what holley is better for raceing on a built 350 (cam,intake,exhaust,headers,rollers,egnition,no smog,so on)
from what i no if u want your car for racing and dont care about MPG then vacuum sec is not the way to go, pluse i hear they just suck for racing>am i right here?
so should i go with a 600 DP or 650 DP i hear anything higher is to much. what carb do i get?

 

i consider a "built" 350 to mean 450+HP so i'd say a 750DP or maybe up to a 950 like we're running on my buddies shop car

 

Most of what you hear is BS.

If you have a high stall converter or a manual trans, get a 750cfm DP. If you have a stock or near stock torque converter get a 750cfm VS carb.

 

thanks for all the help, i called it built becasue allmost all parts includeing tranny are replaced with performance parts..dont know HP i have not been on a dino yet but it should be up there.
so u think i should go with a 750 VS.. i always figured because the secondarys dont open off the line only on load and DP open right up and are not controlled by vacuum that the DP would be the way to go for performance and VS is just for MPG, am i way off here?
if i go put a 750vs on will i need to change anything other then spring? can anyone recomend a link to a site or a book maby were i can learn everything there is to no about VS carbs?
also if u have a high lift cam the creats less vacuum will that effect the secondary in anyway?

 

forgot to tell u i have a Auto trans,th350, less then 10k on it, with a shift kit?

 

The secondaries on a VS carb are not controled by engine manifold vacuum.

They are controlled by venturi vacuum. ( airflow through the primary venturii). If the motor requires it (airflow demand), the secondaries on a VS carb will open right away.
You will not see the secondaries open by winging the throttle in neutral. Doesn't work that way.
There is nothing wimpy or inferior about a VS carb.
Just those that don't know how to tune one.
There are many books on holley carbs including vs carbs and how to adjust and tune them.
There is some bassic info on the Holley internet site. Check it out.
A vacuum secondary carb is smoother than a double pumper carb on a car with a low stall ( near stock converter and low ratio gears. 3.55 and less.) If this is what you have then a VS carb is the right carb for you.
A 750cfm #3310 will do nicely.
There are many much more powerfull cars that came form the factory with a vacuum secondary carb.
If you're ever at a IHRA or NHRA Stock or Superstock drag event. Have a view as to what these factory muscle cars use for a carb. (they must use the stock OEM carb) you'll see lots of Qjets, Carter AFB's and VS holleys. The faster cars in these classes run 9/10 sec quarter miles with these carbs. So this is more than enough carb for you.

 

thanks for the info, i got a 750VS carb and got a haynes holley carburetor manual from the library. i also got a 1" fome or what ever it is made from is the fome spacers fine to use or should i get one of those metal/allumin ones?is there a diffrence
i am going to read through the book tonight and check out the site to learn as much as possible, do u have any pointers or tips on tuneing it right?

 

Here is some stuff that will get you started

http://www.holley.com/HiOctn/TechSer...o/FMCTech.html

http://www.bob2000.com/carb.htm

Why do you feel the need to use a carb spacer?

 

Hey folks. I'm new here to the 3rd gen arena ( my son), but an old time racer. Good to see there's still carb people out in the world. The 750 vac is a good choice and easy to work with. Read up a bit as suggested above and take it slow.
One suggestion I may offer for tuning is to get a quick change secondary cover and install the heaviest spring. Now you can tune the primaries ( if needed) without interference from the secondaries. Once they're dialed in, the you can spend time on the rear set.
as far as carb spacers, don't believe all the ads. I've seen more back to back dyno pulls lose power across the board with spacers than without. However, it's your choice.

 

thanks for the info i have not had to much time to read up the holley book i got because of massive school work but i will do my best to learn everything there is to know. oh about the spacer i got it with the carb i have no clue the point of them if any lol, but i will find out. but for the mean time u suggest i dont install it?
thanks again for help.

 

I wasn't suggesting not to install it. It's something that has to be tested to see for your particular application if it's actually an improvement or a detriment. The only 2 methods are either back to back dyno pulls or track runs. A few people swear by the "butt dyno", but it's highly subjective.

 

I'd use a 750 DP with mechanical secondaries if you are racing... VS are for pulling trees outta the ground IMO.

 

If you've got a lot of converter, then the DP should work ok with some time spent on playing with pump shot to avoid any stumble. I just wouldn't suggest going over the 750. Personal preference for me is vacuum. I run a larger carb and work with secondary control springs.

 

i think i might be takeing the VS back to the dude. probelms>
first my tires like barley spin (more like churping) and for a 350 with mods it should rip them apart (dont no if this problem is from carb though>might be stall converter) also when i put the peddle to the floor the engine makes a loud deep deep tone almost sounds like its trying to catch up or shes flooding or something and when i let off gas a bit car tone changes to more normal and speeds up.

what was driveing me up the wall is that say i am doing like 40 and i press the gas down a good amount it does not move to fast untill RPMs get to 2500 and anything below is just garbage.

i ran my friends with a z24 v6 3.1 older ones with just a CAI and he pulled a car on me right off the bat but once the chrip into second came i flew past him like he was standing still. but that should not be normal i mean i though thats what the v8 ruled in getting off the line..so something is for sure not right!right?

i did not tune the carb yet though but could u guys tell me if these probelms are carb related or possible my stall?

on a side note car is amazing in higher rpms but sucks bad below 2500. oh and there is no hesatation or bog. so what do u guys think??

if i was to get a 650DP would it be better off getting off the line? and do the DP require less tuneing??

 

How modified is the engine?
What's in it it converter and gearing?
If the converter and gearing isn't matched, it won't run until you get up to the engine speed where the power band starts.

 

Need more info on the specs of your car and engine.

More the merrier. A vacuum sec carb is very flexable.
it sizes it self to your cars needs. A DP carb will not do this.
Responce below 2500rpm has more to do with timing, camshaft duration intake manifold type etc.

Probabily more of a tuning, engine/drivetrain parts mismatch problem than a problem directly related to the 750cfm vs carb.

Have used them on stock 302's and 305 with no problem.

 

hey guys well i had a friend of mine thats been around sbc 4ever check it out today and we think we may have found the problem the stall converter does not match to the cam(like u guys said). we tested the stall by holding the brake and pressing the gas and wathing rpms to see at what point the tires brake, my tires start to turn right at 2600 rpms and from what i have been told is the stock converter. so i am going to get a new stall and install it ASAP>(makes me so mad because i just got a new flex plate installed, i could have done it at the same time pluse i want to get onto looks! )anyway i was told that i should not go for no name type ones, and never get one used, is this true? is there anything else i should watch out for? oh and on a side note i hooked up the carb perfect my friends checked it out and i got a quick change spring kit, still cant get over how much they charged me for just springs talk about a rip off.
(we checked out everything again with engine, timeing, compression and what not, everything is just were they should be)

 

Used converters can be a problem not knowing what abuse they've had.
Best bet is to call a company like Hughes or Fairbanks so you have a tech to speak with. Better to get one built for the application, then an off the shelf close enough.

 

Be carefull when you first fit your Quick change kit, make sure the lid screws don't pick up on the rubber diaphragm.

 

What cam are you useing? what intake manifold?
What is your rear gear ratio?

 

thanks for the info. crap i dont remember the specs on cam i have all the papers for the car at my moms house i will get them this weekend. i got a holley intake >INFO on it>>Idle-5500 RPM power band, dual plane design, No EGR, spread bore and square bore carburetor mounting flanges, and i just got 3.42 gears put in about 3 months ago.