Vacuum or mechanical secondaries?
Thread Starter
Le Mans Master
Joined: Sep 2003
Posts: 7,776
Likes: 0
From: Everywhere
Vacuum or mechanical secondaries?
This is the question I have pondered for months now. People that I have asked are split on the decision, so I'm lost. I have even called the Demon tech line, and got two different answers.
I want to install a Speed Demon 650 on the vette, as soon as I get the engine finished, hopefully before winter. Roughly, the engine will make 350hp. The car is auto, with 3.70 gears, dynomax headers, Crane powermax cam(216/228@ .050, 112, .454/.480) 9.0 compression, 2200rpm stall convertor, AFR 180s, and performer rpm intake.
I know that the rule of thumb is auto=vacuum secondaries. But some folks say a low gear ratio can be the exception to the rule. Also keep in mind that I plan on swapping to a 2004R auto, which will result in an even lower final gear ratio in first.
Also, if I were to go with mechanical, can a choke be added?
What to do? :confused: :crazy: :lol:
I want to install a Speed Demon 650 on the vette, as soon as I get the engine finished, hopefully before winter. Roughly, the engine will make 350hp. The car is auto, with 3.70 gears, dynomax headers, Crane powermax cam(216/228@ .050, 112, .454/.480) 9.0 compression, 2200rpm stall convertor, AFR 180s, and performer rpm intake.
I know that the rule of thumb is auto=vacuum secondaries. But some folks say a low gear ratio can be the exception to the rule. Also keep in mind that I plan on swapping to a 2004R auto, which will result in an even lower final gear ratio in first.
Also, if I were to go with mechanical, can a choke be added?
What to do? :confused: :crazy: :lol:
Drifting
Joined: Jan 2002
Posts: 1,484
Likes: 0
From: Northampton Ma
Re: Vacuum or mechanical secondaries? (GDaina)
In your case I would go with vacuum, just check to make sure the secondaries are opening fully at full throttle, if not go to a lighter spring. I'm using a Speed Demon 750 mechanical, but I'm running a 525hp 383ci with a 4 speed, so it's a completely different setup :cheers:
Race Director
Joined: Nov 2000
Posts: 11,872
Likes: 12
From: Waterloo ontario Canada
Re: Vacuum or mechanical secondaries? (Sling Blade)
I am a fan of mechanical secondaries. At least I know the secondaries are openning and with your gearing jabbing the throttle open at low rpms shouldn't be a problem.
I always use mechanical secondaries and run a pair of 850' s on my bigblock and still get 15 mpg around town.
I always use mechanical secondaries and run a pair of 850' s on my bigblock and still get 15 mpg around town.
