The next piston option we are going to look at is one that doesn’t yet exist. That may sound funny, but it will give builders a look at how new options come about, and how we work to make parts that really serve builders needs and make sure they are carefully introduced.
If you do the math. a .060″ overbore (in motorhead jargon this is called “Sixty over”) on a Corvair produces an engine that is 2,775 cc. Pistons already exist in this displacement and we have built plenty of engines for aircraft using them. What is different? The piston I am proposing here is a baby brother to the 2,850 see in part #14. The primary difference is that the 2,850 requires the new Clark’s cylinders to get the .105″ overbore. the 2,775 cc would bring the advanced combustion shape to Corvair flight engines using stock core cylinders. We have actually been looking at details on this design for two and a half years.
In the last post I pointed out that the flat top pistons have a long service history in Corvair flight engines, but it isn’t the perfected design to compliment the combustion chamber in flight engines. If you don’t have a clear picture of the advantages, review part #14.
Just so every one stays on the same page, I am going to always call the flat top forged piston engine a “Sixty over” engine, and just refer to our dished piston engine as a “2,775 cc engine” even though they have the same displacement.
Any piston we would make would sell, however, I don’t base my decision to make products because they will sell, I base it on if they are a real definite improvement over what already exists and can be flight proven to be so. We flew this displacement as the initial engine size in our 601XL in 2004. There are advantages for people who choose to be able to run auto fuel with these pistons.
Who would go after building one of these 2,775’s? Good question. I visualize it as a maximum upgrade on a guy’s engine who is building on a very tight budget. The potential cost savings over a 2,850 is at best $400-$445, not a giant difference, but not pennies either. The engine would end up being 2 or 3 pounds lighter than a 2,850, but that isn’t a big issue.
The main issue is that we have builders approaching the Corvair build from two different angles: Often guys who are looking at 2,850s and 3,000s originally were looking at very expensive engines like Jab 3300s or a 912. To these guys, any Corvair is comparatively low-cost, and an extra $445 isn’t going to change that perspective one bit.
On the other hand, we have plenty of builders who are very carefully budgeting their engine because they were first looking at buying a ‘flymart’ A-65 for their Pietenpol or an O-200 without logs for their 601. They choose a Corvair because they know that it is far better to trust their own engine building and parts selection rather than relying on the naive belief that the inside of a uninspected engine “should be alright.” For these guys, $445 matters. If we can show these guys that there is a path for them to have the same advanced combustion characteristics in a slightly smaller displacement, then we are staying true to out goal of keeping the engine affordable and keeping our R&D in a position where it benefits most builders, not just the ones building engines on looser budget.
Piston and rod group (1300)
1300- Piston set with wrist pins
Our piston sets come with their own pins. Pistons would be set to use either standard Corvair rods or ones bushed for floating wrist pins.
1301- Ring set
1302- Connecting rods -6-
The rods here are standard rebuilt ones with ARP bolts. Clarks 9203ww rods end up costing the builder $261 after he sends in his cores.
Cylinder group (1400)
1400- Cylinders -6-
The Cylinders for a 2,775 cc engine would be rebored ones from your core engine. Again, Clark’s is your best bet, they have bored at least 20 sets of stock cylinders to .060″ for us over the years. After you mail in your cores, the final price on the exchange cylinders is about $150.
1401- Base gaskets -6-
The base gasket that I prefer for all Corvair engines is the all copper Clark’s part number C-1180. As a part number for an individual gasket, you will need to order six of them for a complete engine. We install them in the engines dry, with nothing on them. We built engines for many years with the stock steel gaskets, but they are less forgiving than copper base gaskets. A set of six is about $42.
1402- Head gasket set
For 1965 headed engines, the standard head gasket that we recommend is a .032” solid copper gasket. These are available from Clark’s, part number C-3946 The head gasket set is about $30.
The proposed total for the 2,775 cc Piston/rod cylinder combo is $1,505. We sell the 2,850 kit for $1,950.
That is a reasonable price to pay for a better piston that is designed from the very start to run on reasonable quality unleaded car gas without complaint nor re-tuning. The nominal HP rating of the engine would be 105 hp continuous. If it appeals to you, by all means, drop me a note and say so. But for now, let it just be a proposed place holder between standard and increased displacement engines.-ww