Hey all, not sure how many still mess around with LT1’s, but here I am reliving my youth.
I have a 96 Z28 and looking to convert to OBDI for tuning, already had cables and PCM.
For exhaust I got the Magnaflow which appears to work with both OBDI or II setups, and ebay midlength stainless headers (OBDI) which seem to my untrained eye to be similar to Pacesetters, but stainless. I’m fine converting the whole thing to OBDI, and midlengths, not looking for every ounce of power and not interested in finding if I will or won’t have clearance/scraping issues.
Question I have, and I’ve searched for ages, do midlengths like the Pacesetters hook up directly to OBDI Magnaflow or will there be a gap where cat would go?
From what I’ve read I’d rather put in a cat for smell and sound, just wondering what size I’ll need and if the system would bolt together without for initial driving?

Thanks

 

AFAIK the exhaust differences between different years are essentially emissions related. So, whether or not the headers have provisions for the AIR system, 1 or two cats, 1 or 2 pairs of O2 sensors.

As far as bolting it up goes that depends on the design of the y-pipe vs the the cat back. I’ve read of some people who happened to purchase a particular combination of header and y-pipe being able to join up directly to their existing exhaust and by extension , at least in theory, an after market cat back system.
That hasn’t happened to me though. In my albeit limited experience of compete performance exhaust replacement (just four builds) there was some massaging and head scratching involved. Heck, even replacing stock for stock sometimes requires some messing around.

Your decision to run a cat/cats is sound. Does the y-pipe you have selected already have cats included or are you looking to put a single cat after the merge? I have used a single ceramic “high flow” (marketing term) cat from Magnaflow which is a nice enough piece but I recently was advised to try a metal core cat similar to this one
.

Metal core is deemed less efficient by OEMs so it’s considered a racing piece but it controls the smell of my car just the same as the stock pair of cats did. It is also supposed to flow a little better than a ceramic core. I have no data to support that but there was a slight change in the exhaust note that would suggest that it’s true. Probably not enough of a difference to be reliably measured though.

Magnaflow is a solid choice for the cat back system. I had one for ten years on my previous car. Some people find it too quiet and reserved. I think It strikes a reasonable balance In the sound spectrum between sensible and obnoxious and above 4000 RPM it sounds like a chorus of gear head angels. You may have read that the sound does get a little louder and deeper over the first 1500 miles.

Not sure is this would be of interest but the Magnaflow muffler is essentially straight through on the drivers side tail pipe and more restricted
on the passenger side. You’ll see on a cold morning that at idle the vapour only comes out on the left. If you live on a street with young families or keep weird hours or otherwise feel a need to be mindful of your neighbours placing an exhaust cutout on the left tail pipe cuts the volume some but really cuts most of the reverberating base tones. It’s handy when ordering at the drive through as well.

So...kind of longer than I meant it to be when I started. Hope something of this is of use.

Jon

 

Yes, thanks for the input. I like the sound of my V8 but the days of super loud are well behind me. Along with working shifts, I do a lot of highway driving with wife and/or pre-teen daughter, so idle and cruising loudness/drone are highly undesirable 😁
I wish I still had the 2otl my other cars had along with the SLP headers, but Magnaflow seemed to be the ticket from everything I read, rather have too quiet than too loud, and headers should wake it up a bit.
After looking at more online pics comparing OBDI and II stock y-pipes, and the Pacesetter mid y-pipe, looks like right after the y is the perfect spot for a cat. Might order the cat and have the shop weld the cat to the y and then install and see how much extra pipe is needed to connect to the catback, which should be straight pipe of few inches. Was thinking of the Magnaflow 59959 cat, should fit what you were talking about and it’s only $135 Cdn, although the cat from 93444 would be nice as it might be straight fit from y to cat back, but can’t find part number for just the cat and likely lot more expensive.

Thanks again for the input

 

I was kinda where you are at last year. I just wanted a cheap old car to tinker, cruise, and make a couple passes down the strip.
I cant figure for the life of me why one would want to convert their OBD-II to OBD-I besides computer, wiring harness your going to have to change the timing cover as well- man good luck lol!
As far as exhaust I’ve had loud cars in the past (still have a loud Mustang) but didn’t want to go the loud/smelly route this time. I ended up doing a Magnaflow high flow catalytic converter 2.5” into 3”, 3” Flowmaster cat back while running the stock manifolds.
So now the car sounds 1 notch above stock idling, 2 notches at WOT, no smell, and it looks like it rolled off the showroom floor.

 

Appreciate the pics and ideas.
So to clarify, my OBD1 conversion plan consists of PCM only for ease/cost of tuning purposes.
Unrelated is exhaust conversion to OBD1 style mid-lengths since I don’t have to worry about emissions and the OBD1 mids are a different design and from my research provide better power and plug access. I would still like a cat for sound and smell purposes, which will go in same location as stock OBD1, after the y and before the cat back. Luckily the Magnaflow cat back seems to have the s bent pipe included to work with both OBD1 and 2 systems, so a bit less pipe to fabricate I guess.
So my OBD1 conversion is just the PCM and exhaust, if I’m way off base in my thinking, someone let me know 😁
Thanks

 

Actually OBD-II is far easier to tune.

 

And just to add, plug access is an issue with stock manifolds, and I knew that when buying the car. But it gets on my nerves that I can change plugs on my former 95 Mustang 5.0 fairly quickly, and that my Jeep Hemi for a first attempt wasn’t really bad either (although totally different design) even with 16 plugs. I don’t want to waste a day or $200-300 at a shop changing plugs and wires, and it’s a pain when you are chasing ignition issues, wanting to check individual plugs or wires. So headers are the extra power and access solution in my mind, got the poly motor mounts lined up too as stockers are likely shot. Plus with shifts and kids, I don’t have the time like in did in my 20’s to devote whole weekends to tinkering with the car anymore, and with the age of these cars, lots of things need replacing 😁
Appreciate all the suggestions though

 

I already had the cables for OBD1, picked up a cheap PCM, all else fails or I brick it at least I still have my stock PCM. And could still always go that route but tuning setup seemed a tad more expensive. I guess my feeling was that if I needed a better tuning package and wanted to stick to the LT1 I’d be better off putting that money toward a Torqhead package with LS1 PCM

 

If your car is automatic, obd1 pcm cannot properly tune ‘96 transmission due to 3-2 solenoid and valve body differences. You would have to change valve body with one from ‘95 4L60-E.
on the engine side, you don’t have to change timing cover as it was suggested, but you will need to replace knock sensor with one compatible with obd1. Obd2 knock sensor with obd1 pcm will trigger fault code and pcm will retard timing drastically causing substantial power loss.

 

So those two things I tried to research to death and got bits and pieces of info from posts over last 15-20 years.
From Ed Wright’s posts and tuning tips I gathered it was sufficient to program out code 47 (or something like that) which would disable the knock sensor warning and car would run fine, including detecting knock, so I’ll be trying that. I had in my 97 years ago changed the actual knock sensor when I did the PCM swap. Easy enough either way.

As for my A4, again after much research, I was under the impression that if I program with a 95 bin it should run fine and when I did my 97 I don’t recall any trans issues, and I want to say I even ran a 94 PCM from my other car. But to be fair, in those days I didn’t run it long like that and didn’t know to pay attention to the trans incompatibility, just the knock sensor.
In the end, I’ll try the PCM, so far it’s cost me $70, keep an eye out for those issues and see how it runs. If I need to give up on my cheap tuning dreams I’ll have to save for Torqhead style setup I guess, don’t see the point in wasting that much money on LT1 OBDII tuning package.