Midship Raceabout 1 Seater - Lakester

[bubruins]

Exciting day. Car is home on its own wheels. Race wheels are different sizes and offsets. 

[bubruins]

Long time no update. I have mocked up a couple of triple disc clutches and have a reverse starter ring gear (NASCAR style) that has successfully spun the motor over. I think that's the first Atlas 4200 that's been done with that combo. Now the engine is connected to the rear tires and it would start and run. If it had a fuel system. And an ECU.

Black Friday bought a MS3pro Evo from DIYautotune along with smart coils and several connectors. Not really on track for a 12/31/23 first drive, but progress nonetheless. I've also spent far too much time lately trying to be a cheapskate and learn what I can about turbochargers so I don't have to consult a professional. I'm planning on running e85-e100 fuel. The mass of fuel entering combustion and consequently needing room in the exhaust turbine has been an interesting development. I initially thought that a relatively large compressor was a good idea for Bonneville due to the thinner air. Now I'm thinking an 80/117 compressor 96/88 turbine with a 1.30ar may be the best (affordable) option. Any thoughts on that for a 4.2l on fuel?

For the fuel system I'm leaning towards a cable driven mechanical style pump. Question for the group: Would it be a good idea to run an electric fuel pump to prime a mechanical fuel system, or is it best to keep it simple and only run mechanical?

[Stan Back]

I think there's nothing wrong with an electric "squirter" start-up system.  A push-button thing to get things going.  I've driven a car with one and it helps cranking power to get things going.

[johnneilson]

Huh?
you bought a MS3 pro EFI and want to run a mechanical pump?
OK, it might just be a little easier to run the electric and go.

J

[Dynoroom]

Black Friday bought a MS3pro Evo from DIYautotune along with smart coils and several connectors. Not really on track for a 12/31/23 first drive, but progress nonetheless. I've also spent far too much time lately trying to be a cheapskate and learn what I can about turbochargers so I don't have to consult a professional. I'm planning on running e85-e100 fuel. The mass of fuel entering combustion and consequently needing room in the exhaust turbine has been an interesting development. I initially thought that a relatively large compressor was a good idea for Bonneville due to the thinner air. Now I'm thinking an 80/117 compressor 96/88 turbine with a 1.30ar may be the best (affordable) option. Any thoughts on that for a 4.2l on fuel?

For the fuel system I'm leaning towards a cable driven mechanical style pump. Question for the group: Would it be a good idea to run an electric fuel pump to prime a mechanical fuel system, or is it best to keep it simple and only run mechanical?

Generally speaking, the turbocharger compressor flow rate is directly related to the engine power output. If you want 1,000 hp for example, you need enough air to make it with. The turbine side can have a choking effect if too small, but it is less of a problem compared to the compressor side. Yes, the Pressure Ratio will go up a bit as compared to sea level, so you do need to take that into consideration when designing the system.  

Regarding the fuel pump, Yes, I run a cable driven mechanical fuel pump with an electric primer pump. Works great. Running E-85 or any fuel for that matter in a high horsepower engine a mechanical pump is a good idea. As the flow & pressure demands go up, the amperage goes way up & actual electric pump flow rate drops. Not the best situation for a race engine.

[johnneilson]

Mike,

At what power levels are you referring to that you need a mechanical pump?

Yes, have seen some sketchy electric pump installations, especially the wiring.

John

[Dynoroom]

Mike,

At what power levels are you referring to that you need a mechanical pump?

Yes, have seen some sketchy electric pump installations, especially the wiring.

John

John,
 I'm not saying you can't run an electric fuel pump, what I am saying is a mechanical pump is "better" in an application using E-85 or methanal. Any electric pump will draw more amperage and flow less as the power requirements go up. I've added a chart from RC Engineering showing a very good Bosch electric fuel pump for reference. Many turbocharger racing engine will use a higher static fuel pressure of say 50 or 60 psi. This will be stepped up by whatever boost is used to the engine, so if we have a 60 psi static and 20 lbs boost you are now at 80 psi fuel pressure. using the chart as an example, if you were running a 850 hp engine on gas you might need 75.40 gph of fuel. This same engine on E-85 might need 95.5 gph of fuel. Yes, you can get an electric pump that will do that, it's just easier to use a mechanical pump that the flow rate will rise with engine speed and there will be no power draw on the rest of the electrical system to run the ECU, water pumps, etc. Just my point of view.



 

[bubruins]

One reason I'm favoring mechanical primary fuel pump is for less hassle in regulation. You start having a hard time finding a regulator that'll flow enough fuel to support big power like 1000lph+, but then also deal with an engine at idle or partial throttle. Of course you can turn on 2nd or 3rd electric fuel pumps based on a number of factors, but this adds complexity and room for failure that's potentially devastating.

Edited to say: I have a smaller aeromotive boost referenced regulator I'm planning to run with the mechanical pump. I hope that'll be adequate, but should be able to be tested on the dyno.

[Rex Schimmer]

You need a fuel pump that is oversize to the engine's fuel requirement, i.e. if your engine needs 100 gph to make the desired power you need a fuel pump that is probably at least 1.5 times that flow rate at the max horsepower rpm. The extra 50% is required to provide enough flow through the pressure regulator valve to provide accurate pressure control and pressure change response. All of this of course makes the selection of the pressure control valve very important.

If you use an electric fuel pump or pumps, as the required fuel pressure increases the pump horsepower requirement increases at a faster rate than the pressure, due to increased inefficiency, which means a much higher draw on the battery. If you are looking at substantial boost pressure (40-50 psi) then the required fuel pressure must be increased to maintain a constant differential pressure across the injector which means you may have a fuel pressure requirement in excess of 100-120+ psi. Many electric fuel pumps begin to be very inefficient at these pressures because of internal leakage and may not be able to provide sufficient fuel. A mechanical pump can be sized to prevent this from happening although they also suffer from increased internal leakage due to increased pressure. Good mechanical pumps (Kinsler) are provided with accurate flow vs. pressure curves which helps you to select the correct size pump. Finding this info on most electric pumps is difficult.

Rex