I have my new engine running and I am thinking about a dual 4 barrel set up. A low profile intake with Holley 450 double pumpers with mechanical secondaries would look awesum but are they worth it? Are there any problems I could have other than gas mileage?

Thanks, 68 Vetteman

 

I like the 3 2 barrels setup.

 

I think one carb is more than enough to give you problems over the years. Why double or triple the risk? That's why all the new cars are fuel injected. Besides, 1 carb will give you all the power you need. I remember the 66 427/425 cars as some of the fastest ever. The tri-power 435's were no faster. To me, multiple carbs is for the bling, not really adding any performance and opening the door to more potential problems. If the car was an original 435 or 400 horse it makes sense.

 

I have an Edelbrock dual quad set up on my '73 (two 500 cfm carbs, aluminum manifold, electric chock, mechanical secondaries). It has some bling factor but from a performance standpoint it is not necessary. If you do the math the engine can only injest so much air/fuel without forced induction (rpm, cylinder volume, carb efficiency).

Some issues you may want to consider are:
Get a low profile intake manifold as hood clearance could be an issue. I have the stock hood with the set up. The Edelbrock package has everything and fits perfectly.

The throttle cable will be too long to hook up to the aft carb linkage. A good Locor bracket/cable set up will work well.

If you have A/C and need an idle control solenoid it will be difficult to find a place to mount it without interferring with the linkage.

When it comes time to tune the engine you will need twice as many jets and rods so you may have to buy two carb tune kits at $50 each. For tuning purposes you should get a wide band fuel/air mixture guage.

I have to say that my car starts, idles and runs well with the timing mapped correctly, an MSD HEI billet aluminum distributor, 6AL box, blaster 2 coil, MSD 8.5mm spiral wound high performance wires and platinum plugs.

I would be more than happy to sell you my almost new dual quad package as I intend to put a single 4 barrel on the car.

 

i have a dual quad set up on my car. Dual Edelbrock 500s. I recommend going with them over the Holley 450s for two reasons.
First the Edelbrock carbs (there are two that are designed for the dual intake) come pretty much tuned for that intake and a moderately built engine. I did have to do some work to get them perfect, but not much.

Second, the Edelbrocks have a reputation as easier to tune then those double pumpers. Remember tuning two carbs is 4 times as tricky as tuning one. If you dont have experience in multi carb set ups, i recommend finding the oldest guy at the oldest service shop in your town and taking it to him.

The reason i did this is because i have a nostalgia for these multi carb set ups. I gerw up in a house that had a lot of old school hot rods, and those all had crazy fatheads with way too many carbs.

I can say that the throttle response is good, power is good, and dont worry about the mpg. They will get nearly as good mpg as a single carb. Its when you stop behaving that you really pay for it. Trust me, drive it crazy and your mpg cuts in more then half. You always have to over carb multi set ups. For example 1000 (500X2) CFM dual quads will flow about as good as a single 750 or slightly better.

I cut down my existing throttle cable and it works just fine. That was free.
Again realize that there are cheaper and easier ways to get the same performance. That said there is a major WOW factor is dual quads. Also the intake noise is impressive.

I say go for it, if its what you want, you wont regret it.

 

That's a very impressive engine compartment and engine you have there. Nice!! I have a 600 CFM Holley with vacuum secondaries and I'm not thrilled with it. I remember in my younger days my 71 Camaro with a 750 CFM Holley with mechanical secondaries. When I hit the gas it flew. Maybe a single double pumper is the way to go. Definitely cheaper.

Thanks 68 Vetteman

 

I have a dual quad offenhauser set-up with two 450 hollys with an adapter that moves the carbs forward 1/2 in. That lets room for the dist. This thing screams!!!!

 

Multiple carburation is an anachronism left from the days when engine size and rpm capability were outstripping the size of available carburetors (the '50s). Once larger 4-barrel carburetors became available, multiple carburation began to become more and more the province of exotic race cars. Still, there is something "old skool kewl" about a couple of 4-barrels sitting on top of an engine. I have always thought that a couple of Holley 390 cfm vacuum secondary carbs sitting on a low profile manifold would be uber-cool, and would probably have good street manners.


Keep the shiny side up!
Scott

 

I think the cam and rear end gears and transmission type should also be in the thought process when considering total CFM's in the 900 to 1000 range. Especially if they are double pumpers.

 

The only reason for multiple carbs is for appearance....but, nothing wrong with that. Make sure that the total airflow from the carbs is not much higher than what the engine can actually use. A stock 350 will use less than 600 cfm; if it's beefed-up some, maybe up to 750 cfm. Two small 4-bbl carbs will flow 900 or more, and would not be a good match for a SB engine.

 

anyone notice this dualquad thread is 2yrs. old.

 

Two Holley 390s = 780 cfm.

http://www.summitracing.com/parts/HLY-0-8007/


Keep the shiny side up!
Scott

 

Nope. Didn't look at the date the thread was started. Why can't the CF programming prevent adding new posts to a thread that is more than 2 years old? (maybe along with a notice on the screen to that effect)

 

capevettes I've seen some bone stock 100% orginal big block 66's and the air cleaner decal reads 450hp, I heard they started putting 425hp decals on to play some games with the feds. The '66 really hauls the mail....with modern tires of course.

 

There is nothing tha spectacular looking than a multi carburator setup.

Well that should be an Kinsler fuel injection to beat the look of the carbs.

However i chose to quote the Holley Performance book:

"If you only intrerested in horsepower and function, stay away from exotich carb setups".

But the look is awsome!!

 

Bowerss2---I've got two holly 450s on my 78 with a offenhauser high rise. My only problem is the gas cable. I picked up a Lokor cable but it feels wrong. It is a steel braided cable and feels rough when I press down on it. How can I cut the original cable to fit?