The Basic Guide To Running Dual Quads...Both Low rise and Tunnel Rams

welcome back to unity motorsports garage so i was encouraged to do a video on dual quad tuning by uncle tony of uncle tony's garage and so this video is going to be kind of like an introductory to buying dual quads setting them up on your car to get you going in the right direction i've done other videos about the tuning process but today we're going to cover the basics like carb selection whether to run a progressive linkage or a one-to-one linkage those are the things that we're going to talk about today so stay tuned so another thing you need to ask yourself is what type of engine are you going to be putting this on because that plays a huge part as well you know if you're putting dual quads on a pretty much stock engine the requirements are going to be much different than if it's say a warmed up street engine or an all-out race build so that's two completely different animals that we're talking about here um let's talk about the low rise setups first i'm going to put a picture up so you can see it of a performer rpm air gap dual quad manifold now this is a good compromise situation here but you're limited into carburetors that you can run because it's set up for of course edelbrock carburetors the carburetor spacing doesn't allow even a 4160 holley so that's something to take in consideration when you're doing this also let's talk about carburetor sizing because there is a huge misconception out there about sizing carburetors for dual quads you know people think if you put two 600s on an engine that's 1200 cfm well that's not true and the reason why that is not true is due to the pressure differential of above the carburetor and down below it think of it this way if you have a 600 cfm carburetor a one on an engine you're operating off of those four throttle blades well when you effectively double that by putting another carburetor in place the air speed slows down considerably that goes through the carburetors because there's more surface area for the carburetor i mean for the engine to breathe so even though you may have 200 2 600 hollies that doesn't mean that you're getting 1200 cfm in actuality you're probably getting somewhere around 850 to 900 cfm because the engine is nothing more than an air pump it can only digest what the engine will allow it to digest now another topic that i want to discuss that's not really brought up much is depending on your combination will depend on what kind of booster the carburetor needs in order for the setup to work ideal what am i talking about boosters when you look down the throat of a holley carburetor and i'll put a picture of a booster up right now so that you can see it the style of the booster has an effect as how well the fuel is atomized as it's going into the intake track if you're running a low rise dual quad setup something that gets a lot of engine heat into the manifold you want a pretty much a low gain booster a straight leg booster or a regular down leg booster works really well but if you have say an air gap dual quad set up where you've got air being isolated from the valley to the carburetors the fuel needs to be atomized a little bit better and so a step down lag booster or annular booster is the way to go and on those particular manifolds i would highly suggest the new avs2 carburetors as they actually have annular boosters from edelbrock really good setup all tunnel ram setups that i run i really like to see a step down leg or an annular booster because you're pretty much force-feeding the fuel in a straight line of sight from the carburetor to the back of the intake valve and so the carburetor really needs to atomize that fuel as best it can so that you get a proper burn when it gets into the chamber uh annular boosters will give you a lot more low end mid-range torque than say a straight leg booster wheel up top the gains are kind of marginal because the air speed in which the fuel charge is moving is pretty great but at part throttle operation you can tell a big difference as far as drivability by having a good active booster in your carburetor one other option we need to talk about is the low rise intake dual quad that is a single plane design there's actually no separation of the runners both carburetors feed a common plenum that's another option out there as well you've got the cross ram manifolds you know the low rise tunnel ram setups or street tunnel rams as edelbrock referred to them as of the late 1960s so when it comes to selecting carburetors what do you do how do you go about it actuality if it's a stock type engine you need to size the carburetors on the small side and when i say small 500 cfm 450s 390s in the cases of holleys but definitely probably no more than a 600 cfm and the reason why i say this is because low-speed drivability does come into play but you will get the added rush of having multiple carburetors up top now tunnel ram setups are completely different so which leads us to the next question the progressive linkage or one to one which is right for you progressive style linkages work really well on dual plane dual quad setups if you'll notice back in the late 1960s anything that came with dual quads most of the time that had a dual plane manifold it had a progressive style linkage the factory engineers were smart as they knew that this was going to give drivability and it was going to give you fuel economy and the top-end rush this is achieved because of how the intake design actually works you've got separated runners feeding different cylinders into engine so basically one side of the carburetor feeds four cylinders and the other side feed the other four cylinders with a common polenta manifold such as this tunnel ram right here you see how all of the runners are tied to this common plenum trying to run a progressive style linkage on this type setup is a recipe for disaster for example most of primary setups you would be running off of the front barrels of the back carburetor okay if you're running a progressive setup you've got this common plenum and you notice the angle in which the runners go down into the intake it's a 90 degree turn so for you to run a progressive style engine intake setup the fuel would have to come through the plenum and then make a 90 degree turn it would work really well for the rear four cylinders but the for the front four would be star for air fuel mixture in fact you will run lean in these cylinders up here causing all sorts of tuning issues something to keep in mind from my past experience i every time i set up a tunnel ramp setup i always go to a one-to-one linkage and that is so that i know that all cylinders are being fed the proper air fuel mixture even if you're running a wideband setup in your car it can be confusing because depending on where your pickup point is for your oxygen sensor if it's downstream and you're not actually checking the afr in individual cylinders which 99 of the people out there on the street don't do you may see good air fuel ratios on your meter but what's happening is it's being offset the rear cylinders versus the front and if you pull plugs out the plugs always tell the story when you run a progressive style on a tunnel rim you will see that these plugs back here will look dark and these up here will look like you just took them out of the box so keep that in mind one of the age-old questions when it comes to selecting carburetors too is vacuum secondary versus mechanical secondary for most street driven cars with an automatic transmission that has say less than a 3000 install converter a vacuum secondary carb is going to do really well a mechanical secondary carb you know i would save that if you're going to put a very high style converter in it's a 4000 and above stall and you're running a lot of gear in the rear end because your with the vacuum secondaries it will actually size the carburetor to the engine itself so you will actually get the right amount of throttle opening in your secondaries and what the engine actually needs something to take into consideration now when you do that on a vacuum secondary you will have to experiment with the springs inside the vacuum secondary pot and you will have to find out what your combination likes because it's driven by engine specifics you know a 302 cubic inch engine is going to have different requirements than say a 440 cubic inch engine you know the the amount of air that's being digested is two totally different things in those engines so you got to get the secondaries tuned to where you won't have the bog off the line when you map the throttle that is key to making it all work i'm going to show you a video clip of my friend and mentor david visar driving my truck casper i wanted him to drive my truck because he's a renowned author of automotive books and he's an automotive genius and using his techniques is where i got all of this information from you know just through the years of him teaching me and now i'm bringing it to you so we took my truck casper out for a little drive one day and he was able to take off in high gear with my truck and it didn't stumble it didn't buck or anything of the effect and he told me that that was his grading system of how well a dual quad setup runs if he can do that it's about dead on perfect [Music] yeah right we are going to drop down to around about 10 miles an hour yeah do we need to shift oh really no all right i am going to pull up with these lights here and i'm going to just waft away like i would do in traffic yeah in high gear no gear shift right we're coming up to a stop sign now now it does the brakes by such a big market yeah this okay we've stopped yeah we gotta go right here high gear 2500 rpm and it pulls through with no hiccups no bugging [Music] you have to admit when you go to a car show or anything else there's nothing cooler than seeing dual quads on an engine but most people when they see that they automatically assume that it's a poser that the engine won't run and that can be nothing but false because once you get your tuning down pat and you get your carburetors dialed in you can have your cake and eat it too this setup right here looks pretty radical two holley 660 center squirters that were notorious for being race only carburetors no one tried to drive them on the street but i modified these things to where i was getting nearly 16 miles to the gallon with a 600 horsepower 393 windsor so it can be done and that's with a loose converter and a lot of gear out back it just takes time and effort and if you follow those things you can have your cake and eat it too so until next time this is andy from unity motorsports catch you later

Channel: Unity MotorSports Garage

Views: 48,718

Keywords: Dual Quad tuning, Tunnel Ram setup, drag racing, hot rodding

Id: UVff8o3BPCU

Length: 14min 30sec (870 seconds)

Published: Thu Feb 25 2021