V8 fuel economy

[greasess]

I forgot to mention that I plan on making close to 800 rwhp using a gt45 turbo and run a high 9 second 1/4 with this car. This should take north of 20 psi of boost and I'll probably have to run e85 for that.

[user removed]

Most V8s use .5 gph idling. I told my neighbor my 2002 Insight CVT would go 40 MPH on the same amount of fuel his V8 chevy truck used idling (.5gph). To get to 50 MPG, your car would have to idle, without any increase in fuel burned while moving at 25 mph, with exactly the same amount of fuel it used idling.

My Insight used .11 gph idling, just over 20 % of a V8s consumption and the Insight was a very aerodynamic car with a cd of about .25.

Without some very serious aero modifications your goal is virtually impossible.

The work you have done on the combustion chamber is fantastic and a tribute to your capabilities, but by eliminating the aero factor your enegy consumption will not be reduced driving the car at any speed above 25-30mph.

That being said it still is possible that your modifications could help to improve mpg, but think of it like this, manufacturers spend billions on improving efficiency. You would have to achieve thermodynamic efficiencies approaching 55% which is the best ever achieved with very large diesel engines such as those that drive the largest container ships on the planet, running at less than 100 rpm, with a 3 foot bore diameter and a 9 foot stroke.

http://en.wikipedia.org/wiki/Brake_s...el_consumption

Can you get 50 mpg, within the limitations you have imposed (no aero improvements)? It's possible, but only if you use engine off P&G at average speeds of about 25-30mph.

regards
mech

[greasess]

Old Mecanic, You just made lots of good points. Two things that you may disagree with or may not have realized are that the car manufacturers could do much better and choose not too for financial reasons and most cars including your Insight have a pretty sloppy combustion processes that pass fuel through your engine without burning it. Your Insight along with almost every other vehicle on the road has a catalytic converter for burning that wasted fuel. I'm trying to use that fuel that would otherwise be wasted. I may not achieve my goal but if I do I want to make my findings available to everyone. Time will tell!

[user removed]

Compare the combustion chamber of the 83 era Nissan 280 ZX on the far right in the attached photo. The piston to head clearance was 1 millimeter on the flat portions of the cylinder head. The configuration you have produced looks very similar to the one in the attached photo. Nissan z cars in federal emissions configurations of the era had no catalytic converters. My 76 in factory emission trim had no cat, no air injection and no egr and it was emissions legal in 1976. I put an 83 head on my 76 on top of a factory new short block with flat top pistons. Compression readings went from 160 to 200.

That 76z would pull 28 mph highway andI could control the mixture with a rheostat that added resistance to the water temperature circuit. I was not really interested in maximizing mileage when I owned that car almost 20 years ago but it was a lot of fun to drive. With the original 3.45 diff (later a 3.90) and a .75 od 5th gear and weighing less than 2400 pounds, it was fun to drive, but could not hold a candle to a modern design with 40 years of fuel delivery evolution.

regards
mech

[wmjinman]

Hi greasess,
I really hate to be a naysayer, but I agree with Old Mechanic's opinion 2 posts ago. Getting it strictly with engine efficiency modifications, no aerodynamic work, and no extreme "hypermiling" driving would be a "trick" I would be VERY surprised to see you manage.

Now, with extreme aero (like boattails, fender skirts, grille blocks/air dams, etc) AND extreme hypermiling (driving below 45 mph, pulse & glide, etc) and getting rid of those 315 wide rear tires & replacing with skinny LRR tires and pumping them up to the max, I would be curious to see if you could hit 50 mpg then, because then I think you'd have a chance.

[Frank Lee]

Originally Posted by greasess

When I got 33 mpg I was on the highway between Pinellas County and Orlando going about 80 mph.

That car will NOT deliver 33 @ 80 consistently. Must have had a tailwind and/or fill error (variation in tank fill).

[greasess]

I know that having steam roller 315 rear and 275s in the front won't help fuel economy ANY but they are necessary for my other goals with the car. None of the mods I listed were originally intended to help with fuel economy. Economy is pretty far down on the list for me but efficient combustion helps both power and economy and that's what I have focused on. For the record I did get 33 mpg with a max speed of 80 mph. Some of the trip was at 45 mph on SR92. I would also like to say that none of the ideas I have discussed are mine. I'm combining what I feel to be the best ideas I can find. As far as the Z car not having cats, I'm not sure how many cars did in the 70s. I would like to thank all of you for the thought provoking interjections. Even if I fail to reach my goal I hope to learn from the experience. I welcome chriticism. I would love to hear from those of you that have actually modified your engine for better economy.

[wmjinman]

A few years ago, I modified a '73 Buick 455 in a Riviera for the "Silver State Challenge" road rally in eastern Nevada. It involved mildly ported aluminum heads with thinner head gaskets for a slight compression boost, a more aggressive cam, headers, re-worked Quadrajet carburetor, and Mallory electronic ignition. I also added a Gear Vendors overdrive, even though the Riviera has a 2.93 axle ratio already. I also put an air dam on it to cut drag and had the tires pumped up to 50 or 60 psi, as I recall.

The "run" was 90 miles one way, and my "target speed" was 105 mph, which I missed by about 2 seconds (slow) at the finish line. After the end of the "race", we had to go a few miles down the road and wait for them to open the road so we could return. There was a gas station a few miles further down the road they suggested we go and top off our tanks at, but I didn't go to it, just turned around and headed back. Now, about halfway back, I realized that might have been a mistake... I may not have enough gas to make it back!!! But I did, and then began calculating. From the gas station in Ely where I filled-up, it was about 30 or 35 miles to the start of the course. Then 90 miles down at 105 mph, then another 10 or 15 miles to the turn-around. Then that 10 o 15 plus 90 back to the start, where we drove the car onto the trailer for the ride home. I figured it had to be at least 240 miles, and I only had a 20 gallon fuel cell. So that's at least 12 mpg in a car that when stock and going 55 or 60 gets only 12-13 mpg.

The engine modifications were for the ability to run at speed, not for mpg, but we think it increased the efficiency some, or we would have surely run out of gas on that deal. I know the air dam and high pressure in the tires cut drag too, though. - and I had "salt discs" on the wheels too, which probably also helped the "aero" some...

[The_Jed]

Originally Posted by greasess

I forgot to mention that I plan on making close to 800 rwhp using a gt45 turbo and run a high 9 second 1/4 with this car. This should take north of 20 psi of boost and I'll probably have to run e85 for that.

This post makes me think you're not serious. I'm all for American V8 power and durability and I wish mine were more efficient, but I know 50 mpg and 800 rwhp can not be accomplished using the same engine with the same heads, cam, injectors, intake, tune, etc.

I read about a guy who had a duramax in an sn95 who would drive to the track at low boost and fuel getting 35 mpg, install slicks, crank up the fuel and boost then run 9's. Then he'd cut the fuel and boost and sip fuel on the drive home. That is plausible.

I'm planning to swap a few parts on my 302 that, along with some subtle aero mods, will hopefully enable me to hit 30 mpg.

But 50 mpg is outside the realm of possibility.

[wmjinman]

I agree with The Jed. It takes a certain amount of gas to move a certain amount of weight (and aerodynamic frontal area) down the road. A set-up that will move it really fast (like 9 second 1/4s), is gonna be burning even more gas just for having the capability.

Then you look at the cars that can get 50 mpg, and they're all smaller than Camaros. Then you look at the engines in cars that can get 50 mpg, and they're all smaller than the V8 in your Camaro. Doing a diesel, like The Jed was talking about, gets you a little closer to 50 mpg, but probably farther from the 9 second 1/4.

If you can succeed, you'll be an efficiency god, but I'm afraid for now I'll have to assume you're probably not an efficiency god.