CJ Posted October 22, 2004 Share Posted October 22, 2004 Is there a formula for working out the capacity of fuel injectors? I seem to recall something about a safe load being 80% - but 80% of what? I assumed it was meant to be 80% of the volume i.e. 550cc x 80% gave a safe figure of 440. But is that 440 BHP? And, if so, is that at the hubs? The fly? Quote Link to comment Share on other sites More sharing options...
Syed Shah Posted October 22, 2004 Share Posted October 22, 2004 Yes, that 80% will stand for duty cycle. So, 650cc injectors can work comfortably at 520cc/min. However, they can exceed this for short periods, so they can support more power, especially on a car as powerful as yours, as it is unlikey you would be at WOT for any length of time. Fuel flow is more than just the cc rating of the injectors, it also depends on pulse width and most importantly, fuel pressure. Anyway, to answer your question, as a rule of thumb with our cars, the cc is a good indication of the power you can run, so 650cc injectors, at the fuel pressure that they are quoted of flowing that number, will be good for 650hp @ the crank. Quote Link to comment Share on other sites More sharing options...
CJ Posted October 22, 2004 Author Share Posted October 22, 2004 Thanks Syed Quote Link to comment Share on other sites More sharing options...
stt Posted October 22, 2004 Share Posted October 22, 2004 The safe limit of flow is meant that with say 550cc injectors running at 80% its all gravy,but if you start running higher % then you could be looking at running lean as the injector cant suply enough fuel,what the cc represents is the flow rate per minute,say for another quick example you could put 1000cc injectors on to a mini and they would barely trickle but it wouldny give the car 1000bhp though Does this help at all mate?Sorry if it didnt but then thats more because of me rambling on! Quote Link to comment Share on other sites More sharing options...
Alex Posted October 23, 2004 Share Posted October 23, 2004 FWIW I think modern injectors are less prone to locking up, hell how many j-specs regularly run 100% duty! 80% is probably very conservative...I'd say that closer to 90% is still safe on modern injectors. Quote Link to comment Share on other sites More sharing options...
CJ Posted October 23, 2004 Author Share Posted October 23, 2004 So my 720cc should be more than capaple eh? Quote Link to comment Share on other sites More sharing options...
Alex Posted October 23, 2004 Share Posted October 23, 2004 Originally posted by CJ So my 720cc should be more than capaple eh? I've seen Ian's datalogs for his 720's and BL67...there is a healthy margin atm, but I believe its not fully tuned to 1.4bar running yet. I think he was heading towards 80% if not already there...IMO 800's would be the size that would suit the 67 best and allow for all eventualities. But for the average road setup the 720's are deffo man enough. Quote Link to comment Share on other sites More sharing options...
CJ Posted October 23, 2004 Author Share Posted October 23, 2004 Much horse grassy arse Alex Quote Link to comment Share on other sites More sharing options...
Ian C Posted October 23, 2004 Share Posted October 23, 2004 Yup. With 720's I run 70% duty cycle at 1.2bar boost, 6500+rpm. Plenty of headroom for more boost -Ian Quote Link to comment Share on other sites More sharing options...
MONKEYmark Posted October 23, 2004 Share Posted October 23, 2004 i have a spare set of 850`s low impedence top feed for sale brand new if you need to go bigger turbo later on. gone for 960cc for future proofing Quote Link to comment Share on other sites More sharing options...
LeeT Posted October 23, 2004 Share Posted October 23, 2004 Originally posted by MONKEYmark i have a spare set of 850`s low impedence top feed for sale brand new if you need to go bigger turbo later on. gone for 960cc for future proofing you've got too much money, 850;'s are ample for most hp requirements, if not all. pm sent:D Quote Link to comment Share on other sites More sharing options...
MONKEYmark Posted October 23, 2004 Share Posted October 23, 2004 Originally posted by leett you've got too much money, 850;'s are ample for most hp requirements, if not all. pm sent:D its a long term thing i suppose. mates got a garrett gt42 so have got to get one too. we going to start a gt42 club up i will use the small gtq71 for nipping to shops and back pm replied Quote Link to comment Share on other sites More sharing options...
Dragonball Posted October 24, 2004 Share Posted October 24, 2004 With 720's I run 70% duty cycle at 1.2bar boost, 6500+rpm. Plenty of headroom for more boost I supply Side / Hi Imp Blitz 850's with our kits in case the 650's may be a bit close to their top end if you really start to go T67 with welly Same kind of price range - so why not? Quote Link to comment Share on other sites More sharing options...
dude Posted October 24, 2004 Share Posted October 24, 2004 Its no good just sticking in huge injectors and expecting the stock rail /line/filter/dampner to supply it enough fuel dudes , IMO as soon as you go over the 650's other mods will need to be made. Dude:flame Dev Quote Link to comment Share on other sites More sharing options...
Dragonball Posted October 24, 2004 Share Posted October 24, 2004 Originally posted by dude Its no good just sticking in huge injectors and expecting the stock rail /line/filter/dampner to supply it enough fuel dudes , IMO as soon as you go over the 650's other mods will need to be made. Dude:flame Dev What size lines are the stock set up m8? -6AN or -8AN? Quote Link to comment Share on other sites More sharing options...
MONKEYmark Posted October 24, 2004 Share Posted October 24, 2004 the stock lines are -6 people in america have fitted 850cc injectors on stock rail.they have them modified for twin feeds. i was advised to go with a full fuel kit with bigger fuel rail. terry had 850`s on the modified stock rail. you have to sometimes make your own mistakes to learn. the lines in the fuel kit are -6 so they must beable to flow enough fuel. i always though -8 lines were for the big v8 type cars with lots of power. and is it not better to have plenty of headroom so you not maxing the injectors out. make your choice what you think is best for your plans. do a search on supra forums for injectors and you will find all the info you need. Quote Link to comment Share on other sites More sharing options...
dude Posted October 24, 2004 Share Posted October 24, 2004 IMO for 850's i would like to see either x -6 main feeds and 2x -6 rail feeds with seperate filters and 2 pumps (my personal fav) or 1 x -8 feed and 2 x -6 rail feeds using an aftermarket filter with either 1 big or 2 walboro pumps , and then of course there is the control issue !!!! Dude:flame Dev Quote Link to comment Share on other sites More sharing options...
Ian C Posted October 25, 2004 Share Posted October 25, 2004 Pruned. Ahhh, if only I could do that with some conversations with women I've had Be nice all -Ians Quote Link to comment Share on other sites More sharing options...
Guest Terry S Posted October 25, 2004 Share Posted October 25, 2004 Originally posted by Paul E I supply Side / Hi Imp Blitz 850's with our kits in case the 650's may be a bit close to their top end if you really start to go T67 with welly Same kind of price range - so why not? We can successfully run a T67 car at 2 bar with 650cc Paul, as you now know we have already done it. There are technical reasons not to run too large an injector than necessary. We also supply 800cc injectors for exactly the same cost as the 650cc. Quote Link to comment Share on other sites More sharing options...
Tannhauser Posted October 25, 2004 Share Posted October 25, 2004 Originally posted by Terry S There are technical reasons not to run too large an injector than necessary. Can you elaborate on this, Terry? I have 850cc injectors + modified fuel rail (bought from you). However, I'm only running a BL61. Whilst I knew that this would be overkill for what I needed, I was under the impression that there was no substantial downside to this (other than price). I did search at the time but don't recall what the problems oversized injectors might cause - I know I dismissed them as 'minor', but I might have not grasped the issues properly. Regards Cliff Quote Link to comment Share on other sites More sharing options...
Guest Terry S Posted October 25, 2004 Share Posted October 25, 2004 There isn't an issue for your set up Cliff. Quote Link to comment Share on other sites More sharing options...
Digsy Posted October 25, 2004 Share Posted October 25, 2004 Can someone just clear something up for me? Pumps I can understand but why do you need to uprate the fuel rail for bigger injectors? The flow area of the injector is tiny compared to the flow area of the fuel rail, and you only have one open at once. Even if all 6 fired at one go I bet the total flow area would still be less than the stock fuel rail. Is it really that much of a limiting factor? Quote Link to comment Share on other sites More sharing options...
Guest Terry S Posted October 25, 2004 Share Posted October 25, 2004 Originally posted by Digsy Can someone just clear something up for me? Pumps I can understand but why do you need to uprate the fuel rail for bigger injectors? The flow area of the injector is tiny compared to the flow area of the fuel rail, and you only have one open at once. Even if all 6 fired at one go I bet the total flow area would still be less than the stock fuel rail. Is it really that much of a limiting factor? Nope My Purple car made almost 700 bhp ( engine dyno bhp) on a Modified stock rail. No signs of problems. Had it flow tested ( the rail) with 850cc in, and they rail had more than adequate flow. We modify the rail to twin feed though. Quote Link to comment Share on other sites More sharing options...
TLicense Posted October 25, 2004 Share Posted October 25, 2004 I believe I'm right in saying, that anything above 17% duty cycle will mean more than one injector will be open. At 100% it means the injector is open solidly. As (unless you have been very meticulous in your mapping) all the injectors run from the same map and generally don't have individual trims (although this is completely possible) you could potentially have all 6 injectors open, 100% duty. (Not good for the injectors, but it is possible to do) I've not looked into up-rating the fuel system much, (I'm just happy in the knowedge that what I have is in-adeqaute for my set-up;) ) But would you not just be able to attach a pressure gauge to the rail, maybe at either end, or at least at the far end from the fuel inlet, and just make sure you have a good consistant pressure across the range?(ideally as much pressure as the injectors can safely take) At what point would you NEED to upgrade the fuel rail? Do you end up having to ramp the pressure so high at idle that at WOT you're struggling to flow enough to feed the injectors, and so the only way you can get enough flow is to increase the cross section area? Tony Quote Link to comment Share on other sites More sharing options...
Ian C Posted October 25, 2004 Share Posted October 25, 2004 Isn't there something to do with pressure as well? The fuel system needs a certain pressure at the injectors and if there is a bottleneck at the entrance to the fuel rail it may drop pressure there before it gets to the injectors. Probably not a big factor though unless you go for daft power. I got a HKS rail as I had top feed injectors. The side feed ones only came into our circulation just after I'd forked out. But it looks nice -Ian Quote Link to comment Share on other sites More sharing options...
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