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And what is your ambient temp, intake temp, and injector duty? At 13psi I have gone over 95% duty on the stock injectors on cool days. On a COLD day you might well be over 100%.
This is where the 10 psi rule works even if it is antiquated. It has to do with keeping injector duty reasonable at the lower range of intake temps. It's especially important if you have an intercooler that actually works.
Regardless - if you're using the 3 mod rule, the 10 psi rule, whatever... you're just feeling your way around in the dark. If you want to modify a turbo 13b and be sure it will last, then you need to log the relevant data and tune the ECU with a margin of safety.
OP - I think you're right to back off on the mods. If your boost is low in certain situations it has more to do with the boost control system than the engine. You might have a bad check valve, sticking solenoid, or leak that causes low boost. Need to nail down exactly when it happens.
Good point, I ran these tests in mild (~70deg F) weather, could be different in cold weather. No way to know the injector duty since it was on the stock ECU, I can say that I ran the same A/F tests with a M2-mapped ECU that increased boost to 14.5psi on primary and about 12psi on secondary and the A/F's were if anything richer across the board (same weather conditions, too). I am back to the stock ECU maps, mostly because the 3500RPM hesitation was so bad with the M2 ECU, but seeing the rich A/F's at the even higher boost would seem to indicate that there was still some headroom with injector duty when running the OE calibration which has lower boost pressure. At least on my car. That said, if there was a simple way to regulate down to ~10psi that was bulletproof and maintained the stock boost control system I would probably do it, the performance difference is negligible and it's not like this is a race car anyway that needs the extra 5 hp to get down the road.
3 mod rule.
1st mod = EFR 8374
We still good with Stock ecu?
Exactly.
For the folks that are unaware, 10 psi from the stockers is not to be compared with 10 psi from a EFR 8374 because the CFM (cubic feet per minute) aka air flow is not the same. We merely use 10 psi as a reference point with stock turbos because as a factory setting, we know the AFR at that CFM is good with stock ECU. Also it is a good reference point to gauge how much the system is changing from stock (and with stock turbos) as we know that by increasing the boost, the CFM increases.
In reality, when I mention that my GT35R set up's low boost is 12 psi it really has no correlation with anyone running a different turbo.
I ran the same tests when I had a modified airbox with the adam-c duct, and the AFR's only changed about 0.1-0.2 points and primary/secondary boost was about 13/11psi. So not so sure about the 10psi limit, however I have also gone through my OEM fuel system with a new OE pump, relays, ignition switch, etc. and have good voltage at the pump.
The 10 psi rule is not an absolute. Meaning that it is not a guarantee that you will blow up if you go slightly above it but that ceiling gets close when you do. It just makes sense to stick to stock boost levels as mazda engineers designed it to have enough wiggle room there. It makes sense to set it there because we don't go lean at that boost level unless something is truly jacked. As the boost is raised, things drastically change and there is much less room for error. All components get a little tired from being used, so maybe that is all it takes (a tired injector ect) to blow an engine when going past 10 psi who knows. All I know is that plenty of people have detonated when they exceed it without an ECU. However, this is assuming people have a well functioning turbo set up. Meaning they are boosting past 10 psi and are somewhat equilateral in their boost response across the RPM range. In other words, if they state they are at 11 psi it means they are holding that response across the RPM range.
I mention this because you stated 13/11 psi. I'm assuming 13 psi while on the primary turbo and then the boost lowers to 11psi once the secondary turbo kicks in right? Well the thing is that as the load increases, the danger increases. Meaning most people don't detonate at 4000RPMS, they detonate at 5500+RPMS. So 11psi at the higher RPMS is a heck of lot safer than 13psi at the lower RPMS.
Originally Posted by alexdimen
And what is your ambient temp, intake temp, and injector duty? At 13psi I have gone over 95% duty on the stock injectors on cool days. On a COLD day you might well be over 100%.
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It seems that his 13psi boost response is only while he is on the primary turbo. Much less CFM with only one turbo being online and therefore his injectors are most likely keeping up. But is it even possible to go above 100% duty cycle? I mean they can't supply more fuel than 100% capacity.
Originally Posted by Mod Bugs
Okay... so on the freeway tonight it hit 12-12.8 psi I let off as I saw it spike so I didn’t stay in it. This was in. Third and fourth gear it’s cold at night and on the freeway w load..
but on the street it only hits 7.5 psi or so even through all of third gear.. it pulls nicely on the street even at that boost level..
Does this make sense to anyone? I can see over boosting on a cold night but a difference of 5 psi???
Originally Posted by Mod Bugs
Dale how do you know your motor let go on that 12 psi third gear pull? I only did a few pulls to verify boost but always let off quick and didn’t stay in it.
Oh you know when you blow your engine. There is no denying it when it happens, one second you're on the gas loving life and the next, the car loses power and it idles like dog ****. At first there's a bit of denial... well maybe my map line came off... or... but eventually acceptance sets in... Me personally, I catastrophically over boosted once (wastegate line came off) and blew 4 out 6 apex seals, not fun at all.
Originally Posted by Mod Bugs
the mods will be
power fc ecu
Hks Rs air intake
dp, mp w resonator and hks exaust
i don’t know what the boost would be at this point maybe 10-14 psi?
would I be able to safely keep the stock injectors w this set up?
At this point you should really invest in a boost controller and port that wastegate so you can tame your boost response. Yeah you can always band-aid it by tuning the PFC to the highest reached psi level. I don't know about you but that would bug the **** out of me. Boosting 7.5psi in the day and 12.5psi at night. Screw that.
Once you get a controlled boost response, get your PFC tuned. It is all about your injector duty cycle and as a rule you don't want to go past 85% (there's been reports of injectors becoming unreliable when constantly being run past 85%). The PFC is nice because it tells you exactly your injector duty cycle so you know automatically where you stand. If you go past 85% the two fixes are: Turn down the boost (see that's why you want control) or get larger injectors and a bigger fuel pump.
Alexdimen- ok I’ll try to trace and or rule out vacuum leak boost leak and the solenoids and check valves (should be good I just replaced them).
Montego- yes it is a bit annoying to have that big of a difference in boost.
so a lot of load at a higher speed won’t make that big of a difference in boost?
It really seems like at lower speeds 1-3rd gear the boost is way lower like under 8 psi or so. But still feels FAst! But on the freeway speeds it shoots up fast and I just let off..
thaNkfully the motor still sounds fine and still has power..
I mention this because you stated 13/11 psi. I'm assuming 13 psi while on the primary turbo and then the boost lowers to 11psi once the secondary turbo kicks in right? Well the thing is that as the load increases, the danger increases. Meaning most people don't detonate at 4000RPMS, they detonate at 5500+RPMS. So 11psi at the higher RPMS is a heck of lot safer than 13psi at the lower RPMS.
It seems that his 13psi boost response is only while he is on the primary turbo. Much less CFM with only one turbo being online and therefore his injectors are most likely keeping up. But is it even possible to go above 100% duty cycle? I mean they can't supply more fuel than 100% capacity.
Right, my car consistently gets to 12-13psi on the primary turbo, then in transition there is no real drop like where you have a 10-8-10 pattern, just a steady movement downward from around 13 ish to 10-11 over a second or two. It has always been that way, even with a more restrictive Apexi Noir exhaust, original Y pipe, original airbox inlet, etc. Seems to be okay for this car, at least, very rich AFR's at primary boost conditions to redline, etc.
It seems that his 13psi boost response is only while he is on the primary turbo. Much less CFM with only one turbo being online and therefore his injectors are most likely keeping up. But is it even possible to go above 100% duty cycle? I mean they can't supply more fuel than 100% capacity.
Oh I see that now. Agreed 11 psi in the higher rev range is a lot more comfortable than 13/14 from my experience with stock injectors. Still, here in VA we can see temps in the 100's and down to the teens in winter.
Right. The injectors can't physically deliver more than 100%. But the map can have pulse-widths at certain RPMs that would require the injectors to be open more that 100% of the time even though they can't.
When I was using 550/850 injectors my PFC map got to 100% duty around pressure row 18. You look at the rows above those and there are plenty of cells with duty cycle >100%.
Awe crap... I guess I'm just leaving mine all stock now (Orignal 46k miles). May be a nice Bonez DP ceramic coated for sale soon. 😔
Why is that? IIRC you were concerned with keeping the car all stock for value purposes right? That's a reason right there to replace it with a DP. A melted pre-cat is not a good selling factor (I'm not saying its melted now but if you keep it on there eventually it will be) .
Originally Posted by Mod Bugs
so a lot of load at a higher speed won’t make that big of a difference in boost?
It shouldn't, back when my car had stock twins I was able to hold the boost on a 10-8-10 pattern no matter the gear. From 2900RPM-4400RPMS it held at 10psi, followed by a quick dip to 8psi, then back up to 10psi all the way until redline. When I upped the boost to 12 psi the pattern changed to 12-10-12. However, I should note that I had to tune out a boost spike at transition when I first upped the boost, I tuned it via the boost controller.
As I would add mods I would go back and retune my boost response so it would remain constant and predictable.
Originally Posted by Mod Bugs
It really seems like at lower speeds 1-3rd gear the boost is way lower like under 8 psi or so. But still feels FAst! But on the freeway speeds it shoots up fast and I just let off..
Can you please describe this in detail? Because if it wasn't for this I'd say you had boost creep:
so on the freeway tonight it hit 12-12.8 psi I let off as I saw it spike so I didn’t stay in it. This was in. Third and fourth gear it’s cold at night and on the freeway w load.. but on the street it only hits 7.5 psi or so even through all of third gear..
It doesn't make sense how third gear on the street would be at 7.5psi while on the freeway it would be at 12psi. That is unless the only factor is temperature. .
Originally Posted by alexdimen
When I was using 550/850 injectors my PFC map got to 100% duty around pressure row 18. You look at the rows above those and there are plenty of cells with duty cycle >100%.
On stock injectors and stock twins. What’s the max boost you’d want for a decently safe tune?
i was about to post something on this subject, there are basically three things to balance.
the first thing is that the 92-95 (255/265ps) turbos run out of steam in the higher rpms, so the average JDM tune will run ~13psi in the midrange, and then taper off to 9psi. it keeps the turbo in the sweet spot. i have seen tunes with higher boost, but at high rpm, 13psi is kind of the limit.
second is fuel, the stock ECU is fixed, and its set to run really rich, and the timing is set for this mixture, its forgiving, but if we push it, its not good. with a tunable ecu, we have control over timing and injector duty. the JDM tuners tune leaner, and this gives them more injector headroom, they go for more like 11.5:1 vs 10:1. the factory ecu is set really rich to keep cat temps down, they were under warranty for 7years and 70k miles, if you looked at a map from before they had to warranty the cat, its not nearly as rich.
the third is the tuning part. the JDM tuners go through the car, it gets a compression check, they use RFI suppressing wires, and colder plugs. if parts get replaced, they often get checked between the time they come out of the box and it goes on the car. for example, before the shiny fuel pump goes in the car, it gets tested. you'd be surprised at how many shiny new parts don't work as advertised. this is in addition to the normal fluids and filters.
so to sum up, if the engine is healthy, the fuel system is tested good, 13psi on the primary and 9 or 10 on the secondary are totally possible, and quite safe. if you really have your ducks in a row (bigger IC, cold air intake, cold plugs, big ***** or tuning skills) up to 15psi primary and 11is on the secondary are possible
I’ve seen some for FCs, but why are there not any piggy back systems for the FD? I know there’s plenty of street cars with mild mods like are being discussed here that stretch the stock ECU and owners that don’t want to lose the drivability of stock by going to a full aftermarket ECU. Plus, many people live nowhere near proper tuners. For instance, my nearest recommended rotary shop is about 6 hours away.
i know they’re a bandaid solution and not as adaptable as a full ECU, but I’m sure there’s a market. Was there some testing early on that determined it not a viable solution?
I’ve also got a 95 Miata with a Fastforward Supercharger. Tom provides a timing card, a fuel card, and a fifth injector card. They read pressure/rpm and increase the injector voltage, pull back timing, and open the extra injectors. It’s not perfect or infinitely adjustable, but you can use a wideband to watch and adjust the cards for your particular set up.
I feel like a similar card could be offered for the FD; reads boost/rpm and ups injector flow and pulls additional timing if needed.
Am I just way out on a limb here? I know we’re a niche market to begin with, but it seems like there’s probably enough drivers not wanting track monsters that would jump on it.
I’ve seen some for FCs, but why are there not any piggy back systems for the FD?
in Japan the stock ecu is fully cracked, they can program it. and then there is the Power FC which plugs in, and then there is the HKS F-Cons the V Pro is supposed to be the best rotary ecu, however its in Japanese.
the V Pro is very cool, you can use it as a piggyback, or a standalone, it lets you add or configure just about anything you'd want.
Piggy back systems are a leftover from the 90's, back when people were trying anything to get engines not to blow up.
Our ECU's are very primitive by modern standards, it's basically late 80's technology. Piggy backs just try and modify inputs to change the ECU's output which is a mess. Also there's no piggyback that ever did timing properly for a rotary.
The PFS PMC was a popular piggyback ECU before the PFC came along. By comparison it's CRAZY primitive.
Modern cars have re-flashable and tunable ECU's in many cases - again, this is a 30 year old ECU, it can't do that.
It's really simple - staying with the twins or doing light mods? Need to pass emissions? Get a PowerFC. Going single turbo, want more power/flexibility? Go Haltech. Either of those options cost too much? Stay stock.
It's really simple - staying with the twins or doing light mods? Need to pass emissions? Get a PowerFC. Going single turbo, want more power/flexibility? Go Haltech. Either of those options cost too much? Stay stock.
Dale
in 2019 this was true, in 2020 the Motec is cheaper than the Haltech... M84 vs the Elites
On stock injectors and stock twins. What’s the max boost you’d want for a decently safe tune?
with a power fc and a tune...
is Supra turbo fuel pump the best alternative to drop in? Or a walbro 525 pump?
I am not a fan of walbro pumps. I used to have one and it took a dump on me and after a little bit of research I found out that I wasn't alone on that. So I got a denso (supra) and never looked back.
As a general rule of thumb 85% duty cycle is the maximum that is considered safe and reliable for fuel delivery. The PFC is a stand alone ECU based on custom tuning that when set on monitor mode will display injector duty in real time. So I am hesitant to tell you at what boost level because it is really a function on what you are tuned for. But from what I recall it is somewhere in the vicinity of 13psi. So if you find that you are above 85% injector duty cycle at 12 psi you should verify that you aren't running too rich. Conversely, if you find that you are still below 85% at lets say 14psi then you should check to make sure you aren't going lean.
With that said, the correct way is to have your tuner determine what is a safe level based on YOUR setup. Meaning he/she will verify what your maximum boost level is based on AFR's, injector duty cycle, EGT's, ect...
Edit-
Originally Posted by j9fd3s
the 92-95 (255/265ps) turbos run out of steam in the higher rpms, so the average JDM tune will run ~13psi in the midrange, and then taper off to 9psi.
Just wanted to say that the only times I've seen stock turbos taper off is when the pre-cat is still in in place (and usually everything else because the pre-cat is the first thing we tend to get rid). On a 100% stock set up our boost pattern is actually 10-8-10-8. 10psi from 2900-4400RPM, transition dip to 8psi from 4400-4450RPM, back to 10psi from 4450- ~6500RPM, and then tapers off to 8psi till redline . Once the pre-cat is removed and the car is able to breathe, then our boost pattern changes to 10-8-10.
I should know, on an awful day my wastegate line came off (no turbo control) and I hit 23 psi. This was on stock 92-95 turbos.
I you read through this thread you'll see the effect in boost, afr and power for each mod added on a stock ecu and then pfc with stock injectors. It'll give you an idea of the limits of the car. spoiler alert, 14 psi 340 whp with walbro 255 and stock injectors at 91% duty.
I am not a fan of walbro pumps. I used to have one and it took a dump on me and after a little bit of research I found out that I wasn't alone on that. So I got a denso (supra) and never looked back.
As a general rule of thumb 85% duty cycle is the maximum that is considered safe and reliable for fuel delivery. The PFC is a stand alone ECU based on custom tuning that when set on monitor mode will display injector duty in real time. So I am hesitant to tell you at what boost level because it is really a function on what you are tuned for. But from what I recall it is somewhere in the vicinity of 13psi. So if you find that you are above 85% injector duty cycle at 12 psi you should verify that you aren't running too rich. Conversely, if you find that you are still below 85% at lets say 14psi then you should check to make sure you aren't going lean.
.
On Walbro pumps, you have to make sure you get a REAL pump from a reliable vendor. IRP and Banzai Racing are 2 good sources that spring to mind - they get them straight from the Walbro factory. There are a HUGE amount of knock off ones out there, you will have a bad day with those.
I have a Walbro 255 in my car that's been in there for 12 years. Absolutely zero problems.
IMHO the Supra pump is pricey and doesn't flow as well. I've also installed a number of Walbros in other guys cars here in town with zero problems. Your experience with Walbro is valid but I want people to see the whole story.
Also that Banzai Racing dyne per parts added is one of the best threads ever made, hands down. Solid foundation for modding an FD there.
On Walbro pumps, you have to make sure you get a REAL pump from a reliable vendor. IRP and Banzai Racing are 2 good sources that spring to mind - they get them straight from the Walbro factory. There are a HUGE amount of knock off ones out there, you will have a bad day with those.
IIRC I bought mine from the RX-7 store. I had not heard about knock offs for those pumps but that is very interesting.
Originally Posted by j9fd3s
at what RPM?
It blew somewhere above 5500RPMS.
Originally Posted by j9fd3s
my friend's FD would hit ~23psi on the first turbo, but by 6k rpm it was down to about 4psi.
interestingly it ran fin on pump gas for years like that
Damn... your friend's car was all kinds of screwed up. As mentioned earlier, as the load increases and both turbos come on line there is a greater demand for fuel. Him being at 4 psi is almost 50% below the wastegate spring so it doesn't surprise me that he never detonated. Rarely anyone blows up below 5000RPMS. Still 23 psi is kinda crazy. What were his mods and did he have an aftermarket MAP sensor?
Near stock levels these turbos should not really taper off much. My set up kept me within 0.5psi of set boost, whether it be 10 or 12psi. I should note that the higher I boosted, the harder the boost control became in terms of being constant throughout the RPM range.
Check out this guy, even with a boost spike of 22.9psi he fairly held 20psi on stockers. Granted, It should be noted that he was non-sequential which really simplified things.
For the 2nd run I turned down the boost a tad bit only 2% on the electronic boost controller, made a few less hp, 3rd run I turned it up a tad more than the first run an extra 2%, and made 411hp. Peak boost hit on the electronic boost controller was 22.9 psi, that's the boost spike when full boost hits then it drops to around 20 and slowly down a little more as I was watching it on the boost gauge. HP held up above and around 400 for a good bit through the rpm range so that is pretty nice.
I haven't read the thread and as I skimmed over I saw several knowledgable members have posted and I am sure my comment will contradict several of them. You can do any number of mods you want on stock twins and stock ecu as long as boost stays at 10psi or less. I have owned, raced, abused and sold well over 50 FDs with full 3" back exhaust(No catalytic coverter or restrictor plate what-so-ever), with stock ports and street ports on stock ecu over the last 18 years without a single issue as long as boost is kept at 10 psi or less. It is safe all day every day as long as boost as at 10 psi and you have a healthy fuel pump/system. You can add every bolt on under sun(IC, Twin power, intake etc) without worry as long as boost is limited to 10 psi. Simply remove the factory restrictor pills and bypass the precontrol and wastegate control solenoids and install quality manual boost controllers and enjoy. This goes for sequential or non-sequential setups.
Check out this guy, even with a boost spike of 22.9psi he fairly held 20psi on stockers. Granted, It should be noted that he was non-sequential which really simplified things.
That was on an engine I built for him and that car ended up setting, as far as I know, and still holding the 1/4 mile record on stock twins going 10.8@129. By my standards it had fairly small/medium intake porting and stock exhaust ports. Going off memory I think he made 360-370rwhp on a stock port reman running sequential and the car went 11.1@125-127 before the motor I built and he went NS. Its been a long time but I think that information is all correct.
11-13-20, 03:14 PM
