Mazda3 said:
You guys understand that it is a different turbo in the CX-7 right?
By the way I PMed you last week and didn't get a reply.
Well, we're still trying to figure that out. We can't find much definitive literature on the CX7 turbo, so we're just going by what the magazines and press releases say, which isn't a huge help. It sounds like the turbos are in fact the same in all of the vehicles, but the inlet to the exhaust housing is restricted in some way to increase exhaust velocity at low RPM's. This is of course unless you guys know something we don't (I'm not being facetious when I say that). If you guys know where the restriction is
for sure then we're all ears. But until then we need to get a CX7 in here and take it apart too find out for sure.
I just went and checked my PM's and sure enough I skipped right over your PM. So sorry about that!! I'll resopnd to that right away...
HeavyH20 said:
I think they know, they are just trying to figure out why the boost drops so much at higher RPM's versus the MS versions. According to Mazda, "The refined area of the turbine inlet port enhances throttle response at low rpm and diminishes boost lag." Might also be the problem at higher engine revs.
Exactly, it isn't clear yet if the turbo is different, or if the manifold is different. I think the only way we're going to know for sure is to take a CX7 apart (unfortunately).
Mazdaspeedgirl said:
Thank you for that bit of info. I did not know regardless of searching. How about what size the turbo is? What kind?
Apparently the three vehicles (the CX7, SPEED3, and SPEED6) all have a Hitachi-Warner modified K04. But maybe someone on this forum knows something we don't and can shed light on this subject?
shadow1 said:
The throttle position drops off towards redline. Assuming the pedal is floored the whole way, then the ECU is pulling back on the e-throttle. The answer may be tuning the ECU control of the throttle.
Actually the boost begins to taper off well before the throttle does anything weird. For instance, here's a graph of the SPEED3 when we had ours on the dyno:
If you compare this to the CX7 graph I posted, you'll see that the boost tapers off (~4250rpm) well before the throttle begins to close (~5500rpm). So you're absolutely right in that we do need to get control over the throttle. But the boost taper issue
in the case of the CX7 is probably more related to the exhaust system than the throttle plate. On the SPEED3 however, the throttle is the only boost limitation.
shadow1 said:
A MBC is so easy to install, I'm surprised CPE or someone else hasn't tried it yet. One would need to install a good boost gauge 1st. Also, air fuel should be monitored, since I'm not certain that the fuel system will accommodate additional boost at high rpm.
SuperStretch18 has it right. Our Standback
is a boost controller, in fact it's one of the most advanced boost controllers on the market. It uses a PID feedback loop to constantly calculate and control the deviation from your boost setpoint as opposed to a static duty cycle above or below stock. You literally just type in a boost pressure, and that's the pressure you'll get as long as the turbo can handle it. The reason why I posted the datalog of the CX7 was to show that our Standback is closing the wastegate and boost still doesn't increase. So really
any boost controller you use will run into this issue unfortunately.
This all doesn't mean that there isn't anything to gain from the engine management. If the restriction is in fact in the manifold and not the turbo, then we can still turn the boost up and tune the car. We have the ability to tune the air/fuel ratio as well as the ignition timing, so even if we can't increase boost too much over stock, we still may be able to eek a decent amount of power out of this car. That is at least until we figure out what's going on with the boost issue.
Jordan
