ELI5: Why do I need to delete the cats to get rid of the dip?

[Ernest72]

Originally Posted by NoHaveMSG

Myth. UEL does not have more torque. The headers with the best torque curves are all EL.


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General consensus is UEL more low mid torque, EL higher up top. So get the one that produces the sound you want. Personally UEL better for DD, EL for the track where you will spend more time in the higher rpms.

[NoHaveMSG]

Originally Posted by Ernest72

General consensus is UEL more low mid torque, EL higher up top. So get the one that produces the sound you want. Personally UEL better for DD, EL for the track where you will spend more time in the higher rpms.

It’s myth dude. Look at the torque curves on the ace 350 and JDL 4-2-1. They far out preform any UEL. You just need a tuner that knows on to work with them. Go look at the dyno mike_zn6 just posted in his build thread.


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[Turdinator]

Looks like you have the answers here already. The cat is not the cause of the torque dip. The headers that eliminate the torque dip don't come with a cat generally, this will be for packaging reasons, cost reasons and general market demands. If you really wanted the cat in the header with no torque dip I am sure some one could make it for you. It would be expensive and you would want a good quality cat which will make it more expensive again. The most cost effective option would be the JDL catted UEL or FT86 Speedfactory catted UEL. I believe neither of those will fully eliminate the dip tho.

[Ernest72]

Originally Posted by NoHaveMSG

It’s myth dude. Look at the torque curves on the ace 350 and JDL 4-2-1. They far out preform any UEL. You just need a tuner that knows on to work with them. Go look at the dyno mike_zn6 just posted in his build thread.


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Personally I think it has more to do with the collection and geometry of those headers, then whether it is UEL or EL. Plenty of dynos showing the general consensus for UEL and EL for WRX and STI. But I agree the tune is a huge factor.

[NoHaveMSG]

Originally Posted by Ernest72

Personally I think it has more to do with the collection and geometry of those headers, then whether it is UEL or EL. Plenty of dynos showing the general consensus for UEL and EL for WRX and STI. But I agree the tune is a huge factor.

You can't compare a turbo cars exhaust design to NA. Totally different.

At lower to mid RPMS we need that stronger scavenging pulse to help evacuate the cylinder of exhaust gasses and improve volumetric efficiency. This is why catless helps so much, you are alleviating excess back pressure caused by the cat and allowing improved scavenging since the pulse doesn't have to pass through a medium weakening it. EL is more efficient at scavenging then UEL, but really getting rid of the cat is 90% of the gains.

[steverife]

Originally Posted by Ernest72

Personally I think it has more to do with the collection and geometry of those headers, then whether it is UEL or EL.

Isn't that kinda like saying, "it isn't the shape of the header, it is the header shape...."?

[Yoshoobaroo]

I think @ meant the diameter/length of the primaries and secondaries if applicable, and the collector angle.

[steverife]

Originally Posted by Yoshoobaroo

I think @ meant the diameter/length of the primaries and secondaries if applicable, and the collector angle.

Outside of diameter, are those things not determined by the design (EL vs UEL)?

[re-animator]

Originally Posted by NoHaveMSG

You can't compare a turbo cars exhaust design to NA. Totally different.

At lower to mid RPMS we need that stronger scavenging pulse to help evacuate the cylinder of exhaust gasses and improve volumetric efficiency. This is why catless helps so much, you are alleviating excess back pressure caused by the cat and allowing improved scavenging since the pulse doesn't have to pass through a medium weakening it. EL is more efficient at scavenging then UEL, but really getting rid of the cat is 90% of the gains.

i agree with this but when you compare like to like say for example Tomei testing their EL header vs their UEL header on the same car, the EL made more power up top and UEL did a little better in the torque dip area. SOME EL headers i'm sure will probably be equal or better in the midrange than UELs but i think when you control for other variables UEL is naturally a little bit beefier there. Interestingly, i think the TRD Griffon 86 had a UEL.

[NoHaveMSG]

Originally Posted by re-animator

i agree with this but when you compare like to like say for example Tomei testing their EL header vs their UEL header on the same car, the EL made more power up top and UEL did a little better in the torque dip area. SOME EL headers i'm sure will probably be equal or better in the midrange than UELs but i think when you control for other variables UEL is naturally a little bit beefier there. Interestingly, i think the TRD Griffon 86 had a UEL.

The primary runner lengths are also a huge factor in where the torque is. Most of the gain is still going to just be from removing the cat, at this point we are just nitpicking. There is another question, what would a long tube UEL look like? All the long tubes on the market are EL, probably because they are easier to build.

The primary runner lengths on the tomei EL are very short.

Tomei EL



Tomei UEL

[RToyo86]

Seems like it's worth pointing out there are two variations of EL headers to choose from. 4-1 and 4-2-1. More extreme being the Ace header which incorporates the overpipe onto the design with different configurations for different goals.(I heard through FT86MS that ace is discontinuing their header. )

4-2-1 require specific custom tuning but all the info buried in the forum suggest they make most power everywhere.

Talking about dollar to performance ratio in my opinion a cheap UEL like gruppe-s and a good tune is hard to beat. 90% gains for considerably less money. Money no object I would be running a ace or JDL 4-2-1 right now .

[Kirian_N64]

I am new to the forum, and allready ordered my UEL header. decated, bigger front pipe, will be putting magnaflow 200cell cat in the first tube

Also, from my point of view (based on internet research and real life experience with inline 4 engines) ;
4-1 headers have more top end power then 4-2-1 headers in an inline engine, basically because of longer primary tubes, short tubed 4-1 is inferior to 4-2-1. 4-2-1 also produces more midrange torque then....

Stock cats are ceramic, and restrict alot. For emissions and flow, go 200cell SS cat

For FA20, EL beats UEL in topend power, and max numbers. For street use, UEL is enough because untill 4500 produces almost the same, with better torque curve. I bet 4-1 EL with long primaries will make the most power, but be very expensive https://www.supersprint.com/ww-en/to...verter.aspx#!/

Also, it is not all about SS material, in header construction, aftermarket headers are larger piped, longer runners when possible, and bends are smoother, welds also. That's what provides the flow.

And for somebody that commented , yes, big companies on cars cut costs when possible, and 50usd cast iron header is not the same as 800usd SS bent handmade header, and it does make a difference, and it provides significant cost on thousands of cars sold

[Ernest72]

Originally Posted by RToyo86

Seems like it's worth pointing out there are two variations of EL headers to choose from. 4-1 and 4-2-1. More extreme being the Ace header which incorporates the overpipe onto the design with different configurations for different goals.(I heard through FT86MS that ace is discontinuing their header. )

4-2-1 require specific custom tuning but all the info buried in the forum suggest they make most power everywhere.

Talking about dollar to performance ratio in my opinion a cheap UEL like gruppe-s and a good tune is hard to beat. 90% gains for considerably less money. Money no object I would be running a ace or JDL 4-2-1 right now .

This was my logic. I read everything about ACE and FI and decided I wanted to stay NA for reliability. My car is really a DD with some spirited runs here or there. So the JDL catless UEL was good enough at 90%. Why spend more for DD. If my car was a weekend car or a track car I would do ACE or FI.