Wossner Pistons?

[JKarow08]

Ahoy,

Is anyone on here running Wossner pistons? The machining looks spectacular and they use 4032 which should result in less blow by long term on a street motor than most of the other forged options. They make a set that are rated at 8.5:1 compression on a 2.2l, which should put them right around 9:1 with my 2.4l 70.4mm crank, about max for a pump gas build. The price is definitely right too, can be had on Vivid currently for under $900/set. Any insight?

https://wossnerpistons.com/collections/porsche-products/products/9135

[JKarow08]

I found these pics of a 10.5:1 95mm bore set...

[stownsen914]

I looked at their website recently and found what seemed like conflicting information whether they use 2618 or 4032 for their Porsche pistons. I guess you found a more definitive answer?

[JKarow08]

Originally Posted by stownsen914

I looked at their website recently and found what seemed like conflicting information whether they use 2618 or 4032 for their Porsche pistons. I guess you found a more definitive answer?

I talked with Wossner today and they confirmed their Porsche pistons are 4032. He wasn't able to confirm the exact compression ratio if using these 8.5:1 2.2l pistons in a 2.4l with a 70.4mm crank, but said he thought my estimation that they would be around 9:1 looked pretty accurate. He said the valve pockets were the same between the 2.2l 8.5:1 and the 2.4l 10:1 so there shouldn't be any valve clearance issues either.

[r lane]

I use them with no complaints other than the wrist pen clips are a major pain. But might be so for other after market pistons as well. I think a very good product. The wrist pins are beveled on the outer rim so that as the pin floats back and forth that bevel will tend to force the clip into its groove. With the crown over hang and having to snake the clip under the bevel, is tedious but I think a good design. You have to look carefully to make sure the clip is fully seated and that the pin can turn in its bore. I use a small punch to tap the clip and I tap the pin back and forth a few times to let the bevel help. I have found their staff to be helpfull. Bob

[Henry Schmidt]

Old school forging tends to be heavy.
I don't use them but a few mechanics I know think they work reasonably well.
Advertised compression ratios seem to be optimistic.

[JKarow08]

Originally Posted by Henry Schmidt

Old school forging tends to be heavy.
I don't use them but a few mechanics I know think they work reasonably well.
Advertised compression ratios seem to be optimistic.

Thanks for the insight Henry! I'm considering them as an upgrade over AA hypereutectics, haven't heard anything bad about them so far and they seem to be a great value.

The tech with Wossner I spoke to yesterday said these 8.5:1 2.2l pistons have a 19.1cc dome volume. Does that still make the compression # look optimistic? What would that give me for compression with a 70.4mm crank? I've read varying accounts that using 2.2l pistons with a 2.4l crank bumps the compression anywhere from a half to a full point, curious what your math says. Thanks!

[JKarow08]

I just got off the phone with Wossner again, the dome volume on their 2.4l 10:1 set is 24.6cc, would be curious how that calculates out using your math as well.

[stownsen914]

With piston dome volume, you can run it through the standard compression ratio formula, and you'll have your answer. You'll need your cyllinder head combustion chamber volume. If you haven't measured yours, I'm pretty sure there are published values you can use. I'd mention it, but I'm not confident in my memory. I think Bruce Anderson's book cites a number.

[JKarow08]

Originally Posted by stownsen914

With piston dome volume, you can run it through the standard compression ratio formula, and you'll have your answer. You'll need your cyllinder head combustion chamber volume. If you haven't measured yours, I'm pretty sure there are published values you can use. I'd mention it, but I'm not confident in my memory. I think Bruce Anderson's book cites a number.

It definitely looks like there is some discrepancy on the values to use in the equation though. All of these piston companies have access to to calculators yet there seems to be opinions that the claimed numbers are either too high or too low. As an example, I just checked the specs on the 9.5:1 JE pistons and they have a 27.7 dome CC, which is more than the Wossners that claim to be 10:1. I have heard JEs are generally a little higher than what is claimed though. I definitely trust Henry's numbers/opinion over what has been published by each company or anything I would calculate with my limited database of these specs.

[JKarow08]

My fuzzy math definitely makes it look like they are overestimating compression, JE is as well.

[JKarow08]

They also make an 84mm piston with a claimed compression of 10.5:1 in a 2.2l. Again, it comes up low, comes in at about 9.6:1 with a 70.4mm, about a half a point less with a 66mm crank, almost 1.5 points lower than claimed. Am I doing something wrong with my math or are all of these numbers really that far off!?

[JKarow08]

It looks like JE is using a 68cc combustion chamber for their calculation which is in the range I've seen (67-70.5cc). Apples to apples comparison, it looks like the claimed 10:1 2.4l Wossner piston is actually at about 9:1.

[Rivet]

I have wossner 10.5:1 in use on a 3.0 engine and so far so good. The balance between all pistons is great and the overall design is very well thought out.

And I agree the clips are a bit of a nuisance.

One thing to keep in mind is what squish value are the piston manufacturers using for their estimated static compression value.

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[JKarow08]

Originally Posted by Rivet

I have wossner 10.5:1 in use on a 3.0 engine and so far so good. The balance between all pistons is great and the overall design is very well thought out.

And I agree the clips are a bit of a nuisance.

One thing to keep in mind is what squish value are the piston manufacturers using for their estimated static compression value.

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Are you running those on pump gas? Twin plug? I'm not sure what the math works out to on a 3.0 but their 10.5:1 pistons in 84mm look to actually be 9.6-9.8:1, which looks to be a little too high for pump gas when you calculate the dynamic compression on the dc30 cams I'm planning on using.

I read someplace else that the balance was great, an entire set measured exactly the same.

Well hopefully I only have to assemble it once so I'll only have to swear at the clips 12 times

I understand squish, just not sure how much that varies and how that effects compression ratio. I'm trying my best, but full comprehension on all of these details still alludes me

[PeteKz]

Squish (or quench) doesn't directly affect CR. That's the clearance between the piston tops and the head. General rule of thumb for 4" cylinders is .030" is close to the minimum you want to use to avoid piston-head contact.*

However, adjusting the squish clearance to get it down to .030", like I did by removing the copper base gaskets, will increase your CR. You'll have to calculate what that is for your engine configuration.

Squish/quench is easy to see in an American small block V8 with two valves per cylinder because those have a wedge-shaped chamber when the piston is at TDC, and the squish area is between the flat piston and the flat part of the head. In a hemispheric chamber, like our 911's, the squish is between the part of the piston dome that comes close to the domed part of the head, on the side opposite the spark plug. For twin plug heads, they usually have very little squish zone, and so very little squish effect.

* According to David Vizard, if you use a cast piston with little piston-cylinder clearance in an iron SBC so that it doesn't rock, you can get down to .018" before contact, but .023" for forged pistons with more clearance. That's the absolute minimum, so .030" gives a little margin of safety. FYI, I am currently running a Kawasaki KLR 650 (103mm bore, 87mm stroke, iron sleeved bore, forged JE piston)with .027" and no contact. It also allowed me to add about 0.5 of CR (up to 10.2) with the need to use 89 octane gas instead of 87 octane.

[Rivet]

Originally Posted by JKarow08

Are you running those on pump gas? Twin plug? I'm not sure what the math works out to on a 3.0 but their 10.5:1 pistons in 84mm look to actually be 9.6-9.8:1, which looks to be a little too high for pump gas when you calculate the dynamic compression on the dc30 cams I'm planning on using.



I read someplace else that the balance was great, an entire set measured exactly the same.



Well hopefully I only have to assemble it once so I'll only have to swear at the clips 12 times



I understand squish, just not sure how much that varies and how that effects compression ratio. I'm trying my best, but full comprehension on all of these details still alludes me

Mine I have set at .030 squish, and measured to 10.25:1 with DC60 cams.

It is pump gas, twin plug coil on plug, and running full sequential on modern EFI with 45mm ITBs.

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[JKarow08]

Originally Posted by Rivet

Mine I have set at .030 squish, and measured to 10.25:1 with DC60 cams.

It is pump gas, twin plug coil on plug, and running full sequential on modern EFI with 45mm ITBs.

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I was considering going that high on the compression, originally planned on doing a 10+:1 2.5l "long stroke" build with 86mm jugs. After research and starting a thread on it, I've been convinced to keep it at 9.5:1 or less to avoid detonation issues on pump gas. It looks like the Wossners rated at 10:1 should be perfect since they are actually 9:1.

I'm going to run ITBs and COP as well, being able to run full sequential ignition controlled by a modern standalone with knock control should definitely reduce detonation, just not sure exactly how much extra compression it affords.

[Rivet]

Originally Posted by JKarow08

I was considering going that high on the compression, originally planned on doing a 10+:1 2.5l "long stroke" build with 86mm jugs. After research and starting a thread on it, I've been convinced to keep it at 9.5:1 or less to avoid detonation issues on pump gas. It looks like the Wossners rated at 10:1 should be perfect since they are actually 9:1.



I'm going to run ITBs and COP as well, being able to run full sequential ignition controlled by a modern standalone with knock control should definitely reduce detonation, just not sure exactly how much extra compression it affords.

This is an example of pump gas, 3.2 short stroke 10.5:1 confirmed compression, single plug ported heads, m1 cam, PMO carbs and 123 ignition I tuned on my dyno. Customer assembled and blueprinted the motor himself with some consultation on some details.

The key to making a package work is careful, detailed tuning. That it is the ultimate pro to modernized motorsports fuel injection, it affords the control needed. In this situation the control of the carbs and ignition was limited in comparison but good drivable and safe power was still found, if had been modern efi I could have kept peak power longer with less drastic power drop off and a smoother delivery of both torque and HP.



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[JKarow08]

Originally Posted by Rivet

This is an example of pump gas, 3.2 short stroke 10.5:1 confirmed compression, single plug ported heads, m1 cam, PMO carbs and 123 ignition I tuned on my dyno. Customer assembled and blueprinted the motor himself with some consultation on some details.

The key to making a package work is careful, detailed tuning. That it is the ultimate pro to modernized motorsports fuel injection, it affords the control needed. In this situation the control of the carbs and ignition was limited in comparison but good drivable and safe power was still found, if had been modern efi I could have kept peak power longer with less drastic power drop off and a smoother delivery of both torque and HP.



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Choices, choices...and so many conflicting opinions. Any idea what the dynamic compression on that motor is with m1 cams? The dc30 cams I'm planning on using are fairly mild so they definitely up the dynamic compression, not sure how the m1s compare. A very knowledgeable source on here indicated 8.35:1 dynamic compression is about the highest that is safe to run on pump gas.

I'd love to jump up to the 10.5:1 rated Wossners, looks like they actually make about 9.6-9.8:1, but I'm definitely concerned about detonation at that level, especially if I stay single plugged. It's a street motor, so I'm not sure the potential gains are worth the potential issues.