BIG car

[Andy-Paul]

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

[SVOboy]

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.

[s1120]

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

[01_fast_ride]

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

[s1120]

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.

[Andy-Paul]

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...

[Red]

Didn't the crown vic come in a CNG version? I seem to remember some of the campus police cars marked as such

[Andy-Paul]

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.

[omgwtfbyobbq]

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.

[rh77]

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

[landspeed]

If the engine is coming out, how about increasing the compression ratio a little bit? I think that would give more fuel economy, and maybe even more power (if you can avoid knock at maximum load).

[theclencher]

I applaud his decision to use a sedan to move the 5 big folks instead of the more usual "need" to get a Subdivision or Explosion.

I also understand that since this car practically fell in your lap, that's what you're going to use. Just to mention, though, if you come across a GM full-size fwd with the 3.8 (think Le Sabre, Bonneville, etc.) from the late '80's on, they should give an honest 30 mpg hwy properly driven, stock. For some reason that 3.8 is a decent fe package in those larger cars, equalling or besting the fuel efficiency of the same model with a smaller engine! I wonder how they would perform with a 5-speed stick and removal of all those power-robbing accessories?

IMHO, the four-valve head's main strength lies in high rpm applications, OR, if equipped with a variable valve control system of some sort, low and high rpm applications. Since it is unlikely you'll transplant a variable valve control system (and I don't know if it was ever offered on that engine series???) AND since low rpm operations are our fe friend, my instinct is to stay with the 2-valve head. You may want to research fe ratings for different versions of that engine in as consistant a drivetrain package as possible to see what is really going on out there.

If the 6 speed offers a taller OD than the 4 speed it MAY help. If cruise rpm is too high for best fe, higher rear end gears and/or taller tires could help too without being as big an effort or expense.

Even with these mods I have my doubts about getting 30. It's just such a tall order for a V8 especially in a full-size package. Seems the odds get much better with a 6 cyl.

[sipnciv]

I didn't see mention of changing out the rear gears for lower cruising rpms yet.

[sipnciv]

Yep, it's there.

[s1120]

Well a gear swap may not work. Whats in there now? It is a big car, and those Mod motors like some rev's so if you go to too tall a ratio, you could drop the motor out of its power band, and make the millage worse.

[omgwtfbyobbq]

The power band does not usually equate to efficiency at a cruise.

[theclencher]

i know from my f150 that it's possible to gear too high. it falls "off the cam" and without retuning (cam, intake, exhaust) for the lower rpm ops the fe gains just weren't there for me.

[omgwtfbyobbq]

How do you know it's a problem with the intake/exhaust profile and not the TCC?

[Pyrorocketeer]

Originally Posted by omgwtfbyobbq

The power band does not usually equate to efficiency at a cruise.

peak torque = max efficiency....

engine is most efficient, when it is at the rpm where its making the most peak power.

[omgwtfbyobbq]

I got a few BSFC maps that disagree with that. Not to say that it's impossible for peak torque and minimum BSFC to coincide, just that it generally doesn't happen IME.

[skewbe]

peak torque = max acceleration.

[theclencher]

Originally Posted by omgwtfbyobbq

How do you know it's a problem with the intake/exhaust profile and not the TCC?

cuz i can feel when it locks/unlocks... and the excessive downshifting too

[omgwtfbyobbq]

If it's excessively downshifting then it's likely a problem with the way the trans is setup, not the intake/exhaust profile.

[theclencher]

it did that after i upped the dia of the tires

now tire size 1/2way tween stock and what i had; propensity to downshift also 1/2way

[omgwtfbyobbq]

If the trans is unlocking the TCC and downshifting you definitely won't see any advantages to taller ratios since the trans won't let ya. Like I said before, that doesn't mean the engine is more inefficient w/ taller gearing, just that the driveline is. Only practical and consistent way to test if taller ratios help would be to get a manual...

[s1120]

Originally Posted by omgwtfbyobbq

The power band does not usually equate to efficiency at a cruise.

What I was refering to is that if you gear it to high, you may need to give a lot more throttle input to keep a speed. I played that game with a few trucks, and once I increased rev's to bring the engine closer to its porer range, MPG jumped up. Also in the same vain, increasing HP may also increase MPG if the car/truck/whatever was slighly underpowerd.

[omgwtfbyobbq]

Generally, more throttle is good for efficiency over a given speed range, assuming the mixture doesn't go too rich and the transmission will stay in gear. Like theclencher mentioned bigger automatics are a pain to gear down, since the trans will just start kicking down more and alla that, with the result being no advantage. Manuals are much better in that the engine speed and load is up to the driver, if the driver can set the open loop mixture that's icing on the cake.

[Andy-Paul]

A lot of good thinking going on here, and I am grateful for it!

The only CNG approved 6-cyls are either the Ford Taurus Vulcan (uh-UH!) or the 4.2 liter from the F150. I am unfamiliar with that engine, but will search around in your archived discussions for more input.

The whole exhaust amgle will require some thinking. If I recall, isn't there some relation between exhaust back-pressure and torque delivery?

As to the NG fuel/air mix, the 'octane' rating (which I believe is ethane in the methane) is 120-140, so I don't expect to hear much knocking no matter how lean the fuel trim goes. The compression can go up a bit, but that is a cast iron block, which can't take it like Al (or Al+Si+Sr)

I will continue to think about the whole transmission issue, and also look up the gear ratios for the two trannies. My general thought was that a 6-speed could help out by keeping the revs in a more narrow range than the 4spd. I will also look into variable valve controls. My memory is blank on that one.

[omgwtfbyobbq]

A tuned intake and exhaust will help torque immensely over a narrow range of engine speeds. For instance, the S2000 has ~110% VE at peak power which is great for a NA engine. But... It's a pain IMO to match the exhaust and intake lengths for maybe 10% more torque at some engine speed.

[Andy-Paul]

OK

I have looked it all up. There is a 6-speed available for the Modular V8, but it comes on the late model Ford Explorer/ Mountaineer, which, incidentally, also has 24 valves with some form of valve timing to improve the mileage--needless to say, there's a lot of room for improvement. The Cx is 0.41 for the Explorer vs 0.39 for the Crown Vic, and, simpler valve set-up and 4-spd included, the Vic wins hands-down on mileage.


At this point, I must postpone any more research because one of my neighbors chopped down three shag-bark hickory trees (chd= 27") and I have to figure out where to store roughly 1000 bd. feet of 5/4 x 6 and 5/4 x 8 inch planking while the stuff cures down to the local humidity of 12%. It will make a lovely kitchen floor, and the price is right (currently I have US$365 invested in the whole project).

Let me say, however, that I consider your nay-saying of a 30+ mpg V8 to be a gauntlet of honor thrown down before me in a challenge (cue cheesy trumpets) and I will best that number. Stay tuned!