Gutted Header & Front Pipe - Dyno Inside
 

There's a whole separate discussion regarding gutting the factory front pipe and header... but I never came across an actual dyno showing the gains on an NA setup. So for those interested, here's some reference in case you guys want to do the same.

Baseline is from another local car, which has been used as a baseline for a bunch of the locals. I think its pretty close to what these cars make stock at our altitude.

Based on my logs, the car runs a little rich and the MAF sensor still needs to be re-scaled due to the GS intake. MAF scaling is untouched from the Stg 2 OFT 93 EL map. LTFTs are around 8%, and under WOT/High RPM I think AFRs are low 11s. Was at Castrol Raceway this weekend and the car was backfiring non-stop during each session.

Modifications:
- OFT OTS Stage 2 93 EL tune
- Gutted factory header
- Gutted factory front pipe
- Custom muffler delete
- Grimmspeed Intake
- NST lightweight pulleys (Crank, water pump, alternator)

Was the header and front pipe gutted as in cut the cat out and reweld a new pipe in its place? Or was it gutted as in removed all of the insides of the cat? Pretty nice gains in the dip area.

Gutted the insides of both cats. No cutting, or welding in any new pieces.

Any pics of gutting the cat? What did you use to remove all the material??

Thanks for the post! How and what did you use to gut the cat out?

I thought about taking pictures, but the sun was going down and I wanted to get as much as I could done while the sun was still out. Didn't get a chance to take any pictures.

I used a long flathead screwdriver, and a hammer. Keep hammering the screw driver into the material in as many places as you can, and the both cats will eventually start to fall out in in pieces.

Once a couple chunks fall out, the cat will pretty much collapse on itself. There's insulation around the outer diameter of the cat that comes out with the material as well.

PS. Use gloves, and wear a breathing apparatus!

So just to clarify. You are comparing a stock car with stock tune to a gutted header/fp with OFT stg2 93 tune?

+intake & muffler delete. Though slight, but some gains may come from those too.
Still from looks of it some good aftermarket header even with stock intake / catback should do better. Just like sticky bolton mods guide shows, that looks to be most effective NA tuning. Well, at least OP eliminated torque dip.

It would probably be much better to cut out the cats and weld in suitable pieces of pipe, should flow better

and I'm sure the recycling depot would be happier to take an intact cat


put up a sound clip!

I dunno, maybe, these results look about as good as most of those $1000 cat less headers out there. Maybe the ACE header is better, but not that much in it. Keep in mind this thing is running on a very generic OFT tune from Shiv. Granted the baseline is from a different car, but same dyno at least.

And yes, sound clip please!


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It has been my assertation that the stock header with the cat removed would be as good as any sub $700 header.

Here is the one I made by welding in a collector where the cat was. More pics in my build thread if anyone is interested.
https://i.imgur.com/5FSkHSx.jpg

That said I can't imagine a gutted cat is good for exhaust velocity.

Thanks for putting this on a dyno.

so no need to spend $$ on aftermarket headers, just gut for similar results... not bad...

Yup looks kinda that way, although there are aftermarket catted headers out there that produce great results as well if you want to retain your primary cat.

I think the other reason to go aftermarket would be if you went with a supercharger or turbo system that doesn't replace your manifold - as you dramatically increase your hp via FI, you'd probably see a difference between a stock header with no cat and any aftermarket option.

But if you don't care about emissions, and want a cheap power upgrade (with a tune of course), this looks like a really viable option.

Any sound clips?

Nice! If I had the skills, I would have probably done the same. Wishing I took pictures, but the gutted cats definitely don't promote smooth laminar flow. The transitions in the header/FP after the cat is terrible.

But if you're in the business of paying someone to remove your header/fp, cut out, and replace your cats with pipe, then you may as well buy a budget header/fp. It'll probably cost the same. The car will benefit from slightly bigger diameter tubing as well.

That being said, I'm out a couple hours worth of work and my wallet is untouched, but I've netted a couple ponies and a few ft-lbs. Worth it in my books... :thumbup:

I'll try and get some later today if that helps? But I find recordings don't really come close to what most exhausts sound like in person.

Ever get those clips?

I used a Hero 3 to try and record the sound just now... It doesn't sound as good as it does in person...

Custom muffler delete, and both cats are gutted.

Video shows cold start, idle, minor blips, and banging off 4k launch control.

https://youtu.be/IbA_jWi88ws

[ame="https://www.youtube.com/watch?v=IbA_jWi88ws"]FRS Exhaust - Gutted Header, Front Pipe, & Muffler Delete - YouTube[/ame]

Good looks bro, I haven't heard it yet but I'll take a listen a little later.

Wonder how the 2017 revised manifold will do if gutted.

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Gutted Header & Front Pipe - Dyno Inside
 

is it possible to weld a high flow cat on stock header?

Yes, but why? Unlike with just gutting it you'll get smaller performance gains, and added costs of buying cat and paying for welding work will nullify cheapness bit. And even if primary cat in header is HF one, you won't be 100% safe from seeing cat readiness CELs. If you are ok with doing something to stock cats, aftermarket header with HF cat or even catless aftermarket header will be better choice (one stock secondary cat should be sufficient to pass smog tests, if those don't include visual checks).

Yeah the only reason I can see to gut the stock cat (aside from just for the sake of science) is for those looking to remove one of the major restrictions in our exhaust with basically no cost (other than tuning, which is a given in my book). You'd be much better off finding a proper aftermarket header with a cat if you're worried about emissions impact or noise. If you're looking to stay legal, *any* mods you do won't pass visual (unless you fool them by just gutting the cat and leaving the cat shell intact).

I plan on doing this, but have sourced a cheap OP and Berk HFC FP to go along with the gutted stock header. I am a complete noob in terms of tuning, would it be safe to assume an OFT OTS EL 93 octane tune would be a good starting point for this setup?

My primary use would be for autocrossing

I guess you can use OFT Stage 2 EL tune with gutted stock header, which, while not completely, is EL header, and Stage 2 tunes are for catless headers.

I've been gutted on Stage 2 OTS 93 tune since last summer. No probs

I just found this article. Interesting read on gutting the cats.

http://www.circuitmotorsports-blog.c...-fr-s-86s.html

Yes, in this series, they only allow you to gut the cats, not use an aftermarket header. You can have an aftermarket catback

They tuned with Ecutek

I will let you know. I just did this tonight on my Yellow. Was planing on gettin some dyno numbers after Delicious tuning is done setting up my E85 tune.

I wonder if that's loose wording and they actually replace the pipe with a test pipe. The rules allow for test pipes, and if they're racing it seems they'd be going after every last hp.

Read the article, they are pretty clear that they are not allowed to use an aftermarket header. Gutted OEM header, OP and FP with an aftermarket catback

I read it and the SCCA T4 rules. They are allowed to weld in a pipe where the cat is/was, so why wouldn't they?

Because they made 201 WHP by gutting alone. This is the first real evidence of what gutting and a tune can do that I have seen.

Dont get hung up on the numbers guys. This is a dyno that is more generous than jesus himself. Quoting the article:

So really, the only thing gutting the header gave them was somewhere along 10-15whp. Which is what most "low end" headers give around here and what everyone else has been saying for a while. If anything, this just confirms what has been said for a while here. If you expect to get the same 200whp that a long tube headers will give you (Ace, Nameless, PML, Cosworth), you are in for a surprise.

I'll weigh in as i am sort of in the same boat. I'm thinking about adding a header along with a tune to push whp and wtq a little bit. Thoughts:

- CEL is a given regardless of what direction you go, for most people this doesn't matter because your tune will cancel the CEL from suboptimal/nonexistent cats

- high flow cats vs. catless is a BIG difference in day to day livability and a small difference in horsepower. Between the greatly increased sound (which IMO gets very raspy and harsh as well) catless headers are also going to give you that nasty catless exhaust smell, especially so if you are gutting the front pipe as well and going fully catless. High flow cats greatly reduce the smell and take the edge off the noise without changing the basic exhaust character, which is nice if you already have a catback sound that you like. the difference in horses in an aftermarket high flow catted header vs a catless header of the same design is negligible. you're talking maybe 2-3 whp. makes sense for a dedicated track day car, but maybe not for a DD for most of us

- to my knowledge it isn't really feasible to add a high flow cat to the existing header, or replace the existing cat with a high flow. First, its going to cost money for the cat and the welding if you don't DIY (money comparable to a full aftermarket manifold). Second, going with a cat that was not designed for the specific header configuration is kind of dicey. It could end up more turbulent or effectively more restrictive than the stock design

- since no header is going to pass emissions, it is better in my opinion to hold on to the OEM header so that the car can be brought back to stock spec every 2 years for emissions testing. can't do this if you modify the original header

Damn it...... what a lucky guy with his unicorn frs....:cry:

We all know some car simply makes more hp then others....:cry:

It's nice that they made 201 whp, but they should be after every last hp that is available within the rules since they are racing. I'm not aware of any headers available for any car that incorporate a hollow expansion chamber near the header collector because it makes more power. That is why I question whether it's actually a gutted cat or a test pipe. I'm aware it's a small detail, but to me the numbers make more sense with a test pipe, and since they're in a racing series it makes more sense that they would have a test pipe since that is allowed and it's cheap to do.

none of you read the article. They don't tune for max power and the article covers that. It also talks about comparisons to other high end headers.

RTFA

I'm running e85 and was thinking of doing this. The oft tune for el e85 should work with no problem, but I'm just curious if the second o2 needs to be disabled or if it's already in the tune

Again, I've read the article. They don't tune the ecu for max power for durability reasons. That has nothing to do with the header. Try to think critically for a minute.