is this carb to small?

[ToiletDuck]

eddy 600cfm on a stock 400 w/ a 383 4bbl intake. this is a 4x4 that is just goin to see the trails and some mud.

I checked the plugs (autolite 83's) and they were pretty black with only a few miles on them. Plugs to cold or idle to rich maybe?


thanks a bunch

[dwc43]

Carbs wayyyy to small. Get at least a stock thermoquad (850) or a 750 holley.

[MoparMarcIdaho]

A little of both mabeye,Carb might need freshened if its flooding.Good choice for the street if its dialed in correctly.For off road use run a piece of vaccum line between the float bowl vents and drill small holes in them to help prevent splashing into the venturis.

[ToiletDuck]

Originally Posted by dwc43

Carbs wayyyy to small. Get at least a stock thermoquad (850) or a 750 holley.

would a quadrajet bolt onto this? iv heard they are good at high angles.

[ToiletDuck]

Originally Posted by MoparMarcIdaho

A little of both mabeye,Carb might need freshened if its flooding.Good choice for the street if its dialed in correctly.For off road use run a piece of vaccum line between the float bowl vents and drill small holes in them to help prevent splashing into the venturis.

going to do that and the float adjustment if i keep this carb.

[MoparMarcIdaho]

The q-jet has the float and pivot point in the middle and the T-quad has dual floats that pivot in the rear.I have had good service from both,you decide.

[robboski]

once you've got the carb straightened out you may also want to consider a different brand of plug. NGK has always served me better than any other or at least champions. champion made the factory plugs for most chrysler products where as autolite is actually the maker of motorcraft plugs, not a bad plug but just doesn't seem to work as well for dodge.

[dwc43]

Plugs wont make any diff, but the quad is prone to open the secondaires when it feel like it. The TQ would be a better choice.

[dirty dan]

Originally Posted by ToiletDuck

eddy 600cfm on a stock 400 w/ a 383 4bbl intake. this is a 4x4 that is just goin to see the trails and some mud.

I checked the plugs (autolite 83's) and they were pretty black with only a few miles on them. Plugs to cold or idle to rich maybe?


thanks a bunch

Hey Toilet duck
When you say a stock 400 ,I assume that includes a stock cam.
If so a 600 cfm would give you good lowend throttle response.
A stock cam was made for low end grunt power.
More cfm would help only in top end ,with a biger cam.
Good for mud hole full pull at wide open throttle for the entire run.
But slugish out of the hole (For bottem end)with a stock cam and no stall.
You did not mention your stall or gear ratio.
However I woud recomend an autolite 86 plug.
The factory recomends an 85 .
But I prerfer an 86 for best results.
Up grade to an 86 and get your eddie right and you will be impressed.

[ehostler]

600 is way too small for that engine. I had a bone stock 383 2bbl engine. I put an EB Torker intake on it and a Holley 3310 750 vac secondary, and the engine loved it. Trust me when I say that it did not sacrafice any low end power.

If you have a spread bore intake, I would definately look at a thermoquad. It will give you better low end grunt and better part throttle MPG. Then when you need the power, those secondaries crack open and give the engine all of the air/fuel that she can take.

[rumblefish360]

Many a MoPar engine came with carbs that would be considered way to small. The 383 in fact mostly came with the smaller AFB/AVS carbs.
I also have a parts carb, a small AFB without a secondary air valve, that came off a Imperial w/440.
Though a small Carter is enuff to feed even a large cube engine, it becomes HP/RPM dependent.
Now just what would be good on TD's stuff is outside of my experiance.
I could see where a AFB could be a problem with it's weighted air door.

[MOPARMANJAMES]

If your'e not revving the piss out of it, the carb size is fine up to 5000rpm in a 400ci engine with 100% volumetric efficiency. Actually, the formula only requires 578cfm.
I think your idle is too rich or you have a defective carb.
I would get a thermoquad for best all around results.

[rumblefish360]

Have you tuned it or just bolted it on?

[waldo67]

is the carb new or used thats the question and you can toss ve out the window to many variables to consider on an old engine his engine depending on mileage will need a larger carb chrysler products tend to like to be over carbes just a bit go with a good fresh holley or a good fresh tq

[MOPARMANJAMES]

Originally Posted by waldo67

is the carb new or used thats the question and you can toss ve out the window to many variables to consider on an old engine his engine depending on mileage will need a larger carb chrysler products tend to like to be over carbes just a bit go with a good fresh holley or a good fresh tq

I used volumetric efficiency to give a starting point on whats needed. On a new engine for the street, usually 100% ve is the most you can hope to achieve at a given rpm. For higher performance use, 110% is usually the norm.
He said he was just going on some trails and some mud. I figured that 5000 rpm was a reasonable rpm if he doesn't have much cam in it.
So, in the best case scenario, 600cfm is fine for his application at 5000rpm.
Your right though, alot of variables, most of which would decrease the size of the carb needed.

[Kevin Garceau]

I also agree 600 is perfectly fine.

Also 100% is pretty good for V.E... read a few years ago Pro Stocks were only in the 115% range so I wouldnt figure anything at 100. Most of our race motors are probably closer to 90 than 100...

I see no need to go any bigger. I have always thought and told others most people have way too much carb on their motors.

[waldo67]

mj i wasent busting your balls by the way ive been bulding mopars for 16 years and chevys prior to the turn to the dark side chryslers tend to like a slightly oversized carb hence the reason why chrysler put those huge ass tq on them they respond well to them if i was doing a 4wd i use a tq or a rochester q jet they seem to be better then an eddie for off roading holleys dont mind a bit of bumping around but not a lot of it tuning to get maz ve is the best way but requires a dyno to achieve max ve after the first of the year i will be puting my low buck eddie headed 350 on the dyno and im going to tune for mak tq hp and ve

[MOPARMANJAMES]

Hey no problem Waldo, I wasn't trying to start a pissin contest, just explain why I start with 100% VE, since that's the best you can hope for, then the carb size is fine if your already at that size or a little bigger.

[waldo67]

no worries mj i dont like pissing contest myself the tend to get pissy lol

[MY340]

Use the spring loaded needle & seats offered by Edelbrock/Carter for the AFB's. They were designed for off road use. Sounds like it maybe running rich or try a slightly hotter plug first. If in doubt get the air/fuel mix checked by a shop. If the carb jetting and rods are unknown you need to find out what's in it and use the Edelbrock tuning guide on their website to get the carb dialed in. I think the EB 600 would work fine for your intended use.

[ehostler]

My issue with using formulas based on VE is the fact that the CFM of most carbs aren't based using related formulas. A Holley 750 vac secondary doesn't flow the same as a 750 DP, doesn't flow the same as a Demon 750 vac secondary, doesn't flow the same as a Demon 750 DP.

For my 383, I spoke of first hand experience. The engine was 100% factory 383 2bbl in a 1970 Dodge Challenger. Swapped from the 2 bbl to a Torker and a 750 vac secondary. Using your VE numbers, this should have been wayyyy too much carb for the engine. It wasn't. She ran very strong with that carb.

If a 383 ran very strong with that carb, I am sure that a 400 would, as well.

[MOPARMANJAMES]

E. Hostler
If it had been a 750 dp I would disagree, but with vacuum secondaries set up properly with the appropriate spring, it would be a very good carb.
I do think a 600 vac secondary would be more responsive though.

[cutting torch]

It's hard to overcarb an engine when you use a vacuum secondary carb. If the engine can't use all of the available CFM, the secondaries won't open all the way, since they open based on the particular engine's demand. A TQ, for instance, is a lot more carb than a stock 360 can use, but they still work great because the secondaries won't open more than the engine can use.

torch

[dwc43]

I agree with E. You can use all those formulas you want, but they always show you with too little carb for what any real world engine really needs. They are pretty much worthless.

[MOPARMANJAMES]

Originally Posted by dwc43

I agree with E. You can use all those formulas you want, but they always show you with too little carb for what any real world engine really needs. They are pretty much worthless.

Yeah, damn formulas, we should still be on Horseback, LOL

Cmon, these formulas are not worthless, you deal with high performance, big cammed engines where the volumetric efficiency formula is usually increased to around 110% to compensate for the bigger cam and higher breathing capacities at higher rpm's.
For example, a 366 spinning at 6500rpm would need a 756 cfm carb. But a street engine typically has a smaller cam, less breathing capability and needs less.
These theories are based on yet other theoretical pumping rates. Your rates may vary slightly but not by much unless of course they are far lower.

[webslinger60]

I’d think a 600cfm for a stock 400 is fine. Although a 750 and a little more aggressive cam will really wake it up.

A friend of mine once had a car with a transplanted no-mod 400, with a 2bbl and headers, and it ran fine, was quick and not bad on MPG. It originally was a 383-2bbl/727/8.25-3.23 , single exhaust Challenger convt . The previous owner blew the 383, and swapped in a JY smogger 400. But used the old 2bbl manifold with the 500cfm Holley, and installed headers at the same time.

I rode in this car many times and it was quick. It could out accelerated my 70 Chally hardtop (318/904/7.25-2.91) with 4bbl & headers. Although I could keep up with him on top end