"reasonable" gas mileage for 383 stroker?

[Silverado]

I have a fuel injected 383 stroker in my 97 Silverado and thought I'd ask you guys if you think that 10 mpg in town, and 15 mpg highway is good or bad? Its an ext cab truck and is making about 410-420 hp at the crank (330 rwhp and 381 rwtq) This is not an LS1 oriented engine, but a conventional small block chevy. Any suggestions for beter mileage? (besides a Honda

)

 

[n8wvi]

A Subaru! But if that's out of the question, have you checked you tire pressures? We waste MILLIONS of gallons of gas each day due to this one factor alone. It won't give you 30MPG, but it's free.

Dave

 

[sbc350gearhead]

Most guys who build a 383.....aren't really concerned about gas mileage. You could go with a set of 2.73 or 3.08 rear gears, and still have a decent takeoff due to the amount of torque, and the 3.06 first gear in the tranny (I am assuming a 4l60e).

 

[Propflux01]

for a truck with that engine, you are about right on the money.

 

[Silverado]

I realize that most people that build a 383 arent concerned about gas mileage, but at $2.30 a gallon I thought I'd ask and see if anyone had any tips, or special additive that was cost effective.

 

[Shannow]

Sorta off topic.

I've owned a bunch of Holden Toranas. They weigh about a tonne, and are a 5 seater.

They came in 4, 6, and 8 cyl versions.

At one stage, I owned a 202c.i. six, 253 V-8, and 308 V-8. On the highway, they all got within 1MPG (until I started playing seriosuly with the 202 6cyl, and it got a few MPG better than the rest - didn't play as much witht he others). I later owned a 2 litre 4 cyl.

Around town, the 5 litre V-8 halved the mileage of the 2 litre (was more fun 'though). The rest were spread between the extremes, in relation to capacity.

So on the highway (unless way off the cam/porting) mileage should be similar to any other. Around town, you get to pay for it.)

Cost wise, go to Propane.......might get a little more advance available also.

 

[Shannow]

Really off topic, I saw a Rolls Royce being fitted with Propane in Canberra not so long ago.

 

[Silverado]

So exactly what are we looking at to retro-fit my truck to propane?

 

[Shannow]

It's pretty pricey to install, requiring a pressure tank, pressure lines, a water heated vaporiser, and a gas carburettor.

Down here, it runs a bit over $2k Oz.

But with petrol at 93c/l, and gas around 40c (giving an effective 60c/l - you use more gas than petrol), you DO pay it off.

Caltex used to have a very attractive lease plan, where they paid for the installation, then you paid more for gas for a couple of years.

It's got the equivalent to about 100 octane (RON), versus regular unleaded being 92(RON).

 

[Chris142]

15 mpg on the fwy sounds pretty good to me. My 392 gets 6 mpg.

I don't think that Propane is your answer. Here in Cali Propane is very near the cost of gasoline and sometimes even higher. Dont forget that they add road tax if they fill a tank thats for fueling a motor vehicle.


Propane has less btu's than gas. Less btu's = less power and less mpg. Appx: 20% loss of power and economy.

Propane is 121 octain. You could really crank up the compression and gain some of your power back but this would cost more than paying $2.30 a gallon for gasoline.

 

[Shannow]

Chris,
with an engine tuned for propane, I've never sen a drop in power.

However, economy does take a hit, in proportion to the stoichiometric ratios of the two.

 

[JohnBrowning]

If it makes you feel better I built a small block 355 to replicate the performance charteristics of the Hi-Po 289 and 327. My engine sounded like a swarm of hornets comeing after you accominied by a throaty V8. I averaged 4 miles to the gallon around town and about 9 on the HWY. I had 4.10 gears and 4 speed automatic! I had more RWHP but less torque and had to rev it!

I had Camel Fuely heads and allthe neat tricks!!!

I built it for a Nova but that deal feel through so I put it in a truck! I should have changed out the gears but it was 4X4 and I liked to play off road with decent size tires! I used to spank Monte Carlo SS's and Mustang and older Camaro's stop light to stop light.

[ March 01, 2004, 08:52 PM: Message edited by: JohnBrowning ]

 

[Lost Pup]

I had a stroker in my old El Camino. We did the following.

1. Rear Ratio : 2:73 as mentioned above.
2. Headers
3. Free flowing dual exhaust
4. Auto Transmission Shift Kit
5. Air Intake system Filter Kit
6. MSD Ignition and Wires
7. Holly Carb with Vac Secondarys ( Emissions Carb) 650 CFM
I never had it dynoed so HP is unknown but did swap the cam to a milder profile. The engine was setup up with products that were for "Towing".
We would always drive this car FAST...so mileage was not the best. We advanced the timing until detonation then backed off.
13 mpg city - 19mpg highway was our norm.

I really think cruise control would help the highway #'s a bit as well. Of course an Overdrive would help allot as well but this could be expensive.

 

[TheTanSedan]

Emissions compliance is always the bug-a-boo. Maybe a chip manufacturer can be of help.

Be sure your mileage figures are GPS-corrected. Weigh the vehicle with full fuel, driver and usual load. Chalk-mark a tire, roll one revolution to find exact tire height, and figure overall gear ratio (not just axle gearing). There are calculators on the Net to figure rolling resistance and wind resistance.

For a "best scenario" mpg run, get out on level Interstate, traveling at a GPS-corrected speed (say, 60 mph) after topping tank to first click-off; run 30 miles out and 30 miles back to same station, same pump; fill same way. (Don't top tank until you're 25-30 miles out to be certain of complete warmup.) Ease back onto road, ease off the same way. This makes a good baseline, especially if you have done it more than once. It will also give you info on tuning information.

Bottom-line: Horsepower equals fuel consumption. With those numbers you're looking at big block torque, and, in days of old, a 5200-lb cruiser with electronic ignition and vac-sec carb was 10-12 mpg city and 14-16 hwy. I've seen sharp tuning bring them to 18 mpg, but this was on a high compression (perfect quench head), high vacuum engine where teeny-tiny changes brought it about.

Look to perfect the alignment, keep shocks/springs/bushings new, use synthetic fluids, clutch-operated fan, 195F or higher thermostat temp, underbody air-dam, tonneau cover, etc. Obviously, headers and mandrel-bent full-length exhaust with crossover. A whole lot of changes to inch things upwards.

Best gauge: the less you use your brakes to move through any kind of traffic (smooth, graceful driving) the better driver you are; the longer your vehicle will last; the better the fuel economy.

A dash-mount high quality vacuum-guage (AutoMeter) would be a good tool. Learning to feather the throttle is different in an FI engine over a carb'd one, but it makes a difference.

With that HP number, 15 is pretty good. Achieving 17-18 is spending a lot for a little. Run the figures as a cost percentage over time/miles.

[ March 07, 2004, 09:31 PM: Message edited by: TheTanSedan ]

 

[pacem]

I think it is good ... in such a heavy vehicle.

how much does chevy 5.7L get? About the same? Maybe 1-2mpg more?

I get 11 in a full size truck with 460 and 4.11 rear axle. 230 hp and lots of torque.

454 Gm motor is another very thirsty motor. given the competition, you are doing very well.