Mikuni's VS SU's??

[Marty Rogan]

I was looking for some advice on carbs.

First, here is some information on my car:

Early '71 240Z

currently has stock struts, 5-way Illuminas, MSA lowering springs, short steering knuckles, PU bushings. 15x7 Konig Rewinds mounted with 225/50/15 RA 1's.

'83 280ZX engine, bored 40 over, with '83 5 spd and 4.11 open diff.

I mainly use the car at track day events like NASA HPDE and similar events.

I am looking to wring some more horsepower out of my car. I am considering an MSA Stage II cam kit. So then I started thinking about carb choices. I currently have the stock SU's on my car and they are in pretty good shape.

I was wondering if triple Mikuni's would add signifcantly more performance over the SU's? If yes, are they much harder to tune and maintain? Is the added expense worth it?

TIA,

Marty

[jmortensen]

Having run both SU's and Mikunis, but neither on a dyno, I can tell you that my butt-o-meter says that the Mikunis gave about a 40 whp increase, that's just putting them on, not tuning them. I think Dan Baldwin had dyno sheets posted here showing a bigger increase in his case. In mine, my wife went from pitching the car a little sideways on her favorite corner to literally being afraid to drive it.

I'm sure you'll get Bruce Palmer in here touting the wonders of SU carbs and I have a lot of respect for what they can do and the job that Z Therapy does refurbing them, but you don't see any of the national level autocrossers running SU's, and I've never seen a picture of an old GT2 Z car running SU's. They're great carbs, but I think the Mikuni is the way to go for ultimate power output.

If you're going with the Mikunis, I'd go bigger on the cam. Stage IV if you're going with Schneider would be my suggestion, but I'd also suggest you don't go with Schneider. Get a regrind from ISKY or some other cam grinder, or buy a cam from Rebello. The Schneider cams seem to be the ones that fail most.

[Bruce Palmer]

As with everything performance related automotively, speed relates to $$$. No doubt about it, a triple Mikuni should produce extra performance. The cost of the system and dialing them in may make that incremental increase a marginal investment, especially for a track day car. Again, there are 3 2.8 liter Zs with our standard carbs that hold hillclimb records here at the local event. More bigger carbs might have made the cars faster but the cars or the drivers may then become the limiting factos.

Worse case for starters I'd throw a set of SM needles into your carbs and see what that does for upper end power, then go from there. That's a $30 test.

From there on it's grab your check book and decide how fast you want to be.

Happy New Year everyone...

[26th-Z]

Marty,

To the best of my knowledge the MSA stage II cam is a Schneider cam ground to spec similar to the Datsun competition stage I cam. It should give you a fairly smooth idle along with the increased performance. It will require a different fuel mixture and Bruce's suggestion is the first thing I would try. I'm a real believer in SUs and although they look rather doudy compared to those sexy asian triplets, they deliver quite well.

[Arne]

Marty, I'm a big fan of SUs, and love mine. But in my opinion for track use with an overbored L28 and a hotter cam, I suspect that the SUs will limit performance some. Not to say they won't work, because they will. But I figure a set of triples will bring it alive and get more out of the engine than the SUs can.

[esmit208]

MARTY

Just to ditto what everyone has already chimed in about, simply bolting on different carburettors will add HP's but ultimately they need precise tuning. Higher performing camshafts are not always a necessity but highly suggested. Camshafts with shorter duration may not hold the intake valve open long enough to take full advantage of the fuel air mixture which determines how powerful the explosion will be. In addition if you eventually do install triple carbs having the correct jetting installed for the application is a part of the tuning process. Good luck at the track!

2MUCHZ

[ChrisZ]

You can't beat the sound of triples, i will 2nd Jon's opinion on the cam size, if it is for track, an over bored L28 with a big hot cam and a aim for a high rev engine, then you will probably run out of air with SU's and 40 triples, so i suggest you go for nothing less than 45, if you want triples.

Have a look at this Swiss Z:

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[Marty Rogan]

Having run both SU's and Mikunis, but neither on a dyno, I can tell you that my butt-o-meter says that the Mikunis gave about a 40 whp increase, that's just putting them on, not tuning them. I think Dan Baldwin had dyno sheets posted here showing a bigger increase in his case. In mine, my wife went from pitching the car a little sideways on her favorite corner to literally being afraid to drive it.

I'm sure you'll get Bruce Palmer in here touting the wonders of SU carbs and I have a lot of respect for what they can do and the job that Z Therapy does refurbing them, but you don't see any of the national level autocrossers running SU's, and I've never seen a picture of an old GT2 Z car running SU's. They're great carbs, but I think the Mikuni is the way to go for ultimate power output.

If you're going with the Mikunis, I'd go bigger on the cam. Stage IV if you're going with Schneider would be my suggestion, but I'd also suggest you don't go with Schneider. Get a regrind from ISKY or some other cam grinder, or buy a cam from Rebello. The Schneider cams seem to be the ones that fail most.

Which ISKY cam would you recommend? I definitely want to stay away from Schneider. No sense in doing the job more than once.

[esmit208]

2FAST2Z

That is one HOT video. And you are right, NOTHING beats the sound of a 6 pack!

[jmortensen]

Which ISKY cam would you recommend? I definitely want to stay away from Schneider. No sense in doing the job more than once.

Not sure what they offer, to be honest, but I know that they regrind them which is better than using the new softer cam blanks. I'd shoot for something in the .500 lift and 300 duration range, plus or minus a little bit if the engine is around 10 to 11 to 1 compression. If it's lower, go a bit smaller.

[Curtis240Z]

While triple carbs or injection will give you improved performance when properly tuned, your limiting factor with your current setup is the stock struts. I would invest in coil-over system first as that will lower your lap times significantly even with your SU carbs.

Just my 2 cents.

[Marty Rogan]

I have not looked at the specs on these for a very long time. There is a guy locally that has a set of Mikuni's with the following jetting:

200 Air; 150 Fuel and 52.5 Pilot. Venturi's are 34MM

Does anybody know if that would work well with my engine? (See details of engine post #1).

Also, as I recall, triple carbs do not have a vaccuum port for the distributor, right? I am currently running a ZX distibutor with the E12-80 module. What

would I need to do with that?

TIA,

Marty