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Old 03-16-2009, 06:25 PM   #41
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Originally Posted by theholycow View Post
the ring mates to the pinion, and if you change the size of the ring it will have more teeth, so it changes the ring-pinion ratio.
While that's true, the larger ring gear is going to change where (in the differential case) the two gears mesh, assuming the larger gear can even fit in the case. That says to me that you're going to at least need a modified pinion. If you're changing out both the ring gear and the pinion, there's nothing left that requires the gear teeth be one size or another.
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Old 03-17-2009, 05:27 PM   #42
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OK, I have an '88 CRX DX with a D15B2 and DPFI. From a performance and modification standpoint, everybody seems to recommend upgrading to MPFI, but more than a few people have warned me that it will result in a net loss of fuel economy.

But if I'm not mistaken, the CRX HF was equipped with MPFI. So I'm wondering if the loss in FE that I've been warned about has just been a result of heavy right feet in the drivers in question. Does anybody here have any experience with the DPFI to MPFI swap? I'm especially interested in finding out what happens when driven judiciously and with FE in mind....

The conversion appears to be relatively cheap and easy. So my big issue would be whether it will help or hurt me in the FE dept. Any input will be helpful....
SOHC ZC motor ( which is pretty much exactly the same as the a6 motor w/ a fatter cam, supposedly) w/ mpfi swap, but I'm using the z6 intake manifold and a small IHI turbo from a ford probe gt. average 32-35 combined. 40+ highway. Can't say, as I've never actually driven on a full tank of gas from fill up to E on the highway.

I did the MPFI swap a long as time ago, I didn't keep records of gas mileage or even mentally note it at all back then. So I can't say how it was before the swap. I drive with FE in mind 90% of the time and I'm really having a hard time getting to 40 on my commute in the morning, which is mostly highway, a big hill, and traffic in the morning.

Another thing that might interest you, is that I swap the counter shaft and ring gear for the si (It's an SI now, more or less) one and didn't notich a change in mileage and the car runs way better, likes its more in it powerband and revs WAY faster.
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Old 03-17-2009, 06:10 PM   #43
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The 1988-1991 HF and 1992-1995 DX have non-VTEC motors with MPFI. The 1988-1991 HF ECU will drop right in. But it will not have proper fuel maps for a DX motor with SI MPFI. Also, you will have to use an EGR valve, since it looks for one. This means you will be stuck using the HF intake manifold, which is not the best idea, either. The 1992-1995 DX ECU would actually be the best choice. BUT, it is an OBDI ECU. Not that converting to OBDI is hard. And OBDI WILL get better MPG than OBD0. However, I know that ALOT of people would rather not do this. Also, I have never tried this. But you might have problems bolting the 1992-1995 distributer (which MUCH be used with an OBDI ECU) to the 1988-1991 head. This problem might be best solved by upgrading to a 1992-1995 DX head (which you can get for a song or free these days).



One of the problems with 'proper tuning' is that you are running with a razor-thin margin of error. ANYTHING that might happen to disrupt this could throw your tuning off enough to cause problems. Also, reliabilty may be better with a lightly turbocharged engine that is properly tuned. BUT, don't expect it to be stock-reliable. The way I see it, a boosted D should NEVER be your sole vehicle.

boosted on 87 octane 6-7lbs for 2+ years. Main transportation.

"And OBDI WILL get better MPG than OBD0" Explain this?????

I do like the idea of using a P06 ECU instead of a PM6. Fuel and Ignition mapping will probably be way better. plus heated o2, which is one reason obd1 would be better mileage. can't think of anything else.
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Old 03-17-2009, 07:20 PM   #44
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"And OBDI WILL get better MPG than OBD0" Explain this
To add to the stuff you mentioned, 4 years of advancements in computing hardware and electronic engine management.
The ECUs used in '88-91 Civics and CRXs were designed in the mid eighties... The amount of computing power you could fit in that metal box (with a reasonable price tag) was fairly limited. The additional years of development would allow for faster, more complex computing hardware, running superior software, yielding more precise and efficient results.
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Old 03-17-2009, 08:58 PM   #45
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To add to the stuff you mentioned, 4 years of advancements in computing hardware and electronic engine management.
The ECUs used in '88-91 Civics and CRXs were designed in the mid eighties... The amount of computing power you could fit in that metal box (with a reasonable price tag) was fairly limited. The additional years of development would allow for faster, more complex computing hardware, running superior software, yielding more precise and efficient results.

This is probably true. I can't argue this as I have no way of testing it. but its not like 92-95's are getting a whole lot better mileage. ok, honestly I don't know what people are getting in obd1 civic's except vx's but that's completely different. I know 4th gen 88-91's do really well, 40 easy. I wouldn't convert on the bais that your going to get better mileage without doing anything else. I wouldn't believe unless I seen it.
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Old 03-18-2009, 07:46 PM   #46
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"And OBDI WILL get better MPG than OBD0" Explain this?????

I do like the idea of using a P06 ECU instead of a PM6. Fuel and Ignition mapping will probably be way better. plus heated o2, which is one reason obd1 would be better mileage. can't think of anything else.
obd1 will get the same mpg as obd0 while making more power. its the lots of little things like the head intake manifold, etc. that make the cars of that year better.

i dont know anybody that prefers obd0 over obd1... but an obd1 dx can get 42 highway easy and pull around more car than an obd0. dont misunderstand me, i love the feel of a crx(or obd0 civic) si, but i prefer a obd1 cx with a d16z6 any day except an auto-x day

anyway, why are you boosting with low octane??
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Old 03-22-2009, 04:32 PM   #47
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obd1 will get the same mpg as obd0 while making more power. its the lots of little things like the head intake manifold, etc. that make the cars of that year better.

i dont know anybody that prefers obd0 over obd1... but an obd1 dx can get 42 highway easy and pull around more car than an obd0. dont misunderstand me, i love the feel of a crx(or obd0 civic) si, but i prefer a obd1 cx with a d16z6 any day except an auto-x day

anyway, why are you boosting with low octane??
You can't really compare obd1 engines with obd0 engines. vtec to the si motor or b7 to the b2 dpfi. I bet a b2 with mpfi would make the same horsepower or dam near the same as a b7 with an obd0 ecu. and we'd be talking about 5HP +/-. A b7's not faster then a a6.

All obd0's get 40+ highway. except maybe the STD w/ a 4 speed.

I ran regular cause I was learning how to tune and wasn't going into boost and its my DD, so I ran 87 to save $2-3 a week/or 2 ( whatever I know its not a lot). But the car doesn't detonate. and this is with a a sub par tune, and small turbo thats actually at 75% efficiency at 3k. Nows it become more of an experiment to see how much boost I can run on 87 type of thing.
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Old 03-23-2009, 09:47 AM   #48
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All obd0's get 40+ highway. except maybe the STD w/ a 4 speed.
The STD does get over 40+ on the highway @ 55-60mph steady throttle.
for the STD having a more FE Cam compared to the DX/LX/EX/Si Cams.
To the STD's 4spd... (By the way I just picked up a 5sp HF Tranny Friday )
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Old 03-23-2009, 08:29 PM   #49
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the a6 gets 40+ mpg highway??? i was not aware.... anyway, i was getting up to 42 mpg with a z6 and people on here can vouch for my heavy foot and lack of hypermiling technique the car was super punchy too!
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Old 03-23-2009, 09:56 PM   #50
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the a6 gets 40+ mpg highway???
With different gearing and/or ECU modifications maybe.

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i was getting up to 42 mpg with a z6 and people on here can vouch for my heavy foot and lack of hypermiling technique
+1
I once managed to hit almost 46 mpg with pure highway driving, through 42 highway is more typical. The best I've gotten with day-to-day driving is 44 mpg with light-constant-throttle. Those numbers were with the old 4 speed auto tranny... I haven't had the opportunity/patience to try it with the manual. It's so easy (and entertaining) to flip open the throttle and roar on up to 7k RPM.
Even with my less-than-optimal throttle technique, and 8 mile/15 minute commute trips (the engine is warming up for the first quarter of each trip), I'm getting 32-35 mpg.
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