I have to look at replacing everything from the CAT back on
a 1990 - 780 V6 PRV.

I already swapped out the front Y pipe with a non leaky one from
a local wrecker. Going to remove the heat shields and replace
them with modern wrap and metal tie wraps.

Without going crazy and making a lot of noise, what is the best
setup for replacement? I will be going to a custom stainless
shop to have the pipes made. 2 inch, 2.5 inch? Which mid
and which rear, resonator tip ?

Second question, how much work to change to Eagle/Monaco
exhaust headers? A custom Y pipe will be need to the new
headers. Or is welding a custom manifold better?

Hi again, Ed.

After getting tired of the racket my headers made, I switched to Eagle manifolds. They fit the car fine, the downpipe on the driver side needed to jog pretty quickly to avoid (I think) the steering shaft, but it was a pretty simple arrangement. I had custom built my whole exhaust system and my Y pipe was under the car, behind the transmission, and each manifold needed to replicate the path my headers took. I'm not sure what it would take to get the EP manifolds up and over the bellhousing to join with the factory Y pipe.

As for the exhaust, the biggest thing I can tell you is NOT to go 3". I did and it was awful. Even with the EP manifolds you won't be making enough power to warrant much larger than 2", but 2 1/4" would be a safe bet. 2 1/2" if you really want to hear it, but the engine really doesn't make a nice noise so I would keep the volume down, if I were building another one. My muffler of choice is the Magnaflow - high quality, great flow, acceptable silencing. Dynomax makes a similar muffler but it hasn't got the same build quality.

My exhaust was designed essentially as an equal length 6-2-1 header: the three cylinders on each side merged together with all six 1 3/8" pipes being within 1/4" from longest to shortest. They became two 2" equal length pipes that made a long Y and transitioned into a 3" pipe, no catalytic converter. The 3" swept up into a round muffler, over the rear suspension and back down to level where it entered a second 3" muffler, oval this time. Then a 3" "S" bend of pipe, a nod to Volvo's standard tailpipe design of the era. All my mufflers were Dynomax, which I got for a deal, but I don't expect the sound to have changed much if I'd used Magnaflow. I expected everything to sound wonderful, but it was blatty, raspy, and annoying. Changing the headers to the EP manifolds broke up that initial harmonic that would have sounded much better with more camshaft and compression, and that turned the system into something bearable (but still noisy). The guy who bought my headers (just shipped them out last month) is putting them in a 262C and I suspect the oddfire engine will sound wonderful with them.

If I had to do it all over again, I would have made the headers a little bigger (1 1/2"), the Y pipe would have not been so much a Y as a T and it would have been much shorter. Then I would have made the rest of the system exactly the same, but in 2 1/4" tubing & mufflers. With the smaller tubing, the first muffler may have been unnecessary (it was a very tight fit, so I'd have removed that one if I could have, but with the shorter Y pipe I would have had more room to install it UNDER the car). Going from the 1 3/8" headers to the EP manifolds I expected to lose some performance but I didn't lose much - mostly on the bottom end, where the headers had a lot stronger pull - but I did get a much quieter, nicer sounding car.

That exhaust was one of my bigger, prettier fails.

Edit - oh yeah, my first version of this system looked like this:


Headers:


It had a Magnaflow 3" muffler/resonator tip thing that was quite loud, and I later replaced it with the S pipe and an oval muffler. I know I have a picture of that but I can't find it on my phone or in Photobucket. I went through a few iterations of this system trying to fix the noise - I added a crossover pipe right at the start of the exhaust system to try and break up pulses, I plated in the large V as the two pipes joined because it had developed a crack I couldn't weld, and it needed the stiffening besides. Yeah, it was a mess.

All my questions answered!

I am going to do the exhaust stepwise. Replace the factory stuff first cause it about
the fall off from the cat back. It barely passed Ontario inspection.

2 1/4 inch pipes back and two mufflers (Magnaflow/Dynaflow) and a straight double
tail pipe out (no S, as I like the look of the double pipe on my 89).

Then start hunting for a set of EP manifolds and enroll in a welding course at the
local college.

Is there a cheaper alternative to S/S piping that will last for a car that isn't
driven except on nice summer days?

Magnaflow stuff: $600 for 2 mufflers and hiflow CAT. I looked at the CAT today
and it is not in good shape. Neither is the Y pipe which I already swapped out.
I saved the leaky Y pipe and hope to have it remade with S/S. UlgyDuck said
one muffler would do it, so that knocks it down to $400 for the Magnaflow stuff.

Can the S/S be bent and the various components attached with S/S clamps
(no welding)?

I started pricing S/S piping and it isn't exactly cheap if it is being done by
a reasonable shop (1 days worth of labor).

Aluminized tubing will last a good long time if you only drive the car on summer days. Any welds will rust more quickly but they can be treated with some zinc spray or painted. You can weld stainless (mufflers, V-band clamps, flex joints) to aluminized steel without any special processes, not a problem. If you could find a high quality exhaust system for a 760 Turbo I'd like to hear about it, but it would also be plenty good enough for your car (minus the Y pipe). Might not bolt right up, but it would probably route the same as in the 780.

I said the front muffler MAY have been unnecessary if the tube diameter is kept reasonable. Exhaust pulses are still a mystery to me - we installed a pair of 2" Magnaflows on a small block V8 and it's super quiet & refined. I just installed a 2" Magnaflow copy on a 110 hp 4 banger and it's pretty snarly & loud. No catalytic converters on either, but the V8 did get an X-pipe. You got me on that one - maybe it's the difference between a generic Magnaflow and a real one, or maybe the X-pipe in the V8 mellowed things out.

The muffler brand I just tried out was Full Boar Performance. I went to my local speed shop and pulled a Magnaflow off the shelf, brought it to the counter and asked them if they had anything more generic. They gave me what looked identical to the Magnaflow, Stainless throughout, at less than half ($55 for a single 2", vs. $125. It even has a very similar part number to the Magnaflow. Here it is (prices in Freedom Bucks):

http://fullboarperformanceexhaust.com/m ... er-mf1224/

They have a bunch of mandrel bends too, in case you find a guy willing to scratch build you an exhaust.

I don't know what your exhaust shops are like around you, but in Calgary there are no places with mandrel benders. If anyone still bends tube around here, they'll have a crush bender. And prices will be in the $50/foot range for custom work, in aluminized steel. I can build a hell of a nice exhaust for a lot less than that. You might try asking around your local car-guy forums, not specific to any make or model, and see who recommends whom for work like this.

I found small exhaust shop in a small town (40km from K/W). The drive
down country side roads at 60 and 80 km/h was very relaxing in the
28 year old suspension. Listening to an 80's radio station, over the tinny
Alpine stock speakers. Like being in a time machine.

Watched the old guy work, bending S/S for a custom 65 Mustang. Lost art.

He got a stethoscope out to listen to the pulse noises at various parts
of the OE exhaust. After talking with him, he recommended fixing the
weak Y pipe at the join - leaking already (build entire new Y section
and graft it back to the good pipes off the manifold), mid and rear
S/S mufflers (moderate flow) and 2 1/4 inch S/S tubing. The cost was
very reasonable, so I will see them next week for the work.

He convinced me that with stock/preserved V6/780 should be given
a dead silent exhaust. As is stands right now, the exhaust sounds
like a delivery truck.

Sounds like a great find! Wish I knew of anyone around here like that, not that I'd be using them but at least I could recommend them to others.

Looking forward to hearing & seeing it.

First iteration was a failure. 1 x flowmaster at the rear, 1 x small diameter flowmaster
resonator in the middle, dual exit tip (for looks, contains no muffling capacity).

To much noise at idle. Sounds like a muscle car and draws too much attention at a stop or when
the car starts. Other than that, crusing sound is good. Flow improve is noticeable on engine.
It is a massive fail < 1K rpm unless you want that type of noise/attention.

The noise during acceleration isn't nice, sound like the engine is underload (like the previously
mentionned "delivery truck sound"). This exhaust works (acceptable noise, good flow) well
from 1.2K rpm - 3.5k. There noise after 3.5K rpm is unsettling from the engine/exhaust.

It may well be the engine needs a total tune - valves adjusted and upper decarbonized.
I doubt this engine has seen much > 3K rpm in its live, driven by its one ownder lady
since 1990.

I will crawl under with a camera and get some pictures.

I will do iteration 2 next Friday. Get back that civilized tone. There might be a leak in the
welding which cause the pronouced sounds at low rpms. We will see.

The exhaust guru scoped the system and said the resonator was the
cause of my noise. A new one is being custom made - ready in 2 weeks
time. Iteration 3.

Regardless of the aggressive idle noise, I still don't like the noise from
the PRV V6 when it is underload > 3.5K rpm. Off load, it sounds ok.
This is all subjective - this engine's noise is new to me.

It is possible there is gas escaping from exhaust manifold gasket or
on either side of the Y pipe attaching to the manifold. Classic Volvo web
does not show a gasket part between the Y and the manifold. The
only gasket from the diagrams is the one between the head and the exhaust
manifold.