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Old 12-01-2013, 01:50 PM
josh_s13 josh_s13 is offline
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Default fuel economic engine choice

so i recently picked a z31 for a daily driver, and the engine will probably need 800+ dollars within the next year or so. I dont really want to dump that much money in an old vg30e. i have been thinking that there may be some other relativley low cost alternatives. In my opinion near 30mpg from 87 octane with around 200 to 250hp would be near ideal.
I had thought that a ca18det with a rasied compression, retarded timing, and a lot of intercooler would give me a chance at this.
What are you guy's thoughts on this?
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Old 12-01-2013, 05:11 PM
Def Def is offline
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You can get an NA SR20DE for super cheap. Toss an OEM SR mani and a T25 with an eBay IC if you want a little more power. I'm not sure it'd work on 87, but it might at like 6-7 psi and pulling timing in boost.

The only negative of the DE for the ultimate fuel economy setup is that the 5th gear is .838 vs. the .759 of the S13 DET trans. But I'm sure you can trade that with somebody with a DET trans (heck, I'll do it!).

The CA is going to have to be worked too hard to give over 200 HP to run on 87 octane IMO.
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Old 12-02-2013, 07:03 AM
josh_s13 josh_s13 is offline
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Wouldn't the lack of oil squirters on the sr20de hurt the chances of running the lower octane successfully? Maybe decking the head on a sr20det would yield better chances, although I would assume that mid 20mpg would be all that I could get.
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Old 12-02-2013, 07:29 AM
josh_s13 josh_s13 is offline
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For what it's worth, I still have coilpacks, injectors, and intercooler from the rb20 that I had. I think these parts are interchangeable with the CA18.
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Old 12-02-2013, 07:50 AM
Matt93SE Matt93SE is offline
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A properly tuned VG30E-T will get ~30mpg and they're dead-nuts reliable.

..And they came in the car...

.. And you can make 400+hp on stock internals if you want to turn up the wick..
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Old 12-02-2013, 03:35 PM
Def Def is offline
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No issue with lack of squirters for a DD.

I don't see a VG30 getting 30 mpg in a z31...
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Old 12-02-2013, 03:51 PM
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Quote:
Originally Posted by josh_s13 View Post
Wouldn't the lack of oil squirters on the sr20de hurt the chances of running the lower octane successfully? Maybe decking the head on a sr20det would yield better chances, although I would assume that mid 20mpg would be all that I could get.
An SR20DET would probably do high 20 mpg if driven right in a Z31. On the highway at about 80-85 mph with really draggy aero mine would do about 27-28 mpg with the 4.36.

A DE will have higher thermal efficiency with the higher CR, and if you gear it long enough it'll get pretty freakin' sweet gas mileage. Way better than a VG30.
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Old 12-02-2013, 05:12 PM
josh_s13 josh_s13 is offline
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Quote:
Originally Posted by Def View Post
An SR20DET would probably do high 20 mpg if driven right in a Z31. On the highway at about 80-85 mph with really draggy aero mine would do about 27-28 mpg with the 4.36.
This gives me high hopes, especially with no aero and 3.7 gears (3.54 gears available in some other models)

The first tank of gas yielded 19.6MPG with a mix of easy city and highway driving. Part of the tank was on a bad O2 sensor, and the whole tank was on a couple dozen other broke things.

I assume that the vg30 is also a bit heavier than some of the smaller turbocharged options. I figure that's worth something in the fuel mileage equation.

Without trying to open a huge can of worms what are the major differences in the sr20de and sr20det aside from the obvious turbo assembly? Also, any idea of how much valve to piston clearance the det has on the stock cam?
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Old 12-02-2013, 08:42 PM
Matt93SE Matt93SE is offline
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Quote:
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No issue with lack of squirters for a DD.

I don't see a VG30 getting 30 mpg in a z31...
You haven't hung around on the VG forums much, have you?

Myself and many other VG Maxima guys routinely get ~27mpg on cars with basic bolt-ons.. add a proper ECU tune for lean-burning while cruising and you can easily top 30mpg at highway speeds. I've seen it done several times, even on turbo cars.
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Old 12-03-2013, 06:53 AM
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Quote:
Originally Posted by josh_s13 View Post
This gives me high hopes, especially with no aero and 3.7 gears (3.54 gears available in some other models)

The first tank of gas yielded 19.6MPG with a mix of easy city and highway driving. Part of the tank was on a bad O2 sensor, and the whole tank was on a couple dozen other broke things.

I assume that the vg30 is also a bit heavier than some of the smaller turbocharged options. I figure that's worth something in the fuel mileage equation.

Without trying to open a huge can of worms what are the major differences in the sr20de and sr20det aside from the obvious turbo assembly? Also, any idea of how much valve to piston clearance the det has on the stock cam?
The other thing is friction - more cylinders generally equals more friction.

Piston to valve clearance is fine for any even remotely streetable cam you can put in the engine. Stick with stock cams tho'. That MPG was also with 264/264 cams which generally decreased mileage due to a greater amount of pumping losses and overlap with a bad intake/exhaust pressure ratio at high manifold vacuum conditions.
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