Pulled my header out of storage today to start matching it to the new engine/head (N42) and found there is a big difference between the openings. Looks like the header was made for a stock head and not one as worked as this one.

Here the template is over the header,

Lots of grinding!

Now I do have .4" of header flange to grind away on an angle but the final result will be a funnel that will still shove these wide exhaust ports into 1.5"OD pipes.

The car while I own it may see some track and some tearass driving on quite rural roads but mostly will be used for highway cruising, should I think about a larger header or am I splitting hairs?

Thanks,

Chris

Seems to me that if the heads flow well from the valve openings to the manifold surface, that constricting flow that soon will negate much of the work. On the other hand, if the "work" at the manifold surface is not matched in the bowl, and around the valves (unshrouding), then it may not matter anyway. I know that you shouldn't have flange at all projecting in to the flow path, not even a piece of gasket. It will create turbulence and ruin the flow. Who did the head work, it seems like they would have some recommendations? I looked at your Resto thread but don't see any mention of engine work.

Don't forget to check the collector area of the header. If the flanges look like that it wouldn't be surprising to find a major clog at the collectors also. That header doesn't even look good for a stock head does it?

The head was built by Whitehead performance here in Ontario, it was properly done, they have built a lot of L6 race engines. I was going through the archives this morning and found several mentions of how well the original exhaust manifold flows so I put them next to one another

The port is certainly bigger than on the header but I will have to plug the pollution control bump and grind it smooth.

It's another option.

I ran into the exact thing when I was rebuilding my engine. I ended up sticking with the original OEM exhaust manny with a big 3" pipe and it has worked well with a basically stock head - no duh right! BUT since you went to the time and expense of having your head worked over at a performance shop, I would suggest you try to at least compare another header before settling back to the original, in the end I don't believe it will make that much of a difference - especially if you go with a big pipe to the tail. I have to say though I am pretty damn happy with the way mine turned out.

I ran into the exact thing when I was rebuilding my engine. I ended up sticking with the original OEM exhaust manny with a big 3" pipe and it has worked well with a basically stock head - no duh right! BUT since you went to the time and expense of having your head worked over at a performance shop, I would suggest you try to at least compare another header before settling back to the original, in the end I don't believe it will make that much of a difference - especially if you go with a big pipe to the tail. I have to say though I am pretty damn happy with the way mine turned out.

I wish I had bookmarked the threads on headers that I was reading in the archives because they were very convincing. One comment by John Coffey

(sorry john if I spelled your name wrong) he was responding to the OP who was building a street engine like mine and he basically said take the money you are planning to spend on a header and put into opening up the cast iron manifold and be better off. There were other comments (not by John) of guys running 300 hp street engines with original manifold with no problem.

Since I will be running the engine at WOT at high RPM maybe 2% of the time

it just seems that a header would be there more for looks and since it's going to be covered up by the heat shield anyway... but your right Andrew, I will do some more research. I figured the header I had would be plug n play, didn't even consider that it had been made for a stock head.

Zed, I put it up to the original L24 head (N31 ?) and it matches the exhaust ports well.

Chris

Just to close off this thread, I did work the original exhaust manifold to match the head ports, here it is,

Grannyknot,

Could you provide more detail on exactly what process you used on the original manifold? Did you do it yourself, or have a specialist do it. Any more pictures available?

Thanks.

Peter

Grannyknot,

Could you provide more detail on exactly what process you used on the original manifold? Did you do it yourself, or have a specialist do it. Any more pictures available?

Thanks.

Peter

These are the tools I use, far left are the die grinders for removing metal quickly, then the stone grinders for smoothing and then the emery sandpaper rolls to semi polish. If you don't have air tools you can use a hand drill but it's much more awkward. Youtube has all kinds of how to vids on porting and polishing.

It's pretty hard to screw up a cast iron exhaust manifold but very easy to destroy an aluminum cylinder head, you've been warned.

Also, it's much more important to have your ports match one another smoothly then just to make them bigger.

Chris

Edited March 31, 201311 yr by grannyknot

I'd like to see a tech article on working the stock manifold. Looks easy enough but someone with the experience would have some helpful tips. I could do that while the real mechanic is overseeing the head work.

I'm going for mid-range torque. Don't need to go 130 mph or keep it between 6000 to 7500 rpm. All the headers I've seen have the big primaries for racing. Unless I can find a header made for mid-range torque I might stay with the stock manifold.

Stanley. I've seen pics of this set up that pumps a slurry of abraisive sand through a manifold and smooths it out, I would love to get that done but haven't been able to find anyone that does that kind of work, I suppose some kind of bottle brush honing tool being spun by a hand drill might work.

I rigged up this cat of nine tails by using a piece of 3/8ths aircraft cable, it made very short work of 43 years worth of carbon build up in the exhaust manifold,

Like it. The more frazzled it gets, the better it works.

I rigged up this cat of nine tails by using a piece of 3/8ths aircraft cable, it made very short work of 43 years worth of carbon build up in the exhaust manifold,

[ATTACH=CONFIG]62147[/ATTACH]

Hi Chris,

That thing looks dam scary to use. Cat of nine tales is the right name for it if it ever came out of the port while using it.

Long ago I have seen a similar thing with 1.6mm wires and on each end a round ball shape stone that would grind metal away and that way smooth out the port. It would fit a hand drill and had about 12 stones and 30cm long and was flexable enough to go around bends from what I can remember. Something like that could smooth out the inside of the exhaust runners.