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So hit up the dyno after doing cat deletes. Cat delete only 603/410 which I expected more. My buddies cat w cat back made more power and I expected deletes due to sound to make more but they didn’t. Swapped Soler ported throttle bodies on the dyno and made 619/427 tq. Did probably 4 baseline pulls and 3 after . Base pulls were all within a hp or two of each other. I think w an intake these will make more power as I think stock intake is a restriction. I’m also surprised the base numbers weren’t higher from cat delete. I had just driven 1.5 hrs so perhaps heat was playing into this some I’m not sure. There was a little cool down time after arriving tho. It took probably an hour to swap throttle bodies and we did it on the dyno. I have the graphs here. One has some interference from cam sensor so the rpm changes causing a tq spike so ignore the max torque number. You can see by the curve on the graph that torque picks up across the powerband.
im doing a jlt intake swap soon and now considering a cat back like corsa because of what my buddies car made w just cat back. I think stock must have some restriction and if anything you will save weight.
What were your readings before the mods? On the same dyno?
only baseline dyno was w the cat deletes. I already had them installed when I got there. My friend w a 24 z had almost identical numbers completely stock 603 whp but on a different day.
Right, I am looking forward to you adding the JLT to your current combo with the Solers. That may be the path I take, leaving the exhaust alone unless Corsa or some other shows a substantial change.
Many cars go into catalyst over temp protection and the only way to know is to look wide band data. Most cars do not have an exhaust gas temp sensor and instead, use calibrated modeling to determine when to richen A/F to save the cats. If, with cat deletes, you are going into this protection, you will lose some power.
Thanks for posting. Absolutely love the Z06 high pitch sound below 90mph. Probably the first time ever I want to take the long way home with stop and go traffic. Ha!
I’m a die hard veteran of cat delete and air management, but I’d have to see some good data on this set up. Any aftermarket keeping the high pitch and offering gains? Haven’t heard any in person yet.
I’d assume the cat delete would favor track focused gains with air management (intake) etc. Not sure the dyno will show much. Any restriction that’s removed should help…..certainly with a tune.
A couple of things that I don’t understand here. One, cat deletes I expected to dyno a lot more than they did. My friend at the same dyno the same day w a car with only paragon catback made more whp (about 10 more)Which brings the question either too little backpressure loses power on a stock z06 or the factory catback even though “open” is a restriction. I have seen high flow cats gain whp on these cars but they still provide some backpressure as not straight through. I am tempted to purchase a corsa or one of these Ti exhaust catback and install on the dyno to see if there is any gain or not.
also I have 1/8 mile times on cat deletes at about 700 feet above sea level and they seem about what stock does. Mph 104/105 which is in line with stock numbers I have seen. I think this backs the fact that the deletes themselves didn’t add much power only sound.
Originally Posted by Driv200
Thanks for posting. Absolutely love the Z06 high pitch sound below 90mph. Probably the first time ever I want to take the long way home with stop and go traffic. Ha!
I’m a die hard veteran of cat delete and air management, but I’d have to see some good data on this set up. Any aftermarket keeping the high pitch and offering gains? Haven’t heard any in person yet.
I’d assume the cat delete would favor track focused gains with air management (intake) etc. Not sure the dyno will show much. Any restriction that’s removed should help…..certainly with a tune.
2020 Corvette of the Year Finalist (performance mods)
C4 of Year Winner (performance mods) 2019
Originally Posted by superramvette2
...cat deletes I expected to dyno a lot more than they did...
Why did you expect more from cat deletes? Modern cats flow very well, I remember deleting the cats on my '12 supercharged GS and making maybe 5HP more. To me, the downsides (wife constantly complaining about the smell) was not worth the measly power gain.
A couple of things that I don’t understand here. One, cat deletes I expected to dyno a lot more than they did. My friend at the same dyno the same day w a car with only paragon catback made more whp (about 10 more)Which brings the question either too little backpressure loses power on a stock z06 or the factory catback even though “open” is a restriction. I have seen high flow cats gain whp on these cars but they still provide some backpressure as not straight through. I am tempted to purchase a corsa or one of these Ti exhaust catback and install on the dyno to see if there is any gain or not.
also I have 1/8 mile times on cat deletes at about 700 feet above sea level and they seem about what stock does. Mph 104/105 which is in line with stock numbers I have seen. I think this backs the fact that the deletes themselves didn’t add much power only sound.
Backpressure is not helpful and does not add power. Backpressure prevents some of the exhaust charge from exiting the cylinder, which then reduces filling with fresh air. Less fresh intake air equals less power.
The backpressure myth arose because many cars had narrow exhaust tubes, either in the manifold or the I-pipe or both. The narrow pipes helped cars maintain high exhaust gas velocity at low rpm, which is good for getting the spent gasses out of the cylinder. While the narrow diameter tubing helped low end torque and fuel economy, it is a restriction on the top end when the engine is expelling a lot of gas. Putting big headers and large diameter exhaust systems on the car unlocked power on the top end, but the extra system volume reduced exhaust gas velocity and scavenging on the bottom end. Hence the myth that backpressure was helpful. Systems are better designed now to increase the rpm range that the system supports, but it is difficult to make a system that is ideal at 2000 rpm and at 6000 rpm.
The Z06's wideband will start to correct for changes in the A/F ratio from removing the cats, but generally fixing the tune and not relying upon LTrims works better. Additionally, the spark timing may not be ideal after the change. If the car doesn't make more power from removing the cats it can be traced to a few possible suspects: dyno run variance, the cats flow well, or the tune is optimized for having the restriction and needs to be optimized for a restriction free system.
good points and thanks for the info, I’ll have to do more research on the back pressure theory. But basically the gist is that peak HP should always increase w more exhaust flow and here it didn’t or doesn’t seem to have. I agree there is probably timing / fueling trim adjustments needed to optimize the increased flow which we cannot do at this time. But I still think the factory catback is a restriction otherwise why are the aftermarket ones picking up dyno proven hp. (I have witnessed the gain myself on same dyno from my buddies car. Baseline pulls , swapped that day same air). Repeat baseline pulls still showed the gains within 1 hp on a separate occasion.
Originally Posted by Ragtop 99
Backpressure is not helpful and does not add power. Backpressure prevents some of the exhaust charge from exiting the cylinder, which then reduces filling with fresh air. Less fresh intake air equals less power.
The backpressure myth arose because many cars had narrow exhaust tubes, either in the manifold or the I-pipe or both. The narrow pipes helped cars maintain high exhaust gas velocity at low rpm, which is good for getting the spent gasses out of the cylinder. While the narrow diameter tubing helped low end torque and fuel economy, it is a restriction on the top end when the engine is expelling a lot of gas. Putting big headers and large diameter exhaust systems on the car unlocked power on the top end, but the extra system volume reduced exhaust gas velocity and scavenging on the bottom end. Hence the myth that backpressure was helpful. Systems are better designed now to increase the rpm range that the system supports, but it is difficult to make a system that is ideal at 2000 rpm and at 6000 rpm.
The Z06's wideband will start to correct for changes in the A/F ratio from removing the cats, but generally fixing the tune and not relying upon LTrims works better. Additionally, the spark timing may not be ideal after the change. If the car doesn't make more power from removing the cats it can be traced to a few possible suspects: dyno run variance, the cats flow well, or the tune is optimized for having the restriction and needs to be optimized for a restriction free system.
02-20-2024, 09:49 PM
I dynoed cat deletes and ported throttle bodies
