I'm looking to replace my smoking 3.2L mill with a fresh 3.5L and trick it out just a little (headers, cam, power chip if they have it...).

My question:
To go with those headers, I'd like make sure the rest of the exhaust is up to snuff...does a guy go with a dual exhaust (with an X-pipe) or a simple single?
I'm just not sure what to do with a staight six.

Go with headers and a dual exhaust, youll be good to go. Check out westcoastcustomparts.com, He has replica Hartge headers that you can have coated for a very reasonable price. Then after you install the headers, just run a dual exhaust the rest of the way. Not sure what you want to do about cats and mufflers, but there are TONS of options there i guess too.

-Jeff

Here is what I was planning for my 3.5l M90 conversion:

Stock M90 dual exhaust manifolds, port matched and ceramic coated
Dual 1.75" stainless pipes to catalytic converter
Dual-In Dual-Out catalytic converter (also works as crossover)
Ireland Engineering Stainless Dual 1.75" Cat Backhttps://store.nexternal.com/ireland/images/e28catback2.jpg

Due to local regulations I have to use a catalytic converter, 1.75" seems very appropriate for the exhaust dynamics of the 3.5l mill.
The original M90 exhaust manifolds look very efficient, I am also trying to avoid engine compartment heat issues due to headers and possible interference with my A/C hoses due to a Sanden compressor conversion.

Klaus

Here you go, just what you need, a Metric Mechanic 3700 HiFlo ST Sport Engine, 270HP - $7,000

http://www.metricmechanic.com/catalog/anatomy-of-2500-3800-4000.php

I just put the M90 powerplant in my 78 633 and I don't see how the manifolds are that efficient. I'm not a mechanical engineer (just a materials guy) but having cast log style manifolds are fairly inefficient and decrease volumetric efficiency compared to a manifold with individual primary tubes for each cylinder. :dunno

I just put the M90 powerplant in my 78 633 and I don't see how the manifolds are that efficient. I'm not a mechanical engineer (just a materials guy) but having cast log style manifolds are fairly inefficient and decrease volumetric efficiency compared to a manifold with individual primary tubes for each cylinder. :dunno

Maybe I should have worded it a little bit different, the basic idea was that for the basic design parameters the dual log style manifolds are fairly efficient compared to the single log manifold of the earlier US cars for example. Also header design is relatively complicated and almost never done right due to environmental factors. Most designs for closed engine compartments are compromises between available room and exit position, it would be hard to design a header considering pulse cancellation and runner length and still make it fit into a cramped engine compartment.

Most designs I have seen for M30's seem to be more eye candy then drastic performance upgrade, especially the $400 copies in mild steel. I bet you loose more horsepower by heating up the engine compartment then you gain by better flow.

Klaus

I agree under hood tempts have to be a concern and eliminating heat soak would be a priority. I remember reading a GRM issue comparing intake systems and them noting as the car ran fairly large differences in rwhp could be observed as the under hood temps rose.

Comparing the dual log cast manifold is much better than the gas recirculating / thermal reactor system that was on the 78 633 I was working on last week.
Ever read whether using 320 intake runners will improve performance like on the 3.2 liter early M30?

Ever read whether using 320 intake runners will improve performance like on the 3.2 liter early M30?

I can tell you the results in a few weeks, I matched a set of long E21 320i runners to my M90 plenums, also still have the original short set. My guess would be that the longer runners move the torque curve down and widen it a little bit over the short runners, will be interesting to find out if there is a different result.

Klaus

I just put the M90 powerplant in my 78 633 and I don't see how the manifolds are that efficient. I'm not a mechanical engineer (just a materials guy) but having cast log style manifolds are fairly inefficient and decrease volumetric efficiency compared to a manifold with individual primary tubes for each cylinder. :dunno
My 80 Euro dual cast manifolds are pretty efficient as they are as close to equal length runners I have ever seen in cast manifolds. They actually transition in a smoother path than this picture indicates.

I like kbert777s solution alot.
If I don't already have a good set of cast manifolds, I'll get a set coated.
I also just got a miller welder so custom is the way of it for the rest of the system.
Now, where do I find a Dual-In Dual-Out catalytic converter that also works as crossover? And how about two parallel mufflers in a single case.

CW6er: I hate you! I was going to get a used 3.5L for $600, but now that I know about
the Metric Mechanic option, MUST get it! $$Aargh!$$

Now, where do I find a Dual-In Dual-Out catalytic converter that also works as crossover? And how about two parallel mufflers in a single case.



Have a look at this one, for example:
http://www.discountconverter.com/universal/universal_detail.cfm?productID=3377
http://www.discountconverter.com/discountstore/ProductImages/8015.jpg

It's a single brick converter with dual 2" in and out. I wasn't able to find anything in 1.75", so I ended up flaring the 1.75" to 2" using a torch and tail pipe stretcher.

Klaus

I can tell you the results in a few weeks, I matched a set of long E21 320i runners to my M90 plenums, also still have the original short set. My guess would be that the longer runners move the torque curve down and widen it a little bit over the short runners, will be interesting to find out if there is a different result.

Klaus

Ever get around to putting the different intake runners on?

I have a set of new Racing Dynamics headers that I just got ceramic coated. I'm not exactly sure when I'll be able to put them on, but I'll report back with any changes in sound or power when I do.

From what I've heard though, the Racing Dynamics tubes are supposed to be pretty close to perfect equal length

Hey Klaus, I found a set of used euro manifolds cheap from the first five guys. Did you jet coat yours or something else.?/ Did you go light color or dark??

I can tell you the results in a few weeks, I matched a set of long E21 320i runners to my M90 plenums, also still have the original short set. My guess would be that the longer runners move the torque curve down and widen it a little bit over the short runners, will be interesting to find out if there is a different result.

Klaus

This is a trick I have heard about, can't remember where though (old brain syndrome). I have four and am looking for more.
Did you have any issues mating them? Do they all work in all positions? I remember seeing in your thread the issue with the pressure regulator.
Old hot-rodders need to know!

This is a trick I have heard about, can't remember where though (old brain syndrome). I have four and am looking for more.
Did you have any issues mating them? Do they all work in all positions? I remember seeing in your thread the issue with the pressure regulator.
Old hot-rodders need to know!

I have a complete set of 6 and I think I also have a few extras.

This is a trick I have heard about, can't remember where though (old brain syndrome). I have four and am looking for more.
Did you have any issues mating them? Do they all work in all positions? I remember seeing in your thread the issue with the pressure regulator.
Old hot-rodders need to know!

Grassroots Motorsports did this to an old five series they were hot rodding and there is a right up over on the first fives board. I never remember reading about a problem with the pressure regulator so I don't know.

I really want to know if this makes an improvement or not since it seems to rather cheap and straightforward!

Ever get around to putting the different intake runners on?

This is a trick I have heard about, can't remember where though (old brain syndrome). I have four and am looking for more.
Did you have any issues mating them? Do they all work in all positions? I remember seeing in your thread the issue with the pressure regulator.
Old hot-rodders need to know!

Yes, the runners are installed and line up perfectly, some minor port matching was required. All positions are interchangeable. The only thing you loose are the attachment points for the fuel return hose and some of the wiring, I ended up making some new brackets to hold everything in place.

The bad news is that I have not had any time to put the engine in, it still sits on the stand, nicely covered up. I got involved in a fuel injection conversion on a '69 Mustang, which should just have taken a few days, unfortunately I ended up rebuilding the whole drive train before changing it over. We also had some family emergencies that needed to be adressed...

Hey Klaus, I found a set of used euro manifolds cheap from the first five guys. Did you jet coat yours or something else.?/ Did you go light color or dark??

Bert, I didn't have the manifolds jet coated, I used a local guy that coats exhaust systems for the local chopper guys, lately everybody seems to like the flat black look of drag pipes. The coating is ceramic, don't know how it's going to hold up, I will let you know.

Grassroots Motorsports did this to an old five series they were hot rodding and there is a right up over on the first fives board. I never remember reading about a problem with the pressure regulator so I don't know.

I really want to know if this makes an improvement or not since it seems to rather cheap and straightforward!

There is no interference with the stock fuel pressure regulator, I just want to point that out. I decided to use an external pressure regulator in order leave myself some room for later performance upgrades. The 320i runners install without any major modifications, the only changes involve the fuel return hose and wiring loom.

As soon as I have the engine installed, I will run some base line tests with long and short runners and different ECU's, will be interesting to see what actually happens.

Klaus

I have a complete set of 6 and I think I also have a few extras.

If you have two extras and don't want arm/leg/first born for them, pm me. Thanks. Bill