What boost pressure should I set the WI to come on at

[vaughany]

I drive a MKIV Supra TT, I havea system 1s fitted which is preset to come on at 10psi. My car runs a maximum of 1.2bar (19PSI) Should I change the Boost Pressure switch so the water injection comes on closer to max boost. If so what would you recommend, about 14psi? Is running the water injection at 10psi a waste of time?

Cheers

Vaughany

[Richard L]

If you are not experience knock or high intake charge temperatures, set the WI to come in at 14 psi is not a bad idea. I have to assume that at approximately 14psi boost, the rpm will be quite close to the maximum torque area.

[vaughany]

Hi Richard

My car boosts upto 19psi and produces a max torque of 340lb of torque at the hubs at 5500rpm. At 14 psi my car is producing about 290lb of torque at the hubs at 4500rpm.

Does this help you any regarding what boost pressure I should set. what are the negative effects if the WI comes on to soon?

Thanks

Vaughany

[Richard L]

Hi Richard

My car boosts upto 19psi and produces a max torque of 340lb of torque at the hubs at 5500rpm. At 14 psi my car is producing about 290lb of torque at the hubs at 4500rpm.

Does this help you any regarding what boost pressure I should set. what are the negative effects if the WI comes on to soon?

Thanks

Vaughany

I think at 14psi is a good place to start, the engine is approaching maximum torque at 5500 where detomation is most likely. During that period, there are plenty of heat to evaporate water to add to the overall effective compression ratio.

[Shaker666]

Boost is generally not a good parameter to use for triggering the WI. I would consider using the ACT (air charge temperature), post-blower, reading instead. ACT is directly responsible for detonation. In my experience (and this becomes engine specific based on combustion chamber shape and engine assembly measurements), an ACT of over 200* F is starting to get borderline. Additionally, note that a centrifugal type of blower at 15 psi may produce ACTs of 180* F whereas a Roots style blower at 15 psi may produce ACTs of up to 280* F, simply because of the inherent difference in efficiencies of the blower types.

[rarson]

My question with that though is the response time of a temperature sensor. Most often, they are slower to respond than a pressure sensor.

Now this could be offset by lowering the activation point though, since we know that if the temperature is at a certain point and rising, and we are still creating the same boost (or increasing), temperature will probably continue to go up.

I am curious how a pre-turbo system would affect the effectiveness of this method of triggering.