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Carb sizing for LS3

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Old Oct 6, 2010 | 11:34 AM
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Default Carb sizing for LS3

How much carb would be right on an cammed LS3?Right now I have a Edelbrock 750 on it which runs good but im sure isnt letting the engine breath well as its capable of.Ive saw alot of ppl using 850s and 950s on these things but seems like anything more than a 850 would be over doing it maybe.Anyways im looking for a new carb and was looking at a 750 or 850 Proform race carb.Which one would be better suited for a cammed LS3?The car is 3450lbs with a TH350 and 10inch 4k stall and 4:10 gears.
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Old Oct 6, 2010 | 12:06 PM
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Default Edelbrock carburetor

Originally Posted by 1994t/a
How much carb would be right on an cammed LS3?Right now I have a Edelbrock 750 on it which runs good but im sure isnt letting the engine breath well as its capable of.Ive saw alot of ppl using 850s and 950s on these things but seems like anything more than a 850 would be over doing it maybe.Anyways im looking for a new carb and was looking at a 750 or 850 Proform race carb.Which one would be better suited for a cammed LS3?The car is 3450lbs with a TH350 and 10inch 4k stall and 4:10 gears.
What rpm do you plan on running the motor out to and is this gonna be a car that will be driven in street stop n go traffic or a sunny day toy or a drag only car?

For ease of tuning the edelbrock carbs are hard to beat and they do come in a 850!

Do you have a wide-band installed on the car yet or you gonna tune it using the vacuum method?
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Old Oct 6, 2010 | 12:12 PM
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go to the holley web site.
850-900 is my guess
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Old Oct 6, 2010 | 12:37 PM
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I love my quick fuel carb, Q series mechanical secondaries, I'm running a 950 since it's more strip than street but a 850 would be a good choice for you as well.
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Old Oct 6, 2010 | 01:02 PM
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For ease of tuning the edelbrock carbs are hard to beat and they do come in a 850!
I did not know they made 850 edelbrocks...that might be an option for me now.


What rpm do you plan on running the motor out to and is this gonna be a car that will be driven in street stop n go traffic or a sunny day toy or a drag only car?
The most im gonna spin it is 7000 rpm.It is a street car but not a everyday driver just a sunny day cruiser and take it to the track a few times a month and local grudge racing spot some....Oh and no wide band installed but may here shortly.I do have a vaccum gague and can tune using that.
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Old Oct 6, 2010 | 02:33 PM
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A 750 is perfect for a street driven car, a 850 will give up a touch of torque down low but will have a bit more hope end power and then the next step, a 950 is another bit of HP and touch less TQ, i run the 750 Pro Form, which is about a 800 actually, so it is a good mix, but i drive the **** out of my car.

Elelbrock? Blah, there is a reason all the fastest cars out there run a Holley or Holley base platform carb, and if anyone thinks the Edels are easier to tune, i guess they have never rebuilt or tunes a Holley, ultra simple.
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Old Oct 6, 2010 | 03:25 PM
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Elelbrock? Blah, there is a reason all the fastest cars out there run a Holley or Holley base platform carb
,

That is true Holley based carbs probly do make more power in most applications.Ive had a saw a few street cars run faster with Edelbrocks than with a Holley on them though

and if anyone thinks the Edels are easier to tune, i guess they have never rebuilt or tunes a Holley, ultra simple.
Holleys are easy to tune but all the Edelbrocks Ive owned didnt need to be tuned no matter what they was on.I havent met anyone thats had a Holley that ran great out of the box.Holleys can be a sensitve to weather changes and need tinkering to keep them right.Edelbrocks are set it and forget it pretty much................................BUT like you said before if you wanna make power you gotta run a Holley and thats what im looking for.....Think im gonna go with a AED or Proform.....might use my Edelbrock for the winter months and the 4150 style for the track season.
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Old Oct 6, 2010 | 03:30 PM
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Wow, maybe it is just our Texas weather, but i tuned mine in winter, then in summer it was fine and in summer on a different setup and in the winter it was no difference. But depends where you are, it gets over 100* here in Tx and about 20* is about as cold as it gets, so we never see 0* or less F in Texas, not in Houston area for sure.

Hell, i dont even run a choke and i can get them to idle when cold just fine. Never have to re tune, have had to remove trash from the bowls because of the tank having trash, but that is with any carb.
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Old Oct 6, 2010 | 03:36 PM
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I havnet run a choke on any of my carbs either but all the Holleys ive had would need idle mixture and idle speed adjusted everytime the temapture changed or the humidity went up or down(which we have some humid *** weather here in Alabama in the summer).
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Old Oct 6, 2010 | 03:43 PM
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have you ever considered the holley street hp line?
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Old Oct 6, 2010 | 04:27 PM
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I really want a Quick Fuel 650 DP with Annular Boosters for my 350HO.

But I really, really want to throw it in the ocean and get an LSX.

3rd would be a FAST EZ-EFI.

So many choices. Anything would be better than an edelbrock. I hate those.
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Old Oct 7, 2010 | 10:21 AM
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369 graph is with the Edelbrock 750 (This is with Jet changes and hours on the dyno)
420 graph is my Holley 750 Dp.....all that was changed

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Old Oct 7, 2010 | 10:44 AM
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i run a demon 750 carb which was easy to tune and set up and hasnt given any problems in almost 2 yrs now. No choke, i hold the throttle open a little from cold and within 30s-1min i can let off and the car will idle perfectly.
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Old Oct 7, 2010 | 06:05 PM
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Originally Posted by Ravenous T\A
369 graph is with the Edelbrock 750 (This is with Jet changes and hours on the dyno)
420 graph is my Holley 750 Dp.....all that was changed
Holy crap, makes the Edel look like it is worth nothing.
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Old Oct 7, 2010 | 06:22 PM
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I run an 850 Mighty Demon. it probably flows more than a 950 hp holley. I find it runs awesome on the street, and is easy to tune. I wont ever go smaller than this again. When I get around to building a 40x stroker, I may even step up to a 1050 dominator, or King DEMON.
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Old Oct 7, 2010 | 06:45 PM
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Well, i guess the next time i get my **** straight, i will find someone with a bigger carb and swap it at the track and see what it gains.
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Old Oct 7, 2010 | 08:11 PM
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Here I sit biting my tongue. BIGGER is Better. Not quite that simple. Our experience on the chassis dyno has been very enlightning to say the least. I can tell you that I've got 40 years of racing, 20 of dyno. I've seen good/bad from all brands. We tune stock and super stock stuff, they have to run the carb that was oem. We have customers running in the 9's with rochester quadrajets. Look at the Chryslers with Carter carbs which are Edelbrocks.

With a big open plenum like GM's LS carb intakes a Holley style double pumper helps with throttle response. You need to understand that when you mash the go peddle the air moves right away. The fuel being heavy takes a bit of time to recieve the signal thru the boosters, that's what the acc pump is for. It carries the engine until the fuel can move thru the jets. Annular boosters help when the carb signal is weak such as a big intake,cam or carb are used.
The BIGGER the cam,intake plennum,and carb the smaller the signal. Also the smaller the cubic inch the less carb signal.
Check out Pro Systems carbs. They are custom built for each car/engine combo and not too bad price wise.
Holley carbs tend to flow less than advertised on our flow bench.
Edelbrock carbs have thier floats off from the factory. Don't try to tune until the fuel pressure is correct then the float level.

A long winded post.
Aleck
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Old Oct 8, 2010 | 06:44 AM
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i have the GM plenum and it does seem to work well with the 750 double pumper!
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