NB8A Inlet Manifold Height

[GR124]

Hi Guys,
Currently building a Locost Track Car with a stock NB8A donk.
With the engine in the chassis I'm looking at ways to shorten the height. I'll be shorting the sump by 25mm.
The top I can't do much with,,,,,or can I? The Manifold seems to sit a little higher than the cam cover.

Is there an off the self manifold that bolts on to the standard engine that is a little shorter in height?
I'm using the stock ECU and Loom etc.

I noticed a guy selling a NB8B flat top manifold (now sold), I don't know if this would have suited my purpose?

[StanTheMan]

iTB

[93_Clubman]

NB8B VVT manifold should fit NB8A head, replacing the NB8A VICS manifold, but not sure how much lower it will be. Might be able to check later today.

[GR124]

StanTheMan,
either turbo or ITBs are a far away dream at this stage of the build. just aiming to get it on the track and look at go faster options later.

93_Clubman,
If its not too much hassle that would be appreciated. looking to reduce manifold height by around 20mm

I can weld ally so would there be an option to cut and shut any OEM manifold?

[93_Clubman]

Surprise, surprise - just measured the two manifolds:
NB8A: 220mm
NB8B (ie flat top): 230mm
Measurements were from the outer edge of the tab surrounding the bottom holes for the studs protruding from the head to the top of the plenum.

[GR124]

Thank you 93_Clubman
10mm in it. Let me ponder that for a while.

Would anyone know if the NB8B manifold be any better or worse for the performance of the NB8A engine?
Note: being a track car it will be in the high end of the rev range most of the time.

[93_Clubman]

Flat top manifold is the one all the US Miata racers want as they got a manifold that looks like the NB8A on their NB8Bs. There's a recent thread on here on the best manifold for the NB8A head & from memory it turned out to be the NA8 manifold. However, the NA8 manifold holes are in different locations to the NB8A manifold, so some welding is required. I'll try to measure an NA8 manifold, but it's on car so not as easy & I'll have a look for that thread to confirm if it's the NA8 manifold.

[93_Clubman]

NA8 manifold looks to be about 180mm from the outer edge of the tab surrounding the bottom holes for the studs protruding from the head to the top of the plenum.

[93_Clubman]

Would anyone know if the NB8B manifold be any better or worse for the performance of the NB8A engine?

ADM NB8B (Flat top) then NA8 then NB8A:
http://ww.mx5cartalk.com/forum/viewtopi ... facc42deaa

[manga_blue]

I've got an NA8 (BP05) manifold mounted on a NB8A (BP4W) head using an adator plate. The plate moves the manifold out a further 10mm, but no higher.

Butt dyno says the NA8 manifold pulls a lot longer and stronger than the NB8A manifold. Whether or not it's better than the NB8B manifold I don't know.

My adaptor plate was $175 shipped from the UK, plus you'll need to buy a second manifold gasket. NA8 manifolds should be plentiful and cheap on this forum. Using the plate makes it very easy to port match and shape the inlet tract.

[manga_blue]

I just noticed that you said you can weld alloy. In that case cutting the flange off your NB8A manifold and welding it onto an NA8 one is a good option.

[GR124]

Thanks to all that posted their ideas and links.

I didn't realise the flat top/NB8B manifold is not a direct bolt on to my NB8A/BP4w. Although I understand it can be modified to fit or use a adapter plate.

I may sit on this for a while and do some more research.

One more question If I use the original ECU, would it be a viable to build a manifold? Bit like the photo. However Im not sure what I would do with the VIC connector, and If I could simply disconnect it and the ECU would still run OK.

[manga_blue]

I didn't realise the flat top/NB8B manifold is not a direct bolt on to my NB8A/BP4w. Although I understand it can be modified to fit or use a adapter plate.

Incorrect. I think you need to read what we've said a bit more carefully. To summarise:

1. You have an NB8A (BP4W) motor with the stock BP4W VICS manifold.

2. The NB8B "flat top" manifold flows better than your NB8A manifold. It will bolt straight on to your BP4W head and your current fuel rail. If 93_Clubman's measurements are right it also sits 10mm higher than your NB8A manifold. The NB8B manifold does not have a VICS-like function, so it doesn't need VICS wiring or ECU functionality. Your NB8A ECU will work perfectly well if you just leave the old VICS wire disconnected.

3. The NA8 manifold flows better than your NB8A manifold, although it's debatable whether or not it's better than the NB8B manifold. The NA8 manifold requires either a flange adaptor or a flange swap before you can bolt it onto a BP4W head and fuel rail. It sits about 20mm lower than your NB8A manifold. The NA8 manifold also does not have a VICS-like solenoid and the same comments that I made about the NB8B manifold and VICS apply for this manifold. An NA8 manifold should be much much cheaper and more easily found than an NB8B one.

It would seem to me that your best two options, by far, are to either get a flat top and fab a bonnet bulge for it or get an NA8 manifold, cut the flange off it and weld the flange from your existing NB8A manifold on in its place.

[GR124]

Hi Manga_blue,
You are correct I'm a bit I had the measurements wrong way round.
I'm a new to these engines and what can and can't be done. Still getting my head around the engine codes ie BP4w and the year codes NA8 etc.

So the NA8 is the earlier model car, with the pop up headlights.
You said "Your NB8A ECU will work perfectly well if you just leave the old VICS wire disconnected." This is great news.
I'll keep a look out for a NA8 manifold. Looks like I could fab up an adaptor. (Or cut and weld the flange from my NB8A manifold)

Big thanks for your write up. I also had another read of you thread (below), understanding more now.
http://ww.mx5cartalk.com/forum/viewtopi ... facc42deaa

I assume my NB8A throttle body bolts on the N8A manifold?

[manga_blue]

No problem, how about some pics of your build?

All NA8 and NB throttle bodies are interchangeable on the manifolds. The gasket part number for them all is the same. Just go with the one that comes with your ECU.