A PROBLEM WITH JUNKYARD TURBOS

By 460-BBF-Turbo-In-CC (adapted from the legendary Car Craft turbo blog)

"Don't send a child to do a man's job!" -- old Southern proverb

Someday turbos such as the tiny units used on the current Ford EcoBoost V6 engines will become widely available at the junkyard. And like an earler generation lured by JY T2s, T3s and T28s, some budget Car Crafters will undoubtedly buy the current generation of small JY turbos to use on big V8s with hopes of of dirt-cheap boost.

Years ago, more than a few Car Crafters grabbed up another small turbo, the once-ubiquitous Garrett AiResearch T3, and slapped pairs of them on all sorts of V8s, including Ford's 460.

Did it work?

It depends on what you wanted. If the goal is maximum pump gas power, the answer was no. Here's why:

Here's a turbo compressor map for one of the larger T3 variants. Note that the bottom axis is in lbs/min. of mass air flow. The highest flow mapped is ~ 35 lbs/min. Although the turbo doesn't stop flowing beyond that, the efficiency level becomes unacceptable (excessive air heating, potential overspeeding, and choking of the engine)

Recalling the general rule of thumb that one pound of mass air flow will support 9-10 horsepower, it should be abundantly clear -- even if you've got no idea how to read a turbo compresor map -- that a pair of these smallish turbos would be hard pressed to feed a 460 above 4,500 r.p.m. (If it's not, then stay tuned!)

Two of these turbos working together would struggle to supply enough "boost" at any pressure ratio for 630-700 h.p. And that's exactly what the Car Crafters who have tried to use pairs of JY T3s on 460s discovered.(See e.g. Trevor Cornwell's twin-turbo 460 Ford Fairmont)

And even that level would be adversely affected by excessive charge heating due to compressor inefficiency. Best efficiency would be at around a mere 200 to 225 h.p. per turbo -- a level that an "all motor" 460 should be able to easily achive on its own.

HOW MANY POUNDS OF AIR DOES IT TAKE TO MAKE ONE HORSEPOWER?

By 460-BBF-Turbo-In-CC (From the legendary Car Craft turbo blog)



“He lives most life whoever breathes most air.” – Elizabeth Barrett Browning

The concept is simple: your engine has to take in enough air in order to burn enough fuel to reach your horsepower goal. But for many Car Crafters, the “experts” all seem to be speaking different languages.

At times, it all sounds like an alphabet soup. The tuning experts talk of “AFR” (air/fuel ratio). Then the carburetor and cylinder head guys talk of “CFM” (cubic feet per minute). Yet most of us measure fuel in gallons or liters, not CFM. And the CFM recommendations seem wildly inconsistent. (i.e. “You’ll need a 650 CFM carb and some 200 cfm heads . . . .”) Making it worse, the supercharger and turbo folks talk about “pounds of boost” or other arcane measurements.

Many Car Crafters just throw up their hands and copy what the next guy is doing. And sadly, too many never really understand why what they’re copying works or doesn’t work.

Turbo Car Crafters, however, don’t usually have anyone to copy. So to be successful, we’ve got to understand how to compare and measure air and fuel.

We’ll start with some of “rules of thumb” of power production. They’re not a substitute for working a PLAN in detail, but they’ll get us “in the ballpark” and hopefully give us a basis to understand what the “experts” are talking about.

According to the turbocharger engineers at Garrett, it takes one pound of air per minute to make nine horsepower (See, Julian Edgar, 21st Century Performance, at pg. 161).

Turbo expert Jay K. Miller (Turbo: Real World High-Performance Turbocharger Systems) makes the estimates a little simpler by suggesting that it takes one pound of air mass for every ten horsepower. (Miller at pg. 40).

Engineer Mark Warner also uses the easier 1:10 rule of thumb, stating that once you know the mass flow rate into an engine, you can multiply it by 10 to get a horsepower estimate. (Warner, Street Turbocharging at pg. 29)

Others suggest that at the torque peak, each pound of air will support about 9.5 h.p. and at the horsepower peak each pound of air supports about 10.5 h.p. The popular 1:10 “rule” seems to split the difference.

In actual practice, each of these “rules of thumb” will be varied by many factors. But the basic concept of combining a “mass” of air with a smaller “mass” of fuel remains fundamental.