Zmanco
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Posts posted by Zmanco
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Daniel' date='
As for your project, there is no need to switch over to the N-47 from the N-42. Any gains that you might realize from that swap would be to minute to worry about. Though you do have a much bigger issue at hand, detonation! An L-28 with Flat top pistons and the open chamber N-42 head, (or Z N-47 for that matter). This combination is well known for not being pump gas friendly even at a measly 9.5:1 comp ratio, they WILL detonate even with premium pump gas and a mild cam. I’ve witnessed this first hand on more than a few engines that others built and have also read about from LOTS of other people as well. Yes, the ignition timing can be backed down to help subdue the audible knock, but by doing that you are giving up LOTS of power by retarding your ignition timing. I would much rather loose a whole point of compression using amore ideal head, (P-79 or P-90), and be able to run ideal ignition timing. I.e. sacrifice maybe 3 % HP due to loss of compression ratio to regain 10-20% HP with ideal ignition timing. Don’t rip over dollar to pick up a dime. 10 degrees of ignition timing can be worth more power than even 2 points of compression.
If it were me, I would ditch the N-42 and N-47 for either a P-79 or P-90 head as either of these two heads complement the flat top pistons MUCH better and will allow you to run ideal ignition timing on pump gas allowing your engine to run a max effort. [/quote']Well, Paul, you did call it correctly. Now that I have more miles on the engine and it's been much warmer, I have picked up some pretty audible detonation. It only occurs at low revs, and only at part throttle. By 3500 rpm it goes away (I think - hard to tell due to all the noise from the webers and header), and it also goes away any time I go to WOT.
I tried retarding the timing to 0 at idle, but it didn't make any audible difference. I also tried adding octane booster, even the good stuff (108) but it makes no difference that I can hear.
The frustrating part is that the engine runs GREAT! But I'm guessing that this much audible detonation is not something the engine can live with over the long haul.
I had a spare cam reground to .480"/284 along with regrinding the rockers. I had planned to put this into my N42 head, but given the pinging I'm now rethinking.
So on to my question: I have located a P79 head for a reasonable price. If I just put the cam into it and use a Felpro gasket, LEngine says I should be around 8.8 CR (I'm bored .030 over). I've read about the mod to shave the P79 .080", raise the towers with shims, raise the springs, etc. to get the CR back up around 10:1. Is it worth the extra effort and cost? I'm thinking it is since most of my driving is on the street where I can't be making all the racket that 6k+ revs (and webers and dynomax muffler) make. In other words, I need the engine to be strong over a reasonable wide range of rpms.
Quick recap:
N42 block bored .030 over
flat top pistons
weber DCOE 40 carbs
6:1 header
'80 distributor with no vacuum advance
currently N42 head, thinking about P79
Thanks again for everyone's inputs. It's amazing how much experience there is on this board!
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I noticed you typed "ring" and I typed "rings". The search engine built into this site isn't quite as sophisticated as Google and so it thinks those are 2 diferent words and hence you get different results back for each. You have to anticipate the different ways the term will be used and search on them all.
Glad you found the Deves, I've heard nothing but good things about them.
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Deves makes a good set of cast iron. Google "deves 280zx" and you'll find a few stores selling them.
PS. I know you won't want to hear this, but you could have found your answer yesterday by searching this site. "piston rings" would get you close, and "piston rings source" even closer.
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Thanks for the pictures Spotfitz. Looks like it's a vacuum solenoid. With my webers and their poor idle vacuum, I'm thinking I need to go with an electric. A parts counter guy suggested that early 80's Fords, such as their big sedans, might be a good source for it.
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That's the first time I've heard that. Does it mount on the firewall? Any chance someone has any pictures?The '74 came equiped with the fast idle circuit with carbs. -
Daniel' date='
Have you looked at the way they do it with the 280Z? You might be able adapt that system.[/quote']Phantom, no I had not. My efforts lately have all been outside the cabin and since my current system works, albeit not great, it hasn't made it to the top of the list.
I would be curious if the later 280z evaporator performed significantly better than the "stock" 240.
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I have the stock (dealer installed) AC in my '73 and it's really only effective when driven at speeds above 30 mph. At idle there are two issues:
1) the stock engine fan doesn't pull enough air over the condensor to keep it the air in the cabin cold
2) in stop/start driving the underhood temp goes up and when the compressor kicks in, coupled with the carbs getting hot, the engine doesn't like to idle. You can increase the idle speed to compensate, which helps some, but that means that on a cool day you're idling around 1100 rpm.
Despite that I do think it's worth it. And if you can find a better solution for the evaporator under the dash I'd be very interested!
BTW, has anyone come up with a good (simple) way to increase the idle speed when the compressor kicks in on carburated cars?
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I'm guessing that your idle mixture is just too rich. You might get away just turning the idle mixture down to lean it out, or you might have to go down a size or two on the jets. But without an exhaust gas analyzer you're going to be doing this trial and error, and I'll guess that you are only allowed one more try at the test station.Load HC 81 Pass 400Idle 1360 Failed 400
I very much doubt that the multiple spark ignition will make that much of a difference. Perhaps you can find an indendent shop that specializes on early british cars, or even early Hondas and Toyotas. They ran on carbs, and the analyzer is the only way to set them to pass. Look for a mechanic who is in his 40s or 50s. Younger than that and he probably has little experience with carbs. That's where I'd put my efforts. Good luck!
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Bryan, not sure what you mean here. The mechanical fuel pump bolts to the head, not the block. The N42 head has an opening for a mechanical fuel pump, the N47 does not.The F54 block has the block off plate location, but no spot opening in the block. -
How far off were you on the unburned HC at idle?I forgot to mention that is at idle that I have any problem with high HC. At cruise it passes great. -
If your goal is to get the car to pass emissions, then I'd suggest you find someone with an exhaust gas analyzer who can tune the car to meet the test levels. Basically they put the probe in your exhaust and then can set the mixture to get to a passing level. I had to do that when I bought my Z. It drove like crap, but I only had to go a few miles to the test center. I drove right back to the mechanic and he set things back to make it drivable again.
If you're looking to put a new ignition in, then maybe you should try it. But if your carb is set too rich, which helps with drivability, then I doubt there's anything you can do with the ignition system to get it to pass.
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I think 1 is a NO
if I remember correctly' date=' the N42 doesn't have an opening for the mechanical fuel pump that runs off the cam gear eccentric.[/quote']Just checked my N42 in the garage to be sure - there is an opening, although I have the block-off plate on it. I believe it was the N47 that followed after the N42 where the "opening" became closed.
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Short answers: yes, yes, yes.
Better to use an intake manifold gasket for the early 70-73 since you're using carbs. You will probably have to swap the dizzy mount from the L24 to the L28.
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I had heard I might have detonation issues, but so far (1500 miles) I haven't been able to hear any although I realize that's not the best method. But I have been listening closely, driving with the windows up on the really hot days trying to hear it. Perhaps it's because I live in Colorado and do most of my driving above 5000 feet? Or maybe because I've limited my total advance to about 34 degrees?
Paul, I really value your advice and I'm not trying to argue with you. I'm just trying to compare what you're saying with what I'm experiencing with this engine. Perhaps I'm missing something else?
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The MN-47 is a round port head. The round exhaust ports' date=' (with the liners still intact), are excellent for mild race and hot street engines. Also of note, All the round port heads, (N-47, MN-47, and P-79), have a smaller intake port. At approx 1/2 “ into the port, the port takes on a “D†shape, this helps bias the port centerline which in turn helps to aim the incoming air flow toward the center of the cylinder. This is great, but for maximum effort high RPM breathing, that smaller port is a hindrance to overall flow. These “D†shaped intake ports compliment the round exhaust ports nicely for mild to hot street, and mild race applications. Especially for a street engine that is asked to have some civility at part throttle conditions like having to drive through town back and forth to work and in stop and go traffic on your way to your favorite bonsai back road. These "D" shaped intake ports and round exhaust ports found on the N-47, P-79, and MN-47, in my opinion, offers the best performance with the least compromise in around town drivability and low end and mid range torque.
The square exhaust ports of the N-42, E-88, and P-90, allow for considerable exhaust port alteration allowing the engine to breathe freer at the higher RPMS, though low rpm performance will suffer as a result. The Intake ports of these same heads are also larger than the intake ports in the N-47, MN-47 and P-79, so less carving.
In short, the N-42 offers more “all out†potential, but at the cost of low rpm and part throttle drivability. This same radical head on a street engine that is to be driven around town would be a poor choice. This N-42 works best at WOT and above 4000 RPM, where as the round port heads do their best, (depending on how they are set up and built), from as low as 1500 RPM up to 6500 and will have decent manners around town.[/quote'] I hope this isn't a thread hijack since it has been quiet for a few months now.
I currently have an N42 head that was freshened a few thousand miles ago with a valve job and new seals. My plan before reading Paul's comments was to put a reground cam 284/.480 into it. But I also have a spare N47 head with about 80k miles, history mostly unknown. I'm wondering if I might be better off switching to this head? The rest of my engine is an L28 w/flat tops, triple webers, square port header. My driving is mostly weekend street, and as many track days as I can get to. I do need to be able to drive it "politely" on the street when required, but it's not a daily driver.
So is it worth switching to the N47 with unknown history vs. keeping my known-good and recently refreshed N42? I've spent most of my Z funds on rebuilding the bottom end so I don't have a lot left over to refresh the N47.
And would there be any significant issues running with square port headers on a round port head? I've heard it said that it doesn't make a differnece and that it's only the reverse (round port headers on a square port head) that's a problem.
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Yasin, you might ask the cam shop what they recommend. I just sent my core up to Delta Cam to be reground. They say that for the grind I chose, .180" lash pads are all I need. So I've gone and ordered a set. I'll know more when I actually get it all assembled and check it out, but they say that they've done enough of this grind for Zs that it should just bolt together.
We'll see
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Why don't you just get your existing flywheel lightened? I had my stock L28 lightened from 23# to 16.5# using just a lathe (to keep the cost down). Everything came off the outer edge where it matters most. Going any further would have required machining and more $$$.
Including resurfacing and rebalancing the total cost was about $120. That's about the same weight as the Maxima flywheel, and if you figure you'll still need to get the used flywheel resurfaced and pay for shipping, I doubt you'd save much if any money with the Maxima.
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If you assume that the diameter of the combustion chamber where it touches the head gasket is the same as the bore of an L28, then it's about 1.5 cc. In the real world it's probably a little less.
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I just went through this same issue a few weeks ago. The general concensus was that the ring manufacturer is the one who specs the end gap. Usually it's a function of diameter, for example:
gap = .003" per 1 inch of diameter.
In my case I was using ITM pistons and rings (not sure if they're related to your ITC) with a top moly ring, not chrome. The manufacturer was no help with end gap, so in the end I went with .014" for the top ring and .012" for the second. FWIW, my N42 was bored .030 over.
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Did you bed the pads in yet? The method I've used is to go out on a deserted road and accelerate up to about 60 mph. Then brake hard, but not a panic stop, down to about 5-10 mph. Gradually accelerate up to 60 mph and do it again. Repeat this 4 or 5 times. You want to get the brakes and pads good and hot, but not overheat them. Then drive the car normally to let them cool....the brakes didn't seem to be much more aggressive than the stock calipers were...in reality they might be but I'm not impressed so far by the upgraded calipers...As it has been explained to me, two important things are happening:
1. no rotor is perfectly flat, and this is speeding up helping to get the wear pattern on the pads to conform better to the irregular surface of the rotor. Assuming you have new rotors, this isn't something that is visible to your naked eye, but it happens and means that more of the pad will be in contact with the rotor.
2. some pad material becomes embedded in the rotor surface, much like racing tires leave some rubber on the track. This improves the tires grip, and for brakes, improves the coefficient of friction, meaning the brakes feel like they "grip better".
The first time I ever changed brakes (new pads and rotors) I didn't know about this, and the first few stops felt worse than the old brakes. Eventually after several hundred miles of driving they broke in themselves. This process speeds that up.
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Hi All, I asked this question at the end of another thread but never got a response, so I hope it's ok to ask it again here. Has anyone done the vented 4x4 toyota caliper swap with the later bigger calipers (S12W with 4 large pistons) and NOT swapped to the 15/16" master cylinder?
I ask because I read that this was required for the swap for the non-vented swap, but when I did that and left my stock m/c in, everything was fine. I had no problem with a long brake pedal.
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I'm going to make the switch to the toyota calipers and vented 300zx rotors, my dilema is whether to use 12-8 or 12W calipers. From this thread and a few others, it appears that the 12-8 have one large and one small piston, while the 12W has both large. That makes me think the fluid requirements are greater for the 12W, hence the recommendation for larger M/C.
I was all set to order the 12-8 as I believe they will be more than adequate for my needs, when I checked availability of pads. It looks like there are a lot of choices for the 12W and very few for the 12-8. That concerns me, especially if there will continue to be performance pads available in a few years for the 12-8.
I currently have the 12-8 non-vented calipers installed with the stock master cylinder on my '73 and have no issues with a long pedal. However I wonder if the 12W might need the 15/16' master cylinder upgrade which adds additional cost. I'm sure it's better, but is it required?
So my question is if anyone has tried the 12W caliper swap, and used their stock M/C with good results? For now, I'm going to leave the drums on the rear, if that matters.
Thanks.
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I had trouble finding a Maxima flywheel, so I had my flywheel turned on a lathe and got down to 16 lbs. Going any further would have required machining which was going to start ringing up $$$. The total cost including resurfacing and rebalancing was about $120. Definitely makes the motor rev up and down faster and feel more lively. I'd say it was money well-spent as long as you do it while you have the flywheel out. I wouldn't do this as a stand-alone project as it would be too much work for not enough benefit.
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I found some hard plastic tubing that was the same ID as the vacuum line for the brake booster at my local True Value Hardware Store. It was all of .49 a foot. When I put my triple webers on the nipple was in a different spot and I didn't want to force the old hose to bend in a new way.
After 3 weeks, and a few hundred miles so far it's working great. I think the key is you want something with a stiff wall so the vacuum won't collapse it. This would be much cheaper, and easier, than changing your booster, assuming there is nothing wrong with the booster of course.
Good luck!
Custom Cylinder head building.. What's Involved?
in L-Series
Posted
But last Saturday it was very warm, close to 100 ambient, and I heard the detonation louder, and over a wider range of throttle. That's what convinced me it was really detonation and not some other strange sound. BTW, it doesn't have that somewhat random sound that I'm used to hearing. It's a more regular sound that rises with engine speed. Very strange. Does any of this make sense?