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Thread: 1946 Ford Coupe project

  1. #21

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    You don't necessarily "need" a dyno to tune your fuel map. You can record a full run on the street at full throttle, you just need your buddy to sit in the passenger seat with the laptop plugged into the car's computer to record the a/f ratio. Then you can tweak the fuel map and do it again.
    the cost of the computer connectors and the reprogramming software is not cheap, either... And requires a lot of knowledge and technical know how to create a fuel map.
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    My limited knowledge with Fuel Injection has me leaning toward a carb set-up. From what I've heard from engine builders, if I choose to go FI at a later date, the mild engine combination I'm building should work with the FI, maybe a milder cam if I choose to go that route. I was looking at the MSD FI, looks to be a pretty straight forward plug-n-play unit. I also know FI requires attention with the pump and return lines to the tank. My focus now is getting the chassis completed and the car back on the ground.
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    Quote Originally Posted by Spike View Post
    You don't necessarily "need" a dyno to tune your fuel map. You can record a full run on the street at full throttle, you just need your buddy to sit in the passenger seat with the laptop plugged into the car's computer to record the a/f ratio. Then you can tweak the fuel map and do it again.
    the cost of the computer connectors and the reprogramming software is not cheap, either... And requires a lot of knowledge and technical know how to create a fuel map.
    Yeah, you can do full throttle runs and tune that curve, but what about the 90% throttle runs? Or the 80%, 70% all the way down? On a carb, once you get the right size main jet with a full power run, the carb takes care of most of the tuning at all other throttle positions. Depending on the carb, you normally have 5 adjustments to make and the carb takes care of everything else; Float height, needle height, pilot size, main size, mixture screw. A simple FI system will have at least 10 RPM slots and 10 throttle positions to program. Thats 100 adjustments you have to make, which doesn't count any cold start enrichments, MAP sensor enrichments or any other inputs you're using to tune. You can easily do the WOT runs on the street and tune that, and you can probably do the no load conditions in your driveway, but everything in between is going to be a royal pain in the ###.
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  4. #24
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    Quote Originally Posted by agent4573 View Post
    Yeah, you can do full throttle runs and tune that curve, but what about the 90% throttle runs? Or the 80%, 70% all the way down? On a carb, once you get the right size main jet with a full power run, the carb takes care of most of the tuning at all other throttle positions. Depending on the carb, you normally have 5 adjustments to make and the carb takes care of everything else; Float height, needle height, pilot size, main size, mixture screw. A simple FI system will have at least 10 RPM slots and 10 throttle positions to program. Thats 100 adjustments you have to make, which doesn't count any cold start enrichments, MAP sensor enrichments or any other inputs you're using to tune. You can easily do the WOT runs on the street and tune that, and you can probably do the no load conditions in your driveway, but everything in between is going to be a royal pain in the ###.
    You can do just like a carb and plot a lot of those data points from a mathematical model and not actual testing data. You can even pull down the curves from a lot of popular carburetors as one way to get a baseline. But to be honest even a carb will only be close without some dyno time and for a lot of places the carb will be off and there is very little you can do to fix it (short of major modifications). Carbs do not keep the air fuel ratio ideal everywhere, they are always a compromise. Also so far you have only been talking about open loop FI. If you close the loop, the system can make a lot of these adjustments on the fly. FI gives you more control than a carb, but only if you desire to use it at that level. Some systems are brain dead easy to setup while others are insanely complex. BTW: there are plenty of carbs with a lot more adjustments than that, and FI with a lot less. Good FI will always perform better than good carbs, if the rules allow them. Not that I don't like carbs, I worked in a shop that set a world record and took an AHRA championship with carbs. But we also spent a lot of dyno time getting them dialed in to the best they could be. There is a reason that FI has largely replaced carbs everywhere. Hell, there are EFI lawnmowers out there. There are many types of FI, so you can't really make assumptions about all of them.
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