When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Hi there y'all, I'll start by saying that this question has probably been asked before maybe six or seven million times, but I felt like if I could communicate my question clearly, I'd have a better chance of choosing the right course of action. I'm buying (soon, hopefully) a 30000km 1989 NA. I've been in love with the rx7 since I was about 7 when I got my first (out of numerous) copies of NFS Carbon. My dream would be to get the car to 300 whp, I plan on tracking the car as well as using it as a daily. I understand that as you add more and more modifications the reliability of the car sort of tanks, I also don't want to butcher such a low km model. So once I drive it to 95kkm, I was thinking of both rebuilding the engine, but also squeezing more power out of the car. Can anyone explain what modifications would get me to my goal? I was thinking either a bridge or a pp, but as I have read a lot of places, the reliability kind of goes away. I guess the best course of action would be to swap a tii into it, but I'm scared of not finding one in a good condition. Money is not really an issue, because racecar but also by the time I'd be willing to do any modification, I'd be in a good job.
TLDR or to reiterate: 1. Is it possible to get 300whp out of an NA engine? 2. Why are pp considered undriveable on the road?
Also sorry about probably being in the wrong thread, I'm new to the whole forum thing.
I'm sorta shooting in the dark here, I'm sure someone be along to correct any inaccurate info. I would see no problem in getting an NA engine to 300whp. Maybe I'm naive though. From what I've read the Peripheral Port is the most aggressive, or close to it, as far as porting the 13b. There's a ton of debate on whether or not a Bridge Port is a good idea for the street. I've personally never considered a PP for a street driven car. From what I understand it'll be drinking fuel. I thought that the low end power gets compromised, but again, I may be wrong. Reliability will absolutely start dropping as you gt more aggressive with porting. Race only cars get rebuilt way more frequently than street driven cars. Why don't you just go with an aggressive Street Port. Are you planning to rebuild the engine as soon as you get it? That'd be the only reason I could see to consider porting right away. I'm assuming it's stock or mostly stock. If I were you I'd start with opening up the intake and exhaust so the engine can breathe better. I may be way off base, but I don't think so. I'd plan bolt on mods first. If you're daily-ing this gas mileage is going to suck on even a BP.
I'm also far from an expert, but I can add to what Red Scourge is saying:
Originally Posted by The Red Scourge
I'm sorta shooting in the dark here, I'm sure someone be along to correct any inaccurate info. I would see no problem in getting an NA engine to 300whp.
There is no reason that 300whp from an NA 2-rotor couldn't be done, but as you are about to mention it becomes decreasingly practical as power increases.
Originally Posted by The Red Scourge
There's a ton of debate on whether or not a Bridge Port is a good idea for the street. I've personally never considered a PP for a street driven car. From what I understand it'll be drinking fuel. I thought that the low end power gets compromised, but again, I may be wrong.
When you optimize the engine for more overall flow (ie. A BP that hogs out the stock ports and adds the eyebrow section, or a PP) you de-optimize the engine for low-end performance.
The reason the stock FC NA engine has an auxiliary port setup helps to illustrate this. At low rpm, the primary and secondary ports are always open. They are small in comparison to the port area on a 4 port (turbo, earlier 13B) engine. This promotes low end torque because combined with a well engineered intake they promote smooth and regular flow with little turbulence. Basically, the car can flow air more easily at low rpm with the valves closed (as the port area is effectively smaller) at a compromise of high end performance. Conveniently, this is what the valve is for. Approaching 4000rpm, the primary + secondary ports become a restriction and more flow is necessary.
At high rpm (4000+) the auxiliary valve opens and the port area is increased. Now that we are flowing a lot of air, that port area and flow becomes useful. There is some debate about turbulence, but this is more due to the nature of the valve than due to the auxiliary port itself.
Obviously a BP/PP has much more port area, so this compromises low-end performance in exchange for high-end. Next we need to discuss port timing.
If you consider a BP or PP setup, you not only hog out a lot more area in terms of the actual cross-section but you also end up opening the port earlier and closing it later. This causes intake charge dilution, since the exhaust gases are still exiting the exhaust port at the same time the intake port opens. If this isn't intuitive from my explanation, look at this GIF:
This GIF already shows a peripheral intake, but the principle is the same as a side port. You can see how opening it earlier (moving the opening down) and closing it later (moving the closing up) changes how "long" the intake is open relative to the motion of the rotor inside the housing.
This is a rabbit-hole, so I'll be brief: Opening it earlier sacrifices low-end for high-end. Closing it later has diminishing returns, as there is only so much air you can cram in there. I'm oversimplifying (and I'm also no expert, as I mentioned) but this translates to even more low-end loss and high-end gains. This also decreases fuel economy due to turbulence, and generally means that the engine will want to idle way higher than normal.
Originally Posted by The Red Scourge
Reliability will absolutely start dropping as you gt more aggressive with porting. Race only cars get rebuilt way more frequently than street driven cars. Why don't you just go with an aggressive Street Port. Are you planning to rebuild the engine as soon as you get it? That'd be the only reason I could see to consider porting right away. I'm assuming it's stock or mostly stock. If I were you I'd start with opening up the intake and exhaust so the engine can breathe better. I may be way off base, but I don't think so. I'd plan bolt on mods first. If you're daily-ing this gas mileage is going to suck on even a BP.
Reliability is more of a problem due to consistent high-rpm use. There are mitigating mods to address this, but obviously spinning at 9000rpm+ is more strenuous than redlining at 7000rpm. Some seal wear may be due to port design, but I can't make a meaningful comment on that so I'll leave the topic here.
Lastly, Red hits the nail on the head, porting requires a rebuild so it's quite a job when not otherwise opening the engine. Also, you need a custom intake to make proper use of a BP (and you need a custom intake + ITBs most likely for a PP) plus a computer, fuel system, exhaust (loud), etc. And as far as BP and PP setups go, 300whp is a lot. It can be done, but it's an all-out build.
Turbocharging or swapping a turbo engine will give you faster, cheaper results and more potential.
07-01-20, 11:35 AM
