I'm an old(er) fellow and should know the answer..........but I don't. I like to tell other fellas I'm a "car-guy" but if they axe me a FI question the charade would be OVER! I know FI sprays fuel under pressure into cylinder and air is sucked into the mix......right?! The height of the injector stacks plays an important role in the tuning mix. Question......as RPM increases to 8000+ does the pump speed up that much or what? How do you know when to put in a different "pill"? Is the injector shot adjustable like an accelerator pump? Is there very many reasons why...mechanical FI is not friendly for street rods? If so....why did the Corvette back in THE SIXTIES figure it out so well? Would a few of you FI gurus enlighten me? Thanx, 6sally6
What little I know,,,,,the pump does speed up with rpm,,,,,it’s direct belt driven,,,,or camshaft driven . There is no accelerator shot,,,,,it’s a straight blast as the throttle is opened,,,,,,the barrel valve is shaped to give it a lot,,,,really quick . The valve is kind of a cut away,,,,,but,,,it’s an instantaneous shot of fuel . Yes,,,,,the stacks can tune an engine,,,,,and add a tremendous amount of power,,,,,at different rpm’s . If I remember correctly,,,,Smokey Yunick,,,,,,gained 98 hp on his Indy engine ,,,just by changing the stack length . And,,,,there is some debate as to how street unfriendly mechanical injection is . Some people like it,,,,some don’t,,,,,,,almost anything can be tuned to be reasonably tolerable eventually . Tommy
I'm interested in this, but don't have any answer's for you. I do know that comparing a Rochester FI unit to a Hilborn style stack injection is like comparing apples to oranges.
Yep Yes. Pump is crank (sometimes cam) driven, so pump increases with RPM. When the pistons come out of the exhaust headers as a fine spray of sparkling, burning aluminium. Lol. Change pills when track elevation changes, weather changes, track condition changes, ET being targeted changes..... a real science. Takes a lot of note-keeping to get consistency. No injector shot... but the nozzles keep spraying when the throttle plates are shut (unlike a carb which mostly stops flowing). There is fuel wetting the valve seat ready for the plates to open. No accelerator circuit, no power circuit, fixed mixture.... its basically an engine set up for one run, not the widely varying conditions on the street. Cheers, Harv
No.1: yes No.2: The length of the stack varies with many variables. The pump is driven at cam speed so as rpm rises, so does pump volume. No.3: jetting is about adjusting fuel volume to get the proper air fuel ratio No.4: There is no "injector shot", you richen up the barrel valve to compensate for off idle throttle response. No.5: Mechanical fi has no compensation factor for all of the changes that happen in everyday driving. No.6: The GM fi had a vacuum boost sensor that did some of what modern efi does, only not as well. The GM system was a compromise to find a more efficient fuel delivery than a carb that may have been compromised by production requirements. If you talk to corvette owners, many have stories about it being less than advertised. My exp. has been with older units that have been installed on engines with too much cam timing, hence no vacuum signal to tell the unit what to do. The result is very poor operation.
The early Vette system was designed for a street engine. I don’t know the specifics, but they had to do something to make it easier to start. The stack injectors typically get a squirt of gas by hand at starting time.
Don't know much about Hilborn units but have had a few Rochester units. The one on my 57 Fuely ran extremely well and wasn't a problem after learning about it over the many years we had it. Wife used to drive it to work in town-no problem. Vacuum signal is critical as said. Always carried an extra drive cable--never had to use it. It was not as happy on the newer blends of gasoline.
It's tough to get one setup for the street, some have pulled it off, @Stan Back is one. Now this one makes it easy !
Yes, as well as the 60's and early 70's Porsche 911's. I owned several with that system and found it to be very easy to work on and very reliable, even with 6 separate "stacks".
The Bosch K-jetronic was a quite popular mechanical injection for street cars from the seventies to the nineties. The basic construction is simple, the air flow into the engine forces a door to swing open, the door controls how much the valves controlling fuel flow opens, fuel flows continuous through the fuel injectors - a little fuel when the air flow is small, a lot of fuel when the air flow is large. Downside is that the door restricts air flow a bit, so there is a slight power reduction compared to some other options. Fuel pressure was basically used as a simple hydraulic system, giving the force holding the door closed. Changing this pressure would alter how easily the door opened, and reducing this pressure was used to increase the amount of fuel to a cold engine, i.e. a basic choke function. Later the K-jet was upgraded to the KE-jet, where electronics and an oxygen sensor in the exhaust was used to fine tune the amount of fuel on the fly, by altering the control fuel pressure.
Your egt is your indicator of rich or lean. Lean makes power , to lean kills engine. If my edt got above 1200* I got real nervous.
And contrary to what the "...tronic" bit might suggest, it was all hydraulic/mechanical. The only electric part was the solenoid activating the cold-start injector. I've heard of people running that on a toggle switch i.l.o. a choke.
There is some consensus that the closest a racing-type MFI system got to really streetable was the Lucas system.
Not only does the length of the stack affect performance but the location of the nozzle as well. A higher nozzle is better for gasoline and lower for alcohol or a mixture with nitromethane. Sprint car SBC injection systems do not have the nozzle in the injector body, they are in the cylinder head next to the spark plugs. They can also have high speed lean out pill holders with different weight springs.
There are different size nozzles for different size engines. The "pill" is in the return line so enlarging the "pill" leans out the engine
Well, I ran Enderles on the street for a number of years. Here in San Bernardino, the daily temperature swing of 40+ was not uncommon. I never could get it right for a whole day. (Most of the other street cars wouldn't fuck with it any way.) I could of got a "Dial-a-Jet" like I heard the sprint car ran, but never got around to it. Then, when converting to a Bonneville Street Roadster, I had to pay more attention -- plus I was measuring exhaust temps on both side's back cylinders. Here's a very amateur way we "corrected" it . . .
"I know FI sprays fuel under pressure into cylinder .........." I think into the "port" ( manifold or cylinder head) is closer. Injection into the cylinder , at least after the intake valve closes, is Direct Injection. Like diesels, Mercedes 300 SL, and some quite modern berry boxes.
I ran an old Hilborn setup on the race car which was an alcoholic. I don't think I ever changed the "pill" and it ran very good. One of the guys I raced with used a needle valve setup so he could "tune" the car from the driver's seat for maximum power. Some guys also ran a "dial-a-jet" which had a large knob on the dash and multiple "pills" in it. The Hilborn is a constant spray system. I remember reading about Stu Hilborn and people telling him his system would never work because the fuel spray needed to be timed. His reply was that the intake valve was only closed a very short time when the engine was running so it shouldn't make a difference. Turned out Stu was right on a race engine. As others have said, the pump is positive displacement and tied to engine rpm. We drove the pump off the front of the cam. The more rpm the more pump output you have. The barrel valve is connected to the throttle linkage and also controls the amount of fuel to the injectors based on throttle opening. Throttle response was instantaneous.
There were actually two electric parts (on top of the electric pump), but both quite basic. One was the cold start injector you mention, it had a temperature sensitive timer in the head, that activated the injector up to 7 seconds I think after a start in very cold weather - not in use at all for more normal temperatures. The other was in the pressure regulator for the control pressure (that held the door closed), the regulator had a bimetal spring that reduced pressure when cold to make the engine run richer. The regulator was mounted to the engine so it would slowly adjust pressure according to engine temperature, but it seems that was a bit too slow so there was also an electric heater built into the regulator. This system has been popular in folkrace (a kind of junk car racing) here, as Volvo used it in their higher power engines for the 240 and 740. The pressure regulator would be disconnected from the electricity and moved off the hot engine to make the system run richer all the time, or it was completely switched to an adjustable regulator to make it easy to adjust the right amount of fuel for max power. Reduced vacuum due to hotter camshafts may have been a factor, with less vacuum I'm guessing the injection supplies less fuel. I've connected one cold start injector to a push button myself on a friends folkrace 740, for use as a choke just as you say. Old abused engines with hot cams that make little vacuum and mechanical injection systems that has had their stock cold start enrichening system amputated don't quite seem to like to work together, so some extra fuel from the push of a button made a night and day diference when starting it - especially the first cold start in the morning.
I got a Kinsler complete system I was going to run on a 302 chevy , UNTIL I heard all the learning needed . It sits
The best mechanical injection systems that I have ever run were the Bosch CIS K-Jetronic, and KE-Jetronic (Lambda Sonde). Neither has any business on an American hot rod. Stack injection has only been figured out by a handful of people for the street for a good reason. It can be basically thought of as on, or off. That is fine for a drag car, but downright terrifying on a road-race car, and nearly impossible to use on the street.
I ran Enderle injection on my 32 Race truck where it worked well. Quit racing and put it on the street. It was frustrating to say the least. Get it running good on Tuesday, wouldn't run on Wednesday. Hot rod stack injection (Hilborn, Enderle etc.) isn't as sophisticated as a carburetor, no idle circuit etc. so they can test you. Finally sold the injection to a boat racer and went back to carb. Mick
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