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10-21-2007, 05:41 PM
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#1
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Registered Member
Join Date: Oct 2007
Posts: 57
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Using boost for mileage
So tonight a bunch of us were setting around talking about boosting engines IE: turbo or supercharger. After strongly considering everything, I've come to the conclusion that if one were to take a d15z1 Honda VX Engine that needs rebuilt and do the following:
Rebuild it with 8.0-8.5-1 compression pistons using a smaller turbo with an a/r of around .4-.5 creating a suitable boost range, definitely falling off way before redline, but giving ample boost during highway driving. I was thinking around 8-10lbs of boost. This would not necessarily net a higher hp figure or tq figure, but instead of using compression to create power, it would be using forced air.
I'm not sure if it would be worth the effort, but I honestly think a boosted d15 with low low compression, making about the same whp as a stock engine, would constantly get better mileage, due to internal efficiency. Of course it would have to be properly tuned, but this could also be done by hooking up a wide band gauge to the already present wide band o2 sensor and using an ApexI fuel controller.
I'm sure its been talked about, but using boost to create power, not compression, wouldn't that make the engine more efficient?
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10-21-2007, 08:53 PM
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#2
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Registered Member
Join Date: Apr 2007
Posts: 245
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Nah, I wouldn't bother. Honda knows how to build engines and they don't need to be modified to create good numbers. Oh wait, that's what you said and I didn't agree with.
Still trying to figure out why you would tell someone that Honda had it right when they built their cars so you shouldn't mess with them. But then go on and talk about how your brothers Civic is so much better after the mods and you wanting to boost one for better numbers...
On the realistic side I think boosting would be a good idea if it could be done at 1500-2000 rpm. I honestly thing my car could cruise comfortably at 55 at much lower than the 2000 rpm's that it runs at now resulting in better fuel economy, but I don't know how feasible it is to get a final gear that would allow that.
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10-22-2007, 02:12 AM
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#3
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Registered Member
Join Date: Oct 2007
Posts: 89
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My Regal can get up to 33 MPG on the freeway because its not using any boost at all when your on cruise control or lightly on the throttle.
On the side streets I get 10-15 MPG
Boost does not help fuel economy at all
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1994 Geo Metro

1998 Buick Regal GS

1999 Chevrolet C2500

1998 Corvette
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10-22-2007, 08:08 AM
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#4
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Registered Member
Join Date: Mar 2007
Posts: 812
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Quote:
Originally Posted by Three6Eight
My Regal can get up to 33 MPG on the freeway because its not using any boost at all when your on cruise control or lightly on the throttle.
On the side streets I get 10-15 MPG
Boost does not help fuel economy at all 
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When it's not designed to and when compared to oranges... of course it wont
http://www.fueleconomy.gov/ -- 7.5% On that same page, 12% with direct injection.
From a thermodynamics stand point - higher thermal efficiency (turbo charging is considered waste energy recovery).
Anecdotal evidence isn't a law (or even general rule) - it's really not even evidence, it's just anecdotal
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Time is the best teacher. Unfortunately it kills all its students.
Bike Miles (Begin Aug. 20 - '07): ~433.2 miles
11/12
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10-22-2007, 12:35 PM
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#5
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Registered Member
Join Date: Oct 2008
Posts: 1,873
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Quote:
Originally Posted by Three6Eight
My Regal can get up to 33 MPG on the freeway because its not using any boost at all when your on cruise control or lightly on the throttle.
On the side streets I get 10-15 MPG
Boost does not help fuel economy at all 
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hey man that's a sweet ride! fill out a gas log so i can see your numbers. i've increased the FE in my olds 88 greatly in part by the help of the guys here.
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10-22-2007, 12:50 PM
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#6
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Registered Member
Join Date: Oct 2007
Posts: 57
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I said Honda has a good design, and they do know what they are doing. I'm not looking to make more power, lower compression = less power, using boost to increase the power to stock levels, would create high air velocity into the combustion chambers, also would create better atomization of the fuel. I'm not saying the D15 isn't a great design, but historically Honda has veered away from using boost.
Replacing stock pistons with 8:1 compression would kill hp and tq, but with a small amount of boost would be close to its original numbers, but with a higher intake air velocity, and better fuel atomization.
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10-23-2007, 02:38 AM
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#7
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Registered Member
Join Date: Oct 2007
Posts: 89
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Quote:
Originally Posted by bowtieguy
hey man that's a sweet ride! fill out a gas log so i can see your numbers. i've increased the FE in my olds 88 greatly in part by the help of the guys here.
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Thanks for the compliment
I often go from SD to Fairfield, its a 560 mile trip
I wanted to see if I can make it without stopping for gas. First time I chickened out and filled up at 470 miles because I was un familiar with the area and the gas stops were space 20 miles apart.
On the way back I pulled off 511 miles on 1 tank. I really think I can pull it off with no gas stop. Just gotta stay off that boost. Ill fill a gas log next time I go it should be in the next few weeks.
Im thinking of pulling off the Supercharger belt that way I cant use anyboost at all.
__________________
1994 Geo Metro

1998 Buick Regal GS

1999 Chevrolet C2500

1998 Corvette
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10-23-2007, 08:31 AM
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#8
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Registered Member
Join Date: Jun 2007
Posts: 24
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Lets think about this. In order to run any air throttled engine with no (or very little) restriction your going to need to be at or very near full throttle. If you are running boost at highway speeds your intake manifold runners and head ports are going to have to be TINY. So, if you designed an engine like this, it would have about 10-20 horsepower and would be impossible to drive in any form of traffic.
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10-22-2007, 07:19 AM
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#9
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Registered Member
Join Date: Oct 2006
Posts: 1,108
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Given the head design on the d15z1 (it's designed super well for getting the cylinder filled with air), you could go with a T15 Garret turbo adapted to fit the OEM manifold and leave the internal wastegate unhooked from the actuator. This would keep you out of boost but negate the pumping loses due to high vacuum during acceleration. That, theoretically, would net you higher FE. The only thing is, you'd have to watch the A/F ratio to make sure you don't go super lean. Even though the d15Z1 is designed to run lean in the first place, but it does have it's limits.
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Quote:
Originally Posted by ezeedee
controversy is an idea thought up by weak people who are too afraid to hear the truth.
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10-22-2007, 07:35 AM
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#10
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Registered Member
Join Date: Jan 2006
Posts: 2,444
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I would think that higher compression would make the engine more efficent and boosting it would just give you more power when you want it. Normally you would not need boost to operate at normal highway speeds to keep a steady speed.
FYI - eCycle is experimenting with small superchargers driven directly with their electric motor . . . couple that with your intake and a flapper valve and you could run NA or Supercharged when you want to with variable boost.
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