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Old 09-27-2007, 10:34 AM   #1
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BIG car

Hello neighbors;

I have inherited a late model Crown Victoria. As I have no money in it, and need a car anyway, I will spend the savings that were for the next car on a dedicated CNG conversion.

Here's where I need advice. The current car is a 16-valve V8 (4.6L modular engine) with a 4 spd AT. Since the engine is about to be dropped and reworked anyway, would there be FE benefits from upgrading the head to a 24-valve or 32-valve system (kid brother works in a junk yard)?

How about changing out the 4-spd auto for a 6 spd auto (same kid brother)? Unfortunately, a manual is out of the question.

I am not attempting hypermiler status, just trying to build a highway cruiser that will make more like 30 mpg than its EPA rated 25 mpg--any extra would be gravy, and I will see what I can do about reducing weight as I go.

I look forward to hearing your suggestions.

Andy-Paul
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Old 09-27-2007, 12:19 PM   #2
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Anything better than the 20 my gramma's gets would prolly be decent...

I don't think anything that would give you more power would help you out much, but depending on the gear ratios a 6 speed sounds like it would help, though that money might be enough to buy another car,

Welcome to the site.
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Old 09-27-2007, 12:51 PM   #3
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Well I doupt a 4valve motor will get any better milage then your two valve. Also you cant just swap the heads. You need to change the whole motor. I think you would be best off working with what you have. First I would work on the exoust. The stock system was not the best, and a nice flowing system would probably gain you a bit. Other then that just a good tune up will get you a solid 20+mpg
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Old 09-27-2007, 12:53 PM   #4
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Congrats on the free car.
I tend to agree with SVOboy on the trans. The better overdrive ratio will probably help at cruising speed. Although if you don't really need such a large vehicle there are any number of inexpensive vehicles that could get the goal of 30mpg hwy.

Joe
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Old 09-27-2007, 01:13 PM   #5
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wwll those trans are computer controled. To swap all that over will mean changing the PCM and wiring harness and any trans control units. Tough to justfy that realy eaven if you can get the stuff for free.
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Old 09-27-2007, 02:15 PM   #6
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The 6-spd would come from a wrecked Ford Explorer--which has the same engine as the Crown Vic. The other aspect is that I am shooting for one non-petroleum vehicle on the lot that will carry five large people. That slims down the pickings considerably, and, as stated earlier, the car is a freebie.

I appreciate the warn-off from the extra valves in the head. The 4.6l Modular V8 has been configured with 16, 24, and 32 valves for different models, and I was unsure of the reasoning behind it. As for my brother in the junk yard, it would only amount to a nice discount...
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Old 09-27-2007, 03:20 PM   #7
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Didn't the crown vic come in a CNG version? I seem to remember some of the campus police cars marked as such
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Old 09-27-2007, 04:24 PM   #8
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Yes, it did. Because the platform was available in a fleet setting, any Crown Vic, Mercury Gran Marquis, Merc Marauder or Lincoln Towncar from 1996 to present is EPA approved for nat gas retrofit.
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Old 09-27-2007, 07:14 PM   #9
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What're the ratios for each transmission? Most gas vehicles usually can see a decent increase from taller gearing provided the car will stay in that gear with the tcc locked up. I'm not sure how much gearing would help out a CNG conversion, since you may be able to run it fairly lean.
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Old 09-27-2007, 08:07 PM   #10
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Grand Marq Experience + Crazy Engine Ideas

Hi, Welcome to GS

First -- check the ball joints for wear, if you haven't already. My Father-in-Law's old Gd. Marq collapsed at the front passenger side wheel, luckily while moving it in the driveway (and not on the highway). Same for excess buildup of carbon, which causes constant knocking and the knock sensor to burn-out. Also the intake manifold can be sensitive to fracture (all experiences from this one car).

Depending on how bold you want to go (someone else can back me up on this or not), but how about a 6-cylinder turbo (or even something like the 4.0L from the Explorer)? Usually finding the smallest displacement helps FE and adding forced induction when needed can help with adding some power when you need it, and low fuel consumption at cruise. Keeping your foot out it -- that may be another story

The first thing I thought of was the 2.3L Lima or OHC Turbo -- found in the Merkur XR4Ti, Mustang SVO (intercooled), and Thunderbird Turbo Coupe / Cougar XR7 (intercooled). The latter were heavy cars and seemed to work well with that setup (but they were at 3419 lb. vs. the Vic at 4129). The supercharged models might be a better fit, but not as easy to control for FE

Just brainstorming...best of luck...

RH77
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