you must be confused with another forum.

 

https://www.miataturbo.net/search.php?searchid=5496931

 

last one was more then 6 months ago - believe me I do not come here asking.

 

That's why you were asking about octane vs. timing advance after blowing up your motor in spectacular fashion 3 months ago, right?

https://www.miataturbo.net/build-thr...5/#post1490803

Please leave us alone. You contribute absolutely nothing to this community.

 

I ask nothing for more then six months, just update my build thread. btw the colis were wired in wrong order leading to lean condition.

The emails I get and remote tuning I do indicate that my contribution is more then nothing.

 

 

I am so fukcing sick of this ******* bullshit myth. No engine needs back ******* pressure for ******* anything. NA engines need ******* velocity, backpressure is a price you pay to get ******* velocity. In an ideal fuking world, you have infinite ******* velocity and 0 ******* backpressure.

****

 

But muh backpressure!

 

This. Velocity due to smaller diameter pipes helps scavenging on a naturally aspirated engine SOMETIMES. Too small and the exhaust has too much backpressure and doesn't completely evacuate and definitely doesn't scavenge, hurting power.

With a turbo you don't rely on scavenging to assist in filling the combustion chamber because the inlet charge is pressurized. In fact, those times when valves overlap on a turbo engine can be detrimental to power production due to reversion. This is why turbo camshafts are typically designed with less overlap.

 

I completely disagree.

With overlap you need to gain significant RPM so that the overlap period is short enough (in milliseconds) so that reversion and gases blowing straight through the engine etc cannot happen.

In a forced induction application you need EVEN MORE RPM to achieve this in order to overcome the additional speed and force with which the intake gases are being forced clean through the engine.

These overlap effects are exaggerated even more by even higher boost pressure, so typically turbo cams have less overlap so as not to push the power curve too high in the rpm band. Large duration high overlap cams work just as well in forced applications as turbo cams do, they just move the torque curve even higher on a turbo car than they do on an n/a car, which is often not desirable.

Dann

 

Huh thanks for the info, I'm not much of a tuner/engine guy but I find this stuff fascinating. So is this why people say honda vtec is no good for boost? Right as you come into the power band it gets moved away? Please excuse my ignorance

 

I don't think i've ever heard anyone say that OMGTEVEEEEETTAKKKS are bad for boost.

 

From my readings the reduction in overlap typically found in turbo cars is by design to prevent reversion since the pressure in the exhaust ports is usually higher than the inlet port. This is at least do in part to the fact that gasoline air mixtures typically expand between 3 1/2 to 5 times* their volume when burned (*depends on a host of variables, and whose data you believe).

Contemplating it from a logic standpoint it seems less likely that a lower pressure pushing the turbine blades would generate a higher pressure from the compressor blades. Wheel design might be able to overcome some of this difference but it seems less probable and I've always heard the opposite.