gas mileage and power???

[muscletruck]

i know they dont go together....but my body want to build a samll block 400 for his 62 nova so he asked me to ask this board cause it simply kicks ass....hear is his question......what's the best gas milage i can get w/ a 400ci engine and th350 and 3.08 gears and still stay over the 300hp/350tq mark .......to me it makes no sense.....but i just copied and pasted.....POWER AND GAS MILAGE....is it possible..oh he has a 600 edelbrock.....and i think he is gonna go with the summit 1105 cam....not sure on heads though?......thanks

[Alexis]

i think the key would be overdrive, maybe not a 400 but a 350.

[O'l Buck]

yeah, overdrive, and I would use a well tuned Quadrajet.......small primaries = good mileage......big secondaries = good power

[mikep]

Ive built a few 63's with a friend who was really into shoebox Novas. Gas mileage questions aside as they really all depend upon the weight of his right foot theres a few things you need to consider when doing the conversion to a V8 in those cars. The biggest problem I have seen with them is that they overheat. Not enough good airflow through that small engine compartment. Especially with a moderately high stall converter. Long trips can be a pain. Use a thick radiator , short pump and accesories and for your own sanity's sake dont try to use an electric fan. I know some guys swear by them but I have seen a lot of guys pull their hair out fighting electric fans and the subsequent loss of decent air flow through the radiator. Get a fat belt driven fan that will move a lot of air without sounding like a helicopter landing. Yes it will cost 5HP to drive that fan. Live with it. Also unless your friend never wants to hook up you are going to have to change the rear end. That 62 Nova rear will break under even 350 ft lbs of torque if he ever gets the tires to hook up. Ive changed a few of those old pumpkins until the friend wised up and went with a 12 bolt chevy rear end. A narrowed 9 inch can be put together under $600.

[adamls]

Power does not equal economy. But he is not asking much of the big 400 with only 300 HP and 350 ft-lb. At WOT the engine will suck down approx. 25 GPH, with OD and 308's at highway cruise speed you would expect to see 1/3 of WOT. This about 8 GPH. At 65 MPH your looking at somewhere near 8 MPG on the highway, theoretically. With a good carb and good flowing heads with the right tune up, barring he keeps the pedal off the floor, he might see the low side of 11 or 12 MPG.

[jku72]

Power CAN mean more mileage!!! I am really bucking the trend here, but 300 HP is not much.
I suggest you think outside the norm.
Big things to consider are cost, and your technical skill. Any old schlub can can make power, but to combine mileage and power is a different deal.
There are 2 approaches, high compression vs low compression. With low compression, the big power comes from adders, such as turbo or nitrous.
The high compression route rules out power adders, and is a little more involved to pull off. Since you have a 400 small block, you have the biggest hurdle out of the way. The 400 block os rare, and KEY. I suggest you read an old hot rod article called the 350 chevrolet should have built. There they made a lot more than 300 HP, on 87 octane, running greater than 11:1 compression. Okay, about mileage? The higher the compression ratio, the higher the efficientcy. That means good mileage.
The secret that the better engine works on is long rods, with increased dwell near TDC. Use way longer than stock rods(Fo*d 300 I-6 rods, hung on a 327 crank. This combination yields a shorter stroke, but allows higher RPM's. There are companies who make kits for this great engine. Beware, if you have to pass strict snioffer tests, it is a lot harder with high compression engines. But they can be made to pass with proper tuning.
An excellent top of the line ignition system, like a Jacobs electronic ignition nets both power and mileage.
As well, things like Rhoads lifters, roller rockers and lifters, aluminum heads, TPI all give both power and mileage, if used correctly.
Most people making power do not care about mileage. Therefore, there is little effort among engine builders to push this venue.
The test car for Jacobs electronics is a late 70 Camaro, making nearly 400 HP, and gets 26 mpg. A new corvette makes big power, and on the freeway can get 27-28 mpg.
A person who says you cant have both is not trying.

[jku72]

In my non overdrive 68 suburban, a huge box on wheels, with a 350 and 3.07 gears, and no tricks outside of HEI and increased compression, get 21 on the highway.
My 67 Catalina with 300 HP 400 cid and t 400, near stock, but with dual exhaust, gets 19mpg, on a 3.08 rear. There is no excuse for anything less than 15 mpg on a 300 hp car. Even my 70 longhorn with a 402, auto, and 4.10 rears gets 14.7mpg on the highway, it is a one ton truck, with no overdrive, and stock manifolds and compression. I do have a dual exhaust and an HEI, and I tune the engine.
8 mpg out of a Nova? C'mon!

[adamls]

jku72 is right if you got the money for these things. Jacobs ignition, aluminum heads, Rhoads lifters, and TPI all cost quite a bit of money. I mean aluminum heads alone will cost $1000. With good machining you might as well buy a ram jet 350 for less than 5K, you get mileage and more power than your asking for.

[nate68]

don't forget about weight? first gen nova's are considerably lighter than our trucks and aerodynamics are a little better. that right there will give him better mileage than us truck guys. if you could get a tpi setup for cheap (3rd gen camaro) you'd be gettin awesome mileage and killer torque.

[jku72]

All power costs money. You might as well do research and get the right combo the first time around, it costs no more to do the stuff I talked about than any other hop up job.
What is by far more important than any engine components is gears anyway. For example, a q jet gives good gas mileage and is capable of good power, if tuned right, so instead of TPI keep a qjet and spend the money on a OD trans.
Aluminum heads cost the same at 9.5 CR as they do at 11.5:1.
A Jacobs or equivelent ignition costs the same either way as well. Rhoads lifters cost about the same as any, although rollers do cost more, but it is the same no matter your goal.
If you are really poor, just get nitrous and a good ignition, and tune it right.
ps, i'd dump the 3.08 in either case, a good OD trans will make up for the top end, and nothing replaces deeper gears for launching. I'd say 3.55-3.73 is a good street gear if you have OD.

[72step]

I have a buddy with a 64 Malibu SS, and he installed a 90's 350 LT1 and tranny w/od and all computer components needed from an old Caprice cop car, and he gets 20+ miles per gallon, and 300+ hp!!! He's very happy with the fact that he never has be under the hood screwing with carbs and stuff.

[mikep]

This is all my humble opinion mind you.

No point in aluminum heads. Vortec heads or any of a dozen or so aftermarket iron heads will make as much or more power than aluminum does for less money and less hassle. Aluminum is lighter . Thats it . It also strips threads , warps and cracks and all other things being the same will make LESS power than identical iron heads will.

Jacobs ignition has got to be the biggest waste of money I can think of. A spark is a spark is a spark no matter what Dr Jacobs claims when he is trying to sell his ignition systems. A decent HEI with quality components and good plugs will do everything a hi dollar ignition system will . The only exception being an add on MSD box. They really help out over 4500 rpm where the HEI starts to fall flat.

You'll get more torque than you can put to the ground with the 400 even with 3.08 gears. You just cant stuff enough tire under a shoebox Nova to make lots of power usable and low gears only agravate the problem. I know. I had a 455 trans am that would boil the tires off and it had 2.73 hears. I went to 4.10's and actually ended up losing 3 tenths in the quarter mile.