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Re: Too much carb? 5 mpg at cruising
[Re: HotRodDave]
#3154829
06/27/23 10:17 PM
06/27/23 10:17 PM
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Joined: Feb 2003
Posts: 10,201
Someplace you aren't
SomeCarGuy
I Live Here
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I Live Here
Joined: Feb 2003
Posts: 10,201
Someplace you aren't
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It's all in the carb tune, assuming the engine is tuned correctly. You could put a 1000 cfm carb with the correct tune on that engine and it would run fine. The OP just needs to learn how to tune it. Run fine? I guess if you have a very loose definition of fine. I ran an Edelbrock Perfomer 600 and 750 on the 360 in my Diplomat as a test. That was my daily driver, go to work (75 miles each way) car. With the smaller carb I had about 5 mpg more economy (mid 20's) and better throttle response. With the 750 I had higher top speed, I could exceed the certified 125mph speedo's ability to measure whereas the 600 wouldn't go much past 110. The more you exceed the engine's requirements the slushier the carb becomes. I suspect if I tried to run a 1000cfm carb no tuner in the world, including you, would have made it run fine and the only way it could be made to even get close to the smaller carb's effectiveness would beif it was a spreadbore with the secondaries so restrained as to essentially limit it's total airflow to something similar to that smaller carb's flow. IOW, it would never flow 1000cfm in use. Did the 750 work? Yep, did it work fine? Nope. At any street speed the smaller carb was better in all respects. The 750 edelbrock is a tuning nightmare, lots of "fixes" out there but nobody can get them to work properly, they don't work great on anything, at best they just get by. The 3310 holley on the other hand can work great on that 383 engine, I barely lost anything with one on the superduper MPG 318 engine VS the highly tuned thermoquad. This is exactly right, my built by the factory 383, ran much harder all through the range with a 3310 versus the avs. Mileage was basically unchanged, if I kept my foot out of the power. Alas, guys that have not done such a back to back comparison continue to say it’s not possible. Why I don’t know. The 750 eddy is the only carb I couldn’t tame. Total pos. A TQ is a great carb too. Love those.
I want my fair share
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Re: Too much carb? 5 mpg at cruising
[Re: crackedback]
#3154866
06/28/23 07:31 AM
06/28/23 07:31 AM
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Joined: May 2005
Posts: 1,968
Apollo, PA.
B1MAXX
top fuel
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top fuel
Joined: May 2005
Posts: 1,968
Apollo, PA.
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It's a vacuum carb for gods sake. It's a 2 barrel most of the time. Amen
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Re: Too much carb? 5 mpg at cruising
[Re: d-150]
#3154887
06/28/23 08:55 AM
06/28/23 08:55 AM
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Joined: Jan 2003
Posts: 12,039
Benton, IL.
DaveRS23
Special needs idiot
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Special needs idiot
Joined: Jan 2003
Posts: 12,039
Benton, IL.
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Perfect carb for his combo You can argue that with Holley: ' Mechanical secondary carbs (double pumpers) are the better option for race cars, hot rods, and performance vehicles with manual transmission, automatic transmissions with looser torque converters, and lower (higher numerically) rear end gears. They are designed for engines that rev quickly, demand air flow more quickly, and are more focuses on quick acceleration.
Vacuum secondary carbs make excellent street carburetors. They open the secondaries progressively and are designed for stock-ish to mildly built engines that are heavy, have taller (lower numerically) rear end gears and automatic transmissions with tight converters. By keeping the secondaries closed until considerably higher load, these carbs also help to improve fuel economy over a similarly sized mechanical secondary carb. Holley has a plethora of vacuum secondary carbs to choose from in small and large CFM sizes.'www.holley.com/blog/post/what_is_a_holley_double_pumper_carb_/
Master, again and still
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Re: Too much carb? 5 mpg at cruising
[Re: d-150]
#3154944
06/28/23 12:54 PM
06/28/23 12:54 PM
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Joined: Jan 2005
Posts: 12,419
Kalispell Mt.
HotRodDave
I Live Here
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I Live Here
Joined: Jan 2005
Posts: 12,419
Kalispell Mt.
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The cam on a 2 barrel is different from a 4 I would run a 650 double pumper . In my superduper MPG 318 I ran a 273 2bbl cam, he needs his carb and ignition tuned properly not replaced with a double pumper.
I am not causing global warming, I am just trying to hold off a impending Ice Age!
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Re: Too much carb? 5 mpg at cruising
[Re: d-150]
#3154950
06/28/23 01:09 PM
06/28/23 01:09 PM
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Joined: Jan 2003
Posts: 12,039
Benton, IL.
DaveRS23
Special needs idiot
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Special needs idiot
Joined: Jan 2003
Posts: 12,039
Benton, IL.
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You might want to read his combo again You mean this part?; " The engine is bone stock 383 2bbl engine". If you don't believe Holley's general application guide, why don't you e-mail Holley with the OP's particular combo and preferences and ask them to recommend a carb? Hint: It still won't be a track calibrated double pumper. Let us know what they say. 
Master, again and still
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Re: Too much carb? 5 mpg at cruising
[Re: Sniper]
#3154954
06/28/23 01:23 PM
06/28/23 01:23 PM
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Joined: Oct 2003
Posts: 11,684
W. Kentucky
justinp61
I Live Here
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I Live Here
Joined: Oct 2003
Posts: 11,684
W. Kentucky
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It's all in the carb tune, assuming the engine is tuned correctly. You could put a 1000 cfm carb with the correct tune on that engine and it would run fine. The OP just needs to learn how to tune it. Run fine? I guess if you have a very loose definition of fine. I ran an Edelbrock Perfomer 600 and 750 on the 360 in my Diplomat as a test. That was my daily driver, go to work (75 miles each way) car. With the smaller carb I had about 5 mpg more economy (mid 20's) and better throttle response. With the 750 I had higher top speed, I could exceed the certified 125mph speedo's ability to measure whereas the 600 wouldn't go much past 110. The more you exceed the engine's requirements the slushier the carb becomes. I suspect if I tried to run a 1000cfm carb no tuner in the world, including you, would have made it run fine and the only way it could be made to even get close to the smaller carb's effectiveness would beif it was a spreadbore with the secondaries so restrained as to essentially limit it's total airflow to something similar to that smaller carb's flow. IOW, it would never flow 1000cfm in use. Did the 750 work? Yep, did it work fine? Nope. At any street speed the smaller carb was better in all respects. I can make a 600 slushie on a 440. Did you tune the 750 any? Your (any) engine requires a certain amount of fuel to cruise (idle or WOT) at a certain RPM. If you have the jetting/bleed (Holley) combination right the engine doesn't know if the carb is 650 or 1000. I've never looked at a carb as being ready to run out of the box, sometimes they work great, other times it takes some work.
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Re: Too much carb? 5 mpg at cruising
[Re: Dcuda69]
#3155296
06/29/23 03:32 PM
06/29/23 03:32 PM
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Joined: Sep 2003
Posts: 19,371
north of coder
moparx
"Butt Crack Bob"
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"Butt Crack Bob"
Joined: Sep 2003
Posts: 19,371
north of coder
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all will howl at me, but for a good street carb, i just love the Thermo-Quads. reasonable to good mpg for all engines [WAY better than 5mpg if you keep your foot out of it], big or small block, plus reasonable performance as well. however, one must be able to tune these things with the proper metering rods and jets [which are somewhat difficult to get at times], as well as adjust the secondary air door properly. proper vacuum advance and distributor weight [and spring] curve for your combination is also a must when using these carbs. this is only my life experience and opinion. your MILEAGE will vary. 
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