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.

[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]

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.

[Fidelity101]

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

[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 :(

[Whizbang]

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

[Fidelity101]

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

[12arotary]

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

[Whizbang]

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.

[Fidelity101]

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]

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.

[drewski86]

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.

[Whizbang]

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?

[JunpoweR]

racing beat aluminum end plates?

Balla!

[Whizbang]

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.

[Whizbang]

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.

[Max777]

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.

[nissanconvert]

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.

[Whizbang]

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.

[B.Purdy]

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

[nissanconvert]

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.

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 (http://www.youtube.com/watch?v=Go3Fgd1wgic) shows the runners operating @ about 4:50

[Whizbang]

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

[Whizbang]

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?

[PercentSevenC]

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.

[Whizbang]

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

[PercentSevenC]

What mods are you looking to do?

[Whizbang]

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.

[Whizbang]

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).

[Roen]

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????

[Whizbang]

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.

[Roen]

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.

[Whizbang]

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.

[Roen]

Yea, you should be fine on stock ports.

Hope you get over 180!

[Whizbang]

would be nice! I would be happy with 170.

[NoDOHC]

I never dynoed at a real dyno, but I did not notice or measure with my G-tech any difference between 13.5:1 and 12.8:1 AFR at 7,000 rpm. My power actually dropped off below 12.8:1.

I don't know if the 197 Whp number is correct on 4X460cc/min

Thermal energy of gasoline: 124,000 btu/gal

Injectors = 4 X 0.46l/min = 1.84 l/min X 80% utilization = 1.47 l/min = 88.3 l/hour = 23.37gal/hr.

You put in 124,000 X 23.37 = 2897270 btus/hr = 1138 hp! At an 85% drivetrain efficiency, (227 at the flywheel), This implies that the engine is < 20% efficient!

Lets go from the airflow side. 4 X 0.46 X 80% = 1.47 l/min = At 740g/l this gives 1.09 kg/min or 18.2 g/s. At a 12.8:1 AFR this requires 232 g/s of air or 1.025 X 232 = 238 l/s (edit: at sea level, 70 F)
Because the rotary displaces 1.3 l /rev, this equates to 11,000 rpm at 100% VE.

I don't know if there are more complicated methods at work here, but the way I slice it, 460 cc injectors are PLENTY.

I can also say that my '86 would run 12.8 AFR up to 5,500 rpm on a single set of injectors (no staging until that point). It would also do a 14.8 quarter at 105 mph (it was not that slow/starved for air).

I was using peak and hold on the Haltech.

[Roen]

Try your calculations for 4 x 550 cc's.

I forget what the hp number is, but most people recommend upgrading the injectors to 720 cc after a certain whp for turbo cars. Ballpark 300 whp. What's the efficiency ratio there? (for 300 whp and 4 x 550 cc)

[PercentSevenC]

Nice calculator for injector sizing:
http://www.rceng.com/technical.aspx

[NoDOHC]

Bear in mind that turbo fuel requirements / per horsepower are considerably higher than NA requirements.

Unless designed very carefully, a turbocharged engine is less efficient than a naturally aspirated engine.

300 whp looks like about 25% efficient with 4X550s (this is a little high for a stock turbo configuration) I would be worried with 4x550s at 300whp on boost.

[Whizbang]

throttle body, intake manifold and megasquirt arrived today!!

http://img.photobucket.com/albums/v230/Tsunami_Bomb/CSP%20FB/DSC03735.jpg

http://img.photobucket.com/albums/v230/Tsunami_Bomb/CSP%20FB/DSC03736.jpg

[SleepeR1st]

^^ Can you tell me that setup and where to buy those parts? I'm very interested in setting up an ITB setup but i want to stick with FI not carbeurators.

[Roen]

Bear in mind that turbo fuel requirements / per horsepower are considerably higher than NA requirements.

Unless designed very carefully, a turbocharged engine is less efficient than a naturally aspirated engine.

300 whp looks like about 25% efficient with 4X550s (this is a little high for a stock turbo configuration) I would be worried with 4x550s at 300whp on boost.

Still, we're talking similar efficiency numbers, or at least it sounds similar to my ear.

The person I know had to shut the car off on the dyno since the NA injectors' duty cycles were getting to high at 197 whp.

[NoDOHC]

If they maxed 4 460 cc/min injectors out on the dyno, and made only 197 whp, they either had the parking brake set or were running way too rich to make peak power.

The numbers will not be that close, I really doubt that a 25% thermal efficiency can be achieved with a stock turbo and safe tune on a turbocharged rotary.

I have seen 30% (calculated) on an NA rotary.

[Whizbang]

^^ Can you tell me that setup and where to buy those parts? I'm very interested in setting up an ITB setup but i want to stick with FI not carbeurators.

The megasquirt can come from a variety of sources.

The manifold can come from a few places as well. Same manifold for a Weber.

The ITBs i got used, but new TWM, Tweakit and a few other places have them.

[Roen]

If they maxed 4 460 cc/min injectors out on the dyno, and made only 197 whp, they either had the parking brake set or were running way too rich to make peak power.

The numbers will not be that close, I really doubt that a 25% thermal efficiency can be achieved with a stock turbo and safe tune on a turbocharged rotary.

I have seen 30% (calculated) on an NA rotary.

AFR was at 12.8 : 1, which is slightly richer than where I would've have put it.

[NoDOHC]

Where they running peak and hold on the injectors?
What was the fuel pressure?
What was the injector duty cycle?
What timing advance and split were they running?
Did they have a bridgeport or peripheral port and scavenge a lot of air/fuel charge without burning it? (Making the Air/fuel ratio appear leaner than it really was and wasting fuel.)
I can't think of any other reasons that the injectors would be maxed out at that low of a horsepower number.

Even the online calculators (which assume a higher BSFC than a well tuned rotary has) say that 460 cc.min injectors should make 250 WHp.

[Roen]

Streetport, that's all i know.

[Whizbang]

I am hoping to at least get the car running before i leave for basic. When i get back i plan on building another engine for it. But i should be able to see what kind of power i can get out of a stock port engine.

[Whizbang]

Peejay just made 170 with his streetport setup on a megasquirt via Dynopaks

[Whizbang]

Well the 13B starts. Going to attempt some rought tuning but i leave in 6 days for basic so i wont be back to touch it again til September.

[My5ABaby]

What ITB is that?

[Whizbang]

efi hardware Pro Race with the tapered air horns.

(be non sized down version of that pic makes a great desktop pic)


http://img.photobucket.com/albums/v230/Tsunami_Bomb/CSP%20FB/DSC01189.jpg

[chickenwafer]

Can RX-8's play? LOL

When I was NA I made 202-rwhp and 132 tq on a stock keg (no porting) and running the factory EMS (no tune). I had the stock intake and cat in place.

For all the crap the Renesis gets sometimes in NA form it's actually not too shabby :)

[diabolical1]

no question that their power is comparatively impressive, but i must say that i've been a bit disappointed with reliability - not of the motor, but the whole car.

[NoDOHC]

How did this ever turn out for power?

[Whizbang]

anyone have current updates?

also i would like to have altitude added in. My testing will be at around 4000 ft which will show less than anyone at sea level.

just need a wideband

[NoDOHC]

Only Updates I have are as follows:

216 WHp = 63% Duty cycle on 4 - 460 cc/min injectors on Peak and hold (14.16 V from alternator) giving 13.3:1 AFR. This comes from my Haltech data logging while I was on the dyno making 216 WHp. This is very comparable to online calculators.

I still think that 200 WHp is attainable for you, you have a better intake setup than I do (although mine had been heavily modified from stock). This should offset the altitude difference (I am at 800 ft).

[Whizbang]

i really need to build an engine for the car. The original 200,000 mile 6 port engine will die sometime.

[Tanj!]

i really need to build an engine for the car. The original 200,000 mile 6 port engine will die sometime.

It might last longer than you expect. Mine is up to 245k now and still running strong.

[Whizbang]

knowing my luck that is true, but it wouldnt hurt to get something in the works.

[Whizbang]

only 19 days til idaho. I am going to take on some changes once i get to working on the car again. Primarily going to CAS and having ignition control. Additionally, i am going to get a wideband so i can properly tune the car. otherwise its just guess work.

[NoDOHC]

What kind of port work did you do?

How are you actuating your 6PI?

That manifold that you used has to flow better than the stock 6-port manifold, maybe you can get 200 WHp. I am really convinced that the biggest problem with 6-port blocks is the late intake port close and the second biggest problem is the intake manifold.

[PercentSevenC]

The third problem is the tiny primary ports. If you use GSL-SE end plates you can use a Y or nitrided R5 intermediate plate, but then you have to use pre-'86 rotor housings.

[Whizbang]

my current engine is 100 percent original s4 6 port. I need to build something more suitable.

[NoDOHC]

You have an aftermarket intake manifold though, right? That has to help your power, there is not much worse design than the factory s4 intake for power.

[Whizbang]

yea its aftermarket

[NoDOHC]

Ok, maybe I am missing something, but what makes the P-port expensive?

All you need is a set of housings, some aluminum-ceramic or Devcon and a hole-saw.

Then you can fill your side ports with iron-ceramic or Devcon and you have a P-Port.

I doubt that you would need a 2-piece Eccentric shaft, etc. for a 250 WHp build.

[Whizbang]

eh, i guess homebrew wouldnt be soo bad to try. hmm now my gears are turning. i wonder what the limit of my ITBs would be.

[Whizbang]

im thinking about buying a drill press from the local industrial surplus place, and aside from other things, that should be able to handle some p-port drilling so i might say hell with it and experiment.

[NoDOHC]

rotor housings are cheap.

I want to do a semi-pp, leave the primary ports alone (they close pretty early) and fill the secondary ports, then connect a throttle plate for the two primary runners (I was going to use part of a TII manifold). Each of the peri-ports gets an ITB that feeds the port directly. A progressive throttle linkage will allow the engine to only run on the primary ports until about 30% throttle, at which time the P-ports will start to open.

I think it will work very well. If you don't try it, I intend to. I have the utmost confidence that you can do the project justice.

[RotaryProphet]

I had an idea for a setup where I would connect the primary and secondary ports together, and run each set to two of the ports on a four barrel throttle body, then run a pair of peripheral ports to the other two ports.

With a pair of reasonably small peripheral ports that open late to help keep overlap down, and a staged throttle linkage, it'd probably be reasonably drivable.

[PercentSevenC]

It's been done before. I think it was Jaytech that made a square-bore 4-barrel semi-PP intake manifold.

[NoDOHC]

The trouble with the late intake close P-port is that you might as well go with a side port. All the advantage of the P-port is lost if the intake port closes after pushing 40% of the engine displacement back out the port.

I think that the progressive throttle is the answer, keep the P-port throttle plates as close to the housing as you can get them and run the primary ports normally. The primary ports will not be open after the P-port has closed, so there is no loss of charge air. If you leave the secondary ports functional, your intake charge that just came in the P-ports will leak out the secondary side ports as the compression stroke begins, negating a large part of the P-port benefit (which would be a full compression stroke allowing better torque output).

Overlap is useless under vacuum, but does not hurt that much at WOT. In fact, with a well tuned exhaust and intake, the engine will actually flow unused air from intake to exhaust during the overlap, slightly cooling the combustion chamber and increasing net thermodynamic work from the next air/fuel charge. This will increase Volumetric efficiency and torque output.

If the primary ports (with no overlap) are used for idling and cruising, and the peripheral ports kick in only when the gas is floored, the car should have good driveability. I was going to use 6-460cc/min injectors, 2 in each p-port and 1 per primary port (in the center iron). This should give a decent transition, especially if the engine was tuned on TPS.

[Whizbang]

i am going to try straight Peripheral with the side ports eliminated.

but regarding the semi-pp, i wonder how an rx8 engine would work out with the whole side exhaust thing....hmm

[Whizbang]

well i know that the ITBs i have will flow 400 cfm per runner. What i need to figure out is what diameter runner would flow approx. 400cfm so i can size the port but i cant think of a way without knowing the velocity of the air moved.

[NoDOHC]

400 cfm is all?

The stock throttle bodies flow more than that (I saw a write-up with them tested at 950 cfm when ported).


i cant think of a way without knowing the velocity of the air moved.


Velocity is not the point here, but i will explain how to calculate it later. The point is air flow. Each rotor requires 0.65L of air per revolution, if you crunch some numbers, you can see what the engine will require.

I would put a peripheral ported rotary at 110% VE Average (based on port timing and overlap). This means that each revolution of the engine will require 0.71L of air.
If you figure your rev limiter at 9500 rpm, that gives you 9500 rev/m * 0.71 = 6745 L/min which gives 238 cfm. According to this math, your ITBs are plenty large.

Unfortunately, this math is not exactly accurate, as it assumes sufficient plenum volume to allow constant flow through the throttle plates. This is not so, as you will be mounting your ITBs as close to your P-ports as possible.

The air flow into an engine can be approximated as offset-sinusoidal (we will make this assumption for simplicity).

Therefore, the minimum air flow is 0 and the maximum air flow is 2X the average air flow. This means that the port will require approximately 2 * 238 or about 480 cfm at peak flow. Basically, you will have some pressure drop across your throttle plate during the intake stroke, but not a lot.

The runner should be sized with a velocity stack for the inlet, gradually reaching the same diameter as the throttle body, then with a constant cross-sectional area all the way from the throttle plate to the rotor housing. A slight decrease in section height while passing through the housing should give good fuel mixing characteristics.

To compute the velocity is easy, however it has no real bearing on anything unless you care about Helmholtz tuning. Never the less, you simply take the peak air flow (480 cfm) divide by the cross-sectional area of the runner in ft2 and divide by 60 to give ft/sec. this can then be converted to mach easily by guessing Mach 1 at about 1070 ft/s. You want 0.3 Mach (about 300ft/s) peak intake velocity for best resonance tuning effectiveness.

Tuning for 9,000 rpm, throttle body/runner diameter should be about 2.144" (about 2 - 1/8" or 54mm) Runner length should be around 9 inches from port beginning (cross-sectional area stabilizes at bottom of velocity stack) to port end (the combustion chamber)

These are all rules of thumb, but they are good ones. I think that you will find that your intuition is a good as a calculator on this.

[Whizbang]

from efihardware:

Each throat flows 399.6 CFM @ 20.4 inches of Vacuum.
On the 55/53/50 tapered bore model with a 75mm long Pro-Series Ram tube fitted.

without running both setups on the same equipment with some standards enforced, it might be difficult to compare them.

im assuming the velocity stack going into the throttle body will be sufficient, but if the throat is 50mm (ill have to measure it one day soon) i would not want the runner to be a larger diameter than the throttle body for a variety of reasons as far as i can reason, plus its only going to flow as well as the smallest part of the track.

Then again i will be also limited by what is available for piping. For 50mm, a 2" od piping with a 1.902 ID would be the best to try and maintain consistency and easy to purchase from speedymetals.com. Ill just have to verify if its not too thinned wall for welding or bending. If that is the case, then ill step up the OD.

[Whizbang]

also interesting note regarding mach numbers, the mach number increases with altitude, the difference might not be worthwhile given the lack on fine adjustment on other areas of the design, but i figured id throw that random fact out there.

[NoDOHC]

The speed of sound decreases with increasing altitude, so the mach number of a given velocity would be higher, yes. I forgot that you were tuning for high altitude. You will be moving less air at higher altitudes, so I don't know if that will offset the compressibility effects or not.

You are right, the throttle body should be the same size as the runner. Any change in cross-sectional area will not only adversely effect your Helmholtz resonance tuning, but will also increase pressure loss in the runner (hurt flow).

You are going to keep the two ports on the center iron, right? They will open later and close sooner than the P-port, which means that they will have no adverse effect on the P-port power, but they will allow the engine to idle and run successfully at partial throttle (all the p-ports I have seen have serious issues at partial throttle operation, they liked WOT only).

I really like this idea, it is what I wanted to do for a long time.

Keep up the good work!

[Whizbang]

it might be able to concoct a manifold with the center ports intake (and streetported) since i planned on making the whole thing away. Might a little time consuming, but time is free. Just lots of measuring and tweaking before a final weld. But would there have to be some form of additional throttle to limit the peripheral ports interference at partial throttle.

The first engine will probably but a standard PP, but for future use, its certainly interesting.

[NoDOHC]

Actually, it would take less time to leave the center iron side ports open and just cut the outside runners of a turboII manifold, leaving the primary runners only and a single throttle plate at the end. You would have to leave enough of the flange to catch the two studs in the housings and that single bolt in the center plate, but you should have room for that.

It takes a lot of time to fill ports in (although I would DEFINITELY fill the secondary ports, as leaving them will hurt your power a lot). The primary ports will not effect the p-port at all, as the open later and close sooner.

If you set the throttle up so that 50% on the pedal is WOT on the primaries and 0% on the secondaries (peripheral ports) and the 100% is WOT everywhere, I think you will have something. (I actually wanted the primaries to continue past open until they had closed going the other direction - 170 degrees of throttle plate rotation - but either way will work.)

The slider is a very good means of doing this (has been used on transmission kickdowns, mechanical secondaries for carburetors, etc.)

As I said before, this is my idea of a 6PI system that would actually make more power (although it is technically a 4PI).

EDIT: Oh yeah, don't worry about porting the primaries, just clean the manifold up a little. This is not where your engine will be getting the air to make big power, just the air to idle and cruise, which is better if turbulent (smaller port is better).

[Whizbang]

hmm...its an interesting thought. Im still set on building the first engine as a regular P Port, but the next engine i have to always out do myself. i could probably use two different diameter throttle rotors. have one for the throttle cable to connect to, then attach a second rotor of another size (pending what is being driven) and have that rotate the other throttle cable.

[RX200013B]

If you set the throttle up so that 50% on the pedal is WOT on the primaries and 0% on the secondaries (peripheral ports) and the 100% is WOT everywhere, I think you will have something.

this is what i am tring to build the winter, just a little different
t2 center SP, 6pi ends w/ bridge on the lower ports, itb's
with the 5,6 ports only open at WOT

should bring out some good torque!? i hope

[Whizbang]

i might actually just be opting for a good four port streetport for the first engine in the rally car. I really doubt i will be able to put much more to the ground. Really depends on what mood im in when i get to building the engine. Making the Peripheral just seems like a better way to go. Id rather have more power on hand than less.

[NoDOHC]

I truly believe that you can get 250 WHp out of a streetported 4-port. Maybe not at 4,000 ft, but 250 WHp just the same.

I can hardly wait until I get a chance to find out.

[Whizbang]

i thinking about lowering my standards for the next engine to a full bridge. We shall see. Im somewhat indecisive at this point.

[RotaryProphet]

I would just build the P-Port. It'll make the power, and the low end will be just about the same as the bridge. With EFI, it'll even be streetable.

[Silver86]

I truly believe that you can get 250 WHp out of a streetported 4-port. Maybe not at 4,000 ft, but 250 WHp just the same.

I can hardly wait until I get a chance to find out.


same here.