Ok, first question. I had the car dyno'd with a tailpipe sniffer type wideband. I know the readings are not as accurate as the dp o2 fitting, but would they show a leaner or richer condition?
Now, I had the car dyno'd today. I ran into a very lean condition due to the fact I am running a stock intank. I upped the fuel pressure but not enough. I had fuel pressure at 50 with the motor idling and vacuum attached.
Basically the sniffer was picking up a straight and steady 14:1 a/f ratio. Now, I know that most motors will make their most power at a leaner condition. I realize that you want a 12:1 or so a/f for turbo cars. But will I see better hp and tq numbers when I get the a/f there, or will I see a drop on hp and tq? This is after the much needed fuel pump will be installed.

About the sniffer. I forgot to ask which one he was using (motec, etc, etc.) And I forgot to ask how he was reading it--in lambda values or whatever. I could always call the place and get the low down if its really important.

Thanks, and if you have any tuning tips then please share. I have a chance to use an FJO wideband and borrow a hondata 4b to tune my 3b.

If it helps, I had timing dead on at stock -- white timing mark at about 500 rpm's idling.

 

ttt

 

Raising the pressure wont help if the pump is falling off under high demand.
The tailpipe sniffer should be just as accurate however i dont know what a cat
will do to the readings.

I dont know how many times i will have to repeat this: NEVER take pressure readings
with the vacuum line ON. ALWAYS vacuum line OFF.

typically dynos use the same bosch(i think) sensor as a motec, just uses an interface
to connect to dynojet software.

Regardiing hp/af ratio, if the motor makes more power when leaner then it makes
more power, however most try to keep the a/f around 12.5:1 for safety reasons.

 

Ok, I have a test pipe-so no reason why the reading should differ from the sensor being in the dp.
I know, I am striving to get the a/f around the 12:1 mark. I think I was sent a base map that wasn't designed for my setup.
As far as the fuel pressure readings. What do i set them at with the vacuum off? Everyone says different things--hondata says to use the fuel pump prime when you turn the key on but without the car started. Others say with the motor running w/vacuum others say w/o.
What to do. Hopefully I can get that wideband after I get my new fuel pump which will be this week sometime.
I also spoke with Robert at hondata today. He is gonna email me another ROM and I will put that in and see if theres a difference.

 

always best to measure pressure with hose off and motor running.
priming is okay, but without full power going to the pump the readings
may be off. On my car the readings are a full 10psi off, without alternator power.

I usually set all of my cars to 50psi.

 

the tail pipe sniffer is fine when dealing with motors generating under 350whp in my experience. The difference will not be shown with the air/fuel ratio, but rather with response time. Typically, it is 300-500rpm's behind what the motor is actually producing, depending on the filters condition, and the strength of the vaccum used. This can be compensated for somewhat by tuning in a higher gear than normal once the tuning is somewhat close. I usually use 4th to fine tune. Also remember to compensate slightly by reading when the air/fuel ratio actually comes into to sample. Example - you start the run, and go full throttle, but the air/fuel lags lean for a half second. When you display the chart, you'll see this lag time, and as I said, is usually close to 300-500rpm's behind the motor's acceleration.

You're going to find that when turbocharged, your power levels are going to increase substantially once you get the correct air/fuel readings. 12:1 is a nice safe point, but close to the edge. I prefer 11.7-11.8:1. 14:1 is too lean, and I'd be very careful with driving it in that condition.

Once your air/fuel is correct, begin with the ignition timing values, keeping an eye on your EGT gauge.

Hope that helps

 

steve, i think what 93lsivic is saying is that he is disappointed with the numbers and would like to know if changing the a/f ratio will dramatically change the numbers. He is asking because commonly all things being equal usually cars with leaner mixtures run higher #'s. Dan, please correct me if i'm wrong

 

Exactly adam. I like what I am hearing though, about the hp increase with the safer a/f.
Looking here at the maps it seems like in the first 500-700 rpms after the winpep software starting monitoring the numbers that the a/f was richer--around a 12:1.

 

how does ignition advance affect EGT? advanced timing lowers EGT?

 

right. advancing lowers egt, retarding raises it

 

so theoretically speaking, too much timing advanced on a turbocharged engine would run too lean/rich and end up melting a piston?

 

I'm not doubting,but I always thought that it was the other way around. Could you please explain in a little more depth. I read of people retarding timing when they are running lean to lower thier temps and to prevent detonation. Whats the relation between running lean or rich; timing advance/retard; egts; and detonation?Thanks

 

Think about this. Ignition timing is when the spark is lit, in relation to the piston and crank location. The more you advance the timing, the sooner the spark lights the a/f mixture. The earlier it's lit, more and more of the a/f mixture is burnt.

This has a direct correlation to EGT. Not all of the a/f mixture is burnt, as dictated by the use of oxygen sensors. Some of it is pushed out into the exhaust. But it doesn't just all exit out the tail pipe. The a/f will continue burning, inside your manifold/header, turbo, downpipe and on back until conditions are no longer favorable. So, using that knowledge, it makes perfect sense that if air/fuel mixture is correct, high EGT's are a sign that ignition timing is too retarded, as too much a/f is burning inside the manifold. Cool EGT's are a sign that ignition maybe be too advanced, as there are only small amounts of a/f are burning in the manifold, and this means that most of it is burning inside of the combustion chamber. While this would seem ideal, it's not. This causes high cylinder pressures, and thus, detonation, and we all know what that can do.

You would want to retard ignition timing in a lean condition for that very reason. It's actually very simple to understand once explained I think

 

nicely explained

 

Would that be too high with a 12:1 FMU? If im boosting at 6psi?

 

I'm pretty sure SgT was referring to cars with Hondata. FMU's leave fp at or near stock for base fuel pressure.


[Modified by VaporTrail, 4:22 PM 5/7/2002]

 

good reading

 

Great explantion, thanks!