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Discussion Starter #1
My Son and I currently have an 89 Hatchback, stock short block, Twisted Wedge heads, custom ground cam 555/565 lift, C4 with brake, 4000 stall converter, 4.10 gear. The carb is an 800 double pumper I had from another build. The 800 has been on it since last May, and it seems to run pretty good, as we’ve run a best of 11.71 @ 115mph with no issues at all. It launches hard, pulls the front wheels (60’ times are low 1.50s), and pulls hard all the way through the traps. I know the carb is too big, and the plugs show it’s running rich (they are a dark sooty color). The car is track driven 75% of the time, with an occasional cruise in town or to car shows. What’s the best performing 650cfm carb for track use, with a little street cruising here and there. I tried to post a video, not sure if it will work or not, thanks in advance

 

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car is strong!

Weight? Which intake and shift point? Plugs are dark and sooty after a pass or?
 

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Discussion Starter #3
Car is 2800 lbs without driver, dual plane intake, shift at 6500, traps around 6400, plugs are dark and sooty after a couple of passes. Same plugs have been in there since last summer, I just clean them up after a few runs. We are changing the heat range as we speak because we just added a 100 shot of nitrous (have yet to run it on nitrous). Like I said, this car runs fantastic for a 170k stock bottom end (oil pan has never been off the car since it left the assembly line). It's actually a better 1/8th mile car due to the gear (7.40s)
 

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I don't think a 650 will be enough for the car. I've seen more than one 302 go faster and quicker after switching to a 750 from a 650. And they were more street car than your car.
 

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To me and my research - relative carb noob to be honest but looking at doing same thing so have spent a ton of hours researching - the real question your wanting to ask is: Do I want choke, or not? I have found if your fine with no choke, there are some 650 "dominator" style carbs out there with all the goodies, mech secondary, and adjustable air bleeds etc all setup nice from the factory. I almost bought this one: Quick Fuel BR-67199 650CFM Performance Race Carburetor Double Pumper | eBay Of course it was on sale when I almost purchased, but knowing myself I'll be going boost in the near future, and I built the fuel system for e85 so... I'll only make one purchase and will probably be an e85 prepped Blow through setup.
 

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Keep the carb you have, a 650 is too small. Do a lot of research on how to properly read spark plugs and tune what you have or send your carb to a carb builder and get it set up.
 

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Reading plugs doesn't work like it used to - the E10-E-15 in most pump gas pretty much renders this useless as it's not as sensitive. I am setup now to tune with Vaccum and wideband, using the wideband serial connection to my laptop to log, trying to figure out a way to get my tac logged and vaccum logged so i can overlay them and then properly tune. It's still a guessing game until I get that dialed in, I will be recording my runs, then reviewing them to match up the A/F with the RPM's and vaccum for now. I have a VS 850 I just rebuilt, will make it work but as the OP on this post, I am of the thinking - or assuming he is thinking - we are loosing some of the snapiness from having too large of Carbs. I can tune it all I want, get it spot on, but it will still not respond as quickly as a simularly dialed in 650 when on my little small block.

Hope that makes sense, and flcracker9 am I safe in assuming you are thinking it's too large so it won't ever run optimally and you loose some of the "instant" off throttle due to venturi's being too large?
 

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Im not a carb tuning guy, but if its running rich, why cant you just install smaller jets?
You can and do - but for me (not the OP) it's a response item, and thye have always says if you jet down more than 4 jet sizes you need a smaller carb, or something to that effect.... I have new Powervalves for mine I'm about ot try, and honestly not even sure what hte A/F will show, but plugs did read rich when got the car, but it was on Race gas, so it's a differnt animal now.
 

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What type of booster is in the 850 double pumper? Annular or down leg? An annular booster is larger and will effectively make the 850 carb smaller then the numerical name suggests. Plus it will be more sensitive to lower depressions.
 

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george rupert. PRobably the best holley builder out there.

Patrick (pro systems)-I have had exactly zero luck with him. 4 cars, 5 carbs, zero luck. One went injection one went rupert, the other two went efi (those two are street cars that run bracket class on sunday). Then my brother's 552" 63 fairlane, also was a pro systems carb, junk, went to enderle hat on methanol; picked up about a half second (6.51 to 5.98). N/A street car. Yeah he drove it around with enderle bug catcher on methanol. Patrick always wanted us to try this and try that to keep playing with the carb, and no matter what he "guaranteed" would work, it was never right. Gave up, sold the stuff, and never looked back. Keep in mind I'm fully aware that no carb is every going to be perfect for all applications, we expect to have to tune. Rupert? We jetted up a little, then down a little, settled right where it came, and it works absolutely flawlessly. Impressed, but it was not cheap.

Jet sizes have nothing to do with whether the carb is too big or small. They have everything to do with how the rest of the carb is set up. Jet it down until it likes it, then see how she acts. It might want a little less ignition timing too. When it's set up right, I bet it'll also get more consistent particularly with temp changes.

Mark Sullens is another good carb guy, dunno if he does gas or E85 exclusively. E85 would pick it up a good bit but will also require attention to the rest of the fuel system, and before switching you'd want to be sure E85 is available where you are.

I wouldn't go down to a 650. It'd work but leaves you little room for changes down the road. Depending on how the 800 it set up, it's possible that it could easily be tuned to work well.

People always say "too big" but I haven't seen a carb that's too big yet. Thats why you tune them. I ran a similar setup as yours with a 1050 (9375) dominator on it for a good while and it worked great even at 1200 RPM idling around it was clean. It's the only carb I had other than a 600 double pumper that needed lots of help.
 

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Discussion Starter #14
Reading plugs doesn't work like it used to - the E10-E-15 in most pump gas pretty much renders this useless as it's not as sensitive. I am setup now to tune with Vaccum and wideband, using the wideband serial connection to my laptop to log, trying to figure out a way to get my tac logged and vaccum logged so i can overlay them and then properly tune. It's still a guessing game until I get that dialed in, I will be recording my runs, then reviewing them to match up the A/F with the RPM's and vaccum for now. I have a VS 850 I just rebuilt, will make it work but as the OP on this post, I am of the thinking - or assuming he is thinking - we are loosing some of the snapiness from having too large of Carbs. I can tune it all I want, get it spot on, but it will still not respond as quickly as a simularly dialed in 650 when on my little small block.

Hope that makes sense, and flcracker9 am I safe in assuming you are thinking it's too large so it won't ever run optimally and you loose some of the "instant" off throttle due to venturi's being too large?
Sorry 91ntch, lost track of this post, but yes, you are correct. I’m thinking I may be leaving a little on the table running such a big carb on a stock compression, stock bottom end 302. But I gotta say, it runs good for what it is. We were shooting for mid 12s when modified it, but ran 12.30 right off the trailer 1st time out, and now consistent 11.70s - 11.80s after fine tuning the suspension.
 

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Discussion Starter #15
What type of booster is in the 850 double pumper? Annular or down leg? An annular booster is larger and will effectively make the 850 carb smaller then the numerical name suggests. Plus it will be more sensitive to lower depressions.
It’s actually an 800 with a Proform main body, and it has down leg boosters and no choke horn, might be hard to see in the pic
 

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