VAC or Mechanical Secondaries? which is best

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Dec 7, 2001 | 02:45 PM

Clink69

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Drifting

Joined: Sep 2000

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From: Germantown Maryland

VAC or Mechanical Secondaries? which is best

I am in the process of building up a 383 which will have about 420-450 HP. Assuming I go with a Dual plane intake what are the recommendation s for carbs, specifically VAC sendary carb or Mechanical secondaries? Which is better , I realize mechanical secs will be slightly less fuel efficient but all I care about is power and performance.

Heads are Canfield 195 aluminum 2.055/1.6 65cc
:flag

Dec 7, 2001 | 02:47 PM

QuickVet

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From: CT

Re: VAC or Mechanical Secondaries? which is best (Clink69)

i would go machanical. seems like a lot of people have questions about their secondaries opening, so why not avoid all that an just go machanical.

Dec 7, 2001 | 03:26 PM

norvalwilhelm

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From: Waterloo ontario Canada

Re: VAC or Mechanical Secondaries? which is best (Clink69)

I have both on 2 of my cars and I really like the double pumpers. I know when the secondaries open. Alot say that the vacuum secondaries don't overcarb the engine but I have never experience a problem. I have removed a vac, secondary carb from the mustang and installed a double pumper right after and it really felt alot stronger with the double pumper. I have run dual quad setups with vacuum secondaries and ended up putting in mechanical linkage. For me there is no question.
DOUBLE PUMPER

Dec 7, 2001 | 04:39 PM

gkull

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From: Reno Nevada

2024 C3 of the Year Finalist- Modified

Re: VAC or Mechanical Secondaries? which is best (Clink69)

Any carb properly setup will function fine. O'Dennis who has been a track champion bracket racer uses only vac secondaries. Over carbed is what you want to avoid. 383 and 750 vac or 700 or less mech secs. I only use big mech secs. Because then I make the decision when I want WOT

Dec 7, 2001 | 06:39 PM

Techno

Drifting

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From: 68 427 4.11s Roadster

Re: VAC or Mechanical Secondaries? which is best (gkull)

I'm out on a limb here but trying to reach 450 from 383 ci means you need all the tricks. I think the double pumper to be what your attempting. I don't think either matter at WOT. At this power level from this engine I would think driveabiltaty is secondary.(he He).

Dec 8, 2001 | 09:46 AM

DeenHylton

Racer

Joined: Sep 2001

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From: Prineville Oregon

Re: VAC or Mechanical Secondaries? which is best (Clink69)

Clink, most carb books recommend staying away from the mechanical secondaries unless your "all-out racing". Youv'e left a lot of information out of the equation...what type of tranny and what rear end ratio? A double pumper with an auto tranny, stock stall, and a 3.08 gear will be slower (less torque) off the line with a double pumper than with a tuned vacuum operated secondary. I've run both style of carbs and they both have their place...one suggestion I'd make...it your going to run a race-style carb (double-pumper) get rid of the street-style manifold (dual-plane). Another thing...if your engine builder is installing a mild cam for emissions reasons, why compound your problems with the double pumper? It's definetly not an emissions style carb. You need to look at the "whole package"...Deen

Dec 8, 2001 | 10:56 AM

nastee383

Melting Slicks

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From: Ft. Walton Beach, Fl USA

Re: VAC or Mechanical Secondaries? which is best (Clink69)

If you drive your car alot and are remotely concerned about economy I think vacuum secondaries is the way to go. I have a Q-Jet on a relatively mild setup and it runs very well. Much quicker than most would think and decent mileage to boot.

Dec 8, 2001 | 11:39 AM

ODennis

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From: Littleton, CO USA

Re: VAC or Mechanical Secondaries? which is best (Clink69)

Application is the key. What are you going to be doing with the car? When doing a build-up this is the question one has to be most realistic about. I think most builders would recommend a well-tuned vacuum secondary carb for any car that is primarily street driven. Vacuum secondary carbs (IMHO) are underrated. Remember that an engine is just an air pump (not a gas pump) and at WOT you will hurt performance if over-carbed (that happens more often than you'd think). A vacuum sec. carb can be compared to electronically controlled EFI systems in that gas is added when the engine load demands it. Unless this is going to be an all-out race car, a vacuum sec. carb will probably give better overall performance.

That's just my opinion...........I could be wrong!!! :eek:

Looks like a real nice set of heads! Also, there are a some cool :cool: cars in this thread! I think only Norval has a chance of being UNDER-carbed!! :D

Good luck with your project. :cheers:

[Modified by ODennis, 9:50 AM 12/8/2001]