Which Aftermarket Fuel Injection System?
Return to Part 1
Scenario: two Porsche 914s, one 2L 4-banger street car with stock engine, one 2L 4-banger race car with modded engine.
The street car engine has a fully-functioning Bosch D-Jetronic system, but as noted in Part 1 I don't trust it. It seems to work great at times but every now and then, usually when I'm an hour away from home, it'll have this massive burp and run bad for a bit. Makes me nervous. And it seems to be extremely sensitive to fuel selection; a couple times it just did not like the fuel I got from some stations.
The race car's engine is modified and uses dual Dellorto carburetors. I have given thought to preparing prepping it to SCCA's Limited Prep Production regs, which requires fuel injection using the stock throttle body and intake manifold.
Combine the two needs and maybe I can mod the street car and learn something about EFI in the process that could apply to the race car (once SCCA loses its fear of a 91hp Volkswagen Bus air-cooled flat-four 2-valve pushrod engine competing against a 91hp 1.5L Honda inline-4 overhead cam 3-valve engine...but I digress...sigh...) And with the street car engine coming out of the car and on the engine stand for some oil leaks then now is a good time to do it.
I've helped tune a Megasquirt-equipped 914-4 at Chris Foley's Tangerine Racing shop. Well, "tune" is a bit generous; I basically figured out how to get it to start and idle smoothly (the car is not registered so we can't "street-tune" it). The process wasn't hateful. So Megasquirt was on the table as a candidate. There's a place called The Dub Shop that has a kit to install a Megasquirt system. Their $3500 turn-key system uses dual downdraft individual throttle bodies; that won't work for me because remember I want to build something based on the stock D-Jet throttle body.
But the nice thing about The Dub Shop is that they sell all the components separately. So at that point I was thinking I'd buy the required sensors and leverage the D-Jet's stock fuel pump/regulator, throttle body, and injectors to build an effective EFI system, and continue to use the stock Bosch distributor for ignition.
But the question is...which system? There's Megasquirt, a well-known product; Microsquirt, a compact lesser-capable (but still decent) version of Megasquirt; and SDS (Small Digital System).
Microsquirt is an interesting and significantly less-expensive system. With it, I could build a dependable EFI for low bucks and some elbow grease. It's tempting. But Microsquirt can only do batch injection (firing the injectors on both compression and exhaust strokes, same as the D-Jet) and wasted spark (firing plugs twice, on both strokes, same as the injection.) That's not really a problem, as the intake valve is closed on the exhaust stroke and there's nothing combustible to fire with the plugs. In fact, as noted the 914's D-Jet is batch injection, and it works.
But what if I wanted sequential (individual) injection and spark? It's what modern EFI systems do. That requires going to Megasquirt. But not only would I need the more-expensive Megasquirt (or Megasquirt 3 Pro) ECU I'd also need its associated relay boxes, and I'd have to add a cam position sensor so the engine can differentiate between cylinders 1 and 3 (instead of just firing during both strokes like the Microsquirt does.)
Then there's the SDS crowd. It's really a neat system, designed around the needs for Experimental aviation. It's also batch injection and I'd come in more expensive for that system versus Microsquirt. But it's a viable option that other 914 owners have used.
So a core decision came down to batch injection versus sequential injection. Did I really need such granular fuel control on a (basically) 1930's-derived air-cooled flat-four? Was it worth the additional expense and complexity of sequential injection? After all, the stock D-Jet does batch injection, and I was always pleased with the hydro-mechanical K-Jetronic CIS System in my Rabbit GTIs ("Kontinuierlich” for continuous, Continuous Injection System, because it was constantly injecting fuel into the intake manifold behind the valves).
Then I found this article on DIYAutotune; in summary it states,
"There is generally no significant performance difference with a sequential system over a batch system unless you use individual cylinder tuning. There can be minor emissions and fuel economy benefits at very low speeds though. If your tuning budget allows for individual cylinder tuning, it may be possible to pick up 3-4% more power depending on how much cylinder to cylinder variation your engine has."
That was supported by SDS' Techpage on sequential injection:
"In the end, there are no significant differences in top end, wide open throttle, horsepower between batch fired and timed systems. We have also not seen any significant differences in fuel economy between the two strategies. Emissions at part throttle are likely to be better with timed injection as this is what it was developed for. On performance applications, emissions are often not an issue and most engines not equipped with a catalyst will not pass a modern emissions standard anyway."
My initial thought is that I'd start with fuel injection first and use the stock distributor, then later I could add ignition control. The street car might like individual coil packs but honestly on the race car I'm going to be constantly at high RPM maxxed-out timing advance so that seems a waste for that application. I continued working my design ideas using DubShop's online products list.
Still dismayed that I wasn't getting anywhere, the next day I got an auto-generated email from The Dub Shop, noting I had left items in my online cart and did I have any questions? And the reply-to address was an actual human, not a "DoNotReply@"; it was "Mario". I replied back to Mario, thanking him for the email (pretending I didn't know it was auto-generated) and noted that I'm trying to design something using his parts but I was not getting a reply to my technical questions from his org. Mario quickly replied with apologies and patiently answered my few questions (bottom line: and he hadn't designed anything for my application). He was extremely helpful and that made me decide to spend my money with him.
So I was hooked. I had my design and I had my primary vendor. Now it's time to design and build.
On To Part Three: "The Design" and "The Sensors"
TDC - Top Dead Center, the firing position for #1 cylinder
CPS - Crank Position Sensor, also known as CAS, Crank Angle Sensor
TPS - Throttle Position Sensor
MPS - Manifold Pressure Sensor
IAT - Intake air Temperature sensor
CLT - Coolant temp sensor
AFR - Air-Fuel Ratio
Return to Part 1
Scenario: two Porsche 914s, one 2L 4-banger street car with stock engine, one 2L 4-banger race car with modded engine.
 |
| Greg's street 914 |
The race car's engine is modified and uses dual Dellorto carburetors. I have given thought to preparing prepping it to SCCA's Limited Prep Production regs, which requires fuel injection using the stock throttle body and intake manifold.
Combine the two needs and maybe I can mod the street car and learn something about EFI in the process that could apply to the race car (once SCCA loses its fear of a 91hp Volkswagen Bus air-cooled flat-four 2-valve pushrod engine competing against a 91hp 1.5L Honda inline-4 overhead cam 3-valve engine...but I digress...sigh...) And with the street car engine coming out of the car and on the engine stand for some oil leaks then now is a good time to do it.
I've helped tune a Megasquirt-equipped 914-4 at Chris Foley's Tangerine Racing shop. Well, "tune" is a bit generous; I basically figured out how to get it to start and idle smoothly (the car is not registered so we can't "street-tune" it). The process wasn't hateful. So Megasquirt was on the table as a candidate. There's a place called The Dub Shop that has a kit to install a Megasquirt system. Their $3500 turn-key system uses dual downdraft individual throttle bodies; that won't work for me because remember I want to build something based on the stock D-Jet throttle body.
But the nice thing about The Dub Shop is that they sell all the components separately. So at that point I was thinking I'd buy the required sensors and leverage the D-Jet's stock fuel pump/regulator, throttle body, and injectors to build an effective EFI system, and continue to use the stock Bosch distributor for ignition.
But the question is...which system? There's Megasquirt, a well-known product; Microsquirt, a compact lesser-capable (but still decent) version of Megasquirt; and SDS (Small Digital System).
Microsquirt is an interesting and significantly less-expensive system. With it, I could build a dependable EFI for low bucks and some elbow grease. It's tempting. But Microsquirt can only do batch injection (firing the injectors on both compression and exhaust strokes, same as the D-Jet) and wasted spark (firing plugs twice, on both strokes, same as the injection.) That's not really a problem, as the intake valve is closed on the exhaust stroke and there's nothing combustible to fire with the plugs. In fact, as noted the 914's D-Jet is batch injection, and it works.
But what if I wanted sequential (individual) injection and spark? It's what modern EFI systems do. That requires going to Megasquirt. But not only would I need the more-expensive Megasquirt (or Megasquirt 3 Pro) ECU I'd also need its associated relay boxes, and I'd have to add a cam position sensor so the engine can differentiate between cylinders 1 and 3 (instead of just firing during both strokes like the Microsquirt does.)
Then there's the SDS crowd. It's really a neat system, designed around the needs for Experimental aviation. It's also batch injection and I'd come in more expensive for that system versus Microsquirt. But it's a viable option that other 914 owners have used.
So a core decision came down to batch injection versus sequential injection. Did I really need such granular fuel control on a (basically) 1930's-derived air-cooled flat-four? Was it worth the additional expense and complexity of sequential injection? After all, the stock D-Jet does batch injection, and I was always pleased with the hydro-mechanical K-Jetronic CIS System in my Rabbit GTIs ("Kontinuierlich” for continuous, Continuous Injection System, because it was constantly injecting fuel into the intake manifold behind the valves).
Then I found this article on DIYAutotune; in summary it states,
"There is generally no significant performance difference with a sequential system over a batch system unless you use individual cylinder tuning. There can be minor emissions and fuel economy benefits at very low speeds though. If your tuning budget allows for individual cylinder tuning, it may be possible to pick up 3-4% more power depending on how much cylinder to cylinder variation your engine has."
That was supported by SDS' Techpage on sequential injection:
"In the end, there are no significant differences in top end, wide open throttle, horsepower between batch fired and timed systems. We have also not seen any significant differences in fuel economy between the two strategies. Emissions at part throttle are likely to be better with timed injection as this is what it was developed for. On performance applications, emissions are often not an issue and most engines not equipped with a catalyst will not pass a modern emissions standard anyway."
That decided it for me: I'm'a just going with batch injection and wasted spark. That eliminates the need for Megasquirt (it can do batch, but so can the lesser-expensive Microsquirt).
I contacted both The Dub Shop and SDS to inquire about their systems and if they had ever designed something within my parameters (stock D-Jet pump/regulator, throttle body, induction, injectors, etc). I got silence. I figured they constantly get bombarded by un-serious people fishing for useless info, so I understood. In the meantime I started pricing out stuff on DubShop's pages to see what would be involved in just designing something myself: Crank Position Sensor (CPS) here, Throttle Position Sensor (TPS) there, Intake Air Temperature sensor (IAT), Manifold Absolute Pressure (MAP) sensor, modified Coolant Temperature sensor (CLT). Tossed the parts in the online shopping cart to see total costs as I mulled it over. It was starting to look like an affordable project.
My initial thought is that I'd start with fuel injection first and use the stock distributor, then later I could add ignition control. The street car might like individual coil packs but honestly on the race car I'm going to be constantly at high RPM maxxed-out timing advance so that seems a waste for that application. I continued working my design ideas using DubShop's online products list.
Still dismayed that I wasn't getting anywhere, the next day I got an auto-generated email from The Dub Shop, noting I had left items in my online cart and did I have any questions? And the reply-to address was an actual human, not a "DoNotReply@"; it was "Mario". I replied back to Mario, thanking him for the email (pretending I didn't know it was auto-generated) and noted that I'm trying to design something using his parts but I was not getting a reply to my technical questions from his org. Mario quickly replied with apologies and patiently answered my few questions (bottom line: and he hadn't designed anything for my application). He was extremely helpful and that made me decide to spend my money with him.
So I was hooked. I had my design and I had my primary vendor. Now it's time to design and build.
On To Part Three: "The Design" and "The Sensors"
TDC - Top Dead Center, the firing position for #1 cylinder
CPS - Crank Position Sensor, also known as CAS, Crank Angle Sensor
TPS - Throttle Position Sensor
MPS - Manifold Pressure Sensor
IAT - Intake air Temperature sensor
CLT - Coolant temp sensor
AFR - Air-Fuel Ratio
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