carburator help

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gold68dart

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I am not quite sure what carb I should buy for my first motor build. Here are the specs so far: 340 block stroked to 416ci, 9.8:1, cam is .548" lift 237/242 duration with 108 degree lobe separation, eddy airgap intake, and eddy performer heads, TTI headers. All mated to a 4-spd with 3:91 gears. This will be mostly a street car with occasional track time.

Any suggestions?
 
Yeah what he said. That would probably work real good with a big kyoob small block and manual trans.
 
Check out the new Eddie Thunder Series and do some research on it. Available in manual or electric choke. Call there toll free tech line. Price is reasonable.
 
For a Holley, on a street strip ride, fair weather only, I'd look at this myself since it is a 4spd manual your driving;

http://holley.com/0-82851

An electric choke 850 like the below, IMO, would be a little nicer than the above listed one due to the electric choke. There is no performance gain with a manual choke. The electric choke just makes cool/cold weather driving/warm up's easier.

http://holley.com/0-80531
 
I appreciate the responses. So it looks like everyone is recommending some form of a double pumper. I have one sitting in the garage (850 cfm I think) but I don't know the number off hand. I was hesitant about using it only because of all that fuel dumping in down low. I thought maybe I should try one of my 850 thermoquads but thought I would starve the engine down low with those small primaries.

The other common thing from you all is 850cfm is the size. I wasn't sure I needed one that big.

Keep the suggestions coming! Thanks!
 
I appreciate the responses. So it looks like everyone is recommending some form of a double pumper. I have one sitting in the garage (850 cfm I think) but I don't know the number off hand. I was hesitant about using it only because of all that fuel dumping in down low. I thought maybe I should try one of my 850 thermoquads but thought I would starve the engine down low with those small primaries.

The other common thing from you all is 850cfm is the size. I wasn't sure I needed one that big.

Keep the suggestions coming! Thanks!

If you already have an 850, that is the one I would try first.
 
I think 850 cfm is too big in my opinion. I would think a 750 would give you much better off idle throttle response. If you decide to go with an 850 and are set on that size, I would use a vacuum secondary carb.
Don't get me wrong, I'm still fighting a 650 Holley HP on my 318 build but I'm pretty sure if it was smaller, it would have worked better.
 
Mostly street. I don't think he needs a 950.


http://www.thecarburetorshop.net/bigger2.html

It's understandable why he made the mistake of thinking he'd gotten a "bigger carb." After all, 950 is more than 850 right? Wrong! In this case, Holley decided to rate their new line of "HP" carbs like their competition does, with inflated CFM figures. They had to. Otherwise no one would buy them because they are more expensive. An HP 950 Holley is a 750 main body with an 850 base. That makes it an 800. You can do the math. The "950," in this case, refers to the CFM potential, not the size of the venturi and throttle blade diameter.

So it is actually smaller then the one you recommended...
 
That's really interesting. Thanks, Tony.
 
http://www.thecarburetorshop.net/bigger2.html

It's understandable why he made the mistake of thinking he'd gotten a "bigger carb." After all, 950 is more than 850 right? Wrong! In this case, Holley decided to rate their new line of "HP" carbs like their competition does, with inflated CFM figures. They had to. Otherwise no one would buy them because they are more expensive. An HP 950 Holley is a 750 main body with an 850 base. That makes it an 800. You can do the math. The "950," in this case, refers to the CFM potential, not the size of the venturi and throttle blade diameter.

So it is actually smaller then the one you recommended...

The Holley is wet flowed and the combination of body and base plate are not a simple matter of math but air flow, actual, through the carb in the new configuration which does not follow such basic thoughts on how air flows.

I wish it were that simple. The new ventrui (SP?)shape allows for a great flow of air through it.

If you can me and Holley different, please do.

I was hesitant about using it only because of all that fuel dumping in down low. I thought maybe I should try one of my 850 thermoquads but thought I would starve the engine down low with those small primaries.

The other common thing from you all is 850cfm is the size. I wasn't sure I needed one that big.
An 850 would feed it proper @ max RPM.
The Double pumper suggestion is due to the manual 4spd. trans.

This next line from you is of great concern;

I was hesitant about using it only because of all that fuel dumping in down low.

it is NOT the carb size that is of issue here at all, not one bit. IT IS of fuel control. Bigger does not mean more fuel is being "DUMPED" in the engine. The amount of fuel through the carb into the engine is controlled by the jets that allow the amount of fuel though the carb and into the engine.

The common term used or thought behind this is someone could "Drown the engine."

You can drown an engine with a small carb.

Again, it is the amount of fuel through the carb allowed that drowns an engine. Not the size of the carb.
 
Rumblefish - I'm going to ask the dumb question, why is the double pumper recommended because of the 4spd?
 
Rumblefish - I'm going to ask the dumb question, why is the double pumper recommended because of the 4spd?


A double pumper carb offers better performance due to the instant opening of the secondary side of the carb vs. the slower opening of the vacuum operated carb. With this, certain things on a performance car will like this better. These things are;

Lighter car
Higher gear ratio
and a manual trans. An auto trans can use this easy as well, but, if the described car above was an automatic trans, IMO, I do not think it would really be up to it.

An automatic trans car that can make use of a DP carb is much more racer in orientation than the above. It is often a drag car that will use a DP and a automatic trans.

A road race or street car can regulate what gear and RPM there in, manually of course, to where they need to be or want to be. Which would be in a sweet spot of a quick action of all the 4bbl.'s opening at once. The RPM is higher than a basic street car or even a mildly hopped up car.

When your sweet spot, lets say, is 3500 as a min., and you wack the pedal to go. An automatic will take off well and the secondaries open at a set rate. Slow by compare to the instant opening of a mechanical carb. (This is a problem with Carter/Edelbrock carbs, not DP Holley's, more on that later)

At 3500 RPM, lets say, your around peak torque and entering the higher HP range of the RPM band. The quick RPM's of the engine, the increased volume-metric efficiency of the engine rises up, the air and fuel speed are going really fast. Basically, the engine can use or will take all you can give it. The engine is most happy singing to you, "More the Merry!"

A DP will do just that. Max air and fuel for the engine when you want to give it to the engine. The Manual trans helps keep the engine or puts the engine where it can do the best when that time comes.

The power result is explosive over a vacuum secondary carb. It can be really interesting, or down right scary blowing the rubber off of your wheels in 3rd gear doing 60 MPH. Laying down 20 feet of rubber into 4th gear.

While a powerful engine maybe needed to do such, a manual trans and a double pumper really do the trick.

Full power at the stomp of the foot!
 
IF it is a totally street driven car, no track, just some foot stomping fun from time to time, a 750 would be fine. It still would not be a bad choice though.
 
Wow rumblefish! That was quite an explanation and I thank you for it! Made perfect sense. So if I go with that carb you suggested earlier (http://holley.com/0-82851) any suggestions on what jets to use?

So with this combination of parts I listed in the original post, what kind of power/torque could I expect? I've been told everywhere from 400-500hp and the same for torque. Would I be able to get my dart into the 11's? I'm coming from a warmed over 318 auto so it would be nice to boil the tires in 3rd gear with this stroker!
 
A 950hp would likely make best power. They really are about 830cfm.

If you want yo drive it around on the street and not mess with the rich cruise a 950hp has, put a 4779 750dp on it and go. It will make almost the same power and have a better cruise Air/fuel.
 
Wow rumblefish! That was quite an explanation and I thank you for it! Made perfect sense. So if I go with that carb you suggested earlier (http://holley.com/0-82851) any suggestions on what jets to use?

Glad you understood it. Sometimes, I ramble in circles and never get my point across. I was tired when I wrote it. And worried I didn't make myself clear.

On jet size, sorry, no suggestions except, start with the OOTB and then go from there. A 02 sensor in the exhaust pipe(s) will tell you where you stand for the quickest method of tuning the engine or a trial by error at the track and reading of the plugs and taking down notes of how the car runs in addition to the time slips.

You know you did right when the time falls and the speed rise's.

Get a jet kit to start.

So with this combination of parts I listed in the original post, what kind of power/torque could I expect? I've been told everywhere from 400-500hp and the same for torque. Would I be able to get my dart into the 11's? I'm coming from a warmed over 318 auto so it would be nice to boil the tires in 3rd gear with this stroker!

I'm not really sure about taking a guess at power levels right now. Stroker's tend to throw me off. Due to not messing around with them, it is actually a bit out of my league to take a guess, and be some what accurate about it. So, I'd rather not comment on it.

Some of the other guy's can pipe up and add 2 cents on it. I'm sure there is a few guys here with a similar combo. The best I could do is run a very general "Desk Top Dyno" sym if all the numbers could be plugged into the program. Being the DDT program is , I guess about $40 these days, go get ya one and play with it.

Be aware that it is a general program that is fairly accurate if you understand how it works and it's short comings. IMO, the program is a excellent learning tool to see how things change and what effect it can have on a dyno curve. There are more expensive programs out there that are more accurate for a price. The home hobbyist will have to decide for themselves if it is worth it.

If you want yo drive it around on the street and not mess with the rich cruise a 950hp has, put a 4779 750dp on it and go. It will make almost the same power and have a better cruise Air/fuel.

There is a lot of truth to this! I have noted time and time again that a race is more often won or lost at the line rather than the power made by the engine. With this in mind as well as your intended usage of the car and the question of carb size at hand, the choices are to split the race carb size and the super street docile carb size. This is where I came up with the 850 on a 416 cube engine.

A 950 (or larger) carb will provide the best power, but, it may (Notice the word, "may", a lot like "IF" and "should") cause a slight low speed drive-abilty issue. A lot is in the tuning of the carb, timing in concert with the parts being used. This can be no small task and your abilty and available helping hands abilty is an unknown factor. Enter error on the side of caution to fit the parameter of the engine and question.

A smaller carb, like the 750 will provide a little less HP on the top end. But the smaller primary throttle bores will have the air rushing quickly through and this helps atomize the fuel a little better. This combo helps a lot in drive abilty, response, torque and ease of car movement.

On a smaller engine, a 360 of approx. 400 HP, the difference between a 650 and a 750 carb was 10 hp. You'll never feel it, never see it at the track, or barley but will notice the smaller carb responds better due to the quick velocity through it.

(The cam specs were about 10* smaller than your current cam listed above and the rest of the engine was equipped like yours.)

I'd consider a 750 for your engine to be on the small side, but totally doable, a total drivers carb with you missing some top end HP. To what tune the total amount would be, I do not know. You do have a lot of cubes.
And because you have 400+ cubes and a decent cam in there, I step up a little bit on that and the 4spd.


4spd cars tend to be able to handle and like more cam, carb and gear than there automatic trans counter parts.

:prayer: All hail the 4spd! I love mine and miss it! :sad6:
 
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