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G'day. I'm helping out with a FSAE car this year, and I'm hoping to get some advice for the team.
The engine in question is a single cylinder 450cc, being run by a ViPEC i88. We can reliably get the engine started and running on regular 98octane petrol, without the turbo system attached. In this configuration, the throttlebody is close to the intake valve (as per the OEM setup) and the engine will spring to life pretty easily, hot or cold.
The aim is to turbocharge the engine. FSAE rules denote that if a turbocharged engine runs an intercooler, the throttlebody must be positioned _before_ the intercooler. With this system installed, we cannot get the engine to start from cold. If we remove the turbo setup, start the engine and get it to normal operating temp, we can then reinstall the turbo system and get it started... But this is obviously not ideal!
The problem is made even worse by the FSAE rules requiring us to run E85 (beneficial for power and tuning of course, but harder to start on).
To our senses, it seems like the large added volume of space after the throttle, before the intake valve (turbo piping and intercooler) is slowing the airflow to the intake valve too much under starter cranking, and it wont catch and fire.
The starter spins the motor at around 450rpm.
Can anyone help us out with any ideas (tuning related, or other!) to get the beast fired up reliably with the turbo system installed?
I'm planning on doing some testing shortly as to whether we will actually require an intercooler. As the chosen turbo will be perfectly in its efficiency range, and E85 will remove a lot of heat from the intake charge, hopefully we will find the intercooler isn't necessary. Then we can have the throttle closer to the intake valve and starting will be easier....
Or it's possible we're missing something really simple, and we're about to have a face-palm moment when someone points it out... Thoughts?
Do you have a MAP sensor in the inlet tract near the inlet valves? what does it read when you are cranking the engine with the two different inlet systems mounted? What about Lambda?
I haven't done much on the ViPEC units, do you have to model the VE of the inlet manifold to accommodate the larger mass of air with the turbo setup?
Throttle BEFORE the intercooler?!. LOL!... you can say goodbye to throttle-response... thats for sure!.
"BlackRex" you definitely wouldn't want any kind of sensor close to the inlet valve(s). This would cause unwanted turbulence/pressure-drop.
Where is the injector located?
My first question would be what are you using as a load input for the fuel table?
As BlackRex mentions, it would be interesting to know the relative manifold pressure at crank between both systems. I'd also try logging the injector pulse width during cranking and startup without the turbo fitted and then with it fitted. This may give a clearer picture of what's going on.
Thankyou all for your input. I'll assemble all the requested info and post it up here during out next test run session.
Well if you think about it... the smaller volume (without intercooler) means there will be a higher vacuum on the intake stroke... than would be with larger volume (with intercooler). Depending on the difference in volume.... i would say the pressure (vacuum) difference between the two setups would be quite substantial. Higher vacuum => higher pressure differential across the injector => more fuel delivered. Not to mention the greater turbulence and, thus, greater fuel atomization and charge-homogenization.
... any news? Was i right? ^_^