NUTCSE wrote:You do realise thats a 1400hp turbo, right???
Yeah mate fully aware..
Yes its a maximum 1400hp (or according to the map in the least of its efficiency range at 130-140 lb/min)
But I need 110 lb/min flow at a specific PR as efficient as possible.. 2.2 PR absolute (roughly 18psi gauge) but this turbo sees atmospheric pressure, the other does not..
Here is an extract of a response on ns.com of why these turbos.. "So why a 4718 and a T67-25G together?
I decided that with all the work that went into the motor, a thousand hp was likely to be achievable, so I used 1050 as the target hp..
Using a number of formulas, and knowing the variables in my motor such as Volumetric Efficiency, RPM I wanted to use, Displacement of the motor etc, I found out what my estimated normally aspirated cfm flow is.
I used this figure to calculate the flow and pressure ratio required to reach the 1050hp goal. I must stress for my motor only, other motors will be vastly different and as you move up in displacement requirements change..
1050hp @ 9200rpm = 110 lb/flow @ 5.5 PR (all in absolute pressure)- No big single turbo would do this efficiently, and if it could the powerband would be so insular that it would be useless anywhere but on a dyno or on a drag strip with a 6000rpm stalled up auto lol..
Remember this is peak, I also calcualted this in 2500rpm increments using a 10000rpm limit for all subsequent calculations.. and plotted oncompressor maps (and to a certain point turbine maps) accordingly..
So enter the compound turbo setup, I knew that I needed the 110 lb flow, but at what PR? Logic suggests and research backed it up, that with a compound setup you want to use each turbo in the best efficiency possible, sharing the pressure ratio not to far away from equally but in a high/low relationship. So I played around with multiplying the pressure ratio numbers until a came up with what I think is a good relationship. 2.2PR on the low and 2.5PR on the high...
The low pressure turbo was fairly straight forward, I needed a turbo that could produce 110 lb/min flow @ 2.2 PR, with relatively high efficiency (peak). I looked at several turbos and settled on the 4718, plotted out it fitted the requirement with 74-76% efficiency..
The high pressure turbo was a little more difficult to figure out, as I needed to claculate the mass airflow correction between the output of the low pressure turbo and the output of the high pressure turbo. Note that the density ratio of each turbocharger stays the same relative to the PR.
Running the claculations resulted in requiring a turbocharger that could produce 55 lb/min flow @ 2.5PR. Greddy do not provide compressor maps and I thought I may have to sell off the T67 for a different turbo, so I measured the specs of the wheels (both inducer and exducer on both wheels) and looked up the garrett site to find a turbocharger that would be closeish to the Greddy. Out of pure luck, the greddy turbo seemed to fit the requirement, but the 10cm housing was too big for a quicker spool and I opted for an 8cm housing.
As far as heat goes, as each turbo is highly efficient and with the correct use of intercooling, the egt's should not be any higher."
I haven't worked out wastegating yet, for the exhaust manifold, but at this stage two 38mm gates (primarily to reduce backpressure around the 8cm housing when the 4718 is ramping up to its nominated pr) is looking like the winner out of a couple of configurations..
The 4718 will be gated with a 50mm gate