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454 TBI intake manifold... Even flow
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journeyman
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PostPosted: Fri Feb 17, 2012 6:12 pm    Post subject: 454 TBI intake manifold... Even flow Reply with quote

I have my 454 with the modified centerfire heads running, but barely.

I pulled the plugs to find that the center cylinders were really rich (very black plugs) and the front and rear cylinders were really lean (very white).

Now, of course it makes sense why this was pinging at mid range RPMs... With the two injectors for the TBI trying to satisfy all cylinders, NONE of the cylinders were running efficiently. 4 were too rich and 4 were too lean.



I talked to Robert at Klein Engines in AZ. He said this is a common problem and that they could machine (a feature?) in the separator between the planes and even out the flow.

Questions:
1) has anyone here run into this before?
2) NONE of the aftermarket manifolds advertise how even the flow is from one cyl. to another, runner to runner. (I do understand that this will change at different flow rates, but I am primarily concerned with the 200-300 cfm range. ) Does ANYONE even measure this? Why is it not advertised?
3) has anyone heard of a 'fix' for getting [more] even flow runner-to-runner on a dual plane intake manifold?

Thanks in advance for your replies.
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10sec.et
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PostPosted: Sat Feb 18, 2012 2:15 am    Post subject: Reply with quote

what intake manifold are you running ? have you tried a 1" or 2" open spacer ? what about cutting away some of the divider ?

honestly, in my experiences with TBI, ive found that a well tuned Holley will perform just as good, if not better.

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journeyman
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PostPosted: Sat Feb 18, 2012 3:58 am    Post subject: Reply with quote

I am running the rock stock GM TBI intake and need to keep it that way (I am in California).

I sure would like to see some actual flow numbers for the differential between the runners in factory stock condition.
Are we talking +/- 10%? 15%? 20%???

The engine builder (Klein's) I am talking about is offering to machine the divider somehow to even out the flow. Honestly, I do not feel comfortable with language like that. I understand numbers!
example: for 240 cfm, I would like to see port delivery of 30 cfm +/- 1.2 cfm or something like that (I don't know WHAT numbers I need, just the format of the numbers so I can compare improvement over stock)

If machining out the divider improves the distribution, why wasn't it that way from the factory? Does it sacrifice part of the operating range performance? My engine is a very low RPM engine. Redline for me starts at 3500 RPM and this engine NEVER sees over 4200
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journeyman
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PostPosted: Sat Feb 18, 2012 8:44 am    Post subject: Reply with quote

Found this:
The Dual-Plane manifold is standard equipment on most passenger engines. The manifold plenum is divided left and right immediately under the carburetor (except for a small notch for idle balance)... This method supplies the cylinders as if it were 2 separate V4 engines.

For improved peak power, especially where the carburetor is not large enough, many tuners cut down the height of the divider wall, allowing a degree of “sharing”, where some mixture can be drawn from the opposite side of the carburetor. This will, of course, reduce throttle response, and generally require richer jetting proportionate to the degree of commonality: lower divider = more “plenum” effect shared between the left & right sides of the carburetor. Complete removal is generally not effective - install an open spacer or a single-plane manifold if you have to go this far.

reference:
http://victorylibrary.com/mopar/intake-tech-c.htm#dp
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af2
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PostPosted: Sat Feb 18, 2012 10:57 pm    Post subject: Re: 454 TBI intake manifold... Even flow Reply with quote

journeyman wrote:
I have my 454 with the modified centerfire heads running, but barely.

I pulled the plugs to find that the center cylinders were really rich (very black plugs) and the front and rear cylinders were really lean (very white).

Now, of course it makes sense why this was pinging at mid range RPMs... With the two injectors for the TBI trying to satisfy all cylinders, NONE of the cylinders were running efficiently. 4 were too rich and 4 were too lean.



I talked to Robert at Klein Engines in AZ. He said this is a common problem and that they could machine (a feature?) in the separator between the planes and even out the flow.

Questions:
1) has anyone here run into this before?
2) NONE of the aftermarket manifolds advertise how even the flow is from one cyl. to another, runner to runner. (I do understand that this will change at different flow rates, but I am primarily concerned with the 200-300 cfm range. ) Does ANYONE even measure this? Why is it not advertised?
3) has anyone heard of a 'fix' for getting [more] even flow runner-to-runner on a dual plane intake manifold?

Thanks in advance for your replies.


I read this and I am confused. You only changed the heads and this happened? Like I said I don't quite understand. I am going to look into the heads to see.
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af2
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PostPosted: Sat Feb 18, 2012 11:11 pm    Post subject: Reply with quote

Ok looking at Fueling heads I see no reason the heads would do that. They are configured the same on the intake. The chamber might want less timing from what I see and that is all.
Confused but have some ideas.
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af2
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PostPosted: Sat Feb 18, 2012 11:13 pm    Post subject: Reply with quote

Oh 1 more thing about the secret cut the center out of the intake.

Try it but I do not see that as the problem.
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journeyman
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PostPosted: Sun Feb 19, 2012 12:15 am    Post subject: Reply with quote

The heads raised the CR to 10:1 (small chamber), which made exacerbated a poor (but livable) situation to an "on the edge" situation.

With the 8.25:1, the engine could "live with" the lean burning cylinders. It just was not that big of a deal. With the higher CR, that cyl. imbalance showed up in the form of pre- detonation on the lean cylinders.

Have you ever done this cut on the divider plane? Know anyone who has?
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10sec.et
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PostPosted: Sun Feb 19, 2012 3:33 am    Post subject: Reply with quote

journeyman wrote:

If machining out the divider improves the distribution, why wasn't it that way from the factory? Does it sacrifice part of the operating range performance? My engine is a very low RPM engine. Redline for me starts at 3500 RPM and this engine NEVER sees over 4200


manufacturers have to meet CAFE standards. they didnt care about even distribution, just meeting the latest BS emission standard. i would try an open spacer. im guessing youre concerned about passing emissions ?

one thing that comes to mind that this is an old and very primitave EFI system. it could be that it needs injectors and has just gotten lean to the point that its now obvious on the four corners. when those TBI injectors go bad, they dribble fuel and flood the center cylinders and starve the corners. have you checked fuel pressure ? try hooking up a timing light (inductive clamp around the injector signal wire) and see what the "cone" looks like. you will need an advance timing light for this.

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journeyman
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PostPosted: Sun Feb 19, 2012 8:56 am    Post subject: Reply with quote

Quote:
one thing that comes to mind that this is an old and very primitave EFI system. it could be that it needs injectors and has just gotten lean to the point that its now obvious on the four corners. when those TBI injectors go bad, they dribble fuel and flood the center cylinders and starve the corners.

Interesting and very logical. The injectors have upwards of 90K mile on them.

I definitely am interested in ANY mods that increase combustion efficiency, but at the same time, I live in CA which means every 2 years I have to face the grim reaper... The communist smog police that want you to conform to the status quo.

I am thinking now that a combination of rebuilding the injectors and modifying the separator plate on the intake might be the most reasonable, logical option... IF this intake mod really works. And that is the big question. Will it really make a positive difference?
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Big Dave
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PostPosted: Sun Feb 19, 2012 11:16 am    Post subject: Reply with quote

Your TBI intake manifold is actually a low rise smog era cast iron QuadraJet intake manifold. The TBI uses a heated adapter plate to sit on top of the Q-Jet manifold.





As such any CARB approved manifold will get you past the smog police and improve your power as well as reduce emmissions.

Keith is correct (as usual) and your problem is with the TBI itself. It is worn out. You can buy replacement injectors but check on line for modifications that you can do to the unit to improve the power and still be street legal. (simple stuff like raising the injector so that the discharge is centered in the venturi) I have read in the past two or three boards that specialize in just learning to live with TBI (which I have refused to do and yank them off all vehicles and replace with a Holley because I live in Florida that allows Don Garlits to run his top fuel Swamp Rat on the street it only he puts a brake light on the push bar).

Big Dave
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journeyman
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PostPosted: Sun Feb 19, 2012 5:47 pm    Post subject: Reply with quote

Florida... One of the remaining free states... For now.
Envious. There would be nothing holding me back from the Accel Stealth if I were there.

Does my factory TBI manifold have that heated riser on it that you pictured? Somehow I don't remember that (I am out of the country right now).

I am guessing that a combination of new injectors, machined divider plate and raising the injectors (possibly a spacer plate?) will be a significant improvement.
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Big Dave
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PostPosted: Sun Feb 19, 2012 6:15 pm    Post subject: Reply with quote

That is what I have found on the 1987 and the 1989 motors that I have used as cores. The Q-Jet intake was pancake flat like it had come out of a Corvette which was odd as these where pick-up trucks that had a four inch to an eight inch tall air filter due to all the room under the hood.

Big Dave
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journeyman
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PostPosted: Mon Feb 20, 2012 10:33 am    Post subject: Reply with quote

Unsure I am thinking correctly on this, but it seems that with low flow/low RPM, a heated spacer like the one you have pictured could be a real help.
Atomization should be improved.

It seems like the only drawback to a heated intake would be in the high flow/high RPM ranges.


If that is the case, would it be advantageous to add one of these below my TB?
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Paul P
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PostPosted: Mon Feb 20, 2012 12:19 pm    Post subject: Reply with quote

You could always put the spacer in and not connect the water lines. That would help keep things cool and improve distribution.
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