Which Intake Manifold for a 240Z???

spawpoet

spawpoet

New member
My brother and I are getting a new set of SU's for our 240, and have a question regarding which manifold to use with the carbs. I know 240's came with n-46, e-88, and n33 manifold at various points in it's production. I've read the general internet conjecture about these manifolds performance, as well as the n-36 manifold that came on the 260z's. We have ALL of these manifolds available in our shop to use. I'm skeptical that there will be a substantial difference in performance between them, but curious what the wisened community here feels on the subject. I.E. which manifold would you guys use?? The engine we bought our car with (an ITS 240) is to our knowledge bone stock. Also i'm curious what needles you guys are running, and if you are just using the standard 20w oil in the dampners or if you might have any other advice regarding the carbs. Thank you in advance for your comments.
 
I wish I could help you but I have a 260Z as well, so I've never paid attention to the Z choices. I bet Katman or Steve P might have an opinion when they login, but they aren't daily on the site.

Ron
 
This is all just opinion and regurgitated lore since I haven't put any of it to flow bench testing. I'm told that the N33 flows better than the others. I know of guys who have taken numerous examples of each to a flow bench and picked the one with the best numbers. Not all intakes are the same, even if you are testing one E88 against another.

As for the damping fluid I took the advice of the guys at Z Therapy and use ATF. And not very much of it at that. Just enough to get the plunger wet.

The needles are a tough one. The prep level of your motor will affect which needle works best. I would defer to Katman, if he logs on, but I use a stock needle from the early (70) Z that is "custom ground". (by that I mean that I hit them with a grinder a little at a time during a dyno session until I got the best result). I know that there is a lot more to be had by having needles custom made and dyno tested, I just don't have the time.......
 
E88 or N33, whichever you have that's prettier. Rebello used to claim 10 hp or something stupid like that. We couldn't show enough difference on an east coast dyno to matter. Our ARRC wins were with an E88.

Needles- they need to look like a telephone pole. More metal, not less. SM's, N27's and anything "ground on" will be too fat. N27 was stock for 1971, N54 for 1972. I think we ran something closer to an N58. With everything in perfect blueprint (bottom end, valve placement, cam, and carbs) and a decent header, you'll be too fat up to 5500 rpm and too lean past 6800. So we slow the suction piston down and live with a little leanness over 7200. We used [secret] for the damper oil, so 20w or 10w30 is fine. I don't believe in lighter, like ATF. Makes the piston come up too fast and runs fat.

Now the old school thinking was get the piston up quick so there's no restriction. ATF for damper oil was the rage back in the 70's. Ive found that it just doesn't make horsepower that way. Rich mixture will cure a lot of ills, for example you can run zero point gap (if you had points) on a Z if you put enough gas in it. But if the rest of your system is blueprint you don't need to be rich, you need to be lean. Mixture control is more important than flow up to about 6800. There are some very competent Z pilots out there running the Rebello method of no oil whatsoever, so the piston slams up to the top soon as you crack the throttle. Those guys never beat me. And my car idles and drives around the pits without spitting black smoke all over the place. I like my way.

In the end you need a bigger jet to take care of the over 7000 lean problem, but then you're in for custom needles. It isn't really a problem, you won't melt a piston, but there is a few more horsepower up there to be had. The stock jet limits you. But having said that you should be able to win races with everything perfectly stock, and we never made it to the bigger jet part (we ran to 7400 rpm at Road Atlanta, 7200 tops anywhere else).

You really need a good O2 sensor on each bank (I used cyl's 2 and 5) and a HAL30 or similar lambda or air/fuel sensor. We were fortunate to do our tuning with a proper engine dyno, but if I was on a budget I'd put the instrumentation in car for test days when you can look (I've decided driver's don't see anything during a race unless it's a big blinking red light).

Headers will affect mixture, so YMMV.
 
Thanks K, great info as always.

The secret oil wasn't sewing machine oil comined with 20w was it? Never mind...lol......read that on an SU webpage actually.....
 
Uh, the secret oil is secret because I forgot what the mix was. Man, i miss my brain...

One other thing on the operation of SU's. The common knowledge was running lighter oil in the damper allowed the piston to go up faster and hence you were at a lower point on the needle and therefore had more jet area exposed which equalled richer, which everybody associated with more power. The factory will tell you that slowing the damper down with thicker oil created a bigger vacuum, which resulted in more gas being pulled past the needle and hence a richer mixture. That was the case I always found on street cars, they ran better with thicker, or proper, damper oil.

Now that counters what I just told you in the previous post. We slowed the piston down to make it leaner. However, we're talking about two different regions of piston travel, rpm, and vacuum. The region of piston travel we care about on the track is the upper 1/3 of travel. On the street, the first 2/3. For rpm, above 4000 for track, below 4000 for street. For street rpm the throttle and piston position can affect vacuum greatly, for race the throttle is always full open when it isn't full closed (you Z pilots got that, right? Full open, there is no part throttle or "feathering" in a Z. If you can't do that we need to talk about shocks and setup), so vacuum is more a function of rpm, and less affected by the last 1/3 of piston travel than it is with the first 2/3. What we were slowing down was the last 1/3 of piston travel (and running stock like oil to have stock like piston response in the street range of throttle position and rpm). On a stock setup, when you open the throttle at 4000 rpm the piston pretty much goes straight to the top. The needle is essentially out of the jet so what is affecting your mixture is the vacuum over the jet bridge caused by increasing rpm. It ain't the piston moving the needle in the jet as you go from 4000 to 7000 rpm. So we slowed up the last 1/3 of travel, ran long needles with very little taper at the end, and lived with lean mixtures above 7k.

There used to be a video showing the piston movement during a dyno pull on ZTherapy's website. That was mine, very early in our engine program.
 
Thank you gentlemen for you advice and opinions. Katman it's pretty clear you have probably forgotten more about z's then many of us will ever know. Based on what you said in prior posts we ordered n-54s with the carbs, and Steve at z therapy recommended n-27s for ITS so we got a set of them to test as well. He had said they were the leanest of the stock needles for the su's, but it sounds like they might be too small. Doesn't z-therapy now sell oversized nozzles w matching needles?? I thought I saw them on their website.

I don't think at any point I've ever really introduced myself to the "community" here, but my brother Tim and I (Chris) picked up a ITS 240 a couple of years ago and have been whipping it back into shape for the track in the meantime. We're limited on time and money (isnt everyone?) but weve run a bunch of autoxs and a time trial this past year and probably will be focusing on tt's this upcoming year with the hope of doing the RR double school in 09. At least thats the loose fitting goals right now. I've mostly just lurked on the board til now, but I really appreciate the knowlege all of you bring to the table for those of us who are just cutting our teeth on this. I've been a z guy my whole life, and this car is my third. I really am suprised to see so many z's still competiing in the SE. I look forward to getting up to some of the tracks you guys run at in the near future. We're based out of WPB, Fla and haven't had alot of ITS z's to watch at the tracks down here. I think Guy Marvins car is the only one that's run down here on a somewhat regular basis in the last five years.

Thanks again for the feedback.


Chris Carey
 
Chris, good to see you step out from the shadows.....lol....hope to see you on here more.

TONS of ITS Z cars back in action now in the northern half of the SEDiv. Parrish 1 and maybe Parrish 2, Mackaman, Rock Vest's old car is running again, Shedd, Williams, Earp, Spillman, Paul we hope this year, Jeff R. building one, etc. etc. etc........Hope to see you out soon.

Jeff
 
And you forgot about David Plott, and David Kim. :)

Welcome to the fray. Hope to see you at the track.

While not ITS you have got Greg Ira and Don Ahrens running in the production classes. In fact Jmark just posted up some Ira viideo on youtube.
 
Don't forget Greg & Guy run in the ECR's in Guy's fast #33 ITS 240Z. Here are a few of the SE ITS 240Z's.

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Thanks for sharing the pics Jmark. They're very ggod. I wouldn't forget Guy and Greg. I used to run speed trials with Greg in Equipe Rapide down here in S Fla, and my brother and I pitted for Guy and Greg at the 12 Hours of Moroso a couple of times. I really, really enjoyed that, and they ran a heck of a race both times.
 
And us guys over in RMDiv

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John A. and I at Pueblo

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Animal and I at La Junta
 
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Being another 260, I have no choices. There were a lot of options for the 240. Look into the carb openning, at the middle port. I think that there is one, like the N-33 that you will see a difference in. I am told it is almost as good as the N-36. I have even seen a very fast 240 with a N-36 on it for a while. Seems the dude didn't know, must not have cuz as soon as I mentioned to him that they were a 260 only part, he came back with N-33's.

Mike
 
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