Athena 47.6 exhoust durations questions.

Robert Weirud /

Hello guys. My first post :D

Checked my port durations after i lifted the cylinder 2mm total. 1mm plate and 2 gaskets. and milled the same at the top, sqish is good at 0,5mm

My issue is that i ported the exhoust a bit, and i think too mutch. Lets say 2mm on eatch side and 1.5mm on top. that made the exhoust duration 187° and blowdown 34°. is this way too mutch? my understanding this wont start hit untill 9000rpm with the right pipe. tranfser duration i think is good at 119°..

Greetings from Norway

Re: Athena 47.6 exhoust durations questions.

Johnnie Distefano /

If you want the powerband earlier, youd need to decrease the blowdown by raising the transfers a bit

Re: Athena 47.6 exhoust durations questions.

You’re gonna have to raise the transfers 1.5-2mm to get the blow down back to an acceptable amount in relation to the exhaust durations. Having 187 ex with 120 transfers is asking for a paper thin power and that doesn’t hit very hard. I’d be shooting for 135 degrees on the transfers for 25.5 degrees of blowdown. That should give you a really nice useable power band.

Re: Athena 47.6 exhoust durations questions.

Cut the crown of the piston down at the transfer / boost area...., you will gain some intake duration back. Beyond working it like that , and or raising intake port roof , your blow-down numbers are going to disappoint you as far as performance goes . If one gets above 27 degrees blow off or so I hope they had planned on building a screamer . Good luck brother .

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