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