# What would these choices result in?

Discussion in 'Corvair' started by geosnooker2000, Apr 10, 2019.

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1. Apr 10, 2019

### geosnooker2000

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Starting with a 120Hp version (3000cc), going 60 over-bore, stroker crank from Mr. Clapp, add turbo-normalizing, EFI, and an ECM.

ETA: refinement of question, what would be the resultant engine weight and the resultant HP?
(assume WW is accurate about the 3000cc with standard carb setup @ 220lbs wet and ready to fly)

Imma see how long this takes...

Last edited: Apr 10, 2019
2. Apr 10, 2019

### don january

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You would end up with a strong Corvair engine with no hopes of getting a new set of cases at this time. I worry how the crank bearing journals will hold up under those mods. Don't forget to add 5th bearing mod

3. Apr 11, 2019

### geosnooker2000

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What do you mean by "with no hopes of getting a new set of cases at this time."? By cases do you mean engine block? They are all over the internet if that's what you mean.

Agreed about the 5th bearing (how much extra weight? I guess I could look that up @ flycorvair site). On the bearing journals, didn't the same car come in a 180HP version with the same block?

Last edited: Apr 11, 2019
4. Apr 11, 2019

### don january

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Cases is the block half's and yes there is many used ones on the net but a new set fresh out of the factory is a impossibility. If I was in need of an engine in that weight class and Hp I'd look closer at the 2.5 Subaru. Case half's and all other parts can be bought new with zero wear same can not be said about the Corvair rather a 145 ci or 164 ci which is the same case with mild mods to fit the 164 crank into the 145 case and that mod weakens the case wall near were the rod bolts rotate near the case wall. Like other auto conversions there is PRO and Cons that should be researched intensively before going Corvair or any other type. IMO

5. Apr 11, 2019

### TFF

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Ok, first apples to apples. A 120 hp Corvair at 183 CI is being pushed harder than Lycoming or Continental push the same size engine. That engine would be around 90-100 hp target if it was one of the aircraft engines. The 120hp is legitimate but how it’s delivered is what counts. Smaller propeller. That is where it turns into an orange. A Continental O-200 on a C-150 is turning a 69” prop 100 hp. That engine is also used if a single seat racing planes and that engine makes about 130-140 hp. How? 36” prop. They turn the engine 4000 rpm instead 2500. Racing engine they don’t care if it blows up if they win. They sacrificed life for performance. At best direct drive you can’t turn a prop with any reasonable diameter 3000 rpm. So with fancy parts you can make 180 hp no problem, but it will be at 4500-5000 rpm. You can’t restrain the rpm if you want the horsepower. So now to get the prop back down to 2500-3000 rpm, you have to have a gearbox. The option is 180 hp direct drive, cubic inches, or 180 hp high rpm with gearbox. Parts don’t make magic horsepower.

6. Apr 11, 2019

### geosnooker2000

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That's what I'm doing right now. I'm asking questions of people that know more than I. I appreciate all the responses. What I was hoping for was something along the lines of...
"You will gain 25% hp for every 5 lbs of turbo boost (or whatever the rule of thumb is), but you have to counter that with the extra weight of the 5th bearing, and the reactionary added weight on the other side of the center of gravity to compensate, + the weight of the turbo components and the weight of the ECM equipment, minus the weight of the distributor you no longer need, blah blah blah, etc. the stroker crank will [get you X more HP/do you no good because it only works when unicorns fly on the second Thursday of the month] and Bill Clapp's stroker crank design has been used X number of times to X amount of success/failure."

TTF made some good points. I would counter with: What I'm trying to find out is, can a Corvair be modified with known parts such that yes, it produces 180Hp @ 5200rpm.... SO THAT it can deliver the 140Hp or there abouts that I suspect will be needed @ roughly 3000rpm. That seems to me to be the name of the game. I don't want to run an aircraft engine at 5200rpm. IOW, if you build a supercharged souped up engine, but only run it at 57% throttle to get to the power you need and can use.

Last edited: Apr 11, 2019
7. Apr 11, 2019

### rv6ejguy

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Of course you can get 140hp at 3000 rpm turbocharged. Use a 3L and run about 40 inches. The weight creeps up into the 225-230 lb. range however.

8. Apr 11, 2019

### TFF

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It is possible for sure, but not on a budget. A Corvair running 40” is in for a lot of problems that have to be developed out. It can be done but it will require either talent or dollars; more like both. It’s not going to be a $5000 engine;$25,000 is more like it. And you might have to do it multiple times. It’s where it’s hard to beat the lazy reliable horsepower of a Lycoming. A turbo Corvair is going to be a race car engine probably with a race car lifespan. I would go back to the Subaru. It’s not going to be cheaper, but being water cooled, it’s easier to keep it together. But at the expense of complicated. If all this was easy it would be the the norm not the exception.

Porsche teamed up with Mooney to put an aircooled 911 engine in airplanes. A 911 engine is very reliable. There are ones with 300,000 miles. Designed to go 120 mph everyday on the commute. The airplane engine was a certified engine. One of the most fastidious engineering companies. Porsche and Mooney had to eat it. Those engines were such a big problem that Porsche was paying to swap in the Continental engines and have tried to erase that history. There are only one or two still around just because the owners want to be special more than have a reliable airplane.

I think the best combo for you, first airplane out is a Sonex with a Corvair. Been done and works. It does not check all the boxes, but it can be done successfully with the type of budgets you want to stay within budget.

The dream of cheap high horsepower auto engine does not exist without your own personal machine shop. Probably the cheapest is a new Corvette motor and it goes down from there. More odd the combo the bigger bucks it’s going to be. Reliable , powerful, cheap; you can pick two. You can’t afford three with any engine. Even Lycoming and Continental acknowledges that metric.

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9. Apr 11, 2019

### wsimpso1

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Working from straightforward concepts.

Engines are air pumps. Run the ideal amount of gasoline in a quantity of air per unit time, and a certain amount of work can be done. To do more work, you must move more air and fuel. You can make the cylinders bigger or cycle the cylinders faster or cram more air into each cylinder.

In normally aspirated gasoline piston engines, at the best place on the rpm curve for scavenging the combustion chamber, you will make about one foot-pound of torque per cubic inch. Torque will be lower at higher and lower rpm than at that best place. Run boost and it is the equivalent of running bigger cylinders.

Power is torque at speed. In Imperial units, torque (in ft-lb) time rpm/5252 is the horsepower. Just getting more power may not be much use if it is at much higher rpm.

So, if you add 0.060 over bore, the displacement goes up, and your peak torque, if it can be made to breath as well as before enlarging the bore, should go up pretty much linearly with increased displacement.

Same goes for the stroker crank in that it makes the displacement bigger. If you can make it breath as efficiently and turn as fast as with the standard crank, torque and power can increase linearly with the displacement. Usually, the increased stroke will drive the torque curve lower along the rpm band (greater energy sucked up accelerating the pistons up and down), which can be a good thing if you are trying to turn a prop - you can increase prop diameter and get better efficiency from it.

If the induction and/or exhaust system becomes the choke point for moving air, your peak torque may not increase much, and may occur at lower rpm, resulting in about the same power.

But all of this "breathing the same" and being able to spin at the same rpms, becomes moot if you can increase the density of the air being ingested. Turbochargers do this. If you put more air through the engine, torque will usually go with manifold pressure. Now the question becomes "will the pistons, connecting rods, crankshaft, and associated bearings hold together through all of that? I do not know how much manifold pressure any given Corvair engine will stand.

Going through an example... 183 in^3 is about 183 ft-lb of torque. If it makes that at 3000 rpm, that is 183*3000/5252 = 104 hp in normally aspirated form. Boost to 40" is 104*40/29.92 = 139 hp. Hmm. Looks like Ross and I do the same math, as he estimated 140 hp.

Have fun with your numbers, but remember that the entire think has to hold together at whatever power you get...

Billski

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10. Apr 11, 2019

### geosnooker2000

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When you guys say "boost to 40", am I correct in assuming you are referring to boosting to 40in barometric pressure or something like that as opposed to, boosting in PSI? That term has got me confused. I've only heard of turbo chargers being described as, for example, 5 lb of boost, or some similar.

11. Apr 11, 2019

### akwrencher

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That
That would be the reading on the MAP gauge typically seen in aircraft. 40" is about 10" ish above atmospheric. In inches of mercury. Boost gauges in psi would be more common on cars, as they typically don't have manifold pressure gauges. (MAP sensors, but feed strait to computer)

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12. Apr 11, 2019

### rv6ejguy

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In the aviation world, we express manifold pressure in inches Absolute. 30 inches is atmospheric pressure. 40 inches is about 5 psi boost at sea level. To calculate roughly: 40-30=10 divide that by 2 for psi.

Piston blowdown during the intake stroke on turbo engines contributes to reduce pumping losses so we usually find on a properly turbocharged engine with well matched compressur and turbine sections and good intercooler, we get more than the straight gains from manifold pressure increases would suggest. I've seen a 90% increase in power on some 4 valve engines with only a 50% increase in manifold pressure.

Can you dissipate the heat from the extra power?

Secondly, without a background in turbocharging, I'd recommend you don't attempt this. This is a whole complex field in itself, especially with regards to aircraft. I've seen lots of folks do this all wrong over the years and end up with broken engines and turbos or poor performance.

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13. Apr 11, 2019

### geosnooker2000

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Oh, I wouldn't be doing this myself. I would be enlisting the help of a couple of good mechanic friends, and actually conducting endurance testing, combined with a self-imposed foreshortened maintenance and overhaul schedule.

14. Apr 11, 2019

### wsimpso1

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In airplanes, it is customary to talk manifold pressure in inches of mercury, abbreviated "In Hg". Standard atmospheric pressure is 29.92 In Hg. 29.92 In Hg is about 14.7 psi. So 2 In Hg is about 1 psi, and 40" In Hg is about 5 psi of boost...

15. Apr 11, 2019

### wsimpso1

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I knew of the effect, but did not know that it could be so large. In production cars, so many other factors interfere. I do know that the need for fuel economy, emissions, and the desire for quick throttle response and significant boost at low rpm does result in some awful turbo matching at high power - is that a major source of my not seeing the reduction in pumping losses show up in power output?

Billski

16. Apr 12, 2019

### rv6ejguy

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Yes, turbine and compressor sizing in cars is usually tilted towards the low end and mid range. The turbos are usually poorly matched for top end power and choke off the breathing in and out of the engine up high. Fortunately, we don't care about throttle response or low end power on most aircraft so we can size things to be far more efficient in the operating range which is usually very narrow in aircraft.

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17. Apr 12, 2019

### pictsidhe

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Cooling is going to be the big issue. If you are adding a turbo, I'd forgo the 060 in favour of the minimum to clean up the cylinders and add another half inch of boost instead. It'll be stronger and will distort less.
A turbo Subaru would likely be a better starting point if you want > 100hp.

18. Apr 13, 2019

### TFF

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I agree on not boring it. You need the wall thickness more than displacement with a turbo. Water cooled engines are much easier to tame with a turbo.

19. Apr 13, 2019

### geosnooker2000

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Actually, I have found an alternative to boring. 94mm VW cylinders.
94mm cylinders
new billet .25 stroker crank
ECM with EFI
no turbo
5th bearing
Whatever that yields.
I'm guessing around 125hp @ 3000rpm.
roughly 68" warp drive prop.

20. Apr 13, 2019

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