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Ssaga

Thoughts on my dyno result, 280z, triple webers

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Just got back from a dyno session yesterday.

Would be great if you guys could give me some feedback on the figures

 

 

It´s a 280z-75.

-Engine Spec

-2.8l, 0,5mm oversize flattop pistons with outtake for the valves

-Datsun spirit cam, 290 duration camshaft .490 lift

-Mild Head work, match ported towards intake and Header.

-New stock size valves and complete valve work

-Z-story Header and full 2,5" exhaust system.

-Lightweight flywheel

-Triple Weber 45

-MSD 6AL ignition with zx distributor.

- Compression 10,4:1

 

Ignition is right now at 32 total advance.

Setting towards 37 I lost about 10hp, however no detonations, so then moved it back.

post-4361-0-11371700-1498723517_thumb.jpg

post-4361-0-52136600-1498723545_thumb.jpg

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I think that's very respectable for the peak numbers. It would be interesting to see the scale for the lambda curve as well. The dip in power and torque at 3400rpm is quite interesting. There is also a drop in lambda over this section. Too rich?

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Might add that this is figures on the crank.

Think the scale is the same, divided by 100 then you get 0,93.

 

You are correct there is a quit bad drop at 3500, to rich.

Worked on that a bit without any good result.

 

Carb is jetted:

38 choke

F15 emulsion

150/180 main/air

50F8 low speed

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ZX distributors have 16 or 17 degrees mechanical advance, depending on whether you have one off of a manual or automatic trans car. 6AL doesn't adjust timing at all. The vacuum advance is almost always broken.

Re: numbers. I'd go bigger on the cam.

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Posted (edited)

Here's an 82.  Looks like 19 degrees (edit - 17 like JM says below.  I can't add) at 2800 RPM.  But if it's a reman, who knows.

 

Isn't that dip just an artifact from hitting the throttle to start the run?  I drive my car around at 1500 to 3000 all day.  Always bugs me that the dyno curves are always focused on the top end.  Big numbers!

post-8864-0-41406900-1498756479_thumb.png

Edited by NewZed

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Posted (edited)

Thx för all the comment

 

Do you think a bigger can would improve?

I was leaning towards more headwork??

 

 

The dip at 3500 is only avoided by giving gently throttle until moving past this dip.

 

My distributor has an 8,8 mechanical advance, so 17 then, I'm a bit confused regarding this.

Firstly, the initial advance is set at 11 but is maxing out at 32, this indicates a mechanical advance at 21, but I got 17.

 

Secondly, when putting more and more advance I never got any detonations, simply lost top effect. I always thought you put more and more advance until you detects detonation then you retard it a bit.

 

Have no AFR fig

Edited by Ssaga

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M

Did you monitor the AFR?

Off topic, did you ship the engine to Sweden?

Dunno regarding the AFR, maybe logged in the dyno logs.

 

Built the engine myself in Sweden, however sourced the parts in US.

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Posted (edited)

Thx för all the comment

 

Do you think a bigger can would improve?

I was leaning towards more headwork??

 

 

The dip at 3500 is only avoided by giving gently throttle until moving past this dip.

 

My distributor has an 8,8 mechanical advance, so 17 then, I'm a bit confused regarding this.

Firstly, the initial advance is set at 11 but is maxing out at 32, this indicates a mechanical advance at 21, but I got 17.

 

Secondly, when putting more and more advance I never got any detonations, simply lost top effect. I always thought you put more and more advance until you detects detonation then you retard it a bit.

 

Have no AFR fig

 

No you'll usually lose HP just before detonation. Very sophisticated OEM dual knock sensors can run just at the onset of " light pinging", That's how they maximize fuel mileage. But that's at light load. It's dangerous to try try that strategy at Maximum load. Plus the modern knock sensors will " hear " the pinging well before you can hear it.

 

Turbo motors can swing so fast into detonation that you really need WB Knock sensors on a Dyno and most good Dyno operators will use Det-Cans to monitor for the slightest detonation during a run.

 

Your AFR were logged. It's just in Lambda values. Bottom line. 

Edited by Chickenman

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No you'll usually lose HP just before detonation. Very sophisticated OEM dual knock sensors can run just at the onset of " light pinging", That's how they maximize fuel mileage. But that's at light load. It's dangerous to try try that strategy at Maximum load. Plus the modern knock sensors will " hear " the pinging well before you can hear it.

 

Turbo motors can swing so fast into detonation that you really need WB Knock sensors on a Dyno and most good Dyno operators will use Det-Cans to monitor for the slightest detonation during a run.

 

AFR is one of the single most important Parameters of any Dyno run. Without that info, Dyno chart reading is just guessing. See if Dyno operator has that info.  

Do I need AFR when I got lambda?

I thought AFR and Lambda where two different ways to basically measure the same thing?

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Posted (edited)

Engine goes really rich between 3,100 to 4,000. Lambda values by curve appear to be down in the 0.70 range. Far too rich. That's in the mid 10's for AFR. 

 

Then Curve goes lean towards mid and top end. Lambda 0.93 = 13.67. You want closer to 12.8 to 13.1. Some head designs want even richer. You didn't say what Cyl head you are running. That matters a lot. 

 

Se if you can get the detailed Text print out from the Dyno operator. You'r leaving HP on the Table. Fuel curve can be refined further. 

 

If this is for a street engine, I'd try 36mm chokes. 38MM are a bit large for 45 Webers. More a Race size only. May clean up the fuel curve a bit as well. And you'll improve bottom end Torque and driveability. 

 

Lambda to AFR conversion chart. Gasoline standard at 14.7 Stoich:

 

http://www.tatech.fi/cms/uploads/file/Lambda_vs_AFR.pdf

Edited by Chickenman

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Engine goes really rich between 3,100 to 4,000. Lambda values by curve appear to be down in the 0.70 range. Far too rich. That's in the mid 10's for AFR. 

 

Then Curve goes lean towards mid and top end. Lambda 0.93 = 13.67. You want closer to 12.8 to 13.1. Some head designs want even richer. You didn't say what Cyl head you are running. That matters a lot. 

 

Se if you can get the detailed Text print out from the Dyno operator. You'r leaving HP on the Table. Fuel curve can be refined further. 

 

If this is for a street engine, I'd try 36mm chokes. 38MM are a bit large for 45 Webers. More a Race size only. May clean up the fuel curve a bit as well. And you'll improve bottom end Torque and driveability. 

 

Lambda to AFR conversion chart. Gasoline standard at 14.7 Stoich:

 

http://www.tatech.fi/cms/uploads/file/Lambda_vs_AFR.pdf

Really nice input:)

When you wrote choke 38, i started to doubt. Just ran out to the garage, it´s 36:).

 

Using N42 head.

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Contacted the dyno store today, they where out all weekend supporting rallycross competition,so hopefully on Monday I will have the figures.

 

Regarding the 3500 dip, should I try to change the w low speed jet to 45F8 instead. Regarding the lean on top maybe go down one size in air corrector?

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Do you think a bigger can would improve?

I was leaning towards more headwork??

More headwork is not a bad idea either, but I think ultimately that cam will hold you back from the highest top end numbers you can get out of that motor. I had a very similar build: L28 flat tops with E31 that was shaved, around 11:1 compression, 490/.280 cam, 44s with 37 chokes, header and 2.5", MSD 6AL and ZX distributor, light flywheel, etc. Very similar sounding build. I did a lot of work done in the chamber to get rid of any hotspots, ground off extra spark plug hole threads, had all sharp edges removed, unshrouded valves, cc'd chambers, etc. As much work as I could do to it myself in the garage, basically. The head already had hardened seats installed and had a really nicely done blending of the bowls done by a local machinist. It made pretty good power but I always felt like for a really hot street motor I wanted something more in the .500/300 range. BRAAP was selling a cam that was something like .540/300 or something. That was the one that I had pretty much settled on before I decided on swapping in a V8 instead. It was still streetable but suppsedly made enough of a difference up top that BRAAP was endorsing it, and I trust his judgment.

 

 

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This dyno curve is quite typical. Transition idle jet to main jet. You can change this a lot with keith franks hypos(idle) and obert e-tubes(main) or the new bb tubes(main). Pulls like a injected engine afterwords.

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More headwork is not a bad idea either, but I think ultimately that cam will hold you back from the highest top end numbers you can get out of that motor. I had a very similar build: L28 flat tops with E31 that was shaved, around 11:1 compression, 490/.280 cam, 44s with 37 chokes, header and 2.5", MSD 6AL and ZX distributor, light flywheel, etc. Very similar sounding build. I did a lot of work done in the chamber to get rid of any hotspots, ground off extra spark plug hole threads, had all sharp edges removed, unshrouded valves, cc'd chambers, etc. As much work as I could do to it myself in the garage, basically. The head already had hardened seats installed and had a really nicely done blending of the bowls done by a local machinist. It made pretty good power but I always felt like for a really hot street motor I wanted something more in the .500/300 range. BRAAP was selling a cam that was something like .540/300 or something. That was the one that I had pretty much settled on before I decided on swapping in a V8 instead. It was still streetable but suppsedly made enough of a difference up top that BRAAP was endorsing it, and I trust his judgment.

 

 

 

So would a bigger cam get more power at those RPM? 

 

He now gets ~220 @6500, with a bigger cam would he get more at that RPM? Or less at 6500 but more at say 7500 RPM?

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Contacted the dyno store today, they where out all weekend supporting rallycross competition,so hopefully on Monday I will have the figures.

 

Regarding the 3500 dip, should I try to change the w low speed jet to 45F8 instead. Regarding the lean on top maybe go down one size in air corrector?

 

Richness in AFR is above the point where idle jet ( 50F8 ) should have any effect. I would try a 145 main. to lean out the bottom, and then a 175 or 170 Main to richen the Top end a bit. Getting into twiddly stuff now.  

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The AFR dip is due to the emulsion tube. You can work around it by fiddling with other jets but it will remain. Keith's e-tubes are the better solution but if you're in a hurry, try an F7 or F16. Set floats using Keith's method to 25mm below the jet stack table.

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