eage8

iTrader: (9)

I was thinking the other day (which usually ends poorly...) if you leave stock ports alone and just increase boost pressure you'll get the same volume of air into the engine... but maintain torque (air velocity) at low RPMs....

This of course only applies to intake porting (not exhaust porting... which evacuates heat from the engine...) and also doesn't take into account the advantages/disadvantage of changing port timing...

but would a stock port engine be able to run more boost than a ported engine to make up for the lack of air flow?

RGHTBrainDesign

What happens when you increase pressure on a compressible fluid such as air? --> It heats up.

Whatever gains in torque you'd have are outweighed by thermal losses in efficiency.

peejay

Torque isn't air velocity, torque is mass flow and combustion efficiency. Increased mass flow at a given RPM increases torque whether it is from improved ports or compressing the air before it gets into the engine.

lastphaseofthis

iTrader: (8)

think of it like this
the turbo doesnt need the engine. it needs fuel and air like the engine does and it could run on its own. the fuel and air burning (expanding) drives the turbine which drives the compressor, compressing the air and then mixing with the fuel before entering the turbine housing. thats how turbine engines work.
by placing the stock ported engine in the way of the flow path(of otherwise just turbo), you slow down how much air the turbo compressor feeds into the exhuast turbine. porting increases flow, and therefore gets the turbo into positive pressure sooner then a stock port.
i think with a periport and a small *** efr 7064, we could see 300fts of torq by 2k rpm. positive pressure would come in right off idle maybe 1100 rpm. as soon as you tap the throttle you build boost.

boost takes are of the peri port overlap.. now all you need is two ( or three) more 7064s to be turned on when the first one runs out of flow at 3k rpm.

i think if you took a 100hp brushless motor and put an efr 7670 compressor on it. you could turn the boost on at 1k rpm and achieve ridiculous torque
you need something to power the compressor into the rpms that it makes power.. the stock ports don't allow enough exhaust into the turbine to spin it up that soon.

the focus should be getting air and fuel energy into the turbine to decrease spool time, porting does this.

RGHTBrainDesign

100HP Brushless Motor? Mang, that's huge. You don't need that big to get the 7670 turning happily (you do need a gear reduction box however).

Here's what turns a turbine...MASS, as said before. Ever wonder why people intentionally run richer AFR to spool faster? Let me break that down for you...

#1 Air Density @ 925C (Wide Open Throttle Exhaust Gas Temperature) = 0.296223 kg/m3
Gasoline (combusted) is roughly 719.229 kg/m3
Our ratio of 11:1 Air to Fuel ratio generates an average density of the mass flowing through the exhaust of 722.487 kg/m^3
722.487 / 12 = 60.207 kg/m^3 Estimated Average Density of the Mass

#2 Air Density @ 700C (Mid-Throttle Application Exhaust Gas Temperature) = 0.364713 kg/m3
Assume a 12.5 Air to Fuel Ratio for Mid-Throttle Application
Leave Fuel at same 719.229 kg/m^3
723.788 / 13.5 = 53.614 kg/m^3 for the Mid-Throttle Application Average Mass Density

#3 Air Density for Tip-In (light throttle application) is @ 400C =0.527253 kg/m3
Air to Fuel Ratio is 14.7:1 for this light throttle application
Assume Same Fuel Mass Density of 719.229
726.980 / 15.7 = 46.304 kg/m^3

How to spool a turbo faster? Throw more mass at it.

lastphaseofthis

iTrader: (8)

Basic » TPPOWER

so two questons.
how bigger of a compressor could you drive with that, or how many 9180 efr compressors?
how much flow can a p port handle at 2k rpm? wouldn't that be surge limit on bigger compressors?

RGHTBrainDesign

How many Teslas/Prius/Rimac Battery Packs will you be using? How will they be configured? At what point does the weight become an issue? When you consider the electronics controller to be in the $5-50k range as well as having an ECU that communicates with it to integrate it all, when is the point when you realize you're working backwards? Are you going to be regenerating energy back into your battery cells from spinning the motor backwards as well?

Look, I love the idea here, but the entire point of a turbocharger is to regain lost energy from the exhaust and turn it into a more efficient Otto Cycle (which gains us more power per displacement).

Porting gains us more power per displacement with the drawback being higher emissions and more volatile at lower RPMs. Correct me if I'm wrong here, but you could run 2" ID in and out (peripheral port housings) and leave porting side housings various different configurations to actually effect timing and such. Why you can't live with a powerband from 3k-9k is beyond me. That's MONSTEROUS. Those turbos do it all...which is why I'm getting one. My suggestion? Rev higher and run gearing that benefits your usage.





Next issue... You're running a 12k MAXIMUM RPM Brushless motor and a turbo that runs 116k RPM before falling out of efficiency range. You'd want a 10 to 1 Gearing on that, or a variable (viscous) coupling like how an automatic transmission works.

Let's see a kit. Design us something on here that meets your goals.

lastphaseofthis

iTrader: (8)

oh well, im just throwing ideas out there... but the system will be two or more compressors. the final compressor driven by turbine.
the cost is so prohibitive, this ain't gonna happen by me. unless some millionaire sees my ideas here and desires to fund my dreams.
but yes and yes, so everything in the system would be fully intergrated for regenbraking, only 10kw battery would be needed. no 65s
also a/c induction motors would be better then DC magnet... i don't think i would use THAT motor, but more so showing whats already out there. i dont think i need 100hp to turn a 7670 compressor... and i've found 25 hp brushless motor that turns 100k rpm. no gear boxs! ever!

i may try to do a small scale version.. i just wanna see a maxed 7670 compressor on a p port engine at 2k rpm. developing the rest of the powerband/twin compressor change over all that would come later.

i want a 6k spread. from 1500 to 7500. less revs is less wear from centrifugal force wearing out apex seals above 8k rpm.

RGHTBrainDesign

Aight, make it happen. Leggo!

BLUE TII

iTrader: (9)

but would a stock port engine be able to run more boost than a ported engine to make up for the lack of air flow?

Yes, even the stock rotary ports are huge and without the restrictions of valves and such that piston engines have.

Port flow (if you don't mind high boost) is not really a problem on making big power on the rotary until you hit some pretty big power numbers (though I couldn't tell you exactly what that is).

Pretty sure the 500-600rwhp range has been done on stock ports. I wouldn't doubt more is possible if you don't mind flogging a huge turbo on race gas.

This thread probably isn't about big power or big turbos though since you also are considering low rpm torque.

I was thinking the other day (which usually ends poorly...) if you leave stock ports alone and just increase boost pressure you'll get the same volume of air into the engine... but maintain torque (air velocity) at low RPMs....

Yes, you can maintain the stock torque at low rpms you had and then add more torque with more boost (if the turbo is capable of more boost at low rpms).

Sometimes maintaining isn't the best you can do though.

If you do port, you can do so in a way that also add more torque at low rpms and then you still have the choice to add more torque with more boost (if the turbo is capable of more boost at low rpms.)

Most people port focusing on adding torque at high rpm.

To port for low rpm power one would do-

Earlier intake opening to increase VE at all rpms. Scalloped rotors are best way.

No later intake closing (velocity)

Keep any increase in port/runner volume to an absolute minimum (velocity)

Keep exhaust timing and volume very conservative (velocity). Porting and a flow bench could still help. Turbo car could have earlier opening if you are able to take advantage of anti-lag effect.

Improve flow in any way while maintaining velocity. Semi p-port primary (with side port 2ndaries blocked off with double throttle) would do that or more simply a bridge primary with the stock port filled in completely and double throttle.

Back to these pics I posted in your porting for torque thread-

You can see that p-port increases VE at all rpms (and so torque) unless you choose for it not to (race porting).
https://www.rx7club.com/attachments/...-photo0202-jpg
https://www.rx7club.com/attachments/...-photo0204-jpg

You can see the affect of side port volume and late closing- which largely validates the common misconception that porting will kill torque, since common porting is to make the port bigger.
https://www.rx7club.com/attachments/...-photo0203-jpg

arghx

iTrader: (3)

ding ding ding!

Here's the problem with porting the intake ports. If you make the intake port close later, you will shift the powerband to the higher rpm range. You WILL lose mid range, all else held equal. It's the same on a piston engine if you close the intake valve later with variable valve timing or a different cam grind, but same valve lift. There are a bunch of Mazda papers that talk about this, which are related to the design of the n/a 6 port engines (Rx-8 Renesis and non turbo Rx-7).

So with bigger ports you can actually need MORE BOOST to make low end and medium speed torque than with stock ports. That's because the duration is too long (devil is in the details though, there are more factors than just intake port closing timing). The same applies to Miller cycle piston engines (Mazda's old Miller cycle supercharged engine, but also modern engines like a Fiat MultiAir turbo engine). They close the intake valve so late that it hurts torque.

Yes! Bigger exhaust ports by opening earlier means that the engine loses expansion work. Instead of expansion stroke for say 60 degrees long expansion stroke is effectively 50 degrees long. It's the same on a piston engine when you open the exhaust valve earlier and get an earlier blowdown. You get less expansion work. This hurts low and medium speed torque, where the flow isn't needed. High speed is when you need a lot of exhaust flow to reduce energy wasted pushing the exhaust out. That's where the early exhaust port opening helps you, because less energy is wasted pushing exhaust out of the combustion chamber.

You see the same thing on modern turbo piston engines, which retard the exhaust cam at low speed and then advance it at high speed (also doing this for overlap/scavenging effect).

BLUE TII

iTrader: (9)

Yeah, the only caveat on the exhaust is you may be able to get torque gains from higher boost with slightly earlier opening despite losing a bit of engine torque from less expansion work.

More boost is more torque.

I found the same thing with ignition timing on the dyno (loading dyno). You can retard timing at low rpm and gain torque. Why? Boost goes up.

Its also possible to get a crap feeling engine by tuning this way.

An engine with crisp throttle tip in power can feel like it has more torque than the same set-up with anti-lag (extra fuel, retarded timing) that makes more torque at the same rpm (but does not make more torque in the same instant).

The human body is VERY sensitive to time. You can feel events that take mere milliseconds.

peejay

I did a 6 port with opening as early as I dared without side seals falling in, didn't notice one bit of difference as far as i could tell.

Port closing has nothing at all to do with velocity! If you want intake velocity, you need to manage your cross sectional areas and work on your exhaust tuning to get the intake moving again during the overlap period.

The torquiest non bridge engine I've ever had was a extended street port 12A (NOT any of my 13Bs!) with a rather "interesting" intake manifold. It started life as a shutter valve style manifold but I removed the shutter valve and did a complete epoxy fill of the channels (making it, effectively, fully ITB) and added a ton of epoxy to the #2 runners so they were equal to the #1 runners in CSA. I used to amuse myself by putting it in 5th gear at 1000rpm and whacking the throttle open - it would pull quite strongly!

Bear in mind that when I did the extend port, I did NOT open runner size any more than stock, and the goal of the porting was not "more timing" so much as "direct the airflow to the middle of the chamber when the rotor was at 90BBDC to BDC". You generate the velocity in the ports HERE so the port is still moving when the rotor goes past BDC and the chamber starts closing for 50-80 more degrees before the port is shut.

THIS is why later closing tends to make a later powerband. At low RPM with late closing, if you don't have tornado-like velocity in the runner, the port will shut down before it is closed. As an additional Bad Thing, that also means it takes time (energy!) to get the port moving again for the next cycle. If you have good velocity in the ports, you can close them later and still gain torque at the low end.

BLUE TII

iTrader: (9)

Port closing has nothing at all to do with velocity! If you want intake velocity, you need to manage your cross sectional areas and work on your exhaust tuning to get the intake moving again during the overlap period.

Port closing line does have to do with velocity because the later you close the port the higher velocity you need to overcome the pressure build up from the shrinking intake (really into compression) stroke.

Which you seem to understand and agree with judging from this statement-

THIS is why later closing tends to make a later powerband. At low RPM with late closing, if you don't have tornado-like velocity in the runner, the port will shut down before it is closed. As an additional Bad Thing, that also means it takes time (energy!) to get the port moving again for the next cycle. If you have good velocity in the ports, you can close them later and still gain torque at the low end.

BLUE TII

iTrader: (9)

peejay

I did a 6 port with opening as early as I dared without side seals falling in, didn't notice one bit of difference as far as i could tell.


You gain a small amount of VE going from 32ABDC to 24ABDC which is about the limit of just dropping the 1 side seal in while the other rides the side housing still.

Mazda found you gain more VE moving the side seal on the rotor, porting to take advantage of this move and then beveling the rotor edge. This got them to 0ABDC on the RX-8.

Working on the other side of the corner seal track for early opening and bridge porting provides even more noticeable increase in VE.



On a turbo car, in addition to the VE gain from early intake opening/overlap you also actually benefit from more air and fuel into the exhaust which results in more exhaust volume which results in more boost.

RGHTBrainDesign

Which is why I did that mass calculation above. Richer AFR = more mass hitting the turbine wheel = earlier spool up.

JZG

2x 13B turbo engines both running EFR9180/1.05, 4in exhausts, E85 fuel, same injectors, same ECU, same dyno. Both used for drifting.

One engine has large street porting – 676rwhp. 30psi, dropping to 28psi at 8500rpm – 100k turbine speed.
The other engine has large street & semi PP porting – 663rwhp 25psi at 8500rpm – 101k turbine speed.

Both have totally different fuel maps but almost identical power curves. Turbo response is the same.

Street porting wins for every application except 800hp+ drag racing. More cost effective, easier to tune, less sensitive to turbine back pressure.

The turbo doesn't know or care what porting the engine has. The turbo moves X amount of air at X turbine rpm to make X amount of power. The variable here is the pressure ratio - dictated by port swallowing capacity. As long as intake temps can be controlled the turbo can make X amount of power at X turbine speed regardless of porting and its by product, pressure ratio.

Boost is almost irrelevant. To get the most out a turbo at any given engine rpm we should be looking at turbine speed, turbine back pressure, and wastegate valve position.

lastphaseofthis

iTrader: (8)

i think most of us would like to see the torq curve of those two, i know the torque curve of the semi pp motor from your other thread, do you have a link to the first motor?

BLUE TII

iTrader: (9)

9180 at high boost like 25psi or 28psi on a 13B is an example of a powerband that is almost entirely characterized by the turbo surge line under about 4,000rpm.

So it is no surprise the dyno charts look very similar even with comparing street port to semi p-port.

I wonder if the semi p-port in this application will help cool the apex seal with air/fuel and help it live longer?

Brettus

I recently tried a bridgeport on my turbo Renesis setup . It didn't work . Made pretty much identical power right across the rev range to the previous stock ported engine . While I accept that my turbo (GT35 1.01AR )was perhaps not ideal to take advantage of the bridgeport I would still have expected to see some improvements early to mid rev range before turbine backpressure became higher than boost pressure .

The fact that it didn't work got me thinking about why it works so well on a PP engine having way more overlap. The conclusion I came to was that a high % of the benefit from the bridgeport comes from air/fuel mixture bypassing the engine alltogether and combustion occuring in the manifold . Thus providing power to the turbine which in turn reduces the backpressure inside the engine and allows the engine to make more power .

Does this hold any water or am I missing something ?

lastphaseofthis

iTrader: (8)

and the only way to move the surge line is to use a smaller turbo?

RGHTBrainDesign

No, to supply more air to the compressor.

JZG

I didn't tune the street port and I know the dyno sheet isn't on the net. Next time I'm on they dyno I'll overlay the two engines if I remember.

JZG

More overlap doesn't result in power sooner at lower rpms. I back to back tested this with the 663hp semi pp mentioned earlier. It was a street port until I turned it into a semi PP with no other changes. It just made the same power on less boost and ran out of compressor flow at slightly lower engine rpm (ve vs rpm). It didn't spool any quicker and the tuning window got narrower. There was no real difference in intake temps because compressor speed doesn't change, only pressure ratio slightly.

In my experience the power curve is almost totally dictated by the turbo selected for the job.

Once again, it's hard to beat a good street port in every application except all out drag racing.

JZG

You would think so but in my experience you are more likely to bend seals due to over heating as the turbine back pressure/boost ratio goes above 1:1. More overlap generally means richer mixtures are required to keep the apex seals under their critical temperature.