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Curious what your thoughts would be regarding taking a 4 barrel manifold, like the AZC piece, for example, and adding a throttle body and injectors to it. The only reason this occurred to me was with all the recent discussion about intake manifolds, and the L series having no easy way of putting the throttle blade in the center of the intake, this seems like a viable option. I'm sure a well designed log intake built from scratch will outperform it, but I'm curious about the offset of cost of building a custom intake versus the benefits of having the air enter the intake in the center, as opposed to at the end of a log.


The old turbo tom intakes had the turbo feeding into the center of the manifold, I have heard good argument for that design, but all of the successful turbo EFI intakes I have seen have been of log design. I wonder if thats a result of people not wanting to mess with nature, or complacency? On alot of domestic V8's conventional EFI intakes are discarded for 4BBL intakes with injectors because of the superior flow and runner design. Wonder if anyone has explored how true that is for L series four barrel manifolds?

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This is old school, but some manufacturers had honeycomb under the carb to help atomise the fuel, an old-timer's trick (especially in the days of cold starting  globules of fuel burping out of Q-Jets

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Yep, I think along the same lines and have gotten a bit further than just thinkin about it...... :P


I have the AZC manifold, a Clifford 6=8 manifold, an E32 factory 4 barrel intake and a modified P53 to suit a 4 barrel and now an adapter to suit the twin su manifold, a Cartech piece


They're all different and help change the power and torque curves, exactly like you're theorising ;)


I would love to see how the offenhauser dual plane intake would work on the six. Strangely they made one for the 4 bangers, but not for the six. With some adaption, maybe one from a Jeep could work. The manifolds are very close. :idea: I have the 4 banger one for analysis purposes, to see exactly how the plenum is structured. Very clever and interesting design!!


The weber manifold thingy would work well with the split plenum AZC manifold, I think.


Even the huge Clifford could be made to work with the superior atomisation from the injectors.

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Very interesting! I happened across a four barrel throttle body from FAST.




That may be very useful because of its low profile design, in conjunction with a boost friendly carburetor bonnet like the one from http://www.csucarbs.com

Edited by 240zphilly
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Yes similar but not the same as the one on the E32 manifold.


I looked at those throttle bodies without the fuel injectors. When I found one with injectors in it, I bought it straight away. I wanted to keep the manifold wet flow as locating the injectors close to the head would remove this aspect, along with costing considerably more to set up. I don't mind the idea of throttle body injection at all. Sure it doesn't have the precision or individual cylinder tunability of port injection but its gotta be better than a carb (and it looks different too).


Dunno, I could be looking at this all wrong but it was there, so I bought one. I haven't run it yet, so I cant talk about its performance. The car that its bought for is still being built ATM. (Not too long now ;) )



Edited by ozconnection
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I don't believe you'd see gains over a properly set up carburetor, running a TBI setup. One of the real benefits of a semi-modern EFI system is that you are putting the injector bosses right at the port. This gives you more control, better (even) distribution, and typically leads to better performance, economy, and emissions.


The 4bbl replacement EFI setups are appealing to many because they are an easy swap for a 4bbl carb.


I've attached something else for your consideration. Not sure if you are looking for the best performance, or a compromise with cost and performance out of this.

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In the other thread this contention was made:

"but all of the successful turbo efi intakes ive seen have been of log design."


As Drax pointed out above a plenum feeding the runners a non-turbulent airflow seems in theory and computer modeling to produce the best results.


But several olde manifolds (including one from AZ Z-Car) used a log manifold (plenum) with a CENTER THROTTLE PLATE. That is a very different prospect than the 4 bbl manifolds being discussed. The center throttle plate used the plenum for air storage and runner charging. This does not happen in the 4 bbl setup.


Additionally, port injection is good for EMISSIONS. Ideally the further you have the injection point from the back of the valve the more power you will get. F1 engines inject obliquely to the port wall above the throttle butterfly.


The only reason OEM's went to port EFI is emissions, and cold running emissions at that! For performance the record is clear, atomize it right, and give it time to mix and tumble and you will be rewarded.


Issues on the 4bbl setups which would be alleviated with port injection is (if you have a sophisticated enough EFI ECU) to tailor the individual cylinder mixture for the airflow variations which may be present.

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Thanks drax, I have seen some people design log intakes with what I guess is called a diverting plate in them after the throttle blade before the runners. If I remember correctly it had holes in it of various sizes to try to get an even amount of flow to all the cylinders (large hole infront of the number 1 runner, gradually smaller holes to the number 6). Which is what I believe is being portrayed in your first attachment.


Really, I was more concerned with the budget aspect of quickly converting from a 4 barrel to EFI, and maintaining the benefits of the four barrel intake. As far as designing an intake I think it would be worth considering one of the designs you posted, or something similar.

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So Tony, do you think these designs with the center throttle blade are inferior somehow? why have they mostly fallen to the wayside?

No, they are probably superior, but packaging is difficult as Drax pointed out, if you are not turboing it (even if you are), and it flies in the face of 'me too' marketing. Lot cheaper and easier to sell a large bore throttle body and cheaper to manufacture than a manifold!

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Additionally, port injection is good for EMISSIONS. Ideally the further you have the injection point from the back of the valve the more power you will get. F1 engines inject obliquely to the port wall above the throttle butterfly.



I understand the better the fuel is mixed before the cylinder would be beneficial, but I thought the cooler you could keep the fuel, the more compression you can take. improving the mixture with the tighter squeeze and thus mileage, emissions and power. That was the reason for direct injection, straight to the cylinder. As the way new cars are going. Plus no fuel sticking to the walls to calculate for. Xtau factor in MS I believe. But that theory was given to me by the salesman.


I know with my L. the intake gets too hot to touch after a little driving. Even before the turbo charger under there.

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The reason or direct injection is again: EMISSIONS!


Transients and cold start are radically improved due to never having an unstable tau layer in the intake manifold.


The fuelling feedback loops for direct injection only become possible with increased reliable processor power. That's why now...

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Really, using the 4bbl manifold and TBI isn't going to gain you *much* more than a "perfectly" setup carb would...that is, you would be dealing with the same issues of charge robbing and unequal runner length. You'd gain better precision control over the fueling, and easier precision tuning over a carb, but other than that it'd be pretty equal to a well setup carburator, especially at WOT. Part throttle economy will be better with TBI, though, as would drivability.


The killer on any straight six with a 4bbl, is going to be cylinder distribution. So far, I've not seen a way to mount one carb in the middle of six runners, and get around that issue. The closest an OEM has gotten was the Slant-6 Hyper-pak, which has LONG runners, trying to minimize the differences in length.


Even the SU carb manifold has distribution issues, on runners 2 and 5, in some applications.

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