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Originally Posted by SilverSpear
Garrett, I was wondering these couple of days about the thing you posted here, thank you, I guess this thread will be even more interesting than Tom's. can you ask about these config setups for the cams if they can really give good results without problems.... or messing the valves when using lower compression pistons? and what are the specs of these pistons? 8.5:1 ? 9:1?...
and for more info for some guys who are not mechanically experts in this field (like ME  ) how these valves config can be achieved? modifing the cam heads? or stand alone management thing + cam heads mods? |
Well, in regards to any problems, a moderately aggressive config (like the one I listed for the turbo application) should not have any downsides. Many many many 6 cylinder engines run longer durations, with an equal or higher compression ratio, and do not experience any issues. This includes valve/piston interference and idle quality.
For example, the 2JZ-GE has 10:1 compression, and can run a setup of 9.3mm lift and 264* duration without any interference or idle quality loss. Turning the engine into an interference setup only occurs once lift is in excess of 9.5mm, and idle quality starts to decrease when running 272* duration or more.
In regards to lower compression pistons, well, you'd likely be able to run
more lift and duration... Unless for some strange reason you keep the stock valve clearance, but reduce stroke length to create a lower ratio - which would be dumb. I'm not saying that running more lift or duration would increase performance with a lower ratio, I'm merely saying that it is physically possible to make the config more aggressive.
I believe that the config I was going to attempt was as follows:
Intake: Opens 2* B-TDC, closes 58* A-BDC, centered @ 118* A-TDC, 240* duration; 8.0mm lift.
Exhaust: Opens 59* B-BDC, closes 9* A-TDC, centered @ 65* A-BDC, 248* duration; 8.6mm lift.
Before sending the camshafts to Paeco, my plan was to examine the head to be sure that there was proper clearance for the larger camshaft lobes. If it were possible, I had also planned on checking the springs to be sure that, given this increase in lift, they would not bind.
The general plan was to keep the overlap at TDC the same, thus, in theory, allowing the IRIS system to continue to work. The secondary theory was that with such a low increase in lift, the springs would not bind nor would the engine become interference... However, if the engine did, oh well. I
do change my timing belt when I'm supposed to.
Have I missed anything?