In the late 60"s when I rebuilt a lot of carbs, I played with this same situation on my .030 over 11:1 327 with no headers and 350 HP cam. My car actually ran slower with the 750 Holley than my 600 Holley. I don't recommend it for the street at all on an SBC..
i have the same set up as you do..i took off my holley 600 cfm.. and put a quad 750..alot slower and the throtle response ****s...the 600 cfm had alot of slop in it..and the 750 was fresh rebuild..even with the slop the 600 was faster and ran better at idle and low rpm's..so from experiance the 750 is way to much...im not to motor savy on that type of stuff ..so i thought BIGGER CARB faster car..not the case..my car has dual smittys and the sound was way better with the 600 than the 750 also..so has soon as i can afford another 600 or 650..i will be using the 750 for a anchor..
well "penguin" I just found it hard to believe that someone would be giving really bad advice on the HAMB. Alot of people on here aren't of your "high tech" caliper & will be doing things like that on there not"shut off or WFO" street cars. As far as the string goes, no one said you had to have intelligence to drive, just have to p*** the drivers test.If they even include a IQ test in the driving test i guess you're just ****ed. walking isn't that bad!! Also i'm not too worry about what other people think is dangerous or not, You never see me wimpin away on anything or anything that you think is dangerous. "**** Tracy" PS the expression is "No **** sherlock"
on my 327 in my chevy II I started out with a 750 v/s but I aquired a 600,so I swaped it out. I drag raced the car and it did not do as well with the 600 as to the 750. I also did the swap later on with my 350 with the same mods as the 327 with the same results. yes,the 600 did give me better gas millage,but i was using these cars for the street & strip..I'd rather go fast! drivabilty was the same for both of them.
WINNER WINNER CHICKEN DINNER!!! The easy way to get both? Do the math and add 100cfm. Jet to taste and you're there.
Krylon32, 500-600cfm is the right size range for a medium build 'street' 327. The exact size would depend on the cam you run and any head work that would make your engine more efficient or less. Nobody here can give you better information unless you include, cam spec's, head work (compression ratio would help too). Narrowing it further could be done with additional information, transmission type, rear axle gear ratio and the weight of the car. Oh, and what it's intended purpose is, Daily driver? full on drag car? or somewhere in between? Just need a bit more input to work with! Dan Stevens dba, Steelsmith
First of all, just poking a bit of fun at the thread in general. Unless that 327 is built pretty damned well in terms of cam and heads, a 750cfm is probably too much carburetor, and unless in the hands of a great tuner and a dyno, will not work as well as a more suitably sized carburetor. So, in keeping with that theme, I tossed out a ****load of timing. Hell, if some is good, more must be better. I'll just apologize for getting your dander up and leave it at that.
So anyway, I'd bolt the 750 on so I'd have something to drive while you take your time and do a nice rebuild on the 600. They really are easy to work on, and hopefully you have the one with the electric choke as it's calibrated for economy/ mild motor. You can take a manual choke model and recalibrate it, the Edelbrock tech line (found on their web site) was very helpful for me. My 396 has two 600's set up per their specs.
We're getting a lot of "apples to watermelon" comparisons here. This is not a Chevy II race car we're talking about here fellas. It is an otherwise stock 1/2 Ton Chevy pickup. It's the same one in his avatar. Looks like the intake is a Performer, no headers. Years ago I ran a 600 Holley on a stock 283 Impala with a TurboGlide and 3.36 gear because I needed a carb and it's what I had. Yeah it ran "OK" but it was still WAY too much carb. I had an acquaintance with a '63 or so Chevy C10 long bed. It had a stock 283 4 Bbl. , truck 4 speed and 4.10 gears. He put an Edelbrock Scorpion and a 4 Inch open carb spacer on it with the stock carb. It was either a 4 Jet or WCFB. Yeah, it "worked" but that doesn't mean it worked well and probably the only reason it worked as well as it did was the gearing in the truck 4 speed and the 4.10's.
I would sell the 750, and use the cash to buy a rebuild kit for the 600, some flowers and a nice dinner for the s/o. Trust me, the results will be far better than setting up the 750 to run right.
ya so im gona keep the 600 and rebuild it any tips on improving the finish the carb was on the old engine and it sat for a long time it is a little pitted and just dull any help thanks? the 750 is going on craiglist today thanks for all the info
We all know performance is directly related to air intake,ie ported heads ect.So the only way to achieve performance is getting as much air in as possible.so a larger carb is obviously necc.Drivability is another factor.Signal to the carb is dictated by compression ratio and timing events so a well thought out combination will use all the air it is given even though it is mathmaticly greater than the volume of the cylinder its drawing from.Simply put,low compression weak signal=smaller carb for drivability reasons.Get into double digits on your comp and you can run a much larger carb.Tuning for it may prove to be a challenge but with jetting and timing it can be done.Bottom line you need air to make power go as big as you can.
Why would you have to jet a larger carb down? I've never had to . . . A venturi creates a vaccuum to pull fuel into the airstream and atomize it, so the amount of fuel pulled in at a certain airflow and thus vacuum would be the same wouldn't it? You would have to tune the larger carb for throttle response with the accelerator pump, but "jetting it way down" doesn't make sense to me.
Vacuum is less with a bigger carb at the same rpm because the hole the engine is ****ing through is bigger. I found this out with a 850 double pumper on a street 454, not enough vacuum to run the brake booster!
Idle vacuum, all other things being equal would be the same with a bigger carb so you had a problem elsewhere I think.
Some 750 cfm carbs can support over 600 hp, so if OP's truck's engine is mostly stock he only needs a 600 cfm carb.
The factory 56 265,s and later 283,s with factory dual fours ran two 380 cfm carter wcfb carbs or 760 cfm total. Now why is a 750 cfm too big for a 327? I think if its a spread bore carb it would work ok. Wont cost much to find out. OldWolf
Most factory dual quads ran off the primaries of the back carb when cruising that flowed about 190cfm and gave crisp throttle response and mileage. They had progressive linkage that brought in the primaries of the front carb at part throttle for a total of 380cfm and at WOT the secondaries were vacuum and only flowed what the engine was capable of drawing. On a 283 at 6,000 RPM ***uming 80% Volumetric Efficiency flow would be around 400cfm under ideal conditions. The total package probably never saw even close to the 760cfm it was capable of even on a hopped up 283. Even at 7,000 RPM and 100% VE a 283 could only draw around 570cfm. It was not a bad setup at all but apples to oranges when comparing it to a 750 squarebore.
Totally untrue, a certain cubic inch engine can only handle so much air!!Putting a bigger carb on will do nothing for performance.Only thing it does is let you say" i got a Holley 750" . You can think what you want but its not going to run better. Jimv
All this will to will not.... What it boils down to is, depending on build, use, etc. no one can say that there is one a certain size carb that will be what has to be used on a given amount of cubic inches. Experience building and running many diferent carbs on the same cubic in engines all built to different specs will be a differant size carb..PERIOD. You take a bone stock 327 and yes, I'd agree that a 750 might be too big. It will work, and depending on the style of carb it could acutlly work excellant. 750cfm QJET...this would be a perfect carb for a bone stck 327. It will have all the throttle response of any other brand carb 750cfm or smaller, and will not be too much at wot as it will only give the engine what it needs at wot. Now take a 327, put on a set of ported 461's, 11-1 compression, solid lifter flat tappet can, .535 lift 274 duration @ .050, 1.6 rockers, running a highly modded factory 1970 aluminum LT1 intake, and top it with a 930 cfm holley. This engine runs incredible. It is in a non hamb friendly car, running a 6spd trans with 4.30 rear gearing and 25.8" tall rear tires. It averages 17-18mpg every day driving both highway and town driving to and from work. The car weighs in at 3120lbs with driver and runs 11.0s at 123-125mph driven to the drag strip, raced, and driven back home. When I built that 327 I originally started with a mild stage 2 750dp holley that actually flowed 795cfm. It had way too much signal and the boosters were pulling it at about 1800rpm. I then put on a 850dp that just had the air horn removed and a small radius on the top. The boosters now cam in at around 26-2700rpm but the carb was not able to be jetted and tuned to both idle decent, drive smooth, and perform at wot. I then built the current 930cfm dp that is on it now, and has been for over 4 years now. There are just too many factors for anyone to be able to know for sure what will be the "right" carb. The best thing is experience. If you think you know it all, then you have nothing to worry about because you are right. But for those of you who actually have a couple of carbs laying around, take some time and experiment. Put different carbs on the same engine and see for yourself what they perform like. Hell it does not cost much at all if you have some laying around. Same thing goes with guys who have some fairly highly modified engines. You will be suprised just what you might find out if you just try. It is really fun if you have say a QJET, Holley, Carter afb/edelbrok laying around that are all the same cfm rating....put each one on, and give them all equal chances by tuning/adjusting/jetting them to get them to run as best you can and see what you come up with for the comparison, and what one you honesrtly think worked best. Its fun...time consuming but fun. To answer the OP's question, YES the 750 edelbrock will work ok on a 327. I'm not 100% sure exactly how different the 650-750 primaries are for comparison, but I'm sure the primary side is not that much bigger to really be bad on a 327. The edelbrocks are a vacuum secondary carb and are very forgiving in the aspect of being too big for the cfm/cubic inch theory. It might take a little tuning, adjusting etc. but with some jetting and rod changes I'm sure it would be perfectly fine.
Hmmm, now what would I have done years ago before the internet? Hmmmm. I probably would have bolted on the 750 and TRIED IT!
Well, "kind of", they aren't mechanical in the sense of a Holley DP or full vacuum like a Holley 1850. The secondary throttle blades open mechanically but air and fuel flow on the secondary side is controlled by a secondary air valve similar to a Rochester QuadraJet so actual flow through the carbs is still limited to what the engine can draw not what the carbs can flow. An engine is just a pump and without a blower or turbo it is only going to pull so much air and adding a carb with a higher CFM than the "pump" can possibly flow isn't going to change that it will just make it harder to tune. Before we go any farther I have to admit I was wrong on the linkage, early factory setups had direct linkage so both sets of primaries worked in unison. Most people replaced it with progressive to make the cars more drivable. My old neighbor when I was a teenager back in the arly 70's had a dual quad 283 '60 Vette and my main memory of that car is of him cussing those carbs and threatening to put a single 4 Bbl. on it. He never did because he knew whether they worked or not it was worth more with the dual quads and eventually sold the car back in the early 80's. I understand your argument on the total CFM but we all know just because the factory did it doesn't mean it was right. Despite my curent project I am first and foremost a GM guy. Hell, my initials are even "GM"! But the list of GM factory "*****s" is a long and illustrious one.
if your running a holley 750 double pumper you will have lag and a lot of tunning to keep it from load ing up at idle if its a Quad a jet 750 its probly the best carb you could run on your daily driver with properly adjusted secondary's
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