Corvair Boxer Build

[dieselgeek]

There are quite a few Corvair engines in amateur-built aircraft. You see them all over the place at Oshkosh, Sun-N-Fun events. So there is a community of people who build those engines out there...

I don't think They don't rev much past 3000 rpm in aircraft service

They don't rev them past about 2100rpm. Because prop tip speed can't exceed supersonic. And almost no one puts a gear drive on these engines. In this mode, they're good for 100-110hp. Which makes them very competitive with 100hp general aviation aircraft engines in power:weight. But guys are still having issues breaking cranks and other parts when bringing them up in power, so there is still plenty of development work going on that applies here IMO.

[Shaker455]

Back in the day I built quite a few CA 'performance' Corvairs out of 140s for roadracers & autocrossers. First step was to hacksaw the integral intake manifolds off and TIG-weld stubs on for 40IDA3c Porsche 3-bbl Webers. Then the exhaust tubes come out and you slant-mill the openings for slightly larger tubes that come in at an odd angle. This allows an exhaust tube with no notch to miss the pushrod tube. I used 1.25"OD u-bends so ground clearance was not an issue. A tuned-extractor exhaust & single turbo muffler had the same ground clearance as stock but much better flow. Next is to go over the whole head casting with a hammer & long screwdriver and clear all the flashing out for a tiny bit more cooling airflow. Also staked the intake seats and cut the step out of the combustion chamber. Used 327 Chevy oil pump gears with a recessed billet aluminum cap so the longer gears fit. A large external oil cooler replaced the stock cooler. Stainless roller rockers at the time were made for 110 heads with different valve angles. I ground the tip-rollers on an angle so they contacted 140 valve stem tips flat. Isky ground decent flat tappet cams at the time. Lock-tited setscrews in the cam gear & crank gear (half thread in the gears & half in the shafts) were necessary to keep the gears from moving and a spring-loaded idler pulley kept the fanbelt on. All this effort may have given us 180-200 real horses with 7000 rpm capability.

I built one street engine with Porsche 2-liter barrels but the crankcase locating spigot needed to be cut paper-thin and nearly all the cylinder fin sides cut away to fit. The Porsche head spigot was too shallow for 140 heads so that got trimmed too. Lots of trouble but otherwise the cylinder studs need to be relocated- like the sand-drag builders did that used cast iron sewer pipe for cylinders and BBC pistons for over 4 liters. Good luck with your build.

This is the kind of info I was looking for! tell me more!

[Shaker455]

jsgarage,
If I do a custom build that includes milling off and modifying the intake what heads are best to work with?
The 140hp heads?

[panic]

Re: "They go from 3.750" to 4.125" bore diameter"

That's the twin-cam barrels, the Evo (single cam) barrels are 3.000" to 3.498", in 2 different heights.

[Shaker455]

Thanks,
I got that info also from one of my Harley buddy's

I think my goal is to make over 200hp

10 to 10.7:1 CR
Nice solid roller
Reworked intake with a pair of my Custom Holley 500cfm 2-barrels
Abel to rev high

[wyrmrider]

start working a camgrinder like Mike Jones on some low lash designs
you do not need 1000 cfm
thick sturdy barrels and cases trump big bores with cut down fins or is this a drag only deal
new turbo designs are awesome...

[Alan Roehrich]

With modern technology, blueprinting, and good quality work, 200HP isn't terribly difficult. I don't think you even need a big bore kit, although cubic inches will make it much easier to make that much power, and it will be a better driver.

A well built 140HP engine with a modern camshaft, porting (including big exhaust tubes and headers), and a pair of good three barrel carburetors should do that without too much trouble. I'd certainly run a set of Corvair Connection (or similar) intake manifolds on a set of well built 140 heads with a set of Zenith 36 or 40 TIN carburetors before I'd fool with anything else.

Unless this is a max effort pure race project, I don't think I'd bother with a solid roller.

[Shaker455]

Yes, I need fins & I'm going to do oil as well as ducting more air cooling across cylinders.

This intended combo will be street/strip.

At this point I'd say 70/30 %...so mainly street nights @ NewEngland Dragway

[Shaker455]

Alan,
I want to have the ability to rev it high and I don't want hyd lifters to be my limiting factor.

I build Custom Holley's so a pair of 2-bbls is the plan but does not have to be 500's...

I have plenty of turbo car's and I don't want another.

I want to keep this simple & N/A

If you looked on that youtube vid I posted earlier, the guy who built a drag only 14:1 used a nice sheet metal fabbed intake with a pair of Holley's 500's.
https://www.youtube.com/watch?v=LnvV9EBe7uw

I want to have an intake system along those lines but I don't agree on the size of the balance tube.

Also, looking at his dyno pull & the huge drop in power indicates to me his valve spring was suffering from harmonics

So where do I look for this Underground intake??

I did see a spider type intake with a single Holley 4-bbl in middle.

I'm sure the runner length helps but not interested in that style at this point

[Alan Roehrich]

I wouldn't build a turbocharged engine for what you're doing anyway.

I don't really think the lifter type will be your RPM limiting factor. Once you get above 6500 RPM, you'll find that reliability problems and the cost to solve them will increase exponentially.

You can build it with mechanical flat tappets for a ton less than a custom billet and custom solid rollers.

That should have read "Corvair Connection" intake manifolds. Or you could step up to a set of Leveque manifolds, and the bigger Weber carburetors.

You're trying to make 200HP in the most difficult, labor intensive, and expensive manner. If that is your goal, fine. Solid roller cams and sheet metal intakes are far from simple, and not at all cost effective. you'll only see gains with them at the point where you'll start to experience serious reliability problems that will require expensive custom parts to solve.

[Shaker455]

I see, well I don't want to encounter those issues but I want to make great power.

I know that flat tappets loose power under the curve on v-8's so shying away from that.

Also, 200hp is a min I want to make....300hp would make me very happy but really not out to prove anything...HaHa!

And I'm really trying my best to keep the motor out of my back seat...if I end up racing to some degree that would change.

[Alan Roehrich]

It will run fine with flat tappets. For 200HP, you're only looking at around 1.25HP per cubic inch, the secret there is cylinder head flow, good intake and exhaust, and good blueprinting, you don't need exotic custom valvetrain.

Also, how do you plan to cool this thing if you plan on spinning it to the stratosphere? You do realize that keeping the belt on is going to be difficult at best. Even running moderately hard on the street, rapid RPM changes at the gear change will sling the belt off at higher RPM.

If you want to run a roller, you need to talk to Michael Leveque, and Ray at American Pi.

If you want to make 300HP normally aspirated, then you'll need the Mahle big bore VW kit, a set of heads from one of the guys mentioned above, and some serious aftermarket parts. You're looking at a $10K Corvair engine.

[Shaker455]

Yes no!...hah! not building a 10k motor.
I'm a machinist so I can do most of the fabs & mods.
I've heard a bit about the belt and did not Yanco cure that with a tensioner?

You did recommend to start with 140 heads right?

Is the difference simply the intake runner or is there changes to runners & combustion chambers?

What I'm getting at is it better to start with the more common 110 heads?

[Alan Roehrich]

The 140 heads have their own specific valve angle to allow for the larger valves. Starting with 110 heads for a normally aspirated engine would be an error. A great deal of power can be found in combustion chamber modernizing, modifying the intake side with the Corvair Connection or similar intake manifolds, and the correct installation of angled larger diameter exhaust tubes, and the appropriate porting.

No one has completely cured the belt toss problem, it still happens, it has been improved, but not cured.

You may be a machinist, but I doubt the guys who make the parts and perform the modifications for a living will tell you what you need to do. At that point, it becomes a trial and error process. Could be expensive and time consuming, especially if you have to hunt down extra parts.

[Shaker455]

Okay Thanks.
Are you a Corvair engine building guy?

I do have a very sharp guy in my corner, Lenny Caverly from who competed in EMC:
http://www.hotrod.com/how-to/engine/071 ... ine-build/

Looking at the 140 combustion chanber they look like they could use some modern upgrades like welding them up and CNC machining a fastburn style combustion chamber.

I do see what you mean about the valves and I' not sure if you saw that video and the guy says he moved the sparkplug location.

More than likely in a fastburn style and located it closer to the exhaust valve.

Has that already been done?

Who makes great aftermarket heads for these?

As for the belt, well every time I look at the set up I shake my head....I'm sure the fan & alt/gen can be sepperated or even make the fan electric...just an idea