Budget NA6 supercharge build

Dweezle · Postby **Dweezle** » Tue May 26, 2015 9:50 am

If using the dyno afr and you have a Cat wont the readings be leaner??

By how much im not sure

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wade · Postby **wade** » Tue May 26, 2015 9:52 am

Yep just a track car.

Doing this has mainly been because I bought the supercharger on a whim when I first got the car, and it sat around for ages.

The motor has 360k on it and has the SNC issue, so the plan was to get a new engine and go the whole hog, but in the end I thought I'd just bolt it on and see what happens. Part of it has just been to see what you can achieve on a budget with minimal bolt on mods......pretty happy with 110kwatw to be honest......now if I can just make it safe ......

I actually have bought a 1.8 with cams , full exhaust diff etc to track the car. It will also get a megasquirt.

So I'll do a couple of track days and drive it till it explodes.

wade · Postby **wade** » Tue May 26, 2015 9:58 am

Dweezle wrote:If using the dyno afr and you have a Cat wont the readings be leaner??

By how much im not sure

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Hmm ok...... Thanks Mark, that's interesting and could explain why it didn't explode.

Can anyone quantify the effect that a cat generally has on AFR ?

Paulus · Postby **Paulus** » Tue May 26, 2015 10:41 am

An O2 sensor measures the O2 content in the exhaust gasses. In a catalytic converter a part of this O2 is used to convert for example CO into CO2. At full throttle however, the drop in O2 will hardly be noticable and therefore the reading of the wideband is quite useable

wade · Postby **wade** » Tue May 26, 2015 10:44 am

Thanks Paulus

Dweezle · Postby **Dweezle** » Tue May 26, 2015 10:45 am

Interesting.

I have seen plenty of 949 Racing dyno plots with AFR reading towards 14:1 amd Emilio stating that is due to it being a tailpipe reading with a Cat??

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A.Chen89 · Postby **A.Chen89** » Tue May 26, 2015 10:55 am

That's weird. Depends on the cat but I don't think that it has that much of an impact. Speaking to Mark at MRC he always uses the wideband in tail pipe to tune.

Innovate wideband in my car was reading bang on to the one in the tail pipe.

Probably be the same for other shops too.

Paulus · Postby **Paulus** » Tue May 26, 2015 10:58 am

it's a bit like discharging mine affected water or intermediate level radioactive waste into a fast flowing river. parts per million is small, so it's acceptable (this is actual practice for 'remediation' of waste.)

the flow of exhaust gasses is high enough for the delta in o2 to be negligible. There is a difference, but by all accounts i've ready people don't worry about it.

The dynos i've been to the afrs are the same post cat and pre and the tuner relies on post cat. I'd say you can rely on it with the error margin in readings reducing towards redline as gasses increase.

Really though, the mixture is just one part of tuning... actually listening for det with a microphone on the block and tweaking timing and fuel would be the best use of time.

11.5-11.8 suggests a tolerance 3%. if your dyno o2 sensor says 11.8 or 12 if you aren't hearing det don't worry.

Don't forget, even the best tuned cars still have AFRs fluctuate with each cylinder stroke. target approx 11.5-11.8 and run high octane fuel

trader · Postby **trader** » Wed May 27, 2015 12:49 pm

My Cobalt exhaust has a plug 150 mm behind the cat. From what has been said above it would seem that I can use that to hook up my wideband and get fairly accurate readings rather than weld another plug in before the cat. Would this be correct?
As soon as I can figure out how to post pic I will put up my rotrex dyno A/F graph using 305 supras.

93_Clubman · Postby **93_Clubman** » Wed May 27, 2015 3:33 pm

trader wrote:As soon as I can figure out how to post pic I will put up my rotrex dyno A/F graph using 305 supras.

Here you go Dave:

IMG_0157e.JPG

Postby **NitroDann** » Wed May 27, 2015 4:02 pm

That looks like bigger injectors on a stock ecu?

93_Clubman · Postby **93_Clubman** » Wed May 27, 2015 5:01 pm

Yep, stock NA6 ECU running light green 305cc Supra injectors. Also, max 5PSI, HP fuel pump (255LPH), AFPR, & standard timing I believe, but Dave can confirm.

Postby **NitroDann** » Wed May 27, 2015 5:46 pm

Its outside of what I would run.

An ecu is going to guarantee safety and net a lot more torque.

speed · Postby **speed** » Wed May 27, 2015 6:55 pm

trader wrote:My Cobalt exhaust has a plug 150 mm behind the cat. From what has been said above it would seem that I can use that to hook up my wideband and get fairly accurate readings rather than weld another plug in before the cat. Would this be correct?
As soon as I can figure out how to post pic I will put up my rotrex dyno A/F graph using 305 supras.

Interesting. how many kms would you get per tank? I'm guessing 260 to 300, am I close?
I'm really enjoying all the supercharged 5s lately.

trader · Postby **trader** » Wed May 27, 2015 8:59 pm

Thanks for posting Paul. All you have said is correct although I can't for the life of me understand why Kraftwerks market a kit that was so rich with much larger injectors than the Supra's. And yes speed you're spot on - 261 per tank - cruising steady makes no difference. Just got to pull the preverbial out and finish building the MS. In the meantime I might put in a set of purple injectors from the NB and see how they go.