I got myself psyched to put a 400 SB in my 73, good power, torque and fits right in where the L48 is. A local junkyard has a 72 motor for me, so this isn't theoretical anymore.

Problem is, I was telling this to a friend who put a 400 in his 86 Monte SS and it only got 12 MPG commuting mostly on the highway, compared to 16-18 he got with the 305. I have to drive 60 miles per day, and milage is important.

So, anyone with 400 SBs, what kind of gas milage do you get, and what is your combo: heads, cam, compression?

I think an efficient motor in a vette with an OD tranny can get upwards of 20MPG. I just don't know if I can get there with a 400.

So, anybody have any experience in this area? I guess most people that build 400's are interested in max power, but there has to be efficiency with all that torque, if I can get the right heads and cam and compression ratio.

If this doesn't pan out, I will just rebuild the L48, maybe put vortec heads on it.

Joe



|UPDATED|11/4/2002 8:46:47 PM|/UPDATED|

I have 30 over 400 small block in my 68 conv and will get around 17 mpg if I keep my foot out of the carb. It pulls a lot stronger then the 327 that was in there. I'm real happy with the results and would do it again.

The 400 small block is an okay motor, but there are some problems with trying to get power out of it. Primarily the cylinder wall thickness is at best marginal past .030 over. They tend to overheat as well. That said, get the 400 and use it to make a 383 stroker. All the power and more, plus none of the negatives. Your 350 will need to be clearanced for the crank, and you will need to use the balancer and flywheel as these motors are exteranally balanced.

Alex

|UPDATED|12/12/2002 6:53:13 PM|/UPDATED|

Gas mileage all depends on how much power you want. An O.D tranny will make a diffirence..73,.71,.63. Automatics are usually around .7 O.D. Richmand makes a 6 speed around .6 which drop your rpm on the expressway by at least 700 rpm or more.
If you want to really drive your car like you say, find an LT1 with T56 transmission mounted on it. These came in Comaros, Trans Ams and Vettes. This engine has a factory roller cam in it and one peice rear main seal. Those cars got 25 mpg. The T56 is a 6 speed overdrive,top loader. The shifter can be cut and modifide to come through your stock shifter location. I think you should be able find someting out of a reck. Or just put a T56 behind any engine you want.If your not looking for outrageous hp the LT1 will work nice and has alot of after market high perf. parts
available. The LT1 also came O.D Automatics behind them. You can put a 400 in front of either trans. The 400 will use more gas, but is a snappy low end power motor. The 400 also has the clutch pivot boss for you clutch linkage if you have one. If you want gas mileage use efficient heads, hyperutectic pistons and dont use huge cam. If you have the extra cash install a roller cam, this will produce more hp at lower rpm and create better cylinder pressure making it more efficient. Roller produce more lift less duration.

Pete
lovwaterlb251@yahoo.com

I am running a small block 400 in my red 80 vette. I had it professionally built, 274 comp cam, 9.5-1 comp,Longer rods, had the block notched to keep from hitting, world product heads, 202-160 valves. MSD ignition, 700R4 transmission. On a trip I average over 21 miles a gallon. I am turning 1900 rpm at 60 mph. I also have installed a 2500 lock up stall converter.I changed the rear to a 3.73. It takes off like a rocket but cruises with the best. Good Luck

My '93 has a stock LT-1 with 4 speed overdrive auto trans. I get just over 20 mpg around town and right at 25 mpg on the highway. It does high 14s in the quarter with LOTS of low end grunt. I am not sure how difficult it would be to put it into a C3, but there should be plenty of them in junk yards.

If you want mileage and power then Fuel Injection and Overdrive is the way to go. You can Tune-Port you original engine (might want to change cam) or go with an L98. Could also step up to an LT1/4 or even an LS1.