My custom turbo kit
#84
Former Vendor
![](/mt2011/images_td/ranks/supporter1.gif)
iTrader: (31)
Join Date: Nov 2006
Location: Sunnyvale, CA
Posts: 15,442
Total Cats: 2,103
![Default](https://www.miataturbo.net/images/icons/icon1.gif)
https://www.miataturbo.net/build-thr...5/#post1490803
Please leave us alone. You contribute absolutely nothing to this community.
#87
SadFab CEO
![](/mt2011/images_td/ranks/supporter1.gif)
iTrader: (3)
Join Date: Sep 2012
Location: your mom's house phoenix, AZ
Posts: 4,560
Total Cats: 1,142
![Default](https://www.miataturbo.net/images/icons/icon1.gif)
****
#89
Moderator
![](/mt2011/images_td/ranks/supporter1.gif)
![](/mt2011/images_td/ranks/moderator.png)
iTrader: (12)
Join Date: Nov 2008
Location: Tampa, Florida
Posts: 20,884
Total Cats: 3,075
![Default](https://www.miataturbo.net/images/icons/icon1.gif)
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.
****
****
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.
#90
![Default](https://www.miataturbo.net/images/icons/icon1.gif)
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
#91
![Default](https://www.miataturbo.net/images/icons/icon1.gif)
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
![rofl](https://www.miataturbo.net/images/smilies/rofl1.gif)
#93
Moderator
![](/mt2011/images_td/ranks/supporter1.gif)
![](/mt2011/images_td/ranks/moderator.png)
iTrader: (12)
Join Date: Nov 2008
Location: Tampa, Florida
Posts: 20,884
Total Cats: 3,075
![Default](https://www.miataturbo.net/images/icons/icon1.gif)
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.
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.
Thread
Thread Starter
Forum
Replies
Last Post