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Discussion Starter · #1 ·
Hey Chris maybe you can help me with this if not maybe someone else will jump in, have you ever compared a fuel injection to a carb if so what was the out come? are there any advantages or disadvantages to the fuel injection ? what size injector's do you need for a NA combo and is there anything such as too big? is there a big difference between standard and sequenale? my class allows a 4150 style or a 90 mm throttle body wich would flow more? now since I know nothing about FI but trying to learn here'my thinkin would a FI system with the O2 sensor's on each bank in a open loop ( I think) with nitrous read a lean condition and add fuel to compensate? did ya ever see a post with soooo many question mark's???? Hey Monty you used the FI with the juice howed ya have it set up and did ya see a differance will it work as good as I think
 

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When in open loop, you aren't using the O2 sensors. At wide open throttle it's fixed output of the injectors. You don't have to change a thing on the spray. The nitrous system, if it is a complete system, will take care of the extra fuel and timing issues.
 

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Yes I have fuel injection experience... specifically the FAST system.

If you're limited to a 90mm.... then you need to stick with the carb IMO.

I have done back to back testing with EFI vs. Carb, on high rpm naturally aspirated application.

Going from a good 4150 carb, to a single 95mm 1400 cfm Throttle body EFI they were dead nuts.... within 5 repeatable horsepower... same day, same dyno, same everything.

On an n/a engine making around 800 horsepower, you would want around 55-65 pound injectors. Preferably 55... you want the duty cycle to be as close to 100 percent as possible... 65 pound you will not reach that area, in that hp range. I do not know what hp you are making so I am only relating my experience.

I have no experience tuning Nitrous with EFI, Monty is the man for that.

Honestly, if you're n/a... I don't believe you can beat a carb.... at least not yet. I just don't see it. I sold all my EFI stuff and went back to carb.... It was fun, but the EFI took all my attention away from the car, and things were neglected. If I had more crew, or had I went through the learning curve in the off season(almost impossible for the working class guy) it might have been a better experience.

I'm going to dabble in it again sometime down the road but it's not a real priority as it won't win races in my opinion.
 

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The trick in entire EFI O2 gig is that you ultimately, would like to turn o2 correction OFF. We did finally reach that point where our correction was below .5 percent and that is time to turn it off... and let the fuel map do its thing....and that was a milestone for us in the learning curve but it takes a long time and lots and lots of testing, and doing and redoing the fuel curve....

o2 correction is slow, or was at the time a couple years back.. and it does not respond quick enough during a run. So... you want your map right on the money so you don't need o2 to correct.... worst case if you can't turn it off you want it to only be correcting less than 3 percent.

.. I'm just throwing out thoughts now and rambling. :WGAF
 

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Discussion Starter · #5 ·
Okay so there fairly close but you preffer carb and you want the injectors at or near 100% duty cycle and I was wrong on the open loop it should have been closed loop okay like I said just getting my toes wet, what size carb did you compare it to a 850 or 950 ? everything I can find say's the 90 mm flows over a 1000 but what there flowing it at who know's, and I don't want the FI to supply fuel for the nitrous I was just wondering if it would help stop a burn down if something went wrong, so you want the correction OFF I thought it was a good thing to have it self ajust I know you want you table set as close as possible but why shut it off? and with a power adder dosen't it need it even more? how about the seqenital deal good or bad? needed or not? come on Monty I know you know this stuff help me out I'm lost in FI world
 

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I personally like the EFI unit. I was always lost on the guess work behind a carb. Change this jet to xxx and see what it does.. Add fuel.. subtract fuel.. remove bowls, adjust floats, replace this and that.. Im a dummy when it comes to cars so anything I can have absolute moves on makes it easier for me. Not to say that carbs are not good.. they just weren't good for me. I switched over to an EFI unit with a dry nitrous system. The conversion complete:

Manifold mods, throttle body, EFI unit, fuel pump, injectors and rails, regulator, dry nitrous system and other things I can't remember costed around $7,000. For me it was well worth it seeing a carb costed me $1200 for the unit and over $8000 in trying to figure out what the carb problems were.. :oops:

You will only run the car in closed loop making motor passes to get a baseline for the fuel map. Target a A/F ratio and make adjustments. Then take it out of closed loop and see what it looks like. If it flexs within .2-.3 within your A/F target on the average than let the nitrous fly.

I like the flexibility of being able to add 3# of fuel at 6800 RPM only. I use a FAST unit with some really old DOS version software.. That software in in #/hour compared to pulse width.. Again Im stupid so I need as much help figuring things out as possible.. Pulse width means nothing to me.. But #/hour does.. :D
 

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I picked up a FAST system for my car. Beebe put a system on his to we will be plugging you for info Monty. We have a real good guy from FAST on our side too so that helps :wink:
 

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The Guys at FAST are smart they will help you out. Dave Henninger is a great guy to deal with and is possibly the biggest authority in the nation on EFI.... IMO. He works for FAST.

As for the flow of the carb vs throttle body.... from my experience, and from the experience I've heard from others in the know, it WILL TAKE about 400 more cfm for the EFI to make the same steam as a carb..... My carb was an HP1000 4150... the EFI unit was a 95mm Wilson piece flowing a tad over 1400 cfm.
 

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This is a cut and paste from Pro-Systems (very good info on his site ..got to "under the scoop" section

Hope this helps.


UNDER THE SCOOP

Carburetion Vs. Injection

One of the most oft asked questions is why do carburetors make more power then EFI and why do the car manufacturers use EFI if carburetors make more power?

A few years ago we used some contacts at General Motors to verify some simple facts from some dyno data we had received from a head to head comparison.

An engine was being constructed for Comp Eliminator style racing and the program was going to be electronically fuel injected. Well the system was giving the engine shop some questionable numbers. The shop removed the EFI system and installed some of our Pro Stock carburetors on the EFI manifold top so they could quickly compare systems.

The engine responded immediately with much faster acceleration rates and a 5 percent improvement in power.

The EFI designer was brought out to the site and try as he might he could not out perform those carburetors. When the session wrapped up carburetors were king by 24 horsepower.

I've heard similar stories and similar claims when comparing systems.

So when we analyze this information it really comes down to a simple fact. Carburetors and Electronic Fuel injection are two completely different systems. They share no concepts and each has a different theory.

EFI's claim is this: I will supply sprayed droplets of fuel at the proper air to fuel ratio all the time.

Carburetors claim: I will supply a pre-emulsed froth of fuel and air into the engine at a preset ratio.

The results proved the analysis of the concepts to be correct. In this case, the carburetor was supplying the engine in question with the proper air to fuel ratio, so the EFI's advantage was gone. Remember, EFI has a computer to tune the engine. You have you. If you know how to tune you'll have the advantage. Carburetors (at the risk of sounding chauvinistic) are a man's game. Guessing rarely works. You have to know how to actually tune an engine.

Remember a carburetor is an atomization/emulsion machine. An injection system is a proper air to fuel delivery ratio machine. Two different concepts. If a carburetor can be designed to supply the perfect air to fuel ratio all the time it should consistently outperform EFI. Its design lends itself to have an unfair advantage in atomization.

Obviously adiabatic expansion is the next question on the list. So if we take a good look at the carburetor we see its not only a perfect machine for atomizing fuel, it also has another advantage. The joule-thompson effect.

Tests performed using quartz plates and infra red sensors located in the plenum area beneath an NHRA Pro-Stock engine revealed an intake manifold temperature drop on a 85 degree day of almost 20 degrees as a result of the the carburetor creating this effect.

So when your neighbor with EFI is ingesting 85 degree air, your power-plant could be ingesting 65 degree air.

That's a nice advantage.

But let's not skip over the atomization advantage. In a high end designed carburetor the fuel is emulsed to lift it. Its a controlled froth. I won't kid you, it's very difficult to control. Its much easier to build a carburetor that operates on a vacuum to ratio concept. But the fogging advantage is gone. So when a customer asks, why is this carburetor more expensive than that builders carburetor as they look basically the same. Most of it is all in the emulsion package and the time spent flowing it and tweaking it to do its job. Remember in a high emulsion design .001 of an inch is a big deal. They're difficult to balance and require sophisticated equipment that many shops have never seen. Also, don't go poking things into the metering block passages to inspect them or look around. You might just lose 10 lbs of torque.

The disadvantage of carburetors used to be restriction. I remember back 20 years ago before booster technology really took off you had to size carburetors to operate on 1-2 inches of vacuum in the plenum at the starting line. The restriction alone was probably costing these engines a 2-3 percent power loss.

Tests we performed at Sonny's racing 5 years ago showed us numbers of about .6 in the plenum and spikes of about 1.1 to 1.3 in the runner at the finish-line. That's a pretty huge decrease and just for dynos sake when we built carburetors large enough to reduce this number by on average 40 percent we saw an increase of only about 3-5 horsepower on an IHRA Pro-Stocker. SO that advantage for EFI is now also gone.

Now that these same engines can operate on as little as .5 hg of vacuum at the starting line and only 1-1.2 at the finish-line, the restriction is nil. Really it all comes down to getting the air to fuel ratio correct. If a carburetor can do that, it should win the race every time. After all, by design, it's a superior emulsion machine.

Thanks for reading.
 
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