Fuel economy discussion goes here

[g6civcx]

Due to protest in the other thread, all posts were copied here for discussion if you so choose.

Originally Posted by future240

I wonder what kind of gas mileage this will get

Originally Posted by future240

This [v8] project is making me question the rb25 240 I want to build

Originally Posted by gsracer

last one got around 15 mpg , but that was romping on it 24/7 pretty much, im sure it could do in the 20's if you tried. My sr with 350 whp got 25mpg

Originally Posted by codyace

Duh, because it's fun to jump to conclusions and flame people on forums

I think it's a great question to ask from the curious side of things, as I too wondered how it would do. Seems to me no better/worse than an LSx based V8 (when not using 6th) and or the typical SR20. Good stuff to know!

Originally Posted by David Steele

Looks like this is a hard question for Zilvians to simply anwser. It didn't come off as : ''yeah your MPG is shit now'' .

To give you an idea MPG is largely affected by weight .

90-93 Q45 Curb weight : 4039 14 city / 18 highway *active suspension w/o 15 city / 20 highway

This engine is very well made and will be very efficient it's design trickles down to the SR20 with it's bottom and and upper closed deck design, and it's 4500cc's (4.5L) displacement with 1.76:1 Rod to Stroke ratio make it a very good motor on fuel today's EMS can make it better.

However this engine in a GSRacers S14 with is what 1000lbs lighter +? will have higher MPG think 25 and better.

Originally Posted by Neejay

Damn, that's a very good point. The weight factor totally slipped my mind as far as gas mileage is concerned.

Originally Posted by CrazyTrance

Mine gets like 17 or so i think. idk my speed sensor hasnt been working properly.

i really doubt your gonna get 25. I dont think i am. but my timing i think is still off.... so who knows.

Im interested in that powersteering bracket you made. as i didn't have time to make one before i went out to school. so i'm driving it without PS.

Originally Posted by eek

You will get better mileage as long as you do not have a heavy foot. Since the s-chassis is lighter than a q45, the motor does not need to work as hard to move that weight.

Originally Posted by murda-c

If you did some good tuning had it set to lean burn on low loads and at idle, you could definitely get good gas mileage with a large motor.

Originally Posted by g6civcx

If you're worried about fuel economy, don't forget final drive ratio and cruising engine speed.

Originally Posted by CrazyTrance

I dont... if i did i wouldn't have done it and spent 2 fucking years figuring out how the hell to put it into an s13... durrrrrr


but now that its all said and done it would be nice to not go through a tank in less that a week.

Originally Posted by g6civcx

Please be nice.



I talked to a Nissan factory technician about fuel economy. He informs me that the engine is the most efficient at torque peak, and therefore would yield the best fuel economy if cruised at torque peak RPM.

My V8 has a flat torque curve. I cruise at 1,500 RPM. Small displacement engines doesn't have enough torque to cruise at 1,500 RPM so they need a higher cruising RPM.

The problem is that V8 tends to come in heavier car. So V8 has a bad rep for getting bad fuel economy.

If you took a light car, and compare a V8 to say a KA-T, the V8 would get mid to high 20s, whereas the KA would struggle to get high 20s, and any acceleration at all would knock it back down to low 20s.

Keep in mind this is not theoretical. I compare my V8 to his KA-T. Granted I have carbs so I'm only getting low to mid 20s, but think of LS-series that get mid to high 20s on the highway. Now drop the weight by 500 lbs and I think you can break into 30s.


We both make about the same amount of torque ~400 ft-lbs, but I make that from 2-5000 RPM. Same car. Both of us have S13 fastback. He doesn't make close to that until 4,500RPM and revs to 8K.

On paper he makes more power, but we're about the same on torque.

The advantage is that I don't have to rev so much for regular driving to be in my torque peak = higher fuel economy for V8.

Originally Posted by JRas

[who cares about fuel economy?]

people who are intelligent? who wants a car that gets poor fuel economy specially with gas prices rising?

yeah, because all V8's get poor fuel economy LS1 gets 28MPG

try this new thing it's called thinking before you say/write all the 'cool' people are doing it.