302 z28 motor carb question? - Team Camaro Tech
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post #1 of 29 (permalink) Old Jun 5th, 14, 06:25 PM Thread Starter
Rob
 
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302 z28 motor carb question?

What size carb should I be running on a 302 built up motor? Has .546 cam, dart heads, and 11:1 compression. Also running a Muncie 4 speed, and 4:11 gears.

What size carb should be on this? I have a 750 double pumper and feel this is way too much. And I am leaning towards a 650. I am not racing this and will be just cruising around a few times a month.
Your thoughts?
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post #2 of 29 (permalink) Old Jun 5th, 14, 06:53 PM
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Camarodude67
 
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Re: 302 z28 motor carb question?

750 is a stock setup for a 302, 780CFM was the original size carb in 1969.
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post #3 of 29 (permalink) Old Jun 5th, 14, 06:57 PM
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Cris
 
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Re: 302 z28 motor carb question?

I have a basically stock 302,mild cam,stock heads and run an Edelbrock 750 and it runs great
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post #4 of 29 (permalink) Old Jun 5th, 14, 08:50 PM Thread Starter
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Re: 302 z28 motor carb question?

What are your thoughts on a 650?
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post #5 of 29 (permalink) Old Jun 5th, 14, 08:56 PM Thread Starter
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Re: 302 z28 motor carb question?

Also what rpm does your car idle at?
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post #6 of 29 (permalink) Old Jun 6th, 14, 05:29 AM
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Brian
 
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Re: 302 z28 motor carb question?

Quote:
Originally Posted by camarodude67 View Post
780CFM was the original size carb in 1969.
True, but I always thought that was a little big for a 302 unless you were really spinning it up. I'd think a 650 would be a better fit for cruising... maybe even a 600.

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post #7 of 29 (permalink) Old Jun 6th, 14, 01:35 PM
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Re: 302 z28 motor carb question?

With a slightly modded 302, 12.0 pistons -140 cam, and some port work on stock 186 heads and 4.88's back in the 70's I ran a 750 dbl pump and loved it for the street. I recently ran a 4777 650 dbl pump on a stock spec built 70 LT1 in my Z and loved it. Only problem you really need to worry about is the price of gasoline. In the 70's gas was cheap, today it's a lot more and you will use it up fast with dbl pumpers.

06A 1969 Camaro Z28 X33D80 69 B 711 Black Stripes Console w/tach and gauges.
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post #8 of 29 (permalink) Old Jun 6th, 14, 02:28 PM
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Re: 302 z28 motor carb question?

I tried a 650 on my 70 Z28 in '85 when the motor was 9:1. The engine ran out of air/fuel at 5,000 rpm, so I used a 3310 750 Holley and it was fine. I currently have the stock 780 Holley with 10.2 compression ratio with 4.10 gears and it runs fine too. The 650 is too small for the 302 or even a 350 with the Z28 cam.

You could borrow a friends 650 if they have one to try.

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post #9 of 29 (permalink) Old Jun 6th, 14, 06:33 PM
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Cris
 
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Re: 302 z28 motor carb question?

650 double pump might work out fine,with my edelbrock it idles nice at 750-800 rpm
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post #10 of 29 (permalink) Old Jun 6th, 14, 08:24 PM Thread Starter
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Re: 302 z28 motor carb question?

Ok. I think I'll stay with a 750. I bought a quick fuel 750 dbl pumper with a electric choke. I'm having very low vacuum though and can't get it to idle at 759-800. Any suggestions?
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post #11 of 29 (permalink) Old Jun 6th, 14, 08:53 PM
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Re: 302 z28 motor carb question?

Have you just tried the stuck idle RPM? I'm thinking 900 or 950 should work fine. I'm running right at 1000 RPM idle with an over the counter 4053 and my engine like it there. That of course is the 70 LT1 spec 350 that is currently in my Z now.

06A 1969 Camaro Z28 X33D80 69 B 711 Black Stripes Console w/tach and gauges.
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post #12 of 29 (permalink) Old Jun 6th, 14, 09:09 PM
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Re: 302 z28 motor carb question?

302 12.5:1, 500/300 range cam 8in/hg vacuum 650 Demon double pumper works fine.

68 302 M20 - 85 IROC Z
The older I get the faster I was.
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post #13 of 29 (permalink) Old Jun 7th, 14, 04:44 PM
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Re: 302 z28 motor carb question?

Quote:
Originally Posted by Robgon View Post
Ok. I think I'll stay with a 750. I bought a quick fuel 750 dbl pumper with a electric choke. I'm having very low vacuum though and can't get it to idle at 759-800. Any suggestions?
Get the timing up to 16* initial, 36* total. It should get the vacuum up to 10"-11" Hg.

Mark 70 Z28 M22 3.73 Z21 Z87 - Lunati 20120121 Roller Cam

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post #14 of 29 (permalink) Old Jun 8th, 14, 09:20 AM
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Re: 302 z28 motor carb question?

Quote:
Originally Posted by COPO View Post
Get the timing up to 16* initial, 36* total. It should get the vacuum up to 10"-11" Hg.
stock idle speed on a 69 Z is 900 RPM... 800 is too low. can't hold vacuum with the overlap.
What power valves do you have in the carb?
If they are above the vacuum reading or close then the idle drops/loss of vacuum are causing raw fuel dumps everytime the vacuum drops off.
Power valves help the transition from idle to main fuel metering circuits.

Power valves should be 1.5-2" below the reading at idle, if it (vacuum reading) dithers up and down then the reading needs to be below the lowest reading you see, if it only hold 8" then get a 6 Power valve.
* Double Pumpers have a power valve on each metering plate.

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post #15 of 29 (permalink) Old Jun 8th, 14, 03:39 PM
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Mark
 
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Re: 302 z28 motor carb question?

I didn't think a power valve could kick in when your just idling, being on the idle circuit? I'll have to verify that in my Holley tuning book.

Holley in the past used the method of -2 from your vacuum reading at idle but have since changed to a more accurate method my taking 1/2 of your reading. If it's 8" at idle then I'd be using a 4.0. http://www.holley.com/data/TechServi...wer_valves.pdf

Mines 10 and I'm using a 5.0 and it works fine in my 70 LT-1 roller motor.
16* initial / 36* total

Mark 70 Z28 M22 3.73 Z21 Z87 - Lunati 20120121 Roller Cam

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