85_Z28_305

What should i set the timing at with my new dist.
Base without vacume hose, and advance with vacume hose connected. Thanks... Neal

Sonix

iTrader: (1)

Beats me, what engine is below it?

That text in your personal info to describe your car can be helpful ya know.

10* is a good shot in the dark though.

85_Z28_305

Ok i am set to 10* with the vacume hose disconected. It really made a big difference with the take off from a dead stop. Also new plug wires. Now all i need is a non cc Carb. Any suggestion??? Thanks Neal

85z28guy

Pick a holley vac secondary in your preferred cfm rating. TONS of knowledgeable people out there, and even more parts available for them.

ZZ28ZZ

If you like tinkering with the carb all the time, go with the Holley.
If you want to install a carb and not have to mess with it regularly, get a Quadrajet.

five7kid

iTrader: (14)

Sorry, but that's

They aren't any different than any other carb.

Except the CC carb, of course, which should be considered the preferred carb for a street performance application. One exception would be a manual transmission application, in which case the vacuum secondary Holley, q-jet, and Edelbrock Performer should all be considered as inferior to a Holley/Demon mechanical secondary double pumper.

ZZ28ZZ

I disagree.
When was the last time you saw a Quadrajet with a warped metering block, blown power valve, or leaking fuel x-fer tube?

I don't want to get into a big Holley vs Q-jet debate, but,,
generally speaking, Holleys are high maint; Q-jets are low maint.
I know plenty of old timers that agree with me on that.

black84z28-4spd

my holley has been great...there is a reason you see them on the fast cars

85z28guy

I love when people say you need to constantly adjust your holley, so its a pos. You should be regualrly checking everything on your motor, if you find that taking 5 minutes once a month to "tinker" with your carb is too much, maybe you need a new hobby.

F-BIRD'88

Wow lotsa BS floating around here.

A vacuum secondary carb is not "inferior" to a DP carb.
Different design only. Much superior in most street driven environments especially with auto trans and a stock or near stock stall torque converter. and gives up nothing in performance on a race car **with proper tuning**.
Check under the hood of a NHRA/IHRA "stock" or "super stock" Chevy the next time you're at the drags and walking around the pits. It will be a Qjet or a vacuum sec Holley. Then check the et and MPH that it runs in the quarter mile. Can your car run that fast? Its all in the tuning.

As you buy a carburator it comes with a "out of the box" inital setup of jets, rods, accelorator pump squirters and cams and a inital setup of the secondary opening rate on a vacuum sec carb or one with an air door like a Qjet.

YOU NEEED TO FINE TUNE it from that point. The sec ondary opening charactoristics are fully adjustable and modifyable to suite any car using simple parts, modicfications and some patience and a day or 2 at the local drag strip to dial it in.

Stating a false blanket statement as DP carbs are somehow superior to vac sec carbs is very misleading and in most street driven applications, totally wrong.
Ya just havent bothered to properly tune a vacuum sec carb yet. or a Qjet or a Edelbrock/Carter AFB carb.

A good replacement for a CC qjet on a relitivly stock motor using the stock GM intake manifold would be an older Non CC qjet. these are usually much cheaper to buy as a replacement at your local autoparts store.
You can get jets, rods and other interal parts to fine tune it from Edelbrock.
The old pre 1974 Qjets are very simple to work on but not a dir4ect replacement for your later carb. A Qjet for say a 1969 chevelle 350ci V8 is aobut as cheap a Qjet replacement as you'll get.

You can more finely set your engines ignition timing by getting a "advance timing light" and setting the "total timing at high rpm (32-36deg) and then checking and adjusting the vacuum advance timing at differnt cruise manifold vacuum settings.
You can also do this with a conventional timing light by adding a Mr gasket Timing tape to your engines harmonic balancer so you can observe the full advance timing while at high rpm.

Generaly for a mild engine (near stock) 8 to 12 deg initial timing at idle.

32-36 total mechanical advance at high rpm and up to 51 deg total combined timing ( mechanical and vacuum combined) at high vacuum cruise (hiway speed) works well.

12deg initial +24deg mechanical advance =36deg
total mechanical advance.

15deg of vacuum advance at high vacuum (hiway) cruise added in =51deg

A more radical high performacne motor with a long duration camshaft that has a rough idle and low manifold vacuum needs a different advance curve. Needs much more initial timng at idle 16 to 28 but the same34-36deg total mechanical and about the same amount of additional vacuum advance during high vacuum part throttle cruise (15deg) {total up to 51deg}
The exact amount of cruise vacuum advacnc your motor needs all depends. experimentation finds the right amount. The motor will surge and or ping at cruise speed if there is too much timing.
On a very radical motor with a race cam the distributor is usually modified to lock out the mechanical advance to get 36 at idle and 36 total. A race motor can still use vacuum advance for part throttle cruising so there is really no need to ever remove the vacuum advance on any street driven car. Just a matter of dialing it in properly.

ljnowell

Why does everyone have to be like that?

Thats no where near wrong. In fact five7 hit it right on the head. You will go slower with a vac secondary carb on a manual trans car most of the time. All of the time probably.

85_Z28_305

Thanks for the great info. I will look for a non cc Qjet replacement,
and will play around with the timing to see what works best.

F-BIRD'88

A vac carb only requires a slightly different driving techneique during the shifts between gears on a man trans RACE car.

in fact if you were to employ this same tecnique with a DP carb car you go better too.

ljnowell

Technique or no, DP is better for a manual trans performance car.