VE and compression ratio

Hey everyone, I used the building course to rebuild my 2jzgte. I bumped the compression from 8.5:1 to 9.6:1. I plan on running e85 most the time.

I'm running Haltech 2500 and have the 2jzgte non-vvti base map but wanted to better understand how changing the compression ratio of the engine will affect VE. Should I add/subtract 5% or 10% to the base fuel and ignition maps to compensate for the increase in CR?

Thank you

Usually VE is indicating how well the engine is breathing, how well your intake and exhaust components are working together. CR is a different beast related to thermal efficiency. In other words VE helps to get more air in the cylinder and CR helps to get the most out of it. But still these are two different things and not related directly.

As Shota said - in simple terms, VE is how much gets into the cylinder, and CR is how hard it's squeezed.

About the only relationship is where detonation, and to a much lesser extent pre-ignition, resistance is concerned. Higher CR ratios heat up the charge more and make it easier to ignite the charge, and this can limit the mass of charge in the cylinder, depending on fuel and other factors.

With E85, this shouldn't be a problem, and as a general rule of thumb, higher compression gives better thermal efficiency, as Shota also said - more of the fuel's energy is used in the cylinder, because it burns faster, and less passed out the exhaust.

If you're going to be using 'pump' "E85", rather than from a drum and reputable supplier, I'd strongly recommend a fuel sensor - but as you say "most of the time", I expect you're already doing that.

Yes it will be a flex fuel vehicle so I'm not limited to e85 if circumstances don't permit. I have a Conti fuel sensor in the return line.

Compression change aside, if you find VE has to change, keep in mind an engine rebuild has many factors. For example I find VE values need to increase as rings seat in order to maintain lambda targets. Anything done to the heads during a refresh can have a big impact on VE as well.

100 percent agree. I refreshed 1zz-fe engine for a friend of mine not so long ago, cleaned up all combustion chambers and head runners from burnt oil deposits (that engine is known for high oil consumption), made standard valve job and so on- all regular things and the engine behaviour changed drastically from what it was before... The guy was very surprised to see the change from simple overhaul but to me it's all about improved VE across entire RPM range.