BIG car

[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!