40 mpg engine build
L76 was originally Holden's version of the 5,967 cc (5.967 L; 364.1 cu in) Generation IV engine. While displacement on demand technology was disabled on Holdens, this feature is enabled on the 2008 Pontiac G8 GT and subsequently refitted in the 2009 model Holdens with AFM enabled, but only on models fitted with the 6L80 Automatic Transmission. The engine also meets Euro III emissions requirements. Output is 348 bhp (260 kW) at 5600 rpm and 376 lb·ft (510 N·m) at 4400 rpm for the Holden variant, and 361 bhp (269 kW) and 385 lb·ft (522 N·m) for the G8 GT.[5]
Applications:
2006 Holden
2006 Holden WL Statesman/Caprice - Those built from February 2006 until September 2006 until the release of the WM series.
2008–2009 Pontiac G8 GT
2009 Holden VE Commodore
2009 Holden WM Statesman/Caprice
2009 Holden VE Ute
Easy way to get close to your goal: Find a wrecked G8 GT, put its engine and trans into a Miata or 944 and hover around 55-60 MPH
I think you'll reach your goal, it may take a few part swap outs but 40mpg is attainable.
Gen V will be direct injection equipped which means HUGE mpg gains, however I believe your goal is still attainable with current tech. Hell, I manage 30mpg highway (70mph) with my 300zx and its not even tuned for fuel economy.
Gen V will be direct injection equipped which means HUGE mpg gains, however I believe your goal is still attainable with current tech. Hell, I manage 30mpg highway (70mph) with my 300zx and its not even tuned for fuel economy.
TECH Regular
Joined: Feb 2008
Posts: 458
Likes: 1
From: Keller, Texas
I think you'll reach your goal, it may take a few part swap outs but 40mpg is attainable.
Gen V will be direct injection equipped which means HUGE mpg gains, however I believe your goal is still attainable with current tech. Hell, I manage 30mpg highway (70mph) with my 300zx and its not even tuned for fuel economy.
Gen V will be direct injection equipped which means HUGE mpg gains, however I believe your goal is still attainable with current tech. Hell, I manage 30mpg highway (70mph) with my 300zx and its not even tuned for fuel economy.
On The Tree
Joined: Jul 2011
Posts: 168
Likes: 0
What's the point of this? You'll be spending far more money on the build than you'll save in fuel, not to mention all the opportunity costs.
Anyways, I think a more aerodynamic and lighter car than a 944 would be a good idea. Maybe a 240sx. Then just strip the car down to nothing, adjust the gearing, and drive 55mph. Doesn't sound terribly fun though.
Anyways, I think a more aerodynamic and lighter car than a 944 would be a good idea. Maybe a 240sx. Then just strip the car down to nothing, adjust the gearing, and drive 55mph. Doesn't sound terribly fun though.
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TECH Addict
Joined: Sep 2009
Posts: 2,481
Likes: 5
From: PA/MD
It's not 400hp, but her Ford escort motor died and I had a bunch of Honda parts laying around and ended up putting a 96 d16 head/intake on a 90 d15 bottom end with the 90 4 speed manual and dropped it in. I ended up getting an average of 47 mpg in the car....I fill up about every 2 weeks now 
Teching In
Joined: Oct 2009
Posts: 18
Likes: 0
From: Baton Rouge, LA
I would have to say your main problems with this would be friction and aero resistance. I agree with putting the lightest weight components in, but to really attain that for mpg is not reasonable financially, you could go with a callies magnum xl crank, aluminium rods and titanium pistions, if you could find some for other that a ls7. that combined with a lightened aluminum flywheel and pressure plate would significantly reduce your rotating mass. Also They make bronze inserts that reduce friction on lifters, roller bearings for the camshaft, shaft mounted roller rockers, lightweight valves and valve springs and low seat pressures would all free up horsepower and increase efficiency. You could even see if you could have some custom split caged roller bearings possibly made for the crank, similar to a 2-stroke engine, that would reduce rotation friction. There are many things that you can do to attempt to achieve this goal, but where does the cost to achieve it outweigh the accomplishment. I have a 98 camaro, 370ci motor with heads/cam/rods/pistons, fast 90/90 1 7/8 headers, and 3" exhaust. It made 440 rwhp on a dynojet, and If i'm super easy on it and cruse at 70 on the interstate i can squeek out just over 23 mpg. but to truly make high horse power and maintain good efficiency, I would have to say a turbo is the way to go. just my 2 cents.
On The Tree
Joined: Jan 2012
Posts: 125
Likes: 0
From: Chippewa Falls, WI
People modify the air intake on saturn s-series to draw air from off of the exhaust manifold. If you monitor the temp and get the right mixture you can get 4-5mpg out of an SL2 or SL1. Your power goes down the drain though
The key to high efficiency at part throttle is cylinder pressure. High compression is your key ingredient there. Push the envelope as far as you can on the compression. Then try to tune it so it is happy.
The real problem for you is going to be cam timing. Fuel efficiency and horsepower are diametrically opposed when it comes to cam timing.
You may gain some insight by looking at miller cycle engines. They are supercharged, but the theories might be applicable if your compression ratio is high enough.
Also, I think you are incorrect in thinking that a large bore would be advantageous. If you look at the trend in engine design over the years, GM came to the conclusion that smaller bores would be more efficient for a given displacement.
The real problem for you is going to be cam timing. Fuel efficiency and horsepower are diametrically opposed when it comes to cam timing.
You may gain some insight by looking at miller cycle engines. They are supercharged, but the theories might be applicable if your compression ratio is high enough.
Also, I think you are incorrect in thinking that a large bore would be advantageous. If you look at the trend in engine design over the years, GM came to the conclusion that smaller bores would be more efficient for a given displacement.
TECH Addict
Joined: Sep 2009
Posts: 2,481
Likes: 5
From: PA/MD
The key to high efficiency at part throttle is cylinder pressure. High compression is your key ingredient there. Push the envelope as far as you can on the compression. Then try to tune it so it is happy.
The real problem for you is going to be cam timing. Fuel efficiency and horsepower are diametrically opposed when it comes to cam timing.
You may gain some insight by looking at miller cycle engines. They are supercharged, but the theories might be applicable if your compression ratio is high enough.
Also, I think you are incorrect in thinking that a large bore would be advantageous. If you look at the trend in engine design over the years, GM came to the conclusion that smaller bores would be more efficient for a given displacement.
The real problem for you is going to be cam timing. Fuel efficiency and horsepower are diametrically opposed when it comes to cam timing.
You may gain some insight by looking at miller cycle engines. They are supercharged, but the theories might be applicable if your compression ratio is high enough.
Also, I think you are incorrect in thinking that a large bore would be advantageous. If you look at the trend in engine design over the years, GM came to the conclusion that smaller bores would be more efficient for a given displacement.
How about going back to an egr system that dumps as much spent exhaust gas back into the intake tract as possible so you have less o2 coming in and there for less fuel is needed.....or maybe even somehow set it up where each cylinder can back feed itself through individual runner egrs so you could almost evenly drop output of each cylinder down to almost a zero fuel consumption when the power is not needed....like a set of throttle sensitive trap doors in each head runner to push the exhaust through the exhaust port and right back over the intake valve to be recirculated?
TECH Regular
Joined: Feb 2008
Posts: 458
Likes: 1
From: Keller, Texas
The key to high efficiency at part throttle is cylinder pressure. High compression is your key ingredient there. Push the envelope as far as you can on the compression. Then try to tune it so it is happy.
The real problem for you is going to be cam timing. Fuel efficiency and horsepower are diametrically opposed when it comes to cam timing.
You may gain some insight by looking at miller cycle engines. They are supercharged, but the theories might be applicable if your compression ratio is high enough.
Also, I think you are incorrect in thinking that a large bore would be advantageous. If you look at the trend in engine design over the years, GM came to the conclusion that smaller bores would be more efficient for a given displacement.
The real problem for you is going to be cam timing. Fuel efficiency and horsepower are diametrically opposed when it comes to cam timing.
You may gain some insight by looking at miller cycle engines. They are supercharged, but the theories might be applicable if your compression ratio is high enough.
Also, I think you are incorrect in thinking that a large bore would be advantageous. If you look at the trend in engine design over the years, GM came to the conclusion that smaller bores would be more efficient for a given displacement.