New Engine Question
11-27-2014, 07:06 AM
#1
Melting Slicks
Thread Starter
New Engine Question
Was getting 13.5 MPG with the stock L82 190 HP SB. Had the stock 4MV Q-Jet carb on it.
Now, with a 383 and the same carburetor, MPG is down to 8.5 MPG.
Cam, heads, pistons, rods all different from the stock engine.
Just wondering: Is this the typical MPG change for an engine swap?
Thanks
Steve
Now, with a 383 and the same carburetor, MPG is down to 8.5 MPG.
Cam, heads, pistons, rods all different from the stock engine.
Just wondering: Is this the typical MPG change for an engine swap?
Thanks
Steve
11-27-2014, 08:56 AM
#2
Le Mans Master
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If you're comparing the same part throttle driving conditions before and after the engine change, I don't think you should be seeing nearly a 50% drop in mileage. How does the 383 run otherwise? There should be a huge difference at WOT.
11-27-2014, 09:04 AM
#3
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Part of the problem is that you really can't keep your foot out of it since the 383 puts a smile on your face when you jump on it 
While the 383 isn't noted for fuel efficiency, your drop off seems a bit excessive. With my 61, I switched from a 283 to a 383. Mine seems like a fairly significant drop off in mpg (I haven't computed it), and an equally significant increase in fun 
While the 383 isn't noted for fuel efficiency, your drop off seems a bit excessive. With my 61, I switched from a 283 to a 383. Mine seems like a fairly significant drop off in mpg (I haven't computed it), and an equally significant increase in fun
11-27-2014, 09:10 AM
#4
Melting Slicks
Thread Starter
The new engine runs great! Timed to 11 degrees BTDC per stock setting.
Never did the WOT thing yet, as it only has a hundred-or-so miles on it. I have noticed the secondary carb throat valves (the big ones) don't even budge when I pull the throttle cable back as much as I dare.
Steve
11-27-2014, 11:22 AM
#5
Melting Slicks
Thread Starter
Part of the problem is that you really can't keep your foot out of it since the 383 puts a smile on your face when you jump on it While the 383 isn't noted for fuel efficiency, your drop off seems a bit excessive. With my 61, I switched from a 283 to a 383. Mine seems like a fairly significant drop off in mpg (I haven't computed it), and an equally significant increase in fun
While the 383 isn't noted for fuel efficiency, your drop off seems a bit excessive. With my 61, I switched from a 283 to a 383. Mine seems like a fairly significant drop off in mpg (I haven't computed it), and an equally significant increase in fun My driving habits can be described as boring. I don't push over the posted speed limit. I have no place to really go in a hurry. So, my driving habits with the 383 installed remain the same as with the stock L48 in there.
Since you brought it up; I was talking to Greg the machinist yesterday (whom I delivered the car's original block, heads, and crank to for machining), and I told him I'm not really sure why put a 383 in the car. I don't ever floor it. Last speeding ticket (or any ticket for that matter) I received was in 1984. I guess it's just the thought that if I ever need it (?), it's there for me & the car. I really do like rebuilding motors (and cars) so as to bring them back to life. So perhaps that's the real reason I did what I did.
I perceived Greg as thinking "Geez Steve. Live a little!"
Steve
11-27-2014, 11:44 AM
#6
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Thanks for the response BK,
The new engine runs great! Timed to 11 degrees BTDC per stock setting.
Never did the WOT thing yet, as it only has a hundred-or-so miles on it. I have noticed the secondary carb throat valves (the big ones) don't even budge when I pull the throttle cable back as much as I dare.
Steve
The new engine runs great! Timed to 11 degrees BTDC per stock setting.
Never did the WOT thing yet, as it only has a hundred-or-so miles on it. I have noticed the secondary carb throat valves (the big ones) don't even budge when I pull the throttle cable back as much as I dare.
Steve
You might need to change weights and springs in the distributor.
Re the Qjet secondaries, the top flap opens by vacuum so it will not open when you rev the engine in neutral or if you push the linkage to open the bottom flap on the secondaries.
11-27-2014, 12:50 PM
#7
Burning Brakes
Part of the problem is that you really can't keep your foot out of it since the 383 puts a smile on your face when you jump on it While the 383 isn't noted for fuel efficiency, your drop off seems a bit excessive. With my 61, I switched from a 283 to a 383. Mine seems like a fairly significant drop off in mpg (I haven't computed it), and an equally significant increase in fun
While the 383 isn't noted for fuel efficiency, your drop off seems a bit excessive. With my 61, I switched from a 283 to a 383. Mine seems like a fairly significant drop off in mpg (I haven't computed it), and an equally significant increase in fun
11-27-2014, 08:03 PM
#8
Was getting 13.5 MPG with the stock L82 190 HP SB. Had the stock 4MV Q-Jet carb on it.
Now, with a 383 and the same carburetor, MPG is down to 8.5 MPG.
Cam, heads, pistons, rods all different from the stock engine.
Just wondering: Is this the typical MPG change for an engine swap?
Thanks
Steve
Now, with a 383 and the same carburetor, MPG is down to 8.5 MPG.
Cam, heads, pistons, rods all different from the stock engine.
Just wondering: Is this the typical MPG change for an engine swap?
Thanks
Steve
WOT driving is a different story I have been as low as 8 MPG.
I have a 3.08 diff with a TH350 tranny.
Last edited by cagotzmann; 11-27-2014 at 11:25 PM.
11-27-2014, 08:20 PM
#9
Le Mans Master
In 01 had a 383 designed by a former forum member, MountainMotor. This guy used to build NASCAR engines and the engines for the 1/4 mi dragboat champion The Widowmaker. It had plenty of hp and tq and with the 4 sp I was getting @ 19.5 mpg highway with a Holley 4779. This August Mooser with some help by me swapped in a new GM 383 450 hp and 450 tq. The last tank I got just under 20 mpg. I also swapped in a 3.36 rear to go with the 4 sp. i made no attempt to dial in the Edel 750 carb I had, just bolted it on set timing. Have @ 1500 miles on it and mileage has kept increasing. I figure with a new carb and proper setup it may get another 1 - 2 mpg.
As others have said check the timing, you may also want to send your carb to Lars to freshen it up. Did the builder give you the specs of the cam and other components he put in.
As others have said check the timing, you may also want to send your carb to Lars to freshen it up. Did the builder give you the specs of the cam and other components he put in.
11-27-2014, 10:14 PM
#11
Melting Slicks
Thread Starter
My stock L48 I was also getting 14 MPG with a GM ZZ3838 Swap I started at 12. Once I tunned the carb I was back @ 14 MPG. For me tunning the carb, I went down in jet sizes. stock was 70-75(Primary - Secondary) to 67-70. Also changed from 14.4 1/4 mile to 13.84 1/4 mile. I have a AFR gauge running so I was able to tune for best performance / mileage. Stock settings I would be at 12-13 AFR while highway driving. Now Running 14.5 - 15 on the highway. I also needed to fine tune the timing.
WOT driving is a different story I have been as low as 8 MPG.
I have a 3.08 diff with a TH350 tranny.
WOT driving is a different story I have been as low as 8 MPG.
I have a 3.08 diff with a TH350 tranny.
Aluminum heads, or Iron? Tell me more about the construction.
I too have the AW differential, but the TH400 to drive it.
Thanks.
Steve
11-27-2014, 10:26 PM
#12
Melting Slicks
Thread Starter
As others have said check the timing, you may also want to send your carb to Lars to freshen it up.
Yeeh, I understand Lars is the best when it comes to induction.
Did the builder give you the specs of the cam and other components he put in.
Well, I'm the one who built it, and the cam is a Melling MTC-1.
Yeeh, I understand Lars is the best when it comes to induction.
Did the builder give you the specs of the cam and other components he put in.
Well, I'm the one who built it, and the cam is a Melling MTC-1.
http://www.ebay.com/itm/SBC-CHEVY-383-STROKER-KIT-SCAT-CRANK-RODS-030-FORGED-FLAT-TOP-PISTONS-2PC-RMS-/331231662680?pt=Motors_Car_Truck_Parts_Accessories&hash=item4d1ef21258&vxp=mtr
And man does it run SMOOTH! Balancing is underestimated I think. Sold me anyway. It's critical.
Thanks for sharing your experiences.
Steve
11-27-2014, 11:23 PM
#14
Zeitronix AFR Wideband Meter / Monitor. I also have the Serpentine Accessory Drive System • P/N 12497698 with dual electric fans.
This is the 383 motor.
http://www.chevrolet.com/performance...ck-zz-383.html
Last edited by cagotzmann; 11-27-2014 at 11:30 PM.
11-27-2014, 11:23 PM
#15
Dang , that's down into BB territory. And you aren't pushing the engine hard......wonder what it would do,with a lead,foot driver.
At 8 mpg. You better not wander to far off from a gas pump
Put a manual overdrive 5 speed in that puppy.
At 8 mpg. You better not wander to far off from a gas pump
Put a manual overdrive 5 speed in that puppy.
Last edited by LS4 PILOT; 11-27-2014 at 11:27 PM.
11-28-2014, 11:33 AM
#16
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Your timing is grossly retarded, which will have a HUGE effect on fuel economy. An engine like yours needs initial timing in the 18-degree range with total at 36-38 (you may have to shorten the advance curve slightly to achieve this). You also didn't state if you are running your vacuum advance: Make sure you have a functional vacuum advance with a properly-matched control unit limited to 12-14 degrees, and make sure it's hooked up to manifold vacuum. These timing issues will gain you several miles per gallon. Drop me an e-mail for my timing papers to get it set up right.
In regards to the carb: You cannot "wing" the throttle in neutral to make the secondary airvalves come open - there is not enough mass flow under no-load conditions to make that happen. For a complete description of how the Q-Jet secondaries work you can drop me an e-mail request for my Q-Jet paper.
Lars
V8FastCars@msn.com
In regards to the carb: You cannot "wing" the throttle in neutral to make the secondary airvalves come open - there is not enough mass flow under no-load conditions to make that happen. For a complete description of how the Q-Jet secondaries work you can drop me an e-mail request for my Q-Jet paper.
Lars
V8FastCars@msn.com
11-28-2014, 12:13 PM
#17
Melting Slicks
Thread Starter
Your timing is grossly retarded, which will have a HUGE effect on fuel economy. An engine like yours needs initial timing in the 18-degree range with total at 36-38 (you may have to shorten the advance curve slightly to achieve this). You also didn't state if you are running your vacuum advance:
Yes. It's one of these:http://www.ebay.com/itm/NEW-HEI-HIGH-ENERGY-IGNITION-DISTRIBUTOR-W-TACH-DRIVE-/351237053461?pt=Motors_Car_Truck_Parts_A ccessories&hash=item51c75c1c15
Make sure you have a functional vacuum advance with a properly-matched control unit limited to 12-14 degrees,
I assume it's working, since it's new. "Properly matched control unit." ?? What's that Lars?
and make sure it's hooked up to manifold vacuum.
Currently it's to the carburetor. Will change it to the intake manifold.
These timing issues will gain you several miles per gallon. Drop me an e-mail for my timing papers to get it set up right.
In regards to the carb: You cannot "wing" the throttle in neutral to make the secondary airvalves come open - there is not enough mass flow under no-load conditions to make that happen.
Shows what I know about it.
For a complete description of how the Q-Jet secondaries work you can drop me an e-mail request for my Q-Jet paper.
Lars
V8FastCars@msn.com
Yes. It's one of these:http://www.ebay.com/itm/NEW-HEI-HIGH-ENERGY-IGNITION-DISTRIBUTOR-W-TACH-DRIVE-/351237053461?pt=Motors_Car_Truck_Parts_A ccessories&hash=item51c75c1c15
Make sure you have a functional vacuum advance with a properly-matched control unit limited to 12-14 degrees,
I assume it's working, since it's new. "Properly matched control unit." ?? What's that Lars?
and make sure it's hooked up to manifold vacuum.
Currently it's to the carburetor. Will change it to the intake manifold.
These timing issues will gain you several miles per gallon. Drop me an e-mail for my timing papers to get it set up right.
In regards to the carb: You cannot "wing" the throttle in neutral to make the secondary airvalves come open - there is not enough mass flow under no-load conditions to make that happen.
Shows what I know about it.
For a complete description of how the Q-Jet secondaries work you can drop me an e-mail request for my Q-Jet paper.
Lars
V8FastCars@msn.com
Steve
11-28-2014, 12:20 PM
#18
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You don't have to hook it up to the manifold. The carb has both manifold vacuum ports and ported vacuum ports. Just hook it up to a manifold vacuum port on the carb as recommended in my timing papers.
Lars
11-28-2014, 01:22 PM
#19
Melting Slicks
Thread Starter
Advance vacuum remained ported out the carb port.
Will report back on MPG.
Thanks Lars,
Steve
cavu2usf@***.net
11-28-2014, 01:32 PM
#20
Nam Labrat
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Here's the dope: 1992 350/1:6 rocker arms/Holley 600cfm/HEI distributor conversion/700R4.......in my 3200lb. '34 street truck
After I decided to drive it "normally" LOL, it was getting 14mpg on the highway....After a year of tuning I got 20mpg on the last tank of gas.
I haven't connected the lock-up torque converter, so the mileage should improve 2 to 5 mpg once it is operational.
As for my project Vette.....I'll start working on the gas mileage soon
Listen to Lars......he has bailed me out enough times!
After I decided to drive it "normally" LOL, it was getting 14mpg on the highway....After a year of tuning I got 20mpg on the last tank of gas.
I haven't connected the lock-up torque converter, so the mileage should improve 2 to 5 mpg once it is operational.
As for my project Vette.....I'll start working on the gas mileage soon
Listen to Lars......he has bailed me out enough times!
Last edited by doorgunner; 11-28-2014 at 06:13 PM.