What's the most fuel efficient V8 setup/combination?

[HeatRaveR]

I'd already done a search with keywords like "fuel efficiency" and "gas mileage" with "V8" but didn't find anything. I'd been hesitant to consider swapping a V8 into my 280ZX because my impression has always been that they're "gas guzzlers". I honestly don't know that much about American engines and all the codes and names, so I could use a lil' help here.

 

So I'd like to ask y'all here what is a good engine/tranny/engine management setup for the best fuel efficiency (it'd be even nicer if it ran on 87 octane) in a 280ZX? I know the 350 is the most common swap, but would an LS1 be more efficient because it's newer/lighter/fuel-injected?

 

From bits I've gleaned around here, it sounds like a T56 is some kind of 6spd tranny that would be good for mileage (and performance) because of the 6th gear. Though I get the impression that it's really expensive or rare or something. Is there an auto tranny that's also got good mileage too?

[Guest Magnum Rockwilder]

LS1/T56 or 4L60, LT1/T56 or 4L60, 305TPI or 350TPI/700r4 or T5.

 

Or just get a "regular" 305 or 350 and install a mild cam and an Edelbrock 600 "economy" carb. With the right gears and a 700r4 or 2004r it should get 25+mpg.

[Guest Aaron]

Economy........V8.........does not compute Will Robinson.

[Pop N Wood]

A number of guys are gettting 25 mpg with their ls1 set ups. That is as good as the stock Z ever got

[maichor]

The best I have ever heard of was 30mpg in my buddy's 400rwhp Vette on a long trip from Oklahoma to deep South texas. He gets about 25 during his daily driving and less if he is lead footing it.

[Guest Magnum Rockwilder]

I have two friends with LS1 T/A's, and both of them get 30mpg on the interstate at 80mph. One of them has a T56 and the other has a 4L60.

[Guest tony78_280z]

With the right gears and a 700r4 or 2004r it should get 25+mpg.

What right gears? Are you refering to the rear end gearing? If so what are you calling the right gears exactly? Just curious.

 

I figure if I can get it up to 25mpg It'd be better than my 280z with a 5 speed got, and I can justify the swap as "It's no more gas consuming than it was." Part of my stratagy to get it to that point is propper fuel mixture, better ignition, free flowing exhaust, lightening overal weight of the car, getting a 700r4, and working on the aerodynamics. Any other suggestions on improving milage without sacrificing performance for a v8 car?

 

[ The Z back end is more aerodynamic than many vehicles, the front needs a bit more work. The grill is just a big scoop and is overkill in my opinion. ]

[Phantom]

I have 13 years of fuel economy history in my '77 280Z. 6 years with the L28, 4-spd & 3.54 R200 - 5 years with the L28, 5-spd and 3.90 R200 and 2 years with the LS1, T56 and 3.7 R200. I reset the tripometer at every fuel-up, top off to the top of the filler pipe and record my fuel to the nearest tenth. Then I divide the miles on the tripometer by the fuel added and log my fuel economy to the nearest tenth. I then average each month to the nearest tenth. Yes - I'm anal about fuel economy. It's a predictor of impending engine problems.

That being said. The first combination gave me ther worst fuel economy averaging 18-19 in combined city-highway driving. The 5-spd L28 and the LS1/T56 are very close - both averaging 19-21, depending on time of year in the combined driving and just over 23mpg on the highway.

[Guest tony78_280z]

That being said. The first combination gave me ther worst fuel economy averaging 18-19 in combined city-highway driving. The 5-spd L28 and the LS1/T56 are very close - both averaging 19-21, depending on time of year in the combined driving and just over 23mpg on the highway.

This is all very interesting, These were stock motors and bodies I'm assuming. So you are telling me I gotta get up to 23mpg on the highway and I'm justified? =) Can any other equally "anal" person chime in with their Carbed v8Z and its fuel consumption?

[Guest Magnum Rockwilder]

What right gears? Are you refering to the rear end gearing? If so what are you calling the right gears exactly?

 

Yes, the rear gears. The best choice for a Datsun rear would be an R200 3.36. If you install a different rear, like a 9" or 8.8, you could go with something like a 3.08, or even 2.73.

[Guest tony78_280z]

The best choice for a Datsun rear would be an R200 3.36. If you install a different rear, like a 9" or 8.8, you could go with something like a 3.08, or even 2.73.

*Scratches head trying to remember the rear end on a 78 Manual*

I know it is a R200... But I forget the rest.

[Phantom]

One point I should make. With the above LS1 drivetrain the engine is turning 1,500 RPM at 60 mph in 6th gear and is very driveable. With a 3.36 it would be down around 1,350 RPM which would be fine for flat, steady-state driving but might require downshifts for hills or passing. Going to a numerically lower differential would require increased speed (and increased drag that would negatively affect MPG) to maintain driveability. The first generation Z's biggest enemy when it comes to highway fuel economy is aerodynamics - which is why a heavier but more aerodynamically designed modern car (C-5, C-6, F-body) will get better highway fuel economy.

[Guest tony78_280z]

With a 3.36 it would be down around 1,350 RPM which would be fine for flat, steady-state driving but might require downshifts for hills or passing. ... The first generation Z's biggest enemy when it comes to highway fuel economy is aerodynamics

I live in the flat lands, so that would be perfect for me. Has anyone else seriously tackled the aerodynamics of the Z in a body kit? When I think of aerodynamics I think of a dolphin or a jet air plane (not a jet fighter). Sleek and tappered. The front end can bottle out rather wide as long as it is gradual, and the back end needs to tapper slowly together.

 

[ I think I just hijacked this thread. But it is a subject of interest for me =) ]

[HeatRaveR]

 

[ I think I just hijacked this thread. But it is a subject of interest for me =) ]

 

Hehe, that's ok, I'm just as interested in aerodynamics and its effect on gas efficiency.

 

Is a "4L60" a manual or an automatic transmission, and how many gears does it have? Does a T56 bolt up to regular 350, or does it only fit on the LS1?

 

Also, comparing an LS1 to a 350TPI (what's the "TPI" mean?), do they both use 87 octane, or does the LS1 require premium? I've been told at Chevy dealers that the Corvette uses 89 or 91 octane.

[DavyZ]

If you are going to use a performance engine in a performance car, you can't expect good gas mileage

 

That said, the overdrive transmissions with EFI engines will net you in the 20's as far as mileage is concerned. What limits the mileage, even though the Z is lighter and smaller then a Vette, Camaro or Firebird, is simply very dated aerodynamics and your right foot. To my knowledge (very limited compared to Pete Paraska's) you need to do some serious front end work to make it profoundly better. The '87 VW GTI, box as it was, has a better drag coefficient then the S30 bodied Z. In fact, I think the Z is better off going backward then forward...

 

Davy

[Guest tony78_280z]

If you are going to use a performance engine in a performance car, you can't expect good gas mileage

A performance car can never compare to a compact, a geo, or a hybrid but we can try to get as close as possible without significant power loss by making a few body bods, lightening the car, freeing up the motor and the correct gearing. In fact the first three will improve performance as well. If the car is a daily (even weekend) driver, the savings at the pump will pay for it all. Why is it that whenever a gas milage thread comes up someone has to say that "performance can't equal decent mpg".

 

In fact, I think the Z is better off going backward then forward...

Right, we need to move the motor to the trunk, turn the seats around... LOL I wonder if anyone has ever done that. It'd be a great gag car. Could you imagine seeing something like that flyin down the highway?

[HeatRaveR]

Right, we need to move the motor to the trunk, turn the seats around... LOL I wonder if anyone has ever done that. It'd be a great gag car. Could you imagine seeing something like that flyin down the highway?

 

Actually, I have a video of some tiny hatchback car in Europe where they turned the seat around, put steering on the rear wheels, and effectively drove it backwards. It was hilarious! And you could still turn the front (now rear) wheels too, so at one point, the car was driving at like a 45-degree angle straight down the road.

 

For flipping around a Z, the taillights are easily popped out and replaceable with headlights. Hehe, and as an "emergency 'chute", the hood could be popped as an airbrake.

[johnc]

I also have pretty extensive race track fuel mileage records for my 240Z from 1998 through 2004.

 

In its IT/BSP configuration it would use about 7 to 8 gallons per hour of a 92/100 octane unleaded fuel mix. Using the 2.5 mile WSIR track and lap times in the 1:34 range (with a top speed of 128mph and a max rpm of 6,500)that works out to a 14.1 to 12.3 mpg.

 

In its "science experiment" configuration it would use 12 to 14 gallons per hour of 112 octane leaded fuel. Again, using the 2.5 mile WSIR track and lap times in the 1:28 range (with a top speed of 142mph and a max rpm of 7,500) that works out to a 8.4 to 7.2 mpg.

[Guest Drive-ability]

I don't have my Z/LS1 built yet, however the 93 Mazda Rx7 rotary twin turbo I just sold got me about 12 mpg at it's best. A Z/LS1 will double that along with having double the torque and at least 75 more horsepower. To me that sounds great!!!!