conway62

Im trying to figure out the best Holley carb for my needs. I know Im looking for a 750cfm but not sure which was to decide on weather or not to go with a Double Pumper or not. Also choice between Mech secondaries or Vac. I have a 454 making 470HP and primarily drive it on the street. Not intending to race it on the track. Any suggestions would be much appreciated. :hurray:

Smokehouse69

Personally I'd go with the vacuum secondaries, in the interest of gas mileage, especially since you don't intend to race at all.

LAvetteman

:iagree: If you are not going to the track much, go with vacuum. Especially if its an auto tranny.

By the way, double pumper = mechanical secondaries. ;)

Mystery Machine

I agree with the others...vac. secondaries for an auto transmission. :thumbs:

427V8

If yoou have to ask...Vac Sec :yesnod:

Ganey

Race on the streets then Mech. w/ manual trans.

J/K, only a little.
:cool:

norvalwilhelm

Looks like I am the only one who likes mechanical secondaries. I won't run a vacuum secondary carb. I want to know my secondaries are opening.
I do think the double pumpers run too rich but after remedying that they pull the same gas mileage as a vacuum secondary carb and I KNOW what is happening.
I run a pair of 850 double pumpers. :)

conway62

I guess I should have given more info on the car. The configuration is:
454/470hp 490ft/lb torque, Comp cams 268H, 4 speed M21 trans, 3:36 gears, Hooker super comps, full 2.5 "exhaust into dynomax mufflers. Mostly driven as a daily driver but like to get on it on the weekends. How much vacumme should I have available if I choose to go with vac secondaries. Also, does anyone have experiance with the Street Avenger carbs? Would it be a good fit for my application? :hurray:

Matt Gruber

for automatic get a DP. a 800 cfm 4165 would be nice if you can find a good used one.
For stick a DP can give too much wheelspin on shifts, so vacuum 750 would be safer.

Marc80

I use the Street Avenger that is 770 (or780?) CFM. I don't have a bunch of mileage with it but it installed easily and seems to work great. I am happy with it so far. I am around 425 hp with a 355cd.

Tominator

I love to feel the sec. kick in on a vac. setup.

GDaina

Vacuum..

Matt Gruber

watch out for norvalhe is the only one here that has to wear earplugs because there is so much tire squeal it gives him a headache :rolleyes: .
.
.
.

. :jester

427Hotrod

Big myth that mechanical secondaries and double pumpers mean worse mileage. The secondaries do nothing until you ask them to by mashing into them. Normal driving you are on primaries only and mileage is fine.

What usually happens is they FEEL so good and are so much more responsive you find yourself playing and enjoying them more! Vacuum secondaries make you REALLY mash into them to get any more power.

Race type double pumpers are usually a little rich. No design flaw. Holley has to make sure they work on race stuff which has very low vacuum signal. So to compensate they enlarge the idle feeds and jets to feed the proper fuel to an engine with those characteristics. But when you stick them on a mild engine with lots of vacuum (or a blower sucking on them!), you get LOTS of fuel and they need to be leaned somewhat as Norval said.

The Avengers are OK, but seem to be more of a shiny carb marketing deal to me. Everyone wants shiny carbs these days! If you can swing it, I would lean toward the HP series of Holleys. They are great. Otherwise, if your heart is set on a regular 750 ( I would definitely go to a 950 HP!) the 4779 750 DP is about the most universal easy to tune DP out there. It will easily work on everthing from a 302 to a 454.

I feel the DPs are much more driveable with a 4 speed than vacuum. I want to KNOW when the sec. open and I want to be able to control them with my foot. Vacuum sec's are like driving with a rubber band...about the time you start getting traction, they start to open and add power and then you spin, etc etc. DP's allow you to control it all with your foot!

Plus, DP's can work with mild engines and autos too. Just takes a little pump cam tuning. I ran a 396 Nova with a T-400 and 3.08 gears that loved the 750 DP I had on it. You could walk it out of the hole with almost no wheelspin or flatfoot it and smoke them for blocks.

JIM

Matt Gruber

the Q is like
what year vette should i buy?
or
small block or BB
or
308 or 410
or
Stick or auto?
nobody here will know what you want.
but you can see all the different opinions,
:cheers:

Chuck Harmon

:iagree:

What 427 Hotrod said, word for word!

Chuck

Fevre

Go EFI. :eek:
:leaving:

Scooter70

Cheater! :rolleyes:

GDaina

You have spoken like a true professiona, 427, but the same can be said of the vacuum secondaries...one can fine tune them with the use of lighter or heavier springs, and if that doesn't get you where you wanna be, then a simple crew, (yea I know Bubba), will do the job, in fact, the screw may give you more flexibility in the tunning process.

Like anything else, one recommends what one is more comfortable with. This debate between between vacuum and mechanical secondaries will go on for decades, and the truth of the matter, it really doesn't matter what carb is used, both will do the job if set up the way the owner wants the carb to perform. If a motor produces low vacuum, that is the only time a double pumper is the clear winner.

By now, you have surmised that I like vacuum secondaries... :D Yep, I do. I also believe, that the motor can only use so much air/fuel at a given rpm range, and vacuum secondaries supply what is required. I don't know if mechanical secondaries are capable of supplying the required mix for the RPM range. Common sense tells me when you mash the pedal, mechanical secondaries open and a whole lot of air and fuel is on the way...maybe way too much for the rpm range.

MotorHead

I really like my 750DP Holley but I kinda liked the way I had my 650 vacuum secondaries carb set up with the lightest spring, when you hit it the motor would wind up normally for a second then wham the secondaries would open like a frieght train :D

There is a universal 750 vacuum secondaries (3310 ? of the top of my head ) out there that is much cheaper than the DP that might be OK for your motor.

[Modified by MotorHead, 2:45 PM 9/6/2003]


[Modified by MotorHead, 2:47 PM 9/6/2003]