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Miata MX5 camshaft specifications

Below are the Mazda OEM camshaft specifications. Advertised duration numbers are typically measured at .003-.004" lift. To get the true picture of the profile you should obtain the duration specs at various lifts. The production cams have a range of acceptable profile specifications so yours may vary by a few 1000th here and there.

USA spec 1990-93 Miata 1.6 DOHC

  1990-93 5-speed 90-93 Auto 88-89 GTX
Dur @ intake exhaust intake exhaust intake exhaust
Adv. Dur. (.003") 236° 250°        
.010" 220° 233°        
.020" 210° 223°        
.050" 192° 204°        
.100" 170° 180°        
.150" 147° 156°        
.200" 122° 130°        
.250" 90° 97°        
.300" 37° 42°        
Valve Timing BTDC
51° ABDC
53° BBDC
15° ATDC
BTDC
40° ABDC
55° BBDC
ATDC
BTDC
51° ABDC
69° BBDC
ATDC
Overlap. 20° 10°
Base circle Diam. 1.3"
33 mm
1.3"
33 mm
1.3"
33 mm
1.3"
33 mm
1.3"
33 mm
1.3"
33 mm
Total Lift .309"
7.86 mm
.311"
7.9 mm
.273"
6.95 mm
.306"
7.79 mm
   

USA spec 1990-1997 1.8 BP8

  90-93 HLA
(Protegé, Escort GT)
94-97 HLA 99-00 (USA) 01-05 (USA)
Dur @ intake exhaust intake exhaust intake exhaust intake exhaust
Adv. Dur. (.003")                
.010"   232 218 232 257 278 241 278
.020"   220 208 220 224 232   232
.040"   208 195 208 209 215   215
.050" 196 202 190 202 204 210   210
.080"   190 176 190 190 196   196
.100"   180 167 180 181 187   187
.150"   158 145 158 158 164   164
.200"   134 119 134 132 141   141
.250"   108 89 108 102 114   114
.300"   70 43 70 59 79   79
Valve Timing BTDC
48° ABDC
56° BBDC
14° ATDC
BTDC
48° ABDC
56° BBDC
14° ATDC
BTDCC
49° ABDC
53° BBDC
ATDC
  53° BBDC
ATDC
Overlap. 19° 19° 17° varies from 7° to 50°
Base circle Diam. 1.415"
35.94 mm
1.415"
35.94 mm
1.415"
35.94 mm
1.415"
35.94 mm
1.418"
36 mm
1.418"
36 mm
1.418"
36 mm
1.418"
36 mm
Total Lift .319"
8.58 mm
.338"
8.58 mm
.338"
8.58 mm
.338"
8.58 mm
.326"
8.28 mm
.350"
8.89 mm
  .350"
8.89 mm

These numbers are for reference only. I will not educate on the ability of camshafts to increase power levels or the ramifications of changing a camshafts duration, lift or timing specifications, but generally speaking a boosted car likes cams with minimum overlap (EVC to IVO) to prevent blowing the intake charge out of the exhaust port and also to prevent reversion from exhaust backpressure from restricting the forced intake. Performance NA cams use the opposite strategy of using a longer duration with greater overlap to fill the cylinder to max capacilty with a fresh charge.

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There are a couple of options available for factory based 1.6 performance camshafts (I have not dyno'ed any of these and they are just pure speculation, try at your own risk). The 323 GTX turbo exhaust cam can be installed for 1.6 aftermarket turbo applications or it can also be used for performance NA motors by installing it 1 tooth off (12 degrees) advanced (-->). This gives timing numbers of EVO 57 ATDC and EVC 13 BTDC and an overlap of 18 (-5-13) with the stock NA intake cam. The stock 1.6 NA camshaft can also be made more appropriate for boosted motors in theory by installing the exhaust cam 1 tooth off in the retard direction (<--). This gives timing numbers of EVO 65 ATDC and EVC 3 BTDC and an overlap of 8 (-5-3)with the stock NA intake cam.

FWIW, Mazdaspeed, Mazda Competition, JUNE, HKS, Toda, Gude, Paeco, Integral and Webcam all make aftermarket camshafts for the Miata engines.

Question: 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?

Answer: 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 springs 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.

Question: What cam timing specs produce the best power?

Answer: Every engine is a little bit difference but generally speaking the Miata factory 90-97 cams will produce the best high rpm peak horsepower numbers with retarded cam timing. This has been dyno tested by numerous people and typically 6-8 degrees of retard produces the best high rpm peak. 2-3 degress advance produces the best midrange and low rpm torque numbers.

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