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Mechanical vs Vacuum secondary
#1
With all the carb talk going on I was wondering about mechanical vs secondary. Most everything out there including the Holley site itself says mechanical is only for big power light vehicles. Looking for some advice as I really like the thought of my foot controlling the gas instead of vacuum. I currently have a 2 barrel Holley on a torker 351 intake ( that's how it came) but am headed to grab a 650 with mech secondaries. It's only a $100 so I figure if it doesn't work out should b able to get my money back.
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#2
For a street driver with an automatic trans go with the vacuum. For more of a "race" set-up with a manual trans go with thw mechanical. Whatever carb you get it will take some tweaking to get it right. A mechanical secondry carb will take more set-up time to get everything optimized.

Jeff T.

Low buck, touring style, '73 Convertible "rolling restoration", 351c, 2v heads with a shave and a haircut, Performer intake, Holley 650(ish), roller rockers, screw in studs, guideplates, stainless valves, Duraspark / Motorsports MSD, T-5 conversion. 1-1/8" front, 3/4" rear swaybars KYB shocks and some home brewed subframe connectors. Future plans; JGC steering box, Cobra brakes and... paint, interior, etc.

When I die I want to die like grandpa, peacefully in my sleep... not screaming, like his passenger.

[Image: 1_12_09_14_10_15_11.png]
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#3
There is a lot of C R A P talk about mechanical vs. vacuum secondary's. There is also a lot of G O O D advise. How to tell the difference?

Buy a VACUUM secondary carb, put 500 miles on it. Tell us about the performance and gas mileage and how you drive.

Then replace it with a MECHANICAL and put 500 miiles on it.

Someone here would probably lend out a carb for the cause. We look forward to your write up!!!

[Image: 11jmcuc.png]
351C Bold Manners, Brash Attitude
Favorite Teams: Michigan Wolverines and Whoever Is Playing Ohio State.

When I drive past a herd of cows, the cows MOO at me
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#4
droptop73;81245 Wrote:For a street driver with an automatic trans go with the vacuum. For more of a "race" set-up with a manual trans go with thw mechanical. Whatever carb you get it will take some tweaking to get it right. A mechanical secondry carb will take more set-up time to get everything optimized.

I agree...Plus a vacuum secondary 650cfm flows just as much gas and air as mechanical..Its just mechanical carbs hit faster for racing...At about 40% throttle i beleive...Both carbs can handle mass power...vacuum will be alot easier to handle in town.
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#5
No issues with my MECHANICAL secondariesHuh
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#6
Tnfastbk;81261 Wrote:No issues with my MECHANICAL secondariesHuh

Roy, it shouldn't matter because I thought your car only has two speeds: STOP and LUDICROUS SPEED.

Steve



[Image: 25yvyp3.jpg]
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#7
As usual the answer is,"it depends". Gear ratio, convertor stall speed, tire diameter all determine whether or not a DP works properly. Either way count on calibrating the carb to your vehicle. If the gear and convertor are stock it is likely a vacuum secondary carb would work the best. If it is a working 650 DP for $100 buy it anyway and make a quick $50.00-$75.00 if you sell it. Or you could find someone who has a vacuum secondary carb and wants a DP. Chuck
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#8
Probably going to go with the try both and see what i like. Just trying to get ready for a safety inspection this week and once its actually on the road I'll begin seeing what i'm dealing with.

Managed to run new e-brake setup today. Not ideal rubbing across exhaust but it works.
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#9
I had a screw on my mechanical secondaries that I adjusted for race days and moved back for dailey driving. Worked out pretty well once I found the sweet spots.

[Image: 2rr7aiv.png]

Just cruising along minding our own business when BAM!!! The LAWS show up.
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