Triple Carb vs. Holley 4BBL Carb

[Tony D]

Throw away the latter for the former, what's the gain? I don't understand the attitude that rejects out of hand the format NISSAN engineering chose when these cars were in production......

Curiously, that brings up the original plans for the 240Z---the original preproduction brochures sent to dealers in 1968/9 for ordering the 240 included the 'Sports' 240, a car with 175 HP and Triple Mikuinis. The Standard, lower trim level vehicle had the SU's.

Due to emissions requirements that were instituted in 1967, and their continuing reinterpretation, the Mikuini Option was killed. This was one of the considerations for Toyota not bringing in the 2TG motor option here in the USA as well, while Canada got it...1600CC DOHC Four Cylinder with Dual Mikuini PHH carbs. Just like the Fairlady Roadsters that preceeded it, Nissan's conservative engineering and emissions policy doomed the good engine options to those areas outside the USA. The 432 continued on the track of 'ultimate performance' with 40PHH Mikuinis, and since the target market on the Z was nixed for the Mikuini Option, it was dropped altogether worldwide. Sad...

So yes, considering the Mikuinis give roughly 15-20% more HP as stated by period literature from both Mikuini USA and Nissan (175 versus 150hp for instance) one must 'consider what NISSAN engineering chose when these cars were in development'

If you only consider production you rule out the choices the engineers made, and settle for what the Government Regulations Dictated. Saying the SU's were the choice of engineering is somewhat of a mis-statement. The SU's were what was setteled upon for price point and more importantly long term emissions sustainability. Frankly, Nissan didn't trust technicians in the USA could perform the upkeep properly...and they were probably correct.

[justin260z]

fwiw you dont have to run a 4bbl. I ran a morotcraft 2bbl, and it had tremendous response, tons of high rpm pull, and great mileage compared to my su's. With the 2bbl, I got 26 in the CITY, and with the su's the best I could get was 23 on the HIGHWAY.

EDIT: I dont know if they have an intake manifold for a motorcraft, my application consisted of a custom intake manifold, and a carb spacer.

[Arne]

...with the su's the best I could get was 23 on the HIGHWAY.

How odd. With my stock SUs I get a solid 30 MPG on 60 MPH highway driving, and 20-21 in town. Are you talking about the factory flat-top carbs that the 260Z came with? If so, those don't count...

[justin260z]

How odd. With my stock SUs I get a solid 30 MPG on 60 MPH highway driving, and 20-21 in town. Are you talking about the factory flat-top carbs that the 260Z came with? If so, those don't count...

Im talking about the early round tops. I dont know why i get that mileage.... maybe I need to rebiuld them.

[jmortensen]

Frankly, Nissan didn't trust technicians in the USA could perform the upkeep properly...and they were probably correct.

If Nissan felt that way they had their heads up their asses. If you agree... well you do the math. Aren't you the VW freak? How many sets of downdraft Webers would you estimate have been tuned in the rednecked US of A? I can tell you I used to see quite a few old Porsches running around on downdrafts. You're talking about an easier to tune version of the same basic carb just turned on its side. No big mystery. In fact I think they're a lot less mysterious to the average mechanic than an SU.

Not sure where the self-loathing anti-Americanism comes from, but get over it. I think the reason for importing the SU's and not Mikunis was purely emissions. If I recall correctly Nissan (and many other makes) also kept using carbs on cars in other countries longer than they did here in the US for emissions reasons.

[sblake01]

He was actually talking about Mikunis but that doesn't change anything. Some of his info seems to be based on fact, i.e., what he's read but a lot of it seem to be based on opinion. Not just in this thread but others also. I don't know where that comes from but if he believes it, I guess he's entitled to.

[Carl Beck]

Down-draft vs Side Draft:

Just one case of engineering "choice" for example:

Interesting that Mr. Iida commented in an interview reported by Nostalgic Hero, that when his team designed the first L20 in-line six cylinder, OHC engine (with a four month design cycle), they used side draft carb's because they had less resistance to flow, than the down drafts, and thus produced more HP and Torque. (115 ps or 113.43HP)

Everything in Engineering is a trade-off however. Mr. Iida also said that the reduced resistance to flow of the side draft carb.'s, combined with poor valve stem seals - - resulted in oil being sucked up the cylinder walls, and the oil rings used were not sufficient to initially seal, nor wipe the walls clean - thus high oil consumption resulted.

He also tells us that the twin carb's were difficult to tune and the original L20 suffered from a high idle speed - which caused higher fuel consumption and customers complained about the noise at idle from the engine.

A year after initial production, the second version of the L20 was equipped with a down draft carb. - lost some HP/Torque (now down to 105ps or 103.56HP), but equipped with new valve seals and newly designed oil rings, combined with reduced flow from the downdraft carb - the oil consumption was brought under control, and with the down-draft engine idle speed was lowered to increase fuel mileage and reduce noise in the car at idle.

{on later engine designs, in addition to better rings and seals - Positive Crankcase Ventilation reduced the tendency to suck oil past the rings and valve stems into the cylinders - when pressure went negative in the cylinder, relative to the crankcase - on the intake stroke. Engines designed later had to have PVC to be exported to the US starting in 67 AIR...cjb}

FWIW,

Carl B.

[Tony D]

! I recall people changing from the Zeniths and Solexes wholesale on Porsches because they were 'too complex' to tune. And they went to a Weber...yeah, 'complex'...

And scads of people went with a Single 48IDA or even a 32NDIX on a VW offroader because it was 'easier' to tune than 'troublesome multiple carbs'.

It's not 'self-loathing anti-Americanisim' at all, but a simple observation of everyday facts of life, as well as posssibly revealing some unpleasant facts---don't shoot the messenger!

Corvairs were loathed with two one-barrels, much less the four one-barrels, and the big conversion was to put a single two barrel on them, or even better a 390 Holley (sound familiar?) Resulted in terrible drivability when cold, and carb icing, but hey, there's only a coupla screws to turn, and I don't have to 'balance' anything---whatever that means.

Call all the names you want, but years of firsthand observations show me that maybe Nissan's concerns about their service department throughout the midwest at the time may not have been too far off base!

Keep in mind this was a period when people may have to travel from L.A. and the corporate office to fix customer's cars, or attend to troublesome warranty situations.

In the 1970's multiple carburetor systems on small bore imported cars had the average corner mechanic running for cover. That was something exotic, like on a Ferrari, or other European Marque.

For the same reason, people lifted up the secondaries and stuck galvanized plates of sheetmetal and tar under their Tri-Power Firebirds 'because they sucked too much gas'...

There's a reason I moved WEST. To get away from simpletons who thought because they could fit a spanner to nut that made them qualified to dispense high performance advice. I came to where I bought all my VW parts from. I came to where those funny little jap cars that everybody seemed to like to take sledghammers to every fourth of july for $20 a whack came through the ports.

I don't know if that answers your question or not, but facts of the matter are MYTHS surround the complexities of triple carburettors. About how they need to constantly be adjusted, blah blah blah.

I know they're not true, you know they're not true, but I can see guys who insist that they have to fiddle with it every week or more, and will tell everybody they know that is how they are supposed to be.

The 432's were serviced at specialty dealerships in Japan for just such a reason. Does that mean any dealership mechanic couldn't do it? Probably not...but would you let your Porsche 904 Carrera be serviced at the local VW dealership? Flat Four Air Cooled, same same, right?

Engineers rarely give much credit to the field folks.

You may get extremely pi$$ed off about it, but it's a fact of life. You want to cry about an Engineer's estimation of their service force in 1968, talk to them, don't beat me up over it!

Judging from my experiences in the 70's with midwestern service networks, the Nissan Engineers may not have been that far off base. If it's a personal slight to you, then you'll have to deal with it, but I'd suggest yelling at the Nissan people, not me. While emissions may have been the death blow, the final nail in the coffin, the coup de grace....serviceability longterm was on everybody's mind. You may not want to admit it, but keeping it running with the existing service network is a major concern to any OEM when they introduce a new product.

Just look what Nissan went through trying to get people to understand how a 'power valve' works in the 73-74 Flat-Top SU's. And then the major education campaign for the 'new' EFI system coming in the 1975 model year.(Very similar to the VW Education Campaign done in 1967 with the Type 3 debut and conversion from Dual 32 PDSIT carbs to Bosch EFI...)

But back to the topic at hand: If the car doesn't have forged pistons, and is limited to below 7000 rpms, then you may as well give up on triples and go with the Four Barrel. It will make the power same as anything else below that point, and it's cheap. Cheaper than most any of the alternatives given thusfar.

[Tony D]

How odd. With my stock SUs I get a solid 30 MPG on 60 MPH highway driving, and 20-21 in town. Are you talking about the factory flat-top carbs that the 260Z came with? If so, those don't count...

My wife's 260 with round tops will get a solid 27+ mpg if I keep it on the highway at or below 65mph (you could say 60mph average I suppose).

Get to the 75+mph range, and the car will be in the 22-24mpg range.

Crack triple digits for a tankful, and you will see 19mpg...

In town it can be anywhere from 17-mid 20's depending on how friskily I'm teasing the throttle.

This 260Z has a 3.7 Gearset, late ZX Gearbox, and stock everything else save for the Round Tops. So FWIW, chances are good you have the carbs tweaked a bit rich, or have some other non-optimal componentry.

[jmortensen]

It's not 'self-loathing anti-Americanisim' at all, but a simple observation of everyday facts of life, as well as posssibly revealing some unpleasant facts---don't shoot the messenger!

Sorry Tony, I think we're still in disagreement here. Last week it was that the metric system is inherently more accurate than SAE measurements, this week it is that midwesterners are too stupid to deal with side drafts. As far as I can see, you're not the messenger, you're the one coming to the conclusions. There are stupid people everywhere and your straw man example of people covering up the third carb on their tri-power V8's doesn't prove that everyone in the midwest is a moron. What's more, finding a good mechanic ANYWHERE is a chore. My buddy (a very talented mechanic) used to say about some of his Californian co-workers "I don't know how to spell mokanic but I are one". Turns out California isn't stocked with geniuses either. Surprise, surprise.

[Tony D]

Actually, that was quite some time ago, but if you want to hold a grudge on Metric system being inherently intuitive, I can't help you. it was not last week, check it.

Similarly, after 20+ years of having to deal with Midwestern attitude about japcrap, nazikrautburningwagens, and whatever other racist, narrowminded and ignorant drive you care to hear I got fed up and LEFT.

Rally around the flag if you want to. There was a time in my youth that I felt if I could do it, anybody could. Unfortunately as time has gone by, I realized that this was not the case.

Instead of getting upset by their incompetence, I simply choose to accept they exist and call a spade a spade. People are idiots. But I find the acceptance of Japanese Vehicles, and Imports in general to be the RULE here out west, than back in the mideast.

I will remind you in the late 70's a Ford Executive...one of the annointed 'family' in fact, while being driven around SoCal commented there 'sure were a lot of imports out here'...and when the local Ford Rep explained that people drove great distances, so fuel economy was a big concern as well as reliability the Annointed One insightfully replied that 'It must be some sort of regional anomaly'....

The lights are one, but nobody's home. And that was the environment in which I was raised. Sorry, but it's still distasteful. But with that kind of an upbringing and seeing it all around me, it's hard to shake the impression that there is a dearth of intelligence in that part of the country when it comes to Imports, Import Technology, and generally anything that didn't come out of Detroit.

And they didn't cover up the third carb, the covered up BOTH the secondary carbs. That would probably have gone hand-in-hand with the guys putting the 390's on the Corvairs, both 140 and 180HP models... etc.

Ignore the rest of the examples, I got a million examples. The point was in 1970, multiple carburettor systems were not the standard in the general mechanical knowledge pool. And that is what you have to draw from. Fixate on what you want to argue about, fine. Just don't miss the bigger picture.

Sure there are idiots everywhere, and sure, California is not an exception.

Thanks for making my point about why it was considered a bad idea to go with Triple Mikuinis on an OEM application versus two SU's.

Frankly, with non-adjustable jetting the Mikuinis would be easier to meet emissions compliance longterm than variable jetted SU's. They made JDM emissions requirements till 1980 at least on Toyotas with 2TG's and 18RG's. And those requirements were stricter than CA regulations for a good part of that time... So while on the face of it the 'polite answer' was that emissions nixed the package, there is more to it than that. Primarily nobody KNEW what US Emissions REquirements were going to be one year to the next. THAT is a better explanation than simply saying Mikuinis wouldn't meet emissions requirements. Once they stabilized after 1975, it became easy to make compliance. But from 67 to 75 there was so much fighting, lobbying, and changing of regulations it wasn't funny.

[janaka]

so, where can i get a nice set of triples for a reasonable price gents?!

interesting read for a new member to say the least