Porting primaries and secondaries
03-30-15, 01:43 PM
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Porting primaries and secondaries
Regina Sask
Hey I'm having trouble understanding the benefits and differences porting the primaries and secondaries, both street and bridge applications.
Is there a guide for what causes what, and the benefits of this compared to that?
For example, what if just the primaries are ported, or if just the secondaries were ported.
What if the primaries are bridge ported and the secondaries are stock ported. What if it was the other way around. What would happen in all these situations regarding everything from low end power to high end power to overlapping and spool times and red lines, pretty much every detail you can tell me in each scenario.
Thanks in advance.
Hey I'm having trouble understanding the benefits and differences porting the primaries and secondaries, both street and bridge applications.
Is there a guide for what causes what, and the benefits of this compared to that?
For example, what if just the primaries are ported, or if just the secondaries were ported.
What if the primaries are bridge ported and the secondaries are stock ported. What if it was the other way around. What would happen in all these situations regarding everything from low end power to high end power to overlapping and spool times and red lines, pretty much every detail you can tell me in each scenario.
Thanks in advance.
03-30-15, 09:33 PM
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^+1. The street port flows less air but faster, so idle will be smoother and is able to be lower. The bridge port flows more air but at a slower rate, so that is better for more power, but the engine has a harder time idling.
The secondaries act like a sort of variable valve timing for rotaries. This is the reason you only see half bridge ports with the bridge on the secondary port. At lower speeds the always open primary ports do the grunt of the work while the variable secondaries take over at higher rpms. You get the best of both worlds that way. If the primaries are bridged and the secondaries street ported, you need to raise the idle to support the added air, and you lose the high end potential in the secondaries.
I am not very well versed in turbos yet, so I can't help as much there.
The secondaries act like a sort of variable valve timing for rotaries. This is the reason you only see half bridge ports with the bridge on the secondary port. At lower speeds the always open primary ports do the grunt of the work while the variable secondaries take over at higher rpms. You get the best of both worlds that way. If the primaries are bridged and the secondaries street ported, you need to raise the idle to support the added air, and you lose the high end potential in the secondaries.
I am not very well versed in turbos yet, so I can't help as much there.
03-31-15, 06:17 PM
#4
first of all, check this out: https://www.rx7club.com/new-member-r...rimer-1039179/
as far as which ports do what and what happens when they get ported, you have the basics. yes, the primaries pretty much handle idle and low speed/load driving. the secondaries usually open/activate when load warrants it (generally about 3500 +/- RPM).
at the end of the day, porting is just increasing air flow and altering timing (duration and overlap). it doesn't much matter where you do it, the engine will respond. the engine "sees" the ports regardless of where you put them. the half-bridge is a prime example of that. if you port only the secondaries as most with them people do, the engine still BRAPS, right? so it still affects idle. as for how they drive, i can only regurgitate others' reports of them, i have no personal experiences to share - only theory. so i will leave it at that.
i'm keeping the rest of this response simple for the sake of brevity.
1. you need to keep overlap limited if you care about idle and low end, although early opening can help the torque curve, so keep that in mind.
2. redlines generally increase with overlap, as the engine is able to breathe better. these are your bridges and peripherals. they can be tamed for street use, but time and knowledge is a prerequisite for that skillset.
3. spool can positively be affected by porting as well, but again, time and knowledge. also, keep in mind there are limits, the first of which would be working with the right turbo for your application.
as far as which ports do what and what happens when they get ported, you have the basics. yes, the primaries pretty much handle idle and low speed/load driving. the secondaries usually open/activate when load warrants it (generally about 3500 +/- RPM).
at the end of the day, porting is just increasing air flow and altering timing (duration and overlap). it doesn't much matter where you do it, the engine will respond. the engine "sees" the ports regardless of where you put them. the half-bridge is a prime example of that. if you port only the secondaries as most with them people do, the engine still BRAPS, right? so it still affects idle. as for how they drive, i can only regurgitate others' reports of them, i have no personal experiences to share - only theory. so i will leave it at that.
i'm keeping the rest of this response simple for the sake of brevity.
1. you need to keep overlap limited if you care about idle and low end, although early opening can help the torque curve, so keep that in mind.
2. redlines generally increase with overlap, as the engine is able to breathe better. these are your bridges and peripherals. they can be tamed for street use, but time and knowledge is a prerequisite for that skillset.
3. spool can positively be affected by porting as well, but again, time and knowledge. also, keep in mind there are limits, the first of which would be working with the right turbo for your application.
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