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4 bbl FAST TBI question

socorob

socorob

Donation Time
If I'm installing a 4 bbl FAST TBI on the dual plane offy manifold, how should I adjust the secondaries to open? It has a Holley 20-122 adjustable secondary rod to go between the primary and secondary lever so you can adjust when the secondaries open. Sice this is a TBI and not a carb, would it be better to have them all 4 open at once and let the maps take care of the fuel, or set it up like a progressive carb? Have the primarie open only while cruising and the 2 primary injectors feed it, then when you reach a point, half throttle or whatever, have it set up like a progressive carb. If so, what would be the optimum point to have the secondary open, 30% throttle, 50% throttle, etc.? Im not even sure that the controler can even be set up to do it llike that yet. Im in the very early stages of going to EFI, and just trying to gather everything and all the information I need to get started. So far I've built the controller and loaded the firmware on it, and got the tbi and a few other pieces. I think this one is going to take a while..
 
Barry

Barry

Diamond Level Sponsor
Robbie,

I think you are going to need all the "progression" you can get (and then some) to manage the off-idle throttle response.

The FAST "4-barrel" throttle bodies are far too large large for a 2.8 Ford V6. You only need about 350 CFM and the "small" FAST throttle body is 1375 CFM. Just barely "cracking" the throttle with an available flow of 1375 CFM will effectively be wide open throttle on the 2.8 V6.

Just my opinion, your mileage may vary.
 
V

V6 JOSE

Donation Time
That´s the problem with most after market fuel injection systems. They are just too big to work on the little 2.8 V6. The smallest one I´ve seen so far, is 650 cfm, which is way too large for the 2.8 V6. The closest one that I think will work, is the throttle body injecion from another Ford V6, like we´ve heard about on this forum. Even those may be too large, since they come off of a 3.8 V6
 
R

RootesRacer

Donation Time
V6 JOSE said:
That´s the problem with most after market fuel injection systems. They are just too big to work on the little 2.8 V6. The smallest one I´ve seen so far, is 650 cfm, which is way too large for the 2.8 V6. The closest one that I think will work, is the throttle body injecion from another Ford V6, like we´ve heard about on this forum. Even those may be too large, since they come off of a 3.8 V6
Click to expand...

The 3.8 TBI would be fine for most 2.8 builds as the engine it comes off of is only 160bhp.

The bigger problem though for that throttle body is the old technology TBI injectors it uses have poor fuel control and atomization making the changeover from carbs to EFI of little benefit.
 
Barry

Barry

Diamond Level Sponsor
A correction to my previous post.

It appears that the FAST 4-barrel TBI is "only" 1000 CFM rather than 1375 CFM.

1000 CFM and 340 lbs. / hour of injector capacity is still far too large for a 2.8 V6 that needs about 350 CFM and 120 lbs. / hour (at most) of injector capacity.
 
socorob

socorob

Donation Time
I still haven't gotten to that yet. It' can be set up as a progressive 4 bbl so theoretically you can disconnect the secondaries and run it as a 2 bbl. you can change linkages on it to make it a double pumper style or secondary style. Unfortunately I haven't had much time to commit to the sunbeam lately.
 
V

V6 JOSE

Donation Time
If it has 1,000 cfm, even if you use half of the barrels, it will still be too large for the 2.8.

Jose
 
J

Jon H

Donation Time
Has anyone tried or seen the Holley 550-400 4 barrel TBI system? Their site lists 200 - 400 HP range? A well build 2.8 should have 200HP, correct?
 
V

V6 JOSE

Donation Time
Hi Jon,

It isn´t about the amount of hp., but about how much air the displacement will move. According to Holley´s own numbers, the 390 cfm four barrel itself is too large for the 171 cu. in. displacement of the little 2.8 V6. Fortunately, the little V6 handles it because most of the time it runs on only two barrels, which have 195 cfm. by themselves, while a stock V6 two barrel has a cfm. rating of between 240-250 cfm.

If you can find a fuel injection with a maximum cfm. rating of 400 cfm., you might be able to get it to work.

Notice the the specs of the system you mention,say between 200-400 hp., which is for a small V8, like a 289 sb Ford.

Jose




Jon H said:
Has anyone tried or seen the Holley 550-400 4 barrel TBI system? Their site lists 200 - 400 HP range? A well build 2.8 should have 200HP, correct?
Click to expand...
 
crs

crs

Gold Level Sponsor
Jose,
Dumb question for you - With the Holley 390 cfm, what happens when you "floor" the accelerator with the revs up and the 390 secondaries do open fully?

I have observed that on my V6 if the secondaries open at low rpm on a cold engine, a bit of vapor pop/poofs up through the simple wire mesh cleaner now installed. That was an accident and I have not done it since. The hood is still off so I can see the mist come out of the screen. This has never happened with a warm(270 degrees) engine when running up just over 3000 rpm.
 
Barry

Barry

Diamond Level Sponsor
The secondaries on a Holley 390 should not be be opening at low RPM on a 2.8 V6. If they are, something is wrong with the carb.
 
V

V6 JOSE

Donation Time
Hi Charles,

The secondaries on the Holley are operated by vacum, so at low revs th engine doesn´t have enough vacuum to open them. What I think is happening, is that when cold, the electric choke isn´t working well, in that it might need to be adjusted to a bit richer position.

What you saw is gas being expelled from the carb, because the mixture isn´t rich enough and the engine misfires and coughs up through the carb. Not dangerous, just annoyng. I would suggest adjusting the choke a bt tighter.

Jose


crs said:
Jose,
Dumb question for you - With the Holley 390 cfm, what happens when you "floor" the accelerator with the revs up and the 390 secondaries do open fully?

I have observed that on my V6 if the secondaries open at low rpm on a cold engine, a bit of vapor pop/poofs up through the simple wire mesh cleaner now installed. That was an accident and I have not done it since. The hood is still off so I can see the mist come out of the screen. This has never happened with a warm(270 degrees) engine when running up just over 3000 rpm.
Click to expand...
 
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