carburetor choice

[nazgule6]

Hey for all the sbc z guys out there, what is a good carburetor that can handle 350 to 400 hp?

[Zfan1]

Depends on the type of driving planned. I would guess a 650-750 CFM but weather you want a vacuum secondary or Double pumper remains to be seen.

 

Need more info please.

[grumpyvette]

http://www.holley.com/0-3310C.asp

youll be hard pressed to beat your performance on a basic , 350-383 hydraulic cam engine, with a HOLLEY 750 vacuum secondary carb for both ease of tuning and low cost ,high value in most street cars looking to make under about 450hp.

and a decent street/strip intake that matches is the

8501 - Weiand Intake Manifold

Edited February 5, 2010 by grumpyvette

[long240project]

Darn Grump,

You took the words right outta my mouth on that recommendation! Also a great Carb, to tame the launch on your car.

I'd also recommend not fooling around with a used one. Get you a brand new one to avoid a leaking base plate or one with slack in the shaft. I can't tell you how many guys I ve seen bad mouth a Holley and then you ride over to help them and they are tuning on the biggest piece junk ever bolted to the top of an intake Manifold.

 

Lane

[JMortensen]

Related question. On a 5.3L motor (325 ci) which will be cammed and will rev to 6250, dual plane manifold, shorties, etc. would it be best to run a 650 or 750 cfm carb?

[hoov100]

Related question. On a 5.3L motor (325 ci) which will be cammed and will rev to 6250, dual plane manifold, shorties, etc. would it be best to run a 650 or 750 cfm carb?

 

I would say a 600, but I would like to hear some other opinions.

[JMortensen]

So far I've been told 650, but I think that sounds a bit strange because a 350 isn't that much bigger and most people say 750 for a 350. I realize the car will run on either, probably do fine either way, but I'm still up in the air about what is going to be the better choice.

[hoov100]

So far I've been told 650, but I think that sounds a bit strange because a 350 isn't that much bigger and most people say 750 for a 350. I realize the car will run on either, probably do fine either way, but I'm still up in the air about what is going to be the better choice.

 

I run a mod'd holley 750 race carb on my built 355 which see's 8200 on a fairly frequent basis at the local auto-x and its just right, we have another built 355 thats running 11:1 and redlines at 6600 and the 650 is just a hair too small. I'm sure a 650 would be fine for a 5.3, if you get the tune down.

[grumpyvette]

ok lets look at things logically

a 350 spinning about 6500rpm which is a reasonable upper rpm limit for use of flat tappet hydraulic lifter can at least in theory digest 350 x 6500rpm/2 or about 657 cfm but keep in mind theres potential restrictions to air flow and the draw rates at the carb are computed at a constant vacuum, but on an engine theres not at a consistent plenum vacuum signal, now having run both the 600cfm and 750 cfm carbs on many 350-383 displacement engines Im forced to point out the rather obvious fact that the vacuum secondaries on the holley carb will by design compensate for the engines needs and that max power is almost always reached at an air fuel ratio between 12.4:1-and 12.8:1 and at a vacuum reading in the plenum near the 1.5" to .05" of vacuum at W.O.T.

[CJBrian]

Hey Grumpy,

 

Heres some info I got from the "carb selector" on holleys website. What do do think of this? My setup is a 350 vortec heads with 270H cam, Edelbrock performer rpm air gap, 3:54 rear end and T-56 trans. Vacuum secondarys for me too?

 

"Use of a mechanical secondary carb should be limited to use on a lighter vehicle. The vehicle weight should be less then 3100 lbs. If the vehicles meets the above weight requirement and has a manual trans with a low first gear plus 3:73 or lower rear end ratio, you can use a mechanical secondary carb. If the manual trans has a high low gear, such as a 2:20, you should have a rear end ratio of 4:56 or lower to use a mechanical secondary carb."

[grumpyvette]

Hey Grumpy,

 

Heres some info I got from the "carb selector" on holleys website. What do do think of this? My setup is a 350 vortec heads with 270H cam, Edelbrock performer rpm air gap, 3:54 rear end and T-56 trans. Vacuum secondarys for me too?

 

"Use of a mechanical secondary carb should be limited to use on a lighter vehicle. The vehicle weight should be less then 3100 lbs. If the vehicles meets the above weight requirement and has a manual trans with a low first gear plus 3:73 or lower rear end ratio, you can use a mechanical secondary carb. If the manual trans has a high low gear, such as a 2:20, you should have a rear end ratio of 4:56 or lower to use a mechanical secondary carb."

 

I think youll have fewer problems tuning the car with that cam, rear gear and heads with the vacuum secondaries, its what ID select for a car driven on the street

[CJBrian]

I think youll have fewer problems tuning the car with that cam, rear gear and heads with the vacuum secondaries, its what ID select for a car driven on the street

 

Thanks

[nazgule6]

Thanks for the references, right now im running a edelbrock intake manifold with a edelbrock 600cfm square flange electric choke. I'm not to sure about the engine specs because i did'nt build it, but i know its board .20over 218 duration and a .454" lift cam and these are comp cams, also i believe the heads are still the stock heads just rebuit and clean. I know the motor won't make much hp, but it should shread some tires. The car isint running good at all though, when i the car starts at about 2-2.5 rpm it feels like its lagging and you can feel/hear the car looseing power, but if you keep slowly pressing on the throttle it eventuallys pick up speed, but then again when you slam on the throttle the rpm goes up but the car is very hesitant to go anywhere. Feels like too much air is going to through the exhaust, but im not sure im not performace expert. What do you guys think? oh and it has a rebuilt 700r4

[Michael]

Nearly every such problem, it seems, can be traced to one or more of the following:

 

* vacuum leak

* carb dumping fuel into the intake plenum, or the inverse problem... insufficient fuel entering the venturis in all conditions other than those of idle or high manifold vacuum

* something wrong with timing advance

* weak spark

* wiped cam lobe(s)

 

Blessed is the mechanic who can quickly diagnose the simple problems!

 

But back to the broader topic - carb selection. This is so vast, and so ubiquitous, one has to wonder - why don't we have a FAQ, or at least a Sticky? Or did I miss it???

[nazgule6]

Thanks for the suggestions michael appreciate it, i had a feeling it can be those small problems, but like i said I'm not a performance expert so i just wanted to ask.

[grumpyvette]

If your having a problem tuning your car or getting it to run correctly ,about 1/2 the time youll find its the basic stuff on a car thats out of adjustment or improperly installed, naturally the last thing you added or adjusted will be suspected as the source, of any problem that just started, but dropping back to the basics of checking timing, fuel pressure, checking valve adjustments, vacuum leaks fluid levels etc. is usually the place to start and having a shop manual for you car and basic tools like a vacuum gauge, timing light and V.O.M. meter makes tracking down the source of the problem easier , and having the basics of how things operate at least in theory helps a good deal also

 

http://forum.grumpysperformance.com/viewtopic.php?f=55&t=211

 

http://forum.grumpysperformance.com/viewtopic.php?f=4&t=1337&p=2921&hilit=+infrared#p2921

 

http://forum.grumpysperformance.com/viewtopic.php?f=55&t=109

 

http://forum.grumpysperformance.com/viewtopic.php?f=70&t=875&p=7285&hilit=timing+light#p7285

[dr_hunt]

The biggest problem with using the volume calculations, like was shown in an earlier post, to determine airflow capacity in relation to carb sizing is that it is not apples to apples. Manifold vacuum is at zero if the carb is sufficiently sized and above zero if it is not, it is a simple airflow dynamic situation easily calculated by standard engineering principals. Carb flow ratings are based on 4.5 inches vacuum. So, it's not apples to apples. At zero vacuum carbs, especially holley carbs flow significantly less and it has been proven time and time again. A 750 only flows about 690 cfm at zero vacuum, but flows 750 at 4.5 inches of vacuum, which is why most people run a 750 carb on a 350. I run a 900 cfm C&S aerosol billet carb on my 406.

 

You can overcarb an engine, but considering that GM routinely installed 750 cfm carbs on stock 350 engines, you'd be hard pressed to go wrong with that selection.

[JMortensen]

You can overcarb an engine, but considering that GM routinely installed 750 cfm carbs on stock 350 engines, you'd be hard pressed to go wrong with that selection.

So what would you suggest on my 325 then David? 750?

[grumpyvette]

http://www.holley.com/0-3310C.asp

youll be hard pressed to beat your performance on a basic , 350-383 hydraulic cam engine, with a HOLLEY 750 vacuum secondary carb for both ease of tuning and low cost ,high value in most street cars looking to make under about 450hp.

keep in mind the vacuum secondaries will keep the throttle response, and flow rates in the effective range

and a decent street/strip intake that matches is the

8501 - Weiand Intake Manifold

[JMortensen]

Grumpy, are you a David too?