RNation0001

iTrader: (2)

I may be trading for a l33 aluminum block and im debating on building an engine with one goal in mind, GAS Mileage!! im wondering things like what camshaft, should I build as a 4.8 or 5.3? or something else?? also what would be a cheap car to do this on, datson 280 or similar maybe?? just brainstorming on my options here

stangtrader

iTrader: (2)

Idk about the 5.3 but I do know with my fbody I had a lq4 with a t56 and managed to eek out 31 mpg on a road trip with boltons and a frost tune.my thought is the bigger motor with a little more torque made it easier to push the car.id think a sub 3000 lbs car could do 35mpg on a long drive if set up just right

RNation0001

iTrader: (2)

that's a good point. but at the same time larger Cubic inch the more air the more fuel right (on average engine load) I would think, unless u wanted to get to speed faster, a smaller cubic inch engine would more then be enough power to get up to speed and from what ive read it takes less than 50 hp to keep a car at highway speed. I could definitely see what ur saying tho I wonder if higher or lower compression is desirable, did a search and cant find anything about this topic really, lots of people wondering whats the gas mileage with large cams but no one wondering what parts to build an all out green machine? hmmmm. I just wonder if I built a 300-350hp engine with the right setup what kind of mpg I could put down in a sub3000 car.

RNation0001

iTrader: (2)

I also realize what im asking is retarded and most of you are probably thinking well just swap a damn 4 or 6 cyl into something. which I could do but im just wondering in general, be cool to have the worlds greenest ls engine right lol

Black&White

I've always wondered if you could set up a gen IV 5.3 correctly to use the DOD what kind of mileage you could get. If you want to do a cam swap your best bet is to ask one of the custom grind guys, although I wonder if they have ever gotten that question before.

bczee

iTrader: (12)

I think what would be key is the Cam.. get a custom cam.. ask Pat G for his advise.. Transmission, stall and Rear gear would also come into play.

Get a good Tuner that does more that WOT tuning. Driveablity tuning is more important.

BC

RNation0001

iTrader: (2)

That's what im thinking, cam, compression, trans, rear end, weight and aerodynamics of the car. getting good highway mileage is relatively easy but what about daily driving.

baalic

iTrader: (8)

See this is hard, for in town driving a gear ratio like a 3:73 or 4:11 would be ideal imo because it requires a lot less effort on your motor to get moving from a stop, and therefore less throttle input to gain the same results, HOWEVER, once you get on the highway the increased RPM's is going to murder your fuel mileage... On my A4 with 3.23's I got crap mileage in town and on the highway, my car only averaged 24 on the highway if I recall "i posted it in another thread" and like 14 in town...my V6 with 3.08 gears A4, gets closer to around 20 mpg in town, and around 32 on the highway, my 6 speed with 3.42's gets about 15 in town, and 30 on the highway....


If there was a way to have a variable rear differantial, I think that would be awesome, something that switched from like a 4:11 in town to a 2:73 on the highway.....talk about the best of both worlds.......

Ok so maybe I'm talking crazy it is 2 am and I need sleep ....Thoughts?

RNation0001

iTrader: (2)

we need to put a gear venders overdrive tailshaft that they make for the th400's on a t56 lol

RNation0001

iTrader: (2)

but that makes perfect since to me. I think with a 6 speed tho it would be much easier to achieve, with like a 3.23 gear maybe that way on the highway you would be at like 1100 rpm and u could just use like 4rth gear on the streets and lay off the throttle. after everything ive read they say your foot determines most of ur mpg on city mileage. assuming u don't catch every light in ur city lol, which my town has a whoping 3 stop lights.

lemons12

iTrader: (71)

With an event higher gear ratio you would hurt in town driving MPG and 6th gear would come to the point you couldn't use it unless you were speeding. Keep the 3.42s.

lemons12

iTrader: (71)

Also... Lets say you get a cam for 350$ to help gas mileage... By the time you buy springs/chain/pump/fluids/gaskets/bolts/etc.... You are in well over 500$. If it helps you get 2 more mpg better, how long would it take to offset that price if gas is 3.50$ a gallon?

Is it really worth it to spend 1000+$ to gain 2mpg?

ls1nova71

iTrader: (4)

Not hard to calculate... Depends on what kind of mileage he's currently geting, but for argument s sake, lets say 15 mpg. At $3.50 a gallon it costs $0.23 to drive a mile. 3.50÷15=.23. So if getting 2 mpg better it would be $3.50÷17=.20, so you save $0.03 per mile. Divide that into the $500 and you get 16, 666 miles until it pays for it's self. Double that for a grand...

When you look at it that was it doesn't seem worth it, but why is it when gas goes up a nickle I get so pissed???

lemons12

iTrader: (71)

I was more making a point of just thinking about it in my head for a split second... No way I would spend even a few hundred bucks to gain 1-2 mpg.

Thanks for going ahead and breaking it down though!

ls1nova71

iTrader: (4)

I figured it was a rhetorical question, but I just wanted to see what it figured out to. Besides, you have to subtract costs for driveability and just plain coolness. That's how I justify my swaps lol!

RNation0001

iTrader: (2)

lol this prolly wont be happening just a midnite brainstorming session lol.

RNation0001

iTrader: (2)

but then again all these small things 1 gal/mile here 2 there would eventually add up.

65impalass

Great thread, also want to build my Impala for mpg. I don't think it's retarded. I would want a 6 speed but autos are so much cheaper. I curently have 4.11s which is my first chalenge.

Pop N Wood

iTrader: (1)

Yeah, kinda retarded thinking about gas mileage and starting with a big V8.

But if you follow what GM is doing then start with one of their new motors with direct fuel injection. US cars get worse gas mileage than the same European models cause our feds mandate all sorts of things to keep the catalytic converter happy. Direct injection would allow you to change the tune to do things like completely turn off the fuel when decelerating. You could also bump the compression ratio sky high and set it up to run on E85. Overdrive the **** out of it then never spin the motor above say 2000 RPM. Cam it accordingly and get an intake manifold with loooong *** runners. Light weight flywheel, reduced valve spring pressure to match the low RPM redline.

By the time you are done you will realize it would have been better to buy a mid 80's Honda CRV or old style Ford Fiesta. I think the one I had weighted in at 1700#

usdmholden

Fuel cut off on deceleration is available in most aftermarket EFI systems, and I suspect it's also available in the OEM GM systems.

To maximize gas mileage you want to put the least amount of fuel in the engine possible, which also means putting the least amount of oxygen in the engine possible. This means the lowest VE and the least power possible, not the highest. This is why EGR became relevant. Exhaust gas not only contains no oxygen to burn but it also is hot which decreases the air charge density. Both of these mean less oxygen and less fuel per power stroke.

You want the fastest control system possible. OEM EFI samples the sensors at about 80 Hz. I I remember correctly, Holley EFI samples the sensors at 1000 Hz. The faster the sampling rate the more changes are made on the fly.

At a cruise crankshaft speed of 2400 RPM on a V8 engine, the OEM EFI system at 80 Hz only samples the O2 sensors 0.5 times per power stroke. In other words, two cylinders each fire their spark plug one time per O2 sensor sampling.

In a 1000 Hz control system at 2400 cruise RPM, the O2 sensors are sampled 6 times per power stroke. The faster system make more corrections per injection cycle which increases the overall system resolution, IE, uses less fuel.

Not sure why there are so many spaces between the text and the table? I can't get it fixed.

-	-	cylinders	-	samples / second	samples / second
-	-	8	-	80	1000
rev/min	power stroke / min / cyl	power stroke / min	power stroke / second	samples / power stroke	samples / power stroke
800	400	3200	53	1.50	18.75
900	450	3600	60	1.33	16.67
1000	500	4000	67	1.20	15.00
1100	550	4400	73	1.09	13.64
1200	600	4800	80	1.00	12.50
1300	650	5200	87	0.92	11.54
1400	700	5600	93	0.86	10.71
1500	750	6000	100	0.80	10.00
1600	800	6400	107	0.75	9.38
1700	850	6800	113	0.71	8.82
1800	900	7200	120	0.67	8.33
1900	950	7600	127	0.63	7.89
2000	1000	8000	133	0.60	7.50
2100	1050	8400	140	0.57	7.14
2200	1100	8800	147	0.55	6.82
2300	1150	9200	153	0.52	6.52
2400	1200	9600	160	0.50	6.25
2500	1250	10000	167	0.48	6.00
2600	1300	10400	173	0.46	5.77
2700	1350	10800	180	0.44	5.56
2800	1400	11200	187	0.43	5.36
2900	1450	11600	193	0.41	5.17
3000	1500	12000	200	0.40	5.00