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Kirkham Motorsports

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  • 1 Post By bobcowan
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Old 02-20-2021, 06:27 PM
Lightingrod's Avatar
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Join Date: Jun 2005
Location: Belleville, 15 miles East of St Louis MO, IL
Cobra Make, Engine: Classic 427, I purchased it May 2005, the kit was bought in 1991. I'm not sure when it was completed! Installed GMPP Connect & Cruise 376/525 with T-56 S/M 3.55 gears about 2 years ago! 1/4 miles is with old setup!
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Default I Want to Go To The Strip This Year!

I was looking at the old time slips from 2012, the first and only time I had the Cobra on the strip! I guess it wasn't too shabby! Right off the street it ran 3 12.1s back to back at 112+ mph. This was with SBC 388, 700R-4 and a Junk converter! I have since installed a GMPP Connect & Cruise LS3 525 with T-56 S/M 6spd itís MUCH, much faster. The stock tune is a little off and needs to be refined. I want to get it dyno tuned and then test 125 NOS!

I want to run it THIS year!

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Old 02-21-2021, 07:18 AM
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Cobra Make, Engine: Backdraft, supercharged Coyote
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Pretty consistent!
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Old 02-21-2021, 07:34 AM
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I'd like to run mine to as soon as summer comes. If you've got that much more power now, you'll likely run into traction problems and need some type of street drag tire or dedicated slick. When you start hooking up with that kind of power, 10 second cars are a whole lot more to handle than 12 second cars.
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Old 02-21-2021, 08:55 AM
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Join Date: Jun 2005
Location: Belleville, 15 miles East of St Louis MO, IL
Cobra Make, Engine: Classic 427, I purchased it May 2005, the kit was bought in 1991. I'm not sure when it was completed! Installed GMPP Connect & Cruise 376/525 with T-56 S/M 3.55 gears about 2 years ago! 1/4 miles is with old setup!
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I run 295/55/15 M/T Drag Radials all the time. It's got a bit unruly a couple of times in 1st and 2nd! I think I may have to go to full drag slicks for the NOS! We'll see how she acts when I get it tuned! I know it's running a little rich, I drop the fuel pressure a few pounds, better but NOT right! I still don't like the way the intake tube is run but I can't come up with anything better! :-(
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Old 02-21-2021, 09:38 AM
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Cobra Make, Engine: SPF 2291, Whipple Blown & Injected 4.6
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You want to be careful about using reduced fuel pressure to tune the engine, Al. The reduced fuel pressure will have no effect until the engine is at peak power where the reduced fuel pressure will be inadequate to properly fill the float bowls.

To produce a lean effect the float bowl fuel level will need to fall below the office your main jet which will produce a sharp reduction in fuel at peak engine power. This type of unmanageable stoppage in fuel delivery at peak engine power does permanent damage to pistons and rings. It would be decidedly to your advantage to have the engine tuned under controlled conditions like you can produce on a chassis dyne.

Although some people may use dyne sessions to optimize peak engine power, you are generally better served using them to maintain a consistent air fuel ratio across your engine's operating range. While you can do this with a Wideband oxygen sensor and street tuning it is both not as good nor as repeatable as the steady state environment you can produce on a chassis dyne.

All carbs have changeable jets and power valves. Depending on how closely matched to your engine's appetite the carb is out of the box you might need to change emulsion tubes and air bleeds to match the fuel delivery to the engine's appetite for fuel. When you are finished you will be quite pleased with the engine's driving personality.

Parting thought; Modern pump gas with a 10% ethanol adder does not have a stoichiometric ratio of 14.7, the addition of the ethanol moves the stoic point to 14.08 for a 10% ethanol blend. The actual ethanol in pump fuels can move around a bit so always assume you have at least 10% and tune to the 14.08 Stoich point. Your engine will be safer and run better.

BTW the old saw lean is mean is just foolish. Lean will cost you parts. Properly fueled will produce repeatable, dependable engine performance.


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Last edited by eschaider; 02-21-2021 at 09:56 AM.. Reason: Spelling & Grammar
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Old 02-21-2021, 11:52 AM
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Join Date: Jun 2005
Location: Belleville, 15 miles East of St Louis MO, IL
Cobra Make, Engine: Classic 427, I purchased it May 2005, the kit was bought in 1991. I'm not sure when it was completed! Installed GMPP Connect & Cruise 376/525 with T-56 S/M 3.55 gears about 2 years ago! 1/4 miles is with old setup!
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The LS3 is FI Ed and I only dropped it 3 psi, 60 to 57! All looks good with HP Tuners Scanner! It will be tuned before any trips to the 1/4 mile!

Some good points on carb tuning Ed. Tuned a few myself! Love me some Weber's, used dual 2 and 3 choke Weber's on air cooled VW's and Porsche's. With air cooled engines you BEST have the F/A ratio RIGHT!
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Last edited by Lightingrod; 02-21-2021 at 11:55 AM..
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Old 02-21-2021, 04:50 PM
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Quote:
Originally Posted by Lightingrod View Post
The LS3 is FI Ed and I only dropped it 3 psi, 60 to 57! All looks good with HP Tuners Scanner! It will be tuned before any trips to the 1/4 mile!

Some good points on carb tuning Ed. Tuned a few myself! Love me some Weber's, used dual 2 and 3 choke Weber's on air cooled VW's and Porsche's. With air cooled engines you BEST have the F/A ratio RIGHT!

There are few induction setups with the raw sex appeal of an eight stack Weber setup. It sort of sets the high watermark for cool, sexy and any number of other check marks for the really cool gee-whiz stuff.

My commentary assumed carburetors and not EFI. None-the-less my fuel pressure admonition is still valid but to a much lesser extent. EFI based fuel system pressure is used in the calculation of the mass of fuel that is injected into an engine when the injector is held open for a specific period of time. The ECU can’t control the incoming air mass but it can control the incoming fuel mass by adjusting injector pulse widths. Because the fuel flow through the injector is linked at the hip with fuel mass, the ECU manipulates injector pulse width (the injector on time if you will) to hit the commanded AFR the tuner has programmed into the system based on a number of metrics, one of which is base fuel system pressure.

Once we introduce closed loop operation where the ECU looks to the oxygen sensor for rich / lean guidance, the engine fueling event becomes a private party between the ECU and the O2 sensor. At the private party, the accuracy of the fueling event is determined by the accuracy of the calibration data for things like, base fuel pressure, injector flow rate at 3 BAR differential pressure, fuel specific gravity and a host of other wonky considerations. Not withstanding these other metrics the EFI system will continuously adjust the mixture predicated upon the guidance it receives from the oxygen sensor.

Because things like engine load, which is used throughout the fueling model for calculating the appropriate injector pulse width and therefore fueling shot, can be affected by things like base fuel system pressure I would suggest embracing the GM standard for your engine (60psi) and controlling the fueling through the various fueling tables in the ECU, whether they are Ve based or AFR based.

Just the injector flow characteristics alone can be quite entertaining. In the following link you will find a pdf about an injector attribute most people may hear about but never get to really understand. It impacts low speed and part throttle fueling at the smaller injector pulse widths (read idle and off idle) where you end up frequently driving the car. Quite interesting, possibly helpful for you going forward. Here is the link => Injector High / Low Slope Information

Greg Banish is sort of a modern day Paladin (if you ever saw the old '50/60's series) whose Have Gun will Travel moniker was used to offer help to those who need it but could not get it. Banish's unpublished moniker would probably read similarly but be in reference to EFI calibration. He is a contract calibrator for Ford, GM and Chysler.

Not withstanding his wonky work and skills, he speaks in plain English so mere mortals like us can understand it. He also offers a tuning school for interested aftermarket enthusiasts to whisk away the fog of how to tune with modern EFi systems. At the very least his publications and the few free papers he has published are quite good. I think you'll like them.



Ed
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Last edited by eschaider; 02-22-2021 at 12:00 AM.. Reason: Spelling& Grammar
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