I installed a new 350 long block in my '82 trans am but at the time I couldn't afford new dressings so I used the old ones off of my 305. Now I've finally, piece by piece, have replaced all the accesories except for the carb and intake. People on this site have said that I should go with a carb/intake combo. Does anyone know where I can get a mechanical 650 carb with a decent intake?

 

Are you looking for new or used?

What are the specs on the cam you have?

What have you done with the exhaust?

 

I want a new set.
These are the specifications of my engine via jegs.com
Specifications:
Horsepower: 290 HP @ 5,100 RPM
Torque: 326 FT/LBS @ 3,750 RPM
Max. Rec. RPM: 5,100 RPM
Compression Ratio: 8.50:1
Heads: Cast Iron, 76 cc
Camshaft Lift: Flat Tappet Duration @ 0.050'': 222° I, 222°
Lifters: Flat Tappet
Connecting Rod:
Powdered Metal
Block: 4 Bolt Main
Pistons & Pins: Aluminum
Crankshaft: Cast Iron Nodular, 3.480'' Stroke
Rocker Arm: 1.5
Ignition Timing: 34° BTDC total advance.
Fuel: 87 Octane

I just had a custom exhaust intalled. Its goes from shorty hooker headers to a y-pipe than splits in 2 again after the rear axel with one pipe having a glass pack muffler and the other pipe just running striaght.

 

If you drive it on the street a lot you'll want to consider a vaccum secondary carb instead of a full mechanical that you mentioned. 600 holley will suit you well sitting on top on an RPM or RPM air gap intake.

 

why a 600 instead of a 650? I have a manual transmission. Someone on this site said that mechanical carbs are better for those transmissions.

 

600 is the vacuum secondary and the 650 is the double pumper. It's up to you. The vacuum sec. wiil give you a little better mileage.

 

A vacuum sec carb is not going to hold this combination back.
I would pull the heads, shave .060" off the decks, home port them and reinstall with thin shim style .015" head gaskets.
I would pull the cam and install a Comp cams "dual energy"
265DEH-10 grind. comp #12-208-2
The motor will go and feel like a whole different beast with these simple changes.
I would then use a Edelbrock Performer RPM intake and 750cfm edelbrock carb.

The cam that comes in that crate motor is a mismatch for 8.5:1 compression. (no torque)
Sell it off on ebay.

 

750 is way too much carb for that motor.

 

No its not. I have a 750 vacuum secondary Holley on my 350, which is not much different than his. It works great.

 

Didn't say it wouldnt work, I said it was too big. Do the math. You take your CI and multiply it by the MAX RPM the you'll twist the motor to. Then you divide that by a certain number that I can't remember off the top of my head, I want to say it's 3934 or somthing to that effect. Take the resulting number and multiply by .85 as a rule of thumb for the VE% for a street car and you've got your required CFM.

With my motor, 383 x 6000 RPM it came out to a touch under 650CFM. And I highly doubt he'll be twisting anywhere near 6k with stock heads and it'll be even less than that considering the considerably lower displacement.

Yes the motor will run with a larger carb, but your effiiciency (BSFC), power and driveabilty will decrease by jetting down a too large carb.

 

The factor is 3456

so... 350 X lets say 6000
------------------------ (.85) = 516 cfm.
3456

 

That carb sizing guide is very generalised and for the most part misleading.

Carbs are rate at a manifold vacuum of 1.5". Meaning that if at WOT the manifold under the carb was at 1.5" vacuum(guage) , then the carb would be flowing 750cfm.

If a 1.5" manifold vacuum @WOT was the absolute magic number to hit then the formulas would be right,,,

BUT IT IS NOT

Trouble is 1.5" manifold vacuum at WOT is not the absolute
point of maximum performance. A engine will make max power WOT with a somewhat lower manifold reading.
Somewhere between .75" and 1.5".

So..... now a 750cfm rated carb on a engine that is best @WOT when the guage reads 1" will not be flowing 750cfm.

It will be flowing something less than 750cfm.

Don't have to pressure drop conversion handy but it will be like 625cfm.

Now the engion is making max power and the carb is not too big,
The engine doesn't care if the manifold vacuum reading at WOT is less than 1.5" ( less restriction). It only needs anough air flow velocity throu the venturii to allow proper fuel flow.
Because the secondary side is controled by engine flow demend the carb always has enough airflow speed for proper functioning.

A dual plane manifold with its split plenum also allows for a large carb than your formula indicates becasue any cylinder only sees half the carb.

Experience and dyno testing bears this out.
A performance oriented 350ci engine will most always want a carb larger than you formula indicates.
Even a engine that only draws 550 cfm actual measured air flow on a dyno air flow meter will want a carb that is larger than 550cfm@1.5". It will run fine with this carb but not make max horsepower. it will want a 750cfm carb usually. Especially on a dual plane and especially with vac secondaries.

A stock Fbird carbed 305 come from the factory with a 795cfm rated carb ( Qjet)

A 600 or 650 will run very nicely but a 750 is best for max horsepower output most of the time.

Trust me on this one. I've been playing with performance cars most all of my life. A street 350 will like a 750cfm carb
I recomend a holley 3310 vs or a Edelbrock 1407.
I recomend a Edelbrock Performer Rpm intake.
The PP chinesium knock off works (crosswind) very well too. No difference other than cosmetic.
This is a very powerfull , flexable, driveable combination that will work now and allows room to grow ( engine upgrades) in the future.
This induction system can take you right into the 11 sec range. ( future)

I highly recommend you do the changes I outlined to your 350/290hp crate motor as well. You'll be glad you did.

 

Here is my formula for sizing a carb to your engine.

CID X RPM /3456 X 1.15 for a single plane
X 1.3 for a dual Plane manifold

350 X 5100rpm /3456 X1.3 = 671cfm carb rating

If you do the improvements I listed your engine will make more power and peak at 5500rpm, wanting a larger carb.

724cfm carb a 750 is best.

Install your motor * as is* with any size carb and try it.
Then just change the camshaft for the the one I recomended and drive th car. You'll see that I know what I'm talking about. Get the 750cfm carb and do the heads.

 

Whatever you say

 

A double pumper is better for a manual transmission, unless you speed shift (in which case it doesn't make much difference). You'll get secondary opening & closing lag at shifts with a vacuum secondary carb if you don't speed shift.

 

Does it currently have the Computer Q-Jet on it? If you get rid of it, you will need a new distributer.

My preference for a street/strip car would be a CCC Q-Jet on top of an edelbrock Performer RPM non-egr.

 

I think I'm leaning towards a edelbrock 650 mechanical. I would like the increase in horsepower that a 750 can deliver but the car is still my daily driver and with these gas prices I need to take fuel consumption into account.

 

My 383 made 430hp with a 650 DP, I think you'll be fine

 

Edelbrock doesn't make a mechanical secondary carb.

 

hmm, what's a good 650 mechanical that's fuel effecient but something I can bolt on and be done with it? From what I've heard holly's are good carbs but rather complecated and not very user friendly.

 

Holleys are about as simple as you can get. Jets, power valve, idle mixture, idle speed, pump cam, pump squirter. All have specific functions, fairly simple to determine what to change to accomplish a particular objective.

You have to drain the bowl to change jets or power valve. That's about as bad as it gets.

 

Agreed... Holleys are very user-friendly IMO.. they just sometimes require more frequent tweaks than other carbs.

 

aren't quadrajets something of the order of 700-750cfm most the time?
also your statement their might work to figure out what the motor cfm flow would be but that doesn't mean that is going to be the best sized carb to get.

a single plane vs a dual plane is going to make quite a bit of difference
you get a single plane with 750cfm vs a dual plane for the same 750cfm carb the dual plane is going to be a lot better off.

then comes IR intake design. you know like 8 one barrels or 4 2bbls something like that. you can more or less throw your cfm math out the window. those setups usually run best on WAY more total CFM flow then what the motor would run on with just a single 4 bbl on a single plane manifold

 

do most holleys have adjustable air bleeds and emulsion tubes or are those supposed to be unchangable?

 

Stock Holley metering blocks you have to drill the emulsions to change them, once you change them you can't go back. That's the benefit to aftermarket ones. You can change the air bleeds though.

 

so how do you know when it is time to change a jet vs an emulsion tube vs an air bleed?

 

Okay so I'm looking at getting a mechanical 650cfm holly carb, now I just need a good intake to go with it. O btw thanks for help so far everybody!

 

I can't answer that question for you. Only major carb tuning I've done has been on our engine dyno where we can see differences in A/F. Chassis dyno may give you a ballpark.

I like the RPM and Air Gap manifolds from Edelbrock.

 

would that fit with a holly carb?

 

Yes.

 

You don't. Unless you have access to a wideband o2 sensor and can accurately get data on the whole band of Afr all the way from idle to max rpm, you'd be guessing.
Holley spends a lot of time setting up the air bleeds etc to work right. Most times they are right on the money.
You can tweek them to fine tune the fuel curve but unless you're an old hand at it with the right tuning tools you're more likely to mess the thing up.
Get the jetting, power valve, accelerator pump calibration right and then if there is still a tuning issue ( like high speed rich or lean condition) look to the powevalve channel restrictions and last the airbleeds.
If you start swapping airbleeds and jetting indiscriminatly just 'cause ya can. (HP series holleys) you are most likely to get lost. The different emmulsion tubes and airbleeds work together to fine tune and smooth and flatten the fuel flow curve throughout the rpm band as well as determining the strengh of the vacuum signal from the airflow thru the carbs venturii.