High Altitude turbo-charging...

[SuperMag]

I have first hand experience as to how much of a pain it is to normally aspirate an engine in the mountains, but I was wondering... When it comes to forcefully stuffing air into a motor with wastegated turbos, does it care what altitude it's at? I'm thinking the turbos will just spool a little faster to compensate...

(BTW, I'm leaning towards EFI as the means by which I dribble gas into the engine. Too many altitude issues to deal with when using carbs.)

 

[Anonymous]

A correctly sized turbo with a properly functioning wastegate should provide you with near-sea level performance up to any altitude one can drive to in North America.

 

[SuperMag]

If that's the case, a blow-through carb/turbo set-up should perform in the same manner then? If the turbo will yield sea level performance, then a blow through carb will never know the difference, right?

On the other hand, a draw through set-up would be a real PITA...

 

[Anonymous]

Yes, a blow-thru configuration is generally used for for altitude compensation in thoroughly engineered applications such as piston engined aircraft. However, at the modest levels of boost I am presuming for your unspecified application (towing?) a draw-thru would work fine, and is usually much easier to set up.

 

[MustangSix]

The pilots can correct me if I'm wrong, but I think in aircraft the idea is called turbo normalizing and is used to sustain sea level performance at high altitudes.

The concept works pretty well on Pikes Peak racers! Are you anticipating rapid changes in altitude?

 

[Anonymous]

Turbo-normalizing and turbosupercharging* are not the same thing, Jack, though both appear on aircraft. Turbo-normalizing is usually an after market STC'd modification to aircraft engines that originally were not turbocharged. And as you note, the objective is to maintain sea-level performance to higher than normal altitudes. Turbosupercharging, as the name implies, adds boost to the engine to build more horsepower than the same engine can put out normally aspirated. Tubosupercharged aircraft engines are normally an OEM installation.

* - Turbosupercharging is the technical name for what we commonly call turbocharging.

 

[SuperMag]

Are you anticipating rapid changes in altitude?

Oh yeah! Actually... when I go on the road, it's not unusual to have to adjust carb mix and timing 3 or 4 times in the same day, especially if I've got it tuned right to the edge (which is most of the time) and towing and/or hauling any kind of serious load. I keep the vacuum gauge and 1/2" wrench in the door pocket at all times. Depending on the route I take, from here I'll climb to almost 9000 feet, drop to 4000 again, and then to almost 10,000 again, all in the same day. Day two usually finds me at almost sea level.

I usually stop every 100 miles or so for gas on 'the way down' just to keep the octane level of the gas in the tank up. As I head down the hill, the octane rating of regular goes from 84.5 to 87...

...Yes, a blow-thru configuration is generally used for for altitude compensation in thoroughly engineered applications...

[emphasis mine]

With you and Sr. Ranger giving me advice, how can I go wrong?

Step 1: Finding a non-A.I.R. carb head...

 

[xctasy]

Didn't Ford use a feedback carb with rich lean/ adjustment on the fuel control valve? Is it possible to hook up just the FCV and hook it up with no other changes? Or a Idle Contol Solenoid or even a servo from one of your model air-planes. Any thing so you can trim the fuel air mix, like they do on planes...on the fly!

 

[SuperMag]

I thought about a simplified version of that. Drill a hole in the top of the YF's float chamber directly above the metering rod adjustment screw and then fabricate a linkage actuated by a choke cable.

While that would be a solution for the mixture vagaries, it doesn't do much for my deep seated and long repressed appetite for axle snapping torque. The time has come to build a motor.

 

[xctasy]

Yep. I've been thinking of just the capper for you, SuperMag. A nice, stock 300 with a 4/71 slug on drivers side, hanging above the dissy, and a set of triple Rochestor 2 Jets stored in a letter box, presurised to 9 pounds by the application of a surpentine drive like this one.

found here :arrow: http://www.turboclub.com/RTO/06100005/amc_javelin__rto_06100005_.htm


It's fan clutched, and switches in and out by electricity, just like Mad Max


We'd shove in a fairly minor cam spec, a good set of non forged pistons, 7.0:1 compression and look for about 175 hp and 275 lb-ft before the application of boost (if it was on 10:1, which is what its boosted ratio will be). With about 255 real horsies, and 420 lb-ft of torque. Sort of like a 460, but with a torque curve to move a mountain.

Some people say supercharged blow throughs are not possible. I think they are.

 

[MustangSix]

Thanks Stan. I wasn't quite sure of the differences. I think I have it now.

Seems to me you need to turbocharge that thing. Aftermarket EFI with a mass air sensor would make it easy.

 

[Anonymous]

Jack, I should have made it clear that turbo-normalizers use a big wastegate with the spring set at one bar. That way the turbo doesn't put any boost into the engine at any altitude. As the aircraft climbs, however, the turbo continues to feed a full one bar to the engine, assuring sea level performance up to higher altitudes than a normally aspirated engine could do so.

Engines with turbosuperchargers also have wastegates, but with the bypass door set at a higher boost level, usually 1.5 to 2 bar.

In any case, there comes an altitude where the turbo can no longer supply 0.75 bar to the engine. This is called the 'critical altitude' for the engine. Under standard-day contitions (sea level, 59° F, 30% humidity), 7500' MSL is considered the critical altitude for a normally aspirated engine. That's the point where a 100 hp engine makes 75 hp at WOT. Turbo-normalized engines usually hit their critical altitude at about 12,000', while turbosupercharged general aviation engines can usually hang in there until about 18,000'.

Hope this helps...!

 

[MustangSix]

Stan, thanks for the clarification. Aircraft engines have always facinated me, but I've never had the chance to delve into them too deeply.

I think it was the time I saw that V12 Allison powered thunderbird "Big Al" doing exhibition runs when I was a kid that did it to me. I had to rush out and buy the model.

 

[Anonymous]

I hate to beak the news, Jack, but all Thunderbolts were powered by Pratt & Whitney R-2800 twin-row supercharged air-cooled RADIAL engines.

Not a V-12, but nonetheless pretty much the baddest mo'fos to prowl the sky...

 

[Anonymous]

Old guy strikes again!

The version of "Big Al" I'm familiar with was Jim Lytle's way-chopped '34 Ford tudor. Windows looked like mail slots in a door. Allison powered. Ran in the late sixties. I must have missed the Thunderbird.

Graeme

 

[Anonymous]

Thunderbird? You mean like in a car? Pffft...! :roll:

Sorry...my brain filled in Thunderbolt, as in the P-47...

 

[MustangSix]

There was a version of a 67 Thunderbird that had a blown Allison that ran in the late sixties/early seventies, Stan. I was talking car, not airplane.

I recall an allison powered 34 as well, but I never saw that one run. More than one Big Al?

 

[Lazy JW]

Yes, the P-47 Thunderbird used a huge turbo-supercharger setup that was way cool Actually, the hot rod industry owes a lot to the aviation industry in the fact that a lot of metalurgy, igniton improvements, induction improvements, fuel injection, etc,etc, were made during WW11 out of the need for higher performance aircraft engines. After the war this technology naturally was picked up by the auto makers and ultimately the hot rodders. Not that there wasn't any going on before the war, but all of the government funded R&D work really helped things along.
Lazy JW