Hi guys,
I have a target power figure i\'m working towards and been looking into what size secondary injectors i\'ll need. Being my first rotary, i\'ll admit i know only some basics of engine tuning, though im more than willing to learn.
I\'ve compared what other people are running against what power figure they are achieving. Ive also used the fc3s fuel calculator (http://rx7.com/cgi-local/2ndgencalc.cgi) which ive read seems to make assumptions about your set up, so not too sure about what those are and how accurate it is.
I\'m thinking there must be a basic method of actually calculating what fuel delivery rate you need for what power level that newbies like me can use to work out what size injectors we need.
Would anyone be able to explain? This kind of information seems to be hard to find (or maybe im not looking in the right places) and would come in handy for someone like me, rather than someone simply telling me what injectors to get and then i\'m none the wiser.
Thanks!
Well according to that, my setup will support 259.1 fwhp. Shame as im hoping for 500+ ;)
Spoke to Brett at rxmotors today and he said that I should be okey with standard 550cc primarys and 1000cc secondarys, plus im using an 044 externally mounted pump and swirl pot. And thats on a half bridge with T78.
What Ecu are you running?
i think i\'ve gone bit over kill with 1680cc secondaries.. but all my mods are future-proof for when i get bored of my cheese tub n upgrade it :p
I had a massive post written out then the bloody forum died :(:(
Anyways - I\'ve found a good link here -
http://www.rceng.com/technical.aspx
For rotary engines - the BSFC (Brake Specific Fuel Capacity) is about 0.6
If you take the stock T2 engine with stock ECU, the primaries fire first, upto about 80%, then fall back to 40% when the secondaries stage. The secondaries will go to about 85%, the primaries stay at 40% (subject to coolant temps - cooler = more fuel)
Using their forumula - the stock 200 BHP engine:
200x0.6 = 120 lb/hr
putting in the figures from the injectors :
550 x 2 x 0.4 + 550 x 2 x 0.85 = 440 + 935 = 1375/10.5 = 130 lb / hr
The reason for the extra fuel is because the figures assume stoich or close to stoich, and the rotary likes to run rich (for boost, and also during idle etc.) It does explain why chipped ecu\'s and powerFC will make more power with the stock injectors. Much above 300 BHP and you need to go bigger :)
Im running stock injectors, stock turbo and a chipped ECU and I will only get about 300 out of it, don\'t forget that if the injectors are too big, the duty cycle can be changed and they will work fine lol Im going to be running stock 550 primaries (keeps low down drivability) and then the 1680 secondaries for when extra fuel is needed. This setup is a bit eccessive, but I won\'t need to change my injectors every again lol :)
I would say 550 primaries and 800 or 1000 secondaries will suffice :) if you do NEED more fueling than that you would need to talk to a specilist as you will be running a crazy huge turbo and a HUGE PP lol
You can make 300 from stock injectors? How much boost!!!???!
Quote from: dthebuk;637373You can make 300 from stock injectors? How much boost!!!???!
0.9 bar :)
Quote from: dthebuk;637373You can make 300 from stock injectors? How much boost!!!???!
12 psi (on a T04B hyrbid turbo) and that\'s at 90% duty - was actually 318 bhp and AFR\'s were 12
You need an uprated fuel pump for this then?
My car is running 0.9 bar on stock fueling and cooling and i assumed i was getting about 240 bhp?
ps, sorry for the thread hijack
Quote from: dthebuk;637386You need an uprated fuel pump for this then?
My car is running 0.9 bar on stock fueling and cooling and i assumed i was getting about 240 bhp?
It\'s advisable - although the stock fuel pump is supposed to be good to 300+, but it will be getting old and tired and the wiring to it is shocking !
Rewire it - 1300cc is a good reference for that, and/or get a different pump (I run a walbro)
Quote from: Prof;637397It\'s advisable - although the stock fuel pump is supposed to be good to 300+, but it will be getting old and tired and the wiring to it is shocking !
Rewire it - 1300cc is a good reference for that, and/or get a different pump (I run a walbro)
currently running a rewired pump i believe. I just thought i\'d be no where near 300 with a stock fuel set up. Time to upgrade the cooling me thinks.
awesome :D
Fantastic, this is exactly what i was looking for, thanks Prof.
My target HP at the fly is say 350ish. So from my calculations (been waaayy too long since ive done any maths!!) theoretically on a stock ECU I\'d need over 1000cc secondaries to achieve that.
I know thats obviously not going to happen due to various things i dont understand yet like pulsewidths and the limitations of a stock ECU. So, lets say I\'ve fitted my PowerFC on stock engine ports, and my primaries and secondaries are both at 85% duty.
My target fuel rate is 350 * 0.6 = 210 lb/hr
My primaries will give me (550 * 0.85 * 2) / 10.5 = 89 lb/hr
My secondaries will need to make up the remaining 210 - 89 = 121 lb/hr
so, (z * 0.85 * 2) / 10.5 = 121
cancelling out, z = ~750cc
So lets make it a nice round figure ;) i\'ll need 800cc secondaries.
Does that sound about right? I would have thought 800s would have more headroom, from looking at other peoples setups. Also, I\'m making an assumption about all injectors running at 85% duty. I\'m not sure how realistic that is for a tuner?
I feel like i\'ve learned something! :wiggle
Quote from: Prof;637320I had a massive post written out then the bloody forum died :(:(
Anyways - I\'ve found a good link here -
http://www.rceng.com/technical.aspx
For rotary engines - the BSFC (Brake Specific Fuel Capacity) is about 0.6
If you take the stock T2 engine with stock ECU, the primaries fire first, upto about 80%, then fall back to 40% when the secondaries stage. The secondaries will go to about 85%, the primaries stay at 40% (subject to coolant temps - cooler = more fuel)
Using their forumula - the stock 200 BHP engine:
200x0.6 = 120 lb/hr
putting in the figures from the injectors :
550 x 2 x 0.4 + 550 x 2 x 0.85 = 440 + 935 = 1375/10.5 = 130 lb / hr
The reason for the extra fuel is because the figures assume stoich or close to stoich, and the rotary likes to run rich (for boost, and also during idle etc.) It does explain why chipped ecu\'s and powerFC will make more power with the stock injectors. Much above 300 BHP and you need to go bigger :)
I reckon 85% is ok for the injectors - given that you\'re not running them at this rate for any length of time in real life :driving
Some prefer 80% as a max.
I\'ve picked 800\'s for my secondaries and I\'m aiming for 300 at the wheels - so about 360 ish at the fly - so your figures seem to match my own findings :Thumbs-up
Let us know what you do go for in the end. Seems like Im gonna be similar in the long run, as are a few of us.
Good to know our findings match Prof :Thumbs-up
I will probably be going for 800 secondaries, although the thing is my FC is an s5 and has high resistance injectors. I\'ve read that I either need to run high impedence injectors or use low resistance ones with resistors soldered into the ECU harness. (Or i\'ll fry the injector drivers on my PowerFC??)
By coincidence the largest high resistance injectors i\'ve found so far are 800cc (SARD).
I\'ve also read that high impedence injectors aren\'t very good / don\'t work well above 550cc, so are low impedence injectors the ones to go for? whats the compatibility like with an s5?
I\'m running the SARD 800cc high resistance ones and they work fine. They are a straight swap as well - no custom fuel rail or anything required, although I have a customised rail with a FEED pressure regulator on it.
The other good thing is that the pulsation damper works fine with this size injector as it\'s not massively bigger.
I think the comments about the injectors not working as well may be to do with the fact that most of the newer injectors are peak and hold and are lower resistance. To use these properly you need an ECU that drives an initially higher peak current and then a lower holding current that helps prevent the injector overheating. You can use this type with a series resistor to limit the current - but then you lose the benefit of the peak/hold (slightly more rapid turn on with peak drive).
Any differences in fuel amounts injected are easily trimmed in the maps.
Glad this was all discussed as I was going to post on the same subject. With my almost complete setup:
TO4E turbo, HKS wastegate,FMIC, exhaust and intake etc etc mine is managed by a FC specific Apexi PFC. I have also got the FC datalogit and LC-1 wideband. I was told by Banzai racing that my intended fuelling of 550/850 would not be enough unless I was going to be running 0.7 bar and no higher. You have to remember that injectors are not that accurate and it has been known for 1600 injectors to flow as low as 1400!! With this in mind then best to go bigger and allow for expansion,wear, inaccuracy etc in the injectors.
I have a set of 850\'s waiting to go in but may well change my mind and go bigger to at least 1000\'s for secondaries, I may even use the 850\'s as primaries. Like you i just need good advice and to buy the right combination.
I am now a member of PFC-DL-Tuning which is a forum for FC datalogit and PFC users( invited members only)I will use this forum to get as much as I can map wise and then I shall post back on MRC with maps,good info etc.
I might have some spare stock 550s when I change mine, perhaps you could run a tertuary rail so you can run 6 550s :)
Quote from: m1tch;637622I might have some spare stock 550s when I change mine, perhaps you could run a tertuary rail so you can run 6 550s :)
i\'ll have 2 spare also.. means u can run a Quaternary rail :Giggle
Well just found out my injectors are low resistance and not sure if the PFC will allow for this on just the two. There are some excellent injectors on the US Ebay site, cheap and seem to have all the good flow qualities we need. I have emailed a few to make sure they are high resistance. I think I may well go 550 and then maybe 1200 if they come back in the right specs. Might even add additional injectors, i have spares but need to make sure the PFC can control them.
That\'s interesting that you\'ve been given different advice, Pete. Your set up is surprisingly close to mine! I wonder what reasons they have for saying that, they didn\'t happen to mention them did they? Or it just down to the inaccuracies in injector flow rate?
I\'m guessing you are aiming for a similar power figure as me then, around 350?
I\'m keen to see what you find out about those US injectors. I\'ve fired off an email to a couple of UK tuners, looking forward to seeing what they say on the subject...
:cheers
Just been told by Carl to run 550 primaries, 1680 secondaries and supported with a FPR and uprated pump if this helps as you will have similar mods to mine. With the 1680\'s I am aiming for the 400 mark.....well now I am.
wow... really?? :2eek
1680 seem kinda large to me! But I guess if anyone would know, Carl should!
according to the forumlas on the website Prof found, at 80% duty that set up would flow 340lb/hr of fuel :guinness and and 566hp!
Im even more confused now than when i started haha! There must be some bit of information we\'re missing...
or maybe 1680 secondaries is just a safe bet? Surely they cant cost THAT much more (i have no idea of the cost). So the extra safety and the ability to up the power if need be, is pretty much the best option to go for
I think the key to the formula is quality, buy quality and then being over cautious need not happen ie going bigger.
I have found a set on ebay:
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=370239843055&viewitem=&sspagename=STRK%3AMEWAX%3AIT
but again low resistance so as we are both running the Apexi it might be worth seeing if the Apexi can manage low resistance injectors or is there something else on the market somewhere that suits our needs. I wonder where Liam got his from?
Dont forget my engine has been ported as well so that will make a difference to my fuelling.
It\'s worth bearing in mind that the stock 550 Primaries work for most of the dynamic range - certainly after logging with emanage, the secondaries don\'t kick in at all in the non boost part of the map, and only after 3800 ish rpm\'s and about 4 psi boost, so most of the time driving around you are only on 2 injectors anyway.
I\'m not convinced that the injectors are that bad or non linear over their working range.
If you look at a typical injector waveform, there is a delay whilst the injector turns on - which is voltage dependant so gets called battery offset or lag - the higher the voltage the quicker the turn on time. This is where the injector needle moves to an open positon. It\'s generally in the range 0.2-1.6ms and is often larger for bigger injectors, and lower for low impedance injectors.
Then once it\'s open, the flow rate is reasonably linear with respect to the length of time or duty that you apply to the injector.
At the far end of the scale, if you are trying to rapidly turn on and off the injector, it can get itself stuck in a half open/closed state - and will suddenly only flow about half full rated capacity, - this generally happens at higher rpm\'s and very high (>90%) duty, where the solenoid in the injector simply can\'t keep up. Then as you get to 100% duty the injector will go full open. This is very dangerous as basically you can end up with the fuelling dropping to half right when you are on boost/load and it\'s bye bye engine.
One thing you need to be aware of is whether you have enough time to inject the required amount of fuel at higher rpm\'s, as you have to factor in this lag time before you are on full flow, and the window during which you can inject fuel in the intake stroke becomes progressively shorter as revs increase. Porting the engine allows slightly longer induction times
That\'s why you want to rate your injectors for 80% duty and no more - and if you need to squeeze a little more out, you need to do one of 2 things:
1) Go for bigger injectors
2) Up the fuel pressure
The injectors are rated at a certain pressure - generally around 3 bar, and the fuel pressure regulator recieves a manifold reference so that the fuel rail pressure increases with boost to keep the pressure the injector sees constant. You can get rising rate regulators that have higher than 1:1 ratio - these increase the fuel pressure more at higher boost - but you then have to map for the increased fuel that\'s going in. You can also just adjust the base pressure up, and leave the 1:1 ratio intact and adjust the maps to suit.
There are equations out there to work out the effective size of the injector with the increased fuel pressure.
Obviously large increases over stock ratings are not a good idea, but a little can buy you some headroom.
Quote from: dthebuk;637862or maybe 1680 secondaries is just a safe bet? Surely they cant cost THAT much more (i have no idea of the cost). So the extra safety and the ability to up the power if need be, is pretty much the best option to go for
1680ccs cost about £75 each :)
Where from!! I need two
mazdarotaryparts :)
mine are low impedance also.
how am i gonna get them to work with pfc? i\'ll let james figure that out hehe
u know im nt that techi about cars lol
though though / was planning on just using resistors as i think prof mentioned before.
Quote from: pdtaylor18;637842Just been told by Carl to run 550 primaries, 1680 secondaries and supported with a FPR and uprated pump if this helps as you will have similar mods to mine. With the 1680\'s I am aiming for the 400 mark.....well now I am.
thats what i have in mine. serial fuel rail, not gone parallel as costly and not much point unless you going clost to 500bhp mark.
braided fuel lines in engine bay also.
Quote from: L18M;637923thats what i have in mine. serial fuel rail, not gone parallel as costly and not much point unless you going clost to 500bhp mark.
braided fuel lines in engine bay also.
if you want to go parrallel i may have something that\'ll interest you !
Quote from: dthebuk;637932if you want to go parrallel i may have something that\'ll interest you !
a parallel fuel rail kit..? lol
not me. m1tch prob will though.
need a couple of Y bits, parallel fpr.. might as well get full braided fuel lines from tank to front, better still.. twin pumps :p
Well, i\'ve spoken to a few people who all agree with the advice Pete has been given - keep the primaries stock and run 1680cc secondaries.
Still don\'t fully understand why there\'s such a large difference in size, and I always thought it was recommended to keep injectors as small as possible (to stop lag or running too rich when the secondaries stage - maybe the PowerFC has some way of overcoming this).
The consensus seems to be that the duty on 800s is too dangerous, and its better to go too large, than too small as dthebuk says.
I\'ve also looked into the high/low impedence issue and found these products on offer. You might also be interested in these, Pete.
http://www.statracing.com/buy/aem/aem-peak-and-hold-injector-driver.asp
http://www.fjoracing.com/products/injdrvr/
Also been speaking to a really clever chap on the RX7club forum and suggest 6 ohm resistors, he is the one that has rewritten my map for me and knows his stuff on the PFC and Datalogit.
http://gb.mouser.com/search/ProductDetail.aspx?R=RH0106R000FC02virtualkey61300000virtualkey71-RH10-6.0
That way the injectors will work fine.
It\'s worth keeping in mind that those running the stock injectors on FD\'s are in fact running 550 and 850\'s respectively. I think as long as you keep an eye on duties then you\'d be fine, but if your goal is 400 or over then go bigger :)
Running 1680\'s isn\'t a problem if you\'re ECU has good resolution so can adjust the duty in fine steps. It also helps if it has Peak and Hold capability as it will be able to more quickly switch on turn off the injector.
In any case the finer control is required on the smaller injectors anyway, as they will handle most of the normal driving conditions. The big ones are only on when you trogg it :cheers
Here\'s an interesting explanation from rx7club, most of this has been posted before in some form or another, but i thought it was a good breakdown of why my original attempt at the formulas went wrong:
Quote from: Evil AviatorExplanation of that formula:
350 hp * 0.60 lb/(hp*hr) Brake Specific Fuel Consumption (BSFC) = 210 lb/hr
Why your number is too low:
1) You specified 350-400hp in your thread, but only used 350hp in the formula. Always use your highest planned horsepower number as a target, which would be 400hp.
2) BSFC is fuel efficiency as defined as Fuel Consumption / Power. This number depends a lot on the type of engine and how it is tuned. As you may know, rotary engines suck at fuel efficiency. Also, if you are the typical tightwad RX-7 owner who refuses to pay a professional to tune the engine, you plan on running a lot of boost, retarding the timing, running a silly-rich mixture while chasing a wideband AFR meter reading, you buy cheap Chinese Ebay parts, etc., then that also hurts the fuel efficiency. I would plan on 0.70 BSFC unless you have a pro tune the engine, in which case 0.62 is probably more accurate. If you manage to get .60 or better, then that\'s great. If you plan on 0.60 and run out of fuel, then you will need to buy bigger injectors and/or upgrade other components of your fuel system, which is not fun.
3) You did not compensate for the fuel injector duty cycle. The fuel injectors will burn up if you run them full-open. The rule of thumb is to give them at least 20% rest time, which results in a 80% duty cycle.
4) You did not compensate for fuel pressure. Most (not all) aftermarket fuel injectors are flow rated at 3bar (43.5psi) pressure. The stock RX-7 only runs about 34-40psi pressure. As you may imagine, a fuel injector will not flow as much at 34-40psi as it will at 43.5psi. If you plan on using an aftermarket fuel pressure regulator and increasing the pressure to 43.5psi, then you do not need to compensate for fuel pressure in your planning. A higher pressure will inject more fuel than the injector is rated, and you can push most fuel injectors up to about 4bar (58psi) before they hit a brick wall. The pressure conversion equation is: Revised Pressure cc/min = Original cc/min * sqrt(Revised Pressure / Original Pressure).
5) There are many other factors, but the above are the most significant.
Assuming that you will run 43.5psi fuel rail pressure, I think the following is a little more realistic. I wrote out the equation so you can recalculate with different numbers as needed.
(400hp * 0.70 BSFC) / 80% duty cycle = 280/0.80 = 350 lb/hr * 10.5 = 3675cc/min
Therefore, 720/1200 or 4x1000 should work fine, or you could go with 720/1000 if you tune better, run a higher fuel rail pressure, and/or shoot closer to the 350hp number as opposed to the 400hp number.
Good stuff that. I have now ordered some injectors from Clive (1680cc) so that and the 550 standard ones will be just fine. Although they are low impedance they will work only too well with the PFC without modification. A FPR and uprated pump though goes without saying.
Ah really? so no need to solder in resistors to the injector circuits? thats one less thing to worry about! :cheers
Clives 1680\'s are about 4-6 ohms from what I remember - so should be ok on the PFC - particulary given that they won\'t be on for very long (low duties because they are bigger).
That\'s an excellent post from the RX7club by the way :)
I am using higher fuel rail pressure - so I guess that\'s why I get away with it. I am also aiming for 300 rear wheels - which is about 360 ish on the fly. At the moment I\'m finding I need to cut quite a bit of fuel in the emanage - not add any (apart from the obvious change to 800 secondaries). I\'m still seeing low afr\'s of mid 9\'s under full boost.
I\'m not hitting 80% on the secondaries even at 1 bar boost. This is based on my logging, so actual figures from the engine running - not calculations. I think there is a tendancy to over egg fuelling on rotaries because people are ..... scared of running lean and popping engines, which is perhaps no bad thing.
Over rich is good but then you lose some power because of it but that side of caution is never a bad thing. Innovate reckon 9\'s should be the lowest and aim for 12\'s under boost. I had some readings down as low as 7.5!! until I messed with the map. I have ordered some resistors as a just in case and I think standard Mazda were 12 or 13 ohms but having talked to Carl today and by email with Clive I think running those 1680\'s with the PFC will do no harm. Made a good thread this as so many of us are in the same position.
When you want to have a good session with the Datalogit let me know and when we get the chance I can pop down and look at the map in the PFC for you. Also gives me the chance to copy some map files for you to your laptop.
I can see you becoming pretty popular with that datalogit Pete;)
Quote from: pdtaylor18;639180When you want to have a good session with the Datalogit let me know and when we get the chance I can pop down and look at the map in the PFC for you. Also gives me the chance to copy some map files for you to your laptop.
Thanks Pete, really good of you to offer, appreciate that a lot! Think i\'ll definitely be taking you up on that fairly soon. I do have the hand commander, but i\'ve heard it would take a lifetime attempting to do any tuning on it!
Had a quick look around the FC Edit software, don\'t understand what most of the values mean, but I can see if you know what you are doing it would be much easier to use.
Its quite useful our setups being so similar, I want to learn more about tuning so seeing what you\'ve done with the maps would give me a good starting platform:cheers
1st thing is to make sure that you have an FD air inlet temp sensor, FD map sensor or 3 bar one and that should be enough to get the car going. I actually used my standard S5 boost sensor and that worked fine but its not ideal. I do use my wideband gauge alot to check AFR\'s and thats crucial in getting any map close to what is ideal in all conditions.
The datalogit is very good and I have explored using several maps but none have really suited the car, all engines are different so will need fine tuning along the way. The difference with the Datalogit is that you see the whole map and not just a small portion of it.
I\'ve got the IAT, and im buying a Tomei MAP sensor soon (same Denso part number as the Apexi one, but Apexi have stopped rebadging them) so it should be pretty much plug & play.
The thing im not sure about is if they fit the stock loom, or will i need to fabricate my own harness?
The IAT you can simply use spade connectors to tap into the existing temp sensor harness and the map sensor is the same. I have done it this way for now as at least I can always take a step back to standard if anything ever goes wrong in the early stages. I will make myself a harness adapter like the Banzai adapters, really easy to do, I do expect to cut off any standard connectors eventually and have incorporate it all into the loom properly.
The temp sensor it does not matter which way round the wires go and the map is only 3 wires,
Br/B earth
Br/W Vref
Gr/Y Map
incidently they are the same as the FD map sensor which I have fitted atb the moment til my Apexi Boost kit arrives.
Just a quick question, do you need an aftermarket secondary fuel rail to use the 1680cc injectors?
And how much could I ask for my 1000cc\'s as they arent enough ;)
Sorry thats 2 questions.
Grinder friendly prices are always best ;) £3.50 and half a curlywerly is my best guess.
Seriously though If they are cheap enough I might be interested.
Quote from: G@NDY;649985Just a quick question, do you need an aftermarket secondary fuel rail to use the 1680cc injectors?
nope. can use stock but they need to be mod a bit which im sure any gd tuner can do =)
Oh thats good news, I have a 13bRE rail in my garage, I wonder if thats any bigger?