Keith found a document with the cam spec in it. I plugged it into my spreadsheet and now the numbers make a little more sense:





So for the square top, read left to right, this is 6th wave through third wave. Waves 5 and 6 ought to be pretty weak so I think wave 5 not being on the dyno chart isn't necessarily conflicting. Many miata dyno sheets have a torque hole here. Anyone know why? Otherwise, this correlates pretty closely. It actually looks even closer if you go to a 11.5" runner prediction. You can also change the air temp by about 5 degrees to make it closer, and runner taper isn't factored in correctly. If I keep finding good results I will clean up the spreadsheet and turn it into a public doc.

 

Mine are actually slightly less crazy at 310 degrees. The skunk2 manifold is cut on a bit of an angle so it would be right on 8".

I think harmonic calcs become very fluid the higher the revs with lots of variables like intake length, how smooth the runners are and pressure waves bouncing all over the place. They probably all combine to move the harmonics up or down a bit on the rev range. Thats why there is so much trial an error with intake manifolds.

 

I agree. The fluidity of what is going on in there plus differences between cars and setups is why I am just going to try it myself and see what happens.

Soon we shall see the true result of the S2 Ultra Street manifold on a full bolt on BP5A.

 

Please post that dyno sheet in here when you do. That will be useful info.

 

Awesome... I can't wait to see how it goes. How much the engine gains will depend on where the bottlenecks are. I have no idea what the result will be!

BTW, I had issues with the S2 throttle body. It is a common issue among the Honda guys where the bracket connecting the TPS to the throttle comes loose or fails entirely. If you run the S2 thottle body, make sure you locktight the tiny bolt that holds it all together. I found a S90 70mm throttle body on ebay for $70 and that is 1000 times better.

 

Hopefully I won't have any of those issues. To be fair, I am going to try to run the Miata specific 64mm throttle body. It has been installed for about 1500 miles already with no issues. I have to run the miata throttle body since I am still using the stock ECU and idle motor. I will run an adapter though so I can use the larger Honda TB if I need to later.

 

Does the S2 Miata thottle body run a similar screwed in plate to connect the TPS to the throttle shaft? I would have a look and loctite it in just to be safe. I think my issue might have been related to the lumpy idle and very high revs I pull shaking the throttle body apart.

Either way the S90 70mm is what I'd recommend to anyone looking to buy a throttle body, even for a stock miata intake. It's just build so much nicer than the S2 and a simple conversion plate would fit it to any manifold.

 

It has a screwed on adapter plate for the Idle motor, not the TPS.

Sorry for the threadjack OP, thought some of this may be relevant and useful.

 

yeah sorry OP... back on topic!

It might be worth having a look at ITB dynos, specifically different length trumpets. Since there is no plenum I think the harmonics should be closer to the calcs.

https://www.miataturbo.net/engine-pe...5/#post1267655

I think Emilio said Taxi was running around 9 - 9.5" runners(trumpets to head)... which should give peaks at 4000, 5000, 6750 which is pretty close to the actual dyno results, at least the bottom two anyway.

 

Zzz

 

I think you're in the wrong thread.

 

Silicone cast of intake ports:

 

Looks like an innovative way to clean your intake runners!

 

Any time I have extra mixed silicone rubber I pour it onto workbench surfaces- It does a really good job of cleaning up crap that would be difficult to get with a vacuum.