O2 or ex. temp?

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Stickshifter 55
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O2 or ex. temp?

#1 Post by Stickshifter 55 » Sat Dec 01, 2007 5:36 pm

This winter I would like to add a data acquisition system to my drag car. Price is always a concern so if I am going to invest my money I want to get my moneys worth. Although engine tune up is second on my list of things to figure out, it is the first question I have. I have a Methanol injected engine. I went this route because I felt that I could not melt this thing even if I tried. And believe me I have tried LOL! This engine has a fabricated intake that I made myself. I have always wondered if it was balanced flow wise and I figure 8 EGT’s should give me some insight to this question. I could also have 8 O2 instead. So my question is:
If you had the choice of 8) O2 or 8) EGT, which would it be?

PS. I use and upper end lube in my fuel.

I have a Rons FI system with the typical barrel valve, pill, and electric high speed bypass. In theory knowing the fuel pressure should give me enough information to calculate volume in, out, and bypassed. I could put a flow meter on the output of the pump but that would still leave me not knowing the actual fuel flow to the engine unless I also measured the fuel going back to the tank from both the pill and the high speed bypass. (the bypass is usually not set to turn on unless I’m bored). The barrel valve is part of the distribution block so I can not measure the fuel going directly to the nozzles. I will probably just get the fuel pressure sender unless anyone has any different ideas.

When and if I ever get the car dialed in I would like to measure the pressure in the hood scoop as well as intake and possibly crank case. Most likely use the same sensor and place it in different places as my curiosity warrants. Any thoughts on the subject, let me know.

Thanks for any feedback.

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#2 Post by John_Heard » Sat Dec 01, 2007 7:11 pm

In my opinion I would want the 8 O2 sensors, I think that's going to tell you more. EGT can be high when it's fat becuase of fuel burning in the tube, or lean but the O2 I think will tell you far more about your tune up.

Fuel pressure is a great sensor to have, crankcase vacuum also. I wouldn't buy anything to measure hood scoop pressure, just make you a home made manometer for testing that. Cost is like $2.00 worth of vinyl tubing - they are simple to make. We did some testing with a home made one last summer and it worked pretty good using an in car video camera.

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#3 Post by vegaracer » Sun Dec 02, 2007 1:43 pm

Can you get an oxygen sensor that will read the air/fuel ratio of a motor on methanol?
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#4 Post by John_Heard » Sun Dec 02, 2007 3:47 pm

Yes - I'm not sure which ones are the most cost effective though. I've heard these are very good http://www.ecm-co.com/

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#5 Post by RPM » Mon Dec 31, 2007 11:22 am

Generally, the O2 sensors provide more specific mixture information than the EGTs. The drawback is that they cost twice as much. Adding 8 EGTs to a data logger is about $900, while, for 8 O2s, the price ranges from $1800 to $5000. If you are trying to determine if the manifold is equally distributing the mixture, a reasonable compromise is to run 8 EGTs and 2 O2s, with the O2s in the collectors. The EGTs will allow you to balance the cylinders, while the O2s will provide mixture information for the main tune up.

Depending on which upper end lube you are using, the O2s may not like it. Certain chemicals will quickly render the O2 sensor inoperative.

Monitoring the system with flowmeters (you would need two at $1000 each) would not provide the AFR you are looking for, as you have no accurate measurement of air other than estimating the volumetric efficiency of your combination and calculating theoretical air volume, then if you have accurate air density, less moisture, you could get to AFR.

You can use an absolute pressure sensor to do the scoop/manifold/crankcase pressure measurements.



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#6 Post by sunsation540 » Tue Jan 01, 2008 7:26 pm

i'm cheep and dyno time is not a bad investment dyno tune, egt to match max perf , not dyno numbers.. lean holes learned from dyno and power tune from there everything is fat off the dyno..but this thinking is for sticking with a combination start to finish not changing cam and heads carbs etc once in the car.. some like to beat there heads on the floor alot..
make a plan and stick to it !!

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Jeff Chandler
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#7 Post by Jeff Chandler » Tue Jan 01, 2008 9:03 pm

I have EGT's and I'm almost sure they will run you in circles trying to tune with them :? I still record the readings in my log book for them after every pass(just the avg)because useful or not you can never have enough data.

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Re: O2 or ex. temp?

#8 Post by gmracing355 » Thu Jul 31, 2008 4:35 am

Jeff, What kind of numbers should you be looking for with the egt gauge. Its a 355 chevy on motor,Im not using the nitrous yet.

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CoMax Racing
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Re: O2 or ex. temp?

#9 Post by CoMax Racing » Thu Jul 31, 2008 9:57 am

It looks to me like the O2 sensors are basically 1 or 2 channels only. (unless you want to run 4 of them). This will only tell you the tune of the whole engine or half the engine on a dual channel sensor. 8 egts may not be as easy to interpret but you can at least monitor all the cylinders. Distribution for a flying toilet should be pretty good. If you were running a blower the ability to read all the cylinders in important,( especially with a delta cut Hi-Helix blower).

My 2 Cents

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