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Discussion Starter · #1 ·
i plan on doing ITB's and was wondering what cams to use. i found some J spec intake cams on cork sport, never heard of them? also does anybody have the unorthodox underdrive pulley?
 

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Supporting Member
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I don't have a direct answer for you but I've got a link to help you with your research.

Miata MX5 camshaft specifications

Q: Regarding the '99 engine, ECU, and injectors, do you think a mild street grind cam would work (265 degrees duration, .420 lift, and 30 degrees overlap) without any ECU tuning?

A: No. Those specs are far from mild. The stock 99 intake cam is 237 duration, .326 lift and 17 degrees overlap. Your cams have OK overlap, the duration is marginal, but the lift is waaay too big for valve springs to support. About 9mm lift is all your going to get out of them. I replaced my valve spring s with stiffer units. See www.solomiata.com/street.html

Also, anything more than 9.5mm lift and you'll also have to make a clearence cut at the lifter bosses. The billets don't support that much cam either. My webcam 515's are 270 duration, .370 lift and 48 degrees overlap. I had to get the basecircle cut .035" just so the profile would fit on the billet blank, good thing too with the tight lifter boss cleaance.

The overlap and duration of the 515's adds great peak hp but kills torque. I would need about 13:1 to make them work perfectly (tough to build cylinder pressure when the valves are open all the time). Most people would hate them for the street. Even when adjusting the cam sprockets as tight as possible my cams still give up a little torque potential.

Something along the lines of a 262 duration , 9mm lift and probably 25 degrees overlap would be about the max I would want to use for the street in a near stock 1.8 and stock ECU. Anything larger would definately require a programmable ECU and more compression. Kurt gets away with more overlap since he has more displacement, larger engines tolerate larger cams.
 

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Brah.
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7,486 Posts
i would stay away from the unorthodox underdrive pulley but i would check out this.....aluminum and light weight.




iscracing.net
 

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Discussion Starter · #4 ·
i would stay away from the unorthodox underdrive pulley but i would check out this.....aluminum and light weight.




iscracing.net
whats wrong with the unorthodox, i've never heard anything about them being bad. also do you have any more info on the pulley from iscracing. i couldn't find any on their page
 
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