White_FC

Howdy all, just doing a bit of 'dummy' porting to a spare housing I have before I tackle the real deal.



Do any of ya'll have some pics of some exhaust ports you've done (i've read the stickey) and how they performed?



I gather that opening too early will decrease the power stroke some, and opening it too much later will just increase ovrelap, and going too wide will root my apex seals quicker, so what does everyone here do? for a high HP engine specifically.



Would it be better to port 'down' and decrease the power stroke a little bit than to incrase the overlap too much?

Drago86

I's like to know how high you can port before you get a lumpy idle keeping the intake ports with the same openeing time. Also how wide is too wide?

cach22

Yeah i would like to know the same things



though in my case for a high hp turbo motor



example on a stock 2nd and 3rd gen 13bt



exhaust timing is this

EO 71° BBDC

EC 48° ATDC



on a racing beat street port its exhaust timing is this

EO 84° BBDC

EC 48° ATDC



on the street port they have opend it up a fair bit early though it is closing at the same time, could you close it at like 55 degrees ATDC or even more?





cheers



Lance



ps I hope im not highjacking your thread White_FC

White_FC

Not at all, we're after the same info, just need to guru's to come and chime in, in here.



My apex seals should be here sometime in march... damm rotaryaviation ran out of stock again!

So I'd like to have all my porting done by then, so i'm just trying to get as much info as possible on exhaust porting at the moment.

BDC

Hey there guys,



This is a topic I've wrestled with for quite some time. I've seen all sorts of different shapes and sizes of exhaust ports but I'm still not convinced that's there any real, solid data to show that there's a positive benefit to having humongous exhaust ports. Some might argue against this and that's ok by me but only as long as they have some comparable data to present that substantiates what they say. In my opinion, besides the tapering and angling of the port closing timing, I honestly believe there's no gigantic benefit from making an exhaust port larger in size with respect to the exhaust sleeve. Infact, if it's too big, then you can reduce the time for each power stroke and actually _lose_ power. I say keep it simple. You'll notice that a professional like Judge Ito doesn't make his exhaust ports humongous, either; that ought to suggest something.



The problem with questions like this, and this isn't to place any blame on anybody, is that for every person who does professional and amateur porting, you'll have just that many differing opinion on all of this. That's what I've found. In this hobby and trade, there's so many different approaches yet there isn't much substantive data to corroborate what all of those opinions are.



So, for my exhaust porting, I stick to a few simple rules and keep it like that. What I do is reshape the port walls and sand them down to as mirror finish as possible. I taper everything out to help the exhaust get better 'scooped' in. I believe approaching this from the standpoint of reduction of boundary layers and removal of turbulent, flat spots is the way to go. I don't dramatically change the port opening and closing timing: I do mainly matching to the stock exhaust sleeve. Here's a few pictures to illustrate. Pay close attention to the port and sleeve's smooth and polish-finished look:



Frontal comparison before and after





Rear comparison before and after





Both ports completed





Comments and constructive criticism welcome as always.



B

andynogo

Beautiful ports BDC.



I agree in that there ain't too much use going huge on the exhaust ports as you simply lose too much low/mid range power. Good if you wanna rev between 8-10k all the time...



The simple answer has been solved with the renesis motor. Good port timing for all round power and much larger area for the gas to escape through by using two side ports. I can see these motors being THE motor to have in the next few years...

White_FC

Thanks for the info and pics BDC, very helpful!



How much power did that motor make?

And was it a turbo motor? Would you do things differently for an N/A motor?



Now I know there are always many many differing oppinions on things like this, thats why I want more people to post their thoughts in here



I know theres at lesat someone on this board that likes to take the whole exhaust sleeve out aswell, I think it was Mazdaspeed7(? don't shoot me if im wrong ) what do you think about that BDC? obviously against it from what i've just read in your last post.



So come on people! need more opinions!

rmaiersg

Aren't you supposed to put a little bevel on the port so the apex seal doesn't get caught on the housing when passing over it?

BDC

Yep, ya are per Ito's suggestion. Difficult to tell in those pictures but they're there. I should try and post some clearer ones.



B

BDC

Thanks!



You know, you mention the Renesis... I'm interested in seeing someone do what I would call a 'Double Bridgeport' -- bridgeporting all four intake ports and all four exhaust ports. I wonder how well it'd work.



B