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i'm surprised a search revealed nothing on this forum - i'm certain more than a few of you know about this mod.

basically it's a mod for NA8's and NB8A's where you run a exhaust cam on the intake side (longer duration) and adjust timing accordingly, but leave the exhaust side untouched. general consensus on the big forums is that it results in slightly lumpy idle and improved torque throughout the rev range, particularly past 4000 rpm, and reduced power drop off up near the limiter.

so who's tried it? what did you think?

DIY instructions: http://diymiata.com/exhintake.html

I think most who want to go to that much trouble just stick in a set of aftermarket cams instead.

I have been running this for a year or two. I didn't do any before and after dyno's so impossible to tell what gains (or otherwise) were made. The engine is otherwise stock except for a Mania intake and Megasquirt (and it did alright in the autotest the other day hey Dave ). The bum dyno says that my car has a stronger than stock midrange, some of which may be the exhintake. Long story short, if you can find a cam cheap and can drill a hole accurately then do it.

P

tinsfci wrote:... it did alright in the autotest the other day hey Dave ). ...

For sure, perhaps more a good driver than just a quick car. Even with R comps and less weight I still wouldn't have come close to your times.

Locutus did you find any before/after dyno graphs?

Okibi wrote:I think most who want to go to that much trouble just stick in a set of aftermarket cams instead.

true, but a set of cams will set you back $600-900 where a 2nd hand exhaust cam will give you change from $100.

closest to a graph i could find for an NA8
http://forum.miata.net/vb/showpost.php? ... ostcount=1

NB8A
http://forum.miata.net/vb/showpost.php? ... stcount=29

i think this is the guy that started it all
http://forum.miata.net/vb/showpost.php? ... ostcount=1

more extensive mods:
http://forum.miata.net/vb/showpost.php? ... ostcount=1

I was going to try it, but when I received the donor cam, it arrived snapped into two pieces.
Spewin' cause the cam I found was brand new, genuine Mazda.

From my research and US forums trawling, like you've done, it's worthwhile.
Go for it Locutus.

I was going to take it one step further though, do the usual exhintake mod, but also swap my NA8 exhaust cam with an exhaust cam from an NB8A, thus both sides have more aggressive profiles.

It looks like no one has tried the above combo.

i've seen that proposed on the big forum but i don't think i saw any mention of anyone going through with it. the main issue is cost related to replacing the HLAs on the exhaust side with solid lifters.

Locutus wrote:i've seen that proposed on the big forum ....

A few weeks ago?

ahh... i see what you did there...

Hehehe... yup t'was me.
I was surprised that no one has tried to do it and sticking with HLA's.
A couple have gone to the trouble of solid lifter swap, but I don't see the point. More money, more effort, they seem to forget that this is a "budget" mod.