Paul_G
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My car is a 4000# 72 Charger with a mild built 360, about 250 HP, 330 FT#, at the wheels.
I have been fiddling with two different carbs, both Holleys, one a 670 Street Avenger, the other a 750 with vacuum secondaries. The engine likes to idle pretty rich in the mid to upper 12 AFR range. Both carbs will set up and idle well in that range, but any leaner and the engine idles rough and just doesnt like it. But then they differ.
I can tune the 670 to run very well, idles well in the upper 12 to low 13 AFR range which the engine likes, cruises nicely in the upper 14 AFR to mid 15 AFR range which gives good economy. It's easy to drive and runs pretty well. Will run full throttle in the mid 12 AFR range, pulls hard and and just a nice carb. But it just doesnt make the power the 750 will make at any point in the range. Just barely will crack the tires loose from a stop.
The 750,
when tuned for performance it is much better performer than the 670. It will crack the tires loose from a stop easily, pull steadily to 5000 RPM and about 120 MPH in overdrive. The car is fun to drive with this carb.
This carb idles in the mid 12 AFR range but has stinky exhaust, any leaner and it stumbles, shakes and just doesnt like it.
I have tried to tune some economy in to the 750 since it is a better performer. I have read that when cruising at a steady speed the carb is actually running on the idle and in to the transition circuit. In an effort to lean out the cruise AFR's, I tried restricting the idle feed circuits with small wire. It really didnt like it, stumbles, and cruises rough. It cruises well in the high 12 to low 13 AFR range, but gas gas mileage is terrible.
WOT it runs in the mid 12 AFR range. I have tried to tune in some economy many different ways. Jet changes wont do it, jet sizes have to be set for WOT performance along with the PVCR. I have been using small wire dropped in the PVCR along with primary jetting to get the WOT AFR in the mid 12 range where it pulls the hardest, and at the same time get it to stay in the mid 13 AFR range during mild acceleration on the street, the range where primary jets are in play. Thats where primary jetting and tuning the PVCR have to work together.
I have just given up trying to get the bast of both worlds from either of these carbs. The 750 is tuned for performance right now and does that very well. The 670 runs really nice and smooth with good economy, I just dont expect any performance from it.
Which brings up fuel injection. Can the new self learn units from Fitech and Holley do both? Can they get good economy like the 670, and give the great performance like the 750 does?
I have been fiddling with two different carbs, both Holleys, one a 670 Street Avenger, the other a 750 with vacuum secondaries. The engine likes to idle pretty rich in the mid to upper 12 AFR range. Both carbs will set up and idle well in that range, but any leaner and the engine idles rough and just doesnt like it. But then they differ.
I can tune the 670 to run very well, idles well in the upper 12 to low 13 AFR range which the engine likes, cruises nicely in the upper 14 AFR to mid 15 AFR range which gives good economy. It's easy to drive and runs pretty well. Will run full throttle in the mid 12 AFR range, pulls hard and and just a nice carb. But it just doesnt make the power the 750 will make at any point in the range. Just barely will crack the tires loose from a stop.
The 750,
when tuned for performance it is much better performer than the 670. It will crack the tires loose from a stop easily, pull steadily to 5000 RPM and about 120 MPH in overdrive. The car is fun to drive with this carb.
This carb idles in the mid 12 AFR range but has stinky exhaust, any leaner and it stumbles, shakes and just doesnt like it.
I have tried to tune some economy in to the 750 since it is a better performer. I have read that when cruising at a steady speed the carb is actually running on the idle and in to the transition circuit. In an effort to lean out the cruise AFR's, I tried restricting the idle feed circuits with small wire. It really didnt like it, stumbles, and cruises rough. It cruises well in the high 12 to low 13 AFR range, but gas gas mileage is terrible.
WOT it runs in the mid 12 AFR range. I have tried to tune in some economy many different ways. Jet changes wont do it, jet sizes have to be set for WOT performance along with the PVCR. I have been using small wire dropped in the PVCR along with primary jetting to get the WOT AFR in the mid 12 range where it pulls the hardest, and at the same time get it to stay in the mid 13 AFR range during mild acceleration on the street, the range where primary jets are in play. Thats where primary jetting and tuning the PVCR have to work together.
I have just given up trying to get the bast of both worlds from either of these carbs. The 750 is tuned for performance right now and does that very well. The 670 runs really nice and smooth with good economy, I just dont expect any performance from it.
Which brings up fuel injection. Can the new self learn units from Fitech and Holley do both? Can they get good economy like the 670, and give the great performance like the 750 does?
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