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Does duration under 0.050" matter?


turbogrill
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Hi,

 

Does the duration on a camshaft under 0.050" matter from engine characteristics? I am sure it has implications for ramp speed and such. But given that the valve is barely open at <0.050" it shouldn't matter much?

 

I did see a very interesting plot where they swapped a cam, the only big difference was the duration under 0.050":

 25-20intakecam.jpg.d4f42cf87b52b6caabdb5d0b85cd0c44.jpg

 

intake cam Red line:

Duration @0.010": 268

Duration @0.050": 204

Gross lift: 0.37"

 

Intake cam Blue line:

Duration @0.010": 254

Duration @0.050": 204

Gross lift: 0.37"

 

(Exhaust is identical)

 

But still the red cam is shifted about 500-1000 rpm. The red cam really doesnt make anymore power, just the same but higher up. I would also assume the blue cam is better in any way.

 

Could it be that one cam is advanced/phased differently?

 

(Redline is with a MZR2.0 cam in a MZR2.5 engine, blue line is stock 2.5 cam)

 

edit: corrected numbers.

Edited by turbogrill
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It doesn’t seem like much, but .010” on the full circumference of the valve is enough area and flow.  It’s not going to make huge differences, but it will affect valve overlap and could change the scavenging characteristics.  
 

In that case, I would take the Blue line all day long.  Significantly more torque in the mid range, and more hp everywhere but the top end.  How long are you in that RPM range? 

Edited by petawawarace
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The blue line is the correct camshaft, red is an experiment (from a different mazda). It's interesting why the red is not making more power.

 

Mild aftermarket cams on that exact motor makes very nice gains. But they have more lift and slightly more duration as well.

 

 

 

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4 valve heads have more curtain area so respond to low lift better than two valve heads.

 

0.050" is a good parameter for judging SBC cams and such while 1 mm (0.040") is more commonly used with 4 valve cams. The 2.0 has 212 degrees at 0.040", the 2.5 only has 208. Also has four degrees more duration at over 0.300" lift according to this thread:

https://forum.miata.net/vb/showthread.php?t=564488 

 

Shifts the curve up in rpm but still need centrelines 'n stuff for a direct comparison...

Edited by mender
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9 minutes ago, mender said:

4 valve heads have more curtain area so respond to low lift better than two valve heads.

 

0.050" is a good parameter for judging SBC cams and such while 1 mm (0.040") is more commonly used with 4 valve cams. The 2.0 has 212 degrees at 0.040", the 2.5 only has 208. Also has four degrees more duration at over 0.300" lift according to this thread:

https://forum.miata.net/vb/showthread.php?t=564488 

 

Shifts the curve up in rpm but still need centrelines 'n stuff for a direct comparison...

 

I did see the 0.040" being mentioned, figured that was a typo :)

 

I am also curious to the lack of cams, even for the NA/NB Miatas there are not a lot.

If you take the datsun L engine there are so tons and you can even get a custom grind for cheap.

I guess same with LS/SBC

 

Is it because cams on miata doesn't do much? But cams on a datsun can double the horse power...

 

 

 

 

 

 

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No one runs naturally aspirated Miatas anywhere but spec racing where going for bigger hp is against the rules. With everyone in the normal aftermarket scene just going turbo or supercharger theres not much market for a good cam in a Miata.

It was a shame when I was looking to go n/a in mine way back in the day after I was a dumb kid and bought some high comp pistons and didnt ever finish the project.

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In Europe it is much more common to see these engines in small formula cars, sports racers, and Caterhams. They have a lot of parts and development that we never see on this side of the pond. This is an interesting page that has lots of interesting details about these engines, this guy was able to get nearly 300hp from a NA 2.5L

 

http://duratecindetail.com/htm pages/page5.htm

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It's becoming more popular here as well, new cams popup all the time. I guess it's because you can actually make a new miata resonable fast without  messing with turbos.

 

Thinking about doing a cam swap in our NC, just seems like a pain in the ass (I would drop the motor).

 

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2 hours ago, mhr650 said:

I am thinking about swapping a NC MZR motor into my RX7, the stock rating means I can swap it for only 53 points. Of course then I want to install one of our 2L EcoBoost turbos and really have some fun…

Interesting! 

How many points do you have?

The mazda3 2.5 mzr is also rated at 165hp.

With header the 2.5 outperforms the 2.0 with header. But you should really get a header, wakes them up.

If you can do cam+header the 2.5 becomes 200whp

 

 

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