Quote:
Originally Posted by Dimman
I think I saw in a Toyota service post that the cams were 255° (so 200-210ish at .050"?). Can you share valve size, my estimate is 34.5mm. So I'm putting my lift estimate at ~9mm.
???
Are you guys keeping the stock primary lengths so we don't have to chase returns with the AVICS? I get the impression that a positive return from the primaries is what is killing the top end. So you could size the lengths of the secondaries (catless version) to cancel the bad top end return?
Looks very nice.
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I was looking at 2013 DI Impreza data and I got was ~35mm intake ~32mm exhaust. with 205 duration at .050. My lift estimates were 9mm. :-D I'm guessing for designing this system in a 'shoot close, re-aim' method like we are doing, our numbers are as my dad used to say "Close enough for telephone work." (he worked for the phone company). I put the exhaust port centerline length at 3.25" as these damn Subaru heads have that stupid dogleg port on one valve for a ~3.65" port centerline length and ~3.00" port centerline length. You have no idea how badly we want to design billet heads for the EJ and FA engines. I hate those port designs.
If I plug your valve size estimate in with smaller valve sizes than I estimated I'm still having to round up or down very slightly on the recommended primary/secondary diameter, and the only other item that changes is the overall recommended primary and secondary lengths drop slightly. The problem is, there's only so much you can increase the length and almost none that you can decrease the length. Recommended is 11.4-13 inch if I bump the port centerline length slightly to accommodate the dogleg in second valve section of the port (for those of you who haven't seen inside a Suby head, the 2 exhaust valves have different 'sub-port' lengths, one being substantially longer than the other), but goes up to 13.4 if I cut it back down to 3" for the shorter of the two port centerlines.
To switch the subject entirely (i'm good at that), if we go to a three stepped 4-1 header, and switch to a triple stepped header (rounding runner diameters to primary = 1.5, secondary = 1.625 and tertiary = 1.750), this design seems very do-able in terms of the lengths recommended. This also lends some credence to the idea that a larger exhaust may work well. Otherwise the numbers point to a smaller ~2.5" exhaust.
That's all I've got for now. I'm tired and it's time for dinner. I'll be back tomorrow to weigh in on this more. Unless I can't sleep tonight (probable).
J