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TBI Throttle Body Injection discussion and questions. L03/CFI tech and other performance enhancements.

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Old 01-31-2008, 09:37 PM   #1
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Dual TBI (no not CF)

i read somewhere some one was going to try a dual TBI setup on a 383 b/c the TBI does not flow past 650 or something. Does that need to be done b/c of flow and if so does anyone have a picture and how they set it up? maybe a dual carb manifold with adapters?
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Old 01-31-2008, 10:13 PM   #2
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Re: Dual TBI (no not CF)

im using 2 small block tbis on a heavilly moded 2 4bbl dual planr with 4 90#ers. im mainly doing it for fuel flow at 6500 so the manifold can recover when it upshifts and drops to 3500. absolutely no street running for me.
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Old 01-31-2008, 10:46 PM   #3
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Re: Dual TBI (no not CF)

so it is not really a streetable setup by it's nature or by design? can i dual tbi be done and i just found a BB TBI that says it flows 850 CFM. I guess the real question is this: a 383 meant for low rpm torque (what i want) and respectable MPG needs how much flow. I figure make the power low so i do not need to rev it up where the TBI falls on it's face.

i know there are tons of variables but how much CFM is needed on a "sleeper" street car attmpting 400 horse area with even more torque? If it is more than lets say 850cfm then a dual tbi will be a must correct?
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Old 01-31-2008, 11:34 PM   #4
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Re: Dual TBI (no not CF)

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so it is not really a streetable setup by it's nature or by design? can i dual tbi be done and i just found a BB TBI that says it flows 850 CFM. I guess the real question is this: a 383 meant for low rpm torque (what i want) and respectable MPG needs how much flow. I figure make the power low so i do not need to rev it up where the TBI falls on it's face.

i know there are tons of variables but how much CFM is needed on a "sleeper" street car attmpting 400 horse area with even more torque? If it is more than lets say 850cfm then a dual tbi will be a must correct?
I'll put it this way, I feed a 450+ HP 350 to 7,000 rpm with a 454 TBI unit on a single plane 2bbl manifold.
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Old 02-01-2008, 01:08 PM   #5
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Re: Dual TBI (no not CF)

oh okay thats what i needed to know. thanks!
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Old 03-19-2010, 01:03 AM   #6
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Re: Dual TBI (no not CF)

Can you show us the engine specs & dyno sheets?
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Old 03-23-2010, 05:45 PM   #7
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Re: Dual TBI (no not CF)

Fuel flow is more of an issue than airflow with TBIs. The passages in the injector pod become a restriction at high fuel flows, causing the fuel pressure at the injectors to drop. GM had a special pod for the later TBIs that had slightly larger passages and a regulator inlet. for a hi-po setup, one of those would be the one to have.
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Old 03-24-2010, 02:09 PM   #8
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Re: Dual TBI (no not CF)

Dimented: I may have that 7.4L TBI. Mine was specific for 1994-1995 model year. Is that the one you are speaking of?

This is somewhat close and looks pretty sharp. http://www.thirdgen.org/techboard/tb...tbis-dual.html (Project- Bored TBIs on dual quad manifold)

tripower TBI?

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Old 03-25-2010, 01:02 AM   #9
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Re: Dual TBI (no not CF)

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Originally Posted by dimented24x7 View Post
Fuel flow is more of an issue than airflow with TBIs. The passages in the injector pod become a restriction at high fuel flows, causing the fuel pressure at the injectors to drop. GM had a special pod for the later TBIs that had slightly larger passages and a regulator inlet. for a hi-po setup, one of those would be the one to have.
Is it possible to 'massage' some of these fuel passages on an earlier 454 pod to increase fuel flow and reduce pressure drop???? On a side note I am considering to run external fuel pressure regulator - Aeromotive 13301 with vacuum reference (and EBL to compensate for variable fuel pressure).

454 POD


454 FP regulator
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Old 03-25-2010, 11:19 AM   #10
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Re: Dual TBI (no not CF)

POI... the 13301 comes with two springs. the weaker of 2 (0-20 lbs) allows a larger drop in FP than the stronger. I ran them both at 20 and the weaker dropped FP to around 13.5 lbs I recall. Stronger dropped FP to around 16. Result is better idle. I disallowed asynch fuel in .bin on both.
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Old 03-26-2010, 08:42 AM   #11
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Re: Dual TBI (no not CF)

The later 454 pods have fairly large passages, so it should not be an issue. A possible issue, though, is the return. If your using a large fuel pump, you can get into the situation of having a significant pressure rise within the pod, which will raise the fuel pressure during low demand when most of the fuel is returning to the tank. You can tell if this is an issue by observing the fuel pressure as the engine is revved. If the fuel pressure drops when you rev the motor, then there is a significant pressure drop through the pod. You can enlarge the passages in some places. I did it with a holley TBI pod (has much smaller passages), and it helped quite a bit.

An external regulator is a good way to go. If your running at MPFI pressures, you can dead-head the pod and just supply it with the regulator. The only potential drawback may be the injectors not having a continuous stream of gas to keep them cool. The fuel pump and injectors rely on the fuel to keep them cool, and the injectors actually have bleeds in the sides of them to allow the coils to be immersed in fuel.
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Old 03-26-2010, 09:40 AM   #12
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Re: Dual TBI (no not CF)

I know it is hijacking this thread - but I am considering going with 13301 regulator - the question is by installing VAFPR regulator in return line, down stream from the TB. As you have mentioned FP can rise (at low demand) due to restrictive return path within TB fuel passage ways. Perhaps some inner passage rework (and where) is required. As always devil is minor details.

In both cases OE FPR will be removed and block off plate installed.

//RF
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Old 03-26-2010, 10:08 AM   #13
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Re: Dual TBI (no not CF)

I have stock 84 Vette fuel lines. I have TPI pump. 7.4L(1994-1995) GM TB and Aeromotive 13301 in return line with VAFPR used. 80 lbs injectors at 19.5 fuel pressure(WOT). I shift 5800 rpms and I guess 350 HP at engine. No restriction and cam maintain 12.0/1 on WB. I believe the issues develop with the popular Walbro FP 200-220 series pumps or others of similar capacity. Anyway there were posts suggesting that pump is over capacity of stock GM return lines.
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Old 03-26-2010, 10:08 AM
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