slant six exhaust manifolds

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1930

1930

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I have read an awful lot of data either conflicting or confusing ( for me ) concerning the later slant exhaust manifolds.

I have seen first hand Super six engines in the salvage yard pilfered for parts only to leave the exhaust manifold behind cause the guy removing the parts said that all later manifolds are the same.

I have collected a few manifolds now and am doing some comparisons. Maybe you can see differences with the picture of the outlet diam.

These manifolds pictured above have exhaust outlet diameters in sizes ( from top to bottom )

1 15/16
2 3/16
1 15/16/2ish Closer to 2 depending on where measuring instrument is held, all of these manifolds have a certain degree of out of round
And lastly the one that is still attached to the head I just removed which reads in at 1 15/16

What gives with these variations of sizes? I have read that Super six had a larger exhaust outlet ( 2 1/4 ) I have yet to see this manifold and I have measured a few Super set-ups.

If there is a 2 1/4 outlet manifold than are the intake exhaust ports a larger size as well? I would assume not since there was not a special Super six head.

Can a smaller diam exhaust manifold ( one of the 1 15/16 jobs ) be opened up at the outlet end to the 2 1/4 size and then blended back up into the manifold.

I dont see why not but I have to question if the effort would be worth the outcome....evidently it must be if there truly is a special Super six manifold.

I ask these questions also cause the one manifold I have that measure 2 3/16 ish is in very poor shape, it looks like someone tried cutting off the studs with a heatwrench and scathed the collector mating surface pretty badly in two areas

Also this manifold is pretty badly warped which can be seen with the straightedge.

I have another manifold that is alot straighter that I would prefer to use

According to Docs manifold instruction ( over on slant.org ) sheet 1/8 of a difference between first and last runner is about the maximum amount for a user. I am pushing those limits on my best manifold.

There is quite a bit of meat there Id like to know why I couldnt split the differences with my de-burring bits and make some of these manifolds more use-able. Can someone explain to me why this would not work?
 
It will. You can also use "2" intake/exhaust manifold gaskets at the head sandwiched together. Learned that trick at the dealership in the 70's.File it as straight and close as you can. Remember to keep the special washers in the proper order when reinstalling and all will be good.
 
Darter6 said:
It will. You can also use "2" intake/exhaust manifold gaskets at the head sandwiched together. Learned that trick at the dealership in the 70's.File it as straight and close as you can. Remember to keep the special washers in the proper order when reinstalling and all will be good.
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It will what? ??

I may have confused you, here is a better picture

The red arrows at each end of the manifolds show that the manifold runners in the middle are lower cause the ends of the manifolds have warped a bit.

All of my manifolds have done this to some degree.

Can I or why cant I make the outlets ( marked in yellow ) a bit larger to match the outer runners. Im assuming that an exhaust port in the manifold that is a bit larger than the port leaving the head would not be an issue.

I am assuming that if this manifold were bolted to the head and with the two outer runners being curled a bit as they are that the middle runners may not line up with the middle exhaust ports in the head possibly causing a restriction.

Better yet why cant I bolt the intake and exhaust manifold together and then run my straightedge end to end finding again the two outer exhaust manifold ports and cleaning out everything in between whether it be intake manifold or exhaust manifold?
 
Just answered your question "Can someone explain to me why this would not work?"
It will.Sure you can. You can file the flange marked with the red arrows to get all 6 flanges closer to being even with the straght edge. At least that is my interpetation of your question. The design of the intake and exhaust manifolds with those special washers is during the heat cycle the manifolds move. They were trying to keep it from cracking.And it was mostly successful for the first 20 or so years of the engines life.After thousands of cycles then the cracks start. I have taken some apart that from the constant chaffing there was hardly any gasket left.
 
nm9stheham said:
You want to open the exhaust ports in a way so that the manifold port edges are inline with or slightly larger than the port edges on the head all around, so that there are not any 'steps' for the exhaust air to hit. Of course, then you have to worry over the gasket.....

Chekc out this /6 exhaust manifold article....
http://www.slantsix.org/articles/Sl...n/Slant_Six_Exhaust_Manifold_Installation.htm
Click to expand...
Yes I have seen printed that article.

The article states..........Check any used manifold for warpage, use the gasket as your "inspection tool". If the end exhaust ports are more then 1/8" higher then the intake port next to it, best find another manifold..............

Ok my end exhaust ports are 1/8 higher ( on some of my manifolds ) . Why suggest to find another manifold? It would be easy enough to dremmel out the ports so that they would still match the exiting port on the head.
 
Darter6 said:
Just answered your question "Can someone explain to me why this would not work?"
It will.Sure you can. You can file the flange marked with the red arrows to get all 6 flanges closer to being even with the straght edge. At least that is my interpetation of your question.
Click to expand...
Yes this was my question, is there an issue with opening up all the exhaust ports just a bit so that as the manifold slides there is no chance of there being a step or ledge that the gases would have to go around as they exit the head at any given time during the heat cycle.

I understand that the manifold prob. moves/slides a very minute amount but I wouldnt be surprised that it was enough to make this ledge at some point ( especially with a warped exhaust manifold ) since the exhaust manifold exit openings ( in the manifold) do not appear any larger than the head exhaust ports.

I have not read any threads where opening up these manifold ports was common practice or recommended so that is why I am being cautious.

Have you done this with your own in the past?

EDIT: I know there are ( at least ) two different ways of matching the intake exhaust manifold ports to the head, one is called gasket matching and the other is port matching.

Not certain yet which one of these two I should be going for( maybe both ) ......port matching has me confused cause again why wouldnt we just open up intake ports at the head slightly so there would be no chance of a ledge incoming fuel would stumble on.

And

Exhaust ports ( on the manifold ) a bit larger as well, then the exhaust port on the head so that again no chance of fuel stumble as the exhaust manifold slides.

I hope this makes sense.

To re-cap hog out exhaust manifold ports a bit
Hog out head intake ports a bit
No chance of ledge
 
This bit of info is going to help.

Many people take their manifolds off and just put them back on or replace them with new ones with no headaches. After I tried it and checked everything first I don’t know how most people get away with it. I have to assume most fit better than the new manifold -or the manifold that was replaced before it - but my intake was off also - original from the factory. The first exhaust replacement (that broke and I replaced) was Chrysler - not an aftermarket and was way off.

It is best to make a cardboard template of your head to use to make sure your ports line up. (especially if you have the hotbox milled) I used thin cardboard from a shirt/gift box. Make a center hole to fit over the center stud, end holes for the last two outboard exhaust studs and cut-outs for all other studs. Place it on the head and use a ball-peen hammer around each port to cut it out of the template. Then place it on the manifolds and you might be surprised and your manifolds fits perfect - you might be surprised that it’s nothing like the head.

The center hole on the intake which lines up everything may not be in the correct place. I’ve tried two different manifolds and neither was right. Your intake manifold ports should line up exact or a little smaller than the head ports. Your exhaust manifold ports should be a lot larger than the head ports - mostly toward the center of the head. As you figured out, the manifold has to expand.

It can expand about 0.170 inches at 1100 degrees. If all is perfect they expand equally from the center in two directions - so half that for each side. Point is - if they fit perfect cold, they will be covering the head port a little or a lot when hot. The intake ports don’t expand.

I figured .200 inch expansion to be safe -.100 each side / 12 = .0084 per inch. The port closest to center won’t move much. Each port from there out moves a little more. The last (#1 &#6) ports move the entire .100”. Measure how many inches each port is from center then cut that much out of the inboard side of your template. I added a little more to each one just to make sure they never block the head port.

It will be very hard to find someone to mill the hotbox mounting surface in my experience. 0.003 off at the hotbox moves your ports out of whack about 1/32 inch. Depending on which side of the square they cut wrong it can be up and down or side to side (exhaust port is 1/32 higher than intake port on one end and lower by the same amount on other end.) Make sure you check this or make the machine shop do it.

If all else fails it’s pretty easy to file .003 off of one side to make them line up. If it’s off more than that you may have to return to the machine shop. Hopefully your surfaces are smooth but that isn’t a guarantee they are right either.

You can (And I think most do) just “port” or grind out any material that is in the way to fit your template but sometimes there isn’t enough metal to waste. You will most likely have to port them some. Do this with the hotbox gasket in place...

I just did mine and it made a world of difference but they were pretty “fritzed” to start with. I have an un-synchronized first gear. I’d have to come to a complete stop just to get it in gear when sometimes I just wanted to make a “rolling stop”. NOW, my truck will take off from a complete stop in second gear with no problem when it wouldn’t before. It made a huge difference to make sure the ports are lined up correctly. It takes a little time, a good exacto knife and a good ruler or calipers that measure in .001”s but it’s worth the extra work in my opinion.

Replacing the studs is a good idea. Also get brass nuts so that it doesn’t rust together next time and coat everything with high temp Anti-Sieze compound.

Then hope there never is a next time.

Explaining this to most mechanics would probably be a waste of time. They'd think you were a nut and I'm sure many here think I am - they might be right.

Explaining it to a machinist would be easy. S/he may already know.
 
A.T. PMed me about this and I explained my reason why I have not given much info. about porting factory manifolds, it's because I never spend much time doing that. Here are my reasons:

A factory 1 bbl intake has way more port volume and passage flow then the 1 bbl carb. The port opening is not a restriction.

For best fuel vaporization and suspension, it is nice to have the intake manifold ports / runners smaller then the head port and valve pocket, that keeps the volocity up thru the runners.

Having a "step" on the floor of the intake, where it meets a larger intake port at the head, helps get liquid fuel that is running along the manifold floor, back into suspension. The mis-match acts like a "ski jump".

With factory exhaust manifolds, spending more then 30 minutes on one is a waste of my time. Reach-in with a burr and knock-out any "rough stuff", then break the sharp edges at the port openings. Spend more of your time on resurfacing and doing a careful installation.

We all know that the factory exhaust manifolds are limited by the simple fact that all 6 exhaust 'pulses' have to make their way out one, 2 inch opening. We also know that it is highly likely that the factory exhaust manifold will warp, crack and break sometime during the life of the car so keep this in mind as you spend time on it.

If I were changing a manifold set (or gasket) I would look at installing the lighter aluminum intake manifold or at least use a 'large hot-spot' cast iron intake. For MPG, make sure thr heat valve is working.

Install the manifold set as high on the head as possible and use a large exhaust pipe (2 1/4 works well)
 
Would you mind posting the casting number for the one with the large outlet?
 
RustyRatRod said:
Would you mind posting the casting number for the one with the large outlet?
Click to expand...
A bit difficult to read, I can do a better job over the weekend to clean them up and make the more legible if need be ?

The manifold you asked about I believe reads 3671862-6 in big letters 76 ( maybe )
Another more legible manifold reads 4027567-3 78

What do these casting numbers tell you(?) is the large print ( 76 and 78 ) a casting date 1976 1978

Is there are listing of the various casting numbers for these slant engines that I could see to help me better understand what these numbers mean specifically?
 
Don't quote me, but 76 Feather Duster had a big exhaust, perhaps all slants in 76 had bigger manifolds? And thanks for the photo with ports mismatched! I thought you were saying warped across the mount side, never thought about up and down on ports! Something to think about!
 
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