[Ace23]

Originally Posted by bobcowan

I'v been messing with performance EFI for a few years now. I wouldn't say I'm an expert, but I have done my home work. The learning curve can be steep. But I'll probably never go back to a carb.

Self tuning a myth and a marketing buzz word. Doesn't happen. The computer can get itself to about 75% or so of where you need to be. But you'll need to understand how it works so you can get it where it needs to be. Especially on a performance engine. Some dyno time with a pro can dial it in to run like a stocker.

I think throttle body EFI is not worth the expense and effort. Because it's a wet manifold, you end up with some of the same charectoristics of a carb system. Port injection (like stock engines) work really, parts are inexpensive, and are dead on reliable. Stack system look great, perform really well, but do require some extra work to get them running right. Stack systems are not a simple bolt on and go.

EFI will "tame" a big cam. The problem with a big cam and a carb is that you tend to lose intake charge velocity at lower rpm's. Because the air/fuel mixture is moving at such a slow speed, the fuel falls out of suspension and puddles in the intake; same thing with a throttle body. That's why engines with big ports and carbs idle at such high speeds. Port injection makes a significant improvement in that area. A big cam with big ports will idle like a ***** cat at 800 rpm's, and drive around town without a hiccup.

Cam shaft selection can make a big difference, depending on the EFI system you use. A throttle body will run fine on pretty much any cam that you choose. Port injection will do better with a cam designed for EFI, but can still be fine with the average hydraulic roller cam. An individual runner system really needs a cam with a wide LSA, like 114*. A big cam with narrow LSA will create a lot of reversion, and create that "cloud" effect that Webers were famous for.

Most EFI components are pretty standard, and not a lot of difference between one system and another. The ECU is, of course, the heart of the system. It takes in information, makes decisions, and then acts on them. The more complicated the system is, the better decisions it makes. And the harder it is to tune. It's a trade off. A carb is extremly easy to tune, but it's not very accurate.

Many ECU's have a lot of features to do a lot of stuff. Fuel, spark, turbo, traction control, multiple fuels, cam timing, etc. Don't waste money on features you'll never use.

I like the ability to use E-85. On a hot day or on the track, E-85 really runs well, makes excellent power, and keeps the engine cool. I have a switch under the dash to go back and forth between the two fuels. My ECU can use a factory fuel sensor, but for a variety of reasons I chose not to use it.

Modern engines use some kind of meter to measure incoming air, and O2 sensors in the exhaust to measure outgoing exhaust. It measures those qualities, and then makes decisions on the amount of fuel to be injected and timing to use. That's referred to as "closed loop". These are the most accurate, and if your engine isn't too radical, you should try to use that.

Bob,
Thanks for the insight. I'm leaning towards the FAST XFI Sportman with either their throttle body injection or the multi-port. From what I have been continuing to read the multi-port seems like the better way to go.......on the other hand the FAST tech team tells me that the throttle body injection would be fine for a street car. I feel like I should consult with Brent Lykins on the EFI as I would like to work with him for whatever becomes of the power plant. I want to maximize on the driveability, MPG and manners of the car. With my existing motor I do have a heap of good parts....I'm going to lean on Brent to maximize what I can achieve . I would love to go 385 series big block but I'm sure I can be satisifed with a well running thought out SBF platform. I enjoy the car now so it should be really nice when its not missing all its dang power. The key is going to be finding a tuner to tie it all togther. I don't like doing things twice and would rather spend the money and do it right the first time.

Originally Posted by Tom Wells

Ace23,

Lots of good opinions and some experience above; I'll add mine.

I have two large engines (521 in the Cobra, 557 in an 81 Zephyr wagon). Each has a Holley HP system which is throttle body and multi port.

Each engine started life with a carb and each migrated to EFI because of problems - one Demon carb that couldn't be tuned and one Holley carb that kept boiling the substance we laughingly call gasoline due to underhood heat.

The EFI has given each car a new personality that makes them easy to drive on the street and very nice when running track days at Sebring, Daytona etc etc.

Both have been what I call "learning experiences."

Here are a few examples.

1) Fuel pressure: The Cobra ended up with a sumped, baffled tank after a highway cruise showed fuel starvation due to gasoline running away from the fuel pump pickup on a normal interstate highway curve at 75mph. With a carb you wouldn't notice because the float bowl buffers the momentary lack of fuel pressure. With EFI, the engine stops when its fuel pressure drops to zero. The wagon has an in-tank setup I really like: Aeromotive Phantom. Fairly easy to install and has its own way of resisting fuel starvation that really seems to work.

2) Tuning: The self learning can get you 70-80% of the way there. It still needs work to tune it.

3) Bung(s): All these systems as far as I know need O2 sensors installed in the exhaust system. Mine are one per car, and are located at the beginning of the collector just after the four individual tubes join together. That location seems to work OK.

I'm sure I have forgotten several things - the mind tends to eliminate bad experiences.

The good includes easy starts, decent mileage, good throttle response. The lumpy idle can be programmed in ;-)

I have no regrets about switching. If I were building another engine I'd go EFI from the beginning.

As to different brands, most of the majors are fine. If you have someone conveniently nearby that would seem to be an advantage as long as their hardware is good and their tuning skills are up to snuff - don't ask me how to evaluate that! I like the Holleys because I've been using them for more than ten years and know a little about them.

Have fun with the decision,

Tom

Tom,
I've seen many of your post and I know you enjoy the big blocks with EFI....that is too cool! There seems to be many opinions on carb vs EFI but one thing seems to keep ringing out. I never seem to find a post where someone has used EFI and invested in a good tuner and then come to the conclusion they don't like it. I'm hoping I can buget this all together and get going. When I get ready to ask Lykins if he is interested in putting together a solution for me I'm sure the detail will start coming together. From what I can tell it seems like most of the multi-port intakes are single plane......can you work with a manifold manufacturer like Edelbrock to setup any of their manifolds for multi-port or is that something you have to modify yourself? I've seen where many of the builders favor a single plane like the victor jr on larger inch Windsors but I've also seen where dual plane intakes like a ported RPM air gap can flow pretty impressive numbers that are similar or equal to the single plane units.