LeonV

Vacuum advance is only active at part throttle. At WOT, vacuum advance should not be making a contribution to total timing. Empirically, MBT timing is typically 33-36 degrees on an L-series engine without serious combustion chamber work. If everything else is okay, and your timing is a few degrees off then the engine should still function fine, it will just be slightly down on power. One thing that is apparent to me is that your mixture seems lean. A leaner mixture burns slower, which necessitates an increase in spark advance. You increased advance and the problem shifted to a higher rpm, telling me it's a mixture issue. Also, popping from the exhaust can indicate a lean mixture since incomplete combustion will then cause the unburned part of the mixture to ignite and "pop" within the exhaust. The first thing I would do is check for big vacuum leaks and mal-adjusted valves. Just because they're quiet and were adjusted 2000 miles ago, does not mean that they're okay now. Make sure to include the PCV system during that check as well.

And where did you "see" this 20hp increase? What is the reason for eliminating EGR? EGR has NO effect on power at WOT and also increases your gas mileage at partial throttle. So not only does it not affect max power, but it gives you better gas mileage when you're cruising around while significantly dropping NOx emissions. That's a win-win in my book. So what the headers actually gave you was more noise, more heat, marginal (if any at all) power gain and a drop in fuel economy. You've actually lost power at partial throttle by eliminating EGR. There are no "tuning tricks" unless you consider it a trick to clean electrical connections, adjust valve lash and set timing. You will benefit much more from these three things I just listed, than haphazardly slapping "aftermarket parts" on it.

Concerning the exhaust system, best bang for the buck is to find a good exhaust guy and have him make you whatever you want. If you're after performance, a single 2.5 inch pipe with a resonator and straight through muffler will have great performance and shouldn't cost you much. If you want less noise, get a quieter muffler. My local exhaust guy did a header-back twice pipe exhaust for me, including a total of 4 glasspacks and 2 O2 sensor bungs for $300. Obviously, I can get a single pipe system for less. Find a good local exhaust guy and you won't regret it!

He is an EX-dictator. He has ceased to be!

Sure! Are there car clubs? I did some FSAE stuff but nothing outside of that. Then again, I didn't have a running Z at the time... Heck yeah, Julio! The Hangar is pure bliss for fabrication. I loved Cal Poly, wish I could go back for seconds!

If you're at Cal Poly, I would recommend making friends with everyone that works at The Hangar, especially if you're an engineer! I'm not sure about their current policy on personal projects, but make some friends and see what happens. Take some time to learn some valuable fabrication skills and you'll be able to fix anything on that Z!

Cool, sounds like an awesome project! Definitely post some video when you can!

Just take the wheels off and drop it on the ground. It'll be mad low yo.

Sounds like your countershaft bearing is on its way out.

That guy is so full of BS, I wouldn't believe a thing he says!

Aha, thanks Tom! I thought I had seen Mikunis with the pull towards the cabin, interesting that you can set up for LH or RH positions. I haven't seen that on the Webers, but it may exist as well.

Just FYI, this is not true. Flame temperature is a maximum with a slightly rich mixture (~13.5:1) and gets cooler as the engine is leaned or enriched from there. As far as color goes, I've done lab experiments with a glass engine (glass cylinder, you could see the piston move and combustion happening!) and from what I remember, orange was rich, bluish was probably slightly rich, and light-orange with flashes was lean. Good luck. I'm thinking that installing a WBO2 while also using the colortune may yield some interesting results.

Not exactly. They have cold start enrichment circuits, no choke valves are involved. But yes, they are both cable pull-type actuators. I think the only difference between the two in that department is the direction in which you pull the cable, but I'm not 100% sure on that. If you look at Dave's (cygnusx1) picture, the Weber levers must be pulled toward the hood. I think the Mikuni cables are pulled towards the windshield. Someone with Mikunis can chime in to confirm.

I like your solution, Dave! I chose to remove my choke lever when I put in a new center console.

I'm with Blue, a WBO2 is a much more comprehensive tool for this purpose. Concerning the HC phenomena, the reason behind that is at a certain point, a lean mixture will cause incomplete combustion (slow burn or misfire) which will release some unburned gasses into the exhaust. Thus, HC will increase. The leanest an engine can be run without misfire depends on many factors, with the big ones being mixture homogeneity and combustion chamber design. Anyone have a 5-gas analyzer laying around?

The Weber DCOE and Mikuni PHH both have cold start enrichment circuits (no choke). It depends how cold it is when you drive your car, but around here, I don't need the cables hooked up on my Webers. For me, it takes three stabs of the throttle, one or two turns of the engine, and some blips to keep it going before it settles into an idle. Either Weber or Mikuni is fine, but Weber parts will be easier to find (and maybe a bit cheaper?).

Why not call him?

Sigh... I'll just second what John said, especially the "taking it personally" and "posting more information that wasn't disclosed earlier" parts. Good luck with your build.

This? http://datsunzgarage.com/borg/

Yes. Refer to my first post. Just put a lightweight flywheel on an L28 and it will likely rev-up faster than a stock L24. Stock flywheels are ~25lb. Aftermarket aluminum units can get down to the 8-10lb range. That's 15lb of rotational mass removed from the crank right there. John makes good points. This is why there is no need to focus on differences in R/S, stroke, rod angle, etc. The differences are insignificant for a project such as this. Do the simple stuff mentioned, and you'll come out far ahead.

Where did I "cop an attitude"? This is the insecurity I'm talking about. I did not call you anything (as you did to me). Nor did I imply anything of the sort. The first statement of mine that you quoted means that there is no reason to call one engine better than another simply because of some minor detail (R/S ratio, rod angle, etc.). The "bench racing" is in reference to those that take minute differences in these details too seriously, and seem to discuss their merits down to an atomic level. My statement foreshadowed the post by Zedyone, to which my other statement you quoted refers to. So it was not even in reference to you. You agreed you were wrong in one instance? Great! You acknowledged that you're not looking for a close-ratio transmission. Okay, moving on... I'm sorry if I hurt your feelings with my proposal, it was just the logical progression of your goals. If you had stated your true goal originally, I wouldn't have bothered. You seem to be going in circles here. You know that you can make an L28 do the same thing, yet you don't want to for some reason? You can easily use stock parts to achieve this. This is why your goals must be clearly defined. You started out by stating that you like the L28 but want it to "rev happy like the L24" and then change that to wanting a "rev happy" engine that "revs as fast as I want it to". Do you still want it to rev like an L24, or have your goals changed? I'll tell you once more that an L28 can be just as rev happy as an L24 with minimal effort. This is your stated goal in your first post. If your goals have changed, then say so. If you came in saying, "hey guys, I want to build this engine because I want to be different" then there wouldn't be a problem. Am I supposed to be able to read your mind? If you want to build an engine for the hell of it, then just say so. I never "bashed" your concept, I just explained how and why it could be done easier another way. You tell me no it can't. I explain again, how it's possible. You refuse to believe me and then insult me after a comment is made in reference to something else. Nice. Nobody is saying performance only means power. You're just grasping at straws at this point. I perfectly grasp the extent to which you want your engine to rev, because you clearly spell it out in your first post. Here it is again: "I love the torque out of the L28, but what I really like is the rev happy L24. I figure why not try to mesh the two?". "Tell me what you think!" My response was going off of the information that you gave us. You said you wanted something that revs like an L24. I gave it to you and you got upset. You even asked for our opinion! Seriously? There are absolutely no justifications for your immature replies. Yep, typical response from this generation...

Well by your logic: if you can't take the comments, then don't post. Not everyone is here to stroke your ego about YOUR fantastic engine. Your typical testosterone-laden response, and an inability to take constructive criticism shows your insecurity. You are so blinded by it, that you dont even see what I'm trying to tell you, and instead you throw a fit because someone else's advice doesn't match the picture in your head. I never called you anything, nor did I put-down your wonderful idea. I didn't tell you NOT to build your engine, nor NOT to swap gears around. You can do as you see fit, I was just trying to enable you to make an informed decision. Sorry for trying to help. Wait for your maturity level to catch up, then we can talk. Re-read my posts with an open mind first, as you clearly misunderstood the vast majority of what was written. Here is the premise for his engine build: My response detailed how he can achieve the feel of the "rev happy L24" with less time, expense and struggle, along with better performance. Is that a terrible thing to propose? Clearly, his goal is to build a one-of-a-kind "buried treasure" with performance taking a back seat to how rare this engine is going to be. That's just fine, go ahead. As I've stated, if the goal is to have an exercise in putting an engine together, by all means do what you want. However, don't mistake it as an improvement to actual performance when compared to a plain-jane L28 done right. That's the whole point, and if he stated his original goal as to build his own engine just for fun and bragging rights then we wouldn't be having this discussion.

Wow, okay... a bit insecure are we? I wasn't trying to be "snippy" and never called you any names. You have to learn to not take things so seriously on the internet. Is that how you'd respond to someone giving you advice in reality as well? I was simply trying to help you by giving practical, real world advice but your purely ignorant attitude clearly demonstrates that the advice is unheeded and unwanted. I guess being a mechanical engineer and having experience in internal combustion engine design just doesn't cut it anymore. I'm sorry I gave you the wrong advice, according to you at least. BTW, you're still wrong about the transmission, but I really don't care anymore. Go ahead and swap gears and have fun with your "stronger" transmission.

I had to resist from quoting your phrase in my post: "this is an exercise in internet engineering masturbation"

It is the cam! An 8 degree differences does more than you think. To quantify, it's least 500 rpm if not more. There's your difference, plus you have more displacement to work with using an L28. You can theorize about strokes and R/S ratios, but it really doesn't matter. An L28 is just as "rev-happy" as an L24 if you build it so. I'll bet that given multiple engines, some L24 and some L28, you would not feel the difference in the "rev-happiness" if set up properly. What you will feel is a difference in torque. "Quick revving", "fast-revving", "rev happy" can all be used to perfectly describe an L28 with the work done to it that I described. I find it somewhat ironic that you spec'd an L26 cam. That's just 8 more degrees than an L24 cam. Your words exactly were, "it doesn't have as much to do with the cam as you would think." Then why use an L26 cam at all? On the contrary, it has everything to do with the cam! The camshaft sets the engine's powerband. If you want higher revving, you get a camshaft designed for it. If you want quick revving, put on a lightweight flywheel and clutch. Boom. Done. I'm still confused on why you want the earlier 1st and 2nd gears. Early 1st and 2nd gears were shorter, not taller. You will have more wheelspin with early gears. I'll repeat, the late ZX 5-speed is already a close ratio transmission. By putting in the early 1st and 2nd gears, you are essentially recreating an early 5-speed but with a taller overdrive. This will not be a "close ratio" transmission. Just think for a second. Don't get into all the bore-stroke, rod-stroke, piston speed, rod angle, internet bench racing. You are not building an F1 engine. These things simply do not matter within the confines of our situation. The L24 stroke is 73.7mm, compared with 79mm for the L28. Either engine will go to 7000rpm just fine, however, the L28 will have more power and torque. I know which option makes more sense to me. Now, if your whole goal of this is to build your own engine from an assortment of parts, then go for it. This goal seems to match better to what you seem to want to do. More power to you. Just don't go thinking that an L28 can't be made to achieve the same thing. It likely won't be fine with the cam you spec'd. Let the bore-stroke, rod-stroke, piston speed bench racing continue...