NA8 intake manifold on NB8A?????

jonosx · Postby **jonosx** » Sun Sep 19, 2010 10:06 pm

Hey all,

I've recently purchased an 98 NB8A. Being new to mx5's (coming from Nissans) I didnt pick up on this when i bought the car, but through my reading and in the course of chasing down some problems with the car, i have come across an anomaly.

It appears that my car has an NA8 intake manifold fitted? Did any early NB's have this manifold? (Its an Aug 98 model) Is there any particular reason why this would be changed?

I'm fairly confident it has the BP-4W engine as it has the cam sensor on the front cover. It definitely has the NB intake piping.

However, there is no egr valve on the back of the manifold. The pipe still exists on the exhaust manifold but it has been crimped closed behind the head. The pcv valve pickup is straight across from the valve, not offset as it should be and the manifold is one piece, not two piece with the VICS.

The main problem that led me to discover this is the engine light comes on after the has idled for approx 30 secs, it then goes off as soon as you rev the engine, and comes back on 30 secs after returning to idle.

Any thoughts and opinions on the matter would be appreciated.

Cheers,

Jono

manga_blue · Postby **manga_blue** » Mon Sep 20, 2010 12:17 am

I didn't realise they could be interchanged. There's a general feeling about that the NB8A had the best head but the NA8 had a better manifold. You might just have the best of both.

JBT · Postby **JBT** » Mon Sep 20, 2010 9:37 am

Do you have a photo of the engine bay/manifold and have you checked the engine number?

jonosx · Postby **jonosx** » Mon Sep 20, 2010 2:59 pm

Here is a photo...sorry about the lack of cleanliness, only got the car the other week and havent had time to clean it up yet.

Engine number is BP851454

JBT · Postby **JBT** » Mon Sep 20, 2010 5:20 pm

Hmmm....looks like an NA 1.8 manifold. I thought the NB had a two piece arrangement - see diagram.

manga_blue · Postby **manga_blue** » Mon Sep 20, 2010 6:04 pm

Definitely NA8 manifold. Definitely not an NA8 head. I'm intrigued. I would have done that if I'd known it a year or two ago. How well does it go?

jonosx · Postby **jonosx** » Mon Sep 20, 2010 9:27 pm

So this might be a good thing...??

As for how it goes, well i've only had it for a few weeks, havent dríven any other mx5's (apart from brief test drives) and have come from an s14 200sx with over 200rwkw, so i'm probably not in a position to say.

It does have some other issues though that i am working through as far as driveability and smoothness goes.

I am hoping to get a baseline dyno run this week to see where its at.

I'm also thinking i may throw a proper nb manifold on it and do some back to back testing and ascertain which is better.

manga_blue · Postby **manga_blue** » Tue Sep 21, 2010 2:03 pm

jonosx wrote:So this might be a good thing...??

Maybe ... I don't know. It might also depend on what you want and what else you do. The VICS on the NB manifold should give you a better spread of torque. The clean straight runners of an NA8 manifold make it a better candidate for porting it out into a top end screamer.

Matty · Postby **Matty** » Wed Sep 22, 2010 10:43 am

It's not a bolt-on job. the mounting holes are different. With mods to the mounting plate it can be done (see Keith Tanner's book) but it doesn't look easy.

Are you sure it's not an NB6 motor?

jonosx · Postby **jonosx** » Wed Sep 22, 2010 11:34 am

Matty wrote:Are you sure it's not an NB6 motor?

How would one tell the difference between an NB6 and NB8 engine?

manga_blue · Postby **manga_blue** » Wed Sep 22, 2010 12:04 pm

jonosx wrote:Engine number is BP851454

Does BP still mean 1800 in the NB series?

fattima · Postby **fattima** » Wed Sep 22, 2010 12:14 pm

Out of interest Phil how can you tell it is an NB head?

I have been told but have no evidence that some early NB's had an NA8 style engine.

manga_blue · Postby **manga_blue** » Wed Sep 22, 2010 3:18 pm

I couldn't. I only said it wasn't an NA8 head because it doesn't look like mine. No CAS behind the exhaust cam, different cam cover, some sort of sensor in front of the intake cam (and hooked up), PCV hose heading south somewhere....

I suppose it's possible there's an NA8 head hiding under that cam cover. Was there some sort of transitional step where they built it with an NA8 motor and NB cam and crank sensors then????

I wonder what sort of valve lifters it's got?

Regie · Postby **Regie** » Wed Sep 22, 2010 4:50 pm

that front senor looks like the CAS

Matty · Postby **Matty** » Wed Sep 22, 2010 5:07 pm

jonosx wrote:
Matty wrote:Are you sure it's not an NB6 motor?

How would one tell the difference between an NB6 and NB8 engine?

For starters, the NB6 motor didn't have the VICS manifold...

It was I believe based on the earlier BP motor (not the B6), with a smaller bore and possibly shorter stroke. Hence it looks more like a NA8 motor than an NA6 motor.