For 1985-1992 Volvo 740 and 940 series, there seems to be considerable confusion regarding which exhaust pipe fits which Naturally Aspirated (NA) engine. This post is an attempt to sort through the numerous sources (sometimes conflicting) and present the facts in an understandable, and I hope, reliable form.
Unless you are specifically interested in such esoterica, I suggest you skip this post and move on to another one.
This review is the result of several hours of work trying to determine which pipe was required for a 1990 740 with B230F engine, no EGR, and Regina fuel injection.
The following screen shot is a synopsis of the various part numbers involved, along with what seems to fit which engine. If you click on the screen shot, it will expand to a more readable size:
There appear to be three configurations of exhaust pipe involved, covered by Starla Part Numbers STA-16329, STA-17571, and STA-17570.
Two of those three parts, STA-16329 and STA-17571, are the same length, size, and shape, and either can be used in the place of the other, provided the O2 sensor is located in the Catalytic Converter. Each of these pipes uses the smaller 2″ donut (or gasket) that goes in the flared connection between the exhaust pipe and the catalytic converter. The main difference between the two is that STA-17571 does not have a threaded boss for the O2 sensor. STA-16329 comes with that threaded boss, and also comes with a plug for the hole; thus it can be used wherever STA-17571 can be used.
STA-17570, however, is about 2-1/8″ shorter than the other two, and is not interchangeable with either of them without making other modifications to the exhaust system. STA-17570 is also designed for the larger 2-1/4″ donut.
Here’s a photo of the 5 exhaust pipes examined for this review:
1. At the top is the broken pipe that was on the 1990 740 B230F, Regina, non-EGR vehicle. I believe that this particular pipe had been installed sometime after the car left the assembly plant. The original pipe probably had heat shields, which this pipe never had.
2. Next from the top is a Chinese-made pipe that is very similar to #1, but is poorly made and could not be installed without alterations. More on that later. This pipe was purchased from 1AAuto.com, their Part Number 1AEMK00170, and bore a tag saying “Made in China 13557-1262673.”
3. In the center is STA-16329, which is the pipe that was ultimately installed on this vehicle. As can be seen in the photo, this pipe has a threaded boss for the O2 sensor, located just forward of the outlet flange. The pipe comes with a plug for that hole, making it suitable for either application, those having the O2 sensor in the forward pipe, or in the catalytic converter.
4. Fourth from the top is STA-17571, which is just like STA-16329, except that, as can be seen in the photo, it lacks the threaded boss for the O2 sensor. Also, the outlet flange is of poor quality. More on that later.
5. At the bottom is STA-17570, which is essentially the same as STA-17571, except that it is 2-1/8″ shorter and is flared to use the larger 2-1/4″ donut. Note, however, that this pipe is fabricated from the same size pipes as are used in #3 and #4. The outlet end has a larger flare than the other two Starla pipes, but the pipe itself is the same size.
Each of Pipes #1 through #4 uses the smaller 2″ donut.
Next is a close-up of the manifold flange end of the Chinese pipe, the pipe that the owner purchased for use on his vehicle:
That is a 10mm nut with a 15mm hex. Note that there is insufficient room between the nut and the pipe to put a socket onto the nut. This pipe was therefore considered unacceptable and was returned to the seller. We went to FCP Groton (fcpeuro.com), looking for the proper replacement.
A knowledgeable Volvo mechanic recommend that I purchase STA-17570 to replace this Chinese pipe, so I ordered it. Almost immediately, another Volvo mechanic indicated that it was the wrong pipe and recommended STA-17571, which I also ordered. Then, my own study of FCP Groton’s website indicated that maybe, just maybe, neither was correct, so I ordered STA-16329, just to be safe. I also figured that, with all three pipes in hand, I’d be able to positively identify the differences between the pipes. This review is the result. Sorry, guys.
As it turned out, the last pipe ordered was the first to arrive, and it was clearly the correct pipe. We had to wait another day to get a look at the other two pipes, both of which proved to be incorrect. So, the answer for this 1990 B230F with Regina and without EGR was “use STA-16329.”
Next is a photo of two of the Starla pipes, showing the manifold end flange and a pair of 10mm x 17mm hex fasteners:
Notice that for these Starla pipes (as well as the third one, not shown) there is plenty of room for a 17mm hex fastener and the socket, whereas for the Chinese pipe, there was insufficient room for a 15mm hex fastener and socket.
Next is a photo of 4 of the 5 pipes that were shown earlier. This photo was taken to more clearly compare the lengths of the various pipes:
From Right to Left, they’re #1, 2, 4, and 5. By the time this photo was taken, #3 had been installed on the vehicle. However, that pipe was the same length as #4. Those plugs on the left side of the pipes in the above photo are not for the O2 sensor, rather, they’re for exhaust gas sampling; the O2 sensor will not fit those holes.
Next is a close-up of the above 4 pipes:
Notice that the Chinese pipe (#2, second from right) has the mounting bracket located closer to the outlet end of the pipe. The bracket on Pipe #3, was located the same as the one on Pipe #4. And the bracket on pipe #5 (far left) is located the same distance from the inlet end as that for #3 and #4.
Notice also that the Chinese pipe (#2 from right) is painted, whereas all three of the Starla pipes appear to be made of a more corrosion-resistant steel.
Here’s another photo comparing lengths of two of the Starla pipes and the old pipe:
And here’s a close-up:
The STA-17571 (center) and STA-16329 are each 2-1/8″ longer than STA-17570 (left) and 5/8″ longer than the old pipe (right). The distance from the center of the front mounting bracket to the end of the flare is 26-3/4″ for the two longer Starla pipes. For the shorter Starla pipe, that distance is 24-5/8″.
Next a closeup of the ends of Pipes 4 and 5 (STA-17570, left, and STA-17571, right):
The pipe diameters are the same, but STA-17570 (left) has a larger flare to fit the larger 2-1/4″ donut. The flanges are also the same size, but the one on STA-17571 (right) is a bit dubious. More on that in the next photo:
Notice that the flange on the left (STA-17570) is chamfered on the inside to fully-support the flared end against the donut. But, that flimsy stamped steel on the right (STA-17571) butts up against only the inside of the flare, leaving the bulk of that flare (and the donut) unsupported. This strikes me as a really good way for a leak to develop at the flare, or for the flare to break off at its base. To my “Engineering Mindset” the stamped steel flange on the right is unacceptable. This pipe will be returned to FCP Gr0t0n.
Next a shot of the two flares and the two donuts:
STA-17570 is on the left, with a 2-1/4″ donut, and STA-17571 is on the right with a 2″ donut. Notice that the ID of the STA-17570 pipe is the same as that of the STA-17571 pipe. Only the flare is larger. In the next photo, the donuts are reversed:
Notice that ID of the 2″ donut matches the ID of the STA-17570 pipe on the left, but that the flare extends well beyond the OD of that donut. The 2-1/4″ donut is clearly too large for the flare on the STA-17571 pipe at the right.
Next is a photo of the old catalytic converter that was removed from the 1990 740 with B230F, Regina FI, and no EGR:
The overall length of this catalytic converter is 27-1/8″. It was compared to a brand-new Bosal catalytic converter for the car, as well as a brand new OEM Volvo catalytic converter, and found to be essentially the same size and length as each of the new ones.
A couple of knowledgeable Volvo mechanics raised the question of why the B234F pipe (STA-17570) was shorter, and what differences in the rest of the exhaust system might be to compensate for the shorter front exhaust pipe. So, I put my own 1990 B234F up on the lift and took a few photos, as follows:
A bit hard to see in the above photo, but that’s a tape measure, taped to the exhaust system, with the end of the measure placed at the center of the front mounting bracket, as shown in the next photo:
Next, the same setup again, but this time, we’re looking at the joint between the catalytic converter and the forward muffler pipe:
This measures 51-1/4″ at the forward end of the muffler pipe. We can’t see the end of the catalytic converter pipe, but let’s assume it’s somewhere close to the 53-1/2″ mark. That would make the B234F catalytic converter 29″ long, compared to 27-1/8″ for the B230F cat.
So, the B234F cat is roughly 2″ longer than the B230F cat, and the front exhaust pipe is roughly 2-1/8″ shorter, and the differences mostly cancel out.
- STA-16329 can be used wherever STA-17571 can be used.
- STA-17571 can be used in place of STA-16329, provided the O2 sensor is in the catalytic converter.
- Any of the three pipes can be used in any of the applications, provided the owner is prepared to change other portions of the exhaust system to suit.
- Presence or absence of EGR probably makes no difference.
- Whether the Fuel Injection system is Bosch or Regina probably makes no difference.
- It might be a good idea if Starla discontinued STA-17571 and replaced it with STA-16329.
- Given the poor quality of the stamped flange on STA-17571, I would not buy it, but would always use STA-16329 instead.