mx5cartalk.com

The rev-happiness is related to the absence of midrange in the 1.6, a matter of the cam timing essentially. A similar cam profile in the 1.8 should give a similar feel.

Definitely put the ECU at the top of the list, and ditch the tiny AFM.

from there you have much more flexibility to properly implement further mods (cams, head work, bottom end). In fact, cams and high comp pistons will NEED an ECU to work properly and avoid engine failure.

You can overbore up to about 2mm, which is 1680cc (but if kept a secret still eligible for 1.6 class ;)). In fact a 1mm overbore is usually still legal...

Note that the Escorts probably weigh 800kg...

butters wrote:it's not bad but woundering what others have done past this.

Yeah I was pretty much where you are now a few years ago with my NA8.

First I had the CAI, Zorst (both Loch Stewart) and timing bump. At this point, I had 71rwkw.

Then I added Loch headers. Kinda felt like a zero sum gain, in the sense that there was (subjectively) 10% more top end but 10% less bottom end. In highsight I wouldn't have done it for a light-tuned roadcar (just as Loch himself recommended to me). But now it was more like 73rwkw.

After that I fitted a piggyback fuel ecu, a simple Apexi SAFCII, and then it was 80rwkw. Strangely though, while this is actually a pretty big gain and has been verified on a few dynos (you can turn it on and off and immediately see the difference in power reading), there was rather oddly no actual seat of the pants difference. I really can't tell the difference, even today so it's "dyno" horsepower rather than real-wld "push you in the back" power.

Quite a few years after that, I rebuilt the engine with 10:1 comp NB8C pistons (stock bore), and I also shaved the head 20 thou for an additional 0.5:1 comp. Now it was 83rwkw. Subjectively, the engine feels more muscular and "sharp", although my seat of the pants impression is probably coloured by the fact that the engine was pretty tired just prior to the rebuild.

Lastly, the cams went in, 252/256 Tomei sticks which bumped the power to 90rwkw. There is probably a few more kw to go if I could be bothered tuning the cam gears, but Tomei recommended the stock setting and so far it's proving to be a good compromise. Bottom end is maybe a smidge weaker than before (mainly below 2500rpm) but there is a very distinct (and audible) kick at 5000rpm and at 7000rpm the engine is still straining at the leash and wanting another 500rpm or so. In terms of peakiness, I would say that it's (subjectively) half way between a normal MX5 and a VTEC Honda.

I reckon that there's maybe 3-4kw in headwork (but a really "good" job is expensive) and maybe the same power gain again in quad throttles (but then again that's a significant additional expense).

So there you go

Out of interest would you be allowed to change to another engine and still compete in your desired class? Non Mazda etc? Is capacity the only restriction?

Quad throttles are worth 3-4 rwkw - proven.

bpt4w wrote:im not dissagreeing , im just saying it changes the characteristics of the engine feel more than the pwr in the pants .

Agreed...for me, if I even go down that route, it will be because of the noise and response rather than the peak power gain.








....and the sex appeal factor too

mmmm quads

Great write up Kev.

Lots of IRTB (quad throttle) discussion here:

http://www.clubroadster.net/forum/viewforum.php?f=25

bpt4w wrote:yes i agree babs , the sound is just horn.

any idea on how you would do that route , eg webber manifold with toyota throttles or would you go custom with the motorbike throttles or the ones you can buy straight from japs.

Part of the issue is that racing quad throttles don't have any idle circuit. So to get a stable idle you have to have a high idle, since it relies on the throttles opening a hair. Also there is no idle-up capability for a/c, etc.

So I reckon if I actually went down this path I'd get the RS Aizawa manifold (it's about $600 or so with the throttle linkage adapter kit I think) that allows me to mate up the factory quad throttles from the 20V 4AGE. That would probably have all the usual road-car gubbins on it to get a driveable result...tuning it would require a very high-end ecu and making a Toyota sub-system work with a Mazda ecu map would probably cost a fortune. But it's probably the least-worst way to approach it...

Fuji Racing http://www.fuji-racing.com/fujiracing_004.htm has IRTB kits that bolt on....just need a tunable ECU to manage them.

I will have IRTB's one day

I am warming to the idea of using the throttle bodies off a motorbike, about 900cc class. They are plenty big enough for the MX5 engine and have most of the bits you need.

All I would have to do is build a manifold and get an ECU to control it.

EFI hardware sell a kit too.

CT is a good person to ask about that kind of stuff.

Or ask over here ...
http://clubroadster.net/forum/viewforum.php?f=25