DP carbs with automatics

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66dartman

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In reading the Mopar small block book by Larry Shepard, he does not recommend mechanical secondary carbs with automatics. Anyone have any thoughts on this? I was going to run a mech sec. 650 holley on my 360 with a 3000-3500 converter, but I have no experience with this setup. I have used vac sec carbs on my street engines in the past.
 
If you are a very talented tuner of carbs you can get more performance from a mechanical secondary carb but unless you are racing and every .1 second counts I would never consider one for my car.

Don't know why Larry would not recomend one for an auto car though.
 
I was thinking that a mech. sec. carb would be simple to set up. Never had one, just thought since I would be doing a lot of quarter mile action with this motor it would work better. Haven't bought a carb yet.....
 
Nope: with the mechanical secondary you have four corner idle circuits to deal with, two accelrator pump circuits and the hardest thing to get right the linkage for the secondaries.
 
holley mech double pumper carbs aren't really that hard to deal with. I wouldn't use one without a 3500 rpm and up convertor, though. I have one on my 383 (72 duster) and it works pretty good. You just have to play with accelerator shooters until you can floor it without a bog. A vacuum carb will sometimes never get the secondaries fully open due to the spring, air cleaner design, air filter volume, etc. So I personally think that a mech carb is the way to go if you really want to wring every hp out of your combo. But that's my opinion.

don
 
I have used DP carbs all my life on auto and stick cars. Got a 750 DP on my sons Dart and have an 850 for my 63. I love the DP Holley carbs. Not hard to tune at all. In fact the one on the boys Dart is damn near dead stock. I did do some jetting and drill the squirters but thats about it. We also had it on the mild 383 when it was in the car with a 3000 tight convertor and the 400 in it now uses a Dynamic 9.5" 4200 convertor. And they work great with auto's so I don't know what he is talking about. Ran 12.31 @ 110 with the 383 and 1.77 best 60. With the 400 its run 11.55 @ 116 with a 1.61 best 60. I like them much better then the vacum carb but if you have no idea about carbs then the vac carb works good on a mild street car. Ron
 
I am thinking that I will try a mech sec. 650 on my 360. I have had the issues mentioned with the vac sec carbs, especially up here at 5800 feet.
 
66dartman said:
I was thinking that a mech. sec. carb would be simple to set up. Never had one, just thought since I would be doing a lot of quarter mile action with this motor it would work better. Haven't bought a carb yet.....
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The best advice I could give you is get a 950 hp holley out of the box. Put 2.5 power valves in it. And play with the jetting to get it to the right richness or leanness. My 340 went 3 tenths faster with one of these over the Carb Shop Specialities prepared 750 I took off. These carbs love to be raced!
This is how mine leaves with the 950 and a automatic.

edscartristate.jpg
 
Get the DP, I tried a brand new holley 750Vac and an old worn out swap meet holley 700 DP on a 383 with ported heads, Holley street dominator, MP electronic ignition, a 484 lift cam, 3.91 gears, and an automatic with only a 2200RPM stall torque converter in my old Challenger.
With the 700DP it would blow away the 10inch back tires from a 20MPH roll.
The 750 Vac just didn't have the throttle response even with a spring kit and a bunch of tweaking. I tweaked it for weeks and it still couldn't get more than a chirp from the tires from a roll, and it didn't pull as hard as the 700DP. I just wish I would of had a little bigger DP laying around to see what it would do.
 
ProStreetDuster said:
I just wish I would of had a little bigger DP laying around to see what it would do.
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These 950 HP's are worth looking for in my book. We got a guy here in Iowa that put one on a non built up 350 cheby in a Camaro for street strip use and with the right jetting had one of the most consistant bracket cars around in fact he took it to Topeka that year for the NHRA ET finals and won the sportsman class and only changed his dial once all day and that was just before the finals on a back to back run.
 
I've been using a DP on my 340 for years. It works fine with an auto and even was ok with 3.23 gears.
 
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