Keep my Quadrajet or get another carb for 350HO Vortec ? - Hot Rod Forum : Hotrodders Bulletin Board
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Old 02-01-2012, 05:08 PM
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Keep my Quadrajet or get another carb for 350HO Vortec ?

After a lot of research on the web, I am planning to replace the top end on my 350 V8 and replicate GMPP 350HO Vortec. Based on the Car Craft’s article, I should be at a minimum of 350hp (I hope ). I think this is the best bang for the buck.

http://www.carcraft.com/techarticles...e/viewall.html

http://www.carcraft.com/projectbuild...l/viewall.html

GMPP Stock Vortec Heads (#12558060)
GMPP Cam (#24502476)
The above heads & cam comes in the GMPP 350HO motor
Edelbrock RPM Air Gap or Performer Vortec.
Fel-Pro 0.15” shim head gasket to bring up compression to around 9.1-9.5 :1
Long tube headers

I rebuild my Quadrajet and works just fine. Is it worth replacing it with a Holley 750 cfm or another Carb?

My 350 V8 is actually in a 1977 Olds Omega (Nova) so I dont know if there is any difference in post 75+ carburetor.

Thank you very much

Waid

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Last edited by waid786; 02-01-2012 at 05:21 PM.
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Old 02-01-2012, 05:27 PM
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The Quadrajet is rated at 750cfm. To me it's one of the hands down best carbs ever made. If you make major changes to your combo then you will need to recalibrate it. If you go with a Air Gap intake the only issue is they don't make a performer rpm air gap intake with a spread bore pattern, but they do make the performer air gap with the spread bore pattern.
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Old 02-01-2012, 05:55 PM
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The Qjet and the standard performer spread bore intake, nothing wrong with that.

That GM cam is .460 lift on the exhaust, that may be too much for stock vortec head as a safe bet. You best be looking into better springs for the application anyhow.

Why a .015 gasket? your asking for trouble on a non decked high mileage block, (if that is what you have) I would sooner use a .028 GM gasket and have a little room for un even surfaces.
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Old 02-01-2012, 06:11 PM
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Why would the GMPP Cam #24502476 not work with stock heads?

This is the cam that comes from the factory with stock Vortec heads on the 350HO motor.

http://www.gmperformanceparts.com/En...9711&engCat=sb

http://www.gmperformanceparts.com/_r...ine_Deluxe.pdf
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Old 02-01-2012, 06:42 PM
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That is a good question however the HO motor may have better different springs than the off the shelf heads ending in 12558060? After all they list conflicting values for the chamber size (one spec sheet its 62cc and one its 64cc) just goes to show that not all of the info is accurate.


Maybe the HO350 heads have different springs? I dont know

If it were me I would go with beehive or Z28 springs on those 12558060 heads should you buy them off the shelf.

Search the threads here on vortec head applications. .450 seems to be the majic number for a stock head. My votecs have the Z28 springs (max .525 lift) and I run a .462 exhaust lift. They also have 67cc chambers as they are the summit vortecs. So you see there are no absolute certainties. Check your vortec head max valve lift before the retainer runs smack dab into the valve seal and give your self .010 lee way.
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Old 02-01-2012, 06:44 PM
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the stock vortec head can take lifts to .480
after that they need machining
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Old 02-01-2012, 06:51 PM
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On the bench cold? .480 perhaps, On my motor hot .450

Last edited by Custom10; 02-01-2012 at 07:15 PM.
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Old 02-01-2012, 06:56 PM
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Quote:
Originally Posted by waid786
After a lot of research on the web, I am planning to replace the top end on my 350 V8 and replicate GMPP 350HO Vortec. Based on the Car Craft’s article, I should be at a minimum of 350hp (I hope ). I think this is the best bang for the buck.

http://www.carcraft.com/techarticles...e/viewall.html

http://www.carcraft.com/projectbuild...l/viewall.html

GMPP Stock Vortec Heads (#12558060)
GMPP Cam (#24502476)
The above heads & cam comes in the GMPP 350HO motor
Edelbrock RPM Air Gap or Performer Vortec.
Fel-Pro 0.15” shim head gasket to bring up compression to around 9.1-9.5 :1
Long tube headers

I rebuild my Quadrajet and works just fine. Is it worth replacing it with a Holley 750 cfm or another Carb?

My 350 V8 is actually in a 1977 Olds Omega (Nova) so I dont know if there is any difference in post 75+ carburetor.

Thank you very much

Waid
Welcome aboard, Waid.

Your Omega didn't come w/a 350 SBC, so go by the carb number and build date to tell the year of it. Generally speaking the 76-up carbs w/the 170 castings are better than the earlier castings for performance but they can need work on the idle circuit to get them right for use w/a performance cam.

It's nothing you can't do- if you can rebuild a Q-jet you can do the mods needed no problem. I'd suggest you either research it on Ruggles site and here, or ask Ruggles for his recommendations based on the exact combo you'll be using and buy the parts you need directly from him. Might as well get his book while you're at it.

More info HERE, bottom of the page has links to Ruggles and others w/parts and info.
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Old 02-01-2012, 06:56 PM
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Why buy the heads with good-flowing intake ports, then bolt on an intake manifold that does NOT flow as well as the heads? Forget the standard Performer. If the Vortec RPM non-Airgap is spread-bore, great. Otherwise, you need a square-bore carb. What about the Weiand AirStrike Vortec?
If going to the square-bore, then best performance will be with a 750, but with that tiny cam, best MPG will be with a 570-625.
The later Q-Jets do flow 795 cfm through the throttle blades, but cast-in restrictions in the main body reduce that dramatically, and you can't just grind them out yourself. In theory you could, but good luck correcting the tuning.
May I suggesting switching cams to the one they use in the 330-HP 350 for these reasons:
The 350 HP RamJet gets the last 50 HP from the intake manifold and the 1.6:1 full-roller rockers. Your plan won't see 350 HP. It might kiss 320, at best.
The 330-HP 350, when fitted with a decent intake manifold, also does 350 HP. And even with a basic Performer-style GM Vortec dual-plane, it delivers 300 ft-lbs from 1700-5800 RPM. That's impressive and excellent!
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Old 02-01-2012, 07:02 PM
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Quote:
Originally Posted by waid786
Why would the GMPP Cam #24502476 not work with stock heads?

This is the cam that comes from the factory with stock Vortec heads on the 350HO motor.

http://www.gmperformanceparts.com/En...9711&engCat=sb

http://www.gmperformanceparts.com/_r...ine_Deluxe.pdf
This is something you have to watch, many Vortec heads develop collision problems between the underside of the spring retainer and the topside of the guide with the seal sandwiched between. So you have to check this clearance as the lift starts getting up there around .44 inch. The fix is easy either your local machine shop can remove some height from the guide or you can, the tool is available to run in an electric drill or drill press for about 50 bucks. Some guys do what's called a ghetto grind which is just take a hand grinder and whack 'em down. But that's usually to crude for seal to work there for oil control in the guide.

The Q jet is fine for this, which a little tuning and massaging this can be a 400 horse motor without even breathing hard. Some beehive LS1 springs and retainers for your valve stem size, a 30 degree back cut on the valves to smooth the seat into the back side, a little pocket porting to take off the rough edges, and a set of 1.6:1 rockers is about all the more it takes to get there with everything else you've done.

Bogie
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Old 02-01-2012, 07:10 PM
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The fith number on VIN for GM for 1977 is:

U = Chevy 305
L = Chevy 350
R = Olds 350
X = Buick 350

See the GM Vin Card: http://service.gm.com/dealerworld/vi.../vincard77.pdf

I have the L vin code. It is a Chevy 350 and that is why I bought it.

Check this out:

http://www.olds-omega.com/omega.html

Waid
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Old 02-01-2012, 07:17 PM
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The 800 cfm casting carbs are used in GM trucks and vans up until the end of production of the non electronic carbs in 1986. I don't know what "cast in restrictions" there are. The secondary air valve shaft has a stop that is easily changed to allow full opening of the secondary air valve and if the secondary throttle blades are restricted in their opening point, the linkage can be easily modified to let them open as desired.

Might be a moot point, though- there are no highrise spreadbore intakes at least that I know of, for the Vortec heads. Why is beyond me- even GM only has a low rise intake for the spreadbore/Vortec.

I knew Buick used the Olds 350 (I worked on one, once) but not the SBC 350, thanks for pointing that out. Is that a CA deal?
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Old 02-01-2012, 07:38 PM
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I was thinking about air gap with an adapter for spread bore. I think with air gap intake and adapter, it might be too tall even with drop base air cleaner. Not sure how much room I will have.
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Old 02-01-2012, 07:43 PM
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Quote:
Originally Posted by waid786
I was thinking about air gap with an adapter for spread bore. I think with air gap intake and adapter, it might be too tall even with drop base air cleaner. Not sure how much room I will have.
q-jet good
adapter bad
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Old 02-01-2012, 07:53 PM
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Quote:
Originally Posted by cobalt327
I knew Buick used the Olds 350 (I worked on one, once) but not the SBC 350, thanks for pointing that out. Is that a CA deal?
1977 was the year GM switched Olds engine casting from the Central Foundry in NY to Pontiac Casting in MI. GM missed on the estimates for Olds engines they would need for 1977(Cutlass was the best selling car in 1976). Since all versions of the X body were made at the same plant, it was easy to substitute the 350 Chevrolet without any re-engineering costs. They did the same with the Cutlass and Delta. Quick fix that cost GM a lot when they got sued by owners. It eventually led to corporate motors and the death of Buick, Pontiac, Olds V8's
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