Not all Manifolds are created Equal

[pianist]

Hi all
I'm in a middle of m30 conversion here and I have aquired a second hand inlet manifold:



I have cleaned it and all and I know you guys like the pictures so there it is:



The reason I didn't want to use the inlet that the donor car came with is that it had an early version of LPG fitted in it and the manifold was fitted with two blow off valves which makes it look like a disaster!
In the pic the left mani is the one the engine has came with:



So now to a point. Just today I have received a new set of gaskets that go with manifold and went into garage to fit it, I come to the engine and tried the gasket on it and it is near to perfect fit, by which I mean the gasket folows the intake hole with no overlaping at all. Now when I tied it on the manifold it self I was gob smacked and very upset of what I have just seen. Infact so upset that I went and learnd how to post a photo on this forum lol

Spot the difference:



The one at the top is the original manifold and the one at the bottom is the one that I have aquired, so can you see the difference?

The original one has very nicely shaped holes on it almost like "jely beans" that folow the shape of the cylinder head intake hole.
Now I will show you how badly missmatched manifold this is by atatching the gasket to it:

"New" manifold:



And now "old" one:



You can see that the old manifold folows the gasket closer to the edge where the new one has big amount of "meat" around it

This manifold is already restrictive like hell with that 90 degree bend on it and now the bloody runners are sufocating it

My question to you guys would be:

What should I do? Do I just use my old manifold and every time I open the bonnet I just look away and pretend there are no blow off valves on it that make it look like cr*p?
Or is it not that expensive, or even posible to DIY, to match the manifold to the head?

[DanThe]

I wouldnt be worried by that TBH, looks more like somebody has been at the original with a die grinder, all the ports look different shapes, unless its just the photo

[capnmchl]

Unless you're going to go to all the trouble of bluing it up, matching the ports, and fitting roll pins or dowels to keep the manifold aligned rather than the studs, then there's no need to worry. The moment you fit it it'll probably all go skewif anyway.

[jmc330i]

Do the gaskets match the head?

As Dan said, it looks like someone has been at your original manifold, maybe when they fitted the valves for the LPG?? That said, the other manifold looks like the ports are different shapes too.

[pianist]

Yes gaskets are nearly perfect when I put them on the studs.

I don't know how wel manifold matches the head though cause it is very dificult to tell but I doubt that anyone had a go at the original manifold since the last owner was my step dad ( who fitted LPG) and one and only before was an old guy from germany. I think that that original manifold looks bit out of shape because it has that black carbon all over the inside of the runners and it makes it look like that in pictures but when I hold it in my hands it looks better finished, besides the "new" one looks just oval holes not folowing the gasket at all if you know what I mean, probably it was made on friday evening lol

Unless you're going to go to all the trouble of bluing it up, matching the ports, and fitting roll pins or dowels to keep the manifold aligned rather than the studs, then there's no need to worry. The moment you fit it it'll probably all go skewif anyway.

I just expect better quality it being BMW. So you saying that the manifold will not match the intakes on the head anyway without modifying? It just looks like them little holes will sufocate the engine, I'm on budget here so I just wanted to go for the best I have atm


Edit: I just had to ask this: will it be posible to DIY them shapes using some sort of grinders? Is that the right way to do or do you need to go realy far into runners to make it worth while?

[pianist]

I wouldnt be worried by that TBH, looks more like somebody has been at the original with a die grinder, all the ports look different shapes, unless its just the photo

Its not just photo lol but the new manifold has even more out of shape holes on it

[pianist]

Right just been into garage to double check gasket fitment, and when I place the gasket on the head inlet studs it folows the shape as if it was made on my cylinder head, so I can actualy use my gasket to deside how well the manifol aligns with ports on the head and if you read my post above there's only one winner, the "Ugly Duckling"! so I guess I will need to swalow the bitter pill and get on with it. Just wish there was an easy way to save the other one

[Speedtouch]

It would be fairly easy to enlarge the ports a bit using a Dremel or similar grinding stones tool - it's only fairly soft aluminium alloy.

However, the smaller ports probably won't be that restrictive anyway, so you could just fit the new manifold and be done with it.

[AardHawk]

B34 or B35.

[Brianmoooore]

You could always do your engine a massive favour, and continue to run it on propane, rather than that acid into the oil and bore washing low octane petrol stuff.

[capnmchl]

Unless you're going to go to all the trouble of bluing it up, matching the ports, and fitting roll pins or dowels to keep the manifold aligned rather than the studs, then there's no need to worry. The moment you fit it it'll probably all go skewif anyway.

I just expect better quality it being BMW. So you saying that the manifold will not match the intakes on the head anyway without modifying? It just looks like them little holes will sufocate the engine, I'm on budget here so I just wanted to go for the best I have atm

Even if the manifold, head and gaskets are all the same shape, the studs are still probably 8mm and the holes for in the manifold are around 8.5 or 9mm. So unless you're going to lock the manifold in one place on the head by using dowels, it'll end up sitting skewif and causing obstructions. But this is talking about high performance engines where you want the boundry layer within the intake system to stay as intact and thin as possible. As long as they're not completely blocked you'll fine with them as they are.

[pianist]

Ok thanks everyone for input

As I can gather I won't loose any power cause of them holes as long as mine engine is fairly stock

To answer another question it is b35 and in the future it will have lpg but it'll have it injected and I will not need blow off valves

[Speedtouch]

Look on the bright side; narrow inlet tracts usually provide better low-end torque due to the venturi effect.

[pianist]

don't think that with m30 I would be short on torque

[bss325i]

B34 or B35.

This!

One inlet manifold is from an E28/E24 up to 6/87 and the other is from an E32/E34/E24 from 6/87.

Difference CC, different head, different inlet manifold.

[pianist]

But it says 3.5 on both manifolds, is there a way to tell from what model it is by a numbers maybe? My engine is m30b35 from e34

Anyhow, I was researching this topic and aperantly there is a benefit for a street engine if it has smaller manifold than intake port on the head because the step stops reversing pulses in manifold in lower rpm, so if I beleve in this, until I start chasing more horses I should be fine

[DanThe]

If your that bothered about it get it on a dyno, back to back runs with each manifold
Running them back to back on the road you wont notice anything

[maggspower]

But it says 3.5 on both manifolds, is there a way to tell from what model it is by a numbers maybe? My engine is m30b35 from e34

Anyhow, I was researching this topic and aperantly there is a benefit for a street engine if it has smaller manifold than intake port on the head because the step stops reversing pulses in manifold in lower rpm, so if I beleve in this, until I start chasing more horses I should be fine

Ah, reversion theory

[pianist]

If your that bothered about it get it on a dyno, back to back runs with each manifold
Running them back to back on the road you wont notice anything

Think you right there, I wouldn't be able to feel it on the road and dino isn't cheap, not that I know lol but I gues it isn't, so tomorrow I'll fit the prity manifold on and start sorting wires out

Thanks all for input

[DanThe]

I would expect to be paying £50ish for a back to back run, but like you said, if you have other jobs to be doing then crack on. You can always come back to it at a later date if its still bugging you

[bss325i]

But it says 3.5 on both manifolds, is there a way to tell from what model it is by a numbers maybe? My engine is m30b35 E34

Both inlets have 3.5 cast onto them.

Check the part numbers.

[pianist]

But it says 3.5 on both manifolds, is there a way to tell from what model it is by a numbers maybe? My engine is m30b35 E34

Both inlets have 3.5 cast onto them.

Check the part numbers.

Will check the numbers when get my other manifold from cleaners

For now I have fitted the "nice" one, I thought if I'll go for power hunt in future i'll try to make a new one anyway, without 90 degree bends and stuff

did some pics with phone when fitted

[pianist]

But it says 3.5 on both manifolds, is there a way to tell from what model it is by a numbers maybe? My engine is m30b35 E34

Both inlets have 3.5 cast onto them.

Check the part numbers.

Part numbers do match