Probably an easy question for C4 performance guys but my experience is more restoration of interiors and the electrical side. I'm thinking of getting some headers and implementing a "true" dual exhaust to open up the back end of my 1985. The question is if I upgrade my headers, cats, back pipes, etc., would the ECU automatically sense the changes, or would I have to tell the ECU that there is more flow?

Keep in mind this is a 1985 ECU - I know the '86 on onward were more capable, but I would rather not mess with the ECU on my '85 (except maybe to change it to an '86 of course).

Thanks in advance,
Arbix

 

The ECU won't care and it's a MAF car so it will "see" the more air.
It'll run GREAT with headers and dual exhaust.

 

It will handle it all by itself, it will really wake up the engine.

Just be sure to put the O2 sensor bung in the new header collector. You do not require a heated O2, but it can help some of the gas mileage around town if you're concerned about that. I do not run a heated one.

 

What about 3" headers back to a 3" "Y" pipe and then continuing at 3" (with single 3" CAT) until the split to dual exhaust. The OEM size I believe is 2.25" - I'm guessing I would still see an improvement although probably not as much?

thanks again,
Arbix

 

3' should be plenty for ~260hp. Plenty, IMO.

 

FYI, on my Kart project, I did NO headers, (stock manifolds), and a home made 2" dual exhaust, no cats, straight through mufflers. With that, no air filter, and advanced timing as the only mods, it made 241 RWHP and 350 RWTQ....so probably about 260 chp.

Exhaust is a good upgrade.

 

Good advice all - thanks. So I think what I decided is to do is as stated above: 3" headers to 3" "Y" to 3" CAT (single), to existing aftermarket BORLA 2.25" dual exhaust. Looking at the cross-sectional area, 2, 2.25" back pipes are greater than one 3" straight pipe so I think keeping my BORLA muffs and tips will save me some $. The question now is if anyone can help me with the pieces. For headers, these look like a good value.

https://www.jegs.com/i/Hedman/500/61...hoC0tgQAvD_BwE

and then there are some "Y" pipes for pretty cheap out there...

https://www.ebay.com/itm/17205337561...8e22%7Ciid%3A1

Not sure about the rest yet. I'll keep looking, but any advice is appreciated.

Thanks again,
Arbix

 

First thing is.if you live where you have vehicle inspections find out what the rules are before you plan changes beyond a cat back.

 

There is no emission testing for cars this old where I live. I don't even need CATs, but I actually don't want to make it any louder than it already is - can't hear the radio.

Arbix

 

Check the classifieds first. I bought some SS ARH headers for my car for $500 on these forums' classifieds.

Also, in your local classifieds, you can find ALL KINDS of smokin' deals on take-off car exhausts and fab your system from that. Everything now days is pretty good quality SS, with good bends too, so you can buy stuff super cheap and fab it the way you like. The system I built for the Kart cost me ~$50.

 

Yes, a converter also muffles. Dropping from dual 3" (headers) to single 3" converter ... then back to dual 2.5" exhaust isn't typical though it's been done. If you "Y" right into a belly converter, then right back out, the net result could be like a psuedo "X" pipe. It will equalize/smooth exhaust pulses. The final sound would be smoother and more "factory-like".

If you stay separated (and go thru two separate bullet cats), you'll be able to hear more distinct engine pulses. Many find that appealing. Some do not. Many also don't like the smell when omitting a converter, so you're probably doing the right thing keeping it.

On my performance (383) setup, I tried using cats for muffling. I put bullet cats on the headers then routed thru a belly converter (as you plan). Ironically, the belly converter lasted less then 6 months. Magnaflow said "Boo-Hoo" they can't be responsible for modified setups. I'm not sure if too much fuel killed it or pressure. Both were suggested as possible causes. (In stock config, you won't "overpower" a belly CAT...so that's not a risk.) My point here is the METALLIC bullet cats survived -- and are still on the car over 10 years later. (And, they were "in front" of the belly cat -- making them more susceptible to failure IMO). So, you might want to consider "metallic converters". 10 years ago, 3" main converters weren't made in a "metallic" option. So, I didn't put that [center] unit back in. Consider dual metallic cats for longevity and flow. If you definitely want one center converter (versus duals off the headers) you can use one 3" metallic bullet cat in the belly.

 

This is great info, but as a noob I'm a bit lost in your lingo. I've researched high-flow bullet type CATs and I'm not opposed to running 2 bullet CATs to some sort of X Pipe, but I don't know what a belly converter is. Do you have a photo ?

Thanks again,
Arbix

 

belly converter = one converter in the middle of the car (hence "belly") IOW (in other words)...what you were planning AND what I'm thinking your 1985 had from the factory?

So you know (just FYI)... My 89 had "pre-cats" and a main cat. I could have said "main cat" but that isn't as descriptive IMO (in my opinion). So, I opted for "belly converter".

FYI: "pre-cats" look like "bullet cats".... They are just smaller in diameter (versus larger/boxier). Pre-cats are cylindrical and bulge out about 2" larger (diameter) than the pipe size. Main-cats aren't typically cylindrical. And, they are usually bigger. Aftermarket catalytic converters typically have 400 cell, 200 cell, or 100 cell density. Stock was 800 cell IIRC (if I recall correctly). Better converters typically cost more due to the material used to make them.

Because gases flow straight through converters, HP loss is usually minimal. Performance mufflers are usually straight-through for the same reason.

 

I studied your previous message after this explanation and it all makes sense now.

Thank you very much,
Arbix