The 13B NA Power Thread.

[Whizbang]

Guidelines for this discussion:

1. No power adders.
2. Side ports only since most can't manage a PP setup and the cost difference is pretty high.

One of the biggest things i would like to really compare heavily is 6 port vs 4 port. The 4 port seems to lend itself for power better than the 6 port, but i would like to see just how great a differential exists.

[Whizbang]

I have already started to collect parts for my first 4 port engine attempt.

Basis is an S4 13BT irons (front, middle, rear)
S4 NA housings (de-sleeved)
S5 9.7:1 rotors.
Rx8 eccentric shaft


porting to be determined.

Obviously everything will need rebalanced. My biggest problem is i live at around 5500ft and its get much higher very fast around here (up to 14,000ft...., 7500ft average in mountains). So power levels for me will be about 25% lower than they would at sea level.

[N.RotaryTech]

A few years ago my GTU made 131rwhp, that was with RB pre-silencer an mufflers and a mild port job, A/C components removed. S5 engine btw. (I can't really remember if I had the RB or if I had the stock exhaust system on when I got it dynoed. The time I put the RB exhaust on was close to that time.)

Since then I've removed the emissions components, 5th & 6th port actuator sleeves and rods, wired open VDI.
I've mentioned this on the other forum, some will argue this, but I did notice a difference with the sleeves and rods removed. Mainly: smooth, all the way up the RPM range. Low end: no difference.

I might get It dynoed again in the spring after a needed tune-up. Id like to see what its been making.

[Roen]

161 whp on a stock motor with a rb header, pre-silencer and exhaust system. Rtek 2.0 EMS.

Shoot for 200 whp or in your case, 150 whp on your streetport.

[Whizbang]

my biggest decision is bridgeport or streetport.

this isnt a daily car and thanks to the altitude, more power is certainly not a bad thing.

[Fidelity101]

Originally Posted by Low Impedance

my biggest decision is bridgeport or streetport.

this isnt a daily car and thanks to the altitude, more power is certainly not a bad thing.

if its not a daily go bridge port, in reality you would want a boosted motor for the altitude to make up for the lack of air since your car will become slower as the air gets thinner during a hill climb. But since your sticking NA go with a bridgeport your going to need all the air you can get in there towards the end of the run.

I would go about balancing your rotating assembly too if your going with an rx8 E shaft, its not nessecarly for most applications but unbalance can rob you of power at higher RPM and cause unwanted flexing.

Go with an exhaust port comparable to your intake, you can get your torque band where you want with exhaust tube/header/collector tuning

[12arotary]

ever think of trying to get a hold of just the center section of the renisis engine?
running something with a bridge port plus both p-port and side port exhaust,
make it breath like it has four lungs

though very odd exhaust manifold is there any reason why this would
be an issue?

[Whizbang]

Originally Posted by 12arotary

ever think of trying to get a hold of just the center section of the renisis engine?
running something with a bridge port plus both p-port and side port exhaust,
make it breath like it has four lungs

though very odd exhaust manifold is there any reason why this would
be an issue?

that would be interesting...

[Whizbang]

well i plan on building this first engine using the most common choices for an NA build. (S5 rotors, standard 86-91 e-shaft, etc).

As far as porting the exhaust goes, how much is "too much" or rather, at what point would the exhaust velocity become a bit too low due to a larger port?

[drewski86]

70% of the intake port area is the general rule of thumb. Don't have any facts but I've heard that number thrown around serveral times.
Moving port opening lower reduces torque as the charge spends less time in the chamber
Moving the port up increases overlap. Good for top end power, not so good for low end light throttle.
Moving the port sides out increases port area, and decreases surface area to support the seal as it crosses the port.
A rounder port will make less power, but have a broader powerband.

[Whizbang]

As far as a hill climb car goes, i might wind up using an FB shell for racing for reasons ill discuss later. BUT i am testing out concepts in a shell that is more street worthy and NOT a daily (the turbo II).

[Fidelity101]

Yeah but can you fit in an FB? I would use an FB for rallying since there are more of them around it seems and cheaper but being 6'4" the FC is pushing it. I can't drive an FB with a stock steering wheel, my hand on the wheel will eventually just hit my knee and I gotta move my hand

[12arotary]

Originally Posted by Fidelity101

Yeah but can you fit in an FB? I would use an FB for rallying since there are more of them around it seems and cheaper but being 6'4" the FC is pushing it. I can't drive an FB with a stock steering wheel, my hand on the wheel will eventually just hit my knee and I gotta move my hand

whats with this haha i'm 6'4" too and I fit comfortably in
my 82... I hate driving my fc cause my head is too
close to the ceiling fb is far more comfortable

[Fidelity101]

Originally Posted by 12arotary

whats with this haha i'm 6'4" too and I fit comfortably in
my 82... I hate driving my fc cause my head is too
close to the ceiling fb is far more comfortable

You must be tall bodied and short leg, I'm the opposite. Long legs and a short torso.

[Whizbang]

lower the seat, modify the wheel. I fit in Peejays car alright