Snook

iTrader: (12)

Any experience with boost increasing or airfuel ratios changing doing this?

Does it matter what type the resonator is?

Wanting to switch to a straight through design without retune if possible.

Thanks

adam c

iTrader: (2)

The more restrictive your resonated pipe is, the more likely you will need to adjust tuning with a straight thru mid pipe.

ondabirdhouse

iTrader: (26)

Adam C is correct.
Generally when you swap to a straight pipe from stock people see boost creep on the stock ecu/twins because it far less restrictive. As a result they need a good boost controller to limit/prevent the creep as the stock ecu can't keep up and provide enough fuel for the added boost.

The real question, what setup are you running now? ECU/tune, twins vs single, exhaust?
If you already have a PFC and a good tune then as Adam C mentioned it all depends on how much of a change there is between the the old mid pipe and the new.

Snook

iTrader: (12)

Thanks guys was looking for some real world experience of someone who has done the same.

On seq twins with street ported motor intercooler and full exhaust on custom tune pfc

Monsterbox

iTrader: (6)

If your RX7 is tuned somewhat conservatively, there shouldn't be much of a risk swapping from a Resonated Midpipe (such as the RX7 Store magnaflow design) to a straight pipe. The AFR will be SLIGHTLY leaner, and boost may come on a bit faster, but the difference would be minimal.

I've swapped from Resonated to non-res on 20b and it seems it may be a few tenths leaner on the AFR gauge at full boost, but its so negligible that I can't really plot the change

As long as your in the 11's and your timing is good with boost under 14psi on those twins, you're likely good to go.

Snook

iTrader: (12)

Thank you that's what I was thinking but you never know with how sensitive these cars are.

I know going from stock cat to midpipe would be a disaster, and from a recent experience I heard of a high flow cat to a midpipe can also definitely blow a motor.

I guess this same question could go from switching from a restrictive aftermarket catback to a better flowing catbcak.

I guess the best way to know is to put it on the dyno and test it to be safe.

j9fd3s

iTrader: (3)

that is actually the problem! its a lot of work to find out how sensitive it is.

worst case, is that the resonator is a little restrictive, and the tune is a little lean, so when you unrestrict it, it gets leaner...

in reality its probably not going to make much difference...

Montego

iTrader: (1)

These cars aren't made of paper. Just be smart about what you are doing and become knowledgable and you won't worry as much. For the record I seriously doubt that switching from a Resonated MP to a MP will affect anything. But for fun lets do a more extreme case. Lets say that you are switching from a CAT to a MP. Is that safe?


Think about it for a second: The A/F ratio has two criterions.

A) Air coming into the combustion chamber
B) Fuel delivered into the combustion chamber

So how is a midpipe that is connected on the exhaust going to affect the air going into the engine? Seriously give it some throught before going further. Notice I said air not fuel as we should all know that a MP will have absolutely nothing to do with fuel delivery.

Scenario 1: A less restrictive exhaust will cause the turbos to spin easier and therefore elevated boost occurs. Higher boost = more air. If nothing has been done to compensate for the extra air then the A/F ratio will be leaner. Easy fix: Dial down the boost using a boost controller

Scenario 2: With a less restrictive exhaust will cause the turbos to spin easier and therefore boost spikes can occur. Boost spoikes mean more air. Easy fix: An electronic boost controller can easily take care of that as the boost response can be tuned.

Scenario 3: With a less restrivive exhaust boost creep can occur (Boost creep happens the wastegate cannot bleed off the air fast enough and therefore higher that expected boost levels occur at higher RPMs. Cannot dial down the boost because it is a wastegate inneficiency (boost is controlled through the wastegate). The fix: Not as easy as the other two fixes but easy enough non-the-less: Fix: Port the wastegate. By increasing the size it allows the bleed off to occur at faster rate and therefore allowing boost to be controlled again.

To recap: As long as you maintain the same boost level without any spikes nor creep the MP will have zero bearing on your A/F ratio.

Snook

iTrader: (12)

This is the way I understand it, it has a bearing on A/F, but it may not be enough to cause detonation in this case.

What about when it's cool out, air is more dense so 10psi is not 10psi the cfm changes

The same for 10psi between stock twins and a large single turno, 10psi is not 10psi.

So just keeping the boost at the same boost level does not mean you are not running leaner.

What about the effect a going to a midpipe vs cat or high flow cat or resonator has on shifting the power curve? More exhaust flow usually means more hp
or at least a shift in power curve, could make some areas of the rpm range leaner and some richer correct?

Montego

iTrader: (1)

How? Please technically explain how a component placed on the exhaust changes your intake ratio (other than what I stated earlier)

Agreed but that is two completely different topics. Cold air (more dense) is being sucked through your intake not your exhaust. Apples to oranges.


Changing out turbos is not the same as changing out components on the exhaust side. The turbos are the responsible component for CFM. 10 psi is 10 psi well sort of.... As 10 psi with the stock turbos does not provide the same CFM and a GT35R at 10 psi so the pressure is the same but the flow changes drastically.. And if we are going to be technical about it the CFM is what actually matters. The 10 psi is just a reference that truly only applies to stock turbos because the CFM that is produced is a known safe point (on a stock setup).

If all you are doing is changing out the component that you asked about then yes. You asked a very specific question and now you are throwing components that vary the circumstances greatly.

Lets say someone asks how long it takes to drive in their car from point X to point Y.

Thread starter: Hey guys I want to know how long it takes to drive to Y from X with my CAR?
Forum member: uhm its about 130 miles away... all freeway driving so as long as you stick to 65 MPH it should take about two hours.
Thread starter: Well a bus is actually slower and it makes other stops so the trip can't take two hours.
Forum member: Of course the bus takes longer as taking a car vs the bus is not the same thing... But that is not what you asked

That is what I mean about apples to oranges

Again please technically go in and explain how it affects the A/F ratio. If the boost level remains the same, then what do you think is happening that is changing the A/F ratio. Where are those extra oxygen molecules coming from?

dguy

iTrader: (8)

I think its important to note that an EBC cannot reduce boost below spring pressure.

Snook

iTrader: (12)

It doesn't matter if the restriction is up or downstream. Restriction is restriction. The more exhaust flow, the more suction the engine will have. Increasing air intake, requiring more fuel and making more power. Scavenging and back pressure are altered with exhaust mods.

A/F ratios are affected as can be seen in mpg changes when adding an exhaust even on a NA engine.

lOOkatme

iTrader: (19)

So the way a powerFC works is the tune accounts for many things. it accounts for air temp, coolant temps, etc.

The base map is a map that goes off pressure and rpms. so its load and rpms.

If you change something in the exhaust that decreases the back pressure you run the risk over having the engine boost more than it usually does if you have an EBC that runs off a gain setting. so the risk is going into "untuned" cells off the map.

another risk area is if the map is't smoothed out and the cars now boosts quickier (high psi at lower rpms), those cells may not be tuned correctly.

so you can run the car while changing the mid pipe as long as you don't run it off the high end of the map and don't boost a ton quicker (which I doubt you will, perhaps a little).

If you run the car at 12psi, most tuners will tune it to 14-15PSI to give you a little give in the map. so you should be ok if your tuner did this.

I tuned a single turbo here recently and I tuned him to 17-18PSI on pump gas (we are 6K above sea level). I always dump fuel above that for safety reasons. he changed out his wastegate spring and left his settings the same (stupid move), and he was boosting a max of 21PSI at an AFR of 10 and under. (I do a fuel dump). his engine was fine and no detonation or anything but I got on his *** for boosting that high. He also almost went off the map sensor, right there at the top which I also have a boost cut at.

lOOkatme

iTrader: (19)

I don't think this is 100% right in terms of the tuning world.


so if you now dropped the pressure ratio the turbo is running at it will make more power, but if you keep the boost the same pressure you are making more power by having a cooler charge temp (lower air temps, which are tuned for).


if you removed the restriction and kept the same boost settings, now you might need to retune a higher boost row that is now being run which may not have been tuned before.

so one is a load row that has not been tuned, the other is having an incorrect air temp table/fuel correction. Then you also have the water temp table fuel forrection which contributes to the fun as well.

So its always a good thing when tuning to error a little to the safe side when things get real in the high boost cells to account for any problems in the air temp table fuel correction.


If you really want to make more power, I suggest really looking at your air temps. one of the most important things is to run a large intake filter with low pressure drop and have that filter in the coldest air possible. You can gain many WHP, like 30-80WHP in some by doing this because it has a three fold effect.

1) it lowers the pressure ratio of the turbo which then emits lower air temps.
2) it uses lower air temps to begin with at the turbo.
3) you are less dependent on the intercooler, but the intercooler still will remove heat from the air but the air is already much lower to begin with.

When I swapped my front mount intercooler to a V-mount I designed it in a way to run a super larger air filter in the inlet of the bumper. I also did separate ducts to the intercooler and radiator. I run a longer intake pipe and velocity stack to increase low end and mid range power which made the car easier to drive.

My intake temps dropped a good amount by doing so, I ran the same boost pressure as before buy now my injector duty cycle went up. I had a lot more air due to colder air.

the difference was an injector duty cycle that maxed around 68% before to now having it max at 75%. the difference in WHP is around 46WHP gain. I also noticed that my power delivery was more smooth, it didn't have that ramp up with a FMIC. Air temps dropped from a hot day having air temps in the mid to upper 40c, sometimes 50C during high boost to mid to low 30C. This past weekend I was hitting 9C under boost due to cooler weather. most people forget about this end of things.

Snook

iTrader: (12)

Wow awesome info thank you for sharing!

BLUE TII

iTrader: (9)

Montego
Quote:
Originally Posted by Snook View Post
This is the way I understand it, it has a bearing on A/F, but it may not be enough to cause detonation in this case.
How? Please technically explain how a component placed on the exhaust changes your intake ratio (other than what I stated earlier)

What happens when you reduce intake and exhaust restrictions and keep the exact same boost and the exact same turbo/engine etc is-

The Volumetric efficiency of the whole system shifts to be more positive.

Problem is, the FD fuel delivery scheme is the "speed density" system where the ECU uses reference pressure to compare manifold pressure and temperature with pre-written volumetric efficiency look up tables to estimate how much air is coming in the engine and how much fuel will therefore be needed.

Engine is receiving more airflow than the ECU estimates if the actual volumetric efficiency shifts more positive and the FD runs leaner.

This isn't theory, and its not a small change to the FDs AFRs in actual use.

I ran my FD stock ECU and just a catback, 2 boost controllers, fuel pump and 10psi boost.
AFRs in the 10s and 9s on the high end.

I ran my FD on stock ECU, intercooler, downpipe, catback, 2 boost controllers, fuel pump and 10psi boost.
AFRs in the 10s and sometimes dip into the 11s.

I ran my FD on stock ECU, intercooler, (formerly) resonated downpipe, midpipe, catback, 2 boost controllers, fuel pump and 10psi boost.
Had to add a slight exhaust restrictor to maintain 10psi boost.
AFRs in the 11/12s and sometimes dip into the 13s.

I ran my FD on stock ECU, intercooler, downpipe, resonated highflow cat, catback, 2 boost controllers, fuel pump and 10psi boost. Was able to remove exhaust restriction and maintain 10psi boost.
AFRs in the 11s and sometimes dip into the 12s.

Last step on stock ECU- I kept everything same as above and put on intake pipes and "filters"(Blitz) and back to the exhaust restriction to keep boost at 10psi. 110 octane gas.
Stopped checking AFRs as they were 13s heading to 14s.
---------------

Not really relevant for VE discussion because I now changed my ECU VE lookup tables-

Put in ROM tuned ECU with above, took out exhaust restriciton and dialed 2ndary into the same 14psi the primary turbo was creeping to. 110 octane gas.
AFRs in the high 10s/11s and head down to mid 13s on top end.

VE fuel tables and fuel system maxed out.

Raced it on race gas this way.

Could have increased fuel rail pressure for lower AFRs and run pump gas (but rest of tune besides top end would be very rich in my experience= loss of power).

Skeese

iTrader: (11)

Chuck stated in the thread below the that on his non-sequential car the straight midpipe caused his AFR to be 0.1-0.2 AFR points leaner than when he was running a resonated midpipe.

https://www.rx7club.com/3rd-generati...idpipe-339546/

I recently swapped from a bonez high flow catted midpipe to the pettit non-resonated midpipe. I was running 12 PSI at the time on a single turbo and the change from the HFC to NR midpipe caused me to overboost to 13.5 PSI !

I ended up having to reduce my wastegate duty cycle by 10% to get the boost back down to 12 PSI and I had to add some additional fuel across the upper rpm range (5000+) in order to maintain my target AFR.

Honestly, if you are running on a PFC that was tuned by a professional and you aren't comfortable logging data and updating your tune yourself, you probably should lump all your upgrades that could affect air or fuel together and then take the car back for a touch up tune once everything is in. Safe>Sorry when it comes to boost and fuel on a rotary.

It may be time for a tune touch up soon here anyways since fall is here and the temperature is dropping!

Montego

iTrader: (1)

Agreed. However this scenario does not come into play given that the boost controller is being used to bring down the boost to the level prior to the MP. So if the boost was being controlled at a certain level with a cat, then it is safe to assume that the boost level is at the spring pressure or above it. Which in both instances the EBC can be used to bring the levels down back down to what it was prior to the mod (well as long as the elevated boost is not due to creep).


Actually it does matter quite a bit.


Your intake and exhaust sides of the engine are separated by apex seals which sole purpose is to hold compression. In other words the seals completely isolate each stroke from the other. Without that isolation the engine is worthless.



By freeing up the exhaust side of the engine, it allows the exhaust stroke to be more efficient. You basically increase the efficiency on one of the 4 strokes that make up the rotary engine. And that equals more power. It is literally that simple.


Nope. Your MPG increases because the engine efficiency increases not because you’re A/F ratio changes.

Think of it this way: How you ever worn a wetsuit? If you have you know that it somewhat restricts your movements and makes swimming around harder. Making the swimmer get tired quicker because the wetsuit limits the efficiency of each stroke. Same thing is happening with the engine. By freeing up on the exhaust side, the engine becomes more efficient and therefore has to work less for the same given conditions.

Another way to look at it is to pile on a bunch of overweight people on your car. Drive around like you typically do for a week and you will see that your MPG will drop in comparison to when you are by yourself. Again the engine has to work harder with the people in the car than without and hence more fuel is spent.

BLUE TII

iTrader: (9)

A long-winded aside not meant to confuse the issue, but hopefully enlighten-

Montego-

Your intake and exhaust sides of the engine are separated by apex seals which sole purpose is to hold compression. In other words the seals completely isolate each stroke from the other. Without that isolation the engine is worthless.



By freeing up the exhaust side of the engine, it allows the exhaust stroke to be more efficient. You basically increase the efficiency on one of the 4 strokes that make up the rotary engine. And that equals more power. It is literally that simple.


Just to point out something very important in peripheral exhaust port rotary engine operation (Mazda rotary 1967-2002).

The apex seal does not ever close the exhaust port nor completely isolate the intake and exhaust strokes.

The exhaust port NEVER closes, it only switches between being open to-
1) the power stroke
2) exhaust stroke
3) the exhaust stroke and the intake stroke together

Once you understand that you really begin to understand the nuances of rotary 4 stoke theory compared to piston engine 4 stroke theory.

By freeing up the exhaust you are-

allowing the 1) power stroke to be theoretically slightly less efficient (less exhaust manifold pressure for combustion expansion pressure to push back against = less force turning rotor), but in practice you are dumping more un-reacted air/fuel into exhaust where it will expand for higher exhaust velocity which increase system efficiency as we will see in 2) exhaust stroke and 3) exhaust plus intake stroke.

More efficient 2) exhaust stroke through reduction of pumping losses. Any increase in exhaust velocity and mass flow helps. The rotor doesn't have to waste as much energy pushing the exhaust gasses out of the engine. Don't fall into the "pressure trap", the exhaust pressure is a factor, but it is a factor in a dynamic situation- not static. See below, the siphon effect.

More efficient 3) exhaust stroke plus intake stroke through intake scavenging. Any increase in exhaust velocity helps increase the intake velocity during overlap.

Rotary overlap is strong. At Wide Open Throttle at any engine speed overlap is in positive effect because the shape of the rotor. High velocity exhaust gas below the apex seal exiting the exhaust port opening and lower velocity intake gas above the apex seal is a natural siphon on the intake side.

Higher pressure exhaust?

No problem, as long as it is accompanied by a correspondingly higher exhaust mass flow out the exhaust port. Higher exhaust pressure and higher velocity together will only strengthen the intake overlap siphon effect.

Do you turn your air pressure regulator up or down to increase your siphon guns siphon side flow?

lOOkatme

iTrader: (19)

I know if your going to make as many changes as most of these people are talking about could definitely change the VE of the engine, but we are talking about swapping a resonated midpipe to a non-resonated midpipe....and I don't think the change is going to be too noticeable.


a noticeable change would be going from a cat convertor to a midpipe, or stock exhaust to free flow 3". something of that nature will require a re-tune, Its going to be a small effect going from resonated to non-resonated IMO.

Montego

iTrader: (1)

Oh man.... we are barely learning to walk in this thread and you are bringing in advanced concepts...


For the purposes of the average non-race engines:

adam c

iTrader: (2)

It seems like maybe we are missing the point here. As we free up flow restrictions, more cubic feet of air will flow thru the engine at any given PSI. More air means a leaner condition. A mid pipe will have less restriction than a resonated mid pipe, and will cause a leaner condition. How much leaner is the debate.

Montego

iTrader: (1)

Yeah but by introducing a new variable on the intake side brings a whole new set of conditions and frankly changes everything

Anyway I'm done with this thread. Nothing new to add and from this point on it will just be repetitive.

Monsterbox

iTrader: (6)

LOL this has gotten deep

There's not much difference between the rx-7 store magnaflow resonated pipe and a straight-pipe. The inside diameter is the same, as the resonator pipe is a straight through design. Flow may be slightly less because of the baffling, but its not something that's going to blow your engine, unless you're tuned to a 13.0 AFR.

I've swapped from res to non-res on twin turbos w ported wg @ 13psi, on 13b w/ single turbo, and on 20b. Back and forth multiple times for car shows etc. I'm always changing exhaust setups. All I do is keep eye that boost doesn't move up to high. There really isn't a dangerous difference in Lbs/min from the turbocharger, really I just notice that the boost controller needs to turn-up or down to maintain boost.

This past weekend I took catback off the 20b and resonator and run full 3" straight pipe into dual 4" blast pipes. I added 2.5% fuel to the map for good measure and reduced boost controller slightly, not a single issue. AFR was richer from the increase in fuel (purely for overkill safety, prob not even necessary). The only noticeable difference was WG duty cycle of Profec needed to be turned down a little to maintain the ideal boost from before.

Swap it out, don't worry about it. This is NOT the same as going cat to midpipe.


Now, when you're at 25+ psi of boost, where exhaust backpressure is becoming a major restriction, EGT's are going up, and you're choking out the turbine, making less HP/PSI, and you go from 3" to 4" exhaust etc...this is another story all together