2001 MX5 1.8 Sport and MSM manifold comparison

I took some measurements and pics of my MSM manifold today. It should be the same as 2001-05 VTCS manifolds on USDM cars.<div>I also measured ID and OD inlet and outlet of the MSM throttel body which is probably the same as all Miatas.
</div><div>Some data for MSM manifold:</div><div>
</div><div>Plenum volume: ~ 1.1 l</div><div>TB inlet: 59 mm</div><div>Runner diameter: 42mm</div><div>Runner length: ~31-32 cm</div><div>Weight: 7.3 kg (With EGR valve, no TB )</div><div>
</div><div>JDM manifold: ( from my earlier post )

</div><div><div>Weight: 6.4 kg</div><div>Throttle body opening diameter: 59mm</div><div>Runner diameter: 50 mm</div><div>Runner length: ~ 30 cm</div><div>Plenum volume: ~ 1.5 l</div><div>Calculated runner volume: ( 3.14 * sqr(2.5) * 30 ) / 1000 = ~ 0.59 l each</div></div><div>
</div><div>MSM TB:</div><div>OD inlet 66mm</div><div>ID inlet 62 mm</div><div>Throttle plate / ID outlet 55 mm</div><div>For dummies: The Miata TB is 55mm. NOT 62mm.</div><div>
</div><div>Lets look at some differences between the MSM and JDM manifold. JDM on the left:</div><div>
</div><div>I need to tap for vacum for the MAP on the JDM as it has at least 1 port less.</div><div></div><div>
</div><div>Looks pretty similar from the other side.</div><div>Plenum looks shorter on the JDM manifold but if you compare with the runners they are pretty much the same width.</div><div></div><div>
</div><div>Underside looks the same. Hopefully the manifold brace from the MSM will fit.</div><div></div><div>
</div><div>No obvious changes from this angle. EGR fitted to the MSM manifold and you can see the holes from the removed VTCS shaft.</div><div></div><div>
</div><div>TB inlet has a more straight path and less restrictive bulges and holes on the JDM manifold:</div><div></div><div>
</div><div>On closeups the difference is very noticable:</div><div></div><div>
</div><div>JDM manifold has 50 mm runner diameter vs. 42 on the MSM.</div><div>Also the MSM manifold has a strange second chamber between the runners and Helmholtz chamber. That could mean the Helmholtz chamber on the JDM manifold is bigger.</div><div></div><div>
</div><div>The runner outlets on the JDM is connected to the Helmholtz chamber via small 1-2 mm ports in runner 1-3. MSM does not have these:</div><div></div><div>
</div><div>The runners protrude about 1 cm more into the top part of the plenum on the MSM.</div><div> EGR outlet is also bigger.</div><div></div><div>
</div><div>I’m finishing off with some pics of the throttle body:</div><div></div><div></div><div>
</div><div>So… Which is best ?</div><div>You really don’t know without a dyno or a flow bench as fluid dynamics stuff is a very complex subject ( I have been told…)</div><div>However it is hard to not notice the straighter flow path and more open design on the JDM manifold. The plenum and runners are larger wich could be a good thing for overboosting.</div><div>I would also think there would be better gains of fitting a larger TB as the air doesn’t have to smash into a couple of 45 deg walls before entering the chamber. No restrictive VTCS butterflys or holes to weld if they are removed.</div><div>
</div><div>In my head the JDM manifold is better.</div></div>


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