Turbo 4cyl build thoughts

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Hot Wings

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This, from the 1950s ....
Subaru did it a bit differently:

"The original Legacy speed record was set between January 2 and January 21, 1989, with three Japanese-spec turbocharged RS sedans at the Arizona Test Center outside of Phoenix, Arizona. It broke the 100,000 km FIA World Land Endurance Record by maintaining an average speed of 138.780 mph (223.345 km/h) for 447 hours, 44 minutes and 9.887 seconds, or 18.5 days. Pit stops were made every two hours with a driver change and refueling, while tire changes were made at 96‑hour intervals, or every 13,400 miles (21,600 km) driven"



Wish it had English subtitles. :(
 

AdrianS

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I've worked for Toyota on a dyno used by their QA department.
The test included 40 hours WOT at peak power revs, and some savage temperature cycles.
It's always cooling and vibration that cause problems.
 

pictsidhe

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Yeah, nah.

The belief that bespoke plane engines have magical pistons, conrods and crankshafts, and are the only type that can run all day at "75%", is , as the word "magical" suggests already, is just fairy tales.

The auto-conversion issues are commonly with PSRU failure, PSRU causation, or poor ancillary adaption by amateurs, but nothing to do with the core engine itself.

You can not offer evidence of multiple and consistent failure of major core auto engine components because they just don't exist.

I still don't understand why aviation people want to continually damage their own hobby by shunning rather than encouraging viable, economical options.

This, from the 1950s ....
Not my point Cheapie. My point was that after boosting power/torque substantially above the manufacturer levels, THEN you are likely into a big R&D effort to make it reliable again. Manaufacturers are building to weight and cost, they don't overbuild much past what is needed for reliability as that would be excess cost and weight. I completely agree that the stock engines are built to take full throttle for many, many hours. There are also many successful auto conversions flying. But I don't know of any with substantial tuning about stock power/torque done. The sensible guys get a high power version and avionise it. A turbo or supercharged engine is the sane base for an a turbo aero engine. The hottest version of the 1.6 in my car puts out 210hp, very reliably. Unusually, it has the same core engine as my 170hp one but more boost and a head job. It's a bit on the heavy side, though, or I'd suggest it. The boosted versions have a lot of different internal parts to the unboosted ones.

TLDR, if you want a 180hp auto conversion, start with a 180hp auto engine. A 120hp base is not going to be nearly as easy or as cheap
 
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cheapracer

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It's always cooling
Yup, as I posted on occasion, and Bradsopex mentioned above, get the cooling right and you're 90% there.

Manufacturers' cut costs on cooling size for both water and oil, as well as the quantities of both, easily resolved in custom applications.


Subaru did it a bit differently:
Heh, I'd forgotten all about the endurance records, they used to be quite popular in the 60s and 70s.

 
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pictsidhe

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Pumping enough oil and water for 50% more power than you generate will have 50% more parasitic load on the engine. With the high emphasis on mpg, manufacturers aren't going to want to do that. Just one example of why a 180hp engine is a bit different to a 120hp engine.
 

Bradsopex

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I get your point, pic, but they make all kinds of parts, and the motor I am using has a supercharged variant, from the factory, with the same block and head. I will be using upgraded internals with a treated crank for improved lubrication. Yeah, I'm going turbocharged instead of supercharged, but as far as the EFI system and motor itself is concerned, 7 psi of boost is 7 psi of boost, regardless of the delivery method.

As for reliability, I drove one of my fixed up 4AG engines from Huntsville, AL to Salt Lake City, UT over 2 days. 1000 miles the first day, and 700 the next. Due to the gearing, the engine was cruising down the interstate at 5500 RPM (this engine had an 8000 redline). I only stopped for fuel, but drove for 14 hours straight with no issues. The second day was about 8 hours. I was at 5500 RPM for about 90% of that drive. Now remember, 5500 is what my target max RPM is, so I'm not anticipating many issues. Honestly, my biggest concern is preventing shock cooling.

I wanted to get into an Experimental aircraft to experiment, not do the same thing everyone else is, lol.
 

Vigilant1

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As for reliability, I drove one of my fixed up 4AG engines from Huntsville, AL to Salt Lake City, UT over 2 days. 1000 miles the first day, and 700 the next. Due to the gearing, the engine was cruising down the interstate at 5500 RPM (this engine had an 8000 redline). I only stopped for fuel, but drove for 14 hours straight with no issues. The second day was about 8 hours. I was at 5500 RPM for about 90% of that drive. Now remember, 5500 is what my target max RPM is, so I'm not anticipating many issues.
How many HP/% of max power do you suppose you were making while driving down the highway at 5500 RPM?
I'm happy to have another motorhead working on solutions. I'll be watching your progress.
 

Bradsopex

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How many HP/% of max power do you suppose you were making while driving down the highway at 5500 RPM?
I'm happy to have another motorhead working on solutions. I'll be watching your progress.
That specific build was an all motor, individual throttle body engine that made MAYBE 130 to the wheels, but I never dyno'd it because it was just a fun street car. The internals were all factory. I would figure I was using all of 110-115hp to push that light car at that RPM. I did have some spurts where I was staying around 7-7500, mostly long straights through Nebraska and Wyoming, where I was using probably 125hp
 

BJC

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Yeah, I'm going turbocharged instead of supercharged, but as far as the EFI system and motor itself is concerned, 7 psi of boost is 7 psi of boost, regardless of the delivery method.
Not suggesting one method over the other (I have no experience with either), but your statement led me to a question.

What is the exhaust gas pressure drop across a typical turbocharger?


BJC
 

Bradsopex

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That's a hard question to answer, as there are so many variables. Generally, you want your post turbo exhaust to be as large as possible to reduce the pressure so the turbine isn't facing a lot of resistance to spool. You also want to reduce the turbine inlet pressure as much as you can, without losing turbine efficiency. This starts getting into turbo sizing, which is a topic in and of itself (I hope you like math!)
I can only make my manifold runners so big, because optimally they should match the port size on the head, so that's not really considered. The size of turbo you go with will determine what that pressure is.
 

pictsidhe

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Not suggesting one method over the other (I have no experience with either), but your statement led me to a question.
What is the exhaust gas pressure drop across a typical turbocharger?


BJC
That depends how the turbine and compressor are matched. Cars want the boost to come in at low rpm. That results in good matching when the boost hits, but it is lousy at peak power. At peak power, you will have a higher pressure drop across the turbine thatn across the compressor. IF you build the turbo to suit a prop which doesn't need low rpm torque, you can have the turbine side running much more efficiently at your peak power rpm. Pressure drop across the turbine should be somewhat less than across the compressor. This is good for engine temps, power and economy. It's not easy to build a good aero turbo from regular hotrod turbo parts. Quite often, you'll need to make a compressor side fit a larger hot side than is ever used in a car. perhaps Ross will weigh in, he has built both car and aero turbos.
 

pictsidhe

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Yeah, nah.

The belief that bespoke plane engines have magical pistons, conrods and crankshafts, and are the only type that can run all day at "75%", is , as the word "magical" suggests already, is just fairy tales.

The auto-conversion issues are commonly with PSRU failure, PSRU causation, or poor ancillary adaption by amateurs, but nothing to do with the core engine itself.

You can not offer evidence of multiple and consistent failure of major core auto engine components because they just don't exist.

I still don't understand why aviation people want to continually damage their own hobby by shunning rather than encouraging viable, economical options.

This, from the 1950s ....
I never got a Morris Minor to overheat. Nice big radiator, even upped to 65hp, still fine. Cranks were the weak point on those engines. Minis, on the other hand, required special cooling measures if driven in a 'spirited' fashion. My first Mini had an amazing 38hp. If I held the throttle to the floor for extended periods (not that far above the speed limit), it would overheat in summer unless I had the heater running full blast. Yeah, that spoiled the fun. I got fed up with that, so bought a much larger radiator intended for an MG1300 and made a cowl to shoehorn it in the Mini's pitiful space for a radiator. that worked great. It moved from Mini to Mini. It last saw service in my hands on an 85hp Mini. I never managed to hold that one flat out for over an hour like the first, but never had an overheating problem. I did have an 1098 Mini crack a block after 45 minutes flat out. The 1275 engines (first built for the Cooper S) were a huge improvement, especially the last ones beefed up for a 90hp turbo version. They eventually standardised that block across the range. something they did with a lot of the parts needed for higher power versions. If there is a hotrod version of your engine, it makes a lot of sense to start with that to get a complete package that is developed and tested good for high hp out of the box.
 

wsimpso1

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That specific build was an all motor, individual throttle body engine that made MAYBE 130 to the wheels, but I never dyno'd it because it was just a fun street car. The internals were all factory. I would figure I was using all of 110-115hp to push that light car at that RPM. I did have some spurts where I was staying around 7-7500, mostly long straights through Nebraska and Wyoming, where I was using probably 125hp
The numbers are not working together here... I suspect that the engine power at a steady 5500 rpm was a lot lower than when at 7000. Was the car in the same gear for both the 5500 rpm stretches and the 7000 rpm stretches?

Here is why I am saying this... Aero drag dominates total drag in cars at high speed, and the engine speed goes linearly with car speed. Aero drag goes with the speed squared, and the power goes with speed cubed. At a steady rpm of 5500 rpm, it would be going 79% of the speed it was going at 7000 rpm. At 79% speed, the steady state torque would be 62% torque and about 48% power. If 7000 rpm was 125 hp, slowing the engine (and the car with it) to 5500 rpm, would only require about 61 hp.

Now none of that means that he can not make a sturdy engine that is mildly boosted and makes that power all the time, it just means he did not demonstrate it on that drive across the country...

Since Toyota did have this level of power in their production 4AG engines, I do suspect the base engine was pretty thoroughly validated at those power levels. After that, there is cooling, oil cooling, oil flow to the turbo and return to the sump, making it all sturdy against vibration, and reliable electrically. It also does sound like it will be different from what everyone else is running.

Good luck dude, we want to see it work... Will you be building only one, or will you start selling turnkey systems ready to go on firewalls?

Billski
 

pictsidhe

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I've had a 120hp compact car flat out. 115mph. Good luck keeping that up for any length of time without attracting expensive blue lights. 100mph is probably only 80hp.
 

Bradsopex

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The numbers are not working together here... I suspect that the engine power at a steady 5500 rpm was a lot lower than when at 7000. Was the car in the same gear for both the 5500 rpm stretches and the 7000 rpm stretches?

Here is why I am saying this... Aero drag dominates total drag in cars at high speed, and the engine speed goes linearly with car speed. Aero drag goes with the speed squared, and the power goes with speed cubed. At a steady rpm of 5500 rpm, it would be going 79% of the speed it was going at 7000 rpm. At 79% speed, the steady state torque would be 62% torque and about 48% power. If 7000 rpm was 125 hp, slowing the engine (and the car with it) to 5500 rpm, would only require about 61 hp.

Now none of that means that he can not make a sturdy engine that is mildly boosted and makes that power all the time, it just means he did not demonstrate it on that drive across the country...

Since Toyota did have this level of power in their production 4AG engines, I do suspect the base engine was pretty thoroughly validated at those power levels. After that, there is cooling, oil cooling, oil flow to the turbo and return to the sump, making it all sturdy against vibration, and reliable electrically. It also does sound like it will be different from what everyone else is running.

Good luck dude, we want to see it work... Will you be building only one, or will you start selling turnkey systems ready to go on firewalls?

Billski
My numbers were total guestimates based off a dyno chart, which of course does not factor aero resistance. The dyno measured the car at 137HP @ 8000 RPM, and ~110-115hp @ 5500 RPM.

All external fluid lines will be braided hose with AN fittings, thermally shielded where appropriate. All fasteners that may need removal for any maintenance between overhauls will be safety wired, and all others will probably get thread locker. I used to work at a test facility and have seen the horrors the vibration tables could unleash on things you thought were torqued down "good enough".

This will be a one off, and kind of step one. I would like to then go to a more modern engine that is more prevalent. If that works out, I could look into building out some firewall forward kits on a case by case, but I don't see myself building a business out of it. I would very much like to make it available, but I would want to have a lot of hours on it prior to that.
 

Bradsopex

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That depends how the turbine and compressor are matched. Cars want the boost to come in at low rpm. That results in good matching when the boost hits, but it is lousy at peak power. At peak power, you will have a higher pressure drop across the turbine thatn across the compressor. IF you build the turbo to suit a prop which doesn't need low rpm torque, you can have the turbine side running much more efficiently at your peak power rpm. Pressure drop across the turbine should be somewhat less than across the compressor. This is good for engine temps, power and economy. It's not easy to build a good aero turbo from regular hotrod turbo parts. Quite often, you'll need to make a compressor side fit a larger hot side than is ever used in a car. perhaps Ross will weigh in, he has built both car and aero turbos.
You can mix the hot and cold sizes for the application you want, and play around with wheel trims. Honestly, I have been looking into using a Holset variable geometry turbo. This would address some of the sizing issues, but I'm unsure of the added complexity. They have seen a number of issues with diesel engines, but that was due to soot buildup or neglected maintenance. I'm not sure about their performance with gas engines, and it could end up being way more of a headache than it is worth.
 

pictsidhe

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You can mix the hot and cold sizes for the application you want, and play around with wheel trims. Honestly, I have been looking into using a Holset variable geometry turbo. This would address some of the sizing issues, but I'm unsure of the added complexity. They have seen a number of issues with diesel engines, but that was due to soot buildup or neglected maintenance. I'm not sure about their performance with gas engines, and it could end up being way more of a headache than it is worth.

Yes, you can swap parts to some extent. But, what you generally need for an aero turbo is parts from two different frame sizes that don't usually fit together. Or some custom parts. Playing with off the shelf parts just won't get you there. VNT is overly complex and they generally don't like gasoline EGTs. maybe some do now. But you have added weight complexity and unreliability you don't need or want.
 

pictsidhe

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My numbers were total guestimates based off a dyno chart, which of course does not factor aero resistance. The dyno measured the car at 137HP @ 8000 RPM, and ~110-115hp @ 5500 RPM.
So, you were driving at something over 110mph for long stretches?
 

Toobuilder

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Some random thoughts to the OP after seeing things like planning for a wide RPM spread between takeoff RPM and cruise; RPM in a car on a cross country trip, and other things.

Not sure what your flying experience is, but it's a widely held misconception that there is a big difference between the "takeoff event" and the "cruise event". As far as the engine is concerned, the primary difference is air density. The takeoff event involves full throttle and Max propeller RPM to maximize altitude gain. The cruise event simply trades the work of lifting the aircraft away from the earth and applies it to the drag wall of the airplane. The engine is still working just as hard, only it is fighting drag instead of gravity. A typical cross country flight in an airplane has me advance the throttle to the stop for takeoff, and not touching it again until the top of descent 3+ hours later. The only difference is the adjustment of the mixture to account for diminishing MP in climb and "maybe" twist of the blue knob to pull the RPM back based upon my schedule. The idea that airplanes use a bunch of power for takeoff and then "cruise" at significantly less power is not reality for most "transport" missions.

I've said it before and it bears repeating - "flight" in an airplane is akin to cars only if you consider the "car" is loaded with people, pulling a heavy trailer up a steep grade with the gas pedal to the floor for 3 hours straight. I have no doubt that automotive engines can take this use case, but there is a HUGE difference between an aircraft in cruise flight and a car in cruise on the highway.
 
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