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Old 08-04-2013, 10:07 AM
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Carb vs throttle responce

I've been complaining about the throttle responce on this newly built 355. Hard to explain, but it seems like its not as crisp and responsive as it should. Timing and jetting are spot on. After talking to two sepperate people they recommend to change from the edelbrock 1406 I'm running now to a holly unit. They claim it will affer better responce... What's yalls opinion on this subject?

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Old 08-04-2013, 02:16 PM
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I went from a well tuned eddy 1406 (650cfm) to a holley 750 DP and it was like night and day both power and throttle response. I will never use a eddy again.
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Old 08-04-2013, 03:52 PM
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Carb is part of the throttle response issue.
other factors;reciprocating mass including a heavy flywheel clutch assembly or flex plate with heavy converter,intake manifold,header tube diameter and exhaust back pressure,cam specs,compression,stroke length, and lesserº accessories like A/C,PS, air pump,,, throttle linkage, air filter,ambient temperature and barometer.
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Old 08-04-2013, 05:20 PM
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Timing too!
How much and when.
As much initial with a strong shot from the accelerator pump.
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Old 08-04-2013, 07:59 PM
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Quote:
Originally Posted by Slammedsi View Post
I've been complaining about the throttle responce on this newly built 355. Hard to explain, but it seems like its not as crisp and responsive as it should. Timing and jetting are spot on. After talking to two sepperate people they recommend to change from the edelbrock 1406 I'm running now to a holly unit. They claim it will affer better responce... What's yalls opinion on this subject?
For the timing to be "spot on", the entire curve has to be taken into account. That includes enough initial timing, which is sometimes neglected when only the total timing number is looked at.

More here.
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Old 08-04-2013, 08:02 PM
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Quote:
Originally Posted by vinniekq2 View Post
Carb is part of the throttle response issue.
other factors;reciprocating mass including a heavy flywheel clutch assembly or flex plate with heavy converter,intake manifold,header tube diameter and exhaust back pressure,cam specs,compression,stroke length, and lesserº accessories like A/C,PS, air pump,,, throttle linkage, air filter,ambient temperature and barometer.
as you prolly remember, the motor is a factory rotating assembly with flattops. Auto transmission with a 12 inch 2600 stall. Now i do have a new freak show performance 9.5 inch 3500 stall waiting to go in. Maybe that will help some. The intake is a edelbrock rpm performer, headers are junkie flowtech long tubes with 1.5 primaries and 3 inch collectors. There isn't anything on the front of the motor other then water pump and alternator, and the cam is a 218/218 @ 50 450/450 lift with 1.5 rockers. Im running a set of roller rockers in 1.6 ratio.

After looking at several different carbs im still lost of what i want for this truck. Kinda setteled on this Holly unit. Take a look.

http://www.summitracing.com/parts/hl...51bl/overview/

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Timing too!
How much and when.
As much initial with a strong shot from the accelerator pump.
Timing is set at 23* base and 35 all in by 2800 rpm. Vacuum can is hooked to manifold vacuum. Also the accelerator pump lever is in the middle hole on the cam. Not sure which way increases the shot?
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Old 08-04-2013, 08:04 PM
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Originally Posted by cobalt327 View Post
For the timing to be "spot on", the entire curve has to be taken into account. That includes enough initial timing, which is sometimes neglected when only the total timing number is looked at.

More here.
Thanks colbalt, Base is 23* and 35 total all in by 2800rmp.
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Old 08-04-2013, 08:16 PM
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If you have a friend who'll loan you a different carb that's working as it should, try it before going w/a different ~$500 carb- a carb that may not solve anything. Edelbrock carbs are not the best thing for high performance, maybe. BUT one thing they do not have a reputation for is a lack of throttle response. They might not be as crisp as a Q-jet, but the Holley's larger primary bore/venturi will not be conducive to good throttle response compared to a smaller throttle bore/venturi setup.

Bottom line is the Edelbrock has the potential to have as good- if not superior- throttle response as the 750 Holley, any day.
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Old 08-04-2013, 08:23 PM
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If you have the time and knowledge?
buy a used 650 double pumper,4777 long bowl with metering blocks.
buy a kit to put an 850 base plate on the 650 body. The big throttle plates with the small venturi makes for extremely quick throttle response.I build one for my old stockish 350 and was quite impressed.I got the idea from an old racer.
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Old 08-05-2013, 08:50 AM
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Quote:
Originally Posted by vinniekq2 View Post
If you have the time and knowledge?
buy a used 650 double pumper,4777 long bowl with metering blocks.
buy a kit to put an 850 base plate on the 650 body. The big throttle plates with the small venturi makes for extremely quick throttle response.I build one for my old stockish 350 and was quite impressed.I got the idea from an old racer.
I've herd of people doing that. Didn't know its purpose though. I've looked for some quality used holly units but haven't found much in my area.
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Old 08-05-2013, 11:33 AM
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U may be able to find a core in your area or ebay and rebuild it. I have a holley 750 (4150) on mine I bought for 25$ and I rebuilt it and I love it. The thing I like about volleys is that they are extremely tunable.
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Old 08-05-2013, 11:40 AM
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A 'straight' 4777 would be a good choice. It's my favorite "out of the box" Holley carb, bar none. Used them on everything from a 283 sbc (292 after boring) to a 455 Pontiac and they ran good after tuning on all of them.
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Old 08-05-2013, 11:50 AM
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850 base plate

Quote:
Originally Posted by cobalt327 View Post
A 'straight' 4777 would be a good choice. It's my favorite "out of the box" Holley carb, bar none. Used them on everything from a 283 sbc (292 after boring) to a 455 Pontiac and they ran good after tuning on all of them.
I agree with above statement.

the 850 baseplate flows more(mine flowed around 775 cfm). the difference in the 2 throttle blades is what makes the modified carb so responsive.
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Old 08-05-2013, 12:21 PM
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Carter/Edelbrock 625 on my street/strip 355...



No lack of throttle response, my car has been 1.308 60'
It has a logging wideband. afr's are great, no sign of any slosh or supply related problems. If you spin your engine hard, you will have to pay attention to the step-up springs. If they are too weak, your engine can lean out up top when vacuum builds up enough to pull the metering rods down.
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Old 08-05-2013, 12:25 PM
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aisr, what car is that? Engine's set right on back!
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