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Another... Carb Stroker 489

I run this 850 Holley DP on my 493 in my 63 Sport Fury. I worked it a little so it runs real nice on the street cruising on the primaries and I do most jetting for mph at the track in the secondaries. No vacuum secondaries here as I love double pumpers and run them on all my hotrods. I can tell you I did try two different 950 carbs and it ran about the same. Best with this 850 is 10.76 @ 124.99. Best with a 950 on a different day was 10.78 @ 125.83. It picked up almost 1 mph but did not et any different. So I put the 850 back on because I have worked it to run nice and clean on the primaries and I love how I have it set up. I knew I would have worked the 950 if I stayed with it but since it ran about the same I just stayed with my 850. If you are going to street drive it alot like I do I would go with the 850 or no more then the 950. If it was a race only car then I would try a Dominator. Ron

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I can tell you I did try two different 950 carbs and it ran about the same.

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Hey Ron, can you tell us a little about the two 950s that you ran? Do you know what venturi size they were, and did you track test them?

The "950" is such a misnomer. With venturi sizes between 1.375" to 1.590", and a couple different booster configurations they can flow anywhere from 820 cfm to 1000 cfm, maybe.

I did A/B testing twice at the track between my small venturi "950" and my 4781. The 950 was just a little bit better everywhere on the track. I tried to get the 850 to run with it, but could not get it there. In my case, I think between the gear, and the tight converter's low rpm shift recovery the 950 did better.

The funny part was that in the street, I had to work the 950 hard to get it to run as nice as the 850. Seems backwards. My 950 was so pig fat at transition/ low rpm cruise.

I usually tell folks that if they have a tight budget and are unsure what to buy, buy a used 850 and rebuild it because of how well they can run plus the $ savings. Otherwise, consult a professional and get the "right" 950.
 
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Hey Ron, can you tell us a little about the two 950s that you ran? Do you know what venturi size they were, and did you track test them?

The "950" is such a misnomer. With venturi sizes between 1.375" to 1.590", and a couple different booster configurations they can flow anywhere from 820 cfm to 1000 cfm, maybe.

I did A/B testing twice at the track between my small venturi "950" and my 4781. The 950 was just a little bit better everywhere on the track. I tried to get the 850 to run with it, but could not get it there. In my case, I think between the gear, and the tight converter's low rpm shift recovery the 950 did better.

The funny part was that in the street, I had to work the 950 hard to get it to run as nice as the 850. Seems backwards. My 950 was so pig fat at transition/ low rpm cruise.

I usually tell folks that if they have a tight budget and are unsure what to buy, buy a used 850 and rebuild it because of how well they can run plus the $ savings. Otherwise, consult a professional and get the "right" 950.

One of them was the Proform carb and the other was a Holley 950 race type carb. It was the normal Holley color and had replaceable idle and high speed air bleeds but that's about it. It did not have billet metering plates so it basically looked like a standard Holley inside. I forgot what its actually called but I do have a pic of the Holley somewhere. Neither 950 had a choke airhorn on it. From what I remember they both had the same size throttle plates as my standard Holley 850 DP. I just had a chance to try them so I did. I had worked the 850 idle and transfer circuits and had it cruising nice and clean on the primary side. I had not worked them circuits on the 950's and could tell they were rich when cruising so since they ran about the same I just put the 850 back on since I had already worked it. Ron
 
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Electric choke works better daily driver. Also will close partially under hard off the line acceleration to richen it up so you don't lean backfire through carb. Manual choke will stay open and then you get the lean backfire.

Respectfully disagree with the above. If the choke and accelerator pump are adjusted correctly, there should be no lean misfire through the carburetor once the engine is allowed to warm up...
 
Respectfully disagree with the above. If the choke and accelerator pump are adjusted correctly, there should be no lean misfire through the carburetor once the engine is allowed to warm up...
Electric choke works better daily driver. Also will close partially under hard off the line acceleration to richen it up so you don't lean backfire through carb. Manual choke will stay open and then you get the lean backfire.


Ah no that's not how an automatic choke works. I agree with Colorado. Once the eng is warm and the choke is all the way open and the choke coil keeps enough tension on it that the choke stays open all the time on a warm eng. The only time the choke may close a little when you step down hard on the gas is on a cold eng when the choke still has tension on the coil trying to keep it closed since the eng and choke are still cold and closed. Then when you hit the gas hard vacuum drops off some and the choke vacuum break can back off a little if vacuum drops enough when you hit the gas and then the coil tension will try to close the choke a little because the vacuum break has lost vacuum for a second or so and is not pulling the choke off to its vacuum break setting. But that can only happen on a cold eng and choke. As soon as the eng is warm and the choke is wide open the choke coil tension will keep the choke wide open all the time as long as the eng is running and warm. It wont close any when hitting the gas on a warm eng. Ron
 
Hey Ron
A little off topic but are u running a pvc valve? And does that have any effect when setting up carb
Thanks Bill
 
A 500 cube engine will handle about any 4150 you throw at it. Like already mentioned you can’t just go off rating as they are not all created equal. A regular old 850DP has a 1.56 Venturi. A proform 850 is 1.40 and the 950 is 1.45. That’s considerably smaller than a holley 850. My proform 1050 is a 1.59. They make two versions, one with annular boosters and a down leg version. I would suspect even though they are rated the same the annular would be down on flow compared to the down leg. I think a normal old 850 would work just fine. I have a proform 1050 annular carb I built that I ran on my 511 for a bit. It was an excellent carb. Did everything you would want on the street out of a carb. That would probably be my choice on your combo. Any of the above will work but, who builds a 500 cube engine to choke it off with a small carb. I’ve ran several various carb set ups on my rr. The 1050 annular is up there in the list as one of my favorites. I had actually built that carb with a proform 850 main body at first. I quickly realized it was too small. That’s when I really dug into the Venturi sizes.

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Hey Ron
A little off topic but are u running a pvc valve? And does that have any effect when setting up carb
Thanks Bill

Yes I prefer to run a PCV system on my street cars. My eng pulls enough vacuum to work the PCV valve. Does it have any effect on the carb ? Not really as it only effects idle a little bit since the PCV system is basically a very small controlled vacuum leak. Other then adjusting the carb mixture screws I did not have to change anything with the PCV system. Ron
 
Like Ron says, heck I even had PCV hooked up on the race car yrs ago. This was just before the crankcase evac systems started coming in.
 
My engine 383 stroked to 450 with a quick fuel 830 was set up and dyno at 530 hp. with just breathers on each valve cover just wondering if that will give me any problems
 
Breathers? Too much crankcase pressure, just not sure.
 
My engine 383 stroked to 450 with a quick fuel 830 was set up and dyno at 530 hp. with just breathers on each valve cover just wondering if that will give me any problems


For years that's all most race cars ran was breathers. Myself since I street drive my car I wanted the crankcase to not build up pressure and the breathers may be fine but I wanted the PCV system to pull any fumes and pressure out of the crankcase so I wont have any gasket leaks from pressure building in the crankcase and with the PCV it helps stop condensation from building up under the valve covers. Condensation build up can happen some on street cars that get short drives and don't let the eng warm up to evaporate condensation and the PCV helps fight that. You can run the breathers as I would just keep and eye out so you get no oil leaks and try to avoid short drives where the eng don't warm up fully. Ron
 
Thanks for reply. I will make sure I’ll warm up engine to operating temp. I may get the breathers with nipples and plum in lines from the breathers thru a canister to filter out the fumes to the air cleaner
 
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