Quote:
Originally Posted by adrian@vishnu
JB4135,
I have actually never had a meth bog quench issue with any Vishnu meth system. This is because I have never used a Vishnu setup with large jets. The car I am running into issues with is a cooling mist setup with large jets. It would probably be fine with normal size jets. I am not knocking this system, as I am sure the gen 1 Vishnu system with the same jets would have the same problem as it works in the same way. It is a limitation of first gen type systems that run full meth flow at low RPM. If you hold it under load on the dyno at 2000 for more than a second or so in the preramp before a dyno run starts to ramp to get to full boost, it will completely break down and fall over and you have to pull out of the dyno run. This is at 12+ psi at 2000RPM with recommended min/max setting of 8/12psi. To be clear: I am not saying the cooling mist is any better/worse than any other system that works in the same way. It is just a problem with large jets running full flow and low RPM, and there is evidence of many others having similar issues if you search the forums.... some with smaller jets. So please note that I am saying that I have only experienced this with large jet setups, and have never experienced this with the typical sized setup that most people run, so most people are fine with this system.
You are completely correct that the fuel system is closed loop. This means that regardless of the presence of meth, the DME will attempt to get to the same AFRs. The issue is that it is is possible to put in so much meth that the DME has pulled all the fuel it can, and the mixtures are still too rich. Further to this, meth is harder to burn than petrol, and therefore it will cause a missfire more easily than petrol at the same AFR. This missfire is the cause of the bog/quench. Even further to that, the DME has long and short term fuel corrections. If you squirt alot of meth so that the DME pulls petrol to get AFR targets, the trims will be effected by this, and it will take some time for them to recover which can give some drivability issues. Techically you are correct that the meth you are using is saving you petrol, but I have not met anyone that would rather fill their 5L meth tank than their 50L fuel tank. Especially considering that you will not use the meth system unless in boost, so it will have negligable effect on petrol usage, but may mean you have to fill up the meth twice as often.
Adrian
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Legit question here...
What size nozzles are you talking about where it starts to bog?