Not at all. That is actually the recipe for an engine that only makes power up high.

I have a bridge ported engine now, what does that tell you?

It doesn't take much throttle at all, actually. On my current engine the curve is a little weird, it cruises okay at 60mph but less than that and it starts lumping a little, at 45mph it is just about undrivable because there isn't enough load on the engine, but at 35 it runs nicely in top gear as long as the road isn't downhill.

The hard part is the transition between brap and smooth combustion. It doesn't really transition very smoothly, you have to kinda punch through it, so I mainly drive it on surface streets by giving just enough throttle to run smoothly and controlling my acceleration rate by upshifting. And I take advantage of Greater Cleveland's excellent network of highways to minimize the use of surface streets in the first place.

It does idle smoothly at 700-800rpm but this is at about 80-85kpa (local atmospheric is about 93-94) so off-idle response is a little soggy and there is no power brakes, and the alternator doesn't charge when it runs that slowly, so I usually set it to idle at about 1100-1200, a point at which it doesn't really brap but has more of a popcorn-popper sound, rolling into brap for a couple seconds out of every ten or so.

 

Care to show me dyno examples where opening the side ports earlier improved low end tq and boost response?

 

They're all over the place in this very thread...

 

Its been a long night so I could be mistaken, but you sure we are viewing the same thread? I dont see any examples, the only one example I see on side ports shows the exact opposite of what you are saying. Again, its been a long day so forgive me if I am missing something here.

 

You are correct djseven that there isn't any information in this thread relating early opening to stock opening intake ports with data.

The data shown is peripheral port versus side port. This does show the added volumetric efficiency from earlier intake opening extends throughout the rpm range- at least on the dyno test bench.

When you get the engines into a production car with quiet intake and exhaust you have phenomenon like that same NSU KKM-502 peripheral port motor making 65hp in production car trim instead of 100hp as shown on the dyno test bench. Or Mazda's Cosmo semi peripheral combo port motor making the same power as its later side port only counterpart in the higher production R100.

The information is relevant to us as in racing we don't have the same constraints as OEMs.

The Curtis-Wright small port versus large port chart does not state differences in port timing and I was not able to find this in the chapters text. It could be a study in intake velocity (small port versus large port ) or it could be a study in late closing versus early closing (late closing port would be larger if all other factors were the same). Sorry I don't know.

All pictured side ports shown in the entire book open as soon as possible and it is repeatedly stated that the main disadvantages in the side intake port configuration is lack of sufficient overlap and the 90 deg turn into the engine. The pros are low load performance/smoothness and they do sometimes mention torque despite all the data showing less torque for a side port.

I can only imagine they mean better transient throttle tip in torque response.

Which will really matter in say autocross, but I didn't get into that yet.

Anyways, as stated earlier- Mazda's development of the rotary has been exactly the goal of this thread- how to produce more torque (but still maintain emissions, noise, etc).

Can't go wrong with a stock 13BREW/turbos. Even better, get the whole car.

 

two points.

1. nobody has ever torn the engine down and ONLY ported the intake to open earlier, and shard results. everyone always changes a bunch of stuff. the only thing i've seen that's back to back with just the 1 change is 9.7 vs 9.0 rotors in a turbo car (9.7's were -50hp)

2. Mazda has published intake opening vs power (actually its probably VE), in a SAE paper, its on the other computer though, so please hold

 

Damn, are there dyno sheets for the rotor change? Link?

 

All my experience building/porting is with 13B-Rew turbo setups so I was curious if some of the NA guys had seen something I haven't. Any porting at all has always moved the torque curve to the right on the graph with turbo setups, no matter the turbo/exhaust setup(assuming they stayed the same before after port work). The FDs drive ability really suffers with early opening intake ports and later closing exhaust ports. The last 2-3 years I've really adopted the "less is more" mentality when I port for customers unless they specify they won't large ports. I was just curious if there were any results that show earlier SIDE port opening improves or even keeps the low end torque the same. Always curious to learn something new.

 

team FC3S forum is gone! basically on the 9.0 rotors you already have to tune the thing conservatively, and 9.7's you have to be even more careful to the point where it doesn't run anymore, and/or it blows up.

on this forum there was a guy, Rx7heaven (white vert, did the giant body kit), who did it, with the same results.

the 9.7's can work, but you need race fuel, or some kinda alky-haul

 

The key to remember is, more overlap is good when intake pressure exceeds exhaust pressure. Yes, there is the "exhaust obstruction effect" where the backflow is timed for pulsation effects on the n/a engines. On the turbo engines, you are really killing your off-boost response by increasing overlap due to intake dilution. The problem is the fixed nature of rotary intake ports, compared to modern piston engines with variable valve events.

I'm digging through all the stuff I have right now I am not finding relevant charts on intake port opening timing VE for SIDE intake ports (plenty on pport race engines). Here are a few charts...



This is from Mazda's paper on the original 13B 6 port induction system for the GSL-SE series 3 engine. The pic above is from an experimental rig that doesn't have a real intake manifold plenum.



This is from Mazda's paper on the 20B Cosmo sequential twins. You can see the powerful exhaust pulses of the rotary. On a piston engine, you have the blowdown phase and the high flow phase of the exhaust stroke. A rotary is almost all blowdown. If these pulses blow back into another rotor, due to manifold design and/or overlap, you've got a big performance hit.



Here's my attempt (bottom graph) to illustrate a mild street port with only later intake closing timing. Somebody is free to provide input on this. I'm more used to playing around with cam profiles on piston engines.



Here's the full-lift valve curves for the BMW S63T twin turbo V8 engine in the current M5. Note that this engine has twin twin-scroll turbos inside the cylinder valley. You can see below stats on the old nonturbo V10 engine, the S85. On turbo piston engines with variable valve timing, typically you want to dial in high overlap (advance intake and retard exhaust) during spoolup. This creates a lot of scavenging. The scavenging improves VE and also moves the turbo horizontally on the compressor map to prevent compressor surge. As rpm rises you move the cams much closer to their parked, low-overlap position.

The difference between a rotary and a piston engine with modern variable valve timing and lift is that a high overlap rotary is "stuck" in high overlap at all times, like a pushrod V8 with a big cam. Piston engines with independent cam phasing dial overlap in on command, only when it's advantageous.

Here's one more thing to consider. On continuously variable valve lift engines which are nonturbo, the lift and duration increases with rpm as you go full load. On turbo engines with continuous lift control, with only one exception I can think of, the engines go full lift almost immediately after tipping in, and rely on the cam phaser.

 

SSM RX-7s seem to do well with race gas and 9.7:1 rotors, but yeah- these are real race cars using race gas.

If its for pump gas I prefer 8:5:1 rotors and more boost over 9:1.

I found on a turbo car boost IS torque, compression ratio gives you good throttle response, but I didn't notice any difference in spool between 8.5:1 and 9:1.

The FDs drive ability really suffers with early opening intake ports and later closing exhaust ports

I agree that later closing exhaust ports give you a soggy bottom end. I disagree with the earlier opening intake street ports hurting bottom end though.

The last 2-3 years I've really adopted the "less is more" mentality when I port for customers unless they specify they won't large ports.

I agree with this 100%. As I posted first in the earlier thread, if you want more torque on a turbo car focus on the turbo/exhaust system.

Stock ports will keep you from hurting side seals or power band like the wrong kind of port could...

 

I couldn't agree more. There's more to it than that, but you need to increase mean effective pressure to get more torque. What you'll find on turbo engines with a lot of torque down low (basically, modern stock turbo engines), is that they boost so much at low rpm that they are close to compressor surging. You're talking like 20+ psi at 1500rpm. That's why they have to use scavenging aggressively to increase mass flow.

During overlap, a lot of the air that turbo is blowing doesn't even go into the engine, it just blows out the exhaust.

 

 

Maybe this is what you meant by that

 

Yeah that's more along the lines of what I was saying, thanks.

 

I hope I'm Not Thread stealing , but I was curious about Similar Dilema. With exhaust porting .

But not somuch torque as quicker spool in order to take advantage of Boost torque .

I plan to use the stock twins for now , and upgrade them to BNR's later on .

I know the Limiting factor in exhaust porting with the stock twins is the stock manifold .
Would Porting the exhaust to match the stock manifold Give me quicker spooling?

but I read this , and i'm wondering if its related .

does a soggy bottom end mean I will get slower spooling because of the later closing exhaust , which would naturally happen when you port them .

my goal is to be able to open up the secondary turbo a bit sooner with improved turbo spool.

 

Install 9.7:1 rotors and use the PFC/Dataloggit to transition the secondary a little sooner. Its about all you can do. Its exactly what I plan to do with my 94R2 with 99spec twins if/when the original motor ever lets go.

 

I've got FD rotors , and power FC I already have the twins opening up a bit earlier but I would like to increase the spool if possible. that was another option going with the N3G1 Twins for the quicker spool but

While the engine is apart and getting built if I could get some more spool out of them with some porting why not .

I guess my question focuses on When and what we're concidering bottom end ? , say at 3k RPMs will I be getting more boost from the turbos then I was with the stock ports or less?

does the soggy bottom end reffer to 800-2000 rpms ,

or 800-4000 rpms lol

 

I guess my question focuses on When and what we're concidering bottom end ? , say at 3k RPMs will I be getting more boost from the turbos then I was with the stock ports or less?

does the soggy bottom end reffer to 800-2000 rpms ,

or 800-4000 rpms lol

Good point. I personally would consider bottom end to be 2,000-3,000rpm. Midrange 4,000-5,000rpm and Top end to be 5,000rpm plus.

Idle to 2,000rpm I would call driveability- you are doing something wrong if your vehicle performance is being hindered by power in this range. Then again, if your engine is totally soggy at 1,500rpm I don't see how you are going to have good power by 2,000rpm.

I find myself driving in the 2-3,000rpm band 90% on the street.

While the engine is apart and getting built if I could get some more spool out of them with some porting why not .

I personally wouldn't do a traditional street port to an engine on the stock twins unless I really really wanted more top end power and I was too broke to afford a good sized single. If I was (I am) keeping the stock twins by choice I would keep stock ports. Can smog, has good power band, easy to replace parts quickly, can brag its stock (and fast), can class easier in racing for being stock.

If I was ambitious enough to port I would just have the intake open as early as possible on street port and close as close to stock as possible with seal safety. I would leave the exhaust alone or work with it's shape on a flow bench to get more flow with very near stock timing and seal safety.

You say you might be interested in porting to get more spool out of the stock twins, but they see full boost by 2,000rpm with intake and exhaust and boost control.

Am I misunderstanding?

 

I'm totally with you on the exhaust ports, but how can you open the intake port earlier and not have greater overlap? And then the overlap causes dilution under off-boost conditions (spool up). Whereas later intake closing will hurt low end, but it doesn't affect overlap in the same way.

It'd be nice to have some 1D modeling or an engine dyno...

 

Tem120, I understand now from your other thread what you mean. You want to be able to bring the 2ndary turbo online sooner.

I haven't experimented with that yet.

One advantage I could see to staying on the primary turbo as long as possible would be good response at all rpms below the switching point.

Seems like any time you are getting on the gas above the secondary turbo switching point and the secondary turbo is still locked on you are going to have poor response.

One advantage I could see to bringing the 2ndary turbo online as soon as possible would be that with both exhaust housings being used you *could* have a higher overall system volumetric efficiency for more power at the same boost. Though on the FD the shared turbo outlet may have some negating effect on this.

 

I recommend changes to the secondary turbo hysteresis "Turbo Transition Low" in the Power FC controls to address this. Basically, you make it switch back to the primary turbo more easily after rpms drop.

Without a divided manifold, I wonder about exhaust gas interference on the twins. I suspect changing the exhaust port timing makes it worse.

 

I'm totally with you on the exhaust ports, but how can you open the intake port earlier and not have greater overlap? And then the overlap causes dilution under off-boost conditions (spool up). Whereas later intake closing will hurt low end, but in a different way because it doesn't affect overlap in the same way.

It'd be nice to have some 1D modeling or an engine dyno...

Yes, you would have more overlap with the intake opening earlier.

But, I maintain its the "right kind" of overlap and in about the right proportion.

With the stock opening at 32 or 45 degrees After Bottom Dead Center your expanding intake chamber is "sucking" exhaust into the intake stroke for 32 or 45 degrees before the intake port opens and allows it to start "sucking" intake air/fuel in. Even with an early opening street port you are at around 24deg ABDC. You have to reposition the side seals, put in a larger corner seal and bevel the rotor edge to even get to 0deg ABDC (like RX-8).

Getting the intake port open a little earlier will stop you from sucking in as much exhaust for both less dilution and lessening of the reversion wave when the intake port does open and gets the intake open while the exhaust velocity is a bit higher for more intake scavenging kick starting the inertia needed for good intake chamber filling.

If you port the exhaust up and leave the intake port at stock opening you now have less velocity at the exhaust port when the intake opens since it is further from the blow down phase. This means you have less scavenging from the exhaust to pull the intake mixture through and kick start the intake inertia for good intake chamber filling.

Physical size difference from porting the exhaust port up also means less velocity for less scavenging of intake and exhaust.

I would be very interested to see how a bridge or semi peripheral ported renesis responds with a turbo.

I think you are thinking of exhaust pushing its way into the intake during overlap. This isn't the case, you are losing intake to the exhaust port.

If you eliminate the EGR valve, crankcase ventilation and evaporative emissions from a rotary your intake ports and intake manifold remain clean and carbon free. How is this possible if all that exhaust is pushing up into the intake chamber when the throttle plates are closed?

If you take apart a peripheral port or bridge port race motor is the intake carboned up? Yet there is enough exhaust dilution that the motor misfires constantly at idle.

Its because the closed throttle plate prevents the intake stroke from pulling in enough air to both feed the loss to the exhaust port and fill the expanding intake chamber during overlap so it overcomes the vacuum from the exhaust scavenging the intake chamber and sucks exhaust in. The exhaust is being sucked by the expanding rotor/rotor chamber which is swept clean by the seals. There is no draw from the intake ports so they remain clean.

 

Thanks alot for the information great read from you guys as always .

 

^^ You raise some good points, and I wish I could see empirical evidence that what you are describing occurs at say atmospheric pressure (primary turbo hasn't come online yet) and 2000rpm full throttle.

I think we are all in agreement that the stock ports, both intake and exhaust, are for the most part optimized for spool already.