Hi,
From reading a previous post I am now wondering if the exhaust downpipe runners on a '73 and '74 fuel injected car are the same diamater. I thought they were. Perhaps the original equipment ones were different but the aftermarket replacements are all the same.
Anyone out there have the low down on exhaust pipe runners?
I have just welded in four inch extensions to the ones I have just for fun. I will post any noticeable changes in performance once I have them in the car.
Thanks.
-Ted
'74 144GL
'59 PV 445

Apparently there are two types, but their individual runners are the same: its the 2 downpipes that differ in size. Type one is 1 5/8" and the later one is 1 3/4" (I think). I myself have ever only seen the smaller type though.

What do you mean by welding in four inch extensions? Did you weld in a plate in the #2 and 3 exhaust runner to keep them seperated a bit longer? I also did that, but I used a plate that is only about 2 inches long. If you go further into the manifold the size of the passage will become very small... No difference in performance to be noticed in my case.

cheers, ben

--
P131, '65, B20B+M47. P131, '69, B20E+AW71L+LSD. (www.tinustechniek.tk)

Hi,
I think I may be using the wrong word (runner). The down pipe that bolts to the exhaust manafold has two tubes that join togther in a y near the lower control arm before the 21/4" exhaust pipe that runs to the first muffler. I extended these tubes 4" right before the y by cutting the pipe and welding new pieces in making the y farther back. I think this might provide more low end torque and more high end power when used with a larger exhaust pipe and free flow mufflers. I am using a Magnaflow in front and a Flowmaster with two outlets in back. I am thinking that I may be creating a problem with exhaust pulse by removing back pressure but want to see for myself. If there is a problem I can always 1) put smaller diameter pipe in working from the back forward in phases until I am satisfied with the results or 2) install a blower (which I hope to do at some point).
I did not think of trying to seperate the runners at the manifold with a plate.

-Ted
'74 144GL
'59 PV445

Hi Ted. It sounds like you are on the right track, but the improvement might come mostly at the top end. I quote from the Volvo performance parts catalog:
"Cast iron production exhaust manifold as used on all fuel injected models, is recommended for Stage III and IV engines using "S" or "U" camshaft in high speed rally and racing. For optimun power at 7000 RPM , it is recommended that the separated twin pipe section of both the standard and rally front pipe be extended another 4 inches before joining into a single pipe."

Let us know how it works out. I assume this mod is for your 140 right.


Cheers, Jim 66 122s

What about creating dual exhausts? Yeh, I know, two mufflers etc. but much less back pressure, especially on my B30. Might look pretty neat to have dual exhausts, one on each side.

Klaus
--
98 V70Rawd(108Kmi), 95 854T(88K mi), 75 164E(173K mi)

I don't know how a B30 exhaust is set up, but for B20 at least you need for the dual headpipes to merge into a single common collector. After that, you could go to dual exhaust if you wanted to.

The 1972-1974 fi 164 has dual pipes all the way to the first muffler. Getting two pipes over the axel might be tricky . Getting all the mufflers to fit would be hard too. I would be tempted to try it if I had a 164 and all the different pipe pieces that I have access to now..
My friend gave me the flowmaster and the shop that I work on my car at has a bunch of really nice thick walled unused pipe pieces lying around. The Magnaflow was sixty bucks. I am not paying myself anything to do the work...
-Ted