Go to Four Barrell or stay with SU's?

[Guest mulletz]

I have a 70 model L24 with original block & head still running strong.

I am planning an intake & carburator change to the holley 390CFM, as well as headers, new exhaust, elec. ignition & hotter coil.

I have gotten a few negative remarks about putting a four barrell on this motor in place of the SU's, any input?

I also have already yanked off all the smog & AC stuff, anything to watch out for there.

I'm not much of a mechanic, but dive into stuff like this head-first.

 

Thanks,

[JMortensen]

If you do a search you'll find lots of previous discussions.

 

Bottom line is that the 1 and 6 cylinders starve and the 90* turn that the fuel has to make is crappy. Tune the SU's if they're the round top style, or get the round top style if you have the flat top kind.

 

Sorry, didn't read. Your 70 should have the good carbs.

[Drax240z]

I can't recommend enough that you stay with the SU's.

[Poundz9oh9]

I say ditch the SU's and get the four barrell.........................

 

On top of an SBC that is

[Guest plainswolf]

I am sure not a master mechanic either, besides locomotive systems, so I switched to the arizonaZ dual-plane intake maifold and the holley 390...

 

mostly because I was so inexperienced, and knew nothing about the SU's.. It was also very hard to find parts for the carbs but like I said, I was not nearly as well versed in these twins as the rest of you, so it was more of a practical and economical decision for me.

 

In truth I envy those that know about the SU's as I have yet to hear a bad thing about their performance. but once I had the holley tuned and the different powervalve installed I have to admit it runs fantastic and is lmuch less of a hassle for me.

 

I supppose it all depends on your preference and your expertise.. Or such as in my case, the expertise of those around me who know carbs alot better than I.

[brokebolt]

Here is a link to a discussion on this very topic.

 

http://hybridz.org/nuke/index.php?name=PNphpBB2&file=viewtopic&t=23727&highlight=

 

Mike

[JMortensen]

plainswolf - If you ever decide to go back, these guys have all the parts you could ever need and an instructional video. http://www.ztherapy.com/

[Cjarloz]

well i have had both the SU's and am curently using a holley 600 four barrel in my 70 240z with an 83 l28. Both can be very nice if tuned properly. I didnt like my Su's because mine were in terrible shape and needed a rebuild badly but im positive when in good conditions and tuned preperly they functions perfect. But thing is i love when the last two barrels open up and give a huge boost feeling. Lol kinda sounds v8ish also. But either way ull end up with a good setup.

[arizonazcar]

As the owner of Arizonazcar.com and having sold over 800 of my 4-barrel intakes I would like to add my 2 cents on the subject.

First there is absolutely no way that the SU's give anywhere near the performance that my 4-barrel intake with the Holly 390 carb gives.... that's just a fact and I dont care who rebuilt the SU's or how they were tuned. The overall drivablity, ease of starting, horsepower and even gas

mileage are substantially improved. SECOND THE SO CALLED ISSUE OF MIXTURE DISTRIBUTION DOES NOT EXIST.

Hopefully many of you have seen Gary Meekins' WEST COAST NATIONALS

WINNER 260Z..... Gary is a master mechanic with 30 years Nissan experience and has rebuilt hundreds of SU's ...his opinion of my 4-barrel intake setup is that "it runs perfect and has no issues" as claimed. He also says that the engine has "radically improved performance" over the SU's . Everyone that claimes a mixture distribution problem always says "I heard that..." or "I read that..." . I find that people with no first hand experience are always the first ones to render an opinion. Why not take the opinion of someone who know's what they're talking about for a change.....Gary Meekins can be contacted at coyotegary@hotmail.com or at his Zcar restoration shop (Spank'ys Auto Body) 480-644-0060

Assuming you wont' take my word for it (I've only installed about a hundred of them personally)

Also I think you'll find that any of the customers who have actually installed it correctly have very high praise for it as is the case on this thread. I have seen some other manufacturers 4-barrel manifolds that had numerous design failures that would make the overall

performace substandard compared to mine.

Now I would like to discuss where problems arise:

Many customers choose to use junkyard carburetors..(without rebuilding)..if you build your car from junkyard parts (without proper rebuild or inspection) any money you saved on the purchase will be more than eaten up by the grief of trying to figure out what's wrong.VACUUM LEAKS.....I have seen more vacuum leaks on these cars than I can count........the typical backyard mechanic then jets the carb richer to make up for the lean miss, now the car runs over rich at cruise and fouls the plugs. IGNITION...I've seen every combination of burned points, wrong firing order, bad wires, worn worn distributor,cap rotor ,damaged coil etc. that you can think of........the 4-barrel will NEVER run correctly under those conditions. CAM TIMING......never seen a car run right with the cam timing off. PCV....amazing how many people have NO understanding of PCV...the typical shade tree goof vents the valve cover to the base of the carb and puts a breather on the tube below the distributor.........THIS GIVES A WHOPPING VACUUM LEAK.....the car back fires and blows the power valve, now it runs SUPER RICH! What's the worst solution? of course they now lean the carb way out in a futile effort to make it run right but by now the plugs are fouled and the driveability is crap from the rejetting! FUEL PRESSURE: NO A FUEL INJECTION FUEL PUMP WILL NOT WORK! Carbs typically need 3-5 psi.....60 psi wont make it any faster it'll just crush the floats and spray fuel everywhere.

OVERALL MECHANICAL CONDITION : Customer comes over with a "correctly" installed 4-barrel.....runs horrible.....I do compression test, test shows 165 140 140 80 60 22.....sorry the my manifold won't cure that problem, for that you'll have to get the magic engine restore pills from JC Whitney....that'll probably cure your rod knock and worn valve guides too!

Anyhow I hope this is of some use to anyone considering this option.

Please feel free to contact me on this or related subjects.

Sincerely,

Dave Epstein

Owner

arizonazcar.com

2043 E. Quartz St.

Mesa AZ 85123

dave@arizonazcar.com

480-844-9677

http://www.arizonazcar.com/winner.html

[Guest plainswolf]

I would definitely agree with Dave... I bought the manifold and tuned header setup from him and a Holley 390cfm Fourbarrel.

 

Now I'm not replying just to give him a plug for advertising whatsoever, but at the same time I will give a very honest customer testimonial.

 

I can tell you that I found no evidence fuel starvation on any cylinder. I've ran this sytem for about 2 years now and it works fantastic! But as I said previously in this post, I wasn't versed at all in S.U.'s which I've heard fantastic things about.

 

I chose Dave's manifold because it was the only one of it's kind that is a dual plane manifold(and it was also the cheapest!) and doesnt require any sort of extra clearance issues with a four barrel crab under the hood.

 

that combined with the simplicity of a single holley 390cfm fourbarrel that was designed for small displacement V8's and 6 cyclinder engines.

 

his setup is so easy, so hassle free and GREATLY simplifies things under the hood.

 

He also took the time to explain to me over the phone(TWICE I might add) exactly what to plug off, as far as emissions ports, etc.. and basically everything to do to get it setup.

 

That being said, I now have a completely fiddle free intake system that has caused me not even a single problem in two years running now.

 

Dave is QUITE correct when he says it GREATLY increases overall driveability and CONSISTENCY! I was also extremely satisfied with the quality of his products!

 

I would love to know more about S.U.'s as they are quite the setup, but at the same time I would put my stock 260 with the holley conversion up against any S.U. on the same engine and car platform any day!

[Guest plainswolf]

Jmortensen, Thanks for the link, I really do appreciate it, but I must admit I don't have the time or expertise to keep fiddling with a dual carb setup..

 

I would love to know more about them I truly would but if mine ever has a problem, well hell I can find a mechanic the knows Holley systems alot easier than I would an S.U. system..

[JMortensen]

I would love to know more about them I truly would but if mine ever has a problem, well hell I can find a mechanic the knows Holley systems alot easier than I would an S.U. system..

 

THIS is the reason why people buy the 4 barrel carb setup. Nothing wrong with it, but this is exactly the reason IMO.

[brokebolt]

Dave makes some valid point. I am not a master mechanic but do have some years of experience in Z car related inducitons (one or two). I like the SU as it is original equipment; nice to keep it in the family so to speak. I like the 4 bbl good performer, but I like the Trippple set up best. But leave the third out as this topic is about the first two.

 

SU's lack top end, I had issuses feeding my engine with enough air and fuel above 5000 RPM's to keep the engine happy. I have pics of two exhaust valves to back this claim up. I don't have the head gasket anymore and I didn't take pics of it but it too was no longer usable. Go here to view the valves.

 

http://www.cardomain.com/memberpage/496289/2

 

The SU's are a great daily driver carb and are easy to tune. Performance, fuel ecomony, and reliability are all in the pro column for SU. For "stock" carbs on 1970-72, performancs is good, my fuel economy was in the neighborhood of 20 mpg (driven conservitely) and once tuned (nut on bottom and balanced front to rear and other misc. points of tuning) they were a good reliable daily driver carb. Con is performance above 5000, parts, wear, age, and special tools. Parts are still available though "aftermarket sources" (I used to get parts from Nissan years ago, don't know if they are still available now). Wear is not an issue with Ztherapy SU's (I don't own any so this is what I've read from customers) and age is always going to be a factor with 30 year old hard parts. If your home tuning you need a flow guage to balance the carbs or they will not run correctly.

 

The 4bbl in my experience was never a fuel saver (foot to floor issues), I have no read MPG number, I never used them for daily driver use. They required more carb knowledge (if you tinkered with with jet sizes and such) and installation was not as "bolt-on" as the SU's (you have to fab linkage or a cable set up to some degree and figure out what goes where, Dave covered most of these issues in his post). They are reliable but carb choice is an issue and people tend to thing "big=good!" And junk yard parts are just that, junk yard parts. You may find a mint diamond or you may find a worn out peace of junk that needs complete teardown and cleaning just to see what shape the part is actually in (been there!). However, they use new parts (if bought new) and parts are available at every autopart store from San Diego to Boston. Everyone, including there brother, knows something about downdrafts so you have a good change that you know someone that actually knows something about tuning.

 

I think the comment about Mixture distribution is not correct. The real issue is in the length of runners. The Bob Sharp manifold (AZCar is the same) and the Clifford Research manifold have solved this. The Bob Sharp manifold feeds like a dual plane Log style while the CR manifold feeds like a Plenum. The difference is the Bob Sharp manifold will give good low end power while a Plenum will give better top end, these are how the characteristis of the design work in general. I think the issue of mixture distribution first stated years ago when someone made the comment about the SU manifold and how it has different length runners. And yes Nissan did a good job of not using a Plenum or Log style to make a compact dual set up to feed 6 holes. Nissan compared to European cars have been using the SU style carb for years with great success on 4 banger sports cars. But the Nissan version has different lengths in all 3 runners, front and back carb respectily, while a four hole will not have this use (Nissan should have used three carbs to eliminate this issue altogether). So anywy, the 2nd and 5th cyl. have shorter runners, one and six feed off of two and five and three and four have dedicated runners. This will affect the engine, to such a degree I don't think you could detect it unless you used sensitve diagnostic equipement. The bigger issue I think is the pulse you generate from the SU (and Tripples) vs. the 4bbl with a constant draw.

 

Bottom line if I was to recommend to anyone an induction, I'd tell that person to open there wallet and let the dead presidents decide. Ztherapy may have a good product but at what cost? The 4bbl may be an economical investment for all new hardware but there not original equipement. If the choice was mine, and I'm old school so no computers under the hood for me, I'd use a Trippple carb set up. Even though EFI is "The Wave of The Future" and more performance can be gained easier. I feel nothing looks meaner than three carbs with individual runners. I say the "all original" guys can view my tail pipe, and the Holley crowd can hang out with there V-8 buddies. But that's just me.

Mike

[brokebolt]

Hey mulletz,

Here is another link to a recent descussion on the SU's issue. This is SU's vs. Trippple but the discussion is quality never the less.

 

http://hybridz.org/nuke/index.php?name=PNphpBB2&file=viewtopic&t=33732

 

Mike.

[Drax240z]

The overall drivablity, ease of starting, horsepower and even gas

mileage are substantially improved.

 

This is quite a statement, and I just can't agree entirely. I have drive a 4bbl car that was well setup, and I have had many SU cars, and customers cars to draw this view on. Carbs just plain and simple, don't get any easier than SU's. I had a set on a daily driven Z for 2.5 years, and drivability was excellent. Milage was in the area of 20mpg city and 25mpg highway. Started right away every time with the choke on when needed. (this might be a negative for some, but seriously how hard is it to use a manual choke?) The only thing I would agree that the 4bbl setup had over the SU's was top end airflow, and possibly the gas milage because I hadn't driven the 4bbl car enough to know what kind of milage it got.

 

After adding up all the parts you need for a 4bbl conversion, a set of Z therapy SU's are about the same price.

 

My only recommendation is this. If you know Holley carbs, go ahead and use it. If you know SU's, use them. If you don't know either, the SU's are much easier to tune with only a couple specialty tools that combined cost about $50.

 

Or just go with triples and let the car sing.

[Guest mulletz]

Thanks for all the input guys. Sounds like I've touched on something that has been a raging debate for years. I've decided to go with the SU's simply because I've got the old good ones, and have decided to give them a shot first. If performance isn't what I desire with all the other stuff I am doing now, then I'll probably give the 4 barrell set-up a shot if for no other reason than ease of install/maint. FOr now I can spend the money I save on shiny stuff for the car.

 

Thanks,

[Guest mulletz]

Well I went ahead & did it.

 

I put the Arizona Z-car manifold & Holley 390 on the 70 model, (also elec. ignition, headers & turbo exhaust), and I am very pleased.

 

This car starts with a bump of the key from the time I first filled the bowls till now. Dave at Arizona Z was very helpful, and all of his stuff was exactly as advertised.

 

The only problem I had at all was a "bolt on exhast" purchased from Motersport. I let them specify what exhast went with the headers I bought from them, and there is no way it could "bolt on". It was an hour or so of shop time for a muffler shop to make it work. If I had it to do over the only thing I would change is I would just go to the muffler shop & let them fab the exhaust from the head pipe back.

 

Just in case anyone is interested, the car runs great! All kinds of torqe, and all kinds of top end. Good thing mmy son is going to be driving it, I would burn the back tires off of it, and be in traffic court a lot! He's a lot more responsible than I am.

 

One thing for sure, get this set-up all working right & go down the highway with just an open header for exhast & it is scary loud. But kind of cool

 

later

[Drax240z]

On the flip side, I just finished up a pretty hot engine yesterday in a customers car, and was concerned that the stock SU's wouldn't be enough carb for the car. (2.8L, E31, big valves, F54 block, 8.8:1CR, 2.5" exhaust, electronic ignition, .510lift/280cam) The car pulled HARD from 3800-6500 and had zero issues at that high rpm. After dealing with so many triple carbed cars, it blew me away how much power can be made on the top end with plain old SUs. (heh, ask norm about that one)

 

JUst some more 'facts' for the discussion.

[Tekira]

The owner of the z shop i work at has some really nice set up su's the he has on his Street stock class 240z. 2.4 280z cam and has a guy in california build his heads real nice and still mannages to get 220 hp at the engine. My 2.6 Tripple 40mm mikunis headers 2.5" straights gets 197 to the wheels. And his is easier to tune!!! But like before most people today draw a blank when problems come up with their su's and more people work on holley single carbs. They all can make good power Just get the one u work the best with. I know more about mikunis then ill ever know about su's or holley carbs.