veryhot_post in Carb size for my setup in Engine, Transmission & Rear End Author Topic: Carb size for my setup  (Read 3590 times)

Offline erik70rt

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Carb size for my setup
« on: June 05, 2017, 07:17:40 AM »
My Barracuda is really sucking down the gas - approx. 6 mpg in it's current setup.  It has a 416 stroker, Edelbrock Performer RPM dual plane intake, ported J heads, TTI headers into a 3" exhaust system, comp Xtreme CH292 cam and a Edelbrock Thunder AVS 800 cfm carb.  4 speed and 3.55 gears.  14" rims with 245 60 tires.  I've leaned it out by changing the metering jets, primary rods and spring and it still runs very rich and sucks down the gas.  I didn't expect a good mpg with this setup, but I expected a little better than that.  Is the 800 cfm carb too big? Would a 650 cfm carb be better?

Linkback: https://forum.e-bodies.org/engine-transmission-and-rear-end/4/carb-size-for-my-setup/2151/
Contrary to the opinions of some, I am not dumber than I look.

Offline Cuda Cody

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Re: Carb size for my setup
« Reply #1 on: June 05, 2017, 07:19:53 AM »
800 sounds like a lot to me.  @Chryco Psycho    :notsure:

Offline Chryco Psycho

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Re: Carb size for my setup
« Reply #2 on: June 05, 2017, 08:09:09 AM »
IMO 800CFM is fine it is the choice of carb that is wrong
 With the 292 cam I doubt you have very much vacuum & the Eddy carbs are very difficult to tune for low vacuum , the metering rods may be up most of the time even with very light springs under them . If the carb is tuned welll the sizeof the carb should have no effect on Gas milage unless you have a heavy foot !! Ihave been able to get amazing MPG even with a 1050 dominator carb for example
My choice would be a 750 CFM Proform Double pump carb for your application it is far more tunable for your needs
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Re: Carb size for my setup
« Reply #2 on: June 05, 2017, 08:09:09 AM »

Offline Chryco Psycho

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Re: Carb size for my setup
« Reply #3 on: June 05, 2017, 08:11:23 AM »
Proform 67213 is a great choice
or 67313 if you prefer black

Offline RUNCHARGER

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Re: Carb size for my setup
« Reply #4 on: June 05, 2017, 08:15:16 AM »
Yes: The AVS' are a fine carb for stock applications but you need more tunability for your application. IMO a 650 AVS would be an even worse choice for your application.
Sheldon

Offline Chryco Psycho

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Re: Carb size for my setup
« Reply #5 on: June 05, 2017, 08:18:23 AM »
  :iagree:
I cannot even find specs for a Ch 292 but I am guessing it has 292* duration which is huge I doubt you have 5"of vacuum at idle !
Who picked that cam?

Offline erik70rt

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Re: Carb size for my setup
« Reply #6 on: June 05, 2017, 08:24:35 AM »
I'll post the cam specs tonight when I get home. 

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Re: Carb size for my setup
« Reply #6 on: June 05, 2017, 08:24:35 AM »

Offline Chryco Psycho

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Re: Carb size for my setup
« Reply #7 on: June 05, 2017, 08:31:22 AM »
OK thanks , I typed into summit & nothing comes up . :notsure:

Offline RUNCHARGER

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Re: Carb size for my setup
« Reply #8 on: June 05, 2017, 08:58:50 AM »
Also: Do you know your ignition timing? Hopefully something like 20 initial and 36 total at 2000RPM?

Offline erik70rt

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Re: Carb size for my setup
« Reply #9 on: June 05, 2017, 09:05:43 AM »
Initial is set at 15 and total is about 32.  Any more and it knocks/pings under acceleration. Using 93 octane gas.  Ratio is 9:1.

Offline Cuda Cody

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Re: Carb size for my setup
« Reply #10 on: June 05, 2017, 09:08:58 AM »
That doesn't make sense.  At 9 to 1 compression it shouldn't ping at all.  That's a very safe compression.  I would think it would run best around 36.  I run 37 to 38 sometimes too on my small blocks.

Initial is set at 15 and total is about 32.  Any more and it knocks/pings under acceleration. Using 93 octane gas.  Ratio is 9:1.

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Re: Carb size for my setup
« Reply #10 on: June 05, 2017, 09:08:58 AM »

Offline erik70rt

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Re: Carb size for my setup
« Reply #11 on: June 05, 2017, 09:18:53 AM »
I can check/set the timing again, but where it is seems to be the sweet spot.

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Re: Carb size for my setup
« Reply #12 on: June 05, 2017, 09:38:07 AM »
I'm using 16 initial with 11:1 on 93. It really runs awesome at 21-22 on 110.  Do you have a wide band A/F gauge? One of the best investments I made for tuning was one of those.

I was having a similar issue and it was my timing the whole time. Everything from improper initial advance to my total and how fast the curve was. I could not make lean or rich conditions with my carb until that got set correctly. 

I'm not saying that your problem is all timing but your mileage should be better than that unless like Chryco said about the heavy foot thing. :)       

Offline Chryco Psycho

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Re: Carb size for my setup
« Reply #13 on: June 05, 2017, 09:56:30 AM »
Lack of quench will cause detonation well below safe range

Offline Cuda Cody

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Re: Carb size for my setup
« Reply #14 on: June 05, 2017, 10:05:28 AM »
Lack of vacuum will cause a lot of problems.  Good cams that make good vacuum can not be stressed enough.  That's why I run the Mr. Six Pack cams.  They make great vacuum and that in turns makes it easy to tune and great running engines.  The 340 engine we just tuned on the dyno last Friday made 18 pounds of vacuum at 850 idle.

What is your vacuum at idle?

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Re: Carb size for my setup
« Reply #14 on: June 05, 2017, 10:05:28 AM »

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