Mechanical vs Vacuum Secondaries for this build

[Prine]

I 11th Mech. Secondaries. Period. I personally have built myself, 5 mopar engines...and went off on the "ohh, for the Street - Vacuum Secondaries is the Best" stuff...bought numerous VS carbs....ended up pawning them ALL off on people in the same boat...and getting a properly sized Mechanical Secondary Carb....and to be specific, the carb I ALWAYS go to...is the Holley 750 Double Pumper.

You jet/spec it out for your CID, max RPM, set the float level, and drive it....If its rich on idle or mid....adjust jets 1 - 2 #'s smaller and try it....or if its popping at 6000 and the plugs are real white....change the jets bigger to compensate.


Easy to work on, tune, adjust, maintain, upgrade, repair, modify,................need I go on?

 

[cudaman51]

well i still haven't heard any reply's about the passing gear shift points working at the right rpms for moderate street driving with out a manual valve body. you guys said im rolng but haven't said you got that to work or not. I love to be rolng when i can do something i couldn't before. now did that part work for you or didn't it. I'm sure it would work just fine with your foot on the floor. educate me. i love to learn things.

 

[1wild&crazyguy]

well i still haven't heard any reply's about the passing gear shift points working at the right rpms for moderate street driving with out a manual valve body. you guys said im rolng but haven't said you got that to work or not. I love to be rolng when i can do something i couldn't before. now did that part work for you or didn't it. I'm sure it would work just fine with your foot on the floor. educate me. i love to learn things.

If you are asking weather'er not I still had kick down with the dp, yes i did.

the secondaries begin opening before you reach wot in the primary side.fwiw
the diff would be that instead of letting the vacuum accelerate for you [to a point]
you do it manually with yer foot..

 

[mshred]

id go with a mechanical secondary just for the fact that it seems easier to tune (no springs to deal with) and makes more sense for a track effort car (only you will be able to know though how serious of a track car it is and decide)...imo there is nothing wrong with a holley, but the amount you are going to spend buying a new one you mine as well buy a nice tuned carb for your application i.e. prosystems, biggs, etc...for the money they are tuned outta the box...prosystems and quickfuel are just rebadged holley's with lots of nice parts...
i personally am using a carb builder out of PA, he built me a totally custom 750 mechanical secondary carb with an HP main body shipped to me for cheaper than a brand new holley!!!! its an excellent peice, the workmanship was top notch!!! if you want his info pm me! hes underground but all the guys in his area use him OVER pro systems stuff..he knows his stuff!!

 

[340sFastback]

well i still haven't heard any reply's about the passing gear shift points working at the right rpms for moderate street driving with out a manual valve body. you guys said im rolng but haven't said you got that to work or not. I love to be rolng when i can do something i couldn't before. now did that part work for you or didn't it. I'm sure it would work just fine with your foot on the floor. educate me. i love to learn things.

I use one of these brackets on my Holley 750 DP:

http://www.summitracing.com/parts/HLY-20-7/

It allows your stock throttle cable and kick down linkage to hook up to the carb correctly. With this set up my kick down linkage works correctly.

 

[RDJ]

Thanks for the info. Seems lots are happy with the MS. Are most of you using the Holley Classic Double Pumper Carb or the Holley 4150 Street HP Carburetor, or the Holley Chokeless 4-bbl Race Carb? Sorry to be so clueless, but which one of these would be best for my application or one that is most preferred for street and occasional track time.

 

[cudaman51]

thanks i used that bracket on my streat avenjer carb and every thing works great. i dont think i had it when i had the dp on and the secondaries where coming in to soon

 

[340sFastback]

I run the standard Holley 750 dp.

 

[moper]

cudaman, the transmission's throttle valve (kickdown) setup on any carb is critical. If you remove the factory carb, you have to get the right parts to keep the factory alignment and adjustment in order to keep the part and full throttle shifting correct. Regardless of the carb if the tranny's not set right it won't work well. However a carb not mtcehd and tuned properly, of any design, will make the trans behave differently becasue the power produced isnt consistant.

 

[dgc333]

id go with a mechanical secondary just for the fact that it seems easier to tune (no springs to deal with) and ....

A vacuum secondary is by easier to tune. With a mechanical secondary carb you have two accelerator pump cams and squirters to get right verse one on the vs carb. And the process of swapping springs is simpler and much more intuitive than fiddling with the mechanical ratio of the secondary linkage to get them to open at the right rate.

 

[2 Darts]

The old rule-of-thumb I've heard is VS for automatics and MS for manuals. I like the idea of not opening the secondaries until the engine can handle it.

 

[1wild&crazyguy]

A vacuum secondary is by easier to tune. With a mechanical secondary carb you have two accelerator pump cams and squirters to get right verse one on the vs carb. And the process of swapping springs is simpler and much more intuitive than fiddling with the mechanical ratio of the secondary linkage to get them to open at the right rate.

yeah real easy when the diaphram housing is caught under the lip of the main body, so now you take out the screws to remove it then you can change the spring.
But what about secondary jetting, oh you have a plate instead that cost $$ more than jets do huh? and gotta love those funky screws on the older ones.
love that cross over tube as well...like when it leaks due to dried rubber grommets.

I'm not bashing the vac sec, just your reasons for using it.

btw I love the one where you basically say you don't can't tune the pump shooters.lol

 

[340sFastback]

The old rule-of-thumb I've heard is VS for automatics and MS for manuals. I like the idea of not opening the secondaries until the engine can handle it.

On a stock or very mild engine I agree. But on a more powerful quick reving engine with light weight internals those types of engines can take the secondaries pretty much instantly.

 

[moper]

1wild... your describing the std oldschool 3310-750 and the smaller 600-650 carbs. The Avengers and HP versions have the secondary jet plates and quick change secondary spring assemblies. Not that the earlier stuff is hard. If someone cant get the tubes to seal or thread in screws without punching holes in the diaphram they probably should be paying someone to take care of everything but oil changes...lol.

 

[1wild&crazyguy]

1wild... your describing the std oldschool 3310-750 and the smaller 600-650 carbs. The Avengers and HP versions have the secondary jet plates and quick change secondary spring assemblies. Not that the earlier stuff is hard. If someone cant get the tubes to seal or thread in screws without punching holes in the diaphram they probably should be paying someone to take care of everything but oil changes...lol.

wow pinching holes in grommets??

yeah 'they' should pay somebody else to do it.lol:cheers:

 

[dgc333]

FWIW, anyone that has an older vacuum secondary Holley and doesn't already have the quick change cover I would recommend that you get it. It's available without springs for $15 or with a complete set of springs for $26 from Jegs.

There also seems to be some confusion regarding Holly carbs and the features they have. Here is an explanaton of the more common series numbers.

The 4150 series carbs are or have been available with; mechanical or vacuum secondaries, with side or center hung bowls (side is the single fuel inlet with cross tube) and all have a secondary metering block.

The 4160 series was introduced with the intent of offering a lower cost carb. They have been available with: mechanical or vacuum secondaries, with side or center hung bowls (the popular list# 3310 750 is an example of a 4160 with center hung bowls) and all have a secondary metering plates. You can convert a 4160 to 4150 with a secondary metering block kit from Holley or Quick Fuel sells a metering plate that accepts screw in main jets.

4165/4175 are spread bore carbs the difference between the 65 and 75 are the same as the 50/60 in regards to the secondary metering block/plate. I have only seen these carbs with vacuum secondaries.

4500 or Dominator are the high end race carbs. The single most defining feature is they have a larger spacing between the venturi's resulting in a bigger mounting pattern. They won't bolt to a manifold designed for a 4150/60 carb without an adapter.