383 Hi Pro Poor Takeoff: Spark or Torque Converter?

[SF-CHSE]

Hi, I love to drive my '68 Charger especially on the highway.
On the street however the car runs rough, prompting me to shift (auto) out of gear at stoplights.
About six weeks from now I am scheduled to take the car to Joe Donavan's Speed Shop in STL for a thorough diagnosis.  Maybe you could help me, help him with where to begin.

Performance Issues:
The car loads up and backfires.
Dies at stoplights when re-fired and blows blue spoke out of the tailpipes.
If I don't let the car warm up for 20 minutes it stalls when I hit the accelerator.
Engine regularly fowls plugs.
Takeoff is sluggish and unpredictable.
Its like I have no power when I takeoff from stoplights.
Car runs best at highway speeds, really sounds and runs good at 75 MPH to 80 MPH.
Performance from 55 MPH to 130 MPH is outstanding.

Vehicle Specs:
383 Big Block Engine Bored .30 Over = 389 CI
Hughes Camshaft HE2330 BL   INT .504/ EXH .515
Hughes Prepped 516 "Stage One Heads" 2.14 / 1.81 valves
Hooker Comp Headers
Speed Pro Forged Flat Top 9:5:1 Pistons
750 CFM Edelbrock Electric Choke Carb
Edelbrock RPM Performer Intake
Torque Converter 2500 Stall
3.23 Gears Sure Grip
Rear Tire Size P270.
Mopar Electronic Ignition.

Thanks in advance.
SF

[firefighter3931]

Where is your timing set...idle timing and total ? My guess is that the engine is wanting more spark lead at idle.


Ron

[SF-CHSE]

Adjust the timing and add a hotter spark coil?
Can the stock Mopar distributor handle the load?
Do I need the whole nine yards, a MSD box, distributor, and coil?
JR

[firefighter3931]

Adjust the timing and add a hotter spark coil?
Can the stock Mopar distributor handle the load?
Do I need the whole nine yards, a MSD box, distributor, and coil?
JR

The MP electronic ignition/distributor can definately handle a hotter coil. The MSD Blaster coil is excellent....works fine with the MP box & distributor.


Before doing any parts swaps check the base timing and total timing. How much advance do you have at idle ? How much total ? where does the total stop advancing...what rpm ?


Here's a good tutorial link on tuning ignition/carburation for a similar 383 build to yours :

http://1970chargerregistry.com/70messageboard/viewtopic.php?t=1207



Ron

[SF-CHSE]

Thanks Ron,
I ordered an MSD Blaster 2 Coil and E3 plugs for the car.
Hopefully the new gear combined with Joe Donavan's know-how will get my rear wheels turning at stoplights.

Thanks.
SF

[4aThrill]

had the same problem when I had a isky cam in my 383 timing was way off just watch the distributor cap they like to jump off and give a nice zap

[Rob R]

It's lean..!!  that's a lot of engine for that E carb...the engine want's fuel and it's pulling it through the boosters and not metering it...See it ALL THE TIME...I bet it wont pull a weiner off a plate.Does it make any power?will it spin the tires at all? I bet not...just my take on it

[SF-CHSE]

Rob R you are correct!
The engine is starving for fuel.
We metered the fuel pressure during our chassis dyno pulls and found that the fuel pump is inadequate.
The fuel pressure is way off, causing our HP curve to fall from 375HP to Zero.
To install a new Holly performance fuel pump and dyno again on Thursday.
Hopefully we'll get to 400HP.
Maybe then I will get to spin the big 270 rear tires.
At least "pull a weiner off a plate".
JR

[SF-CHSE]

Guys my 389 (383 .30 over) topped out at 326 HP at the rear wheels on the chassis dyno.
Should this engine make more than 391 HP at the flywheel / 326 HP at the rear wheels?
Rob R you mentioned that the engine build is allot for a 750 CFM Eddy.
Do you believe that the carb is the wrong size or wrong brand?
For more power I should have gone with a higher compression piston than the Speed Pro L2315F 9.5:1 correct?
If want to get more HP out of this engine what can I do?
SF

[firefighter3931]

That engine is making good rwhp given the mild combination....about what i would expect. 

You need a carb with a more agressive fuel curve, inmo. A profrom or holley 750 dp would fit the bill 



Ron

[Rob R]

That engine is making good rwhp given the mild combination....about what i would expect. 

You need a carb with a more aggressive fuel curve, inmo. A profrom or holley 750 dp would fit the bill 



Ron

Like Ron said...

I like the QuickFuel carbs same as proform I'd guess...about 95% of the times I've switched from an E carb to a Quickfuel-Proform style carb it's picked up 8-10 hp without doing a thing...I can generally coax about 20 plus hp more out of a Holley style carb over the prepped AVS style carb...
a good set of 50 ohm plug wires (MSD or alike) will do wonders to help when it comes to setting your combo up...

[SF-CHSE]

SF here, back with the same problem.
Must be the Torque Converter and timing.
1,000 later on a now broken in engine takeoff from stoplights is still sluggish.
From dead stop to 60 MPH the car is a dog.
Upsetting as it should perform, see specs from initial post below.
Once I hit 60 MPH the car is a stud.
It's like a switch is thrown and the car turns from a Slant Six Duster to a Daytona.
60 MPH to 130 MPH is a thrill, the engine provides very satisfying throttle response.
At 60 MPH the engine begins to sing a new tune like the 4 bbl engages.
Boy this is frustrating!
SF

[charger Downunder]

Whats your power valve.

[firefighter3931]

SF here, back with the same problem.
Must be the Torque Converter and timing.
1,000 later on a now broken in engine takeoff from stoplights is still sluggish.
From dead stop to 60 MPH the car is a dog.
Upsetting as it should perform, see specs from initial post below.
Once I hit 60 MPH the car is a stud.
It's like a switch is thrown and the car turns from a Slant Six Duster to a Daytona.
60 MPH to 130 MPH is a thrill, the engine provides very satisfying throttle response.
At 60 MPH the engine begins to sing a new tune like the 4 bbl engages.
Boy this is frustrating!
SF

That cam should have lots of lowend grunt.  Was the cam degreed in during installation ? from what you are describing the cam timing is installed retarded and/or the ignition curve is waaay off.


Ron

[max]

SF here, back with the same problem.
Must be the Torque Converter and timing.
1,000 later on a now broken in engine takeoff from stoplights is still sluggish.
From dead stop to 60 MPH the car is a dog.
Upsetting as it should perform, see specs from initial post below.
Once I hit 60 MPH the car is a stud.
It's like a switch is thrown and the car turns from a Slant Six Duster to a Daytona.
60 MPH to 130 MPH is a thrill, the engine provides very satisfying throttle response.
At 60 MPH the engine begins to sing a new tune like the 4 bbl engages.
Boy this is frustrating!
SF

That cam should have lots of lowend grunt.  Was the cam degreed in during installation ? from what you are describing the cam timing is installed retarded and/or the ignition curve is waaay off.


Ron

i have to agree it sounds like the cam was installed in the retarded position.

many years ago i did have a weird experiance with a rebuilt convertor that wasn't acting right. if i brought the engine up against the convertor and left at 1200-1500 rpm you could get out and run faster then the car was taking off, but if i just hammered the engine from a dead stop the back tires would go up in smoke.

[tommymac]

Well,what helps?Ive got a similar build,but it seems to run great on both ends,it just dosent break the tires loose ,it just goes.

[magnumdart]

Try changing the distributor.  Cars do all sorts of crazy things when the shafts are bent, or there is a bad bushing or bearing.  Had trouble with a Demon and after tons of messing around, I took the distrbutor out of my 318 Barracuda put it in the Demon and it fired instantly and ran like a raped ape.

[tommymac]

Brand new MP ing and Dist,I might think about changing the carb to a double pumper Holly,my motor stumbles off the line,Like its not getting enuf gas.Can I adj the Eddy 750 to give more gas?

[Ghoste]

Yes, a little bit.  Looking at the carb you will see a plunger going into the top of the carb on the front drivers side corner.  The linkage attached to it has a number of different holes to pick from, make sure its on the hole furthest from the plunger so that it has the most travel.  If it is already set to give the longest plunger travel, you may have to change the accelerator pump nozzles in the carb to a different size.

[firefighter3931]

my motor stumbles off the line,Like its not getting enuf gas.

It sounds lean off idle at the transition/tip-in so you need to increase the pump shot. 

The timing curve might also need some tuning as well.

What is the combo, what gears/stall/converter/cam etc...



Ron

[tommymac]

383 New pistons,Flat boerd .30 over, 727 2500 stall 323 shure grip,comp xe274H-10 .488 lift. I timed it like you told me last summer like 18 degrees I think. I already have it in the last hole for more of a shot ,is their a kit I can get for this carb?

[firefighter3931]

383 New pistons,Flat boerd .30 over, 727 2500 stall 323 shure grip,comp xe274H-10 .488 lift. I timed it like you told me last summer like 18 degrees I think. I already have it in the last hole for more of a shot ,is their a kit I can get for this carb?

Tommy, have you calculated the static compression ratio of this engine ? Low compression might be contributing to the soft off idle performance. Also....was the cam degree'd in ? If so, what was the installed intake centerline ?



Ron

[Rob R]

I'd imagine that your cam has 230@50 duration ... with that short a cam you should have no problem tuning the hesitation out of it with the hardware "ign/carb" you have...

[tommymac]

Yes it is 230@50 Dur, and I dont know if they Degreed the cam to any certian #,they "engine shop" diddnt seem to know what I was talking about,just saying its timming marks are lined up.I havent had any trouble with this motor ,it started right up and it runs great,I just thought it should have more balls than it does on the start Hell the old worn out motor that I had rebuilt could spin the tires, it just smoked and leaked oil.I think I have the carb pump rod in the wrong hole ,Its at the topof three holes Ill play with it when it warms up a lot more than now.Say what is "Degreeing the cam mean and how do you do it?

[FLG]

Degreeing the cam simply means the camshaft position as opposed to the crank shaft. For example stock would just lining up the marks on the timing chain and running it. But you can advance the cam (get more on your bottom end) or retard the cam (to get more off your top end). Advancing the cam will cause the intake valves to close earlier which will give you increased cylinder pressure. Most engines will respond well to having the cam advanced a bit. Ron gave me the whole run down on this when i replaced my timing chain, i lined up the marked to get a 4* advance and was happy with the results.

Also make sure you know your cam, i believe some manufacturers will grind cams so if you do line up the marks its already advanced.