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Old 11-02-2008, 08:31 PM   #1
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Default Carb Jet Size

My LQ-4 which has not been really tuned just yet, as I just got it up and running may need to be rejetted. I'm running a 750 HP series with the stock jetting which is 75 primary and 80 secondary. Just wondering what others may be running for jets. When I dyno the car in the spring we will have a air/fuel ratio sensor in the exhaust to determine the correct ratio. I was just wondering if the jets I have are a good place to start. Like I said it's a 364 ci lq-4 with L92 heads and a GMPP single plain intake. Thanks
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Old 11-03-2008, 05:08 AM   #2
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im running a holley 750, vacuum secondaries,72 primaries, 76 secondaries (roughly as they are adjust-ajets) a 50cc acclerator pump, #35 squirter, a 5.0 Power valve (you will want something like 6.5 since my cam produces next to no vacuum), and im running the white spring right now (lightest) but im going back to the short yellow spring.

I am using a Fast Dual Wideband to monitor all of my AFRs too. With this setup I have it at 13.8 at idle, 12.6-13.0 at cruise and 12.3-12.8 at WOT. I am also running a Holley 97GPH fuel pump wired with 10AWG house wire that makes 8psi at 14.2volts.
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Old 11-03-2008, 08:07 AM   #3
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i would start with stock jetting first, do some plug readings, get it close before dyno time-mine needed a pretty agressive shot off idle, i had to switch to the green pump cam, but your head/intake is diff(i had lq9/vic jr)
you just have ti drive it, see what it does, tune from there
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Old 11-03-2008, 09:41 AM   #4
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Thanks for the info
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Old 11-03-2008, 12:53 PM   #5
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Originally Posted by forcd ind View Post
i would start with stock jetting first, do some plug readings, get it close before dyno time-mine needed a pretty agressive shot off idle, i had to switch to the green pump cam, but your head/intake is diff(i had lq9/vic jr)
you just have ti drive it, see what it does, tune from there
i wouldnt, i would start off with square on the jets spreading the jets is like dirt track racing tune or something also why not just buy a spreads bore carb. bigger squirters front and rear.
make sure your idle air screws are adjusted properly,more than a full turn is out of adjust.
50cc pumps???
come on now, if your using 50cc for street use, you really need to get to the basics for carb tuning.
especially on a simple motor as such.
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Old 11-03-2008, 01:59 PM   #6
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Quote:
Originally Posted by mred View Post
i wouldnt, i would start off with square on the jets spreading the jets is like dirt track racing tune or something also why not just buy a spreads bore carb. bigger squirters front and rear.
make sure your idle air screws are adjusted properly,more than a full turn is out of adjust.
50cc pumps???
come on now, if your using 50cc for street use, you really need to get to the basics for carb tuning.
especially on a simple motor as such.
And what are you running on your carb'd LS motor?

I pretty much have Shawn's set up, as are most of the other guys on here. Has been talked about in great detail. These motors seem to need more of a shot than the first gen SBC's

http://www.ls1tech.com/forums/showthread.php?t=972427
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Old 11-03-2008, 06:25 PM   #7
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Quote:
Originally Posted by mred View Post
i wouldnt, i would start off with square on the jets spreading the jets is like dirt track racing tune or something also why not just buy a spreads bore carb. bigger squirters front and rear.
make sure your idle air screws are adjusted properly,more than a full turn is out of adjust.
50cc pumps???
come on now, if your using 50cc for street use, you really need to get to the basics for carb tuning.
especially on a simple motor as such.
Yeah LS1s flow ALOT more than any SBC due to their 15 degree style heads and catherdral ports. Mate that with the Victor JR intake and you need ALOT of fuel when the throttle blades open. I still have a slight stumble in gear cruising but thats just a matter of swapping out a few cams. This is a on a vacuum secondary carb, not double pumper.

I'm runing my screws turned 1 1/2 turns out. I've been tuning this carb for quite sometime now. Tried a couple accelerator pumps, tried a 25, 29, 35 squirter with hollow screw. A few cams, a few jets (running adjust-a-jets now), a few springs, a few power valves. It's all been trial an error not just assumption. I'm also using one of the most accurate A/F monitoring systems, mated with a computer controller and monitored ignition system with a MAP sensor. It's not like changing the springs and weights and turning of the old systems nor the 'plug reading' like the old school.
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1994 Z28 - 13.52@110mph 2.1 60ft T56, bolt-ons, suspension
1978 Datsun 2+2 - 6.0L LS1 swap in progress
1968 Firebird, 2820 dry- 2000 LS1, D&D Viper T56, RAM clutch/flywheel, 236/236 .651/.651 110+4LSA cam, victor JR EFI, 4150 TB, 42lbers, painless harness, Moroso 7qt pan, sfc, trac bars, 3" x pipe side exits, Telstars-30"MT streets/skinnies, mini-tub, 8.5" posi, richmond 4.56s, Hooker lLTs, Denny N20 DS, Fast dual wideband, Shotgun street scoop.
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Old 11-03-2008, 06:25 PM
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