SNAFU; high performance 318is build that lives up to the name, Turbo M42 ➞ Turbo M20

[varg]

Maxed out my injectors this week, duty cycle in the mid 90s at 18/19psi of boost. It's still not fast enough.

[Northern]

Heating the metal will cause it to grow, so cylinders 3&4 will see almost no flange movement, but cylinders 1&6 will see a large lateral shift (or at least lateral forces) which could shear exhaust studs

My (24v) rapidspool manifold was much straighter than that, maybe I got lucky?
I think a mild convex shape to the turbine housing flange would help it seal on the sides where it would blow out. The hardware is what, M10 or M12 so I'd probably trial the turbine housing on it and see if the gap closes much? IDK

I kind of buy the thermal expansion idea?
If T304 has a thermal expansion coefficient of 1.6e-5, and the flange is like ~550mm long.
Temp is hard to quantify. Sure you could get some high EGTs of like 1000degC but with the flange having a ton of surface area in contact with the head, will it even come close to half of that?
Even if it sees something in the delta 500degC region, that's ~4.5mm across the entire flange if the flange were free to expand, so 2.25mm per end... Fitment varies, but the holes are quite O/S and there's a lot of hardware restricting it.

I've never heard of someone snap a stud on any of these engines, so unless that or something else crazy happens with my manifold, I probably won't slice it up either.


Edit:
I probably will pick up a D600/610 once I'm done school, just one of many things I want but shouldn't buy right now haha

[varg]

Thermal expansion coefficient is units of length per unit of length. The further out you are on the piece of material the greater the difference in position is as it heats, but lengthwise movement of the flange due to thermal expansion is not the main issue, it's the residual stresses on the pipes, welds and flange from when it was welded together, which are pulling it out of flat. Warps are unavoidable because of the nature of the process so it's better to weld to thicker than required flanges and machine them flat, skilled fabricators know this, outsourced factory workers do not care, if they even know it. And they don't seem to machine the stuff after the welding process. The order of the welds and position of the pipes will change how it warps from initial fabrication. Mine was bowed such that the ends were further from the head than the center. This deformation is preferable because thermal expansion actually tended to flatten the warped header flange, the outer pipes are longer and expand more, and the "pulling in" the welds did relaxed as they expanded unevenly vs the head facing surface of the flange. This is why my header leaked a lot less when hot. It ticked horribly when cold but you could barely hear the leakage after the car warmed up for a few of minutes. Once the flange is machined flat and clamped properly (no missing hardware) it's less likely the thermal expansion of the pipes will tend to make it leak because of the clamping, though the heat cycles can loosen the hardware. I have the added benefit of having mine flattened after many heat cycles; it's not likely it will warp significantly in use from its current state. Post weld heat treatment can reduce the residual stresses and lessen the tendency to warp, but it's not practical for fabricators because of how large the header is.

Slicing it apart is a gamble probably not worth taking. Depending on the amount of residual stress on any given piece of the flange, when you slice the connecting parts it will 'spring' back to where it wants to be, which could be far worse than it was with the warp since the flange is constraining some movement. What if it twists and you can no longer line one flange up with the studs? As an aside, I would be shocked to hear of thermal expansion ever shearing an exhaust stud even on a long I6 flange, improbable. Would require a long flange, with relatively poor fitment and high flange temperatures even with 304SS (high thermal expansion coefficient relative to mild steel).

The exhaust stuff is the only thing that makes me miss my previous turbo 4s, especially my turbo redblock. The shorter flange and well designed ported cast manifold I had back then never gave me a lick of trouble. Perfect sealing every time and it wasn't even that much of a pain to remove.

Also I think the D610 is great, and I've been watching D600/D610 on ebay for a while because they seem like the best deal going if I want to stay Nikon.

Go for it. D610s are good bang for the buck now. I stuck with Nikon because even though the AF lens choice is inferior to Canon, the sensors seem to be measurably better (dynamic range and SNR). Combine that with the fact that you can keep old MF lenses with Nikon vs Canon and I stuck with Nikon. I knocked Sony out of the running early on because for the same money I was going to get less camera and the secondhand lens market is worse. For the same money spent I would get a slower Sony camera with far worse battery life than the D610, and old mirrorless EVFs suck. I didn't even consider any Sony DSLRs.

[McGyver]

Agree 100%, but I think it would also take less force to straighten it when you tighten it again if you're only fighting the runners instead of runners+flange?

Corky Bell has a small section on this and mostly says that sectioning it into smaller flanges prevents it from warping in the first place.
He claims that warping is caused by a combination of a temperature gradient across the flange (hottest in the middle) and between the flange and runners (runners expanding more as the flange heatsinks to the head)

Separating the flange to mess with the thermal gradient across the flange, but I don't see how it would change the second half.
And then you're left with a bunch of small flanges which might relax in the L/R Up/Down directions and give you problems that can't be solved with a belt sander...

This is exactly what I was going to point out / ask. I have the turbo manifold pictured below, and the flange is clearly warped out of the box.

IIRC, Corky's thought process for sectioning a long manifold (he specifically calls out the L6 configuration):

• Repeated heating will warp the flange, causing you to loose flatness, resulting in a bad seal
• Heating the metal will cause it to grow, so cylinders 3&4 will see almost no flange movement, but cylinders 1&6 will see a large lateral shift (or at least lateral forces) which could shear exhaust studs

It also makes sense to me that trying to flatten a 6-cylinder flange has a lot more to fight against (flange and runners) than trying to flatten a 3,2,1-cylinder flange. I was considering cutting mine in half, then belt-sanding the two halves flat to each other. Thoughts?



The turbo flange is an even worse mess....

[Northern]

Also I think the D610 is great, and I've been watching D600/D610 on ebay for a while because they seem like the best deal going if I want to stay Nikon.

[Northern]

Wouldn't cut the flange since it might wind up worse due to residual stresses

Agree 100%, but I think it would also take less force to straighten it when you tighten it again if you're only fighting the runners instead of runners+flange?

Corky Bell has a small section on this and mostly says that sectioning it into smaller flanges prevents it from warping in the first place.
He claims that warping is caused by a combination of a temperature gradient across the flange (hottest in the middle) and between the flange and runners (runners expanding more as the flange heatsinks to the head)

Separating the flange to mess with the thermal gradient across the flange, but I don't see how it would change the second half.
And then you're left with a bunch of small flanges which might relax in the L/R Up/Down directions and give you problems that can't be solved with a belt sander...

[varg]

I'm sure the heat cycles don't help but man was that thing out of wack. Wouldn't cut the flange since it might wind up worse due to residual stresses. I've stuck with the OE style gaskets because of the heat shields, they definitely do not have a lot of give, not enough to make up for a significant warp at least.

As for the camera I bought a Nikon D610 and a 24-70 f2.8 lens. In January I had a good excuse to upgrade to a full frame camera with dual SD cards so I took the opportunity. I liked my D200 but was never entirely happy with the low light performance, the D610 is an immense improvement.

[Northern]

I think the warp is just par for the course with heat cycling a flange that's had a bunch of welding done. Sure it's in a fixture and straight for first install, but I don't think there's anything you can do about the warping other than resurface it after every uninstall.
I know you can cut the flange into several smaller ones but I'm not convinced that does enough to avoid resurfacing the flange fully...

I assume the M20 isn't unlike 24v stuff, where aftermarket turbo gaskets are complete garbage and stock ones seal better 10 times out of 10.

Interested in camera info as well

[moatilliatta]

Photos are fantastic! What kind of camera did you get?

Its amazing how many flanges are warped. Headers or turbo manifold.

[roguetoaster]

Impressive flange distortion, pretty good to know someone with something like a linisher. As to sealing in future, have you seen any additional or alternate gaskets that might be good for an application like yours?

[varg]

This fix has been a long time in the making. I finally got the spare head I bought recently rebuilt at wot-tech, it unfortunately had a bit of a rough cam (pitted) which forced me to do a full rebuild with new cam and valve job. I went with an Ireland Engineering 272° cam.


When I removed the head and pulled the header I discovered that the exhaust leaks were far worse than I had feared. It wasn't just #6 with its broken stud that was leaking badly, there were only two sealed ports. The header flange, when checked for flatness, was bowed by at least 1mm at the ends. Horrible.


Luckily a buddy of mine is a marine diesel mechanic and has access to a massive belt sander that they use for surfacing heads. This was a lucky break, he saved me a considerable hassle taking it to a machine shop and paying for an hour of shop time to have the flange made good.


Dirty engine.


After cleaning the deck and pistons a bit. Did not bother to try and get the pistons spotless.


New Goetze head gasket


Clean new head on the engine.


I'm very happy with the result. So far no exhaust leaks and the engine has a nice mildly loping idle. Can't really tell how much of a difference there is from before with the new cam and valve job because I didn't drive the car for 3 weeks or so before the re-tune, it does seem to have less falloff above 6,000rpm.

[Digitalwave]

Great photos!

[mike.bmw]

The photos look great. I think this one is my favorite of the set.

[varg]

I upgraded to a newer, full frame camera recently, had to do a new photo session with my E30 and experiment with the vastly improved dynamic range and low light performance over my 13 year old D200.
(edit)
This forum software is a giant piece of crap and makes posting photos quite frustrating.

[Bearmw]

I like that efficient way to check heads, a lot like checking for tire leaks. Old tech and high execution.