Tell me about Single Point Fuel Injection systems

[Linux23]

Throttle body fuel injection systems, also known as single point or central fuel injection is the subject of this thread topic. Tell me everything you know about this older fuel injection technology.

 

[Linux23]

^miagi^

 

[Toastedlightly]

It is useless...

 

[slag]

Originally posted by: Toastedlightly
It is useless...

i wouldnt go that far. its much better than a carb'd system because you dont have to worry about floats, chokes, levels, etc, but its really just a high tech carb system.

One fuel injector, 100% duty cycle, injects gas for each cylinder, but it is located at the top of the intake manifold instead of each cylinder like mpfi is.

 

[The Stigenator]

the older ones are mechanical fuell injection systems..

but the TBFI is not as effecient as today's MPFI or EFI which inject fuel directly into the cylinder area outside teh valves. The TBFI /TBI injects it further up, near the throttle body plate, so it mixes with air. However this is not effecient, you dont have control over how much fuel goes into each cylinder etc etc. However TBI is easier to setup, lesser wires.

 

[Linux23]

Originally posted by: TheGoodGuy
the older ones are mechanical fuell injection systems..

but the TBFI is not as effecient as today's MPFI or EFI which inject fuel directly into the cylinder area outside teh valves. The TBFI /TBI injects it further up, near the throttle body plate, so it mixes with air. However this is not effecient, you dont have control over how much fuel goes into each cylinder etc etc. However TBI is easier to setup, lesser wires.

why can't the valves open and close as needed to control fuel to each cylinder?

 

[boomerang]

There is only one injector (valve, as you call it). With 4 to 8 cylinders requiring fuel, it is impractical to have this single injector try to fire for each cylinder.

Although the injector is in reality being pulsed. It's technically referred to as duty cycle. The ratio of time it's open versus closed. This is how the fuel ratio is controlled from lean to rich.

As was said earlier, this was a vast improvement over a carburetor.

 

[alpineranger]

It was basically a quick and dirty hack to put fuel injection on carbeureted cars. Obviates the need to redesign the intake runners, no need to worry about the fuel atomizing well in the short space before it enters the cylinder, as you can simply remove the carb and put a throttle body with a fuel injector there. AFAIK, metering in these injectors works as it still does in modern systems: PWM. I'm not sure about the control system. I'm speaking only about electronic units, not the old mechanical fuel injection systems. I know very little about those as they're long before my time.

Edit: A little aside about the relative efficiency of single vs multi point fuel injection, I do remember some multi point systems that were not sequential multi point. Thus, you didn't have synchronization between the cycling of individual cylinders and the firing of the injectors for that cylinder. Sort of like the fuel injection analog of wasted spark ignition systems. Multi point fuel injection, but nowhere near as efficient as the standard sequential multi point systems we have today.

 

[Howard]

Originally posted by: boomerang
There is only one injector (valve, as you call it). With 4 to 8 cylinders requiring fuel, it is impractical to have this single injector try to fire for each cylinder.

Although the injector is in reality being pulsed. It's technically referred to as duty cycle. The ratio of time it's open versus closed. This is how the fuel ratio is controlled from lean to rich.

As was said earlier, this was a vast improvement over a carburetor.

Let's say that the injector fires 5 seconds and is closed for 5 seconds (for every 10 seconds). By your logic, the duty cycle is 100%.

:roll:

 

[damonpip]

Originally posted by: Howard

Originally posted by: boomerang
There is only one injector (valve, as you call it). With 4 to 8 cylinders requiring fuel, it is impractical to have this single injector try to fire for each cylinder.

Although the injector is in reality being pulsed. It's technically referred to as duty cycle. The ratio of time it's open versus closed. This is how the fuel ratio is controlled from lean to rich.

As was said earlier, this was a vast improvement over a carburetor.

Let's say that the injector fires 5 seconds and is closed for 5 seconds (for every 10 seconds). By your logic, the duty cycle is 100%.

:roll:

He meant to say open time versus total time per cycle.

 

[Iron Woode]

Originally posted by: alpineranger
It was basically a quick and dirty hack to put fuel injection on carbeureted cars. Obviates the need to redesign the intake runners, no need to worry about the fuel atomizing well in the short space before it enters the cylinder, as you can simply remove the carb and put a throttle body with a fuel injector there. AFAIK, metering in these injectors works as it still does in modern systems: PWM. I'm not sure about the control system. I'm speaking only about electronic units, not the old mechanical fuel injection systems. I know very little about those as they're long before my time.

Edit: A little aside about the relative efficiency of single vs multi point fuel injection, I do remember some multi point systems that were not sequential multi point. Thus, you didn't have synchronization between the cycling of individual cylinders and the firing of the injectors for that cylinder. Sort of like the fuel injection analog of wasted spark ignition systems. Multi point fuel injection, but nowhere near as efficient as the standard sequential multi point systems we have today.

What you are refering to is called BatchFire Fuel Injection. Where a batch of fuel is fired at roughly the right time before the valve opens at a cylinder.

While not as efficient as SPFI, it is still more efficient than TBI or a carb.

an example would be any Ford Crown Vics from 1986 - 1991 with the 5.0L v8.

 

[Heisenberg]

Originally posted by: Iron Woode

Originally posted by: alpineranger
It was basically a quick and dirty hack to put fuel injection on carbeureted cars. Obviates the need to redesign the intake runners, no need to worry about the fuel atomizing well in the short space before it enters the cylinder, as you can simply remove the carb and put a throttle body with a fuel injector there. AFAIK, metering in these injectors works as it still does in modern systems: PWM. I'm not sure about the control system. I'm speaking only about electronic units, not the old mechanical fuel injection systems. I know very little about those as they're long before my time.

Edit: A little aside about the relative efficiency of single vs multi point fuel injection, I do remember some multi point systems that were not sequential multi point. Thus, you didn't have synchronization between the cycling of individual cylinders and the firing of the injectors for that cylinder. Sort of like the fuel injection analog of wasted spark ignition systems. Multi point fuel injection, but nowhere near as efficient as the standard sequential multi point systems we have today.

What you are refering to is called BatchFire Fuel Injection. Where a batch of fuel is fired at roughly the right time before the valve opens at a cylinder.

While not as efficient as SPFI, it is still more efficient than TBI or a carb.

an example would be any Ford Crown Vics from 1986 - 1991 with the 5.0L v8.

Another example of a batch fire system is the TPI system found on the L98 motors.
As far as TBI is concerned, I was under the impression that the major weak point was not lack of fuel, but lack of airflow.

 

[Iron Woode]

Originally posted by: Heisenberg

Originally posted by: Iron Woode

Originally posted by: alpineranger
It was basically a quick and dirty hack to put fuel injection on carbeureted cars. Obviates the need to redesign the intake runners, no need to worry about the fuel atomizing well in the short space before it enters the cylinder, as you can simply remove the carb and put a throttle body with a fuel injector there. AFAIK, metering in these injectors works as it still does in modern systems: PWM. I'm not sure about the control system. I'm speaking only about electronic units, not the old mechanical fuel injection systems. I know very little about those as they're long before my time.

Edit: A little aside about the relative efficiency of single vs multi point fuel injection, I do remember some multi point systems that were not sequential multi point. Thus, you didn't have synchronization between the cycling of individual cylinders and the firing of the injectors for that cylinder. Sort of like the fuel injection analog of wasted spark ignition systems. Multi point fuel injection, but nowhere near as efficient as the standard sequential multi point systems we have today.

What you are refering to is called BatchFire Fuel Injection. Where a batch of fuel is fired at roughly the right time before the valve opens at a cylinder.

While not as efficient as SPFI, it is still more efficient than TBI or a carb.

an example would be any Ford Crown Vics from 1986 - 1991 with the 5.0L v8.

Another example of a batch fire system is the TPI system found on the L98 motors.
As far as TBI is concerned, I was under the impression that the major weak point was not lack of fuel, but lack of airflow.

I disagree on both points.

The GM TBI wasn't all bad. However, by using existing manifolding it compromised efficiency. You can make considerable power from a TBI 305 v8, its just not worth the effort.

ever see the rare hi-po dual TBI small blocks?

PS: Ford's TBI was called Central Fuel Injection.

 

[Heisenberg]

Originally posted by: Iron Woode
I disagree on both points.

The GM TBI wasn't all bad. However, by using existing manifolding it compromised efficiency. You can make considerable power from a TBI 305 v8, its just not worth the effort.

ever see the rare hi-po dual TBI small blocks?

PS: Ford's TBI was called Central Fuel Injection.

I don't think I ever saw one of those dual-TBI setups. I remember the horrid Cross-fire injection they used for awhile in the early 80s, but I don't think that's what your talking about.

I had a 305 TBI in my Firebird before I swapped it out for a 350 TPI setup, and that thing was weak. Of course, that was with stock heads (which were crap on that motor) and exhaust manifolds instead of headers, so it's not a fair comparison.

 

[Iron Woode]

Originally posted by: Heisenberg

Originally posted by: Iron Woode
I disagree on both points.

The GM TBI wasn't all bad. However, by using existing manifolding it compromised efficiency. You can make considerable power from a TBI 305 v8, its just not worth the effort.

ever see the rare hi-po dual TBI small blocks?

PS: Ford's TBI was called Central Fuel Injection.

I don't think I ever saw one of those dual-TBI setups. I remember the horrid Cross-fire injection they used for awhile in the early 80s, but I don't think that's what your talking about.

I had a 305 TBI in my Firebird before I swapped it out for a 350 TPI setup, and that thing was weak. Of course, that was with stock heads (which were crap on that motor) and exhaust manifolds instead of headers, so it's not a fair comparison.

Thats what Cross-fire Fuel Injection was, dual TBI. The nick-name was Cease-Fire Fuel Injection.

My friend did up his 1985 Camaro. 305 TPI with worked heads, headers, true dual exhaust, 5 speed and 3.73 factory gears. Not sure if he did the cam or not. All I know is that it was one hard accelerating car. He managed a 14.00 quarter mile.

 

[Heisenberg]

Originally posted by: Iron Woode

Originally posted by: Heisenberg

Originally posted by: Iron Woode
I disagree on both points.

The GM TBI wasn't all bad. However, by using existing manifolding it compromised efficiency. You can make considerable power from a TBI 305 v8, its just not worth the effort.

ever see the rare hi-po dual TBI small blocks?

PS: Ford's TBI was called Central Fuel Injection.

I don't think I ever saw one of those dual-TBI setups. I remember the horrid Cross-fire injection they used for awhile in the early 80s, but I don't think that's what your talking about.

I had a 305 TBI in my Firebird before I swapped it out for a 350 TPI setup, and that thing was weak. Of course, that was with stock heads (which were crap on that motor) and exhaust manifolds instead of headers, so it's not a fair comparison.

Thats what Cross-fire Fuel Injection was, dual TBI. The nick-name was Cease-Fire Fuel Injection.

My friend did up his 1985 Camaro. 305 TPI with worked heads, headers, true dual exhaust, 5 speed and 3.73 factory gears. Not sure if he did the cam or not. All I know is that it was one hard accelerating car. He managed a 14.00 quarter mile.

Heh, "Cease-Fire Fuel Injection". I hadn't heard that before. So was CFI used on those hi-po small blocks you mentioned, or was it something else with dual TBI?

 

[Iron Woode]

Originally posted by: Heisenberg

Originally posted by: Iron Woode

Originally posted by: Heisenberg

Originally posted by: Iron Woode
I disagree on both points.

The GM TBI wasn't all bad. However, by using existing manifolding it compromised efficiency. You can make considerable power from a TBI 305 v8, its just not worth the effort.

ever see the rare hi-po dual TBI small blocks?

PS: Ford's TBI was called Central Fuel Injection.

I don't think I ever saw one of those dual-TBI setups. I remember the horrid Cross-fire injection they used for awhile in the early 80s, but I don't think that's what your talking about.

I had a 305 TBI in my Firebird before I swapped it out for a 350 TPI setup, and that thing was weak. Of course, that was with stock heads (which were crap on that motor) and exhaust manifolds instead of headers, so it's not a fair comparison.

Thats what Cross-fire Fuel Injection was, dual TBI. The nick-name was Cease-Fire Fuel Injection.

My friend did up his 1985 Camaro. 305 TPI with worked heads, headers, true dual exhaust, 5 speed and 3.73 factory gears. Not sure if he did the cam or not. All I know is that it was one hard accelerating car. He managed a 14.00 quarter mile.

Heh, "Cease-Fire Fuel Injection". I hadn't heard that before. So was CFI used on those hi-po small blocks you mentioned, or was it something else with dual TBI?

CFI was used in 1982 on the Z28 305. It is listed as dual CFI: 165 hp @ 4200 rpm 240 lbft @ 2400 rpm Vin Code 7. 1982 - 1983.

On the corvette it was RPO code L83, vin code 8. Listed as CrossFire FI (twin TBI). 1982 -1984.

 

[boomerang]

Originally posted by: damonpip

Originally posted by: Howard

Originally posted by: boomerang
There is only one injector (valve, as you call it). With 4 to 8 cylinders requiring fuel, it is impractical to have this single injector try to fire for each cylinder.

Although the injector is in reality being pulsed. It's technically referred to as duty cycle. The ratio of time it's open versus closed. This is how the fuel ratio is controlled from lean to rich.

As was said earlier, this was a vast improvement over a carburetor.

Let's say that the injector fires 5 seconds and is closed for 5 seconds (for every 10 seconds). By your logic, the duty cycle is 100%.

:roll:

He meant to say open time versus total time per cycle.

Yes, but actually it's been so long since I've messed with cars, my recollections were incorrect.

 

[radioouman]

I loved my old throttle body injected K-cars. One injector to replace if needed. One o-ring to go bad. The fuel system was very easy to work on. I like the efficiency of the multi-point injected engines, but I hate heving to pull an entire fuel rail and hope to the the o-rings back in the right places.