dougg01
09-04-2002, 02:16 PM
Cylinder pressures juicing at low rpm. What is and what isn’t ‘safe’ and why...?
The patient – 355, 11.5:1 comp, solid bottom end, ported LT1 heads, LT4 HOT cam……
The juice – compucar wet plate, 175 shot, Jabobs NMM.
Previously we’d launched at 1,000rpm on our 2,400 stall and 3.42 gears and got a 1.59 60ft with the NMM set to come on at 2,000rpm and reach 100% at 2,500 on a 150shot and 6-deg of retard. I personally felt this was safe. Some have stated this is spraying too low due to the high cylinder pressures generated. I know the potential dangers of spraying at low rpm, but how low is too low and what factors influence this….? I have seen countless folks spraying 150 shots on heads/cam, stock bottom ends from the line (off idle) and having zero known problems. I would just like some help determining the comfort-zone as far as cylinder pressures are concerned when spraying at a particular RPM. I don’t want the pins, bearings, crank, etc reduced to matter that filters past a kitchen strainer.
So, what can I do here...? We have good rods and heavy SRP pistons. I shift at only 6,100rpm so we’re not running the thing to death. Can I start the spray at a lower rpm or should I leave it alone on the 175shot…? I do not like hitting the whole deal at once because of the shock to the drivetrain and chassis. We’ve made several upgrades here, but I do not want to come out trying to set the world on fire. I do, however, want to get this turd moving and run a good number.
Would launching off-idle (700-800rpm) and begin introducing the spray at 1,500rpm be okay or should we try launching at a higher rpm. Say we brake it to 1,500rpm and leave the nitrous coming on at 2,000 and reaching 100% flow at 2,500. I do not want to blow the tires away (11.5 ET Streets) with too much too soon. I prefer to keep the car easy to control, but am experienced enough to ‘drive’ it if I have to though I am fairly confident (no comment…there’s always an element of ‘what if’) the car will stick and go straight.
many thanks....
The patient – 355, 11.5:1 comp, solid bottom end, ported LT1 heads, LT4 HOT cam……
The juice – compucar wet plate, 175 shot, Jabobs NMM.
Previously we’d launched at 1,000rpm on our 2,400 stall and 3.42 gears and got a 1.59 60ft with the NMM set to come on at 2,000rpm and reach 100% at 2,500 on a 150shot and 6-deg of retard. I personally felt this was safe. Some have stated this is spraying too low due to the high cylinder pressures generated. I know the potential dangers of spraying at low rpm, but how low is too low and what factors influence this….? I have seen countless folks spraying 150 shots on heads/cam, stock bottom ends from the line (off idle) and having zero known problems. I would just like some help determining the comfort-zone as far as cylinder pressures are concerned when spraying at a particular RPM. I don’t want the pins, bearings, crank, etc reduced to matter that filters past a kitchen strainer.
So, what can I do here...? We have good rods and heavy SRP pistons. I shift at only 6,100rpm so we’re not running the thing to death. Can I start the spray at a lower rpm or should I leave it alone on the 175shot…? I do not like hitting the whole deal at once because of the shock to the drivetrain and chassis. We’ve made several upgrades here, but I do not want to come out trying to set the world on fire. I do, however, want to get this turd moving and run a good number.
Would launching off-idle (700-800rpm) and begin introducing the spray at 1,500rpm be okay or should we try launching at a higher rpm. Say we brake it to 1,500rpm and leave the nitrous coming on at 2,000 and reaching 100% flow at 2,500. I do not want to blow the tires away (11.5 ET Streets) with too much too soon. I prefer to keep the car easy to control, but am experienced enough to ‘drive’ it if I have to though I am fairly confident (no comment…there’s always an element of ‘what if’) the car will stick and go straight.
many thanks....