holley 4 barrel question

[ozconnection]

E32 manifold and with throttle body injection for something 'different' .

[sblake01]

Mark, thanks for that. I'd much rather hear an answer from someone based on their own expierence rather than the anecdotal stuff you always seem to get when someone asks such a question.

[azkyinc]

I thank all of you for your input specially ozconnection for the all the information, its steering me in the right direction. I'm definitely going to do lots more homework on 4bbl to get the tuning just right. I really want to stick with the 4 bbl carburetor since I'm already knee deep in the project . By the way ozconnection, who makes the E32 manifold and with throttle body injection? Thanks again guys.

[LeonV]

Mark, thanks for that. I'd much rather hear an answer from someone based on their own expierence rather than the anecdotal stuff you always seem to get when someone asks such a question.

I would hope that you're not referring to my post as "anecdotal", unless you don't understand the reason why down-drafts are at an inherent disadvantage to side-drafts.

Like I said, people make it "work". Mark is a good example of that (and knew he'd chime in ) and am not saying that his setup is "bad". I don't deny that max power numbers can approach stock SUs, but as Mark found out, this involves greater compromises in other areas.

Here's a quick rundown:

(1) When mounted on an inline engine, the air coming in through a down-draft carb must make a 90 degree turn in order to line up with the intake runners. This leads to a pressure drop (loss).

(2) The fuel must make the 90 degree turn with the air. This leads to more fuel pooling underneath the carb. This makes tuning more difficult and inefficiencies in transient conditions.

(3) The manifold geometry is forced to make the central runners shorter and the outer runners longer. This leads to a more uneven air-fuel mixture distribution and forces you to run a richer mixture in order to get enough fuel to the lean cylinders, while you dump more fuel in the cylinders that already had a good mixture.

(4) Because of the manifold geometry, pairs of cylinders are tuned to differing rpm. The middle cylinders breathe better at high rpm, while outer cylinders breathe better at low rpm. This doesn't allow for intake tuning to be as effective.

This is an explanation of the main disadvantages. It is not to say that those that use 4-barrel carbs are wrong, or that they should change. Everyone is free to do as they wish. If someone thinks that a 4-barrel is the bee's-knees, then so be it! I find it is good to provide information and let the end-user make their own informed decision.

Good luck with your 4-barrel, azkyinc.

[sblake01]

I would hope that you're not referring to my post as "anecdotal", unless you don't understand the reason why down-drafts are at an inherent disadvantage to side-drafts.

No, I just meant in general.

[ozconnection]

I thank all of you for your input specially ozconnection for the all the information, its steering me in the right direction. I'm definitely going to do lots more homework on 4bbl to get the tuning just right. I really want to stick with the 4 bbl carburetor since I'm already knee deep in the project . By the way ozconnection, who makes the E32 manifold and with throttle body injection? Thanks again guys.

Genuine Nissan E32 intake manifold. You can't just go and buy one of those E32 manifolds, it took me quite a few years to find one AND at the right price. That injection throttle body (with megasquirt) is for a future project I have in mind for my coupe. You can buy those on ebay. Cheers.

[rcb280z]

azkyinc, post how you make out with the 4 barrel setup. I'm curious. It's nice to have people to run your ideas by. People that are willing to post ideas and info regarding your situation. I'd rather hear something that might be able to help me, give me something to think about, than to receive no help at all. All too many times I see people post nothing regarding the members question(s) like one post above. Keep us posted on your progress. My buddy in Vegas is trying to talk me into the arizonazcar setup. It is what he is running and is happy with it. I'm not convinced it's the right thing to do yet.

[sblake01]

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Edited March 18, 2012 by sblake01
pointless comment.....

[rcb280z]

hehehe

[azkyinc]

Thanks you all the information it has really help. everyone here has given both sides of the picture which has let me know of my options.

[azkyinc]

Update: I'm waiting on a jet kit to tune it right. Still cant get it to idle right ( might be putting up a video on the problem, if i could figure out how As for now finishing up the body work and getting it ready for primmer and paint. I was also suggested that upgrading the ignition system and switch to and electric fuel pump might help with the 600cfm setup so please let me know if that would help.

rcb280z: I'm not sure if the bob sharp and the arizonacar setup are the same, but from what i have read the only difference is the throttle linkage is different. once i get it all working right i will have it dyno and post the numbers up so you can get a good idea of what its capable before you decided. Thanks again.

[ozconnection]

A quick reply....an electric fuel pump can be a good thing...you can check the float levels without the engine running, for example. An ignition upgrade is simple and effective for ignition reliability and consistancy.

The jet kit you mention, what parts does it have? Jets won't effect the idle. Get the idle right. You may need to go to your library and borrow a Holley book or two and read up on the subject if you don't have much experience. If you have time...then take it...don't rush. Understand what you're doing. Throwing parts at a carb doesn't mean success.