Tuning on a 3 circuit 1200 Dom.....carb guys ?
#2468027
03/18/18 11:04 AM
03/18/18 11:04 AM
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Joined: Sep 2005
Posts: 620 Deep DEEP SOUTH
LAD 524
OP
mopar
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OP
mopar
Joined: Sep 2005
Posts: 620
Deep DEEP SOUTH
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I've been doing some tuning on the Pro Systems 1200 Dom on my 572 Hemi. I have analog dual wideband gauges, one in each collector. Both read almost identically bank to bank when warmed up.
I have it close to where want it atm, with idle in the mid 15s warmed up (runs awesome/clean with low load) and at cruise in the mid to hi 14s. The engine runs beautifully, no surging at cruise, off idle tip in is great. Idle is at 1100 rpm in gear, with just a small square showing on both PRI and SEC transfer slots thanks to the locked out timing and the 112LSA.
The car has a full exhaust 3.5" into 3" after the X pipe and over the rear end. I'm running NGK BP6ES plugs - they look really good; the whole base ring of the plug has a full circle of dark brown colour. The timing is locked out at 32, the timing mark on the ground strap is pretty close to where it needs to be and the plugs are pretty close to where I want them on the street. Fuel is pump gas 98 here.
Punching the throttle puts me into the hi 10s; mid 11s after the initial pump shot wears off.
Engine made great power on the dyno with open headers/more jet/same PV so I'm a little on the leaner side of the tune now that its on the street with a full exhaust/mufflers etc.
Current tune is as follows :
Idle AB: 57 Inter air: 77 Inter fuel: 40 Main air: 37 PRI jet: 88 SEC jet: 92 PV: 5.5 PV feed/jet: 86
I'd like to dial WOT a bit better and of course I'm thinking on possibly leaning out the PCVR jets in the metering block a tad. The question is by how much and how will it affect the mains ?
I have'nt touched the Intermediate fuel jets in the metering block as the carb has responded well to the IAB/jetting changes to get me to this point.
Any thoughts as to the best way to get the WOT number into line ?
Thanx !
Last edited by LAD 524; 03/18/18 11:58 PM.
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Re: Tuning on a 3 circuit 1250 Dom.....carb guys ?
[Re: J_BODY]
#2468278
03/18/18 08:37 PM
03/18/18 08:37 PM
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Joined: Feb 2005
Posts: 20,172 PA.
pittsburghracer
"Little"John
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"Little"John
Joined: Feb 2005
Posts: 20,172
PA.
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I'd convert it to a 2 in a second and have it cleaner n meaner yet.......They ALL respond better and are faster as long as the carbs big enuff for the application and my baby 470 BB wears a billet 1250+ and has the flattest fuel curve I've ever seen..........Smaller carb on bigger motor has a tendency to go rich because of the Hugh draw of air that the bigger motor demands............. interesting that when the DA is below 800 I can't throw enough jet at my carb without it going into lean misfire. I considered the 4825 on my "small block" (439) fairly under carbed. Also running power valves. With 84 jets in Vegas I recorded afr on the left bank in the high 11's. At Famoso with 98 square I was at 14.6 with a DA of 800+. Sunday morning it was -800 when we set up, and around 100-200 when I made the pass which resulted in a lean misfire. I used my power valves for fishing sinkers 40 years ago and haven’t used one since
1970 Duster Edelbrock headed 408 5.984@112.52 422 Indy headed small block 5.982@112.56 mph 9.42@138.27
Livin and lovin life one day at a time
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Re: Tuning on a 3 circuit 1250 Dom.....carb guys ?
[Re: LAD 524]
#2468310
03/18/18 09:23 PM
03/18/18 09:23 PM
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Joined: Sep 2005
Posts: 620 Deep DEEP SOUTH
LAD 524
OP
mopar
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OP
mopar
Joined: Sep 2005
Posts: 620
Deep DEEP SOUTH
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Cab my thought was this initially ie: pull some PRI and SEC jetting but wont that only affect the mains? Yes AFRs are nothing but a guide - Im giving it what it likes ie in the 14s-15s at idle and cruise and still no surge and runs super clean. I could prob go a tad leaner as well but decided to leave it there for idle, transition and cruise. PV tuning is for WOT right? My understanding was that if you have an 88 PRI jet, then the PV jets n the metering block should be in the order of around half of what your PRI jet is, in order to provide approx 25% of the extra fuel at WOT. As mine are at 86 now, that would mean that they are way too big and allowing too much fuel at WOT which would explain the readings. That, plus the Intermediate circuit (which would still add fuel at WOT) would explain my numbers at that point in the curve ? What do you think? Im about to grab some 6-32 and 8-2 brass blanks
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Re: Tuning on a 3 circuit 1250 Dom.....carb guys ?
[Re: J_BODY]
#2468336
03/18/18 10:24 PM
03/18/18 10:24 PM
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Joined: Jul 2004
Posts: 19,317 State of confusion
Thumperdart
I Live Here
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I Live Here
Joined: Jul 2004
Posts: 19,317
State of confusion
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I'd convert it to a 2 in a second and have it cleaner n meaner yet.......They ALL respond better and are faster as long as the carbs big enuff for the application and my baby 470 BB wears a billet 1250+ and has the flattest fuel curve I've ever seen..........Smaller carb on bigger motor has a tendency to go rich because of the Hugh draw of air that the bigger motor demands............. interesting that when the DA is below 800 I can't throw enough jet at my carb without it going into lean misfire. I considered the 4825 on my "small block" (439) fairly under carbed. Also running power valves. With 84 jets in Vegas I recorded afr on the left bank in the high 11's. At Famoso with 98 square I was at 14.6 with a DA of 800+. Sunday morning it was -800 when we set up, and around 100-200 when I made the pass which resulted in a lean misfire. Where's the misfire at rpm wise and if the problem is down low then what idle bleeds, ifr's and where are the mixture screws set at from seated if up top what hi bleeds .............
72 Dart 470 n/a BB stroker street car `THUMPER`...Check me out on FB Dominic Thumper for videos and lots of carb pics......760-900-3895.....
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Re: Tuning on a 3 circuit 1250 Dom.....carb guys ?
[Re: LAD 524]
#2468373
03/18/18 11:27 PM
03/18/18 11:27 PM
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Joined: Jan 2003
Posts: 8,022 Tulsa OK
Bad340fish
master
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master
Joined: Jan 2003
Posts: 8,022
Tulsa OK
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if it were me I would adjust the PVCR down to get your wide open air fuel where you want it. If you are happy with everything else that is. When I did my 830 I was happy with the wide open AFR so I took the area of all the fuel flow orifices and wrote it down, I then took main jet and IFR out of it until I was happy with low rpm and cruise AFR, then I stuck that flow area back in via the power valve channel. I was happy with the results it was just a beat down to get there.
68 Barracuda Formula S 340
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Re: Tuning on a 3 circuit 1250 Dom.....carb guys ?
[Re: LAD 524]
#2468380
03/18/18 11:44 PM
03/18/18 11:44 PM
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Joined: Dec 2014
Posts: 304 Florida
Mark Whitener
enthusiast
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enthusiast
Joined: Dec 2014
Posts: 304
Florida
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The header says 1250, the first line says 1200, which is it? A PS 1200 is an 1150, not a 1250.
Mark Whitener [url=www.racingfuelsystems.com[/url]
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Re: Tuning on a 3 circuit 1250 Dom.....carb guys ?
[Re: LAD 524]
#2468435
03/19/18 01:50 AM
03/19/18 01:50 AM
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Joined: Aug 2003
Posts: 43,157 Bend,OR USA
Cab_Burge
I Win
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I Win
Joined: Aug 2003
Posts: 43,157
Bend,OR USA
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Last edited by Cab_Burge; 03/19/18 01:51 AM.
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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