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Old 10-21-2007, 06:41 PM   #1
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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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Old 10-21-2007, 09:53 PM   #2
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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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Old 10-22-2007, 03:12 AM   #3
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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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Old 10-22-2007, 08:19 AM   #4
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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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Old 10-22-2007, 08:35 AM   #5
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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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Old 10-22-2007, 09:08 AM   #6
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Quote:
Originally Posted by Three6Eight View Post
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
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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Old 10-22-2007, 10:13 AM   #7
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the savings from blowers come from fitting a smaller displacement engine from what it would have had naturally aspirated

di could improve fe on any size engine
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Old 10-22-2007, 01:35 PM   #8
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Originally Posted by Three6Eight View Post
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
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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Old 10-22-2007, 01:50 PM   #9
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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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Old 10-22-2007, 02:10 PM   #10
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Boosting it will have to push more air in to increase the velocity which would mean more fuel and more power which would require you to throttle back to the needed power levels and then you are right back where you started from. Maybe you want to make smaller intake passages to increase the air velocity and THEN boost it back to normal power levels with even HIGHER air intake velocity then maybe you will have the better air fuel mixing.
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