SlowMoe Posted January 10, 2017 Report Share Posted January 10, 2017 Its fairly common knowledge that the transfer ports quickly become the bottleneck once you've opened the exhaust up so much. My question is, is the main botttleneck at the windows or in the runners? Quote Link to comment Share on other sites More sharing options...
J-Madd Posted January 10, 2017 Report Share Posted January 10, 2017 Its fairly common knowledge that the transfer ports quickly become the bottleneck once you've opened the exhaust up so much. My question is, is the main botttleneck at the windows or in the runners? I can't answer that, but I think another "bottleneck" in porting is how wide you can make the Exhaust port before it eats rings. Quote Link to comment Share on other sites More sharing options...
SlowMoe Posted January 10, 2017 Author Report Share Posted January 10, 2017 75%? Quote Link to comment Share on other sites More sharing options...
SlowMoe Posted January 10, 2017 Author Report Share Posted January 10, 2017 And what about roof shape? How flat is too flat Quote Link to comment Share on other sites More sharing options...
trickedcarbine Posted January 10, 2017 Report Share Posted January 10, 2017 Lotta cylinders on my bench. The best running, and stuff from guys with top notch reputation are pretty similar shape. Pretty much a symmetrical trapezoid. Quote Link to comment Share on other sites More sharing options...
bigweav81 Posted January 11, 2017 Report Share Posted January 11, 2017 (edited) Seems like the shape in general dictates just how wide you can go, and be safe. I've talked to guys that have went 80%, or better, but they have there shit down as well. If I remember right You want the sides of your exhaust roof to taper off 3-5* from the middle. Sent from my SM-S820L using Tapatalk Edited January 11, 2017 by bigweav81 Quote Link to comment Share on other sites More sharing options...
SlowMoe Posted January 11, 2017 Author Report Share Posted January 11, 2017 (edited) Lotta cylinders on my bench. The best running, and stuff from guys with top notch reputation are pretty similar shape. Pretty much a symmetrical trapezoid. Are you talking about a flat roof with the exception of radiused edges? If so what would the minimum radius be with, say, a 75% port? Pics? Edited January 11, 2017 by SlowMoe Quote Link to comment Share on other sites More sharing options...
trickedcarbine Posted January 11, 2017 Report Share Posted January 11, 2017 Not a flat roof. I'll try to remember to snatch a pic next time I'm out there. Quote Link to comment Share on other sites More sharing options...
SlowMoe Posted January 11, 2017 Author Report Share Posted January 11, 2017 Cool Quote Link to comment Share on other sites More sharing options...
registered user Posted January 12, 2017 Report Share Posted January 12, 2017 My question is, is the main botttleneck at the windows or in the runners? it should be fine even if the cross sectional area of the runner is equal to the window because the piston is partially covering the window most of the time anyways. like putting a finger on a garden hsose and varying how much you cover it. if the runner diverges slightly may still be fine also since like I said before the piston blocks da window most the time anyhow rather than make the exh roof flat as possible your best bet is add addition exh ports if you have the meens. theres good reason why monoports went out of style 25yrs ago. mcdaddy gave a good demonstration in the dyno section Quote Link to comment Share on other sites More sharing options...
SlowMoe Posted January 12, 2017 Author Report Share Posted January 12, 2017 So you are saying that window size is more important then runner size? Quote Link to comment Share on other sites More sharing options...
registered user Posted January 12, 2017 Report Share Posted January 12, 2017 what im saying is if the runner is eqaul or diverges a hair i wouldnt be concearned. Quote Link to comment Share on other sites More sharing options...
SlowMoe Posted January 12, 2017 Author Report Share Posted January 12, 2017 What do you think about this exhaust port shape? Quote Link to comment Share on other sites More sharing options...
bigweav81 Posted January 12, 2017 Report Share Posted January 12, 2017 What's the purpose of the roof in the middle? Sent from my SM-S820L using Tapatalk Quote Link to comment Share on other sites More sharing options...
SlowMoe Posted January 12, 2017 Author Report Share Posted January 12, 2017 Not sure. Possibly to reduce cranking compression. Or maybe broaden the powerband Quote Link to comment Share on other sites More sharing options...
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