a98pmalcolm Posted August 28, 2012 Share Posted August 28, 2012 Hay all. Did a little research and nothing came up that was 100% clear. Whats the max BHP level that an 850cc injector will do? Thanks Paul Quote Link to comment Share on other sites More sharing options...
tkddav3 Posted August 28, 2012 Share Posted August 28, 2012 i thought it was kinda the rule of thumb 850's gotta be near 800? Quote Link to comment Share on other sites More sharing options...
Parry_10 Posted August 28, 2012 Share Posted August 28, 2012 Id get some id1000's mate, thats what ive got for mine and im looking for 650bhp but then you have room for more power in the future should you want it Quote Link to comment Share on other sites More sharing options...
Luxluc Posted August 28, 2012 Share Posted August 28, 2012 I (still) have 850cc SIEMENS injectors on my Supra. At 1.8 bar and 651 rhhp, the injectors were at 86% DC. I guess at 700 rhhp, they will be maxed out. Quote Link to comment Share on other sites More sharing options...
johnny g Posted August 28, 2012 Share Posted August 28, 2012 Well 85% should be your max duty cycle... Quote Link to comment Share on other sites More sharing options...
Luxluc Posted August 28, 2012 Share Posted August 28, 2012 Well 85% should be your max duty cycle... Yeah, I changed the injectors therefore as Ryan said he didn't want to push further. Quote Link to comment Share on other sites More sharing options...
V8KILR Posted August 30, 2012 Share Posted August 30, 2012 I have a Supra injector calculator on my website that allows you to exactly calculate what they will do. http://mkiv.supras.org.nz/injectors.htm Quote Link to comment Share on other sites More sharing options...
Ian C Posted August 30, 2012 Share Posted August 30, 2012 Well 85% should be your max duty cycle... I don't really believe in that rule of thumb any more, I think that's from way back in the early days of EFI. I've never heard of an injector failing apart from being gummed up, and all the BPU Supras out there run 100% duty once they get over 1bar Quote Link to comment Share on other sites More sharing options...
V8KILR Posted August 30, 2012 Share Posted August 30, 2012 I agree with Ian about injectors being able to run to 100% with no problems so long as they are not at 100% for an extended period of time (as they can overheat) which is very unlikely for most people. Mine are at about 90% at the moment. Quote Link to comment Share on other sites More sharing options...
Ian C Posted August 31, 2012 Share Posted August 31, 2012 Mine hit about 95 to 98% at 7200rpm 1.45bar so right on the raggedy edge But they are there for such a brief moment it's meaningless really. Quote Link to comment Share on other sites More sharing options...
Paul Whiffin Posted August 31, 2012 Share Posted August 31, 2012 I would say about 750bhp but that can depend on the size of the turbo too. Quote Link to comment Share on other sites More sharing options...
V8KILR Posted August 31, 2012 Share Posted August 31, 2012 yep, 636rwhp at 100% if running a manual which is about 750bhp. Quote Link to comment Share on other sites More sharing options...
Ian C Posted August 31, 2012 Share Posted August 31, 2012 Poached into tech Quote Link to comment Share on other sites More sharing options...
Wez Posted August 31, 2012 Share Posted August 31, 2012 Also depends on your base pressure and fuel being used. You should first work out your goal and then size them appropriately. Quote Link to comment Share on other sites More sharing options...
V8KILR Posted August 31, 2012 Share Posted August 31, 2012 Poached into tech Very good. Also depends on your base pressure and fuel being used. You should first work out your goal and then size them appropriately. My Supra injector calculator allows for base pressure and fuel type as well. Quote Link to comment Share on other sites More sharing options...
Ian C Posted August 31, 2012 Share Posted August 31, 2012 Your calculator doesn't take into account a higher rev limit, does it? I've just had a play and it's accurate for my car if I only went to 6800rpm, not 7200 Quote Link to comment Share on other sites More sharing options...
V8KILR Posted August 31, 2012 Share Posted August 31, 2012 (edited) Your calculator doesn't take into account a higher rev limit, does it? I've just had a play and it's accurate for my car if I only went to 6800rpm, not 7200 The calculator use WHP and AF ratio as the two main inputs and what RPM this power is made at is ignored by the calculator. Thinking about it, you make a very good point that at higher RPM, there will be more internal friction inside the engine (mainly from the pistons) so that the BHP figure would be higher then it would be for the same WHP that was made at lower RPM. As it is BHP that is made from the fuel (not WHP), I will need to adjust the calculator to take this in to account. Thanks for pointing this out. Are you able to send me some data logging (dyno type, injector ms, rpm and whp) that shows your increasing fuel usage with rpm? I'll have a go at incorporating RPM in to the calculator this weekend. Edited August 31, 2012 by V8KILR (see edit history) Quote Link to comment Share on other sites More sharing options...
V8KILR Posted September 2, 2012 Share Posted September 2, 2012 OK, I've had a go at allowing for the extra friction losses at high rpm. Ian, does this agree with your logging as I don't have any suitable data logging to compare to. You may need to refresh the page to see the rpm option. http://mkiv.supras.org.nz/injectors.htm BTW, this now puts my injectors at 97% as my max power is around 8000rpm. Quote Link to comment Share on other sites More sharing options...
Ian C Posted September 3, 2012 Share Posted September 3, 2012 The reason I mentioned rev limits isn't because of friction or anything, it's just that the max duty cycle becomes shorter as the revs get faster. For a given amount of boost, you need pretty much the same amount of fuel per ignition event no matter what the revs are (within engine breathing abilities of course). So a cylinderful of air at 21psi boost needs the same amount of injector duration at 5500rpm as it does at 6500rpm and 7200rpm. But the window of opportunity to deliver that duration is much shorter at 7200rpm than at 5500rpm. You get 20ms between ignition events at 5500rpm, and only 16ms at 7200rpm. If you need 16ms of duration per ignition event with your boost/injector/fuel pressure setup, that's 100% duty at the top end but only 80% duty at 5500rpm. Yes, the power goes up as you go up the rev range, but that's only because you're doing more ignition events per second, the power increase has nothing to do with boost pressure. So your target maximum revs are very important to sizing your injectors, a small increase in revs can quickly make injectors run out of time to deliver the fuel Quote Link to comment Share on other sites More sharing options...
Ian C Posted September 3, 2012 Share Posted September 3, 2012 Putting the numbers into your calculator, it does make sense if you allow for a 6800rpm limit. My rwhp at 21psi at 85% duty gives me 720cc injectors, which is all correct. That's 15.6ms duration, so upping it to 7200rpm mean 94% duty which is roughly what I'm seeing. Quote Link to comment Share on other sites More sharing options...
V8KILR Posted September 3, 2012 Share Posted September 3, 2012 (edited) I don't think the injector ms vs rpm makes any difference, as when you are at 100% injector duty cycle, then its still 100% duty cycle no matter what the rpm, so you never run out of time to deliver the fuel. All that matters is if the quantity of fuel delivered at 100% is sufficient for the maximum fuel requirements of the engine, irrespective of whether that maximum fuel requirement of the engine is at 6800rpm, 8000rpm or 10000rpm. Friction losses however do play a big part at high rpm as the friction losses increase at about 2 ^ 2.84, if you double the rpm. i.e Doubling rpm will increase friction losses by 7.16 times. Because my calculator uses whp and the engine is producing bhp and using fuel for bhp, then the engine losses do make a big difference to my calculator, as the extra fuel required to cover the extra friction losses increases very quickly at high rpm. Have a read of the link below (this is page 2 but you may need to read page 1 as well) where I was educated on how much friction losses do occur inside our engines. http://www.supraforums.com.au/forum/a80-mkiv-discussion/79385-12-injectors-vs-6-injectors-400rwkw-na-2.html Edited September 3, 2012 by V8KILR (see edit history) Quote Link to comment Share on other sites More sharing options...
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