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L33 5.3L Aluminum block 799 heads .581 220/224 112+2 with Demon 650. Dyno results: 337 whp, 334 tq. Looks like he grabbed the wrong run and so it shows 330. Take my word for it. 1f609.png;)

Needless to say all the moves I did on the carb in preparation were WRONG. Catastrophically wrong, like it would barely make it through a pull wrong, check out the massive dip in the torque curve! I put bigger jets in it, then brought still bigger jets, we needed to go smaller on everything.

Leaned it out, leaned it out some more, more leaning, more lean, then finally it put out the 337 number. It sounded like it had a miss at the start, and as we got further along it was running rougher and rougher. Suspect bad plugs or wires. Didn't have time to change them out, as he didn't have plugs and wires there. They thought this was the cause of the rough graph. A BMW came in and did a pull and theirs was smooth.

While we were making jetting changes we started talking about running it 1:1 where primaries and secondaries open together. I had tried setting it up like that and it just fell on its face, but we made it work. I'm happy about that because I won't get into the secondaries as I'm midway through a corner.

It's not dialed in but it's safe to race and I'm happy with the numbers, of course I have to wonder where it would be running on all cylinders...

dyno.jpg

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I feel like I can handle tuning a carb if I have some track time and my wideband. I got my triple 44s to run pretty well. I was guessing on the carb and guessed wrong, but I am way more confident in my ability to troubleshoot a carb than troubleshoot EFI.

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The nice thing about carbs is that you can actually see the parts that are doing the work - take it apart - put it back together.  It's like tuning an EFI system but with a screwdriver and changing out parts rather than tapping on a computer keyboard. The bummer side is that it isn't once set, always set.

My son only knew EFI and then he bought a '71 Chevy pick-up with a carb'd 350.  Seems that no one knows how to work on them any more.  I never thought they were all that hard with a little trial and error.

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Posted (edited)

Interesting to see this one pop back up. I figured out what was going on with the rough running. Wasn't wires or plugs; it was faulty battery disconnect switch and alternator charging. Basically the alternator was charging intermittently and on the dyno day it wasn't working, and the voltage got low enough to cause the ignition to start to fail. 

Went to an autox after this, ran great. Then went to another and it ran horrible and I saw a tiny wisp of smoke out of the battery disconnect. Swapped out the switch and wired it differently and then it still wasn't charging correctly. Cut the old switch open, the contacts were bent and it was BARELY making a connection. Was looking around for loose connections and turned out the dash idiot light in the charging system was intermittent as well. Moved the bulb around in the housing and suddenly had 14V on the gauge.

Point is that the rough running was something entirely unrelated to carb or spark plugs/wires. 2nd lithium battery was killed in the process of figuring all this out. New LED light installed, new switch, new battery coming. Should be back in action very soon. From what I understand it should be making somewhere in the neighborhood of 370ish whp when running right.  

burnt.jpg

Edited by JMortensen

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On 4/18/2019 at 12:44 PM, Neverdone said:

and yet you're choosing to fiddle with carbs which as far as I'm concerned, are a black magic box of the super unknown.

 

It's a generational thing.  Persons who are sufficiently old as to remember when the 240Z first came out, would likely feel more visceral comfort with carbs.  Those who weren't yet born when the last OEM carburated car left the assembly-line, would presumably have the opposite proclivity.

 

On 7/17/2019 at 10:45 AM, JMortensen said:

Interesting to see this one pop back up. I figured out what was going on with the rough running. Wasn't wires or plugs; it was faulty battery disconnect switch and alternator charging. Basically the alternator was charging intermittently and on the dyno day it wasn't working, and the voltage got low enough to cause the ignition to start to fail. 

 

This reminds me of the adage, that most fuel-flow problems are actually ignition (or other electrical) problems.

 

Jon... not to hijack the thread, or to cause offense, but when did you change your philosophy, to favor the V8?  Were you not, for many years, in the inline-6 camp?

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No offense taken. When I was 16 I had a bunch of friends who got me into Datsuns and they were all purists, so I came up believing that pushrods sucked and OHC was fantastic, that V8s couldn't rev, that the L series was a fantastic engine, etc. Mid 90s we had Carl Beck's email group and I started seeing people with V8s and who just generally weren't so closed minded.

The guy who, up to that point, had taught me everything I knew about Datsuns (and was a Nissan master tech and legit Z car whiz) was one of these "don't go too big on the cam" guys. So I had tiny cams in my truck and my Z. Some people on the internet disagreed, and I remember him saying something to the effect of "how do you know that they know what they're talking about?" I decided to get a much bigger cam than he suggested, and it was a huge improvement, at which point I realized that I could actually have a pretty good idea if someone knew what they were talking about. BTW after driving my L28 with .490/280 cam, he immediately went for a .580/310 or something like that for his L18. At least he realized he was dead wrong.

Then I started to notice a lot of people like Pete Paraska were talking up V8s and that put a little seed into my brain. 

Later I was looking for GOOD suspension tech and John Coffey suggested Hybrid Z, and I took a look and found tons of good information. Same friend had a standard autox alignment: -1.25 degrees front, -1.5 degrees rear, 1/8 toe in front and rear, 3 degrees caster. As it turns out, this is a shitty, understeering autox alignment. Hybrid Z recommended a lot more camber and caster, and more neg camber in front than rear, and zero or toe out in front. Again, huge improvement.

And all these smart people on this forum were ditching the L series and running V8s. I came to realize that all of my preconceived notions about adding huge amounts of weight to the front end were just wrong, and I realized that I wanted more power than I was getting from the L28/44 Mikuni combo I had, and it was probably going to cost $10K to get another 50 hp if I kept on with it. Also realized that having intake and exhaust on the same side of the motor is pretty shitty, and since these engines are all smog era designs the combustion chambers aren't great, in short, the L series isn't the best engine design. Had the same revelation about my Toyota truck with 22RE. For the longest time I thought that was a GREAT motor. Now I wish I had pulled my head out of my ass years earlier...

Anyway I was looking for more power and by this time I had changed my mind and realized that hp is hp and it doesn't really matter what you use to get it, if the goal is to go fast. In fact, the cheaper the hp the better, since race engines tend to wear fast or break, so I decided on the LS since it's cheap and easy. I still love the sound of the L series and don't hate them, but I feel like I have a better handle on what makes a motor good or bad than I did when I was a kid.

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On 4/19/2019 at 5:22 AM, JMortensen said:

I am... electronically challenged. I can cut and weld stuff together, but I can't wire a lamp. 

 

Pffft, just get a plug and play system, if I can do one so can you. Then it's ready to roll off to be tuned, it really can be that simple.

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Posted (edited)

Eh, I fixed the battery issue and it's running great now. If I find myself putting in a different motor I might switch, but lack of power is not an issue, currently. The only issue I have that I think FI would fix is that when tuned for acceleration there isn't enough fuel to rev the car with no load, so it doesn't heel/toe very well at all. I tuned the carb to rev quickly and that's why it was so incredibly rich on the dyno. I think this is a function of the flexplate and button clutch. It revs so fast that the carb can't keep up, or the carb keeps up and then when that same rev is under load there is way too much fuel being dumped in.
 

 

Edited by JMortensen

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