
The fins all the way around are not so much for the cooling, but they serve to keep the cylinder round, the half fins of the 3.3 cylinder causes the bore to go out of round from thermal stress.
In the fully finned 3.4L cylinder you put the block off plates to cover the fins on the top of each cylinder like in a 3.2. the trick cheaper cylinder is to boure out the 3.2L cylinder to 97mm and replate it.
David
Performance EngiNerding

Thanks David for all the valuable information. So since my car won't be tracked or raced (just a few spiritual drives) then its totally fine to not to use the shims.

[kamaro]

Originally Posted by David

How about sending your 3.2 cylinders out to have them bored and plated to 98mm and then run JE pistons?

It will be expensive for me to ship my cylinders back and forth from Qatar to US, and by the time I do that and then buy a set of new pistons I would better buy a new Mahle 3.4 pistons and cylinders set.

[reclino]

Yeah, I would skip the shims. It has added complexity, time and a bit of the unknown to my build. I understand the heat transfer equation they are designed for, and I am still slightly stressed about using them.

[spuggy]

Originally Posted by David

How about sending your 3.2 cylinders out to have them bored and plated to 98mm and then run JE pistons?

^^ +1 this.

Or just order a set of JE pistons with the desired C/R and run those in the stock cylinders, as most Nikasil cylinders don't seem to wear out?

From 3.2 to 3.4 is only a small (6%) displacement increase anyway. Twin-plugging and fire-ringing seems like a better ROI to me.

[kamaro]

Originally Posted by spuggy

^^ +1 this.

Or just order a set of JE pistons with the desired C/R and run those in the stock cylinders, as most Nikasil cylinders don't seem to wear out?

From 3.2 to 3.4 is only a small (6%) displacement increase anyway. Twin-plugging and fire-ringing seems like a better ROI to me.

I once been told that I can't just order a piston based on a size, I need to send my cylinders out to be replated if I need to get a custom piston. not sure how far thats correct, but anyway it still expensive solution compared to getting a good used set of 3.3 P&Cs.

Do I really need twin plugging for such a low C/R? .. I know twin plugs are needed for a large bore with high C/R, but again, what do I know?

[mikedsilva]

Originally Posted by kamaro

I once been told that I can't just order a piston based on a size, I need to send my cylinders out to be replated if I need to get a custom piston. not sure how far thats correct, but anyway it still expensive solution compared to getting a good used set of 3.3 P&Cs.

Do I really need twin plugging for such a low C/R? .. I know twin plugs are needed for a large bore with high C/R, but again, what do I know?

When using a new set of aftermarket pistons, the best practice is to send the cylinders off for boring and plating with 1 of the pistons. This way they can ensure the final piston/cylinder clearance is correct.
Is this more expensive than finding a used set? absolutely. However, I doubt you'll find a used set that you are happy to use. They will have some wear but hopefully still within spec.
Also, you need to budget for new rings and circlips where the new pistons will have them already.

[spuggy]

Originally Posted by kamaro

I once been told that I can't just order a piston based on a size, I need to send my cylinders out to be replated if I need to get a custom piston. not sure how far thats correct,

Plenty of pictures of high-mileage (some even 250-300K) Nickasil cylinders on the original plating with factory honing marks still visible.

If they're in-spec for roundness/taper, wouldn't bother me overmuch. If they're not in spec then would need to be bored/re-plated anyway.

I think I would consult someone who knows more than me (not hard); Charles Navarro of LNE discusses the metallurgy of J&E pistons and recommended clearances in this thread: JE Piston to Cylinder Clearances

I seem to recall reading that all J&E pistons are basically custom-ordered; although a supplier may have stock sizes/specs on the shelf - but you can order whatever you want, thermal/friction coatings, C/R, bore, pin size/placement etc. Very probably Charles again, in another thread, but I couldn't swear to it. I have so many bookmarks...

I've also read that J&E QA can be a concern. Mine came from L&N with their 3.4 Nickies, so LNE did the QA as part of their service. Very happy with them - I don't hear any piston slap when cold.

Mahle Motorsport 3.4 slip-ins were getting pretty scarce 10 years ago... About 15 years ago, someone was clearing out 20 NOS sets @ $1800 a pop. Didn't think I needed them at the time - been kicking myself ever since, LOL...

Originally Posted by kamaro

but anyway it still expensive solution compared to getting a good used set of 3.3 P&Cs.

I'm not the best person to talk to about "cheap builds", LOL.

I've got a used set of 3.3 P&Cs on my wrench's shelf I don't intend to use again. I'd ask if you want them - except #6 has light visible scuffing on the cylinder/piston from a spun rod bearing. That said, it didn't affect ring sealing or leakdown #'s at all and I ran them for years after the $$$ rebuild before going 3.4/MoTec etc...

But there's lots of used 3.3 sets around. Kind of tells its own story, right?

Originally Posted by kamaro

Do I really need twin plugging for such a low C/R? .. I know twin plugs are needed for a large bore with high C/R, but again, what do I know?

My $0.02; don't see it as "do I need it" so much as "what works best" and "what is easy/convenient to do while we're in there anyway". Have you considered Pauter rods? Stronger and lighter than factory (eg less reciprocating mass)...

Diameter of the bore is the main issue, the offset location for the plug obviously ignites the flame path on only one side. Yes, turbo pistons don't tend to have the squish band/dome to obscure the flame path (the reason why it becomes necessary sooner on smaller bore - but higher C/R - N/A motors), but the bore diameter is still getting up there - wide enough that the speed of travel/propagation of the flame front becomes an issue. Apparently.

A 3.2 is 95mm, 3.3 is 97mm, and 3.4 slip-ins are 98mm. You'll note that the 3.6 964, with a bore size of 100mm, came twin-plugged from the factory... (and 964 lower valve covers need only the stud size opening out - I think from M6 to M8? - to bolt up to 3.2/3.3 cam boxes).

Someone who has forgotten more about Porsche engines than I'll ever know told me once that 3.3 turbos run far better twin-plugged, and that he does the machining as a matter of course whenever the heads are off. I generally try to pay attention when guys who've been doing it professionally for 40+ years tell me things.

Twin-plugging gives a faster, more even/complete burn - and 2 chances to ignite the charge, if anything is marginal. Better ignition for more power/cleaner running. With less advance.

Only down-side I see are the contortions to fire the second set of plugs with legacy/older ignition systems.

Coil-on-plug delivers more power to the plug for better ignition. Turbo Cayenne stick coils I use were developed by Beru for Porsche with a design brief of "at least 25 % higher spark energy and spark duration compared to the current sports-car ignition coil". Eliminate the distributor, tie the COP control lines together - and trigger both packs from the same ECU ignition driver output. Simple.

The static C/R is only part of the picture; dynamic C/R is what the motor "sees" and what you need to consider; this is affected by cam timing and profile/overlap as well as boost pressure.

The "hotter" the cam, the more overlap - and the greater the tendency, especially with forced induction, for the charge to "blow through" from the inlet through the (still open) exhaust valve. And the lower the effective, or dynamic, C/R. So you not only can,you actually should/need to, run more manifold pressure ("boost") on RSR cams than 930 cams, for example.

SC cams are pretty mild - (basically same profile as 3.2 cams) but the profile is done and power falls off a cliff @ 5500 RPM - with the trade-off being good low/mid range response with lots of torque.

I'm told there are more modern SC-based profiles now that don't sacrifice low-end for more top-end, Ho-hum...

[kamaro]

Spuggy, you really enlightened me now, thats why I never do any step without hearing from you guys, you are real asset when it comes to 911 world!

Originally Posted by spuggy

Plenty of pictures of high-mileage (some even 250-300K) Nickasil cylinders on the original plating with factory honing marks still visible.

If they're in-spec for roundness/taper, wouldn't bother me overmuch. If they're not in spec then would need to be bored/re-plated anyway.

I think I would consult someone who knows more than me (not hard); Charles Navarro of LNE discusses the metallurgy of J&E pistons and recommended clearances in this thread: JE Piston to Cylinder Clearances

I seem to recall reading that all J&E pistons are basically custom-ordered; although a supplier may have stock sizes/specs on the shelf - but you can order whatever you want, thermal/friction coatings, C/R, bore, pin size/placement etc. Very probably Charles again, in another thread, but I couldn't swear to it. I have so many bookmarks...

I've also read that J&E QA can be a concern. Mine came from L&N with their 3.4 Nickies, so LNE did the QA as part of their service. Very happy with them - I don't hear any piston slap when cold.

Mahle Motorsport 3.4 slip-ins were getting pretty scarce 10 years ago... About 15 years ago, someone was clearing out 20 NOS sets @ $1800 a pop. Didn't think I needed them at the time - been kicking myself ever since, LOL...



I'm not the best person to talk to about "cheap builds", LOL.

I've got a used set of 3.3 P&Cs on my wrench's shelf I don't intend to use again. I'd ask if you want them - except #6 has light visible scuffing on the cylinder/piston from a spun rod bearing. That said, it didn't affect ring sealing or leakdown #'s at all and I ran them for years after the $$$ rebuild before going 3.4/MoTec etc...

But there's lots of used 3.3 sets around. Kind of tells its own story, right?



My $0.02; don't see it as "do I need it" so much as "what works best" and "what is easy/convenient to do while we're in there anyway". Have you considered Pauter rods? Stronger and lighter than factory (eg less reciprocating mass)...

Diameter of the bore is the main issue, the offset location for the plug obviously ignites the flame path on only one side. Yes, turbo pistons don't tend to have the squish band/dome to obscure the flame path (the reason why it becomes necessary sooner on smaller bore - but higher C/R - N/A motors), but the bore diameter is still getting up there - wide enough that the speed of travel/propagation of the flame front becomes an issue. Apparently.

A 3.2 is 95mm, 3.3 is 97mm, and 3.4 slip-ins are 98mm. You'll note that the 3.6 964, with a bore size of 100mm, came twin-plugged from the factory... (and 964 lower valve covers need only the stud size opening out - I think from M6 to M8? - to bolt up to 3.2/3.3 cam boxes).

Someone who has forgotten more about Porsche engines than I'll ever know told me once that 3.3 turbos run far better twin-plugged, and that he does the machining as a matter of course whenever the heads are off. I generally try to pay attention when guys who've been doing it professionally for 40+ years tell me things.

Twin-plugging gives a faster, more even/complete burn - and 2 chances to ignite the charge, if anything is marginal. Better ignition for more power/cleaner running. With less advance.

Only down-side I see are the contortions to fire the second set of plugs with legacy/older ignition systems.

Coil-on-plug delivers more power to the plug for better ignition. Turbo Cayenne stick coils I use were developed by Beru for Porsche with a design brief of "at least 25 % higher spark energy and spark duration compared to the current sports-car ignition coil". Eliminate the distributor, tie the COP control lines together - and trigger both packs from the same ECU ignition driver output. Simple.

The static C/R is only part of the picture; dynamic C/R is what the motor "sees" and what you need to consider; this is affected by cam timing and profile/overlap as well as boost pressure.

The "hotter" the cam, the more overlap - and the greater the tendency, especially with forced induction, for the charge to "blow through" from the inlet through the (still open) exhaust valve. And the lower the effective, or dynamic, C/R. So you not only can,you actually should/need to, run more manifold pressure ("boost") on RSR cams than 930 cams, for example.

SC cams are pretty mild - (basically same profile as 3.2 cams) but the profile is done and power falls off a cliff @ 5500 RPM - with the trade-off being good low/mid range response with lots of torque.

I'm told there are more modern SC-based profiles now that don't sacrifice low-end for more top-end, Ho-hum...

[Akila]

Since this is the subject, I bought a set of used 3.4 Mahle P&C's some years back, from a Pelicanite, I won't be using them. They are on the main Island & I would have to get em back, if there is interest.

[kamaro]

Originally Posted by Akila

Since this is the subject, I bought a set of used 3.4 Mahle P&C's some years back, from a Pelicanite, I won't be using them. They are on the main Island & I would have to get em back, if there is interest.

Sure I'm interested. you have a PM.