The 940 exhaust system is flawed.
 

I am very ready to be told I am wrong. I am basing my experience and findings on a sample size of two cars. That said, I’d love to hear from someone who knows about this.

I have had two 940’s. One turbo, one NA, both 2.3l, both estate. The turbo one, I wound the boost up on with a Heath Robinson boost controller. Regardless of how tight I wound the spring, I could only ever see 7.5psi until I cut off the exhaust before the cat. This magically ‘allowed’ 15psi.

A much slower animal is the NA one I drive (and love) now. I know it was never a performance car, however, I was driving on the motorway the other day and a lambda blanking plug blew out (pre cat). The car became intolerably noisy and is now fixed. For that brief period, the car seemed far more willing, free revving and peppy. Car is 209k mi but very well serviced, totally standard.

My main question is this: Is the exhaust system of a 940 restrictive?

Sub questions: If it is, why is it? Is it worth addressing? Is it likely to be a blocked or buggered cat? Have you experience with this?

Aside from this small curiosity, I am really proud to be an old Volvo owner. It is utilitarian, people love it and it is a nice counterpoint to modern vehicles that don’t do much for me.

The exhaust system on a Volovo 940 isn't there for performance, it's to stop harmful gases entering the atmosphere and also to make it quiet. it's clearly doing that job so therefore isn't flawed.

It's a bit like saying the engine is flawed as it doesnt come with 300bhp from the factory

It's like any car. If you stick a well-tuned header on, gut the cat (or run a bypass), and tune the exhaust to match the way the engine exhausts waste gasses you're going to get more performance. Not much on an NA car, maybe 7-10%. It will be noisy and be less kind to the environment but you will get more power.

Back in my youth I had a twincam Toyota 4A-GE engined car. 1600cc, measured on the dyno at 140bhp, up from around 115bhp stock. Now, that is a very racy engine (they used it in the American equivalent from Formula Ford) but it was the Janspeed exhaust and remap that unleashed most of the beast. It made the engine so loud (Mk1 MR2 so it was behind me) that I had to turn it off so I could be heard at the MaccyD's drive-thru (these things are important in your 20s!).
I came very close to sticking Mikuni motorcycle carbs and a high lift cam on it until I found out it wouldn't pass noise regs at most circuits for trackdays.

If you want you could certainly make the B200F sound faster but the drone would probably drive you nuts on the motorway. I have thought of doing it but came to the conclusion I wouldn't be able to hear Radio 3 on the stock stereo. Priorities change :)

All cats are restrictive, they reduce engine efficiency by ~15% in most cases. That's 15% less power or economy (sorry you still can't have both by decatting! :nah: ) so will feel more powerful and will allow a turbo engine to develop more boost.

What's often forgotten is that cats clog up with soot and other unburned fuel particles over time, running some Cataclean through the fuel tank combined with a few Italian tune-ups should restore factory performance (in the cat at least) but the ultimate is to decat it and only refit the cat for the MoT.

Usually cats aren't used for silencing, gutting a cat will normally only produce a slight increase in noise and sometimes a tinny rasp as the case resonates, a decat pipe has neither of these problems as it neither acts as a silencer or is the right shape to resonate.

As Mark says, the exhaust system is designed for being quiet and removing the exhaust gases as effectively as possible within the compromise of remaining quiet. However on Volvos, they use relatively large bore pipework in the exhaust sytem so unless you're running a lot more power than standard, changing the exhaust isn't productive - removing the cat would be but that depends whether you want to temporarily refit it each year for the MoT then remove it afterwards and fit your decat pipe.

Alternatively, convert to LPG and legally remove the cat permanently. :thumbs_up:

This makes LPG more and more appealing.
Especially when the cat in mine at the scrappy would go a third of the way to pay for the LPG conversion!

Cheers

You should be able to get 15psi boost with the standard stock exhaust and cat.

I did this in my 1995 car, although 15psi is a bit close to the limit for the max air flow reading allowed by the ECU. You will be running a bit lean then. I would recommend staying under 13psi without other fuel mods and a wideband AFR meter. I just used a bleed valve.

I'd say almost certainly you have a blocked cat.

I also run the similar 97 B230FT engine without a cat in my 360 and don't find alot more power, in fact its less, possibly because of a slightly defective HG. I have replaced it now, but havn't track tested yet. My 940 has a full stainless system using a cheap aftermarket sports cat. Both cars have the same emission results at the MOT, which is only checked at idle in N.Ireland. Mileage is similar 150-200K but the 360 engine did have valves ground in and is just a bit more spoilt, bigger bore exhaust etc.

This.
14.5psi is perfectly achievable with standard stuff as that’s what Turbo+ models ran (albeit for 30 seconds WOT only) 👍

Cheers