Vacuum Vs. Mechanical secondary

[Dunc03]

I looking to get a Demon carb for my GM crate motor. The one I'm looking at is the Crate demon for the 350 HO. It comes in vacuum or mechanical secondary. What are the advantages and disadvantages to these two types of secondary. The vehicle stays on the highway for the most part. I'm just wonering what would be the better setup. The vacuum carb is about $50 more than the mechanical. Is it worth the extra money.

The setup is 350/700r4/np208/3.42, and it sits on 33,s

Thanks for any ideas.

 

[shane74]

I personally like the mechanical secondaries better. Once it's set, it's there all the time. No vaccum lines to crack or go bad. Then again, I'm a mechanical n-gin-ear type guy, so I'm a little biased.

 

[84_Chevy_K10]

Mechanical secondaries have little or no place on a truck. Go vacuum. Especially since you're way undergeared for the tires you're running. You'll be much happier, I think.

And get a Qjet.

 

[rcurrier44]

Demons arn't a very good off road carb so don't be surprised if it gives you trouble the fiew times you go wheeling.

But at the track they work very well.

The only time a mechanical secondary carb is of real benifit is when you are running a setup that is so agressive that you are not getting a good/consistant vacume signal. I would go with the vacume setup.

 

[Dunc03]

GOT A Q-jET

I actually have a Q-jet now, and when I hit the gas the damn thing just wants to die out. The reason I'm going with the demon is because I lack the tuning ability to make an emissions carb run on a high performance engine. Actually if I could find the right power system spring I'd keep it, but GM discontinued the one I need. So I'm going to try the demon as an alternative to going injected. Maybe injection later.

 

[1-ton]

I think you should go with vacuum secondaries as well. Vacuum secondaries are better for a street driven vehicle. Mechanical is better for racing because, as stated already, mechanical secondaries are for very high performance vehicles with very little intake manifold vacuum, due to very large camshaft profiles.

 

[motorheadnelson]

Ditto. Heavy street rigs especially with automatics like vacuum secondaries. You can get a spring kit to tailor the secondary opening. Better off road, also. Mashing the throttle with mechanical can either cause a bog or too much power. Vacuum allows what the motor can handle at the time.