Boring out a 2.7

[DohertyCM]

Has anyone ever heard of "boring out" a 2.7 motor up to a 3.0 or a 2.9...???
Heck just boring out period...like you would a chevy or ford motor?

Someone mentioned this in a conversation, and I couldnt believe it.

Give me some feedback here please..

[Flieger]

You have to bore the spigots where the cylinders fit into the case to make a <2.7 liter into a 2.7 or greater. Other than that, I have not heard of actually boring cylinders other than honing to remove scratches.

[911TT33]

Depends how thick the barrels are.

95mm barrels have been bored out to 98mm for a 200cc increase many times... 3.2 to 3.4L.

Once bored, it would have to be replated in nikasil. Been done many times, just not sure if done on a 2.7.

Ask EBS Racing.

[DohertyCM]

Is this common?

This is the first I have heard of it.

EBS does the boring?


Interesting....

[Walt Fricke]

The 2.7 case has been used with 91, 92, and 93mm cylinder bores. The 92s Mahle made for Porsche for the 2.8 RSR motors. The others I don't know, other than that SCCA allowed a 1mm overbore (left over from earlier days when that was standard for extending engine life rather than increasing displacement).

I think all these inolved the same spigot diameter. With the 2.7 there isn't much room left for boring a spigot larger - the head studs are so close as it is that they tend to push some material toward the spigot as they are stressed. This just means that the spigot part of the cylinders gets thinner and thinner. Anderson also lists 92.8mm for a 935 turbo (there is squeezing things to the limit of something!).

Of course, you can't make pistons wider, so any of this requires all new pistons. Compared with 10 or 15 years ago, getting custom piston sizes is a lot less expnsive than it used to be, and aftermarket pistons seem to have begun to approach Mahle is serviceability.

There are outfits (U.S. Chrome in Wisconsin is one) which will bore and nikasil to your specifications. I had this done on my 95mm Alusil cylinders to return them to standard and Nikasil.

But I'd have to say this is not really common. It is a racing thing. It is cheaper to buy a 3.0 or 3.2 engine than it is to boost a 2.7 this way, I think. With V8s you overbore to be able to keep the crankcase. Here you are just looking at the Ps and Cs.

[Bobboloo]

Walt is correct. The spigot size remains the same when increasing a 2.7L to a 2.8 or 2.9. The unfortunate aspect of this however is thinner cylinder walls so there are draw backs. Specially in the case of the 2.9 conversion. Even with the 2.8 conversion it's best to use a cylinder that doesn't have a CE ring so that rules out starting with a 2.7 cylinder and boring it out. That means new P+C's.

I think your best bet for more displacement beyond 2.7 is to start with a larger 3.0, 3.2 etc. motor. Cheaper and stronger.

[HawgRyder]

The main problem is the head stud gap size.
2.0 - 2.7 L have the same stud spacing....for the 3.0 and above the spacing is different...so an overbore (of the case) eventually runs into the stud and that diameter becomes the biggest you can go and still be able to bolt the cylinder down (with the stud having any grip on the case).
Bob