Foolish of me....

[wwest]

It occurred to me...

Has anyone owning a CX-7 already wired the wastegate open to see what the resulting FE improvement might be/is....

I know that this would result in a significant reduction in the power band but for constant speed, relatively constant speed, highway cruising it wouldn't be so noticeable.

If simply wiring the wastgate open does improve highway cruising FE somewhat then I would better know whether or not it would be worthwhile to purchase a CX-7 for an FE improvement, maybe 50%, experiment.

 

[evilmonkeyMSP]

so you dont want to build any boost? wth?

 

[wwest]

No, I'm just curious, as an EASY experiment, what the FE would be if boost could be fully avoided during an extended constant speed drive on the freeway.

 

[evilmonkeyMSP]

well, if you're cruising on a freeway then you wouldnt be in any kind of boost anyways until you step on the gas a bit. ever driven in a turboed car w/ a boost gauge? Yeah, when cruising you're typically NOT in boost so this experiment would mean pretty much nothing...

 

[wannabe]

(werd) the cx7 is designed to build boost fairly low in the range, but in 6th gear your cruising at 2500 rpms at 75mph. your not boosting.

 

[Shadow102]

well, if you're cruising on a freeway then you wouldnt be in any kind of boost anyways until you step on the gas a bit. ever driven in a turboed car w/ a boost gauge? Yeah, when cruising you're typically NOT in boost so this experiment would mean pretty much nothing...

Actually I hate to burst your bubble but just because your boost gauge isn't reading boost doesn't mean the turbo isn't making any.

HOWEVER... to the original poster. Your fuel mileage would infact suffer by wiring the waste gate open and highway cruising. First off at that point all the turbo becomes is a huge clog in the exhaust system making the engine less efficient. On the topic of efficiency the turbo allows you to get better fuel mileage as its aiding in the power of the engine even down low in the rpm range.

Case and point...a protege5 manual will consistantly get worse gas mileage than a mazdaspeed protege will get because the volumetric efficiency on the msp is way better due in part to the turbo which increases the efficency of the engine itself.

 

[evilmonkeyMSP]

meh, true, but either way, stupid idea lol

Actually I hate to burst your bubble but just because your boost gauge isn't reading boost doesn't mean the turbo isn't making any.

HOWEVER... to the original poster. Your fuel mileage would infact suffer by wiring the waste gate open and highway cruising. First off at that point all the turbo becomes is a huge clog in the exhaust system making the engine less efficient. On the topic of efficiency the turbo allows you to get better fuel mileage as its aiding in the power of the engine even down low in the rpm range.

Case and point...a protege5 manual will consistantly get worse gas mileage than a mazdaspeed protege will get because the volumetric efficiency on the msp is way better due in part to the turbo which increases the efficency of the engine itself.

 

[wwest]

First, in test driving the RDX and the CX-7 I found very hard to stay out of boost range, even the slightest level of acceleration required and the boost comes up.

And having driven a Prius on the highway the display makes it VERY obvious when it transitions to boost, brings in the battery for accleration assist.

So the only way to really know the potential for FE improvement is by doing a test with the wastegate fully open. Then one can "accelerate" as needed on the highway without incurring the FE penalty of the turbo.

The new Toyota I4 in the 3945lb Venza F/awd is rated at 20/28mpg & 187HP and does not use DFI. If the F/awd CX-7 (3929lbs, 16/22 mpg) engine's compression ratio could be upped to the DFI "standard" of 12:1 it could probably outperform the Venza in both FE and performance. Obviously that would mean detuning the turbo, lowering maximum boost level, or discarding the turbo altogether.

 

[jersey_emt]

First, in test driving the RDX and the CX-7 I found very hard to stay out of boost range, even the slightest level of acceleration required and the boost comes up.

Cruising on the highway you are not accelerating, so it doesn't matter. The <1% of the time that you actually ARE accelerating (to speed up for 5-10 seconds to pass a car, etc.) won't make a difference either.

And having driven a Prius on the highway the display makes it VERY obvious when it transitions to boost, brings in the battery for accleration assist.

This comparison makes absolutely no sense. Two completely different animals. You can't compare the two like that.

So the only way to really know the potential for FE improvement is by doing a test with the wastegate fully open. Then one can "accelerate" as needed on the highway without incurring the FE penalty of the turbo.

(boom07)

The new Toyota I4 in the 3945lb Venza is rated at 20/28mpg & 187HP and does not use DFI. If the CX-7 engine's compression ratio could be upped to the DFI "standard" of 12:1 it could probably outperform the Venza in both FE and performance. Obviously that would mean detuning the turbo, lowering maximum boost level, or discarding the turbo altogether.

(boom07)(boom07)

 

[wwest]

Actually I hate to burst your bubble but just because your boost gauge isn't reading boost doesn't mean the turbo isn't making any.

HOWEVER... to the original poster. Your fuel mileage would infact suffer by wiring the waste gate open and highway cruising. First off at that point all the turbo becomes is a huge clog in the exhaust system making the engine less efficient. On the topic of efficiency the turbo allows you to get better fuel mileage as its aiding in the power of the engine even down low in the rpm range.

Case and point...a protege5 manual will consistantly get worse gas mileage than a mazdaspeed protege will get because the volumetric efficiency on the msp is way better due in part to the turbo which increases the efficency of the engine itself.

Yes, the fact that you can externally COMPRESS (at least partially) and then COOL the airflow entering the engine offers a huge advantage......WHEN BOOST IS REQUIRED.

The problem is that OFF-BOOST the engine efficiency is so severely derated/detuned it would be better if the turbo wasn't "there". On the other hand if you could make use of VVT to delay the intake valve closing when on-boost you would have the best of both aspects. 12:1 compression ratio "off-boost and 9.5:1 in full boost.

 

[wwest]

Cruising on the highway you are not accelerating, so it doesn't matter. The <1% of the time that you actually ARE accelerating (to speed up for 5-10 seconds to pass a car, etc.) won't make a difference either.

In a more perfect world, no other traffic on the highway, or a FLAT roadbed, you would be correct. That was the use of my Prius as an example. With the Prius you have a display right in front of you so you can tell cruising vs even the slighest level of acceleration.

This comparison makes absolutely no sense. Two completely different animals. You can't compare the two like that.



(boom07)



(boom07)(boom07)

Maybe some of you owner/drivers can tell me...

When on the highway and using cruise control consistently how often do you see the CC "requiring" boost.

 

[Shadow102]

First, in test driving the RDX and the CX-7 I found very hard to stay out of boost range, even the slightest level of acceleration required and the boost comes up.

And having driven a Prius on the highway the display makes it VERY obvious when it transitions to boost, brings in the battery for accleration assist.

So the only way to really know the potential for FE improvement is by doing a test with the wastegate fully open. Then one can "accelerate" as needed on the highway without incurring the FE penalty of the turbo.

The new Toyota I4 in the 3945lb Venza F/awd is rated at 20/28mpg & 187HP and does not use DFI. If the F/awd CX-7 (3929lbs, 16/22 mpg) engine's compression ratio could be upped to the DFI "standard" of 12:1 it could probably outperform the Venza in both FE and performance. Obviously that would mean detuning the turbo, lowering maximum boost level, or discarding the turbo altogether.

The Venza and CX7 are two totally different animals. That engine in the venza is also quite a bit different than the CX7 engine. Its comparing apples to oranges a more fair comparison would be the GR v6 in the venza to the DISI mazda engine.

And like you stated its near impossible in the RDX or the CX7 to stay out of "boost" so to answer your other questions yes the cruise control gets the turbo spooling because the turbo spools anytime your applying throttle. Also it would never be better if the turbo wasnt "there" even off "boost" because the performance without it there would be even more piss poor with it there. Coming from experience dynoing my mazdaspeed protege with basic bolt ons i produced near 180tq at about 3200rpm when the turbo was at peak spool. The torque never dropped below 150 at any time. However a Protege5 with full bolt ons AND an ECU reflash peaked at 100tq. So where can you say that not having a turbo on an engine would make more sense power wise or efficiency wise.

 

[evilmonkeyMSP]

I've heard of one talking out of their ass, but never actually seen it put down in text. Well done. This thread makea absolutely no sense

 

[hectik1]

When on the highway with the CC, you will seen boost maybe 1% of the time, when accelerating. This is with my MS3, but it still applies. I have used the CC going through the hills and mountains in PA and TN. When it did get into boost (literally happend once, maybe twice) it never got above 3, 4 psi.