i currently have a 795cfm edelbrock performer on my olds 403. she kind of pig down low considering the 3:73 gears i've installed, but at higher rpm's she does o.k. does anyone know if i've got too big of a carb on it? the car is a 1978 pontiac trans am and weighs dam near 4000lbs. should i go with like a 600cfm or 650cfm carb instead?  

More than likely there are other factors effecting low-end output rather than poor atomization. I would think that mixture ratio and overlap would have more of an effect...  

On a low compression 403; you could have a little too much carb. Before buying a new smaller one I would check the tuning on the carb and especially tuning. If you tune it for maximum power, advancing the timing and such; it could possibly fix your low rpm lack of performance.

Since your original carb was a 750 cfm Quadrajet for that motor; I don't see why a 795 Edelbrock won't work. But just realize that by that time the stock carb had been leaned out for emissions. You may have to lean out your Edelbrock for the same reasons.  

Edelbrock carbs are very good at low speed metering.  As David Vizard says, as long as the carb can meter the fuel it's not too big.  Having owned a 403 in a 79 T/A in the distant past, I'd say look at timing issues and other parts of the tune up.  Depending on the intake, timing and gearing, you might need a bit more pump shot to get the car moving.  Those motors were rated around 180 HP and I think GM tested them in the arctic to get that rating.  I put a 600, Edelbrock intake and headers on my T/A plus a shift kit.  Cat converter, what's that?  The Falcon had a cheap low compression 302 in it at that time with an iron intake, stock converter and 2.80 gear and it would run away from the T/A like a scared cat.  But I was lookin' good, polyester shirt and bell bottoms.  I was ready for the 80s.

If I had a time machine, I'd go back and put in a small cam to raise cylinder pressure, dial it in right and screw with the advance curve some.  Maybe even change the heads.  There's no telling where the cam sits in those smogger motors - at least 4 degrees retard in there, I'll bet.  

thanks for all input guys. i definately have a timing issue right now as i just stabbed in a new distributor with a 50,ooo volt coil. i have not set the timing on it as my timing tab is missing and i don't own a timing light. here are the current specs on my car adn what i have planned for it. she's a daily driver and i drive the *** out of her i mean that's what there for right? well so far she 's been rebuilt and bored .30 over, i have an edelbrock performer (not rpm performer) intake, the 795CFM performer carb spread bore, MSD6a, MSD 8mm wires, new summit distributor with 50,000 volt coil (hei set up) that's really it for the engine the rest is stock. teh th350 was worked over with a shift kit and seems to shift fine, and out back she has new axles and a set of richmond 3:73 gears ( limited slip). oh yeah dual exhuast 2 1/4 flowmasters, i just removed the cat. future plans are, a comp cams cam kit. the cam will have a 475/480 lift and 262/274 duration much better than stock and still streetable, i also plan an doing a head swap i bought some olds 330 cores and i going to get them ported and matched to the intake of course. i'm going to use the valves from my 403 heads though as they are fairly descent in size 1.999 intake and 1.559 exhuast. the head swap should raise my compression ratio to around 9.50:1 or so, dynomax headers and th200r4 tranny. so with what she has and future plans should i just get the timing worked out and keep my 795cfm get a a samller carb? any suggestions out there?  

Get a timing tab and a light first. Everything else is a waste of money until you get the ignition timing dialed in.  

Exactly.  Fashion a piston stop and find the true balancer TDC for #1 cylinder and mark it with a bright paint line.  Fashion a pointer or tab that can be marked plainly to show true TDC.  Go to Sears and get a good dial back timing light, it'll be in your tool box a long time (33 years in mine).  Then you can get your timing dialed in and work from there.  Devil's in the details - get the details right and you'll be pleased with the results.  

The Edelbrock carbs use a weighted secondary air vane.  They have a mechanical throttle linkage, but the rear air van doesn't open until engine air demand is sufficient to overcome the weight.  Think a modified Holley vacuum secondary action.  The primary bores use a double booster design and a smaller bore than the secondary - they are not a "square bore" design like a Holley.  Even the "square bore" flange Eds (like the 1406 model 600) are bitty spread bores.  These tweaks in the basic carb design help the Eds work as good street carb with typically good low end response.  Usually better than a Holley in the same size range because of the Holley square bore design and minimal signal generating stock dog leg booster.  So, it's not too big if the rest of the tune up is there.  You'll be running off the primaries most of the time anyway.  The Mustang here raced with a 600 Ed for years with good response and no hassles.  For all out performance, a tuned Holley DP carb should outperform an Ed, but it has to be sized correctly for the combo.  

The rest of the parts sound OK to me, but I'm a Ford guy and not too smart on Ponchos.  Again, work the details.  Get a degree wheel kit and dial the cam in - verify TDC and the balancer mark(s) - you'd be shocked at how far off some are.  Checking the cam timing keeps you from getting bit by crank keyways cut off, timing chain sets not made exactly right, etc.  If you nail the valve timing and the balancer mark, then you have precise control over timing.  

CC the heads while they are off and check deck height and piston dish - then you can calculate your exact compression.  The best detonation control is to have the pistons right on the deck, which you could plan for in a later rebuild.  

man thanks alot. i'll look into the timing before i go any further.  

Your timing is most important.I learned how t find True TDC for the frst time when I put an Edelbrock 1406 carb and performer intake on my 80 Malibu. Make sure you remove the distributor when rotating the engine by hand. You can machine something like a stud welded to a spark plug to make your cylinder stop, or you can use a screwdriver and feel for when the piston hits the top of the #1 cylinder in it COMPRESSION stroke. This is very important as finding it on the Exhaust sroke, will cause you to not be able to start the car. When you find TDC these guys are right you may want to mark it, but your timing mark on your pulley damper should be close to to the 1 o'clock position if you were facing it from the front of the car. When you put the distributor back into the car the rotor should be facing the #1 cylinder. As for finding the compression stroke, make sure you have the fuel line disconnected or no spark plugs hooked up, in case of a backfire. You will need to have someone crank the engine with the key, while you hold your finger over the #1 cylinder. You'll feel the engine's compression blow your finger out of the hole. This will occur before TDC as your finger will move well before the 115psi of compression is generated. After that you can crank the engine by hand 2 more times, in case you go past TDC when your helper shuts the key off. You must rotate it 2x so that you aren't on the exhaust stroke. When you stab the distributor, it should go in with the rotor facing the #1 cylinder.

Now onto your carb....a 795 cfm should work fine. You will need to lean out your main metering system. Reason being that these "Performance" carbs are dyno tested at Edelbrock on specific big blocks like say a 427 Chevy. They are calibrated to fit on most popular race engines, like say a Chevy 350, Olds 455, etc. By putting that big of a carb on a smaller engine you are probably running a little too rich in the "Cruise" mode, where the metering rod is down or in the "lean" position. Also is your carb a "Thunder AVS" series, or a "Performer" series. I have a owner's manual for the performer series carbs and can give you a metering reference to go by for jet and rod sizes, for your main system, and the jet size for your secondaries. As for your camshaft, I recommend the Performer series Edelbrock camshaft. It is designed for your specific intake manifold, and since you have a daily driver it'll improve your low-RPM torque, while giving you a noticeable improvement in High-RPM power. If you go with a higher lift and duration, you may need to upgrade to the Performer RPM intake manifold. The Performer RPM package may be an excellent choice for you. You have a large engine so it won't really affect your low-RPM torque to a point that you can't drive it on the street, but it'll have more performance gains better suited to your carb, and what you want to do with it. Keep me posted on what happen I have a co-worker who is 16 and rebuilding a Trans-Am with the olds 403 in it and I could use your workmanship as a foundation for helping him finish his.