Well guys its been a busy last few months.
I've pulled the aluminum engine from my car and found a couple of interesting things. Cylinder #4 is slightly marred on the intake side, all 5 piston tops show signs of higher heat on the intake side of the engine (close to the intake valves). Piston #4 burnt through on the intake side. No signs of Knock or detonation. Just running hot. The Cylinder head looks normal with all valves nice and black.

Here is some surprising numbers. The pistons have a bore of 79.48 mm which is normal for a Sport Quattro which has a bore of 79.5mm; however, the engine block has a bore of about 80.7mm which means its been honed. AAN and 3B pistons which have a bore of 80.98 will not fit into the engine. Thats fine, but I'm not sure why they (the original builders) would use pistons which are now way too small for that bore. The other cylinders are near perfect in straightness. So With almost 1/2 a mm on the sides of the pistons I would almost certainly have considerable piston slap and blowby and I am wondering with the tilt of the engine (leaning to the exhaust side) if this played a part in its demise.

There is also the shape if the pistons which because of their smaller bore creates almost a knife edge where the intake valve reliefs are cut in. This knife edge on either side is where the burn through occured so I am thinking this is a classic hot spot with alot of surface area with very little mass. All 5 pistons show signs of this being very hot (white in color) and in some cases have melted away slightly to remove the knife edge, while the same 5 pistons look completely normal on the exhaust side. So clearly the evidence indicates the pistons on the intake side were getting red hot to the point of melting. This could be possible from the knife edge or the piston slap.

So thats the bad news, the original engine lower appears to have had some pre-existing issues. I didn't really look closely at it back on the first tear down as I put faith in the original builders. Either way, it was way messed up based on the piston clearances alone. That explains some of the extremes I had to go through for oil blowby, etc.

Good news, the shortblock is at a very reputable race engine shop here in Texas that has been building competition engines from the mid 70s. Their latest engine is a V8 Porsche engine for the 24hrs at Daytona. So the block will be resleeved to a bore of 79.5mm. I am ordering a set of forged custom pistons with a CR of 8.5 and a milled top which will not have any hotspots. I also plan to replace the Sport Quattro rods with Titanium rods while Im in there.

In the interim, I have a 3b block and head which will go into the car while I convert and upgrade the race engine. Waiting for a early style pilot bearing so I can put it back in the car.

Someone obviously bored out the engine, but didn't order custom pistons.

I took the engine to Lozano Brothers (LBP) in Cibolo TX.
They do engines for GTP, Trans AM, Nascar, Can Am, Indy, Camel Light, and ARCA racing, Rolex.
Much experience with aluminum racing engines and sleeves.

James;
I think this is typo error"leaning to the intake side)" - should be exhaust ???
Sorry you find out this things - how about cooling on intake side. You have this adapter plate beetwen intaka manifold and cylinder head.
Remember that this Sport Quattro intake manifold is visualy very nice but fubctionally
almos cost Dr. Fritz Indra his job. Perhaps there is no cooling there.

Cast iron sleves or AL? There are places which can build up with AL and than coat with Nicasil or Alusil.

They run to the top of the deck so they're pressed in.

Leaning on Exhaust side, that leaves alot of the intake piston side exposed given the slop in the cylinder. More exposure could equate to greater temperatures in the piston.

Do you think this type of repair will solve your overheating problem ? Lowering CR to such low level ??? Rally car need to have wide power band, what about bottom end drivebility?
Iron sleves nicasil coated - this sounds strange. After pressing in they will colapse few .0010" and must/should be honned to keep
clerance beetwen piston and bore. Thickness of nickasil is usualy no more than 5 microns, something is missing here James. Just my 5 pennies.

I have no issues with that CR works fine.

Engine didn't overheat, but I'm not limiting the rework to this repair. The engine didn't ping, so I am going to look at everything across the board. Fueling was in the 12.2 according to the wideband. Timing was very similar to a non-aggressive AAN timing scheme. there are always 1 or 2 cylinders which will run hotter than others so I am going to retune to those cylinders; however, Cylinder head and valves look normal. Just the pistons are off so I think I will start there as I found a build problem in the engine. What I'm saying is that there were no warning signs at all prior to the melt, and I have found a build quality issue on the bottom end which is very wrong. So I will start there and for now I think that is the biggest culprit. I am going to run the 3B engine for about a year and push that really hard and then diagnose that seperately.

Regarding the sleeves, I will know more when LBP looks at the engine in detail. Their initial visual assessment is that the cylinders are nicasil coated and had been honed. Im not sure what you're missing. My engines bore should be 79.5mm and its closer to 80.7mm which means someone bored the **** out of it. Im not really sure why, but either way, It logical to return it to 79.5mm so the sleeves are thicker and then get custom pistons made as Im not happy with the Sport Quattro pistons as they clearly have a hot spot in the design which is not present on the 3B and AAN pistons which have the edge of the piston where the intake valve cutoff milled away so its flat with no ridges.

The cutouts that is? Minus the stuffer area of course.

<img src="http://wetzelsracing.com/images/piston1sm.jpg">

since it needed it and they didn't or couldn't have it done "properly". An 80% repair.

But don't discount Audi design quirks. Everything was done for a reason. Sometimes we can't figure out the reason, but here was a reason.

I look at mine all the time and just say...huh?

<center><img src="http://www.bufkinengineering.com/piston.JPG"></center><p>The hotspot is the knife edge right along the edge of the piston. Seems to have gotten very hot right there on each piston.

I thought about it and perhaps it could be temperature expansion, but the gaps is just too big for that.

Mine are just higher compression as reflected in the raised stuffer, Your pistons are dished out to make yours 8.5 and mine are just taller. But the cutouts for the edges for the valves are pretty much the same.

Look at where the valve cutout diminishes on the edge, your pistons have this knife edge ground down at a bevel to remove the hot spot. Its a good design.

My pistons have the edge which is very sharp resulting in a hotspot. It seems Audi removed this edge on all their later piston designs and rightly so. My pistons are not a good design.

And if you look closely, you can see in my picture the front piston actually already shows signs of melting! This was before I did any work to the engine. I didn't even notice it.

That sliver makes a bad area with high surface area with little mass. Hot Spot.

<img src="http://www.bufkinengineering.com/piston1sm.jpg">


<img src="http://www.bufkinengineering.com/pistonSQ.JPG">

they're lighter. The main issue with them appears to be the sliver which was cut away on all later 20V piston designs. Obviously this is a fault in the original Sport Quattro piston design.

They're Kolb racing pistons, not Audi at all.

You see the extra relief cuts that are present on all the later pistons to remove the hotspot? The SQ pistons are the first 20V pistons Audi made. They obviously learned something between when the SQ pistons were made and the later style were produced. That is my point.

<center><img src="http://pictureposter.audiworld.com/84174/sppicture1croppedsmall.jpg"></center><p>James:
Hot spots frequently occur where knife edges exist, as you already know. I used the recommendation of Fred Apgar, a well-known Porsche race engine builder, to approach Swain Coatings, of NY, to have my engine coated in critical exhaust areas. Piston crowns, exhaust valves, ports, manifolds. Fred said to expect a significant reduction in oil temps as their turbo Air-cooled Porsches were able to run more boost with cooler piston temps, with oil temps going down.

I found my engine still had high oil temps on the track 270-280 degrees on a hot 90degree day. We installed a large 12.5" oil cooler where the Aux water rad was and it lowered oil temps 60 degrees!

You might want to investigate Swain. Good reading your post, I just do not come here often.

Phil