Tuning a 5.7 Hemi with a Carb HELP ***

Uncle Don

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i thought i would start a new thread to help me learn and see what has worked for others on tuning these carb'd 5.7's. seems most have went fuel injection but i am Carb'd so i have to deal with what i got.

2004 Durango 5.7 hemi
new 260H comp cam and lifters
new timing chain
removed VVT
stock valve springs
770 street avenger carb (out of box with no adjustment)
Indy modman intake
904 transmission new fresh built with all the goods...
stock 8.75 rear with 2.something gears...??
TTI headers
Hemi 6 controller

engine starts good, idles good, revs up good.
it drives good, smooth and well mannered as long as i dont push it much.

current timing curve is 10 deg at idle, peak 27 deg at 3,000-3,500 rpm, levels out to 24 deg flat rest of RPM's.....

car doesn't seem to have much power. i would assume it has 375-400 hp and my worn out 273 v8 i pulled out of it ran better i think.
sluggish and doesn't take 4 barrel very well, like if floods it. the car is super rich in fuel, tailpipes are black, top of carb is black etc... (no i do not have AF monitors) someone welded plugs up on my TTI headers.
my 904 trans shifts good under normal driving. however with my factory floor shifter currently the car is not going in 1st gear manually. so cable is out of adjustment obviously. and also when it kicks into passing gear it doesnt pull very hard at all just rpm's go up...not much pull. again think the cable is out of adjustment.
i can do a baby burnout, turns the wheels over but not much lol... so i feel like something is not right. way down on power.
is it the carb?
is it the trans?
is it timing in engine?

all the above?
needing help from anyone who has a carb 5.7 engine who can lend some advice on tuning and troubles they had lining out there gen3 conversion.

IMG_4247.JPG
 

mgoblue9798

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Have you pulled the plugs and inspected them to help figure out your tune? If they are black and sooty it is probably time to go down a couple jet sizes all around.

Also you mention a 2 something gear. I am no hemi expert but do know they like rpms. I have driven older 5.7 hemi trucks and did not care for them as I had to step on it and get it turning 3500 rpm to get it to move.
 

DGE330/NC

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Carb is too big . and too high of a gear . in my opinion . And 2004 didn't have VVT . But it did have MDS. nice ride though !!
 

Uncle Don

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ahh thanks for clarification... MDS yes. still learning the new stuff.
carb is what i have at the moment, can i rejet it? calm it down? lol...
 

Uncle Don

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Have you pulled the plugs and inspected them to help figure out your tune? If they are black and sooty it is probably time to go down a couple jet sizes all around.

Also you mention a 2 something gear. I am no hemi expert but do know they like rpms. I have driven older 5.7 hemi trucks and did not care for them as I had to step on it and get it turning 3500 rpm to get it to move.

i have. my plugs look brand new actually, they are burning clean.
see pic of where i took breather off of carb, it was choking it you could say lol....
but plugs looked ok.

breather1.jpg


engine1.jpg


plug 1.jpg


plug 2.jpg
 

RemCharger

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car doesn't seem to have much power. i would assume it has 375-400 hp
345hp at 5400 rpm
try bringing it up to 4500 and stand on it.
As stated, its basically a 340 but hemi, with big heads.
2 something gears with that type of motor is just a bad combo.
 

Uncle Don

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345hp at 5400 rpm
try bringing it up to 4500 and stand on it.
As stated, its basically a 340 but hemi, with big heads.
2 something gears with that type of motor is just a bad combo.
i would think it would have 375-400 with my cam change, tti headers, dual exhaust etc... but yes this engine was 345 factory.
 

5.7 hemi

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Get rid of the 2 something rear gears! Period! Go with 3:23’s, possibly 3:55’s depending on rear tire size.
 

Uncle Don

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anyone have experience on timing these carb'd hemi's? like to have a baseline or what has worked not worked.
 

furious70

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It's just 345" with really good heads and still small cam. Nothing magic about the carb though Indy may have advice on jet stagger for that intake.
I would throw that carb hat in the garbage, air doesn't want to bend like that. I get you're trying to get fresh air but that hat is not helping.
While it ought to be a big step up from a 273, it's not going to have overwhelming torque
 

mgoblue9798

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anyone have experience on timing these carb'd hemi's? like to have a baseline or what has worked not worked.
Uncle Don, another thought. You did not mention what converter you are running.

Also you mention the trans linkage being out of adjustment.
What about the kickdown linkage?

Need to make certain it is adjusted properly or you could burn up the trans with low line pressure.

Moparts has a board just for the hemi motors with lots of good info if you can't find your answer here.
 

392heminut

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Carb is too big . and too high of a gear . in my opinion . And 2004 didn't have VVT . But it did have MDS. nice ride though !!
Get rid of the 2 something rear gears! Period! Go with 3:23’s, possibly 3:55’s depending on rear tire size.
That carb will work fine with the 5.7. It is a vacuum secondary Holley and can be tuned to work just fine by swapping vacuum secondary diaphram springs. The jetting may need to be changed as someone else stated. I am running an Edelbrock 750 on my 5.7 with no issues at all.

I agree with going to a 3.23 or 3.55 gear in the diff.
 

sam65

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That carb will work fine with the 5.7. It is a vacuum secondary Holley and can be tuned to work just fine by swapping vacuum secondary diaphram springs. The jetting may need to be changed as someone else stated. I am running an Edelbrock 750 on my 5.7 with no issues at all.

I agree with going to a 3.23 or 3.55 gear in the diff.
First off I think that is the worst intake for carbed application. I run 30 degrees from 1,000 rpm to 3,500 then slowly ramp back to 24 degrees. 65 Coronet 2005 5.7 260 comp cam, 727 trans 2.96 gears 275/60/15 rear tires.15 mph rolling stomp the gas and leaves 2 black marks. Also I don't use the map sensor on the Hemi6 it seemed to mess with the carb adjustments the way it varies the timing. I started with the XV motorsports single plane intake it was ok but I now have the Joe Ocone dual plane and it is way better.
 

DGE330/NC

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First off I think that is the worst intake for carbed application. I run 30 degrees from 1,000 rpm to 3,500 then slowly ramp back to 24 degrees. 65 Coronet 2005 5.7 260 comp cam, 727 trans 2.96 gears 275/60/15 rear tires.15 mph rolling stomp the gas and leaves 2 black marks. Also I don't use the map sensor on the Hemi6 it seemed to mess with the carb adjustments the way it varies the timing. I started with the XV motorsports single plane intake it was ok but I now have the Joe Ocone dual plane and it is way better.
i have been waiting on one of the Joe OCone intakes for a while now myself
 

Uncle Don

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First off I think that is the worst intake for carbed application. I run 30 degrees from 1,000 rpm to 3,500 then slowly ramp back to 24 degrees. 65 Coronet 2005 5.7 260 comp cam, 727 trans 2.96 gears 275/60/15 rear tires.15 mph rolling stomp the gas and leaves 2 black marks. Also I don't use the map sensor on the Hemi6 it seemed to mess with the carb adjustments the way it varies the timing. I started with the XV motorsports single plane intake it was ok but I now have the Joe Ocone dual plane and it is way better.
this is what i was looking for. someone very close to my set up. what timing do you use at idle? the hemi 6 default i think is 8 degrees? maybe 10. you are one of the few that has gone to 30 degrees, most say your crazy for doing that, and to stay under 24 all the way.

just for updates my car has 3:55 gears posi, 2600 trans converter.
the kickdown linkage is set to where it does not kick down at all now, i adjusted it out to much, but it was binding the full throttle but now it is not.
my tailpipes are black. when i bring it up on converter and nail the throttle the carb cough's and dies. if i hold it in first gear roll out and nail it it coughs and sputters a little and has no power, i have to bring it back half throttle to 2 barrels and it will pull decently hard.
its a head scratcher for sure but im determined to get this thing running properly... but like your all's advice.
 

chtampa

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I am puzzled as to why you installed a modern motor and vintage fuel system. I have a 5.7 with a mild cam, Hemi 6, convertor, 2.94 gears, 4150 style intake and a bolt on EFI. My desire was a OE looking highway cruiser that is maintenance free. I have used the factory tune and am tickled. It will break the tires loose and it loves the Interstate.
 

392heminut

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First off I think that is the worst intake for carbed application.
I've read some stuff in the forums about that manifold having poor distribution properties, mostly running lean at the four corner cylinders.
 

sam65

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this is what i was looking for. someone very close to my set up. what timing do you use at idle? the hemi 6 default i think is 8 degrees? maybe 10. you are one of the few that has gone to 30 degrees, most say your crazy for doing that, and to stay under 24 all the way.

just for updates my car has 3:55 gears posi, 2600 trans converter.
the kickdown linkage is set to where it does not kick down at all now, i adjusted it out to much, but it was binding the full throttle but now it is not.
my tailpipes are black. when i bring it up on converter and nail the throttle the carb cough's and dies. if i hold it in first gear roll out and nail it it coughs and sputters a little and has no power, i have to bring it back half throttle to 2 barrels and it will pull decently hard.
its a head scratcher for sure but im determined to get this thing running properly... but like your all's advice.
I think being carbed it takes more timing,I had the stumbling problems to until I started adding timing. I had a bigger cam in mine and it was a turd swapped in the 260 cam still a turd started upping timing and it came to life.
 

Red Baron

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Hi

Ive been running a dual quad 6.1 with the MSD box for 8 years.

I’d like to examine your timing curves, both RPM and MAP.

I have a suspicion your MAP curve is not set up correctly and is pulling timing from your RPM curve.

I’ve added a pic of my timing curve - note there is nothing below the 0deg mark.

358FBA45-1659-4BBE-B523-208C75D5E172.jpeg
 

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