Is my 800cfm carb to big for my engine

[Petri.]

Hi, some people here at home in sweden tells me my carb is oversized for my engine so i would like to know what you guys think,i dont know much about carburators but i am trying to learn,my carb is  Edelbrock 800 cfm mod #1412 4 bbl carb.
Does this carb have secondary that works by vacum?
People tell me that carbs that have secondary that works by vacum takes less fuel when you just cruise slowly,true or not?
I want to have a carb that dont give more fuel that i need,i will mostly cruise and ofcourse sometimes go full throttle and with swedish gas prices its stupid to feed the engine with more than it needs,the car is a 68 charger and here is all info i have about the engine.
I think also the swedish fuel is a little better than you got.


Block Hi-Nickel Content (not original block)
Bore .030 over
Mopar steel rods
Keith Black 9.0 to 1 comp pistons
Moly rings
Clevite 77 main & rod bearings
Forged steel crank shaft
Complete balanced assembly
Cylinder heads (906) large valves with hard seats
Valve job with comp springs
Comp hyd cam 272 degree x 480" of lift
Cloyes dbl roller chain & gears
Melling high volume oil pump
Intake manifold is a HP 383 with Edelbrock 800 cfm mod #1412 4 bbl carb
Pertronics electronic ignition with MSD coil (no points)
Exhaust is a 383-440 magnum HP manifolds

/Petri

[1 of 1]

There is no such thing as to much carb! just not enough cam

[John_Kunkel]

my carb is  Edelbrock 800 cfm mod #1412 4 bbl carb.
Does this carb have secondary that works by vacum?

No, all Edelbrock square-bore carbs have mechanical secondaries.

People tell me that carbs that have secondary that works by vacum takes less fuel when you just cruise slowly,true or not?

Not, the secondaries don't open until near full throttle so "slow cruising" fuel consumption isn't affected. I think what people are trying to tell you is that vacuum secondaries don't necessarily fully open at WOT unless the airflow demand is there. Although the Edelbrock secondaries manually open fully at WOT, on some models there is an air valve above the butterflies that limits airflow (and fuel flow) so the effect is the same.

I don't think 800 cfm is too big for your build.

[bobs66440]

What size motor do you have? It depends on engine size, max rpm and volumetric efficiency (v.e.) and what you plan on doing with the car.

Here is a pretty good calculator for cfm requirements for a given engine.

http://www.gtsparkplugs.com/CarbCFMCalc.html

If you go by the calculations, a mild build 383 with a 6000rpm max will run well on a 600cfm. A 440 will do well with 750.  Over carburetion is one of the most common causes of tuning issues. As an example, the local circle track guys run 800hp 460ci big block cars at 8000rpm with 850 cfm carbs with good results.

[Petri.]

Sorry forgot to tell the size,its a 383 and thanks for help so far,so what you think of this carb for cruising,keep or go smaller,last owner told me it gets about 11 to 12 miles per gallon when cruising.

Petri

[Petri.]

Have not been able to drive so much yet because its not showed for inspection,but i noticed that it goes best at high rpm and when go slow att low rpm and wot it dies,you have to back of little and then wot again and then it works fine.

Petri

[bobs66440]

The Carter carbs that came on the cars from the factory I believe are 625cfm and they worked fine. If you are just cruising, my opinion is that an Edelbrock Thunder Series AVS 650 would be a good choice. I certainly wouldn't go any bigger than 750.  

For confirmation, I would call or email the Edelbrock tech line. Explain your situation to them and they will hook you up with the right setup.

[Petri.]

So what is the differense between thunder and performer series that i have, and is it worth to look at holley also,i checked holleys homepage yesterday and got headache when i saw all the different series.

/Petri

[bobs66440]

So what is the differense between thunder and performer series that i have, and is it worth to look at holley also,i checked holleys homepage yesterday and got headache when i saw all the different series.

/Petri

The main difference is on the AVS, the air valve (flap over the secondaries) is adjustable to open early or late. Otherwise I think it's basically the same. For most people, the performer series will work good. I suggested the AVS because it's offered in a 650 where the performer is 600.

Some people like the Holleys, and they are a good carburetor, but for street use I've always had really good luck with the Edelbrocks...they have always worked well for me with no maintenance.

http://www.jegs.com/i/Edelbrock/350/1806/10002/-1

[Petri.]

Think ill try edelbrock again,i will write a email to edelbrock in the beginning of next week and see what they say,how does the electric choke work,how do you wire that,i have manuall now and its not hooked up,just need to pump the pedal a couple of times and then it startes right up,dont know if i need any choke,only use the car when its nice warm weather.

/Petri

[John_Kunkel]

Best keyed power source for the electric choke is the double blue wire on one side of the ballast resistor.

[Petri.]

Checked att my carb today trying to learn a little about them, does the secondaries work like this, they wont open until it gets enough air to open, noticed that there was one "weight" at each side of the "ports" on the secondaries, and does the thunder series have the weights also.

/Petri

[John_Kunkel]

The Thunder Series is an AVS (Air Valve Secondary) which has a visible spring-loaded air door above the secondary venturies. The spring-loaded door limits the airflow even though the throttle butterflies are wide open.

Your Performer Series more closely resembles the old Carter AFB which used a counterweighted air valve below the venturies but above the butterflies. The counterweights will also only allow as much air flow as the engine demands even though the throttle butterflies are wide open.

[Chryco Psycho]

the math simply doesn`t work the carb will not flow as much as it says , the math I use is simple , 2x the CID , 800 on a 383 should work great

[Petri.]

I will drive with the 800 for a while and see how everything works, have another question about exhaust emission, im going on friday to get it inspected to get swedish plates on it,they will also check the emission,if it is to high ill have to try get it down over there, is it the two screws at the front end of the carb that will help me with that and do i screw them in or out to get better emission,maby put the idle down a little also will help.

/Petri

[elacruze]

I will drive with the 800 for a while and see how everything works, have another question about exhaust emission, im going on friday to get it inspected to get swedish plates on it,they will also check the emission,if it is to high ill have to try get it down over there, is it the two screws at the front end of the carb that will help me with that and do i screw them in or out to get better emission,maby put the idle down a little also will help.

/Petri

That depends on what emissions they look at. Too rich or retarded timing will bring high hydrocarbons, too lean or advanced will bring high NOX. Take your idle and timing adjustment tools just in case.

[Petri.]

They only take one sort and its at idle and its called CO and the max value is 4.5

/Petri

[bobs66440]

Those two screws in the front are idle mixture. This is the proper procedure for tuning idle mixture:

1. Fully warm engine and ensure choke is fully open.
2. Air cleaner in place.
3. Set desired speed with the idle screw.
4. Adjust the IMS on ONE side to get the maximum possible RPM.
Do not go rich beyond the maximum speed point.
5. If the above changed the idle speed more than 40 RPM, then readjust the speed.
6. Adjust the side OPPOSITE of that in Step 4 to get maximum RPM.
7. Reset the speed.
8. Carefully trim each IMS to again get the maximum idle RPM.
9. Go leaner just enough to get a 20 RPM drop in speed.
10. Reset the speed to the desired RPM.
11. This is a Lean-Best Idle Set. Setting richer than this will not
improve idle quality or performance, but could tend to foul plugs.

[Petri.]

Thanks but of course i have problems with this kind of translating,can we sort out my difficulties.

1. Fully warm engine and ensure choke is fully open. OK
2. Air cleaner in place.  OK
3. Set desired speed with the idle screw. OK
4. Adjust the IMS on ONE side to get the maximum possible RPM.
Do not go rich beyond the maximum speed point.
5. If the above changed the idle speed more than 40 RPM, then readjust the speed. OK
6. Adjust the side OPPOSITE of that in Step 4 to get maximum RPM. Ok when i know number 4.
7. Reset the speed.
8. Carefully trim each IMS to again get the maximum idle RPM.
9. Go leaner just enough to get a 20 RPM drop in speed.
10. Reset the speed to the desired RPM.
11. This is a Lean-Best Idle Set. Setting richer than this will not
improve idle quality or performance, but could tend to foul plugs. OK

4. You mean adjust in or out until i have so much rpm it will make of this adjusting and what do you mean by Do not go rich beyond the maximum speed point.
7. Reset the speed,do you mean by the idle screw?
And leaner is it the screw in or out?

It works nice as it is know, i only want to get the emission down when i am there,after that i will take all back to as it is know.

/Petri

[tan top]

 nother way & what i do !! connect a vacuum gauge to mainifold vacuum  , with motor fully warmed up ,  adjust idle mixture so you get the highest vacuum reading !! then if necessary   adjust idle speed as required !  


sometimes you might need to tweek it a little rich  after getting the vacuum  highest reading !!  depending on what the idle quality is like  but 99.99% of the time  its a smooth even idle ,  although coolent tempreture can sometimes  rise a little at idle if you have been previously running rich  

[Piston_Freddy]

Petri, do they measure CO on every old car in Sweden? In Estonia(Estland) they will not measure the CO if the vehicle is made before 1972. I will go to inspection in Friday and see what they will tell me about my '68.

[Petri.]

Yes these days the take the idle c/o,it has been like that a couple of years,only cars before -50 dont have any emissions.

/Petri

[bobs66440]

4. You mean adjust in or out until i have so much rpm it will make of this adjusting and what do you mean by Do not go rich beyond the maximum speed point.
4. Adjust either idle mixture screw (IMS) in or out as needed to get the highest RPM. In is lean (less fuel), out is rich (more fuel). If the idle changes more than 40rpm then re-adjust the idle screw to get it back to where you had it. Then do the same thing with the other (opposite) screw.

7. Reset the speed,do you mean by the idle screw? Yes

And leaner is it the screw in or out? Lean is in.


It works nice as it is know, i only want to get the emission down when i am there,after that i will take all back to as it is know.
This should get you the best idle tune for the carburetor, and I would think, the lowest emissions at idle, but that's a guess.

[bobs66440]

nother way & what i do !! connect a vacuum gauge to mainifold vacuum  , with motor fully warmed up ,  adjust idle mixture so you get the highest vacuum reading !! then if necessary   adjust idle speed as required !  

That will also work if you have a vacuum gauge.

[Petri.]

Does the vacum gauge have to be in the manifold or does it work if i put it in the carb also,i have a vacum unit near the IMS screws that i dont use,there is two of them and the other goes to ignition vacum.

/Petri

[tan top]

Does the vacum gauge have to be in the manifold or does it work if i put it in the carb also,i have a vacum unit near the IMS screws that i dont use,there is two of them and the other goes to ignition vacum.

/Petri

connect it to any vacuum port below the throttle plates   ,!!    easy way  is just temporally  pull the vacuum pipe off that goes to the vacuum canister for the head light doors !!  on the rear of the intake , plug it in there 

[Petri.]

Nice,thanks to you all, ill get back how it went at the inspection.

/Petri

[Petri.]

So know it is inspected and has swedish plates,went pretty good, c/o was just under maximum 3.8 and max is 4.5 ,only problem was rear brakes that i have to show up again, 1.3 at left and 1.9 at right ,its 11" drums so i believe they have manual adjustment that i read here,propably just some adjustments because everything looks new behind the drums when i looked long time ago just to check one side,have any tips at the brakes for me,were also at cruising saturday,near 8 hours driving,had to screw the idle up because it wanted to die when cruising at idle,what causes that problem its propably over 1000 rpm,and damn it takes fuel,you get 12miles at one gallon,know way you can go under that,400d fuel this weekend.

Petri

[firefighter3931]

Petri, the venturies on that 800cfm carb are large so it will use more fuel than it would with a more moderately sized unit. 

A 650cfm carb would have smaller venturies yet still provide plenty of air/fuel for your 383  The smaller carb would certainly be more efficient and have better throttle response.   


Ron

[Petri.]

Thanks,will i loose any power with a 650 and will a edelbrock 650 work right out of the box on my engine or do i have to change anything in it, and what is the ventury,some kind of fuel air channels?

Petri

[bobs66440]

The 650 should work very well and have good power. It will most likely run much better than the 800. The only thing I ever had to do after installing an Edelbrock carb was adjust the idle. And I only did that because I felt like I should do SOMETHING...it really needed nothing. Just to drive it! That's my experience anyway.  

On the AVS, the air valve for the secondaries are adjustable, so you may want to play with that to get the best response...

[Petri.]

Hi again have been a while ago,have been driven the charger all summer with the 1412 800cfm,we have adjusted the carb and the ignition at the beginning of the summer and it wont work good when cruising at idle for a longer time, then it dies and its tuff to start again and run well after that,  ok friends i have a proposol and lets see if you like it and want to help me.
Last week i got home a new car from dubuque iowa,one owner chrysler 300 -67 440 2dr with all the papers,he ho sold it to me is 83 years old today and i have spoked to him a couple of times,he also wrote me 3 a4 papers about the car through the years,also got speeding tickets from 70 and 78 from highway state patrol, but lets go to the questoins, the 440 is missing a little at idle and upp about 200rpm but the worst is when you hit the throttle when the engine is fully warm it dies and only goes  at idle and 1 more inch of the pedal,i now 1 thing that is bad and it is very very old spark plug wires,so i will change the ignition to msd performance or put in pertronix and efcourse everyhing else new in the ignition line,so i checked the car numbers upp and googled it, holley 4160,r3667,2843151,date code 683 what that means? so i found out that it is the stock carb on the 440 and that it is only 570cfm,  is that the stock carb and why is it so small on a 440, so what i want to know is can i put the 1412 800cfm on the 440 and get it work well with good mpg or is the holley good for the stock 440, so if the edelbrock 800cfm would work good on the 440 i would put it there because i anyway have to change the carb on the charger, finally here is a video of the 300 and my uncles 300 4dr.
http://www.youtube.com/watch?v=qLXMcQJHaYQ

/Petri

[bobs66440]

As previously stated, these engines don't need big carburetors unless you are racing at high RPMs for extented periods. For street use, the small ones work fine.