Paul... The Gibson 110 Thanks for all the input fellas. after reading all of this, i'm thinking i just dont drive the car enough to put this kind of effort and money into it. i am interested most in the multi port as described by paul. so is that the one with the fuel rails that TA offers? please pardon my ignorance. i think i will put my time and effort in figuring out why my car has such a difficult time starting, and not just band-aid it with fuel injection. maybe ill save it for another day. (like if my tax refund is more then expected)
TA is the only one that offers a Buick intake out the door with injector bungs and fuel rails. I'm sure they can work with you on getting the intake, injectors and fuel pressure regulator then you can just wire in your choice of ECU. Hey, I fired up my q-jetted and points powered Centurion today and after the initial cranking (hasn't been started in a couple weeks), it re-fires up quicker than "any" EFI system I've seen, OEM or otherwise. It's not impossible to dial in a carb and distributor, but they can be as confusing as EFI, lol!
You can send any style intake to Wilson manifolds in Ft Lauderdale Fl and they will do the conversion from start to finish and they do 1st rate work. Don't know what EFI you're comparing your carb application to but if it starts better than an EFI system then you have a crappy EFI system, or at the very least a less than good tuner. Jmo
Or I have a superbly tuned Q-jet and points set up. Instantaneous fire up, as quickly as you can turn the key. No waiting for the fuel rail to pressure up, no waiting for the timing signal to sync. Call it what you will, it starts quicker than any OEM new car I've ever started in the last 15 years.
Basically this is the breakdown. Carb: dumps fuel and air into the engine in a lump based on the throttle position which moves valves and levers mechanically. TBI (throttle body injection): dumps fuel and air into the engine in a more atomized lump based on the throttle position and a few sensors and which open valves electically. Batch-fire Multiport Injection: Squirts fuel into each cylinder directly by way of an injector positioned in the intake track just above the intake valve. It's controlled the same way as the TBI but with more sensors. This system fires every injector at the same time regardless of which cylinder needs the fuel. Some such as the F/Y-body TPI (tuned port injection) also have an "upstream" injector which fires fuel into the intake when cold to richen the mixture and allow the engine to warm up faster. The vortec 4.3 in the mid 90's used a "spider" located under the intake to distribute the fuel from the line to the cylinders via plastic tubing and poppet valves. Sequential Multiport Injection: Mechanically the same as the batch-fire above, but with better control. This system fires fuel to the specific cylinder that needs it just before the valve opens fully to ensure no fuel is wasted in cylinders that aren't burning. It's main difference from batch fire setups is that it uses both a crank and cam sensor to know which cylinder is on the compression stroke during the intake opening sequence. Fuel injection can also be broken down into speed density and Mass Air Flow systems. Speed density uses a graph and dumps a certain amount of fuel based on your rpms. It's downfall is that the graph must be perfect and the engine may still have issues if you change altitude or the air temp changes. Mass Air Flow measures the amount of air moving into the engine as well as its temp to determin the proper amount of fuel needed to maintain the proper mixture. It's downfall is the added sensors such as the MAF, IAT, and O2 which can be avoided somewhat with speed density.
I understand you're trying to generalize EFI but imo you gave less than accurate and misleading info.
I kinda have to agree. Bammax mostly described an Alpha-N system for speed density. Alpha-N uses only rpm and throttle position for sensors (practically mechanical injection, but electronic). Speed density requires** the whole suite of sensors (cam sensor optional for sequential), and you build a fuel table off rpm and engine load (vacuum/atmospheric pressure) and uses the suite of sensor to calculate air density, where as a MAF system uses a heated element and calibrated tube diameter (the MAF sensor) to calculate the mass of air passing through) and the suite of sensors to trim the fuel calculations. **I use 'requires' loosely in the sense if one or two sensors fail the system won't quit, just not operate optimally.
Every component in any system is a potential trouble source.... the power will not be that much different, the economy will not be that much different,,, the expense and the hassle will be way more.... for 2700 bucks you can pretty well install a huffer..... and that would boost both the mileage and the power .... I converted a jeep to efi and after 5 years of hassle finally took it back to a holley carb.... it ran better with a carb with way less hassle....... IMHO,,,, mistake,,,,
Then you had a poorly laid out and/or tuned EFI. Just an FYI -take a look at my vid on youtube. There's a guy on there with a '80 El Camino with a 350 Ramjet. It had the GM MEFI IV on it, He had to run 93 and got about 10mpg average. Sent it back twice to Arizona Speed to be recalibrated. No change. Put a true adjustable system on it, he now runs regular (87) and gets 15+mpg. Granted on a stock application there typically won't be a huge difference. But I get a kick out of the people that say their carb ran better than their EFI, they just had a crappy EFI I guess. Jmo.
Actually,, I used a 89 jeep set up,,,, from a wrecked comanche,,,, tuned it up several times,,, replaced all the injectors.... with brand new ones,,,, and I am a certified mechanic.... efi just did not do that much for that particular vehicle...
Doc You were correct when you said that going a factory EFI system or any system that does not allow the user to tune the fuel or the spark tables can be a Mistake. That was the very point at the begininng of this thread that systems that allow the user to have full control have the advantage over systems with limited or no access to the control unit. It was also pointed out that systems with full access give the user the most flexibility for success as well as the most freedom to screw it up. So it depends on how much support comes with each system and how much a person is willing to take on. Also there are many variables in going to a "Huffer" that can make the project a success or a frustrating situation also. If a person wants a supercharger system that doesn't violate the hood, then in most cases we are back to EFI again. Anyway this thread was successful because it gave Dan (the one who started this inquiry) the information he needed to make an educated decision BTW I love supercharging for street use! Paul
Dead on,,, Paul,,, :Smarty: Goes back to my statement about adding more components makes for more opportunity for failure of some kind....:laugh: :laugh: In my case,,, the truck was a 81 and the efi was the stock set up for 89 and still pretty primitive.... not laptop tunable.... In my humble,,,,:Brow: simple is better...
I was going with a generalized breakdown since it makes it a bit easier to undertsand the fundemental differences. If you get too specific than it becomes way too confusing to someone just starting out. For example I left out the double injectors per cylinder for nitrous setups, and the Bosch analog injection on the Olds motors in the late 70's, or the mechanical fuel injection from the 60's. For the most part speed density comes down to a fuel map that doesn't fluctuate while maf systems have a little more on the fly variability to the enrichment. Remember that this will come up years later on a google search so don't make things too specific and leave out the non-engineers p
Where I simply can drive from 7500+ feet in elevation to sea level on a single trip. And as the year progresses drive in conditions with air temps less than -10*F to greater than 120*F. Huge variations in atmospheric running conditions. That's my main motivation. I can get a Q-jet to start and run great at each of those, but I'd have to break the screw driver out everytime I drive off this mountain because my idle goes up 300+ rpm, plus it has off the line hesitations if tuned for one elevation and driven in another. Not to mention choke settings in winter versus summer. I've finally become complacent enough with the EFI I can now "Set it and forget it" and it's good. :TU:
So say what the difference is then? The point of this thread is to help people understand but all you're doing is harping on me about the exacts of outdated technology. Either give us the actual explination as to the differences between speed density and maf and why the oems ditched speed density or find a new target to sling crap at. I'm basing everything I say off of the findings of someone using junkyard GM parts in a retrofit. The most common speed density system someone will come across is the 80's f-body. It's great in hot rods but there's a reason why it was dropped prom production cars fairly quickly. Here's a great writeup explaining what each does and how it works. It also shows what years they were used. It's a great starting off point when going junkyard hunting for efi parts from GM's http://www.carcraft.com/techarticles/electronic_fuel_injection/index.html
From what I gather, OEM's went to the MAF system (that actually works in conjunction with the speed density system, MAP sensors are still on new cars) primarily for pre-warmed up conditions. Before the O2 sensors fired up, and to get a better grasp on air density before heat sinking under the hood took place. The MAF sensor helps calibrate the computer on knowing how much oxygen is in the engine and can back check against what the speed density system is calculating based on air intake temperature and engine vacuum(compared to atmospheric). OEM's are under government pressure to make sure emissions are met, so it's in effect a redundant system, if one doesn't agree with the other then you get a check engine light but the car doesn't quit running (anymore..). The MAF sensor can help back check the calibration on the baro table as like the O2 sensor can do feed back for atmospheric condition changes, where as a strictly Speed Density system with no O2 feedback turned on or second baro sensor (and calibrated table) can go astray. Most aftermarket speed density systems utilize an O2 feedback, some utilize a second baro sensor and table, and some both. The aftermarket embraces the speed density system most often because it's so flexible. A speed density system doesn't care if it's on a 100cc engine making 2HP or on a 5,000HP big block. Simply upgrade the fuel system and throttle body and go. A MAF system is limited by the MAF's available. Can you find a MAF for a 2HP engine? You could probably successfully use one from a small car, but if you upgrade to even 800HP, or more, how many MAF's are available and at what cost compared to a simple throttle body? They are rarely as upgradeable as projects progress because of their physical limitations, so only a few aftermarket companies go that route. If you can build a product that fits 300 applications, or build a product that can fit those 300 applications plus another 700, which route would you go? Economically the one that has the broadest reach. As mentioned, if you can not adjust the system on an aftermarket setup, then it sucks, no matter what type.
Now that's some good info. One thing to keep in mind too is that aftermarket mafs have a habit of producing poor performance on some cars since the maf isn't the same calibration as what the ecm is expecting to see. It's common on the LT1's to have a car become unreliable when the maf is swapped out for the bigger aftermarket unit. One common between all systems though is the need for a good temp sensor. On the TPI cars a bad temp sensor causes the upstream injector to stick on and it kills mileage. On the LT1 cars a bad temp sensor causes the entire car to go haywire. On the old Bosch analog units the temp sensor going bad would cause a no start condition.
