Does deleting cats affect ignition timing or just air/fuel?

[EJSS]

My question is how does changing the exhaust flow affect the engine? I know that the upstream o2 sensor and ECM'closed loop will correct the air/fuel ratio but is timing impacted by a less restrictive exhaust flow?
I'm trying to visualize the 4 stroke process and it seems at first glance that if the exhaust stroke is able to be sped up as a result of less backpressure at the exhaust valve you might have a problem with the timing of ignition spark and fuel injector timing. Is this true and if so, is the change negligible?

Im a newby just trying to understand this stuff. Thanks for any and all help.

[Sparko]

Not really......Less restriction of the exhaust flow could have a slight effect on the mixture being drawn into the cylinders through scavenging but only occurs during the overlap portion of your cam rotation. I wouldn't suspect a significant spark change from a cat delete. Your mixture is really only effected because it's being fine tuned by the O2 feedback system. If you disable the feedback loop and monitor your baseline lambda pre-delete, the lambda post delete is likewise going to remain largely unchanged.

Back to that scavenging, the best way to optimize that would be with tuned headers. Less pipe restriction will increase the velocity of the exhaust gas which will aid in pulling waste out and mixture in during overlap. A high flow cat or cat delete can help enhance the effect from tuned headers.

[EJSS]

Ok thanks, that makes sense. But now I'm trying to make sense of how 15rwhp can be gained by deleting cats, from mechanical perspective, without sacrificing timing and/or air/fuel. Where are the extra horses coming from? I guess I have more googling to do.

[VR Baron]

Originally Posted by EJSS

Ok thanks, that makes sense. But now I'm trying to make sense of how 15rwhp can be gained by deleting cats, from mechanical perspective, without sacrificing timing and/or air/fuel. Where are the extra horses coming from? I guess I have more googling to do.

I think the restrictions mechanically is you now have two cats and not four. And the cell count of the honeycomb is 400 stock vs only 200 for hiflows.
I tested the power of hiflows with shortys. Across the board was 10 lb ft if tq. Average hp was 10. Peak ho from 5200-5700 was 13-16. 5809 to 6300 power steadily dropped to 5 at 6300

[Sparko]

Things to keep in mind too.....Does whoever is making the gain claim state if the car has ANY other mods to support or if it is bone stock. Simple things like a CAI or header will support that delete. Also, that gain is going to be a peak gain. It wont be evenly across the curve as the removal of a restriction will cause the air flow through the motor to gain efficiency only when the velocity of the air out is sufficient to aid in scavenging. Think kinda like spooling up a turbo, only instead of creating pressure in front of the intake valve it's creating a vacuum behind the intake valve.

*Quick thought* the power gained also isn't just power gained. It is going to be a mixture of gained power and power freed up from less resistance to the mechanical exhaust stroke.

[VR Baron]

Originally Posted by Sparko

Things to keep in mind too.....Does whoever is making the gain claim state if the car has ANY other mods to support or if it is bone stock. Simple things like a CAI or header will support that delete. Also, that gain is going to be a peak gain. It wont be evenly across the curve as the removal of a restriction will cause the air flow through the motor to gain efficiency only when the velocity of the air out is sufficient to aid in scavenging. Think kinda like spooling up a turbo, only instead of creating pressure in front of the intake valve it's creating a vacuum behind the intake valve.

*Quick thought* the power gained also isn't just power gained. It is going to be a mixture of gained power and power freed up from less resistance to the mechanical exhaust stroke.

True. And seat if the pants feel, as I removed them, seems I lost tq below 2800 rpm with a 3” catback I added. To little backpressure down low. But 3000 rpm on up you feel the loss of power the hiflows gave. Not a lot but they help.

[EJSS]

Originally Posted by VR Baron

I think the restrictions mechanically is you now have two cats and not four. And the cell count of the honeycomb is 400 stock vs only 200 for hiflows.
I tested the power of hiflows with shortys. Across the board was 10 lb ft if tq. Average hp was 10. Peak ho from 5200-5700 was 13-16. 5809 to 6300 power steadily dropped to 5 at 6300

I didnt realize that about the cell count, makes perfect sense though.

[EJSS]

Originally Posted by Sparko

Things to keep in mind too.....Does whoever is making the gain claim state if the car has ANY other mods to support or if it is bone stock. Simple things like a CAI or header will support that delete. Also, that gain is going to be a peak gain. It wont be evenly across the curve as the removal of a restriction will cause the air flow through the motor to gain efficiency only when the velocity of the air out is sufficient to aid in scavenging. Think kinda like spooling up a turbo, only instead of creating pressure in front of the intake valve it's creating a vacuum behind the intake valve.

*Quick thought* the power gained also isn't just power gained. It is going to be a mixture of gained power and power freed up from less resistance to the mechanical exhaust stroke.

I see. Most people claim that the high flow cats give them about 15rwhp alone, which I'm going to find out for myself within the next 24 hours.
I guess I was trying to figure out how that vacuum, or lack of pressure that you speak of actually contributes to more hp. And also how the change in exhaust flow through the exhaust valve doesnt screw the timing or a/f up. Based on what you said and some other reading I did i believe I was just thinking about it wrong. The vacuum creates less stress on the engine and power that would have been used to push the exhaust out is now freed. Is that a decent way of thinking about it, for a newby like me? Lol

[Juiced1]

The stock cats (and manifolds) are the most restrictive parts on the factory exhaust. They are restrictive. Get rid of them and there is power there. We dynoed a car before and after a set of Solo high flow cats and made 16rwhp. With long tubes and high flows we routinely make 36-40rwhp

[VR Baron]

Originally Posted by Juiced1

The stock cats (and manifolds) are the most restrictive parts on the factory exhaust. They are restrictive. Get rid of them and there is power there. We dynoed a car before and after a set of Solo high flow cats and made 16rwhp. With long tubes and high flows we routinely make 36-40rwhp

16 peak is what I got with jba. That’s below peak stock though. At peak stock I got 11, plus 9 more with shortys. Another 10-12 with tune. Not bad altogether

[EJSS]

Originally Posted by Juiced1

The stock cats (and manifolds) are the most restrictive parts on the factory exhaust. They are restrictive. Get rid of them and there is power there. We dynoed a car before and after a set of Solo high flow cats and made 16rwhp. With long tubes and high flows we routinely make 36-40rwhp

That's really good numbers. I just put high flows on my car yesterday but I can already tell this is the beginning of a long journey. The mod bug finally got me

[EJSS]

Originally Posted by VR Baron

16 peak is what I got with jba. That’s below peak stock though. At peak stock I got 11, plus 9 more with shortys. Another 10-12 with tune. Not bad altogether

Can you clarify what you mean by what you got for peak stock? You mean only high flows on an otherwise stock car?

[VR Baron]

Originally Posted by EJSS

Can you clarify what you mean by what you got for peak stock? You mean only high flows on an otherwise stock car?

Not stock. Peak stock, or with just a intake is 5850-5900 rpm. My car at the time had Jba shorty headers, ported tb, halltech cai And magnaflow axelback. 416 whp on a 90 degree day total. They seem to get a max peak of 15-18 from all the posts on camaro5. Two friends, almost exactly same setups got the same hp with the shortys, about 20 total, 10 more with tune.
The test showed 13 hp at 5000 rpm, 16 hp max at 5300, 11 hp at stock peak of 5850, 5 hp at 6200

[EJSS]

Originally Posted by VR Baron

Not stock. Peak stock, or with just a intake is 5850-5900 rpm. My car at the time had Jba shorty headers, ported tb, halltech cai And magnaflow axelback. 416 whp on a 90 degree day total. They seem to get a max peak of 15-18 from all the posts on camaro5. Two friends, almost exactly same setups got the same hp with the shortys, about 20 total, 10 more with tune.
The test showed 13 hp at 5000 rpm, 16 hp max at 5300, 11 hp at stock peak of 5850, 5 hp at 6200

Ok thanks. Man 416 rwhp for only shorties, tb, and cai? I didnt even know that was possible. I just did my high flows and I already cant wait to get my next mod, cai next. I cant believe how loud my car is now with high flows and muffler delete. My jaw dropped when I started it up.