Quote:
Originally Posted by DWR
Agree the pressure ratio is the first order of business, for each individual turbo. The higher horsepower guys (obviously you) have another problem and that is the x-axis.
Let's do a simple calculation with some conservative asumptions. Do you know the AFR at these full load rpm points? Smoke limit on the best of injection systems seems to be 16:1. I would use 18:1 to maximize the conversion of fuel to power. Let's take a middle 17:1. To get a targeted 350hp we'll need fuel to the tune of 0.38 lb/HP-hr. So, 350 X 0.38/60 X 17 = 38 lbs/min. Hmm, outside of the map ... this is why every tuner's torque curve drops off at higher rpms. For what it is worth, Meth/H2O injection will allow you to cheat this whole thing, by suppressing smoke and EGT. EGT is easy to understand. Lowering total AFR with Meth/H20 is much more complicated.
Do have a KP39 compressor map? That little bugger has a max speed line @ 200K, but a lower max pressure ratio. This image combined with the previous should help. To get the system pressure ratio at any point just multiple the two together. Looks like a pressure ratio of 3.2 is very safe at 2,500rpm, as long as you are using the 2 turbos to do it.
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Yes, I have AFR and I'm adding large amounts of H2O/methanol + extra fuel in a progressive fashion after a specific rpm. The base map seems to target ~16:1. Stoichiometry of methanol is significantly lower than diesel. My AFR's get lower than 16:1 in the upper rpm range with ~800 ml/min of 50/50 mix. The H2O portion helps balance the EGT's at these high hp levels.
I haven't seen the KP39 copressor map, but I'm at lower boost psi at the rpm's where it's being primarily used. Hardly above stock levels... It was the big turbo I was mostly concerned with.
In the SCR mod thread I linked some calculators for calculating air flow amounts. The only point I think I may be just off the K26 map based on the analog gauge is at ~3900 rpm. But it's not substantially off the map... But this is also not accounting for the psi drop in the intercooler ... but the measurement is also after the H2O/methanol injectors which are adding dramatic levels of cooling and extra pressure from the extra injected mass...
I should really be measuring the boost directly after the turbo compressor, but didn't think it was worth the extra fussing around to find a good way to tap into that area.