Mechanical fuel injection.

I love the simplicity of mechanical fuel injection. I started out with the early Corvette and quickly learned about Hilborn.
     Actually my first exposure to to mechanical fuel injection was on the old Offy 250 sprint cars used. But one thing I never figured out is how can you get mechanical fuel injection to adjust to boost ? 

I've never worked on a mechanical fuel injection setup, but I'd imagine that you'd do it the same way you did with early EFI systems, a rising-rate fuel pressure regulator?

In reply to WonkoTheSane (Forum Supporter) :

Isn't that also the same way you do it with a turbo and a carb?

I've never done or seen it, but sounds like an interesting challenge.

I'm thinking maybe some kind of PWM valve on the main pill, but then it's not mechanical 

Or maybe a boost referenced regulator on the main pill. Sounds sketchy.

Or Maybe a secondary fuel system that supplied for boost only < this sounds like it might be the easiest to implement.

Basically it needs to have a reference to the amount of boost to provide similar fuel pressures + boost.  Often this is through a rising rate fuel pressure regulator that is boost referenced.

EFI works similarly, except you can adjust the length of time the injector is open for each cell of the table within the EFI Computer.  So instead of getting it "close" and "not detonating" you can make a bit more power and efficiency through running a bit more close to "ideal" 

By mechanical injection you mean a constant flow Enderly or Hillborn style?

If so a RRFPR wont work as the fuel pump is driven at cam speed and pressure is determined by rpm, nozzle size and bleed-off orifice (pill) size.

The barrel valve opens a low speed relief port and has a tapered slot for fuel flow.

Once you are past 1/4 throttle it basically runs on the main pill and pump rpm.

On an advanced system there may be an additional bleed-off (high speed lean out) using a pressure regulator and an orifice. So if the main fuel pressure goes over a preset pressure it will dump pressure through an additional orifice.

Rochester fuel injection is a rising rate system.

There's two diaphragms that sense inlet air pressure and manifold pressure. They work together to operate the spill valve in the fuel pump which controls output pressure.

The injectors are just spray nozzles, fueling is controlled by fuel pressure and each port receives fuel during all four cycles.

It's not a fancy system by any means but was very high tech for the day.

You should be able to run it as a blow-though system but you'll have to put in some brain work getting the springs and diaphragms calibrated for the air flow.

Played with full mechanical Tecalemit-Jackson injection on a British car. The mixture curve was set by a cam attached to the throttle shaft that increased fuel as throttle opening increased.. Tuning consisted of grinding a new cam if you wanted to richen or weaken mix in a specific rev range. Very time consuming.

Frenchy - a friend raced a BMW 2002 that had factory turbo and early fuel injection. A real PITA I was told, as the lag between when you floored it and you actually got boost was atrocious - he had to put his foot to the floor as soon as he had finished braking so that it would be pulling again by the time he had gone around the corner and got reasonably straight again.  He said it took forever but it was probably only 1-2 secs.  That car had an interlink between the boost and enrichment, but I don't know the details of the mechanism.

In reply to wspohn :

That's what the D type did. Each change required a different camshaft profile in the injector pump.  

If you look at Hilborn they keep it a simple. A  2 stage ramp.  Basically idle and power. .  Part of that is due to the broad range alcohol works at compared to gasoline. I was able to use a Kinsler dial-a-jet to allow starting and driving around the pits,  Then switch from that to racing conditions on the straight right before the main straight.  My plugs would be clean and I had someone watch the air density gauge . If Air got thicker I'd dial a richer jet. Considering I had 5 more jets to go I could stay right on top of weather changes. 
Guys with carburators would start out rich and sometimes load up so they'd stumble at the start. With my clean plugs I'd take off and pass faster cars. Until they cleaned out their plugs.   Then as air density changed I'd be a little closer to perfect. And still remain ahead. 
 

       The lag was likely do to a poor match between the size of the turbo and the size of the engine. A  Small engine can put out really great amounts of power but  doing so requires a big spool up lag.  
Faster response requires a closer mating of  sizes. 

ShawnG said:

Rochester fuel injection is a rising rate system.

There's two diaphragms that sense inlet air pressure and manifold pressure. They work together to operate the spill valve in the fuel pump which controls output pressure.

The injectors are just spray nozzles, fueling is controlled by fuel pressure and each port receives fuel during all four cycles.

It's not a fancy system by any means but was very high tech for the day.

You should be able to run it as a blow-though system but you'll have to put in some brain work getting the springs and diaphragms calibrated for the air flow.

That's the part of the Corvette system that gave me fits.  They gave you spring and diaphragm information but nothing for modification.  It was strictly a Dyno and exhaust gas reading trying to figure out what will work . 

ShawnG said:

Rochester fuel injection is a rising rate system.

There's two diaphragms that sense inlet air pressure and manifold pressure. They work together to operate the spill valve in the fuel pump which controls output pressure.

The injectors are just spray nozzles, fueling is controlled by fuel pressure and each port receives fuel during all four cycles.

It's not a fancy system by any means but was very high tech for the day.

You should be able to run it as a blow-though system but you'll have to put in some brain work getting the springs and diaphragms calibrated for the air flow.

I'm thinking of some way to select the various by pass pills as boost increases. One pound of boost triggers pill #1 2#'s triggers pill #2 etc.  again since alcohol is so tolerant you could get by between too rich and too lean 

wspohn said:

Played with full mechanical Tecalemit-Jackson injection on a British car. The mixture curve was set by a cam attached to the throttle shaft that increased fuel as throttle opening increased.. Tuning consisted of grinding a new cam if you wanted to richen or weaken mix in a specific rev range. Very time consuming.

Frenchy - a friend raced a BMW 2002 that had factory turbo and early fuel injection. A real PITA I was told, as the lag between when you floored it and you actually got boost was atrocious - he had to put his foot to the floor as soon as he had finished braking so that it would be pulling again by the time he had gone around the corner and got reasonably straight again.  He said it took forever but it was probably only 1-2 secs.  That car had an interlink between the boost and enrichment, but I don't know the details of the mechanism.

Much of the lag was due to the design of the turbos as they were little more than paddle wheels attached to a shaft with some oiled bearings to ride on.

Modern turbos use a lot of tech to optimize the aerodynamics and weight of the wheels to make them incredibly efficient.  Coupled with better bearing solutions, they are much more responsive and with a wider power range.

Improvements in fuel and ignition controls also make large advancements in efficiency and power output, but quite a lot of work on the actual turbo tech makes a much more noticeable difference.

In reply to Stefan (Forum Supporter) :

So the Chinese turbo's offered for modest prices are they current design, obsolete design or someplace in between?  
 

I've been impressed by their low cost and reported semi decent reliability. 

frenchyd said:

In reply to Stefan (Forum Supporter) :

So the Chinese turbo's offered for modest prices are they current design, obsolete design or someplace in between?  
 

I've been impressed by their low cost and reported semi decent reliability. 

Design is often OK but build quality is a crapshoot.  I don't think that having a Chinese turbo of unknown quality, possibility getting ready to shed pieces of turbine blade into my intake ports would sit well.

My Fiero V6 build used a rather expensive IHI turbo (the same one that Callaway used on his Corvette - but he used two of them). Excellent bearings and a water cooled centre bearing, plus I added an oil flow after shut down to prevent ashing (was running dino oil). Dead reliable - ran for a decade before I sold it to buy a Solstice.

frenchyd said:

In reply to Stefan (Forum Supporter) :

So the Chinese turbo's offered for modest prices are they current design, obsolete design or someplace in between?  
 

I've been impressed by their low cost and reported semi decent reliability. 

Look at the impellers, if they are nicely shaped then they are newer design, if they are relatively straight edged blades then they are older design.

wspohn said:

frenchyd said:

In reply to Stefan (Forum Supporter) :

So the Chinese turbo's offered for modest prices are they current design, obsolete design or someplace in between?  
 

I've been impressed by their low cost and reported semi decent reliability. 

Design is often OK but build quality is a crapshoot.  I don't think that having a Chinese turbo of unknown quality, possibility getting ready to shed pieces of turbine blade into my intake ports would sit well.

My Fiero V6 build used a rather expensive IHI turbo (the same one that Callaway used on his Corvette - but he used two of them). Excellent bearings and a water cooled centre bearing, plus I added an oil flow after shut down to prevent ashing (was running dino oil). Dead reliable - ran for a decade before I sold it to buy a Solstice.

My friends are still using Chinese turbo's going on 5 years now. Basically they are 10 cents on the dollar  compared to American made. Most are used in drag racing so it's not like road racing where they are under boost for an hour and a half.  
But the couple that are in road racing aren't running SCCA  just local club stuff. They seem to be holding up. To my knowledge they haven't failed yet.