Abarth forged piston thermal expansion information needed

Competition engines and ancillaries - general discussion
tmvolumex
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Abarth forged piston thermal expansion information needed

Post by tmvolumex »

Guy,
Years ago, I bought a set of forged Abarth pistons for a supercharged 16 valve, 2 liter, Fiat / Lancia engine. Since then I have been collecting the rest of the parts required to build the engine. One thing I don¢ž¢t know is the recommended piston to cylinder clearance for these pistons. I also do not know which aluminum alloy Abarth used for their pistons. Do you happen to have that information? Do you think I can heat the pistons in an oven, measure the thermal expansion amount at an elevated temperature and use that information to arrive at a piston to cylinder clearance?
Tom McGaffigan
Fahrell
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Post by Fahrell »

When we use forged pistons in turbo engines here in brazil, normally we use more clearance than usual, I use 0,09mm in my car (but I use the original cast piston from the turbo engine), but have heard of people using 0,1 or more... if you use knock sensor, maybe a too wide clearance can confuse the sensor, if the piston doesn't expand properly, making metallic noise...
Andr’‚© Farkatt
Guy Croft
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Post by Guy Croft »

Tom, is the bore or piston size not stamped on the crown?

They will be Mondial if for Abarth and thus only made for a nominal bore of 84mm, 84.4, 84.6mm unless a big bore set at 85 or 86mm.

Check it out or measure across skirt at gauge height with a micrometer, they will be 0.04 -0.06mm or so under one of those nominal bore sizes.

GC
tmvolumex
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Abarth forged piston to cylinder wall clearance info needed

Post by tmvolumex »

My question relates more to the different aluminum alloys used in the forgings and the corresponding difference in the thermal expansion of the piston when hot. I know that different manufacturers use different aluminum alloys with different thermal expansion coefficient values and thus specify different values for piston to cylinder clearances, for a given bore size. Since I don¢ž¢t know what aluminum alloy was used, in the Abarth forged pistons, I am still trying to determine what piston to cylinder clearance to use. The pistons are 84 mm standard bore size. From what I can find on the internet, a variation of up to 15% in the thermal expansion coefficient between alloys is possible between the alloys commonly used for forged pistons. I will be using these pistons in a supercharged engine running up to 10lbs of boost.
Tom McGaffigan
petert
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Re: Abarth forged piston to cylinder wall clearance info nee

Post by petert »

tmvolumex wrote: From what I can find on the internet, a variation of up to 15% in the thermal expansion coefficient between alloys is possible between the alloys commonly used for forged pistons.
That's correct, there is a difference between hyper and hypo eutectic alloys. I think it's the latter that need less clearance. You should be able to tell by the colour of the metal. If in doubt, I'd run them at 0.0035".
Guy Croft
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Post by Guy Croft »

Tom


measure the skirt width - I think you will find they are 'sized' for 84.00mm bore, not actually 84mm ie: your pistons will be smaller than 84mm by the amount of running clearance.
Abarth pistons were, in my experience, mostly made by Mondial, there will be a little logo under the crown. I have no idea of the exact material forging alloy used by them.

GC
tmvolumex
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Abarth forged pistons and piston to cylinder wall clearance

Post by tmvolumex »

Guy,
I took a look at my forged pistons and indeed their is a small M in a circle forged in the piston, under the crown. The pistons are also marked on the top 84.0 and are also marked B. I also compared them to a photo on your site and they are identical to ones that you labeled "037 works pistons". They are flat tops with two very small valve cutouts on one side (they are for a 16 valve engine). The nature of my question was how much piston to cylinder wall clearance to run with these pistons. From doing some research on the net it seems forged piston to cylinder wall clearance is dictated more from piston design and application than the aluminum alloy used to make them. If it is a boosted application, you run more clearance the higher the boost. I intend to run around 10 lbs of boost, from a nonintercooled Volumetrico supercharger.
Thanks,
Tom McGaffigan
Guy Croft
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Post by Guy Croft »

Tom, OK, thanks.

Go with 0.08mm (3 thou") skirt to bore clearance, OK? They could be class B so just measure them.
I have a set as you rightly say and they are for 84mm bore and stamped piston size is 83.92mm.

You could run them looser, say 0.10mm but - watch the ring gaps as they increase by 3 thou" per 1 thou" in bore diameter, ie: roughly 3 times (pi).

In all likelihood those Mondials are made something like RR58 low expansion forging alloy, I don't know of anyone using high expansion in Europe.

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tmvolumex
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Abarth forged pistons and piston to cylinder wall, rings

Post by tmvolumex »

Guy,
Thanks for the information. Do you know if the Lancia 037 Stradle and the works rally car engines both used these same pistons?
In addition, I am not sure I have the right size ring set for these pistons. The ring set is not marked and the rings were not boxed with the pistons. The rings are very thin as you know. What is your recommendation on ring thickness for a supercharged, street / track engine? The thin rings I assume are to prevent ring flutter at high RPM. The Abarth competition VX engines were revved to 8,500 RPM, I don¢ž¢t plan on going that high. Can / should I get these pistons regrooved for wider rings? Do you have a ring material and manufacturer recommendation? I have used Deves rings on my all my engines in the past, both NA and supercharged, and have had good luck.
Thanks,
Tom McGaffigan
Guy Croft
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Post by Guy Croft »

Tom, hi

criteria:

1. Rings must be of a size to suit the bore and give typically on 84mm bore 14-16 thou end gap. More = power loss and blowby/oil.
2. Rings must be of a thickness that suits the ring groove and gives say 1-2 thou side clearance. 1.5 thou is good, 3 thou is rather too loose.
3. Rings must be of a radial width that the ring outer face does not protrude beyond the skirt.

Thin rings are great, I'd want steel or ductile iron top ones of course/ coated/plated.

I would not be for machining the grooves unless I had to and then it would be only the top face that I'd do, not the lower.

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tmvolumex
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Piston ring information

Post by tmvolumex »

Guy,
Thanks for the information on the rings. I will give it a go.
Tom McGaffigan
Greenwood037
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Abarth 8v pistons?

Post by Greenwood037 »

Did Abarth ever race that 8v head? I have a set of forged 8v mondial high compression pistons. No one, that I have talked to, knows of anyone ever selling forged mondail pistons. Does anyone have any pictures of what the pistons looked like?

Thanks,
Jason Greenwood
http://www.ferrarikillers.com
Guy Croft
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Post by Guy Croft »

Sure Mondial in Italy used to make and sell forged pistons, all the Abarth works cars had them. I bought quite a few HC pistons from them years ago. They belong to Mahle since dunno, 90's and I have no idea whether they do things like that now.

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Greenwood037
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Post by Greenwood037 »

Is there any way to tell if I have Abarth Mondial pistons, or just Mondial pistons?

Jason Greenwood
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Guy Croft
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Post by Guy Croft »

No and it really makes no difference.
As far as I know, Abarth bought only Mondial. And they would, wouldn't they, having such a first-rate supplier on their doorstep. Mondial designed for them to order, I have some old blueprints, that's how I know.

GC
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