Another engine theory Q - Blowers?

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rv6ejguy

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I see various folks here on several threads conjecturing on detonation being a big limitation on SI turbo engines. You really have to look what OEMs and racers are doing these days to see this isn't much of an issue. We have lots of OEM turbo engines outputting 125hp/L on 87 octane and some over 200hp/L on pump gas, some up to 250HP/L on E85. We see some race stuff at 500-900hp/L on better fuel.

As dwalker says, success here is all about proper ECU calibration.
 
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dwalker

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As noted, i'm not interested in turbo and the questions don't have to do with thermodynamic efficiency.
Well, thats where you are going wrong, a turbo would 100% solve your issue

A direct drive flat 4 VW engine can only swing small diameter propellers at typical cruise rpms of 3300 to 3600 rpm.
Dropping cruise rpm to 3000 would allow usefully more efficient propeller length for better TO & initial climb, but the HP drops some 20% for cruise at that rpm (2900 - 3,000). Stock/non-boosted torque does not drop much in that range, so another (modest) 15 - 25% from boost could be impressive.
The VW can only swing that small prop because of available torque. Turbos make torque. With proper sizing they make torque in impressively low power bands. This is simply a matter of some math and practical experience from a person with experience in turbo sizing.

Looking at it from the other end, a PSRU to go from 3600 cruise rpm engine to 3000 rpm prop seems like weight and complexity for the gain. Also, only Marcotte, of unknown continued availability puts the propshaft aproximately inline so engine location need not be compromised significantly in terms of streamlining.
I think a gear reduction setup like the Ross might help, and with modern CNC machining could be made to handle the 100hp or so, but I do not think the juice is worth the squeeze there. First s the weight. Second is the additional wear and heat the higher RPM brings in. Additional complexity is the last strike.

I like the reported cruise of my Sonerai 2 project in former owners' & guest pilots' hands.
I don't like the 52" prop and the "long" TO runs on hard pavement.
The engine has the HP & torque to do better; if the system were better.

IOW, choosing one-
controllable prop
PSRU
Mechanical boost - I don't see turbo adding much to TO without controllable prop.

smt
I am building a Dragonfly Mk2/3, which is traditionally powered by a VW. I did a LOT of research and made the determination that IF I go VW it would be an EFI turbo powerplant. Using a properly sized turbocharger and wastegate on an EFI 2380cc high compression build I would plan to use the additional power to allow for more prop without sacrificing takeoff performance or climb rate, which would be the only times the turbo would be needed. Using good charge cooling and engine cooling practices, a dry sump oil system with more capacity and efficient coolers along with water/alcohol injection would keep the service intervals the same as the non-turbo powerplant.

Right now I am planning the same strategy- turbo and all-using a Covair motor on the Dragonfly.
 

dwalker

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I should also note that I see the allure of the supercharger as a draw-through carburetor simple setup. I would never put such a setup on an aircraft myself. I know of a fellow using a draw through carb setup on a Corvair motor without an intercooler and so far he has been fine, but IMHO he is literally playing Russian Roulette with a loaded gun. At some point that engine is going to lean out under boost and a piston is going to burn, or a valve is going to drop. Been there, done that.
EFI is so simple and easy these days that it will be the least trouble of the entire project, and no reason not to use it.
 

wanttobuild

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dwalker
curious where and how you you will place the injector nozzle on the corvair head. would you share your thoughts on this matter?
 

dwalker

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dwalker
curious where and how you you will place the injector nozzle on the corvair head. would you share your thoughts on this matter?
Sure.
I am machining the cast in intake log for "port" injection.
Start by locating the injector as in line with the intake valve as possible/reasonable for each cylinder and using a 45deg angle I will drill a hole for the injector bung and TIG weld the injector bung in place. I will fabricate the fuel rails from aluminum fuel rail extrusion and weld whatever boss/standoffs needed to locate the fuel rails. As I will be bolting my intake elbow on per Mark Langford, I will be able to adjust the intake elbow as needed to allow for fuel rail clearance, as it is tight. I am using a throttle body post-turbo, with positioning to be adjusted according to other component placement.
With no long intake tube runs, carburetor hanging down, distributor and the coils mounted on the firewall- one per cylinder- there is a fair amount of available space if used carefully.
 

BRAAP

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Great information here, most of the input in regards to the compromises brought about in evaluating the various ways to achieve certain performance levels is spot on. 👍
Just my $.02, In regards to the original post about blowers, that has been covered here very well. In short, if specific RPM range with given displacement doesn’t yield the desired power level for the application, such as small displacement for size/weight/packaging reasons and spinning it faster and utilizing a PSRU to keep prop speed in check is not an option, forced induction will deliver, (forced induction can always be had with all those other enhancements for even greater gains😉.)
For most applications/missions including aircraft service where the power plant runs under high loads for extended periods vs sprint applications, turbo charger checks most of the boxes with only a little compromise, mostly for its superior efficiency in the energy consumed to produce the added HP it delivers. Super Chargers do have the advantage of usually being easier to package. Of the 2 major types, Positive Displacement and centrifugal, the Roots or Positive displacement is great at filling the cylinders at all RPM’s but at the compromise of elevated charge temperatures for given boost level, (high charge temps are undesirable for many reasons), and required HP to deliver desired HP gain at the prop, (net power). Centrifugal has comparable air charge heating as Turbo though at the expense of requiring more input power from the crank for given level of power output at the prop vs turbo, (takes out more tax in terms of power required if same impeller/housing used. The turbo will generate more available “net” power for given boost level on same power plant). Also the centrifugal boost curve isn’t linear and that nonlinear curve is “rpm” dependent for the S/C, Turbo is exhaust flow dependent which is a byproduct of load.

As an aside, as been mentioned a few times, there is no replacement for displacement, that adage still holds true today as it did in the 60’s, especially if max RPM is limited. Power levels for a given RPM and displacement, (torque output at a given RPM when built and tuned for max output), have increased a little since the old days but not substantially. Where it has increased is due to refinement in control and delivery means of air and fuel to the chamber, chamber design, and some reductions in induced internal frictions. The big gains were seeing in today’s automotive, ATV/snowmobile, etc, power plants at the production level is enhancements in the engines ability to breathe more efficiently at higher RPM’s, the finer control over the tune, fuel delivery etc, couple that with some of the advancements in materials used for critical components and the reliability/longevity is increased.

Regardless, for all my projects the first design criteria for the power plant is always choose as much displacement as can be had for a given weight/package for the application, then power adders after that such as boost or higher RPM with regearing for the desired output, (PSRU). If boost is required I would first try to incorporate a turbo. If a Turbo can’t be made to work/fit then would I look at centrifugal S/C or possibly higher engine RPM with a PSRU.

Thank you for letting me share my $.02, really enjoy following along these types of threads, lots of good valuable insight and experience being shared in this group.
 
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TFF

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It’s not meant to be derogatory, but it’s another how can I make a VW act like a A-65. Two engine with same range of horsepower but two different characteristics. 170 cubic inches beats 120 something. The Sonerai 2, in away, takes the brunt of this. The single seat had a purpose just like the F1 planes; you play against the rules. Open the rules up and the only rules imposed are ones arbitrarily added. Sonerai brand is VW, but the 2 seat really needs the muscle of a small Continental if there really is such a thing. The Corvair makes a really good A-65/80 replacement but pushed to the O-200 O-235 it’s huffing and puffing. An adjustable prop will definitely help ground runs, but it is an expensive solution and adds weight, plus do they really have a solution for a VW? Gearbox, do you have room for one? The cowl lines would not be close to the same. What is the mission of your Sonerai? The first question was very theoretical and that’s where the theoretical answers came from. You have a practical question, so specs are the only way. If speed is all you are after, you will get different answers than if a 50 mile radius sport plane. I think, I wouldn’t sweat the small prop if you are flying off of pavement. Short grass field in s different.
 

Tiger Tim

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On top of it all that’s a very elegant looking installation.

I recently took a look at some sort of Subaru with a home-brew PSRU and what a monster it was! Just a tangle of wires and plates and stand-offs and belts and hoses and...
 

dwalker

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On top of it all that’s a very elegant looking installation.

I recently took a look at some sort of Subaru with a home-brew PSRU and what a monster it was! Just a tangle of wires and plates and stand-offs and belts and hoses and...
Was it in a Cozy 4 using ViPeC ECU?
 

PMD

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The whole issue of supercharging with centrifugal blower to allow direct drive at best prop RPM was solved 80 years ago by simply flat rating takeoff power by limiting manifold pressure. My R-985s did that admirably well, and it is something that could work with an Eaton 45 on a VW - ESPECIALLY with EFI to flat rate it. Also flat rating can allow enough HP at start of takeoff roll to eliminate the need for constant speed prop making a nice tradeoff for the PRRU + heavy prop and governor. Of course the problem with doing this on a VW type I engine is cooling capacity - something easily improved by using a Type 4 engine instead.

Of course, you just KNOW I have been biting my tongue to point of that all of these things could be accomplished much easier with a 2 cycle diesel - AND allow use of better range of fuels.
 

slevair

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I should also note that I see the allure of the supercharger as a draw-through carburetor simple setup. I would never put such a setup on an aircraft myself. I know of a fellow using a draw through carb setup on a Corvair motor without an intercooler and so far he has been fine, but IMHO he is literally playing Russian Roulette with a loaded gun. At some point that engine is going to lean out under boost and a piston is going to burn, or a valve is going to drop. Been there, done that.
EFI is so simple and easy these days that it will be the least trouble of the entire project, and no reason not to use it.
Most sanctioning bodies in the vintage racing world don't allow any electronics of any sort. A few allow only hidden points replacement modules. Combine that with the historic aspect of it having to be of the type originally used. That really limits your options.
 

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dwalker

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Most sanctioning bodies in the vintage racing world don't allow any electronics of any sort. A few allow only hidden points replacement modules. Combine that with the historic aspect of it having to be of the type originally used. That really limits your options.

HSR and even SVRA do not care what electronics you use as long as they are not obvious. I personally installed Motec in a half a dozen 911 RSRs and 930s. If you are going for the concours judging then, sure, you want to keep it as original as possible.
But sure, ib has to deal with Weber and Solex and Zenith-Stromberg and even SU. When I retired for a short time I did mechanical restoration of old, unique cars, almost all carb'ed. I have tuned and serviced mechanical injection on various cars including the 935s. At one point I was the youngest person in the US that could service and tune the Bosch MFI used on the 935's, and I might still be.
But, EFI is far better and there is no reason to not use it where reliability and performance are the main concern.
 

dwalker

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935s are not what I call vintage even though they are cool to see. MGs and Elvas or Shelblys and Alfa GTAs are vintage racing.
935's are 70's racing cars. So are the S, R, RS, RSR and 934's. Huge fun all of them.

Neat factoid- other than where it was specifically not allowed by the rules, all factory Porsche race cars starting with the 911 were fuel injected in some form. I actually had a D Production 924 with the original mechanical fuel injection, which SCCA would not allow the use of in GT3, which is where the car landed after the SCCA did away with D Prod.

Still I did restore and maintain a few Elvas, Lotus, and a huge number of early Trans-Am/Can-Am cars from the 60's and 70's. I raced an MG Midget and Triumph Spitfire for a while with HSR and SCCA, and I miss my 510 Datsun almost daily.
 

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Hot Wings

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Of course, you just KNOW I have been biting my tongue to point of that all of these things could be accomplished much easier with a 2 cycle diesel - AND allow use of better range of fuels.
But until someone puts one in a sled, PWC, or a hybrid auto it is going to be a clean sheet/screen project. Our market just doesn't warrant the $$$s needed.
If you know of an in production base to start from I'd be interested.

//end thread drift
 

TFF

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I know the era. Although I get the 70s cars being vintage, it’s an era that mostly was Porsche. Porsche owners want to run their cars, I get it. To me 917 and before caps off what I want to be around. The good cars are too valuable to race, the slow cars don’t have enough ego. For a fast cool car it’s the 70s. I look at the lists of legal cars and my 80s GTV6 is there. The problem is filling the fields except at the big races. Local Porsche club will always show. 935 is high dollar for sure and they will be too valuable to race soon, unless the car market falls out.
 

dwalker

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I know the era. Although I get the 70s cars being vintage, it’s an era that mostly was Porsche. Porsche owners want to run their cars, I get it. To me 917 and before caps off what I want to be around. The good cars are too valuable to race, the slow cars don’t have enough ego. For a fast cool car it’s the 70s. I look at the lists of legal cars and my 80s GTV6 is there. The problem is filling the fields except at the big races. Local Porsche club will always show. 935 is high dollar for sure and they will be too valuable to race soon, unless the car market falls out.

The 935 was too valuable to race back in 98-2001ish when I was most involved with them. The distributor cap was $5000- yes FIVE THOUSAND dollars if you could find one. The titanium axles and spool were.. more. A 935 motor back then was $80,000 as a long block. Add turbos, the proper intercooler and fan/alternator, turbos and exhausts and you could buy an Ferrari off the lot new. The bodywork, which there are very few actual molds left for, so if you want "the real deal" you have to work with those guys- is made per order and is less expensive than the parts but still more than a new Hyundai.

In 99 at the Walter Mitty Hystericals at Road Atlanta the owner of the blue and white 935- which is a real Dave Klym/Fabcar K3- wrecked in in the 10A-B complex. He did $60,000 in damage. We could not get it done fast enough for him to "make the event" at VIR, so he bought the Ex-Danny Ongias BP 935 for $180,000. At VIR he blew the engine, with a titanium rod coming detached from the piston and then making a valiant attempt to saw the engine case in half. The oil caught fire, but no real damage done. About $200,000 later, he had both cars back up and running and we did Sebring and Daytona. In vintage racing. Where there is no real point in winning.
The first and third pictures are random 935 pictures, the middle pic is a 934/935 where the intercooler was mounted over the engine instead of where the back seat should be, as required by some rules
 

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