Starting with square carb, tuning for boost.

[Paul_G]

A little history, When I got this 69 Road Runner it had a hurt 528 Hemi in it with the an F1 Procharger, and using an antique water meth system. It had a horrible tune on it, too much timing and way to lean. No wonder the Hemi was damaged. Three cylinders scored, broken rings, compression under 80 pounds in those three. The Hemi is out for rebuild. I have a low compression 440 refreshed, opened ring gap, and running very nicely.

Time to dial in the tune with the Procharger and water meth system. I am using the custom built Holley 950 DP blow through carb that came with the car, it is fully rebuilt. Using a standard PV in the front with boost referenced PV in back. Timing set at 15° base with total at 26°, all in by 1500 RPM. I put a 5" pulley on the Procharger. The most boost I have seen from it is 5 to 8 psi, and it does not start to make measurable boost till 3500 RPM and above. It might go up a bit more with more rpm, but I have not gone there yet. The meth is set to start spraying at 3 to 4psi. I am using Boost Juice.

I have the carb set up square using a combination of jets and PVCR sizing. This is where I may need some guidance. This is a street cruiser convertible. It wont see any track time. I still want a very safe tune for full throttle runs even on the street. I am trying to use smaller jets in the primary side with more fuel coming from the primary PVCR. This is for economy. Secondary side has larger jets with a smaller PVCR than the primary side to keep both side equal. I plan to keep the total amount of fuel the same, primary and secondary sides, keeping it square.

Using the wideband A/F ratio gauge I want to have my street and highway cruise AFR's in the 14.5 to 15 range for economy by using smaller main jets and more fuel from the primary PV. On street acceleration when in the main jets and main PV is open, but before the secondary's come in, I am shooting for AFR's in low to mid 12 range, boost not even coming in yet. When at full throttle, secondary's open, and RPM climbing to 5000 is 11's a good place to be?

 

[pnora]

I can not offer any advice on set up as I have never owned a Procharger set up. The one thing I will recommend is reading about the water and meth. From what I have read it is a disaster waiting to happen. Seems like when the meth system changes or fails the rest of your tune will be way out of wack. Hence engine failures. My advice would be to ditch the water meth and tune from there. For a street car you will be better off. If you enjoy failures and an empty wallet carry on.

 

[Paul_G]

I can not offer any advice on set up as I have never owned a Procharger set up. The one thing I will recommend is reading about the water and meth. From what I have read it is a disaster waiting to happen. Seems like when the meth system changes or fails the rest of your tune will be way out of wack. Hence engine failures. My advice would be to ditch the water meth and tune from there. For a street car you will be better off. If you enjoy failures and an empty wallet carry on.

I believe that is what killed the Hemi that was in the car. I am tuning as if there was no meth. When the meth comes in it will cool the air charge and add some fuel enrichment. If my AFR goes richer with the meth on it should not be a problem. I am tuning for a safe system, not tuning for max power.

When the Hemi comes back and gets back together I am switching to EFI and a Snow water Meth system. They each have provisions, fail safes, if the water/meth system runs dry or just fails it will pull timing and warn the driver.

 

[pnora]

I believe that is what killed the Hemi that was in the car. I am tuning as if there was no meth. When the meth comes in it will cool the air charge and add some fuel enrichment. If my AFR goes richer with the meth on it should not be a problem. I am tuning for a safe system, not tuning for max power.

When the Hemi comes back and gets back together I am switching to EFI and a Snow water Meth system. They each have provisions, fail safes, if the water/meth system runs dry or just fails it will pull timing and warn the driver.

Rich mixture can be just as bad if not worse than a lean mixture.

 

[furious70]

at only 5-8psi I wouldn't think meth would be needed. Water is helpful. I run water on my turbocharged 383 with EFI and no intercooler. My tune is safe either way, but the water drops the air inlet temps 40* and it just makes more power that way. Technically I'm sure I could run some more timing and a little leaner with the water on but I'm not looking to be on the razor's edge for a street car.

Your approach on the carb setup is sound enough, I'd only suggest that if you think you need a BRPV in the back, why wouldn't you need one in the front? They are equally susceptible to closing under boost.

I have not had success with wedges running that lean at cruise without some lean surging or poor transition into the power circuit. I have my WOT at 11.5:1 but that's a wedge. Tip in of mid 12's sounds reasonable if it feels good.