Moparts Tech Archive

Big Block

383 dyno final results....fast68plymouth

well....sort of 440Jim is preparing the data as we speak, and im sure he'll be posting some charts/graphs as soon as he has them ready.
i dont want to give it away until he gets them ready, but i want to say right up front that if i hadnt built the motor myself, knew exactly what was in it, and tested it myself, that i wouldnt believe the numbers i got out of it.
a few things made more difference than i would have ever thought, and a couple of others didnt do much at all.
in the end, it was MUCH better than i was hoping for.
the first pull with the new intake and HP750 carb put the motor solidly over 450hp before the oil was even thorougly warmed up.
this first set of tests was done to just see how much difference there was between the carbs.
all tests were done with the timing at 36deg total, and a mix of race gas/pump 93. 3 gals racegas, to 5 gals 93.
the only thing changed from one test to the other was swapping the carb itself.
each carb got a couple of warm up pulls to stabilize all the temps, and then a run was made and the data was saved.
13 carbs were tested in all.
as you will see, once the better intake was installed, the bigger carbs worked better.
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451 Jim
Moparts Member
Posts: 1440
From: Lexington Park Maryland
Registered: Dec 2000
posted 06-22-2002 10:02 PM

Here is the carb comparison with the Edelbrock Performer RPM intake, Dwayne will have to describe this and tell what each carb is.

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fast68plymouth
Moparts Member
Posts: 2692
From: so burlington,vt usa
Registered: Aug 2000
posted 06-22-2002 10:36 PM

the carb line up is as follows....
-HP750 #2, a carb built from all new parts using a Proform main body.
-HP750 #1, same as above, only this was the first one i built. the jetting was 2 sizes leaner on the primary side, which the motor didnt seem to like. this one also has a baseplate with thinned shafts...which didnt seem to amount to anything here.
-HP950, a carb i built from all new parts using a genuine Holley main body and HP metering blocks. these main bodies come "bare" with no boosters. i tried some supposedly "trick" Braswell boosters in this one and have never gotten the fuel curve to be "right". it starts lean, and richens up throughout the pull. a booster change is going to have to be done to fix this carb.
-850DP downleg, this is a Holley 4781-2 that has the choke tower milled off. otherwise its just stock. rear PV is removed, and the jetting is 80/92 to get the front/rear balance close.
-CFS 905, this is a ported annular 850 Holley i had built about 12 years ago by Norm at Competition Fuel Systems in Az. its always been a very good carb, and always makes decent power.
-Holley 4779-6, stock 750DP with choke and stock jetting
-Holley 4778-2, stock 700DP with choke and stock jetting
-Speed Demon 650, 650DP carb that i installed adjustable air bleeds into, and recalibrated the fuel curve on.
-Holley 80508- 750VS right out of the box. the secondary spring is too stiff and doesnt allow the rear blades to fully open.
-Speed Demon 850, 850DP carb right out of the box
-Carter 750 AFB, manual choke version, right out of the box
-stock AVS, stock 68 383 AVS, rejetted for this application
-Ebrock 750, #1407 with stock calibration
for the money, the stock 750DP holley had the best "overall" performance.
it had very sharp, crisp throttle response, idled strong, and made decent power. it had the best balance of response, power, idle quality, part throttle A/F ratio for the money, and did a few of those things better than any of the other carbs regardless of cost.
for less that $400, this would be the best choice, IMO.

the only carb that didnt actually run well was the Ebrock carb. it just didnt do anything well. poor idle, too lean everywhere, didnt take a load well, etc.
when i had a chance, i pulled it apart to see if there was any dirt or debris inside, and it was nice and clean. i also verified the calibration.
it was calibrated to the specs in the catalog.

XX340, the heads were originaly prepped for NHRA stock competition....then i bagged the project when i found out i had no V/P clearance.
what has been done to them since then is:
they were machined to accept dual springs, and the port opening was brought out to the size of the valley pan gasket.
since so much had been milled off the deck surfaces of the heads and block, there was a pretty bad mismatch from the heads to the intake. so i corrected that.
there is no porting in the runners or bowls, and they still have oe replacement 2.08/1.74 valves in them, which have had the back side of them re-profiled for better low-lift flow
oh, and the final number of pulls was...114
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451 Jim
Moparts Member
Posts: 1440
From: Lexington Park Maryland
Registered: Dec 2000
posted 06-22-2002 11:43 PM

Here is the water pump drive comparison.

There is a little scatter in the data, but here are some selected points:

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fast68plymouth
Moparts Member
Posts: 2692
From: so burlington,vt usa
Registered: Aug 2000
posted 06-23-2002 11:19 AM

well, to answer a few questions, and make a few comments:
Runner...no alternator was used for any of the tests so the current draw isnt a factor.
we run two batteries on the dyno, and have a 30 amp charger running when the motor is running. the system voltage is right about 13 volts during a pull.

Dram, Jim posted the complete dyno info in some of his links.

MY340...yup, that carb did work pretty well for the cost.

TJ...thanks!

AZ...in future posts you'll see it actually got even closer than whats posted here.
its a little hard to see in the graph, but the peak tq/hp numbers with the electric W/P were:
473.1 ft/lbs@4500
475.3 hp@6100

thunderhead...regardless of the power output, the Ebrock carb had pretty poor overall manners. as for comparing stock vs stock, 7 of the carbs tested were "stock" with the as delivered calibration, and they all worked fine, except the Ebrock. since the Ebrock and the Carter are both made by Weber, and are basically the same carb, the fact that the Carter ran good and the Ebrock didnt just shows that Ebrock has the calibration set up for much milder combos.
the Holley 4779, 4778, 80508, the Demon 850, the Carter AFB, the Ebrock 1407 were all jetted just as they would come if you got them from Summit or Jegs. that is a fair, real world, apples to apples comparison (IMO).
the Proform HP750 #2 was built from new parts, but was calibrated with the jets and air bleeds that come with the main body.
if someone had a 4779 Holley, and swapped out the main body with the $99 Proform kit, this is what they would have gotten.
as it was i had the motor on the dyno for 4 days and made 114 pulls.
from experience i can tell you it can sometimes take 20-30 pulls to find out how to get the most from one particular carb on one particular application.
since they come "out of the box" the same way to everyone, i felt this was a valid way to compare them.
throwing a few modified carbs in the works just shows that you dont always see big gains from spending alot of money for a reworked carb.

JohnRR, with the 106lsa and moderately fast ramp speed of the cam, i wouldnt think it would run well with exhaust manifolds at all.
the Carter AFB is brand new, just got it the day before the tests. i wanted to see how it would compare to the stock AVS.

one final note....
i dont have anything against Ebrock carbs. it seems some here have a hard time grasping that it didnt run well. trust me...it didnt run well. its that simple. its not hard to tell if its good or bad when youve already made nearly 70 pulls on the motor before installing this carb.
yes, the problems it had could be tuned out of it. thats obvious since the Carter 750, which is the same thing ran just fine.
it ran how it ran...which wasnt good.
this is one of those "dont shoot the messenger" situations.
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451 Jim
Moparts Member
Posts: 1440
From: Lexington Park Maryland
Registered: Dec 2000
posted 06-23-2002 12:15 PM

I spent some time "racking and stacking" the carb results:

I stacked them by averaging their performance over a rpm range (5700-6200 for HP, 3500-4500 for TQ). This covered the peaks of each carb and averages out small fluctuations. I included the peak numbers for reference.
The CFS 905 annular topped both the average HP and average TQ lists; and it peaked best too. The Speed Demon 850 and the Holley HP950 made good showings. They both peaked very well, and one showed a good HP avg., while the other showed a good TQ avg. The Holley 850 DP ranked high on both counts.

What do you think?
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fast68plymouth
Moparts Member
Posts: 2692
From: so burlington,vt usa
Registered: Aug 2000
posted 06-23-2002 12:21 PM

nice work Jim, i think that does a better job of summing up the differences in power output from the carbs as they relate to each other.
its sometimes pretty easy to look at only the peak numbers and not see how it all averages out.
you are the numbers guy!! actually....maybe we should call you the numbers guru

Brad, i cant recall if i ran the lower pulley on the street or not. i havent run the car on the street since 91, and i just dont remember what it had on it then.
i would think that on a motor like yours it would be "iffy" at best. even at the track, when i had the car running in the tens i could tell it didnt cool down as well on the return road as it did with the stock pulley set up.
since they are cheap, and easy to install, it might be worth seeing if it works or not. it may be one of those things thats okay in the spring and fall, but not in the summer months.
114 pulls is a rather large number of runs for one "session", but all in all it really went pretty smoothly.
the only problem i encountered at all was the defective MP ignition rotor.
once the inner springs had been installed, i never pulled the covers again.
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451 Jim
Moparts Member
Posts: 1440
From: Lexington Park Maryland
Registered: Dec 2000
posted 06-23-2002 03:05 PM

OK, I had a chance to eat lunch and fiddle with the header data... More Results from Fast68Plymouth!
You thought that "little" 383 made power before? Well see what some Hooker Competition 1-7/8" tube headers did for this thing:

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fast68plymouth
Moparts Member
Posts: 2692
From: so burlington,vt usa
Registered: Aug 2000
posted 06-23-2002 07:50 PM

one thing to note on the header test:
after i did the water pump test and saw there wasnt much difference between the moroso pulley and the electric drive, i went back to the moroso pulley to eliminate one more thing to mess with.
so, all three of these tests are with the moroso underdrive pulley, not the electric pump drive.
Jesse, we are at about 300-400ft altitude where the dyno is. this was a pretty high correction day for us with the really high vapor pressure. the SF program uses vapor pressure instead of % of humidity. i would guess its to eliminate the need to correct for "relative humidity" with th flucuating inlet air temp(CAT on the test data).

we dont usually see VP numbers this high until August, but it has been rather humid here this past week.

during the cold winter months the VP will often be less than .20, and when you get that, coupled with some high pressure, and cool temps...we often see the corrected numbers being lower than the uncorrected numbers.
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451 Jim
Moparts Member
Posts: 1440
From: Lexington Park Maryland
Registered: Dec 2000
posted 06-23-2002 08:04 PM

Dwayne,
You have to be happy with that engine making 486.7 HP. No porting, no stroker crank, no welded intake, no N20...
Thats 486.7/390 = 1.248 HP/CID,
on a 446 that is 556 HP. Ofcourse, that might not happen since the heads might not breath that much air without the Volumetric Efficiency dropping off, still no porting!
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fast68plymouth
Moparts Member
Posts: 2708
From: so burlington,vt usa
Registered: Aug 2000
posted 07-01-2002 09:07 PM

well, after all the carbs, spacers, intakes, headers, and water pumps had been tested i figured id put the best of everything on the 'ol 383 and see how close to 500hp it would be.
this is with the CFS 905 carb, the 1" open spacer, the 1 7/8" headers, and the electric water pump drive.
i also made an extra warm up pull to put a little more heat in the oil to thin it out...this is almost always worth a few horsepower.
then, i switched from the mixed pump/race gas i had been running to a heavily oxygenated race gas; Sunoco GT+ unleaded. on this type of motor its almost always worth 5-10hp.

here is a chart with a recap of the "highlites" of the testing with the gains that were made with the various different parts i tried on the motor

thats a gain of 48ft/lbs and 85hp without changing anything on the basic long block.
also keep in mind that although alot of attention to detail was paid during the machining and assembly of this motor, it doesnt have any real "trick" parts in it.

i'll be the first to admit that these results exceeded my expectations by over 40hp.

the next step will be to see if it will run in the car like it did on the dyno.

also, id like to thank 440/451Jim for his help with all the charts and graphs. it really gave the whole series of posts a very professional feel

Runner, the 383 Chevy made about 485tq/495hp with 1 to 1 W/P pulleys(no underdrive), the same CFS905 carb, 1 3/4-1 7/8 stepped headers, mixed gas, no carb spacer(i never even tried one on it)and a dual point distributor.
the 383 Mopar was tested with a recurved oe electronic distributor and an MSD 7AL ignition.
i have to admit, the 'ol Mopar came much closer to the Chevy than i expected.
its the first race type 383 Mopar ive built, so i wasnt sure what kinds of numbers it would put out.
i think one of these with some E heads on it would really make a pretty good street/strip motor.
king, i should have it in the car by Mopar day at the valley. i always enjoy that meet there, so the plan is to bring it along.
last year i had my fathers 360 'Doba, and was running low 12's with that.
if the 383 will run 11.50's or 60's at the valley...id be happy with that.
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