OEM Header Mod ?
 

I've seen a picture on the forum of someone who cut out the factory 'cat' from the OE header and welded in a new pipe... has anyone tried to simply chisel out the factory cat instead?

I have access to a spare OE header... and limited (ie. next to no) budget; would love to find some 'free' power for street and HPDE; any feedback on this idea would be most appreciated.

I have an OFT so am assuming a flash to their 'stage 2 EL header' tune would both take advantage of the lower restriction and also deal with any CEL issues if I were to do this? Can anyone confirm?

Any feedback on power gains vs. a welded in pipe vs. finding a used EL or UEL header instead?

What should I expect from a driving experience perspective from this 'mod' (where in the rev range would any power be made and any impact on sound)?

Keeping an OE 'look' would be a bonus in my mind.

Thanks in advance for any help/feedback/suggestions!

No point in cutting the cat out. Just gut it with a hammer and long screwdriver. The empty cat won't hurt anything. Some tuners believe it has anti-reversion characteristics once gutted.

Gains after tuning on a gutted stock header are similar to most aftermarket catless headers. It will be noticeably louder.

Using the canned OFT tunes aren't what I'd consider to be a good idea, but YMMV. I prefer EcuTek and a proper dyno tune.

I tried to find before/after dyno charts on this but was unsuccessful.

My understanding is it's generally about 90% of the gains you'll see with a regular catless EL header.

Someone used a gutted header (but it was a supercharged build) and dyno'ed it against an aftermarket catless header and the gutted header made a tiny bit less power, but not by much. It'll sound worse I'm sure even though I haven't heard one vs the other myself.

Gutting and cleaning works and works well with OFT Stg 2 EL tune. Gain is roughly just a tad under an aftermarket header. Sound isn't great (no rumble really, just deeper in tone than OEM). It isn't much louder than full OEM. Keeping the stock heat shield is a plus as well as the OEM look.

I've had a straight pipe welded in place of the cat. My reasoning was that it would be less turbulent than gasses flowing through an empty canister. If you have it off the car already I doubt it'd cost much to get a pipe welded in.

this is intriguing...maybe I'll do it to my stock header one of these days and see what kinda gains I'm getting compared to my jdl catted uel header....

Yes, you 'll get large portion of aftermarket headers gains for less .. but i still wouldn't gut stock header but instead would buy aftermarket header. Reasons in addition to even slightly more gains being - if you'll need to pass some technical smog inspection you'll still have stock one around to temporary mount back. Also you won't have to buy it back with stock cat intact, if/when you will be selling your car.

I did it, and it wasn't that hard to do. I'd give it a couple hours to perform. I bought a used FP and header from someone locally as back ups in case I have to go back to stock and together they were less than $150 off craigslist. You need new header gaskets but besides the tools to do it, that's about it.

It sounds great. I'm very happy with it. I also have a Berk dual and a cherry bomb on the mid pipe. Most of the noise comes from gutting the secondary cat, the primary cat wasn't too much louder. There is one bad thing though in regard to noise- when the oil and car are up to temp, sometimes when I shift from 1st to second I get a hellacious loud bang from my exhaust. It started after I gutted the primary cat. Eh, what do you want for free?

Yes, the gains are there (though I have not dynoed it yet) and noticeable. I'm using OFT Stage 2 tune and my numbers are very good (LTFT is a little too high negative for my taste- around -7 at idle and -4 at 2500 rpm, but that's nothing to worry about). There's lots more torque than before. The idling sound is friggin fantastic. My gas mileage is right around 31MPG, so it hasn't effected that at all.

Thanks! I actually had found the same post about a week later, and tried it for myself. Excellent butt dyno results, hoping to have it on a dyno shortly to verify and to have a comparable graph.

I (finally) did this as well. I purchased a used OE "header" from the classifieds and gutted the cat in it. Took about 5 mins and I then used new gaskets to install it. I've kept my original to re-install if and when.

I'm using the OFT stage 2 EL as well. Noticeably better power and torque everywhere, but particularly at the top end where it really charges to redline now (and thanks to OFT, the fuel cut off is less harsh). Can't wait to get it on the track.

Everything south of the header is stock still on my car and, even so, there is considerably more noise after installing the gutted OE header, most noticeable at around 4000rpm where, I think, the OFT program is trying to compensate for the 'torque dip' with more aggressive fuelling (anyone know?). I wouldn't say its 'good' noise either, just noise (raspy). Worth it in my case though; IMO the car is much much more enjoyable to drive, even when shifting at 3500 on the way to the 'office.

The added noise is tinny/raspy and, at first, I thought I'd messed up with the install and had a leak, but I tested comprehensively with the help of a local (good...) tuning shop and its fine.

I'm going to compensate for the noise when time and funds allow with a nicer sounding aftermarket exhaust... I think the "raspiness" from the header, when complimented by a decent sounding silencer, will make it all come together (finger's crossed).

All in all though, for $50 + around $100 in gaskets (not including the OFT) I'd say its about as much bang for your buck as is possible in an '86... I didn't have access to or budget for a dyno, but my 'butt dyno' says I added around 10% torque and power... and would not be surprised at all if that's a conservative estimate.

Try flashing your ECU back to stock and see if you still hear that raspiness. You might be hearing the aggressive cam overlap in the OFT tune for EL headers (I'm assuming you're using EL stage 2).

https://youtu.be/7n3pgL9czCc

It's a little boring for a few minutes int he middle- if you really want to do this though, you'll get an idea of what driving around town will be like. You can skip to the end to hear it in an autoX when I'm getting on it.