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azkyinc

holley 4 barrel question

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Hi, I'm a new Z owner. The car came with a Bob sharp and Holley 8007 390 cfm 4 barrel conversion. The carb secondary vacuum barrels were seized probably since he garage it 12 years ago. I tried a rebuilt kit but still had problems and I didn't trust it as a daily driver. So being new to carbs I asked around and was advice to just replace them. I purchase a new Holley 600 cfm 4 barrel carb thinking that more cfm is better. Now the car turns on with minimum effort and idles ok. Once the motor warms up I open the choke and it starts to idle high and goes up and down in idle from 800 to 1200 and seems as though its running rich. Ive revived all the way just to see where recline is and it on occasion has passed 8000 rpm. Air/fuel has been adjusted with vacuum faucet but its a self float adjusting carb. Not much to adjust except jets. My question is : is the larger 600 cfm carb to blame for all problems or can it be something else. I figured bigger carbs =higher idle and more gas consumption but not sure about rest. Thank for any help you can give. Sorry for the long post but I figure all the info I can give couldn't hurt.

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Not a 100% sure but I believe my buddy in Vegas runs the arizona holley carb setup and he said you can only run with a 390 cfm max. Stock 260 engine. You didn't say what Z you own either. You need to supply more info about the engine also....stock, 240, 260, 280, etc, etc. You may want to check arizonazcar.com also.

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Sorry, miss that. Its a stock 240z rebuild motor. But I cant confirm unless I take it apart. I feared the bigger carb is the problem, Ill confirm with arizonazcar.com thanks.

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Thanks everyone, i will try and get old 390 cfm carb to work or just buy a new one. Would the larger carb explain the motor revving pass 8000 rpm. I cant really imagine the motor being able to handle it without any modifications or is there no rev limiter on the l24?

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Thanks everyone, i will try and get old 390 cfm carb to work or just buy a new one. Would the larger carb explain the motor revving pass 8000 rpm. I cant really imagine the motor being able to handle it without any modifications or is there no rev limiter on the l24?

Correct, no rev limiter on stock ignition.

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The car came with a Bob sharp and Holley 8007 390 cfm 4 barrel conversion.

Well there's your problem! LOL Down-draft carbs don't belong on an inline engine, especially one with high-performance in mind. Some will be drawn to contradict me because their's runs great, but that setup is just inherently inferior to proper side-drafts.

Slap on some SUs (or triples) and be done with it. People make the 390cfm "work" but that 600cfm Holley is probably no where near jetted correctly for your engine.

Oh, and there is a rev limiter on the L24, it'll stop revving once you see a piston flying through your hood!

An SU-equipped L24 will rev to 8000rpm just fine, just ask Greg Ira.

Edited by LeonV

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Well there's your problem! LOL Down-draft carbs don't belong on an inline engine, especially one with high-performance in mind. Some will be drawn to contradict me because their's runs great, but that setup is just inherently inferior to proper side-drafts.

Slap on some SUs (or triples) and be done with it. People make the 390cfm "work" but that 600cfm Holley is probably no where near jetted correctly for your engine.

Oh, and there is a rev limiter on the L24, it'll stop revving once you see a piston flying through your hood!

An SU-equipped L24 will rev to 8000rpm just fine, just ask Greg Ira.

Agreed, you're cheapest, fastest and best end result is to go with a set of stock SU round top carbs. Have never heard anyone say they have a reliable 4BBL driver.

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Agreed, you're cheapest, fastest and best end result is to go with a set of stock SU round top carbs. Have never heard anyone say they have a reliable 4BBL driver.

Boys, please help the guy out here...some people like to do things a bit differently and that should be respected, not dissed. AND my 4 barrel Holley setup runs beautifully,. Took some work but the fruits are there for my effort. Magic doesn't happen without waving ones wand. LOL

There is a small but loyal following of people running 4 barrel carbs on their sixes. Not all of them run Holley's but most do. I do. The most significant thing about running a 4 barrel is the manifold that it's bolted to, not necessarily the size of the carb you use. The effect of the manifold is dramatic in the way the carb has to be tuned. The V8/carb boys understand this the best, they know an 850 double pumper wont work well at all on a high rise single plane manifold on a 4V headed Boss 302 Cleveland motor for the street, for example. However, with the same carb, a dual plane torquer manifold will be far more civilized than the other manifold. The jetting and power valve values will need some adjusting too because of the reversion effect and harmonic tuning that takes place when you begin to separate the firing into two groups, like you do when you apply a dual plane manifold to an engine. Detailed theory is out there if you want to dive into it that much. What the HELL has all this to do with our engine, an inline 6 cylinder? Lots.

The manifolds that can use a four barrel carb are out there. Did you know that NISSAN made a 4 barrel manifold for the L series six? They did. I have one. It was an evolutionary thing from the down draught 2 barrel carb that nissan designed for their domestic and some export market cars that had sixes in them. The 4 barrel verion was fitted to a domestic market car only. Arizona, Clifford and Cartech all make manifolds/adaptors for 4 barrel conversion. Depending on what you use will determine what type of 'induction' you'll be left with. The Arizona will be a true 'dual plane' setup, the Clifford a single plane (can be modified into a dual plane) and the Cartech will adapt the twin su manifold to a single plane type manifold. A dual plane manifold will never have the top end of a single plane or that of triple carbs but a Clifford single plane can match a dual su carbed engine setup for top end power.

A 600 cfm carb will work on all of these manifolds. I know, I've used one. The top end was great and I achieved over 103 rwkw in a stock N42/N42 combo through an auto trans (L3N71B) with the air and steer belts on and the fan in place. Why don't I run this on my car now? The response down low was average, economy average and if get really picky, thought that I could do better. Power at the top end isn't everything for a daily. For the track.....fantastic....but not the street. The process continued, testing this one, combining it with that one and ended up with a 465 Holley on a Arizona dual plane manifold. My old Cedric weighs in at almost 1500kgs. For a responsive drive, I chose this combo. It's fantastic...reliable, economic, torquey and 'different'.

In summary, you can use a 600 and on an Arizona manifold, it's not bad, you'll just need to work it to get it to work as you'd like it to. No free lunch unfortunately.

Good luck with it mate. Cheers. :)

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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.

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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.

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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. ;)

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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.

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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.

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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.

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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.

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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.

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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.

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Your right , this is all new to me. Is there any particular books you recommend? I did try putting in the jets from the old 390 cfm carb on the 600. Alot of the white smoke from the tail pipe is gone except on hard acceleration ( 600 cfm jet size 65 and 390 cfm jet size 45). One thing i did notice is the car went through 4 gallons of fuel just revving and idling in the garage for warm up ( hasn't been driven) Is that common? thanks

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