Are these Euro 3.2 pistons?

[Bobboloo]

Hi guys,

Can any of you tell which Carrera pistons these are? They are in an 87' Euro motor that has been "rebuilt" but I don't have the build sheet hence the question.

When I first got the car I noticed that I could here detonation when you put your foot in it so I immediately started adding race gas with each fill-up. Problem solved temporarily.

The motor had a big port CIS setup on it when I bought it but I have since gotten a Carrera EFI induction setup. I also bought a 964 twin-dizzy and splitter. So if these are Euro pistons I'm gonna have the heads tapped for twin plugs.

Question number two. Have you heard of any clearance problems with a twin plug and Euro pistons?

Thanks

[Flieger]

Those are definitely CIS pistons with the domes to promote swirling of the air/fuel mixture. With EFI, you should have better fuel atomization with higher pressure and I would think, therefore, that you could switch to a flat piston style You could also do an RSR style dome which fills the combustion chamber but has cutouts for valves and spark plugs and raises compression. The CIS and RSR pistons would tend to split the combustion chamber more with the domes and so the twin plugs would be especially necessary. With a flatter style, you may not need the twin ignition. I know RSR domes could have serious clearance issues and I think the CIS pistons would, as well, with their tall swirl domes.

[Bobboloo]

Don't believe they are CIS pretty sure they are EFI. The motor is an 87' Euro 3.2. To have converted this motor to use CIS pistons would have required modifying the rods to accept a different wrist pin size. Doesn't seem logical.

[tom1394racing]

Bobby

Those are the original 3.2 DME style pistons. It is very difficult to tell the difference between the Euro 10.3 CR pistons and the the USA 9.5 CR versions. visually they look identical.





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Both are marked 95P36 under the domes. The dome ht on the Euros is only slightly higher. I had to measure them with a handheld caliper to tell the difference. Check this post out for the measurements.

Help - Identifying 3.2 Carrera Pistons

I don't know of a way to differentiate them without removing them from the cylinders and measuring them.

[Bobboloo]

Thanks Tom!

[kenikh]

Actually they look similar, not identical, but your point is well taken. Almost impossible tell when not side by side. If you look closely at the Euro piston you can see the ridge of the swirl dome is set just a little further back (visually), giving away the higher dome of the piston. The height disparity is really given away in the 3rd pic.

[aigel]

You can calculate the actual compression ratio, if you measure (cc) the piston dome and the head volume. Voila! Much better than going with factory numbers anyway!

George

[Bobboloo]

Well it turns out my Euro motor has U.S. pistons. Sure would have been nice to have had the build sheet on this motor.
My guess is the detonation issue was probably dizzy curve.

It's still good to know there was no detonation damage to the P+C's or rings.

Anyway what to do now? Button her back up and stay single plug or go through with the twin-plugging and swap pistons.

The motor only has 10k. I think I'll probably just button up and install the OEM Motronic induction and dizzy. I mean what are we talking about here? 10HP to 15HP max between the two. Nothing wrong with a healthy stock 3.2, Wong chip and early exhaust.

Maybe down the road I'll go with ITB's, cams and then twin plug at that point.

[aigel]

Am I missing something? How did you determine that they are indeed US spec pistons?

George

[Bobboloo]

In Tom Butlers' last post he has a link to a previous thread where he measured U.S. and Euro pistons. Here's the measurements.

Originally Posted by tom1394racing

I measured from the the bottom base of the piston beneath the pin hole to the top of the dome using hand help digital calipers.

The Euro's gave an average of 64.66 mm with a max of 65.08 and a min of 64.45.

The USA's had an average of 63.41 mm with a max of 63.81 and a min of 63.26.

The variation is as much the crude measuring technique as it is variation in the pistons.

I used a cutoff of 64.00 mm to sort between the Euro's and USA's.

The first one I measured was 63.3 so I think it's safe to say they are U.S. They even look more like the U.S. ones in his post. Very similar but different.

[aigel]

Thanks for clarifying!

Cheers, George