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Just in...my CTSC before and after dyno

Joined
22 November 2001
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760
1992, 6 PSI CTSC, B&B headers, Anytime exhaust.

I'm curious what everyone thinks about the air/fuel ratio. The before CTSC run was done with a probe up the tailpipe. The after was done in the bung on the Anytime exhaust, but after the cats.

Max fuel pressure was 86 PSI. It started dropping around 6,000 RPM and fell to almost 70 at 8,000 RPM.
 

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And here are all three runs from tonight. Notice the inconsistency in air/fuel at high RPM.
 

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Nice! Looking forward to my install at Applied Motorosports in a few weeks.
 
Two Things

Air-fuel ratio is alarmingly lean.

Accurately measuring this parameter should be upstream of the cats, especially if you are adding the bung.
 
I can't see the graph very well. Where should the AF ratio rest ideally? 12.9 or so? Not trying to start a debate, Just FMI.
 
I think what I might do is buy a set of cat replacement pipes and test from there. I'm not sure that there is much I can do to fix the problem short of an AEM type thing (which I want to avoid at all costs).

Also note where my air/fuel is with supercharger compared to before. Its clearly lower than before which makes me think the dyno simple measures high from where we are testing.
 
gobble said:
I think what I might do is buy a set of cat replacement pipes and test from there. I'm not sure that there is much I can do to fix the problem short of an AEM type thing (which I want to avoid at all costs).

Also note where my air/fuel is with supercharger compared to before. Its clearly lower than before which makes me think the dyno simple measures high from where we are testing.

You can install it in the mid-pipe before the cats too, as I did. I have cat replacement pipes on my car, but didn't want to run the o2 wires that far back.

I took some pics during my wideband install, the following url might help you out.

http://www.blazen.com/mike/flyingmonkey/wideband/

Cheers,

-mike
 
I have a track day tomorrow. Is this thing safe to run with these air/fuel numbers? Comptech hasn't returned my messages.
 
Looks like between 4k-5.5K you are consistently too lean (13+ to 1)for comfort for me, especially being at full boost by then. I would not be driving that hard on the track just yet. I beleive you should be able to richen it up, but you need to talk to Shad. You may also wish to try to get a hold of MarkB for advise.

HTH,
LarryB
 
Larry Bastanza said:
Looks like between 4k-5.5K you are consistently too lean (13+ to 1)for comfort for me, especially being at full boost by then. I would not be driving that hard on the track just yet. I beleive you should be able to richen it up, but you need to talk to Shad. You may also wish to try to get a hold of MarkB for advise.

HTH,
LarryB

Do you think measuring air/fuel behind the cats gives bad numbers?
 
Looks like that car would be lots of fun to drive !

Dyno of the SC looks really nice.
I used to wonder how much I would feel a difference id feel (daily driving) by having a SC on my 02, but after looking at the dyno and seeing a difference of nearly 30 lbs of torque and 15 hp right at 3000 rpms, thats awesome. That would most definitely be felt by everyday driving.

Im hoping to buy myself a blower for my Nsx someday in the next 1-2 years .
 
Modernceo said:
Looks like that car would be lots of fun to drive !

Dyno of the SC looks really nice.
I used to wonder how much I would feel a difference id feel (daily driving) by having a SC on my 02, but after looking at the dyno and seeing a difference of nearly 30 lbs of torque and 15 hp right at 3000 rpms, thats awesome. That would most definitely be felt by everyday driving.

Im hoping to buy myself a blower for my Nsx someday in the next 1-2 years .

It really does feel like a whole new car. I'm very pleased with the increase in performance. I just hope its safe.
 
Gobble,

Was the wideband 02 before the cat in the header or after? If your car is a 1992 and you used the header bung then it was before the cat and I think it is too lean, as all of us have mentioned:).

If you measured after the cat it is inaccurate as Andy mentioned.

HTH,
LarryB
 
The wideband O2 was in the pipe between the cat and the exhaust can. I don't have a bung anywhere before the cats. I think what I need to do is buy cat replacement pipes and try again.
 
Just as a point of reference:

-My 91 with 6lb CTSC gave almost identical gains over pre-install (57rwhp vs 59rwhp).
-Also tested on Dynojet with WinPEP, using tailpipe sniffer for A/F
-Showed similar (but not as bad as yours) very lean condition
-Showed similar variance in A/F between runs

I was all freaked out, and had it dyno'd at a different place where they put a pre-cat bung. Unfortunately the place did not test with a wideband, but the sensor did show much richer A/F as compared to the tailpipe sniffer. Still not as rich as I would have liked, but I think I need to verify it properly with a wideband to be sure. No problems with daily driving, but I'm not going to take it on the track until I'm 100% certain I'm not running lean.
 
Looks like a clogged fuel filter to me, replace it and test again (when a lot of fuel flow is needed, pressure drops due to delivery problems to the injector rail, THIS WILL KILL YOUR ENGINE IN SECONDS !!!!!!) :eek:
 
If I recall a conversation with Shad correctly, some dropoff in fuel pressure at the higher RPM's is normal. Maybe Larry B or Mark B can chime in with their experience with this. I was also concerned about the fuel filter and had mine replaced, but I still see the same thing.
 
My idle fuel pressure is 45 psi. I've read some posts that say to lower this because the ECU will learn a lower baseline and compensate at higher RPM's. I've read other posts that say to raise it because it will provide more fuel across the board. Does anyone know what would be the correct adjustment to lessen the lean condition at higher RPM's?
 
Arshad said:
If I recall a conversation with Shad correctly, some dropoff in fuel pressure at the higher RPM's is normal....

A drop off in boost is normal, and because the fuel pressure rises with boost, a drop in boost = a drop in fuel pressure. So, if you do in fact see boost peak at mid RPM then taper off, a drop in fuel pressure at high RPM is "normal".

As for cats causing bad O2 sensor readings, they certainly can at idle and where the mixture is fairly lean. However, my understanding is that they are inherently inefficient at richer mixtures such as 12:1 and therefore have little impact. Under full load and high RPM they are also trying to "process" a huge volume of exhaust much of which just blows by unaffected, or so I'm told. I've been meaning to confirm this but never get around to doing the tests.

Another less recognized impact from cats and mufflers is backpressure which causes widebands to read leaner than actual., and very few sensor controllers correct for it. So placing a bung ahead if the cats isn't perfect either.
 
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