Straight pipe

[MRC01]

I'm very familiar with the Ford EEC programming (EEC-IV in particular) which is why I made the remarks I did.

Sounds like you know more about this than I do, so perhaps you can explain:
Car with '98 Cobra V8 is dynoed, makes 285 RWHP, AF probe measures 15:1 in cruise, 10:1 at WOT.
Car has shorty headers installed, dynoed, makes 294 RWHP, AF probe measures 15:1 in cruise, 12:1 at WOT.
All dyno numbers corrected for temp/pressure/humidity.
The numbers don't lie. How do you explain?

The change in AF can explain the increase in RWHP. But how/why did it get leaner?

PS: one possibility is the headers provided more efficient combustion, which increases power without increasing airflow through the intake, and is detected by the AF probe as slightly leaner (more complete combustion = less unburnt fuel in the exhaust = leaner). But that is speculation on my part, just a possible explanation that fits the observations.

 

[OVERKILL]

Sounds like you know more about this than I do, so perhaps you can explain:
Car with '98 Cobra V8 is dynoed, makes 285 RWHP, AF probe measures 15:1 in cruise, 10:1 at WOT.
Car has shorty headers installed, dynoed, makes 294 RWHP, AF probe measures 15:1 in cruise, 12:1 at WOT.
All dyno numbers corrected for temp/pressure/humidity.
The numbers don't lie. How do you explain?

The change in AF can explain the increase in RWHP. But how/why did it get leaner?

PS: one possibility is the headers provided more efficient combustion, which increases power without increasing airflow through the intake, and is detected by the AF probe as slightly leaner (more complete combustion = less unburnt fuel in the exhaust = leaner). But that is speculation on my part, just a possible explanation that fits the observations.

Does the car have an aftermarket CAI?

The headers can explain the power bump (better exhaust flow) without the A/F having any role. I'd be more inclined to question the accuracy of the equipment if nothing else was changed.

10HP sounds about right for the headers. I was 270RWHP at 10:1 with the 30's, car would have been 290-300 with 12:1 A/F and that's with no other changes, FWIW, so think how that might apply to your situation with respect to the accuracy of the A/F

 

[MRC01]

Yes, Panoz used the Ford crate engine with their own intake & exhaust to fit the different dimensions of the Roadster. Seems their intake & exhaust flowed a little better, as dyno operator said it was about +10 RWHP compared to Mustangs having that same engine (285 vs 275).

It looked like this:

 

[OVERKILL]

That (CAI) can definitely impact metering, but they are using an airbox, so I'd be more suspect of the dyno A/F meter personally. Was it just a tailpipe probe?

 

[MRC01]

Yep, tailpipe AF probe at the dyno. But the probe did measure the same AF in cruise on both sessions. The difference was at WOT.

 

[atikovi]

Modular Mustang V8's have some of the best sounding engines when a catback is installed. A V6 with the muffler removed is going to sound like you have a hole in your muffler. Why not sell the librarian's car and get a GT?

 

[OVERKILL]

Yep, tailpipe AF probe at the dyno. But the probe did measure the same AF in cruise on both sessions. The difference was at WOT.

Yup, it would. They are sensitive to placement in the exhaust. When flow is low they tend to be more accurate, then, when the flow increases that accuracy decreases. I own an Innovate wideband setup, which requires a bung and is an in-stream sensor used for tuning. I've used it a few times over the years on several cars. It is very accurate, far moreso than a tailpipe probe.

Some higher end tuning shops will actually weld-in a bung and use something similar to what I have, but the tailpipe probe is the most common because it's easy and I believe is what comes with DynoJet's.

 

[OVERKILL]

Yup, it would. They are sensitive to placement in the exhaust. When flow is low they tend to be more accurate, then, when the flow increases that accuracy decreases. I own an Innovate wideband setup, which requires a bung and is an in-stream sensor used for tuning. I've used it a few times over the years on several cars. It is very accurate, far moreso than a tailpipe probe.

Some higher end tuning shops will actually weld-in a bung and use something similar to what I have, but the tailpipe probe is the most common because it's easy and I believe is what comes with DynoJet's.

https://www.hotrod.com/articles/nova-dyno/

You can use a tailpipe probe (shown) similar to that used by smog-testing stations, but sometimes the air/fuel readings aren't as accurate because the probe is affected by air from outside getting pulled up the tailpipe and there may be a lag in the readings.

Ideally, have a standard O2 sensor bung welded into the header collector about 4-6 inches from where the primary pipes enter the collector. This should take about 15 minutes at any muffler shop and costs about 20 bucks. After the session you can plug the hole with a pipe plug.

 

[atikovi]

My Fiat 500 is probably the best sounding car I have ever owned. It has nothing but a turbo and a dual exit straight pipe, and it sounds like a rip-snorting beast.

Always wondered what government regulators Fiat had to bribe to allow a car without a muffler to pass whatever exhaust standards they passed.

 

[Cujet]

A single exhaust 6 cylinder can sound wonderful with a glass pack exhaust. Crisp, sharp and not at all like a V8.

 

[spasm3]

A single exhaust 6 cylinder can sound wonderful with a glass pack exhaust. Crisp, sharp and not at all like a V8.

I used to run them on my cutlass cieras, the sound was great. Even on a V-8 with the cats still there, they are not that loud. I like how they sound, as long as they are not too short, they are not that raspy.

 

[OVERKILL]

A single exhaust 6 cylinder can sound wonderful with a glass pack exhaust. Crisp, sharp and not at all like a V8.

Yes, on say a BMW. I've heard some inline 6's that sounded decent with a slightly louder exhaust. The 3.8L is not one of those engines in my experience.

 

[OVERKILL]

I used to run them on my cutlass cieras, the sound was great. Even on a V-8 with the cats still there, they are not that loud. I like how they sound, as long as they are not too short, they are not that raspy.

Did it sound like it was under water? I remember hearing the Grand Ams and other GM cars with those V6's that kids would put a cherry bomb on and they always sounded like they were under water, it was bizarre!

 

[MRC01]

Always wondered what government regulators Fiat had to bribe to allow a car without a muffler to pass whatever exhaust standards they passed.

It's common for turbos to quiet the exhaust. They absorb exhaust energy & sound. I had a '95 RX-7 twin turbo and completely removed the muffler. Straight pipe from the catalytic converter on back. Easily passed legal noise regs; it was still quieter than some V-8 engines with a muffler.

 

[spasm3]

Did it sound like it was under water? I remember hearing the Grand Ams and other GM cars with those V6's that kids would put a cherry bomb on and they always sounded like they were under water, it was bizarre!

I dont recall that sound, but I never used the short ones, iirc i ran the magnaflow brand.
To me it sounded like and old straight 6 with a split manifold.

 

[spasm3]

Did it sound like it was under water? I remember hearing the Grand Ams and other GM cars with those V6's that kids would put a cherry bomb on and they always sounded like they were under water, it was bizarre!

Mine sounded something similar to this. ( no mine, i dont have a ciera anymore)

 

[atikovi]

It's common for turbos to quiet the exhaust. They absorb exhaust energy & sound. I had a '95 RX-7 twin turbo and completely removed the muffler. Straight pipe from the catalytic converter on back. Easily passed legal noise regs; it was still quieter than some V-8 engines with a muffler.

Rotary engines are quieter to begin with so the comparison isn't totally accurate. And yes, the turbo does act like a mini muffler, but sound from the Abarth is still rip snorting spine tingling loud.

 

[DriveHard]

It's common for turbos to quiet the exhaust. They absorb exhaust energy & sound. I had a '95 RX-7 twin turbo and completely removed the muffler. Straight pipe from the catalytic converter on back. Easily passed legal noise regs; it was still quieter than some V-8 engines with a muffler.

The Fiat 500 Abarth was not the only car to come from the factory with no muffler...if memory serves, the old Dodge Neon SRT-4 came from the factory without a muffler as well.

Yes, exactly right - the turbo does a great job of quieting the engine down, especially under cruise conditions.

 

[DriveHard]

Did it sound like it was under water? I remember hearing the Grand Ams and other GM cars with those V6's that kids would put a cherry bomb on and they always sounded like they were under water, it was bizarre!

The old 3.1's and 3.4's always had a VERY distinct sound. They sounded much better than their output might suggest ;-)

I had a Cavalier Z24 in my first couple years at university. I swapped out the stock 2.8 for a 3.4 - that was a ton of fun. Stock 5-speed, it sounded good, and for me at the time was a hoot to drive. It was pretty much the most performance I could afford at the time. This is not my car, but it looked identical.

 

[OVERKILL]

The old 3.1's and 3.4's always had a VERY distinct sound. They sounded much better than their output might suggest ;-)

I had a Cavalier Z24 in my first couple years at university. I swapped out the stock 3.1 for a 3.4 - that was a ton of fun. Stock 5-speed, it sounded good, and for me at the time was a hoot to drive. It was pretty much the most performance I could afford at the time. This is not my car, but it looked identical.

View attachment 45771

I remember those! My buddy had a Sunbird GT that was a bit of a weapon, but similar situation. That's probably the engine I was thinking of, it was a bizarre under water sound, always stood out.