Exhaust manifold: AHU/1Z vs. AFN

Steve Addy · Feb 5, 2020

Hey all
I did a cursory search on the forum to see if something existed but I couldn't find anything about this.

Looking at upgrades for the new project and would like to switch to VNT without having the fitment problems with the right rear engine mount and the Mk4 VNT setup so I'm wanting to know what the differences are between the AFN exh mani and the AHU/1Z?

I've seen the images in the parts catalog but those aren't really that great. Also anyone who's implemented a VNT setup I'd like to hear from on issues they've run into and anything else they think relevant.

Thanks!

Steve

d24tdi · Feb 5, 2020

Looks like the AFN manifold aims the turbo flange back towards the firewall while the AHU/1Z points down towards the ground.

AHU/1Z part number: 028253031S
https://www.google.com/search?q=028...XDvZ4KHXRqBYEQ_AUoA3oECAsQBQ&biw=1366&bih=609

AFN part number: 028253031AJ
https://www.google.com/search?q=028...XDvZ4KHXRqBYEQ_AUoA3oECAsQBQ&biw=1366&bih=609

I would have thought there would be different AFN manifolds depending on whether the motor was in a transverse car (A3/B4) or longitudinal (B5, C5, etc) but it looks like the part number is shared with both types of applications, from what I can see looking briefly at it. Lots of them on German ebay and elsewhere.

Like you, I would probably rather get the right AFN parts and pay a little overseas shipping than try to fudge ALH parts onto it and screw around with the motor mount -- mainly just to save the time. Always less trouble and better result to bolt on something that was already meant to be there, if you can get it, rather than reinvent the wheel....

Mozambiquer · Feb 5, 2020

Steve Addy said:
Hey all

I did a cursory search on the forum to see if something existed but I couldn't find anything about this.

Looking at upgrades for the new project and would like to switch to VNT without having the fitment problems with the right rear engine mount and the Mk4 VNT setup so I'm wanting to know what the differences are between the AFN exh mani and the AHU/1Z?

I've seen the images in the parts catalog but those aren't really that great. Also anyone who's implemented a VNT setup I'd like to hear from on issues they've run into and anything else they think relevant.

Thanks!

Steve

I had a vnt 15 in my mk3 Jetta. (1.6 turbo diesel) I made my own rear engine mount out of 1/4"plate, and it worked pretty well. I sadly don't have any photos of it, since I recently sold the car.
I used the whole mk4 manifold setup.

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jhax · Feb 5, 2020

Bew manifold is the same as afn

Steve Addy · Feb 5, 2020

d24tdi said:
Looks like the AFN manifold aims the turbo flange back towards the firewall while the AHU/1Z points down towards the ground.

AHU/1Z part number: 028253031S
https://www.google.com/search?q=028...XDvZ4KHXRqBYEQ_AUoA3oECAsQBQ&biw=1366&bih=609

AFN part number: 028253031AJ
https://www.google.com/search?q=028...XDvZ4KHXRqBYEQ_AUoA3oECAsQBQ&biw=1366&bih=609

I would have thought there would be different AFN manifolds depending on whether the motor was in a transverse car (A3/B4) or longitudinal (B5, C5, etc) but it looks like the part number is shared with both types of applications, from what I can see looking briefly at it. Lots of them on German ebay and elsewhere.

Like you, I would probably rather get the right AFN parts and pay a little overseas shipping than try to fudge ALH parts onto it and screw around with the motor mount -- mainly just to save the time. Always less trouble and better result to bolt on something that was already meant to be there, if you can get it, rather than reinvent the wheel....

You won't with ALH since all ALH turbos have hot side housing and exhaust manifold combined. You would have to cut the turbo housing off and weld on a flange, which I would prefer not to do actually.

I'd like to do this with factory parts unless it involves some NLA stuff.

I already have the part numbers for all that stuff, but I thought I'd found a different number for the B5 cars with AFN but maybe I was mistaken, I don't remember back that far, and I wanted to be sure and get it for transverse mounting.

jhax said:
Bew manifold is the same as afn

I don't believe that's true. If you look in the parts catalog according to VW the BEW uses the same type of integrated turbo & manifold setup like the ALH and that would be consistent with what I've seen in the JY too for BRM and BEW. Have you seen one where it is separate?

I think the AGR from that period, an engine we didn't get, uses the trapezoid mounting you're thinking of, not a triangle mounting like the AFN. The AGR exhaust manifold is separate and more in keeping with the older 1.6 TD engine manifold.

Here's the AFN manifold, it is similar to the AHU/1Z but as d24tdi said it seems to point the turbo back somewhat instead of down like the AHU.

Thanks for the info guys!

edit: the pic I included does look the same as the one you posted Jhax, but I don't think that's a native manifold for the BEW engine, if that is a BEW.

Steve

Mozambiquer · Feb 5, 2020

Steve Addy said:
You won't with ALH since all ALH turbos have hot side housing and exhaust manifold combined. You would have to cut the turbo housing off and weld on a flange, which I would prefer not to do actually.

I'd like to do this with factory parts unless it involves some NLA stuff.

I already have the part numbers for all that stuff, but I thought I'd found a different number for the B5 cars with AFN but maybe I was mistaken, I don't remember back that far, and I wanted to be sure and get it for transverse mounting.

I don't believe that's true. If you look in the parts catalog according to VW the BEW uses the same type of integrated turbo & manifold setup like the ALH and that would be consistent with what I've seen in the JY too for BRM and BEW. Have you seen one where it is separate?

I think the AGR from that period, an engine we didn't get, uses the trapezoid mounting you're thinking of, not a triangle mounting like the AFN. The AGR exhaust manifold is separate and more in keeping with the older 1.6 TD engine manifold.

Here's the AFN manifold, it is similar to the AHU/1Z but as d24tdi said it seems to point the turbo back somewhat instead of down like the AHU.

Thanks for the info guys!

edit: the pic I included does look the same as the one you posted Jhax, but I don't think that's a native manifold for the BEW engine, if that is a BEW.

Steve

I'm thinking that may be the bhw which is in the b5.5 Passat. Looks just like the one in my Passat, at least.

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Steve Addy · Feb 5, 2020

Mozambiquer said:
I'm thinking that may be the bhw which is in the b5.5 Passat. Looks just like the one in my Passat, at least.

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Appears that it might be very similar, thanks for the heads up. The B5.5 BHW apparently does share a manifold with the AFN but according to VW parts cat it is not direct fit or supercession.

Here's the B5.5 info I found

Engine Manifold part number
BGW / BHW 038253031L
AVB/AVF/AWX 038253031N which supercedes 028253031AJ

The 028253031AJ is the number I have for AFN exhaust manifold. But why that isn't used by the BHW in the US I cannot say. I'm still not convinced that it's the same one but I will say that pictures for the B5.5 BHW exhaust manifold look surprisingly similar.

I will see if the ..31L part number is actual for those or not. The part number should be readily visible on the manifold, I'll ask the JY for the number on the one they have.

Thanks again for the help!

edit: I've just noticed that on the BHW exhaust manifold there's a probe fitted in the exhaust pathway that isn't there for the AFN version. Here's an image of it, you can see the opening in this picture. This could explain the difference between versions.

Steve

jhax · Feb 6, 2020

Yeah I did mean BHW, I get the two confused.

Mozambiquer · Feb 6, 2020

Steve Addy said:
Appears that it might be very similar, thanks for the heads up. The B5.5 BHW apparently does share a manifold with the AFN but according to VW parts cat it is not direct fit or supercession.

Here's the B5.5 info I found

Engine Manifold part number
BGW / BHW 038253031L
AVB/AVF/AWX 038253031N which supercedes 028253031AJ

The 028253031AJ is the number I have for AFN exhaust manifold. But why that isn't used by the BHW in the US I cannot say. I'm still not convinced that it's the same one but I will say that pictures for the B5.5 BHW exhaust manifold look surprisingly similar.

I will see if the ..31L part number is actual for those or not. The part number should be readily visible on the manifold, I'll ask the JY for the number on the one they have.

Thanks again for the help!

edit: I've just noticed that on the BHW exhaust manifold there's a probe fitted in the exhaust pathway that isn't there for the AFN version. Here's an image of it, you can see the opening in this picture. This could explain the difference between versions.

Steve

That probably explains the difference. That would be good for installing an egt probe. I wonder if the turbo from a Passat would work on the ahu... It's a vnt turbo.

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jhax · Feb 6, 2020

Im almost positive a BV43 bolts up but that's not a VNT. The VNT turbo will work but you have find an ASV ecu or reflash an 80 pin ALH ecu with the ASV firmware

Steve Addy · Feb 6, 2020

jhax said:
Yeah I did mean BHW, I get the two confused.

With so many variations from different hp engines and differences between Europe and NA etc I'm not surprised, I can't keep them straight in my head either, I have to write everything down.

Mozambiquer said:
That probably explains the difference. That would be good for installing an egt probe. I wonder if the turbo from a Passat would work on the ahu... It's a vnt turbo.

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The probe yes, a good idea I think for EGT, and since the area is already setup for a probe there's no problem with the casting being too thin.

As for the turbo haven't gotten there yet, don't know what turbo is on the BHW for starters, I was heading to the GT1749v route but that might change too. The original AFN turbo was VNT, the big difference between AHU and AFN to be honest. I was also reading up on the GT2052 and 2056 but finding triangle flange mounting could render those two options moot.

jhax said:
Im almost positive a BV43 bolts up but that's not a VNT. The VNT turbo will work but you have find an ASV ecu or reflash an 80 pin ALH ecu with the ASV firmware

Yes, I believe that certain BV43 will bolt up to that manifold but also true it's not VNT. I was already planning on chip tune to bring hp to 140-150 on stock JB ecu so that's already been accounted for. I'm still inclined to think of GT1749V as best solution at this point. I know that RC2 tune on stock AFN gets close to 140 (+38hp / +56NM torque).

I have also found this thread that i need to read through completely first also.

Thanks for all the comments guys, will be back for more I'm sure.

Steve

jhax · Feb 6, 2020

I mean, with an adapter plate from Whitbread I went with the gtc1549vz

Steve Addy · Feb 6, 2020

jhax said:
I mean, with an adapter plate from Whitbread I went with the gtc1549vz

I have been reading that thread about that turbo, it sounds like more trouble than it's worth being clocked in an odd direction and requiring the adapter plate.

Are you running a tune with yours? I read in the comments on that thread that it's a fairly small turbo that seems more suited to quick low end power? Does it really provide much benefit over the GT1749V unit? Why did you select that over something else?

Do you know what it was originally fitted to? I see general posts online that say it's a good upgrade but since I can't really find specifics I don't know whether that's true or just someone's marketing hype.

Thanks

Steve

jhax · Feb 11, 2020

I chose it because the size accounts for good power throughout the entire rpm range, better for affordability and daily driving and it provides 23psi boost safely. I will be running a tune and 3 bar map with did 1019s and sbc stage 2 clutch with lsd. I originally wanted a vnt17 but didn't want to have to wait until high rpm every time it kicked in. It came off a euro model a4 cr tdi from 2011-14

Exhaust manifold: AHU/1Z vs. AFN

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