Of course it will be a slug if you disconnect the SC.
the compression ratio for SC and non-SC are different. the non-SC has higher compression ratio at 9.3, SC has only 8.9. that's why under boost, the SC adds 5 PSI more than the non-SC, which makes more power.
Gee, why am I reminded of those LOST recap episodes with the subtitles like:
"This is Benjamin Linus. Benjamin Linus was the leader of the Others."?
Anyone who watches LOST already knows that; most people who own Previas and have internet access know the difference in the static compression ratios between the 2TZ-FE and 2TZ-FZE.
I also have an SC model, if I had to rebuild my engine, i would increase compression to match the non-SC, then keep the boost at the stock 5PSI. the SC internals can handle up to 7PSI safely. take note of the keyword "safely". that should give you enough "umph!"
I've considered that myself, and briefly considered throwing in a 2TZ-FE to take advantage of its higher compression ratios, until I recalled that there are major valve timing differences between the two engines, and that the -FZE is ODB-II compliant. Other differences are that the -FZE has a more robust lubrication system, the head gasket is better, and the piston skirts are shorter and lighter, as well as resin-coated for reduced friction. In short, the -FZE is just that much better an engine.
I'm beginning to wonder if the valve timing is the largest reason for the difference in compression ratios-- the -FZE's intake valve opens at TDC, while on the -FE it opens at 10 degrees BTDC; closing occurs at 46 degrees and 40 degrees after bottom dead center, respectively. (Exhaust timing is similarly modified, and the overlap between exhaust closing and intake opening is 0 degrees, which keeps the air-fuel mixture in the combustion chamber where it belongs, rather than being pushed through by the supercharger.) I'd have to run through one of those compression ratio calculators to know for sure.
EDIT: Update on driving without S/C for just a day:
I'm already getting used to the reduced power, and am driving like a vehicle this size with as little power as it has should be driven-- a little more gently and with a little more planning when it comes to left turns and just pulling out into traffic.
I may wire in a dashboard switch to return control of the S/C to the ECU, make it sort of a "Sport/Econ" mode switch. If nothing else, I can feel better about putting only 87 octane in it to save money (I often put in 89 octane even though it can run on 87 for light duty, according to the manual, but I'm trying to save money by getting the cheaper stuff).
If I put in a switch, I'll post a new thread with a photoessay on it.
