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Old 04-03-2004, 01:54 AM
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2 much power is almost enough
 
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too much carb, uh uh

hi all, i have been going through past posts where people talk about too much carb. I have a 350 sbc stock heads, 8.5 : 1 cr, .447 .487 cam, holley street dominator intake... i was running an edelbrock 1406 600 cfm carb. A friend of mine has a 302 with a 750 holley and he told me to try one. So i went out and bought a new 750 holley. Oh my, much better off the line power as well as freeway power. Along with that i went from 10 mpg with the edelbrock to 14 mpg with the holley. How can the 750 make such a huge difference???? I would think it's too big but looking at all i gained over the 600 ...... whats your opinion?

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Old 04-03-2004, 02:09 AM
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My truck has a 355, iron intake, 993 heads, stock cam, iron manifolds, ram air and a 1406 Edelbrock.

I have had people tell me the same thing about my 1406.
All I know is it runs much faster than a Q Jet powerd truck.
I surprise a lot of people.

If you want to save gas, run a Q Jet.

If you want power, run whatever makes it.
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Old 04-03-2004, 02:32 AM
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750 is way too much for the 350, and just HUGE for the little 302. Run a 600 on yours and a 550 on his.

K
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Old 04-03-2004, 02:51 AM
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I tried a 850 Holley DP on a 289 once, ran great once we got it tuned.
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Old 04-03-2004, 07:22 AM
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didn't the camaro's with the 302 have big carbs on them from the factory?
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Old 04-03-2004, 10:43 AM
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If you picked up 4mpg and more power by switching from a 600cfm Edel. to 750 Holley then your Edelbrock's tune must be WAY off from what your engine needs.
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Old 04-03-2004, 11:53 AM
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ghetto jet, i agree with you but, i called edelbrock a month or two ago, i bought the kit and swapped out jets, springs and the needles to what they said would work best..... made no difference on the car at all..... oh and the 750 on the 302, yeah i felt that was way too big for his truck too, his response is that it has a good amount of engine work, over .500 lift cam, ported heads and 10.5:1 cr. He says engines love to breath and they love big carbs. so for now i'm going to keep the 750, i'm pulling the spark plugs today, gonna make sure they look good then once i install my hyfire box i think that'll make a good improvement with this bigger carb.. who knows.... hey thanks for the replies. and that 850 dp, thats crazy. he he he, i guess it's all in tuning. This holley, right out of the box, i did nothing except make it idle slightly higher. That was the best part of all. i took it to my carb pro. buddy, he messed with the idle screws and said it was dead on and i did a great job setting it up. holley rocks.
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Old 04-03-2004, 12:29 PM
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These guys are right, your carb was way out of tune, or just plain defective. I had simialer happen to me.
I put together a mild 360 Mopar for a buddy, topped it with a 600 Carter ( same as Edelbrock carb obviously), performance was less than impressive & got horrible MPG no matter what I did. After messing with it off & on for weeks I bolted a 750 Holley on that I had & made a huge improvement. As it turns out the carb had a defective casting. I had him buy a 570 CFM Holley street avenger & man what an improvement, even over the 750 Holley.
Based on the cam that you have Id say your power range is 5000 RPMs to maybe 5500 RPMs. Based on that RPM range a 600 CFM carb is more than adequete, I would try either a 570 or 600 CFM Holley I think youll have much crisper thorattle respons & better MPG. From my experiance a 350 Chevy doesnt need 750 CFMs unless your running 7000RPMs. John
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Old 04-03-2004, 12:35 PM
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Pick up a copy of Chevy High Performance magazine (the March 2004) issue. They tested and tuned 7 different Holley carb sizes on a dyno and the results are not what most people would have expected. The engine was a mild 383ci Chevy, they started with a 390 CFM and worked up to a 1,000CFM carb. It is very interesting to see the trends the different carbs had on the power.

Also remember a 750 CFM carb does not in most cases actually flow 750 CFM.

Royce

Edit: Here is a link to the article I was mentioned. Very interesting reading take the time to read it. http://www.chevyhiperformance.com/te...8_0403_choose/

Last edited by camaroman7d; 04-03-2004 at 12:46 PM.
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Old 04-03-2004, 12:49 PM
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Also, I forgot to mention, consider having the Qjet rebuilt & calibrated to your vehicle by somebody who is good with Qjets, there a tricky carb to tune, but somebody who is good with them, like The carb Shop or val Hedworth for example can set it up for great MPG & probably out perform any of the other carbs weve mentioned because of its spread bore design. When Qjets arent working properly there a pian, but properly tuned, man they sing. John
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Old 04-03-2004, 01:26 PM
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Quote:
Originally posted by camaroman7d
Pick up a copy of Chevy High Performance magazine (the March 2004) issue. They tested and tuned 7 different Holley carb sizes on a dyno and the results are not what most people would have expected. The engine was a mild 383ci Chevy, they started with a 390 CFM and worked up to a 1,000CFM carb. It is very interesting to see the trends the different carbs had on the power.

Also remember a 750 CFM carb does not in most cases actually flow 750 CFM.

Royce

Edit: Here is a link to the article I was mentioned. Very interesting reading take the time to read it. http://www.chevyhiperformance.com/te...8_0403_choose/
I have been saying the same thing that article illustrates for the last 20 years, the misconception that a 750 carb is too big for a 300 ci engine is pure bunk.

Thanks for the link Camaroman7D.
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Old 04-03-2004, 01:46 PM
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i'll go ahead and assume bunk is bad?
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Old 04-03-2004, 01:53 PM
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you never got ahold of any bunk wee..... oh never mind.... yep, it definately ain't good.

good read btw,
i think i might participate in the next carb thread.
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Old 04-03-2004, 01:55 PM
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after last night i'll stay away from carb threads. you can keep em.
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Old 04-03-2004, 02:15 PM
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For a 350 you should run a 750, for a 302, 305, 307 you should run a 650-660.

A 750 is perfect for a 350, not too much.

It's that old rule again EngineCI X 2 = your CFM requirement.
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