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Old 12-10-2009, 01:50 PM   #51 (permalink)
1995 Previa LE S/C Driver
 
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My own Previa is supercharged, so it doesn't seem to gasp for air like my '01 Corolla does at the same altitudes-- it's pretty much like a turboprop airplane at 30,000 feet getting all the air it needs to run properly but not having to fight the air resistance.

Looking at Orange4Boy's quick-glance profile by his posts, I would actually guess that his Previa is not supercharged, seeing as S/C started as an option with the '94 models and then was standard on the '95 and later. Maybe his mileage will go down after all, or stay close to the same.

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Old 12-10-2009, 01:54 PM   #52 (permalink)
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Old 12-10-2009, 06:45 PM   #53 (permalink)
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inertia

Quote:
Originally Posted by orange4boy View Post
Update:

Kamm is working very well at turning heads. Helping with mileage too but that is subjective because I have not been able to do tests. Terminal velocity on my coastdown was noticeably higher with the coroplast addition. High speed glide seems much better.

I wish I could quantify the change more scientifically but I never have the time for testing and I don't live near a flat stretch of road.

My improved overall mileage and some numbers do point to an improvement:

I did get a record highway run of 36 mpg, previous record: 33.3 All other recent runs have been higher as well.
Vacuum gauge shows 17inches at 80kph used to show 16.5

Since my overall mileage has been trending up, I will say that it works and I'm keeping it on but would like to rework it and finish the bottom sides. That will have to wait till spring.

V2 will be even better. More stainless, more lexan, less drag.

In the meantime, check out my Prius rescue thread, link below: Transaxle guts and takedown gore to ensue shortly...
If you get around to testing and do A-B-A runs,with and without the tail,consider adding ballast to the van equal to the weight of the tail when you run without it.
The tail's added mass will add inertia and increase momentum,adding coasting difference ( more ) even without drag reduction.
By ballasting,you simplify your testing and data reduction to a single variable.
I know it sounds anal,but multiple variables will drive you insane when you attempt to make sense of your results.
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Old 12-10-2009, 08:40 PM   #54 (permalink)
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Quote:
If you get around to testing and do A-B-A runs,with and without the tail,consider adding ballast to the van equal to the weight of the tail when you run without it.
That's easy. I'll just put it into the back of the van.

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Considering aerodynamics, orange4boy, have you noticed if you get better mileage at high altitudes?
I have heard of this effect but have not been on a trip high enough to see. I know high altitude is better for aircraft FE. Must be for the same reasons: lower drag from thinner air = higher ground speed per engine revolution. You will read the same airspeed but have higher ground speed. The lean burn is also true if your engine can't compensate. I remember having to re-lean the engine after an altitude change.
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Old 12-11-2009, 11:32 AM   #55 (permalink)
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Originally Posted by orange4boy View Post
I have heard of this effect but have not been on a trip high enough to see. I know high altitude is better for aircraft FE. Must be for the same reasons: lower drag from thinner air = higher ground speed per engine revolution. You will read the same airspeed but have higher ground speed.
I would suppose "airspeed is airspeed" at any altitude or air density. And as far as taking off, you should fly INTO the wind to get the airspeed up for the lift you need-- groundspeed is not really a factor on takeoff (maybe a lower groundspeed helps as there is less drag from the wheels and such, but that might be a marginal concern).

Otherwise, yes, high altitudes result in less drag-- the supercharger just makes sure the engine can still run in the rarified atmosphere.

What I need (or think I need) is a light that will come on when the supercharger comes on -- the supercharger is not full-time, but is engaged by a signal from the ECU.

I suppose a vacuum/boost gauge would do the same thing, more or less, but having a definite signal when boost is on would be interesting. One thing I want to avoid is the potential for detonation and potential spark retarding when boost is on, but I'm not sure if running with lower dynamic compression (unboosted) is actually more wasteful than boosted anyway. I suppose that running unboosted a lot will reduce pumping losses since the static compression ratio of the 2TZ-FZE is 8.9:1 rather than 9.3:1, but I'm just guessing at that.
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Old 12-11-2009, 03:21 PM   #56 (permalink)
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I should have said indicated airspeed. At altitude, indicated airspeed will read low relative to true airspeed because of the "thinness" of the air and the way airspeed is measured.

A boost light would be good. I have a fancy digital vacuum gauge that you can set to change colour when a certain setting is reached. It's very handy because you don't have to be looking at it to see the change point.

Why would running unboosted reduce pumping losses? Isn't it the other way around or are you referring to compressor/SC losses?

It would also be a good thing to have a fuel mixture gauge to see when you are enriched. I imagine that under boost, it runs rich. Keeping out of that zone would help your FE. I need one too.
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Old 12-11-2009, 03:30 PM   #57 (permalink)
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I imagine that there would be pumping losses due to the higher dynamic compression ratio. Would, at certain loads, an engine with a higher compression ratio have more pumping losses than one the same size at a lower compression ratio? (For example, just tooling around a parking lot or in very light traffic.)

If this weren't true, then why would the supercharger be controlled by the ECU in the first place?

I suppose running at a certain amount of boost could cause the system to enrichen the mixture and possibly reduce the amount of spark advance to prevent predetonation. (Maybe water injection could help with that.)

Last edited by AlaricD; 12-11-2009 at 03:38 PM..
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Old 12-11-2009, 04:37 PM   #58 (permalink)
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Ah. lower pumping losses with respect to the compression ratio. That makes sense. I'm not an expert on this stuff by any means, especially when boost is added to the mix.

Quote:
I suppose running at a certain amount of boost could cause the system to enrichen the mixture and possibly reduce the amount of spark advance to prevent predetonation. (Maybe water injection could help with that.)
I found a great article on home brewed water injection using a cold start injector which the Previa already has. Mine is disconnected with no ill effect. Could easily be modded to be a water injector.Found here along with some other great Toyota tips (see his signature)Cheap water injection. The "free" mod series. Also see his thread on cheap A/F mixture monitoring.

Also for the Previa, have you seen my thread on TCC lockup switch?http://ecomodder.com/forum/showthrea...tch-10028.html
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Old 12-11-2009, 04:42 PM   #59 (permalink)
1995 Previa LE S/C Driver
 
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Now THAT is awesome! Who'da thunk it could be that easy to add water injection?

I'll look into that, and also show that to a friend of mine who's a mechanic for a small used-car dealer here in town-- he might get a kick out of it.
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Old 12-11-2009, 04:50 PM   #60 (permalink)
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Love those mods. Don't forget to try the quicker shifting adjustment. That's a good one too. Better for the tranny and FE. Just takes minutes.

I'd love to do the home made electronic shifter at some point.

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