Turbo Guru's! Air Fuel Ratio #'s
#515801
11/04/09 11:28 AM
11/04/09 11:28 AM
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2cudabuck
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Thanks to all you folks' help I got my trans in and ready to roll last night. Now, I have a 318 with a single Garret turbo in a draw thru setup, with a Holley Boost referenced 750 on top. I have a digital ignition with boost retard, and a digitial wideband a/f gauge. All that being said, what should I shoot for for a baseline on my setup? I will be running a max of 9 lbs of boost. So, how much timing retard should I set up per pound and from what initial number?, and what a/f number should I shoot for at idle and what number at ____ RPM? Thanks guys, just don't want to shell my goods first fire!
Buck
67 273 Dart GT
69 RT 440 Charger (SWEET!)
70 318 Cuda
74 Cuda Packin a 426 roller Hemi
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Re: Turbo Guru's! Air Fuel Ratio #'s
[Re: 2cudabuck]
#515802
11/04/09 01:16 PM
11/04/09 01:16 PM
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2cudabuck
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No boosted guys surfin today?!?!
Buck
67 273 Dart GT
69 RT 440 Charger (SWEET!)
70 318 Cuda
74 Cuda Packin a 426 roller Hemi
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Re: Turbo Guru's! Air Fuel Ratio #'s
[Re: Sub95]
#515804
11/04/09 02:19 PM
11/04/09 02:19 PM
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2cudabuck
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Bone stock 1970 318 with all new consumables. Top shelf, studs, rod bolts, head gaskets etc. Stock manifolds modified with flanges on top to turbo loop in front of motor. Pretty stock 70 Cuda, manual brakes. Your right, never thought about an EGT. So 12 should be considered my low A/F ratio threshold eh?
Buck
67 273 Dart GT
69 RT 440 Charger (SWEET!)
70 318 Cuda
74 Cuda Packin a 426 roller Hemi
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Re: Turbo Guru's! Air Fuel Ratio #'s
[Re: Sub95]
#515806
11/04/09 03:52 PM
11/04/09 03:52 PM
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2cudabuck
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8.7 Comp. YOur talking 12 to 1 A/F right? Any insight into how much timing to retard per pound of boost? I think I have it at 12 initial and 36 at 2500 right now (unboosted).
Buck
67 273 Dart GT
69 RT 440 Charger (SWEET!)
70 318 Cuda
74 Cuda Packin a 426 roller Hemi
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Re: Turbo Guru's! Air Fuel Ratio #'s
[Re: 2cudabuck]
#515807
11/04/09 04:11 PM
11/04/09 04:11 PM
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Posts: 28,067 Irving, TX
feets
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Bring it back 2 degrees per pound of boost and adjust it up from there. Detonation will scatter the pistons so don't go crazy. 12:1 is best for safe power. Keep the carb to intake tract as short as possible. Be VERY careful with every connection and running ANY kind of boost gauge. You will be pushing a fat fuel/air mix through the gauge. If you get a vacuum leak (boost leak) then you will be blowing an explosive fuel/air mix through the leak. You don't need that fogging the exhaust manifold. Car go boom. Remove any worm gear style hose clamps that will see boost. Replace them with higher strength T-bolt hose clamps. A stock style 318 should live without a problem under that boost level. I'd think you could see around 300 rwhp max. Probably closer to 250. Either way, it'll wake up the car and make for some fun.
We are brothers and sisters doing time on the planet for better or worse. I'll take the better, if you don't mind. - Stu Harmon
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Re: Turbo Guru's! Air Fuel Ratio #'s
[Re: DaytonaTurbo]
#515809
11/04/09 04:41 PM
11/04/09 04:41 PM
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2cudabuck
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Thanks guys, great tip on the clamps, one of those things you wouldn't know except for experience. I am drilling and tapping directly into the under carb (ie boosted) aluminum housing for my boost gauge and also barbed fitting for ignition sensor and carb input. I will thread sealer it up well.
Your right about my goals, up here at altitude, (9000), what was once a fun car just sucks! This is kinda my test platform, once I get the bugs of the turbo system worked out, I am going to build a full tilt 318 and put the system on that. Maybe shoot for 450 hp up here in the mountians.
Buck
67 273 Dart GT
69 RT 440 Charger (SWEET!)
70 318 Cuda
74 Cuda Packin a 426 roller Hemi
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Re: Turbo Guru's! Air Fuel Ratio #'s
[Re: 2cudabuck]
#515811
11/04/09 04:48 PM
11/04/09 04:48 PM
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Joined: Nov 2006
Posts: 2,255 IL
furious70
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I think feets would say that you've just reached the starting line, not the finish line. The real work in making it drivable now begins!
70 Sport Fury 68 Charger 69 Coronet 72 RR
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Re: Turbo Guru's! Air Fuel Ratio #'s
[Re: furious70]
#515812
11/04/09 04:52 PM
11/04/09 04:52 PM
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2cudabuck
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lol, your right for sure!! at least after this weekend though I will be able to turn the key again! But you right, and you set me up perfectly, fella's get ready for me to use up some bandwidth in the next couple weeks buggin you!!!
Buck
67 273 Dart GT
69 RT 440 Charger (SWEET!)
70 318 Cuda
74 Cuda Packin a 426 roller Hemi
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Re: Turbo Guru's! Air Fuel Ratio #'s
[Re: 2cudabuck]
#515813
11/04/09 05:07 PM
11/04/09 05:07 PM
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Joined: Jan 2003
Posts: 28,067 Irving, TX
feets
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Senior Management
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Irving, TX
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Are you kidding? He's running draw through. Even I could tune that in an afternoon with enough time for a run to Hooters. Plop a carb on a turbo and go.
If he was running blow through things would be different. Putting the turbo first really complicates the tune. That's when you have tuning issues. It's also where you start making power.
One thing he will have to watch out for is the altitude. 9000 ft is ugly. Temps tend to drop. When the turbo starts sucking air through that carb on a cold day he'll have to be careful. It can lead to carburetor icing. Hopefully it's relatively dry when cold up there.
We are brothers and sisters doing time on the planet for better or worse. I'll take the better, if you don't mind. - Stu Harmon
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Re: Turbo Guru's! Air Fuel Ratio #'s
[Re: feets]
#515815
11/04/09 05:17 PM
11/04/09 05:17 PM
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Joined: Jan 2003
Posts: 28,067 Irving, TX
feets
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Senior Management
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For the uninitiated: Draw through turbo: Blow through:
We are brothers and sisters doing time on the planet for better or worse. I'll take the better, if you don't mind. - Stu Harmon
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Re: Turbo Guru's! Air Fuel Ratio #'s
[Re: feets]
#515816
11/04/09 05:20 PM
11/04/09 05:20 PM
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2cudabuck
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lmao! Plop on a carb!!! Hopefully a simple system to get my feet wet and build a functioning fun system. Car will stay in the garage when anything close to icing temps are present!!
Buck
67 273 Dart GT
69 RT 440 Charger (SWEET!)
70 318 Cuda
74 Cuda Packin a 426 roller Hemi
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Re: Turbo Guru's! Air Fuel Ratio #'s
[Re: 2cudabuck]
#515817
11/04/09 06:01 PM
11/04/09 06:01 PM
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Posts: 8,180 Detroit, MI
CokeBottleKid
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There's a reason they don't run draw throughs anymore...
Anyhoo, A/F and timing on a boosted engine depends alot on compression ratio, inlet air temp (right before intake valve), cylinder head chamber design, cylinder head material, and of course largely the fuel you run.
As a rule of thumb though low 12s is the absolute lean limit IMO for most home built boosted applications. And that's low boost IMO (6psi or less). Most people run in the high 11s, and when you start really pushing the boost (20+) more like high 10s.
Timing is the same, it's relative to how much boost and how well cool your inlet temps are. Rule of thumb though aim for 25 or less under boost. More boost and less octane means more timing retard.
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