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Old 07-20-2012, 07:03 AM
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Carb selection

Howdy all,

I recently dropped a 355 in my 92 z71 and I think the Holley 450 is a little low on cfm. I've got a chance to get an edelbrock 750, mech secondaries cheep and freshly rebuilt.

My motors a 95, bored .030 over, speed pro hypereuectic(sp) 4vr flat tops, stock crank turned down .010, melling MTC-1 cam, new lifters, stock heads rebuilt off the 95, and a Holley Contender dual plane intake with a stock HEI. thoughts on upgrading to a 750?

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Old 07-20-2012, 07:22 AM
How fast is fast enough?
 
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Quote:
Originally Posted by MrPhotographer06 View Post
Howdy all,

I recently dropped a 355 in my 92 z71 and I think the Holley 450 is a little low on cfm. I've got a chance to get an edelbrock 750, mech secondaries cheep and freshly rebuilt.

My motors a 95, bored .030 over, speed pro hypereuectic(sp) 4vr flat tops, stock crank turned down .010, melling MTC-1 cam, new lifters, stock heads rebuilt off the 95, and a Holley Contender dual plane intake with a stock HEI. thoughts on upgrading to a 750?
An edelbrock with mechanical secondaries? Really?

The 450 is a little low for peak power, but it sounds like you built a towing engine, so NBD. I'd just send the holley to a reputable shop and tell them you need it rebuilt and tuned, it may actually cost a little more, but the end result will be better on the street.

That being said I have two Edelbrock 1406's I'm running now and they work well and are idiot proof.
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Old 07-20-2012, 07:29 AM
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As you suspect, 450 is too small. 600-650 CFM is "perfect" for a 350 used for towing. Cam and intake will have a major effect on this. The MTC-1 is "good" to about 4,800 in a 355. Is "Contender' roughly equal to "Performer"? I must ask, as nobody I know uses Holley intakes. Edelbrock or "stock"...

Agreed, no Edelbrock carbs are "mechanical" secondary. They have an "air valve" in the secondary. While the butterflies ARE mechanically controlled, the air valve is vacuum controlled (just like AFB/AVS and similar to Q-Jet), and "meters" how much air/fuel passes through the secondary. The 750 is a little "big", but won't act like it due to the vacuum secondary.

Jim
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Old 07-20-2012, 08:03 AM
How fast is fast enough?
 
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Originally Posted by Mr. P-Body View Post
As you suspect, 450 is too small. 600-650 CFM is "perfect" for a 350 used for towing. Cam and intake will have a major effect on this. The MTC-1 is "good" to about 4,800 in a 355. Is "Contender' roughly equal to "Performer"? I must ask, as nobody I know uses Holley intakes. Edelbrock or "stock"...

Agreed, no Edelbrock carbs are "mechanical" secondary. They have an "air valve" in the secondary. While the butterflies ARE mechanically controlled, the air valve is vacuum controlled (just like AFB/AVS and similar to Q-Jet), and "meters" how much air/fuel passes through the secondary. The 750 is a little "big", but won't act like it due to the vacuum secondary.

Jim
Also, a 750 Edelbrock doesn't flow close to 750cfm... though neither does a holley...

If you rarely go over 3500 RPM you won't notice a difference with a cfm increase, but you will notice a difference with proper metering.
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Old 07-20-2012, 01:26 PM
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The 750 will work just fine. Be sure the fuel pressure is below 6psi at idle.
You can adjust the jetting using the edelbrock tuning kit made for that carb.
The stock jetting will be very close.
These carbs tend to like a wood carb spacer. (Carb body heat control.)
Divided or 4 hole style for a dual plane manifold.
No, its not too big. The air valve controled secondaries make this carb very flexible and runs very well on engines of various size and air flow requirements.

99% of the time a 750 will out perform a smaller cfm carb, on V8's from 302 up , reguardless of carb cfm size selection theory.

Excessive fuel pressure and carb body, heat riser temp must be avoided.
Other than that they are pretty much fool proof. Its up to you to fine tune the carb jetting.
refer to the edelbrock carb tuning/calibration manual.
A afr gauge and a vacuum gauge is a big help.

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Old 07-20-2012, 05:30 PM
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Awesome guys. Thanks. After I read my post just now I realized I said mech secondaries on the eddy, when my Holley I have now has mech. Lol

But thanks, I believe I'll go get it. I'm averaging 14.5 Mpg's on the truck with 33"x12.50 tires on it. Not bad. Maybe the 750 won't hurt it too bad.
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Old 07-20-2012, 05:56 PM
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450 is too small. A 600cfm vacuum secondary carb would be best for a mild 350.
A 750cfm vacuum secondary would be OK too,a bit big but should work with tuning.
Personally I get rid of all metering rod carbs(Qjet Eddy AFB) as I don't have the patience for that BS. To me a Holley is best as they are a cakewalk to tune.But thats up to preferance.
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Old 07-20-2012, 07:53 PM
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basic rule of thumb to pick carb size=cubes times 2.IE: 350 cubes will work well with 700 cfm,so a 650 will work great and so will a 750.Bigger carbs for dual plane intakes and someone thing a more sporty tune now or in the future. The 750 will not hurt fuel economy.
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