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Time:2018-02-11 14:20Turbochargers information Click:

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Thanks for the feedback, I went back and revisited the garrett boost advisor (shown below), but this time I enabled an intercooler of 70% efficiency (which I am not sure yet what a 70% efficient intercooler means). When I was playing around earlier, it obviously made a big difference.

Also, the BSFC numbers I seem to have used look like they are very optimistic. So I should dial that up as well (using info from ... g_bsfc.htm as a reference). The updated inputs and outputs are below.

It's interesting you have come across this post. I've actually read through your information already as it is very relevant for what I am doing, and you documented it very very well. If you look on the earlier Aulro link you will see that I was even using your excel sheet

Regarding the squirrel calculator, I'd say the only place it accounts for the intercooler is in the pressure drop of it, and it leaves it up to the user to input the expected post intercooler temperatures.

I plan to use two top mounted intercoolers which I will weld onto either side of the standard rover plenum and have each turbo feeding each side. I'll then add thermal insulators to the plenum connections and also remove the coolant circuit from making contact with the plenum to make it as cool as possible.

Anyway, back to calculations:

Below are the Inputs:
Power target: 300hp
Engine Displacement: 241cu.in
Twin Turbo
Air/Fuel Ratio: 15.5:1
BSFC: 0.45
Valves per cylinder: 2
Volumetric Efficiency: 0.80
Mid Range RPM: 3500
Peak Power RPM: 5000
Type of intercooler used: Air/Air
Pressure Drop: 1psi
intercooler effectiveness: 70%
Pressure: 14.7
Air Temp: 21

For the above inputs I'm given the following results (Mid Range; Max Power):
Power: 209hp ; 299hp
Boost Pressure: 11.75psi; 11.75psi
Pressure Ratio: 1.87; 1.87
Intake Manifold Temperature: 112degF; 112 degF
Corrected Air Flow: 12.23lb/min; 17.48lb/min
Torque at Crank: 314lb/ft; 314lb/ft

The pressures are still coming out to be very high...Part of what is killing me here (and I didn't realise before) is that LPG is working against me here. The reasons it works against me is:

LPG uses more volume than petrol - Reduces Volumetric Efficiency, i read somewhere that it is around 4%! which I haven't shown in this calculation.
Air to Fuel Ratio - LPG is about 15.5:1 (Petrol is about 14.7:1). Since the calculation of actual flow rate is HP x A/F x BSFC/60 it is easy to see that for LPG you need more air. However, 15.5/14.7 = 1.05 which is pretty negligible.

So perhaps I'm using the wrong BSFC, but I don't think the Rover v8 engines are particularly efficient. Looking at that BSFC link I gave earlier it says:
4-stroke (high compression, closed loop) - 0.35 @ Peak Torque
4-stroke (turbocharged, closed loop) - 0.45 @ Peak Torque (this is the value I used)

Running the calculator again with a BSFC of 0.35 the Boost adviser gives 5.25psi. Maybe a turbo charged Rover v8 runs somewhere around 0.40 BSFC (which gives 8.5psi)?? It's all guess work now

Anyway, the reality of the matter is that it doesn't change the turbo selection.

One thing that is a concern for me however, is that I want to keep the engine at 10.5:1 CR. If I boost it to 8psi, that means the effective CR is 10.5 x 1.65 = 17.3:1 CR. As far as I know, LPG can only really go as far as 15:1. Is this assessment correct or have I missed something when calculating the effective CR?

Thanks in advance guys

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