weber DCOE vs early 240z SU carbs

[Guest tejas74260]

i just want to know the main advantages/disadvantages to these carbs. i know this might have been covered before, so let me know the link cause i couldnt find it. would it be better to go with the superior airflow and tuning flexibility of the webers or the simplicity of the SU's. thanks

Mark

[RedNeckZ]

Would like to know something about what you are going to do with engine, before we can give you an answer. Are you going to run mods and run high RPM? Or will it be used as a street runner? I am running the 45 DCOE (triples) package on a 71 240Z with an L-28 block and E-31 head. It is used mostly on track now and doesn't see that much street time. I like the DCOE over stock SU's for tuning and power (high rpm). The engine has not got any stock parts on it and is not very streetable. I am also building a new higher compression engine (race gas only) to go in it and will stay with the DCOE's. So please give us some more info on what you planning on doing with your car and we should be able to help you find out which will be good for your car. Take care, Rich.

[Guest tejas74260]

i just plan to have this as a weekend car for fun. (so it will probably be mostly street action). in the future im wanting to build an l28 block with a p90 head and a mild cam, (possibly even run a stroker to get some more displacement) run some high compression (but still run pump gas) im not real concerned with fuel milege or anything, just whatever would be the best for street performance and fun driving. that's why im debating between the carbs. i want all the power and tuning capability, but i want it to be streetable. im thinking the max rpm im going to run is somewhere just short of 7k. Mark

[JMortensen]

If you want power from 4 to 7K, get triples. If you want power from 1500 to 5500, use SU's. I think the SU's will choke off a stroker pretty badly, so in that case maybe the triples will do better. Here comes Norm...

 

If you don't know how to tune them, be prepared to learn or spend big bucks to have someone else do it for you. Triples are not the best street carbs, but if you like high rpms, you really can't beat them. When I put them on I was immediately slower at autox, and immediately MUCH faster on the big tracks, if that gives you any idea...

 

If you're willing to spend some $$$, you may want to look at a set of bored out SU's. I think Ztherapy sells them. That would be the hot street car ticket IMO.

 

Jon

[Drax240z]

I just installed a set of Ztherapy carbs on a 70 Z yesterday, and they are the cat's meow. Definitely a good option for those wanting to run SU's.

[Guest LAYTON]

i had tripple 45's and after fighting them for quite a few round of jets i went to the z-therapy su,s over bored small shafts and wow what a difference smooth idle lots of power and with a high compression l-28 and big cam i havent ran out of top end yet ,cats meow ---lions roar with a itg filter and twm horns mmmmmmmmmmmm good stuff always starts and ready to whip a** ,cant say the same for the tripples

[Guest tejas74260]

awesome, well, looks like you guys helped a lot, thanks. now i can get rid of my evil flat top hitachi carbs!

-Mark

[Nismo280zEd]

I'd go Weber's all the way, easy to tune in my opinion, run fantastic, consistent, i can make my car idle at 400 rpm !!! and thas with a Cam! Not saying i want to but i can. Just don't go big... Get some Triple 40's DCOE Weber's... you'll love em. Really arn't that hard to tune. Most peole just don't know what they are doing.

-Ed

[brokebolt]

I'll toss in my $0.02.

 

If your looking for an easy to tune carb SU's are the ticket, if your looking for potential power use a Trippple set up. That's it in a nutshell.

 

But you did mention some mods down the road, if your interested in a one time investment, than maybe you might want to look closer at the Trippple set up. Yes as mentioned the SU can be bored out to run with the big dogs but a choked up Trippple can be tuned for smaller displacement engines and than when the mods are done opened up for bigger and better engine mods, like cams headers and such.

 

Personally if your looking at perfomance I'd recommend a performance oriented carb like the Tripple carb set up. Yes SU's can be modified to preform but the Trippple carb has those mods built into their design so no modification is needed, you only need tuning parts to do so. I believe that the Trippple set up is more tunable than the SU's but that statement may spark a debate. What I mean by "more tunabiltiy" is that the Tripple set up has more specific controll over a paticular RPM range though the use of the tuning parts. SU's have controll over the dashpot only which in-turn controlls the other parameters of the carb.

Mike

[JMortensen]

Here's another potentially controversial statement about why SU's make better low end power. The oil dampened action of the pistons means that the holes that then engine sucks air through get larger slower.

 

On triples, you've got 6 of the equivalent size holes to the SU's instead of 2, and when you slap the hammer down, all 6 butterflies open almost instantly. Intake velocity goes to 0 (or close) until the rpms come up enough to suck enough air for them to start working again. So at low end port velocity is bad and fuel atomization is bad, even if you have relatively small chokes in them. On the high end, no problems.

 

This is why the SU's work better on the low end IMO. On the SU's the velocity is much higher at any engine speed but especially at low rpms, so the atomization of the fuel is much better at low rpms. The triples are more adjustable unless you grind needles and nozzles for your SU's, and IME once you get them set up they don't need a lot of tuning once they are on and set correctly unless you change altitude drastically or move from Florida to Wisonsin or something like that. I've heard differently about Webers, but this is in reference to Mikunis.

 

Ed says that most people don't know how to tune their triples. This is exactly correct. That's why I said previously that if you know how to tune them great, but if not, then you'll either have to learn or pay someone who tells you that they know big bucks to do it, then hope that they have as much expertise as they said they did.

 

I LOVE my triples, and I'd can't forsee any change in the SU's that would make me want to go back. It was a HUGE top end power increase on my car. But the SU's would be a better street carb IMO.

 

Jon

[Guest tejas74260]

cool, i'll post this in the wanted section, but does anybody have any early SU carbs for sale? i just lost an auction on ebay and figured you guys would be more helpful and i could get more information about them. thanks a lot.

-Mark

[Guest bastaad525]

I loved the Ztherapy SU's, ran them for a year and had no real complaints, this was on a 2.9L with N42 head, mild cam, high compression. The only thing I did NOT like about them was the SM needles, which I believe are NOT the best choice for this motor combination.

 

Just like you must spend money and time to really get a set of tripples tuned right, trying different jets and all that (expensive), if you really want your SU's to perform the best they can, you need to get a set of needles designed for your particular application. The SM needles will work fine on most setups, they made really good power for me, but just keep in mind there will be potential there for you to unlock later.

 

SU's are definately the better way to go for a street driven car, whether just on weekends, or a daily driver. Around town driveability will go way down with tripples, they lack low end torque so feel like a slug in street driving. SU's are extremely simple to tune... tripples are NOT though they are getting easier since so many guys have run them, you can bet someone has run them on a setup similiar to anything you might build, so it's easier to get a good baseline. But I know of very few people who, even using other's starting points, were able to get them running really well w/o dyno time. You can easily get the SU"s tuned near perfectly in about 30 mins on your own.

 

And yeah, speaking of Norm he is a perfect example that tripples are NOT the only way to get a lot of power out of SU's.

[brokebolt]

If your not making enough HP on the low end than your not set up correctly, with either induciton. Trippples can produce more power on the low end and pull hard thought the RPM's if set up correctly. The real difference you will see with Tripples over SU's is the Trippple set up will be more tuneable. I ran Bell top SU's for years on a 3.1L engine, good response but no top end performance at all. I couldn't get enough fuel to flow through the needle, nozzle combination. Yes, the Dashpot with heavy oil (30 Wt.) did give the needed accelerator pump fuel action but on the top end it ran lean, even with custom machined needles and nozzles; note the carb bodies were unmodified. With the Trippple 40 set up, I had much better low end and even better top end performance.

 

Story:

With the SU's from a rolling idle if I punched it, the tires might squeal a little bit, and pull hard to about 5000 RPM's but then I could tell a tappered off effect to 6000 and some real effort to reach 7000 RPM's. With the Dellorto 40's I ran, same idle roll it would light up the rear and I had to feather the throttle a bit to get them hooked back up and than the old heap pulled hard thought 7000. The MSD shift light is set at 7000 and I was well into the light before shifting from first to second.

 

Moral:

If your Trippples are not tuned correctly than you will never see the performance and your induction will run like a tired old mule.You should see a perfromance advantage with Trippples over SU's thoughtout the RPM's, if you don't your not tuning them correctly.

 

Conclusion:

I like the SU's great drivers carb but not as much performance potential as a well tuned set of Trippples. And I concure that if not set up correctly the Trippple set up isn't worth it's cost.

Trippple carbs; six main jets, six emultion tubes, six idle jets, six air correction jets, six idle jet holders, six pump jets, six chokes and six auxiliary ventures.

Twin SU's; only two nozzles and two needles.

 

Mike

[Guest norm[T12SDSUD]]

And yet I have been waiting for years now to hear about a Daily driven 240Z car running triple carbs that pulls 12's in the 1/4 mile AND gets 23 mpg.

Them SU's just won't flow.........

 

later,norm

[Guest bastaad525]

Trippple carbs; six main jets' date=' six emultion tubes, six idle jets, six air correction jets, six idle jet holders, six pump jets, six chokes and six auxiliary ventures.

Twin SU's; only two nozzles and two needles.

 

Mike [/quote']

 

You just said it all right there when tuning tripples, be ready to possibly replace all of the above listed parts, in sets of six of course, until you get it right... $$$$$$$

 

With SU's, you're just turning two knobs and two screws (okay well there are other things to tweak of course, oil weight, piston spring, and of course the needle grind, but with just adjusting those two knobs and screws you can get a very good running Z... and though it is true SU's dont usually make good power above about 5500rpm, they can easily be modified for more flow and be made to pull higher than that very well.)

 

A good option and middle ground are the big bore (commonly reffered to as the Jag SU's, but I'm not sure this name always applies) SU's that you can get from Rebello. They flow much more than the stock SU's, while still retaining the benefits of the stockers. A set of these isn't much more than a set of rebuilt SU"s from Ztherapy (I think they are about $700-800 vs Ztherapy's for $600). If I EVER build another N/A, carbed Z, this would be my first choice.

[JMortensen]

Moral:

If your Trippples are not tuned correctly than you will never see the performance and your induction will run like a tired old mule.You should see a perfromance advantage with Trippples over SU's thoughtout the RPM's, if you don't your not tuning them correctly.

If you're talking about slow corners where you come out of the corner at 2000 rpm, you would be the FIRST person who I've ever heard talk about getting a triple carb to do that better than an SU. This would include Rebello, Malvern Racing, Nissan Comp, and others I've talked to about making that situation better. ALL of them said that is the give and take with triples. You pay on the low end to get the top end.

 

Maybe you're just that good, or maybe you haven't driven a Z with a properly setup set of SU's. Not sure. If you can tune them to be stronger there, that should be your business.

 

SU's have an infinite number of jettings if you make your own needles and nozzles (every slightest bit of the taper change is a "jetting change" on an SU. Even the factory ones have 8 or more stages on the needles IIRC, so they still have more variation than the trips. WOT is WOT. Both the Mikunis and the SU's have a setting for it, and I don't think ANYONE would doubt that triples are going to kill SU's at WOT.

 

Jon

[brokebolt]

It's been stated before, cost vs. performance. And you don't get something without giving up something. Slow corner; SU vs. Trippple, you can set up a Trippple to preform there; but you loose somewhere else. You have to tune the conditons through sacrifice and gains. No carb is "best in all conditions", only EFI can give better than carb performance.

 

Ever seen a Hilborn guy tune, I'll take my Trippples or even my Bell top SU's over that ball of wax. But I'll bet my money on the Hilborn guy in the 1/4 mile.

 

Mike

[JMortensen]

It's been stated before, cost vs. performance. And you don't get something without giving up something.

Agreed. I have no doubt that my Z with triples is faster in the 1/4 than my old SU's were. And I'm sure that you are correct that you could choke off the trips to perform better than the SU's at low rpms. That's just not what they're good for. They're good for screaming at high rpms and scaring children with the giant sucking sound, I think you'd agree.

 

I'd still love to see what Norm's car would do with properly set up triples. I bet he'd be a convert too. The real decision maker is racing or street driving IMO.

 

EDIT--Norm, I'm not a 1/4 mile guy, but I did a Gtech test once with a badly slipping clutch and it said 108 trap speed with my buddy in the car (still not sure I believe that thing, that seems pretty high, but that's what it said). Did I mention I get 20 mpg on the highway...

[brokebolt]

I think we totally agreee, Trippples are best at high RPM's, SU's are best for a daily (the best MPG I ever got was 21 or so with the SU's, the worst was 8 or so). I like the comment about scaring children, but you forgot the small animals scurrying to their haven.

 

On a side not, I raced a 1/4 mile in my old heap wih SU's, the guy on the other side, 260 Z with Rebello tuned Trippple Weber DCOE 40's. I did win (yah me) but not by much. On another day, a 90ish Camero with a 350 was yet another barely win situation. Oh, but the best story of all was a 427 Chevelle. I was way quicker out of the hole with my SU's, but when the C.I.D. of that big block kicked in at about 3500...well we would rather forget that. But I do remember the California liceinse plate "66LICKS".

Mike