4.8l 13.5 PSI: Tuning, IAT/Intercooler, 1/4mile time question
10-24-2015, 08:52 PM
#33
Well, the converter slip calculator we used last night was way off, and I do not believe its slipping 35%. I did some analysis taking RPM and MPH from the HPTuners log from last nights pass, and calculating converter slip. My formula for converter slips comes out to be:
Slip = - (mph x 60/rpm x Trans Ratio x Rear Ratio x 12/(pi x Tire Size) x (5280/3600) - 1)
It would've been much easier to calculate slip from input/output trans speeds but I didn't log that. Obviously tire growth isn't factored in, as well as other factors probably, but its close.
My slip values come out slightly smaller than the TCI Calculator (which is reported to be fairly accurate) Racing Calculators - TCI® Auto.
1st Gear Graph:
-I'm not sure how valuable looking at the 1st Gear Slip percentages is.
-The truck dead hooked.
-After thinking about this pass last night, I went back and looked at the logs. I had increased the 2 step to 3600 rpm prior to my last pass. Sure enough, I did NOT turn on the 2 step for this pass! I staged, rev'd the engine in neutral to get greater brake pressure, threw it back in gear and went WOT. I monitored the boost gauge and left at 12psi! Looking at the logs, I left at 4400 RPM! I didn't mean to do this, but that's what happened. From what I was told, I should have a 3600 stall... Of note, my 60ft time did not improve leaving on such high boost and rpm, compared to 3400rpm and and 8psi on prior launches.
2nd Gear Graph:
-After the RPMs and MPH increased after the 1-2 shift, my calculations put converter slip at a max of 21% (TCI Calculator stated 26.6%).
-As RPMs increased and I got away from peak torque, slip decreased to 6%.
2nd Gear Locked Converter Graph:
-Tried to tune the truck to lock in 2nd gear WOT, but it didn't seem to work so we manually locked the converter with the VCM control and then WOT. Calculated slippage stayed between .28-2.1% throughout the rpm range pictured.
Thoughts?
Slip = - (mph x 60/rpm x Trans Ratio x Rear Ratio x 12/(pi x Tire Size) x (5280/3600) - 1)
It would've been much easier to calculate slip from input/output trans speeds but I didn't log that. Obviously tire growth isn't factored in, as well as other factors probably, but its close.
My slip values come out slightly smaller than the TCI Calculator (which is reported to be fairly accurate) Racing Calculators - TCI® Auto.
1st Gear Graph:
-I'm not sure how valuable looking at the 1st Gear Slip percentages is.
-The truck dead hooked.
-After thinking about this pass last night, I went back and looked at the logs. I had increased the 2 step to 3600 rpm prior to my last pass. Sure enough, I did NOT turn on the 2 step for this pass! I staged, rev'd the engine in neutral to get greater brake pressure, threw it back in gear and went WOT. I monitored the boost gauge and left at 12psi! Looking at the logs, I left at 4400 RPM! I didn't mean to do this, but that's what happened. From what I was told, I should have a 3600 stall... Of note, my 60ft time did not improve leaving on such high boost and rpm, compared to 3400rpm and and 8psi on prior launches.
2nd Gear Graph:
-After the RPMs and MPH increased after the 1-2 shift, my calculations put converter slip at a max of 21% (TCI Calculator stated 26.6%).
-As RPMs increased and I got away from peak torque, slip decreased to 6%.
2nd Gear Locked Converter Graph:
-Tried to tune the truck to lock in 2nd gear WOT, but it didn't seem to work so we manually locked the converter with the VCM control and then WOT. Calculated slippage stayed between .28-2.1% throughout the rpm range pictured.
Thoughts?
Last edited by lycominghunter; 10-24-2015 at 09:00 PM.
10-24-2015, 09:45 PM
#35
GMCtrk, No I am not really getting any time in 3rd due to how high I WAS spinning it. These 3.42s aren't ideal either.
From last nights run, it shifted to 3rd somewhere around the finish line. From those few data points:
-My Calculations say 18% Slip at 5753rpm @ 115mph
-TCI Calculator says 21.8% at 5753 @ 115mph
I guess the way that I calculated it is really "Drivetrain" Slip. I'm not ruling out that maybe there is something wrong with the transmission, however it seems that the "2nd Gear Locked Converter" data above would rule out that 2nd gear was slipping.
I don't have anything to base these slip numbers off of - this is the first truck/car I've built. In some ways, it makes sense. The converter was spec'd to a heavy turbo truck with tall gears. It is loose off the line to get it rolling and tightens up top. Maybe I'm not making enough power yet to get it tightened up through the midrange without locking it. I don't know the first thing about building a converter, but it was also probably built assuming the user would be locking it since it is, in fact, a triple disc.
Who knows, I'm just trying to wrap my head around it. I'll shoot Circle D an email and see if theres anything I'm missing. Maybe a restall is all that's needed. We'll see.
From last nights run, it shifted to 3rd somewhere around the finish line. From those few data points:
-My Calculations say 18% Slip at 5753rpm @ 115mph
-TCI Calculator says 21.8% at 5753 @ 115mph
I guess the way that I calculated it is really "Drivetrain" Slip. I'm not ruling out that maybe there is something wrong with the transmission, however it seems that the "2nd Gear Locked Converter" data above would rule out that 2nd gear was slipping.
I don't have anything to base these slip numbers off of - this is the first truck/car I've built. In some ways, it makes sense. The converter was spec'd to a heavy turbo truck with tall gears. It is loose off the line to get it rolling and tightens up top. Maybe I'm not making enough power yet to get it tightened up through the midrange without locking it. I don't know the first thing about building a converter, but it was also probably built assuming the user would be locking it since it is, in fact, a triple disc.
Who knows, I'm just trying to wrap my head around it. I'll shoot Circle D an email and see if theres anything I'm missing. Maybe a restall is all that's needed. We'll see.
11-02-2015, 01:50 AM
#40
Thing needs the stock intake on it and some meth injection or E85 and 15~16 deg of timing to start with. The triple 12 cam will rev to 6800 RPM in a 4.8L long as the springs are set up right. Single pac's will need a .030''~.-45'' ship to reach that rpm, BTR duals should be fine at std height. If you want to make power on low boost like 13 psi the thing is going to need some timing and a leaner AFR. That turbo is pretty small on the exh side but still should reach goal or faster if things are right. The reason the converter slip is so high is because there is not enough RPM there for it to couple with that gear ratio and mph. Get mph up around 130+ with more power and it should couple a lot better. 