rgs944

I have been debating what to do in the future. It is a 87 s4 5-speed. I do not need to worry about smog tests and I do not want it to be shy on the street. If I went with RMB and test pipe first, would I see good gains? Would those gains be bigger then just the x-pipe alone, or not as big? After the RMB and test pipe gains, how much more HP could I expect from adding the x-pipe? I realize these are all just guesses but what do you guys think.

Cosmo Kramer

Best hp mod out of those, considering that you don't have smog is an x pipe with no cats and keep the stock muffler. RMB doesn't add nearly as much power as an x pipe. Having both an x pipe no cats and a RMB will make it pretty loud.

dprantl

X-pipe by far will net the largest HP increase. Even if you're not worried about emissions, you should get the new style cats. You only lose 2-3hp with them and they clean up the exhaust so it doesn't stink.

Dan
'91 928GT S/C 475hp/460lb.ft

hopwood

Why is no one pointing out that the RMB does not gain any power. None, zero, zilch.

Joel

AO

But it does. Been verified to gain somewhere between 10 and 18 RWHP.

auzivision

AO are you being serious?

I always thought the RMB makes it sound faster while the X actually makes it go faster.

Are those real ponies or seat of pants ponies?

Shane

As Andrew has pointed out the RMB does potentially add HP if the rear muffler happens to be clogged like it was on my S/C '86.5 auto. With the '87 you will have good sound since you most likely have the larger resonators (mid-mufflers) which will not be too loud or raspy like some have found with the GT resonators.

AO

Dyno proven... I think DR at 928 Specialists was the one who posted the dyno sheets WAY back.

RKD in OKC

Before there were x-pipes my 90GT had an RMB and I LOVED the sound. In the quest for more power I got some junk yard cats (cats on the car were good), gutted them and swapped em out. The gutted cats, GT resonators, and RMB was WAY TOO LOUD!. I got a rear muffler and put it on because the hp loss was only around 3 between RMB and stock muffler. I think the gain for the gutted cats was around 15hp. I liked the sound of the stock cats and RMB better than the gutted cats and rear muffler, but just couldn't bring myself to swap it back and take the 12hp loss.

When I got my GTS it had stock exhaust. I did the RMB first and was disappointed that it didn't have the same sound as the GT with stock cats/resononators/RMB. I went ahead and did the X-pipe AND from my LOUD experience with the GT put on sport cats too. So my GTS is running x-pipe, Sport Cats, stock resonators, and RMB. It sounds great, has butt-o-meter power gains, and isn't too loud.

Here is a vid of the GTS running around an autocross with this setup.

inactiveuser1

That sounded great,nice video too.

Jim M.

Years ago at Devek Days I watched an S4 (auto IIRC) on the dyno. Aftr three runs they installed an RMB. No other changes to anything, three more runs and the gain was 10 HP, plus it's a savings of about 15 lbs.

I agree with everyone else, the X-pipe is the best bang for the buck (on most cars 25HP). On an 87 you should have the big resonators so the exhaust sound shouldn't be to loud.

rgs944

Thanks for some great things to consider guys. So here is what I am leaning towards. Doing the x-pipe and keeping the resonators, doing the cat delete, and either keeping the factory muffler or getting an aftermarket that may get a little more flow and be a little lighter. What actually is the difference between a resonator and a muffler?

vsalvato

Hi all! I am thinking of fitting an x-pipe on my S4, MY88 (dual cat). Someone in an earlier post wrote:

X-pipe by far will net the largest HP increase. Even if you're not worried about emissions, you should get the new style cats. You only lose 2-3hp with them and they clean up the exhaust so it doesn't stink.

Can any of you point me to the best stainless steel x-pipe with or without new cats? How much, roughly? Where to buy? Need someone willing to export to Europe/Italy.

NoVector

Contact Roger at 928s R Us. He sells the Dave Lomas exhaust stuff and ships overseas. See this thread for more: https://rennlist.com/forums/928-foru...7-to-95-a.html

Just spent last week in Italy (Venice, Pompeii, Sorrento, Naples, Rome, Florence and Pisa); didn't see a single 928

GlennD

Can someone help me understand the difference between the X-pipe and the stock pipe from the exhaust manifold back? I am talking about the dual exhaust 86.5 + cars. (assume on cats on both)
The stock pipe (I have seen them called H pipe on this forum) brings the two exhausts together at the O2 sensor port (connection tube). I believe that also allows each bank of cylinders to see both exhaust resonators and back. This should result in lower exhaust back pressure.
What does the X-pipe do differently to justify the cost? I am not knocking the X-pipe, just want to understand.

Thanks ....


And to add to this thread, I also wanted the deeper rumble from the 86.5 so, on my spare H pipe (or whatever is the correct term), I had the cats replaced with resonators. I already had a RMB so thought I would err on the side of a bit controlled noise. Result - missed the cats. The stink was immediately noticed, not only by myself but everyone else. The CO was adjusted correctly (twice) and still the smell. In my opinion, made the car smell like a beater (probably was acceptable for the 80's but not today in my opinion). Replaced the resonators with 100 cpi cats and the smell was gone and no "seats of the pants" difference in get up a go.
Before I put my car back on the road (damn snow), the RMB will be coming off and the stock pumpkin will be going on. I recognize that there will be a slight loss of power but I believe the tone will be more mellow. That would leave me with a pair of 100 CPI cats, stock mid mufflers, and the pumpkin. I will see how that goes before deciding what to do with the RMB. I find the 928 a classy car and want to ensure the sound is also "classy"

Cheers
Glenn