All things being equal, cam, heads, exhaust etc what increase if any in fuel consumption would you expect turning a 350 into a 383?

 

10%

 

Technically it's a minor difference, but since my 383 is AWESOME I tend to mput my foot down much more often

If I drive calmly at a pace of around 65 -70 mph I manage between 15 to 17 miles per gallon. This used to be around 20 miles per gallon.

Edit
I don't know your motivation for this question, but look at it this way: unless you obtain the 383 for free, how many miles would you have to drive (considering your mileage) to even spend the difference in fuel consumption compared to not switching to a 383?

My 383 cost me around $4000,- I drive around 1000 miles per year which comes down to 17 gallon more gas on a yearly basis. If I wanted to save money I best not have built the 383 at all.

 

the fact is it may get better mileage, the 383 assuming it has more power would require less throttle opening to obtain / maintain the same speed. given similar build levels you could easily come out ahead. in any case the extra torque is worth it.

 

It really depends on which 350 we're comparing to. A low compression, mid 70s L48 with a total (stock) advance maybe around 28º at WOT compared to a relatively high compression, built up 383 could easily net better mileage in spite of bigger cubes, or at least be too small to worry about. (Does anyone give a rats Azz what fuel mileage they get in their Corvette??)

 

My take on this issue of the 383 versus a 350 considering that I just went through a complete rebuild of my OEM L-82 350 is this:

If you are planning on buying a complete crate engine then I would definitely go for the 383. However, if you are using the OEM GM block, then I would go my route-bore the block to 355, my choice for my engine-Howards retrofit roller cam-.525/.525, LSA 110, 219/225 duration, Forged JE 9:1 pistons, AFR 180/65 CC aluminum heads, 10-10.2:1 compression, new RAM clutch kit, motor mounts, etc. My build was $6,000 dollars all in with tons of my labor added for free and lots of aggravation for good measure -the GM 383 below is $7,000 plus another $1,000 for intake, carb, distributor, misc part etc. Looking at the specs below for the 383 I highly doubt that it will make more HP and very little more torque than my 355 (maybe 25 ft lbs)-the difference will be VERY small and most likely not even noticeable. As for gas mileage, again, probably the same, with very little significant difference. The 23 cubic inches in displacement is not enough, in my opinion, to amount to much more HP/Torque or gas mileage. Once my L-82 is dialed in and broken in, I will get it on a dyno to see what the real differences are BUT crate engines are rated in GROSS HP, not NET, or RWHP so will have to rely on folks that have had their 383's on a dyno.


THE CLASSIC SMALL-BLOCK STROKER AS ONLY CHEVROLET PERFORMANCE CAN DO IT
The ZZ383 delivers Big-Block power with Small-Block efficiency. We use the sturdy 383 bottom end, including a brand-new block with four-bolt mains, a forged crankshaft, and heavy-duty rods, and finish it off with Fast Burn cylinder heads to enable 425 horsepower and 449 lb-ft of torque.
The Fast Burn heads use high-flow intake runners, 2.00/1.55-inch valves, and a unique combustion chamber design to process air quickly and efficiently. A roller camshaft with more than 0.500-inch lift on both the intake and exhaust sides helps this potent engine maximize airflow. It is complemented by friction-reducing aluminum roller-tip rocker arms.
The ZZ383 comes in Base crate engine form, with a cast-iron water pump and balancer. The induction system, ignition system, and other accessories must be purchased separately. Use high-rise intake P/N 12496822 and Holley 770-cfm four-barrel carburetor P/N 19170093 to achieve the listed horsepower and torque ratings.
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Part Number:
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Engine Type:
Chevy Small-Block V-8
Displacement (cu. in.):
383
Bore x Stroke (in.):
4.000 x 3.800
Block (P/N 88962516):
Cast-iron with four-bolt main caps
Crankshaft (P/N 12489436):
4340 forged steel
Connecting Rods (P/N 12497624):
Heavy-duty PM steel
Pistons (P/N 12499103):
Hypereutectic aluminum
Camshaft Type (P/N 19210723):
Hydraulic roller
Camshaft Lift (in.):
.509 intake / .528 exhaust
Camshaft Duration (@.050 in.):
222° intake / 230° exhaust


Cylinder Heads (P/N 12464298):
Fast Burn aluminum; 62-cc chambers


Valve Size (in.):
2.000 intake / 1.550 exhaust
Compression Ratio:
9.6:1
Rocker Arms (P/N 12367345):
Aluminum roller style
Rocker Arm Ratio:
1.5:1
Recommended Fuel:
92 octane
Ignition Timing:
Base 10° BTDC, 32° Total
Maximum Recommended rpm:
6000
Balanced:
External

 

Very good question! I have seen quite a few posts lately with questions about improving mileage on a 40 year old car. Honestly, if you are worried about fuel costs, you can't afford an old Corvette or any old car for that matter! Buy a hybrid Prius and be happy.

Personally I spend way way more on parts and maintenance than on gas in a season. I may spend $40 on gas to go to a weekend show, but, it was $20 to enter and food and drinks another $20. Buy a shirt and pretty soon having the car parked costs more than the drive there and back!

 

next question might be "what % gain in mileage would you expect with an overdrive tranny?"

 

This is purely an academic argument since older Corvettes are not economical to operate in most instances. Modern drivetrains do wonders for fuel economy.

So, since this is academic, there are the hard facts: 1)A bigger displacement gasoline engine uses more power just making the engine run due to higher pumping losses. The less the throttle opening, the higher the pumping losses. 2)The longer stroke increases piston speed, which increases friction from the rings.

Now, the differences between a 350 and 383 aren't going to be huge or even noticeable and, outside of a laboratory, not measureable by conventional means and the differences that you could pick up are statistically within the margin of error.

So, what you should be more concerned over is fuel efficiency. This is a measure of how good a job the engine does in converting fuel into power. The economy part will trail efficiency.

 

Exactly correct!

The only real way to increase your fuel economy in a C3 is an automatic OD tranny or better yet, a 5/6 speed with a steep overdrive-.62. Any car, new or old, with significant HP/TQ will accelerate in top gear on the highway to maintain speed with traffic or pass other cars in top gear. OD gears are NOT for strong acceleration. Heck, my 2001 Pontiac Grand Prix with 200 HP, 3.29 final drive, 155,000 miles on the engine, and .70 OD will accelerate in top gear to pass-not well but it will do it. BUT, the tradeoff is 29-30 MPG at 75 MPH!!

Displacement is NOT the overriding factor in getting great MPG. Engine revs are the primary driver in determining what MPG a car will achieve. My 2010 Z06-7.0 liter/427 gets 28 MPG at a steady 70-75 MPH, turning 1,800 RPM!

 

When i switched from a base LS5 454 to the zz502 the consumption went 10% up.
Yes it thas ~10% more displacement and ~70% more power (which I use hehehe) but consumption went up only 10% in combination with the OD-tranny.

 

I just bought a new ZZ383 Deluxe (450 hp, 450 tq). I pd significantly less than $7k cdn all taxes in. I have a carb, but do need a few parts as it comes with a flywheel meant for an auto and will need a couple other low $ parts to complete the swap. If I ever get to a dyno I will post the #'s.

 

It's easy to make 1hp/ci..so a 383 should make 33hp and at least that much more in torque over a 350. That is significant, as that is about 3/10's in the 1/4 mile.

There seems to be some debate on the cost difference between the two engines. I don't know, but I'd pay $1,000 for an additional +33hp.

 

are you going to use your current 350 block to do a 383 stroker ?if so consider doing a 396 sbc ,using a 3.875 crank .

 

In my mind it's an apples to oranges comparison. Given more stroke or cid for that matter the cam shaft would need slightly more duration to operate efficiently. Imo The same cam that worked well in the 350" would fall short in the 383". In terms of fun a properly cammed 383'' would be the way. In terms of fuel economy you always read from vendors who are trying to sell you parts "that more power means less throttle to move the vehicle" but take three things into account here,
1. Rpm through the same power train is just that an rpm, power doesn't make the tires turn faster at the same rpm, this is why the mph calculators work so well.
2. Power adds increased acceleration, in my case it's tougher to keep my foot out of it.
3. Increase in cubic inches usually takes more fuel to be efficient.

So if you want your cake and want to eat it too a modern engine and drive train would get closer.

 

That is true but the only problem is that the 383's generally make 425-450 Gross HP and I anticipate based on my own knowledge and that of the very experienced builder that my 355 setup the way it is with slightly more lift roller cam than the 383, higher compression (at least .5 point) and AFR heads (better than GM's heads) will easily make 425 HP with the potential for 450 HP, with commensurate torque. The difference in HP/Torque will be very small-<20 HP. When you are dealing with engines that make >400 HP, 20-25 hp is insignificant. When you are talking about 35 hp in a 200 hp engine, that is MUCH more meaningful, not 425-450 HP motors.

 

All things being equal not enough to worry about.

 

The larger motor will usually use more fuel but as posted above not enough to fret over.
It is absolutely worth the money 33 in doesnt sound like much, its that extra stroke that makes it fun you feel it everywhere.

 

In a haphazard attempt at doing an apples to apples comparison I rec'd quotes on both a ZZ5 (400/400) and the ZZ383 (450/450). The add'l 50 hp/tq was $310 cdn, my decision was very easy.

 

I have already added a 200R4 so the overdrive is taken care of, but the 3.08 diff means the car is over geared at the moment. So if I increase the torque maybe a side benefit would be the car could pull the 3.08 ratio effectively? Has anyone done this before rather than change the diff ratio?
Fuel cost - if fuel reaches $7.00 plus per gallon as it is here others may start thinking the same? A bit of weekend running around and a short trip say 120 miles will easy run me $140 - $160 in fuel. I would like to use the car more not less so I see it as a challenge to make it run as well as possible within certain parameters. ie it must develop enough power to get out of its own way but torque seems to be the key for the type of driving I do, hence the interest in a 383 and a stroker kit is relatively cheap here. I know a later model engine would be the easiest route but when I open the hood of the car I still want it to look something like an engine of the era. I used to rebuild Diesel engines for locomotives for a living but as far as cars go I have never had to do a full rebuild on an engine so far but have for motorcycles. I am trying to accumulate knowledge for the future when I most likely will pull the engine to upgrade it and having it run as efficiently as possible is the aim.
jb78L-82 your take on engines interests me but I need to digest what you've posted:-)
Is there a head, valve, cam combo which yields good running characteristics at low rpm but will still provide enough power to make the you feel it is not going to be beaten by every little hatchback on the road?