Cats or no Cats

[Hector247]

So I was told today by a UTI instructor that it is better to go with LT with the high flow cats for better track times. He said you will get better dyno numbers going catless but it will be at higher rpms which will not result in better track times. Anyone have an input on this? :shrug:

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[Screwdgie]

Well at the drag strip you spend the most of your time higher in the power band so... I hate to say his reasoning is a bit off

 

[powerhogger]

UTI? :lol::lol::lol::lol:

 

[ero 5.0]

UTI? :lol::lol::lol::lol:

LOL! I thought the same thing....

 

[cp5899]

An engine is like an air pump. Any time you restrict air going in or out it takes away from peak performance. This is an example and everything has extreme. Meaning 5" dual exhaust isn't going to help you since you would have lo back pressure.

 

[Hector247]

Didn't seem right to me either. That's why I asked.

 

[nicktechla]

An engine is like an air pump. Any time you restrict air going in or out it takes away from peak performance. This is an example and everything has extreme. Meaning 5" dual exhaust isn't going to help you since you would have lo back pressure.

if you don't want to restrict, why would you want back pressure?

 

[Taneras]

Well at the drag strip you spend the most of your time higher in the power band so... I hate to say his reasoning is a bit off

This x 100, which is why I want to get an aftermarket manifold. I don't mind a little power lost down low, when I floor it I'm spending all my time at higher rpm's ;)

 

[Semp1]

I assume what ever a “UTI” instructor is, is factoring in that when catless you lose bottom end torque and gain top end hp which on a track, torque, I assume he assumes that, that will affect your track times. And he may be right it might affect it by a tenth. Who knows. Are you a pro driver where a tenth is going to matter because you’re driving at top tier skill level? Do you only race your car on a track? If not who cares do whatever you want. I’ll tell you this i have high flow ctas with headers and a catback and it’s loud and catless would be even louder. So maybe that’s appealing to you. Lol. Also if you’re boosted catless becomes more of a thing to consider. NA You should keep high flow cats imho. Low end torque loss is something you feel seat of your pants more than 2-5 more hp top end. Add 4.09 gears and a driveshaft and you’ll feel way more than catless can ever make you feel And will also go up about 2hp on a dyno. Means nothing In the end.

 

[K4fxd]

A good set of long tubes will give you more power under the curve. In a road race this will help get off the corners.

You will not lose torque by removing the cats. At worst it will stay the same. No engine likes back pressure. You can get too big and lose velocity which will kill some torque down low.

However with the cam event timing in the coyote, it likes larger exhaust than most engines. Look at some of the header shoot outs and exhaust tubing dyno's. The 3 inch on NA works well, same with 2 inch primary's on a NA

I believe this to be due to most of the overlap on the intake stroke instead of across TDC.

 

[Semp1]

A good set of long tubes will give you more power under the curve. In a road race this will help get off the corners.

You will not lose torque by removing the cats. At worst it will stay the same. No engine likes back pressure. You can get too big and lose velocity which will kill some torque down low.

However with the cam event timing in the coyote, it likes larger exhaust than most engines. Look at some of the header shoot outs and exhaust tubing dyno's. The 3 inch on NA works well, same with 2 inch primary's on a NA

I believe this to be due to most of the overlap on the intake stroke instead of across TDC.

I mean honestly, I think we need to agree to disagree on this topic but at least from what I’ve seen and many others I 100% will say you are losing at least a little low end torque going catless with longtubes. I have very high quality catted ARH longtubes and will probably go catless once I install the supercharger. But NA it’s absolutely unnecessary. Guys chasing 2-5hp gains make no sense gaining 2-5hp catless with longtubes when you’re losing torque and you’re working with small gains for each mod to begin with. Torque to me is possibly more important than hp. Only way to know is to dyno the car before and after catted and catless header install. Not losing a lot but you’re losing. Which btw I’ve seen many times and low end torque is lost every time. And when it comes to 3in vs 2in. What exactly are you saying. The best longtube header size is 1-7/8x3in for almost any application on the gen3 and gen2 coyote motor. You can do 2x3 but at that point you should be pushing very high numbers to even bother with that though, again unnecessary for most people, and at that size you 100000% lose low end torque. Call American Racing they’ll tell you the same. Now if you’re saying just install a catless header and you won’t lose low Tq end vs stock. Of course you won’t. But if you install a catted longtube vs a catless longtube you will gain low end and hp and not just “possibly” stay the same with tq and get a hp gain. That’s my point. Every mod is give and take. Nothing just goes up without something coming a little down. It’s a balancing act. Especially when you’re NA.

 

[K4fxd]

Please show me a dyno run back to back that shows a torque loss when removing cats.

You have a problem understand things I wrote. 3 inch exhaust is not a 3 inch primary.

I think it was engine masters did a shootout with different primary sizes on a coyote, 2 inch was the best for avg power.

A 3 inch exhaust was best for avg power also.

Never will you gain torque by putting a plug in the exhaust unless it is way over sized to begin with.

Either you subscribe to the back pressure is good myth, or you are a tree hugger and don't want people removing their cats.

So as they say in Missouri, show me.

 

[Semp1]

Please show me a dyno run back to back that shows a torque loss when removing cats.

You have a problem understand things I wrote. 3 inch exhaust is not a 3 inch primary.

I think it was engine masters did a shootout with different primary sizes on a coyote, 2 inch was the best for avg power.

A 3 inch exhaust was best for avg power also.

Never will you gain torque by putting a plug in the exhaust unless it is way over sized to begin with.

Either you subscribe to the back pressure is good myth, or you are a tree hugger and don't want people removing their cats.

So as they say in Missouri, show me.

Listen, I don’t have before and after dyno sheets. I also don’t get my info from tv or YouTube. I have and am around modified to Different extremes mustangs all day every day. Some with the same set ups some with different set ups and have seen before and after. This is a forum and am speaking from personal experience. Like I said agree to disagree but if your experience stems from “engine masters” you’re not within the realm to really speak on the matter in an accurate way.

 

[K4fxd]

If adding a cat would increase torque every race car in the world would have one.

I've been building engines for 30 years

Post up those sheets, with video showing if there was a cat or not on the pull. Also show the correction factor.

 

[K4fxd]

Here is how confident I am.

If you pay for the dyno time at Turn in concepts in Cincinnati I will do before and after same day pulls with cats and no cats. If I lose torque I will pay you back double.

If you don't like them we could do Pauls automotive.

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