All: My newly purchased stock GS 350 needs a new carb. I have a carb (part 7043240) 800CFM that was rebuilt years ago by Holley and is still in the wrapper. Can I put this carb on my GS 350 and have any chance it will be driveable? The orginal carb that was in the trunk (7040244) looks exactly like the bigger 7043240). I know the jets rods will be different but Buicks like big carbs. The car just showed up and I would like to avoid screwing around with having the correct GS carb (in the trunk) rebuilt. I want to drive the thing! Your advice is appreciated.:3gears:
Can't guess why someone would have sent a QJ to Holley for a rebuild?The venturis on the 800 cfm are larger (1-7/32 vs 1-3/32). 4/32 difference doesn't seem like much but when you calculate area it is. I have an 800 cfm on my SBB right now and it is coming off next week. Although contrary to what I thought, it actually runs very lean on my 350. I am thinking it is not pulling the required air through the primaries to draw in the fuel. If the venturi was small I would have a higher pressure drop. My 350 is pretty darn stout. I would recommend going with the 750cfm with the smaller venturis. Buick's don't necessarily like bigger carbs. The 750 was universal and is self metering to flow only what is required. GM used this carb on everything from V6 to 500 cube Caddies. Most of the air flow is from the primaries for most conditions. Only at peak rpm under WOT will you see a near full draw and even that is not 750cfm on a stock 350 motor.
The 800 CFM carburetors were installed on 455's. A 455 needs alot more air at idle than a 350 does. The idle system on the 800 carb is bigger for this reason. It is better to stick with a 750 CFM for the 350 unless you have a really wild 350.
I was hoping I could get by with the larger carb while the original gets rebuilt. A new toy in garage and the weather is so nice outside. Something that would maintain an idle and that goes down the road for a few weeks, that's all. I'll send out the original right away. Thanks
I disagree with all of you guys. Like my signature says, I have a 800 CFM Qjet on my mostly stock 350, and it is AWESOME! When I first got this carburetor from John O. I still had the stock cam in my 350 and everything was perfect. Secondaries worked flawlessly and pulled MUCH harder than the old 600 CFM edelbrock I used to have. Now with the bigger cam this carburetor is really showing its worth. If you want some hands down proof that 350s like big carburetors, Sean Gaskin (sean Buick 76) built a 350 with only TA 212 cam, forged pistons, and a home head porting job. When he was having the dyno test on the engine done he insisted that they try a 1000 CFM carb, and although the dyno guys thought he was crazy they did it and the motor made 398 HP at 5600 RPM, which was considerably more than with the smaller carbs. 350s love big airflow! Even in stock fashion.:3gears::laugh: Why don't you just try the Holley reman carburetor and see what happens since you already have it? As long as nothing is seriously wrong with it, it should work fine.
I am not saying that the engine won't make more power with the 800, it's a Buick after all. But there MAY be driveability issues with the 455 carb on a 350. You can get away with the BBB carb on a SBB, but a SBB carb on a BBB will definitely give you idle problems. Ask me how I know.
When jetted and rebuilt by John O have had no driveablity or idle issues with my 800 cfm q jet on any of my 350s from mild to bone stock low compression. Yes there are mods to the idle circuit that can be done to optimize the 455 800 cfm carb on the 350 and Mike Williamson will be performing those mods on one of these carbs that I already had sent to him or that purpose. he customized his 800 cfm q jet to run great, idle fine, and run 11.9 in the quarter so the potential is there and YES THE BUICK 350 CAN HANDLE more fuel than most smallblocks.
Anyone who wants to blame drivability issues on an out of the box carb is a fool. Any aftermarket engine/carb combo is going to be its own unique beast. I am certain that a Buick 350 with ported heads and a decent cam would truly enjoy a 1000cfm Dominator. Tune the primaries for throttle response, then LET IT EAT! To compare the 350 Buick to any other engine is like saying apples and oranges are all just fruit. Why do apples grow in Washington, and oranges grow in Florida? They AREN'T THE SAME! Neither are the Buick engines. If your 350 blows black smoke at full throttle, it is too rich, like any other engine. An 800 455 carb isn't going to cause that problem by itself. Tuning. Jetting. Timing. 50CFM more isn't the make-or-break of a small block Buick!!! A simple A/F gauge and sender isn't over $100! Are you guys still looking at your plugs to see where your fuel curve is at? C'mon, I just had to vent on this one!
The absolute maximum VE for a naturally aspirated motor is 115%. Never before been exceeded even with 4valve DOHC, at the highest levels of racing. For any 350 motor at 6000rpm (darn high for stock Buick motor) the "ideal situation" would yield a scfm of 700 @ 115% VE. Does a Buick flow better than most other GM 350's?...perhaps because they have better flowing intakes, a stronger resonance pulse, etc. But unfortunately they have smaller valves, which is the most significant consideration. Jury is out and it would be almost impossible to compare. Can a Buick 350 handle a bigger carb, sure just tune it. Is it a better solution than a 750? No way. I respectully ask for the math or kindly request a dyno comparison of carbs with VE over 100%. If a larger carb has a higher VE than the smaller 750QJ, it is only because the QJ is not properly tuned. My John Osborne tuned 750QJ had a VE of 98% (awesome result) @ 6000rpm on my SBB motor, which has big valves, a healthy cam and professional port "shaping". That is 610cfm. My Z28 has a 780 Holley that dyno'd at 96% VE @ 7200rpm, has larger valves, hi-rise intake and more lift and duration than a stock SBB. That is 710cfm. Don't think a statement SBB needs more carb than SBC always holds water.
Adam your engine would make more power and torque with a 850 demon as have other hot 350s. More dyno tests are upcoming but it is plain to see that any hot Buick 350 loves a 800+ cfm carb. These quarter mile tests prove this and thats before the head porting so I'm not sure what more you need for proof. http://www.v8buick.com/showthread.php?t=120004&highlight=kb+testing Sonny Seal ran two 750 cfm carb with a tunnel ram on his 350 athough his was VERY HOT.
I have tried it and the 800 on a 350 making 410hp is too much. Two different 650 carbs made more power on my 410hp motor than the 800. Sorry guys but there a laws of physics here that just aren't voodoo. 100% VE = displacement x RPM / 3456 = 350*6000 / 3456 = 607cfm show me a dyno sheet with more than 100% on a naturally aspirated motor Required VE = (9411 x HP x BSFC) / (Displacement x RPM) Brake Specific Fuel Consumption = 5.92 x Fuel Flow (gph) / HP BSFC of .45 is essentially the lower limit. Any higher fuel consumption and you are going to need a boost to get VE up. So a 500hp 350 @ 6000rpm would need the following cfm Required VE = (9411*500*0.45) / (350*6000) = 100% 1.0*607 = 607cfm If you only need 600cfm why would you put a 800 carb on it? You can put on whatever you want, but it doesn't need it. And you aren't going to get over 100% VE. Even if you miraculously get 115% you only need 690cfm.
I think the point of this thread is if the 800 can be used on a 350, not if it is the optimum choice. David, go for it. It will need some tuning like any new carb, but shouldn't cause drivavbility issues. Like you said, you can always swap it out later, but this gets you going!
Re: VE.. OK.. It's not uncommon for a ported head, single plane manifold, header motor to exceed 100% VE. I have built many that justed touched 100%, and a good handful that have surpassed 100% VE. In relation to the discussion. What Adams says is theoretically correct. By simple math, and by the Superflow's air turbine reading, the engine in this dyno sheet only needs an 850 cfm carb. But, in practical application, the cfm ratings of the carbs can be deceiving. Many carb companies play with the flow bench settings to get them to flow more. Carb flow testing is nowhere near as standardized as head flow testing is. Secondly, we have found thru experience, that a given engine typically likes a carb that works at 60-80% of it's rated airflow capablity. The pervailing theory is that is the "sweet spot" for atomization quality of the fuel, thru the boosters. That's why this race motor had a 1050 dominator on it. It's working right at 70-80% of the cfm rating. There is no set rule as to what engine likes what carb. Camshaft timing plays a major role in how the carb will function in the car. Almost always, for drivablity, the smaller carb working in that 80% range at the mid and lower rpm ranges will be more responsive to the throttle. For years, when we were bracket racing with a throttle stop, I ran a race preped 750 Holley on my Regal. Simply because it was so much cleaner and more responsive on the race track, when the stop came off. But on the dyno, a 1050 outpowered it by quite a few numbers. This was a 550HP iron head 462 BBB. I would question a 650 Holley making more HP than a 800 Q-jet on any buick engine, I guess my first thought would be there is something amiss with that Q-jet, or that motor is closing the intake valve way late, killing the booster signal. How rich are you running the Q-jet?. Because of the unique nature of the secondaries of that carb, Q-jets typically like to run a bit on the rich side, for optimum power production. 11.5-12.5-1 A/F ratio. Because the mixture quality of the Holley's, having both primary and secondary boosters, the 4150's typically like 12.6-13.1, and dominators always want right about a 13.1-13.3 A/F ratio. What do the dyno printouts show?.. Did it go lean with the bigger carb?
Maybe. As long as you're mentioning the laws of physics, be sure you pay attention to ALL the laws... 1. Just because a mass-production carb is "rated" at some CFM number, does not mean it actually flows that much. 2. You have to flow fuel in that air, not just "dry" air. 3. 4-barrel carbs are flow rated at 1.5" of vacuum. Problem is, 1.5" of vacuum is just like having a throttle. Less vacuum in the manifold produces more power. But less vacuum in the manifold ALSO won't pull as much air through the venturis, either. For example, the old Mopar 3X2 system used two 500 CFM end carbs, and a 350 CFM center carb (1,350 CFM when rated as two-barrel carbs, at 3" of vacuum) But when rated at 1.5" of vacuum like 4-barrel carbs, the CFM figure goes to about 930. Lower vacuum--less CFM getting pulled through the venturis. Imagine how low it'd go if you rated it at .5" of vacuum. Which is why you have CRAZY HUGE multi-carb systems on all-out race engines--they need that additional throttle/venturi area to get the manifold vacuum as low as possible at WFO--max RPM. 4. Carbs are CFM-rated with all four barrels open and being acted on by steady, regulated vacuum. When actually bolted onto a dual-plane manifold, however, the carb is seeing "pulses" of vacuum that switch between the two planes. A larger plenum will dampen the pulses; as will cutting away some of the divider between the two planes--but--you still aren't sucking on all 4 venturis at full strength 100% of the time. Therefore a dual-plane manifold will need "more" carb capacity than a single plane manifold. As intake manifold efficiency increases, carb capacity can be reduced. Nope, not Voodoo. But lots more complicated than just RPM X Displacement X VE.
I tried but there is interfence with the manifold and throttle armature, for lack of the correct word. When the car came off the trailer, it barely stayed running. The seller dismissed the original carb as worn and threw a brand new carb on. He added a spacer to raise the carb high enough for the throttle to function. The result seemed to cause a significant vacuum leak as well as a bunch of unburned fuel out the tail pipes. I have a JO 750 that was used when my Apollo's motor was dyno'd. The car runs much, much smoother with it but will need the stocker rebuilt to be reliable.
Re: VE.. Now that is great post!!!:gp: Exactly what I was asking for. Spanked me. I am in Russia until the weekend, I will post the dyno sheets when I get back. If the valve was closing late, it would be the same problem with all 4 carbs. The 800 actually runs lean. Moved the total timing down to 25 and with 110 fuel it still knocks like crazy with the 800. Starts going away in the mid-range and has no top end. I am sure it could be dialed in to work, but it is not the most efficeint application for this 400hp 350. The Osborne prepared 750 is the best carb. Unfortunately it is now sitting on my brother's motor. I can see your point that carb ratings are not always as advertised and that for extraordinary applications a carb with a higher "rating" may be appropriate. If your motor needs 850cfm over a wide power range that a carb rated at 1000cfm is a better choice. Your single plane, big valve, Tri-Shield ported, race cam'd 462 motor is a long way from the stock 350 that initiated this discussion. That is one special motor (great build!) in your sheet and it would be hard to draw analogies to the vast majority of SBB's needing anything more than the stock 750.
