topsdrop

Ive been told that at some point, someone did a cutaway of a early 1.8 head and then a 99-00 head showing the differences in inlet in the head.

Ive searched around but couldnt find the details.

Thanks
Cory

Doppelgänger

iTrader: (12)

NA 1.8 top - NB 1.8 bottom

Full_Tilt_Boogie

iTrader: (1)

Ive seen that damn picture a million times, but cant remember where.
I would try searching over at M.net
If you can stand reading through all the retarded bullshit posts there is actually lots of info over there

Edit:
Neeeeeevermind
The uncanny man was on the case.

Thucydides

Interesting. The runner layout looks better in the NA (raised roof on intake side, larger radius in the floor of the exhaust side).

NA6C-Guy

iTrader: (1)

I was very confused at first by this picture. Then I realized the cat was off center. I'd love to see one right down the middle, going through the center of the valve guides. I thought the ports and the seats looked a bit...off.

Braineack

iTrader: (62)

The NA has a horrible turn into the chamber, and there's an odd hump at the bowl. the NB head is a nice tapered straight shot into the chamber.

Thucydides

That's not necessarily how Smokey Yunick would see it.

With the valves out, and looking only at the runners, what you say makes intuitive sense.

The problem is that flow into and out of the combustion chamber is tremendously influenced by the valves, and the orientation of the runners relative to the valves. All else being equal a straight runner section over the valves, so flow around the valves has a chance of being somewhat symmetrical, is preferable to a straight run at the combustion chamber but cocked with respect the the valve.

Check the angle of the valve seats to the final portion of the runners; the closer to perpendicular the better. When they designed the NA they got it right the first go around.

18psi

iTrader: (76)

Then why do the nb's flow more and make more power up top?

94blackmx5

you could really port the shi!t out of the NA head, especaily the exhaust side. I'm not sure it would flow any better than the 99-00 head, but it would be an interesting comparison.

Thucydides

Compression, better ECU tuning, and most importantly, cam timing.

There's no difference between the 95 head and the 96 head, but with the OBII ECU and perhaps a smidgen extra compression the 96 motor makes five more HP (128 vs 133).

The biggest difference between the variable valve NBs and the non-variable valve NBs is the valve timing where they found another 9 hp or so (133 vs 142).

It's also possible that the NB head does flow better; it just doesn't look like it should. It would sure love to see some flow curves of stock heads measured on the same test stand and at the same valve lift.

Thucydides

Good point about the off-center cut. A center cut, or at least one where they both came from the same section of runner, might look quite different. Here I'd say the NB head was cut closer to or pretty much right on center, and the NA head would look even better than it does if they'd done a better job with it.

Of course this is a four valve head so center of runner isn't center of combustion chamber because the runners run parallel rather than radial (like some single cylinder motorcycles).

topsdrop

Thanks again for posting those photos Doppelganger.

So, when I hear about most guys swapping in a 99-00 head, is it safe to assume that people are choosing the 99-00 because its the improved 1.8 head, minus the variable timing? I can assume that 1990-1998 guys would want the improved head, but cant use the variable timing due to not having a pcm that could control the variable timing devices.

Im also assuming that theres no benefit to someone with a 2001-2005 NB to swap in a 99-00 head, other than to eliminate the variable timing.

neogenesis2004

iTrader: (12)

I know Adaptronic can control VVT, MS3 can or is working on it, AEM can run it, and I believe there is a member on here that has made a computer programmable/mappable VVT controller that works independently of your ecu. So there is no reason not to gain the benefits of VVT.

y8s

iTrader: (8)

doesn't someone around here have a destroyed 2001 head? I think it needs to be sawn.