The 13B NA Power Thread.
 

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.

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.

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.

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.

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.

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...

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?

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.

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

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).

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 :(

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

well I already got an FC and I prefer the body style over the FB so not that much of a loss :)

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

Started to pull the motor from the Turbo II last night, hope to get it out of the car completely tomorrow, then break it down this upcoming week sometime and see what i have going on inside.

Already have two good housings lined up though.

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

i have heard conflicting info on 1/2 bridges and streetports regarding them being essentially the same in power output in a naturally aspirated situation. Any one have more info on this.

They are very similar as far as power output in N/A applications, but you still get the poor drivability with the half bridge. If you plan on going half bridge, you might as well go full bridge. If you have the resources you might as well go PP instead of full bridge. PP will make more power and actually be milder down low as bridge ports usually have more overlap. Once you get into high overlap ports, free flowing exhaust becomes VERY important. Power falls off hard as you try to muffle it and there will come a point where a streetport will make more power at the same db level.

PP is actually in the line up for the next engine i build unless i start feeling spunky and just opt to do it with this one. Might try to kill the some 6PI irons then if i am going that route. I know people opt for the four ports because there is less port to fill. Or maybe ill try the racing beat aluminum end plates?

Balla!

well i think im going to try to still put an NA motor into the turbo II to get her running til i can do something else with it. But i want to make something i can transfer to a first gen chassis down the road. SO once i get done with tech school and have some funds, ill start to be able to play.

so does anyone have any interest in seeing what kind of max power people can pull. Maybe do a contest and the top person gets a interview section in the digizine or something. Not to be like the other thread on Rx7club, but i think its a great concept. I would love to see something similar for the 12a as well. Probably limit it to street porting.

i have always wanted to see what a 4 port N/A with ITB's and a MOTEC could do, I bet it could do lots with the right tuner and engine builder, but it seems like one one worth while, like judge ito, or Racing beat, or mazdatrix has tried the setup with their professional experience, or at least not documented publicly.

Try to source some variable length runners too. Drive them on an RPM output. You'd have to spend hours on a dyno but the results could be impressive.

does anyone actually produce such an item? I mean i have ideas how i would make something work for a naturally aspirated engine but i lack some of the tools needed to make one.

Fuel Pump
 

Hey my name is Bennett,
I'm looking for an electric fuel pump for a 86' RX7 13 B.
If anyone has any information about this I would really appreciate it.
Thanks!
Ben

well, the honda kids source their itbs from motorcycles. I know the R1 has variable length runners, but i'm not sure how much.

This video of the 787b shows the runners operating @ about 4:50

well the MS site has a good thread of throttle bodies from motorcycles. Maybe ill pick something up off ebay and see what the deal is

http://www.msefi.com/viewtopic.php?f=29&t=6627

well i am in motion on my project.

13B s4 stock port as the base for now.
going to run an MS unit and a 12a dizzy.

Ill get some baseline info here soon once parts come in and i get the motor running.

What i am curious about is what i can do to the dizzy to make some more power? What is way to go with the split timing? Any other advice?

Over on the other forum, Adrian (Hyper4mance2K) just did 189.65 WHP from a 6-port 13B with smoothed ports but stock port timing. Not too shabby. He said his timing was 26 degrees BTDC at full advance. Not sure what the split was. I know a lot of NA guys like to run zero split.

Is there a write up anywhere about how to modify the dizzy?

What mods are you looking to do?

well im kinda stuck between running the dizzy and the FC CAS. I have both and i can utilize both, im just not sure which route i want to go. Having the ability to play with the timing would probably not be a bad thing, but would be another issue in tuning.

i think im going to opt for the dizzy, cut the slots a bit to bring the split in and only use the vac advance on the leading. Then run an array of MSD boxes (especially because ill need an output signal for the MS to read off of).

I was running about 26 BTDC on my stock port FC, made about 161 whp @ 7500 rpm. The car really started taking off north of 5500 rpm.

I think at one point in my timing curve I was at zero or negative split, forgot which.

K&N Drop-In
Rtek
Racing Beat Header, Pre-Silencer, Catback.

Took the same ECU to another FC, but with a weak compression motor. Exhaust was changed to an RB True Dual. Made 140 whp @ 6500 rpm. Power was lost most likely solely due to the motor being weak. Power just dropped off like a cliff after 6500 rpm. None of that taking off feeling was felt on this motor.

My guess for a good recipe for a high powered NA.

Cone filter getting ambient air.
Ported or Aftermarket Throttle Bodies
Intake Manifold with straight shot runners, Port-Matched, Extrude Honed, then Ceramic Coated
ECU that adjusts both fuel and timing
Making sure you have enough fuel with an aftermarket fuel pump and 4 x 720 cc's. If you have an ECU that can compensate for that much fuel at idle, no reason not to go bigger.
Large, Aggressive Streetport on a freshly rebuilt engine, with good dynamic compression. Get even crazier by re-balancing the rotating assembly and using lighter rotors to spin the engine even faster, with a matched intake manifold
Ceramic Coated Headers, with Header wrap
Expansion Chamber Collector
Pre-silencer and dual mufflers if you care about noise or straight pipe and single muffler if you don't care

As an anecdote, when I bought my latest FC, it's aux ports were frozen open. Thing was such a mule in the low end, you really had to step on it for it to go anywhere. I will never forget that feeling, since all my other FC's had working aux ports. I was like WTF????

i would have to say that four 720cc injectors is far far more fuel than any streetport engine will ever need. Same probably goes for 1/2 bridge. The stock 460 injectors are more than the engine needs from what i have found. Or at least while running an MS. I have noticed that the stock ecu control over the injectors limited the injectors pulse width considerably.


On a side note, im hoping to have my stock port s4 13b up and running in the next week or two. Hope to be good enough to dyno before i leave in late April.

4 x 460 cc will run out of fuel at about 195 - 197 whp.

4 x 550 cc will net you more than that, but if you're shooting for big power, at least go 2 x 550, 2 x 720 or 4 x 720 if you're going to be replacing injectors.

true, but with a stockport 460s are plenty. Logan is the only person i know of making anything considerable on a streetport @ 230hp. bridges i rule out since there are far more factors (like rpm) to contend with. I am probably just going to use the four 460 injectors i have currently with my setup. Mostly because for the stock port i think that is all ill need and i dont have any funds budget towards injectors replacements.

Yea, you should be fine on stock ports.

Hope you get over 180!