B6 Exhaust Manifold Mods

[Christ]

Works great on stationary toilet bowl flanges, too. Ones where no flexing is required, unlike the VW toilet flange, which serves as a pivot.

[blkfordsedan]

Although I didn't get a chance to do much more yet, I did do some comparisons of the manifold-to-downpipe connection to determine how I am going to attempt to match things up. I made a paper template of the flange on my new custom 2.125" ID downpipe and slipped it on the factory manifold outlet to see how things lined up. I never noticed before, but appearantly the factory downpipe was not perfectly centered on the flange. It appears to be slightly offset rearward (toward the engine block). Due to the larger diameter of the new 2.25" OD mandrel bent elbow, my brother had to center the opening in the flange to allow a nut to be installed on each of the three manifold studs. The result is that the rear (engine side) of the holes line up, leaving all the material to be removed on only the front side.

At first I was worried, but upon closer inspection, I don't think it could have worked out better. :p The thickest part of the casting is at the front, and there is plenty of "meat" to get things matched up. Also, when you look inside the manifold outlet, the back wall of the collector chamber lines directly up with the opening......but the front wall of the chamber is actually skewed rearward in order to match the offset location of the factory downpipe. Opening the front wall of the chamber up to match the new downpipe will actually provide a much straighter flow path.....which is a good thing! So, not only will I be removing a choke point and gaining more flow volume with the new downpipe, but it will be creating a better, more direct flow path as well.

I'll probably end up with set-up that loses all the low end torque and MPG advantages of a stock manifold and still doesn't flow as well on the top end as an actual tube header, LOL. But, even if I gain nothing from any of this in terms of performance, I'm having more fun messing with it than I've had in a long time!

I'm having internet issues right now, but I'll post some more pics to help explain when I can.

[blkfordsedan]

Here's a couple pics to help explain....

[Bert]

In my opinion this is 'cutting edge' stuff. We (collectively) never stop learning. Merely bolting on JY adaptations/improvements is obviously not enough when you're thoughtfully aiming high. Thank you imparting these experiments on to the rest of us.
Rightfully so not everything about Festys revolves around ground clearance, the size of the wheels or how big the motor is or how much boost a tagged-on turbo puts out.

[blkfordsedan]

It's all just half baked theory and speculation at this point. It would be nice to be able to actually test
some of this stuff to validate any changes, good or bad.

[BigElCat]

I'm working on a proto-type divider to see if it's feasible to extend the primaries. I post some pics maybe by this weekend.

[blkfordsedan]

Sorry Cat, took me a while to figure out what you were talking about, LOL. Now I get it!
Nice idea!

[Christ]

Deja vu...

[BigElCat]

Here's the proto-type.

I don't have a B6 manifold, so this is just food for thought.

I use 1" angle iron, and milled the point off of one piece.





The gasket is from a B3. This divider will not work with the B3 manifold. I could post some pics of the B3 manifold, if anyone wants to see why its performance potential is limited compared to the B6.

IMHO, the B6 eManifold could be developed to the point where it would out perform a tube header.

The primaries could be made equal length by cutting one wall out of this divider. The primaries from cylinders 1 and 4 are the longer of the two sets. (They are the ones closest to the engine block.)

Look at my divider. The wall between 1 and 4 primary could be cut back allowing the pulses from 1 and 4 to combine above and before the pulses of cylinders 2 and 3.

In effect, we could make the B6 manifold a Tri-Y header. The primaries could be equal length. The second legs of the Tri-Y would not be equal length. We could make one pair of primaries slightly shorter than the other pair, which would enable us to make the second leg of the Tri-Y more balanced.

I'm strugglin' to explain this. I'll post some sketches.

BlkFord...if you want this prototype, I'd be glad to send it to you.

[BigElCat]

It would be a bolt-on mod. The dividers wouldn't actually seal to the outside round walls of the head pipe or manifold, but they would channel 95% of the exhaust flow.

Different ones could be designed and swapped out easily.

Nothing beats a long primary. Try one these clear down to the mandrel bend in the head pipe!

[blkfordsedan]

You realy need a B6 manifold to look at. It's a totally different beast than the B3. You'd have to put some bends (or an "S" curve) in the angle extensions to get it to fit. You may also have to relocate the O2 sensor, which may create issues. I like the idea of making a Tri-Y design using a single divider plate, however. You should see if you can find a used B6 manifold.

BTW- there may also be a difference in design & construction between the 2nd GEN manifold and the 1st GEN like I have.

[blkfordsedan]

Well, the wife was out of town all weekend, so I got some time to devote to the important things in life......like working on the Festy! I wasn't able to do exactly what I wanted in terms of modifications, but I did the most I could, given the thin casting.

The first thing I did was remove all the external casting flash. No real functional purpose, but it should decrease the chance of cutting my hand or knuckels on the razor-sharp casting line!


Next, I cleaned up the entry of the exhaust ports. They were pretty good, but I did grind out a little casting flash, followed by a quick polish with an 80 grit sanding drum.


The outlet was then enlarged from 1.75" to 2.00".......mostly on the front side as I decribed in the earlier posts. Since the casting is soo thin in the collector chamber, I could only grind in the area of the flange. I was mostly able to bevel or radius the opening through the thickness of the flange. The over-all "choke point" was still increased from the original diameter, but not as much as I was hoping for. Here is a "before & after" pic with the downpipe gasket used for comparison. NOTE: There is a black magic marker ring around the paper template. In the second pic, the opening is actually flush with the hole in the template (optical illusion, lol).
BEFORE:

AFTER:


Once the opening was enlarged, I had much more room to get the 1/4" HF die grinder in position to work on the collector merge. I cleaned up as much of the casting flash that I could get to. I wasn't able to do it as well as I wanted because the space was still pretty tight, but it was still an improvement.

The side with the sharp, flat wall was re-worked as much as I could. Once again, casting thickness limited how much I could do. It's hard to tell from the pics, but the sharp wall edge was radiused a fair amount and the approach from the chamber wall to the outlet was reshaped for a much smoother and gradual flow.
BEFORE:

AFTER:


The rest of the photos show the general imrovements made. The pictures don't really do it justice, however. The flow from the front of the chamber was really opened up.



Finally, I painted the manifold with VHT Flameproof 1500* header coating. It has Silica (sand) and ceramic, and should be baked in the oven in several steps to help it cure. I would have preferred a cast iron grey color....but this is what I had.


The next task is to do some work to the intake manifold.........then assemble the engine!!! At this rate, it should be done by next summer, LOL.

[Kraig]

The B6 manifold will bolt on a B3?

[BigElCat]

The B6 manifold will bolt on a B3?

Yes. There two styles of B6 exhaust manifolds, 1st generation and second generation. Both will bolt to the B3.

[blkfordsedan]

I believe the 2nd gen has a slightly different bolt pattern, but I could be wrong. Some have put the 1st gen B6 on a B3, but it supposedly kills the low end.