Bruthish

Did a search but couldn't find the advice.....

mild built 350 with 280 magnum cam...4 speed..

vacuum or mechanical secondaries best?

bluedawg

Mechanical.

resdoggie

I have the Magnum 280 cam w/4-sp and have run it with the stock Quadrajet, Holley 4011 650 w/vacuum secondaries and currently with a Holley Street HP 650 w/mechanical secondaries. Hands down, the 650 Street HP is the most responsive and has more seat of the pants power.

7T1vette

For 'usual & customary' street/highway use and better fuel economy, you probably want vacuum operated secondaries. For best performance, you want mechanical secondaries.

Bruthish

Thanks guys...that was kinda what I was thinking but needed confirmation before shelling out $$.

Bruthish

How do you like it? I have only been out on the streets for a few quick trips and so far it seems ok, but I am thinking my stock gears are not enough and I really don't want to switch tranny's.

TedH

Got a Crane Energizer 272H cam setup. My qjet rocks! If you are leaning toward originality, You may want to refresh the q'jet. It is VERY responsive when calibrated to your installation. Minor primary and secondary metering rods and primary jets adjustment (if your qjet is otherwise healthy) and you WILL be surprised.

I miss Lars' input...

7T1vette

In case anyone is confused about it, the Q-Jet secondaries are mechanical. Depending on its configuration, there may be either a vacuum or a mechanical 'limiter' that prevents the secondaries from opening when they should not, but if the engine is warmed up and functioning properly, the secondary throttle plates open completely with WOT demand. Yes, there is also an airvalve at the entry to the secondary venturi, but if properly adjusted, that just makes an optimum transition from a 'low power' to 'full power' condition; it does not reduce engine performance. That airvalve also allows the Q-Jet to work for nearly any sized engine without major modification to the carb (as long as the engine airflow requirements do not exceed the maximum capacity of the carb).

When properly set up, any good carb will produce nearly equal "WOT performance". But, doing that as well as operating efficiently during "daily" operation is something the Q-Jet can do that most others cannot.

resdoggie

I also have the M21 close ratio and 3.55 rear. The carb sits on an adapter plate on top of a spreadbore Edelbrock Performer intake (1995 vintage). I will soon be removing the intake and heads and replacing them with AFR 195 Street Eliminator's and a Weiand Team G single plane intake. Can't wait to try that out! Next year I will install a roller cam and in a few years more a 427 small block. I'm not concerned with originality, price of gas nor gas mileage as the car is a weekend only driver.