Mongo

I've decided to replace most of my exhaust system on the '87 later on and have been compiling a list of parts to get. I realized Flowmaster made a scavenging kit that is similar to an X-pipe. This is a universal kit that can be adapted to manifolds/collectors. The interesting part is that it's not a True-X (at least I don't think), but there is a band of metal wrapped around where the dual pipes collect for scavenging before exiting the chamber. I have attached a picture below of this design. My theory is I will gain power, maybe not as much as the Motorsport x-pipe, but enough to definitely get some more pull from this car.

Flowmaster #15932 2.5" Scavenger Kit


The scavenge kit will then go into 2 Dynomax 3-way catalytic converters. I had great luck with these converters on my past 2 944s and have had zero complaints from others I had reccommended these to (my buddies at the time had American Muscle).

The 2.5" piping will follow all the way from the manifolds on back to 2 Moroso Spiral Flow Mufflers - inspired by tv's setup on his Euro 928S. I have heard these mufflers (which look more like glass pack resonators externally) and the sound is intoxicating.

I'll be keeping that 928 International RMB. BTW, I still have not found exhaust tips that look as attractive as the black ones on their RMB.

I guess I'll be the first to test this setup on a 928 I take it, so I'll be documenting how this car sounds and performs once this upgrade has been completed. The total amount for the Flowmaster Scavenge kit, Dynomax cats, and Moroso mufflers is just shy of $400 through Summit (not including shipping). Not pricey at all for an exhaust refurbishment. Not including labor to install and bend new 2.5" piping to replace the old stuff

88porsche928

Out of curiosity are you a welder or have a pipe bender?

Mongo

I've welded before, but definitely don't have a pipe bender and don't think I'm good enough to do a full exhaust. I made friends with a couple guys that have a muffler shop about 14 miles away from me where I get the work done.

Daniel Dudley

I think if you were to punch the guts out of the cats, or replace them with cherry bomb type mufflers, you will get the gain you are looking for. X pipes don't just reduce backflow, they increase scavenging.

IMO, buying those pipes would not be a good way to spend money. I would wait until I could buy an X, and put the cats in a box myself. If you have friends with a shop, they have pipe and can do a cat delete. Probably for less than the cost of those pipes in the picture. If you have the RMB, you already have the sound. Why not do it right and get the power ?

69gaugeman

Do a dyno run pre and post so we have some empirical data, if you can.

Mongo

Daniel, I can't delete the cats. I live in California. I also don't feel like crawling under the car every so often to put them back on for smog purposes. I have done this in the past and it just gets annoying, especially when you find new bolts were rusted 2 years later after installing them and having to lay on your back using little leverage to break them loose.

Those pipes also appear to be mandrel bent in the scavenge kit, something my friends definitely can't do.

bigmac

You might want to consider Carl's "New Product: SS Hi-Flow Intermediate Exhaust" from 928 motorsports.
Although I ordered them in Oct 2007 and they shipped one correct side and one wrong side and have not yet shipped two correct pieces, it looks like a great product.
Hopefully I will soon be able to fully endorse the system.

Mac

Airflite40

stainless steel bolts are your friend, I dont use anything BUT those for exhaust hardware.....just sayin u know

tommytomaso

+1 bigmac's advise. and Carl has performance cats too.

Mongo

I saw Carl's cats. The 100 cells seem very nice with the metallic substrates. I don't know if 100's will pass in CA or not. Stupid CARB

Bill Ball

You can gut the cats if your car runs clean enough to pass smog. I have a set of gutted cats - the full factory H-pipe cat section. They were cut open and glass packs were inserted inside, so they look factory. Anybody want them? $50 + shipping.

Ketchmi

The 100cpi cats I had made for the crossover are not CARB exempt in any state for the Porsche 928. They must be tested and approved on the specific vehicle to get an exemption number and doing so would greatly increase the cost.

They will easily pass the sniffer test if the car is in good enough tune to operate in closed loop mode while providing almost no flow restriction.

Mongo

I have never heard of a car that has passed smog with gutted cats.

Bill51sdr

My 86 did in the pre-dyno smog-check days. Nowadays you are asking for a huge NOX failure without them, not to mention savvy smog-check techs can tell by the exhaust fumes if a cat has been gutted/deactivated. I used to make a LOT of money nailing ricers in their Honduh's for this. And no, their cars never passed the initial tailpipe test. A good running 928 will pass on everything but NOX.

FlyingDog

It's an H-pipe with a short crossover. It's nowhere close to an X. It's also quite long. If you're just going to weld up a bunch of el's to make it fit, at least get a Magnaflow Tru-X.