06-13-2008, 08:38 AM
Hello all, I'm brand new to this forum and actually accidentily stumbled upon it. I am in the process of swapping a SBC 350 into a vehicle. I know with a carburetor I can be looking at single digit gas mileage if I'm not too careful with the pedal. This will be in a fairly light car 2800lbs, and I was wondering if I converted to an aftermarket EFI setup would I be able to get decent gas mileage?
The EFI system would have a wideband and operation would be in a closed loop setup whenever possible. I know this may sound like a somewhat vague question, but I figured with the amount of experiance on this board, someone may have an answer for me.
I'm sure the EFI would provide better mileage, but I'm not sure how much more. It would definitly be a cleaner burning car.
06-13-2008, 11:35 AM
Anything has to be better than the carburetor that it came with. I know that the LS family of engines get a rediculous highway average when in a Corvette. I would like to attribute that in part will be the gearing of the 6 speed, the light weight of the car, and also the processor speed of the ecu.
I've also heard that the cylinder heads on the LS engines are very efficient. The efficientcy(sp? haha) might be regarding flow and not combustion chamber characteristics, how ever. Either way new technology has greatly improved gas mileage and I was hoping to jump on the bandwagon.
BTW it cost me $75 to fill up my 280zx the other day, it sickens me to have to give more and more of my money away to gas companies when I could be saving up for the future or perhaps buying groceries .
I've also heard that the cylinder heads on the LS engines are very efficient. The efficientcy(sp? haha) might be regarding flow and not combustion chamber characteristics, how ever. Either way new technology has greatly improved gas mileage and I was hoping to jump on the bandwagon.all of the LSx motors have great heads as far as flow goes as well as the combustion chamber shape is a leap and a bound over old school 350 heads
06-13-2008, 06:23 PM
The efficiency of the mid 90's and later SBC isn't just flow; they must burn pretty efficiently. My 98 Suburban 202,500 miles 2wd 5.7 (350) got 21.3 mpg at 70 mph last month on a 3000 mile trip.I've had it for just a year, and the highway mpg stunned me. I had no idea that an ancient 5300 lb brick could get over 21mpg at 70 mph. The EFI is just one generation newer than an old throttle body,so it isn't GM latest and greatest. Too bad you couldn't put a 5.3 in your car; they make more power,and get better FE.
I'm guessing you would get a Throttle body with your EFI? You should be able to tune a good aftermarket system to get 25 mpg hy( with the right gearing, no 4.56).
2800 lbs is pretty light; which GM car is this? You would have to go back a long way to find a RWD GM that weighed 2800 lbs from the factory- Nova or a Vega??
Too bad you already have a motor. You can buy a new-GM Performance- 5.3 for $3200 delivered. It has a "hotter cam" and graphite coated pistons to make 327 hp-not bad. You could hunt down the electronics from a 2000 or so truck,and off you go! It would get good FE , and be a rocket(with a warranty).
06-14-2008, 12:26 AM
Well the good news is I haven't purchased more than a crossmember at this point. I was leaning towards a 350/400 sbc type set up because of cost. I'm confident that an LS engine with SBC conversion mounting plates will fit just as well in my engine bay.
The car I am modifying is a 1991 Nissan 240sx. Because there is so much extra weight going into the front end this would be somewhat of a temporary setup, projects are never done haha. I want to swap this and then start saving for an aluminum block/head setup. GM LS as well as aftermarket LS is expensive as all hell. This why I'm opting to go with the old school chevy small block
My main goal out of this project is to get a daily driver, that is fun and I can get at least 20mpg out of considering most of my commute is highway. My current daily driver is a 1979 Datsun 280zx. If I end up going with the 350 build, I can always throw it in the Datsun and stroke it to 383. Thats good for maybe 550 :P
I would also like to go with an aftermarket EFI system. I've always found tuning interesting and would like to persue it as a hobby. I see an aftermarket tune over stock as a good investment to help me maximize my gas mileage.