Port Runners; n/a vs FI?
03-27-2006, 04:40 PM
#1
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Join Date: Feb 2002
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...sooo I've been sitting on a set of S4 13BT Irons for a minute. I'm going to assemble them w/ a high-comp rotating assembly and run it all n/a. I had them ported a while ago by someone reputable in the area. I'm very happy w/ the port-openings, but the port runners haven't really been touched. I'd like to get good power out of this thing, so leaving an area of an n/a untouched is not an option...
...now, I've read Ito's thread, and he says to make it flow as much as possible, no restriction, with a smooth but not polished surface. That would seem the way to go... but thinking about it; would there be a difference in porting an n/a motors runners? I've heard somewhere that you don't want to touch the bottom-floor of a 12A's runners, or you could end up with worse flow than you started with...
Cliffs notes; these are my ports. This is going to be an 4-port 13BT running N/A. It will be street-driven daily, but doesn't have to pass emissions, and I have a warped sense of what a 'street car' is. Is there anything you'd reccomend done? (closing-edge bevels are already planned as an extra precaution; I don't believe the ports are large enough to warrant them)
...now, I've read Ito's thread, and he says to make it flow as much as possible, no restriction, with a smooth but not polished surface. That would seem the way to go... but thinking about it; would there be a difference in porting an n/a motors runners? I've heard somewhere that you don't want to touch the bottom-floor of a 12A's runners, or you could end up with worse flow than you started with...
Cliffs notes; these are my ports. This is going to be an 4-port 13BT running N/A. It will be street-driven daily, but doesn't have to pass emissions, and I have a warped sense of what a 'street car' is. Is there anything you'd reccomend done? (closing-edge bevels are already planned as an extra precaution; I don't believe the ports are large enough to warrant them)
03-27-2006, 06:42 PM
#2
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Join Date: Nov 2005
Posts: 93
I would leave the runners stock size, just clean up the casting. They have plenty of area for n/a, too big and you'll lose gas velocity. In my experience n/a exhaust port opening wants to no earlier than stock, MFR exhaust ports open even later than stock.
03-28-2006, 07:05 AM
#3
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Well in the first pic you can already see where its losing velocity by not being portmatched. I would knock off the casting and make all surfaces smooth. (not polished) Also theres plenty of meat aroun there to make those ports scream.
If you want it to be well behaved on the street then just knock the casting off the primaries and hog out the secondaries.
If you want it to be well behaved on the street then just knock the casting off the primaries and hog out the secondaries.
03-28-2006, 03:52 PM
#4
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Location: California
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the 12a irons ports are way taller than the 13bt, due to the fuel injector bosses.
i think i agree with the port runners being big enough, a 4 port renisis engine has teeny port runners, but huge port openings.
i think i agree with the port runners being big enough, a 4 port renisis engine has teeny port runners, but huge port openings.
03-28-2006, 03:59 PM
#5
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So... Port-match the openings to the gasket; then try to blend into the ventruri shape, not taking too much away. Pretty much opening up the bellmouths on either side of the port runner/venturi, but not increasing the cross-section too much...
03-29-2006, 11:48 AM
#7
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...thanks for the quick reply of forwarding pictures from a thread that I've already mentioned reading...
...yes, those are worked port runners; for force-inducted engines. Those pictures show nothing to me, except how to port to lose intake velocity in an N/A setup...
...yes, those are worked port runners; for force-inducted engines. Those pictures show nothing to me, except how to port to lose intake velocity in an N/A setup...
03-29-2006, 09:54 PM
#8
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Location: Bayou-self Louisiana
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wow really... I ported them just to match the gasket and ITO cleaned them up. I didnt hog them because on the turbo I didnt need to. I have done the same on my 4 port 13B because the timing was in the port shape.Just because I did this on the turbo didnt mean I didnt know what you were asking.
Sorry.I submit another angle (I guess from that these are on the thread also) He sent me copies before hand. I believe you can see the gasket out line still visible. The other is of the 4 port NA and its runner cleaned up the same way (not hogging it out)
Just trying to help dude.
Sorry.I submit another angle (I guess from that these are on the thread also) He sent me copies before hand. I believe you can see the gasket out line still visible. The other is of the 4 port NA and its runner cleaned up the same way (not hogging it out)
Just trying to help dude.
03-30-2006, 01:02 PM
#9
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Sorry man; didn't mean to come off sharp. I didn't mean offense.
The pictures that keep getting refrenced all seem to be examples of the runner being hogged out. If that's not the case, then I blame the angle of the pictures. Perhaps a straight-on
I'll say I have very little knowlage of fluid dynamics. I know that with an N/A setup, the smaller the intake diameter, the faster the airspeed; and I know how venturi's work. Based on this and previous responces, I'm just planning to do as told; clean up casting, gasket match, and blend. Pics of the timing-side of the ports below. THX everyone for the help; feel free to give further input.
*on a sidenote, I just got another jub w/ access to a CNC router. ITB's here I come.
The pictures that keep getting refrenced all seem to be examples of the runner being hogged out. If that's not the case, then I blame the angle of the pictures. Perhaps a straight-on
I'll say I have very little knowlage of fluid dynamics. I know that with an N/A setup, the smaller the intake diameter, the faster the airspeed; and I know how venturi's work. Based on this and previous responces, I'm just planning to do as told; clean up casting, gasket match, and blend. Pics of the timing-side of the ports below. THX everyone for the help; feel free to give further input.
*on a sidenote, I just got another jub w/ access to a CNC router. ITB's here I come.
03-30-2006, 01:08 PM
#10
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Join Date: Feb 2002
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Sorry man; didn't mean to come off sharp. I didn't mean offense.
The pictures that keep getting refrenced all seem to be examples of the runner being hogged out. If that's not the case, then I blame the angle of the pictures. Perhaps a straight-on shot that showed the buildup in the venturi would clearify for me? Reguardless...
I'll say I have very little knowlage of fluid dynamics. I know that with an N/A setup, the smaller the intake diameter, the faster the velocity; and I know how venturi's work. Based on this and previous responces, I'm just planning to do as told; clean up casting, gasket match, and blend. I don't want to get too crazy with it and bring the powerband up more, because this will be a daily-driven car, and I don't intend to go any higher than 10k (limited by fuel computer).
Pics of the timing-side of the ports below. THX everyone for the help; feel free to give further input.
*on a sidenote, I just got another job w/ access to a CNC router. ITB's here I come.
The pictures that keep getting refrenced all seem to be examples of the runner being hogged out. If that's not the case, then I blame the angle of the pictures. Perhaps a straight-on shot that showed the buildup in the venturi would clearify for me? Reguardless...
I'll say I have very little knowlage of fluid dynamics. I know that with an N/A setup, the smaller the intake diameter, the faster the velocity; and I know how venturi's work. Based on this and previous responces, I'm just planning to do as told; clean up casting, gasket match, and blend. I don't want to get too crazy with it and bring the powerband up more, because this will be a daily-driven car, and I don't intend to go any higher than 10k (limited by fuel computer).
Pics of the timing-side of the ports below. THX everyone for the help; feel free to give further input.
*on a sidenote, I just got another job w/ access to a CNC router. ITB's here I come.