F355GTS Posted July 6, 2004 Share Posted July 6, 2004 Following a RR session at Steve Greenald's yesterday it is evident the injectors on my car are not up to the job, they are currently 744's and are failing at around 6,700 rpm where the engine is producing 207BHP. The power line was climbing strongly and Steve felt it needed an 8.5k red line (currently set to 7.5k) but to do that it would need the bottom end uprated. So in the short term it would seem that a change of injectors will release a bit more power and allow the engine to rev freely to it's red line. Anybody have any recommendations? Mark Link to comment Share on other sites More sharing options...
caterhamnut Posted July 6, 2004 Share Posted July 6, 2004 😬 - now Mark - what did we say only last night about not really needing more power 😬 (Car almost passed MOT - just the bloody rear lights playing up ) 'My First Race - SPA' pictures here 60,000miles in 3years Link to comment Share on other sites More sharing options...
jon1 Posted July 6, 2004 Share Posted July 6, 2004 I also had a rolling road session with Steve. He suggested i go to Bosch 'reds' whereas my car currently has 'greens'. However, still producing 240bhp !!!! Apparantly reds are the optimum and will smooth out the power delivery. Hope this helps M. Link to comment Share on other sites More sharing options...
Peter Carmichael Posted July 6, 2004 Share Posted July 6, 2004 0-280-150-744s are 214.4cc/min at 2.5bar apparently. The JPE fuel pump is happy at 4 bar and this would take the flow rate of the injectors up to 271 cc/min. I was running 250bhp off a 381cc/min setup, with some fairly significant duty cycles, so I am amazed the 744s are working for you at all! On the basis of that I would definitely get an uprated set of injectors. Link to comment Share on other sites More sharing options...
EFA Posted July 6, 2004 Share Posted July 6, 2004 Mark, I ran 744's in K2 RUM until the last engine rebuild @ 4.5 bar - this is good for well over 260bhp at around 95% D/C so I would look at the pump end of things. The JPE Pump gets to about 4.5bar @ 13.8v before the flow rate falls off - a better 14.4v alternator will see you obttian even more pressure. Ex Fat Arnie Hauling Less Lard.... Link to comment Share on other sites More sharing options...
Alba 7 Posted July 7, 2004 Share Posted July 7, 2004 Arnie et al, 744's - are these the Bosch 'Cream' injectors or am I getting my colours and codes all in a muddle? Interested because my SBD208 engine will shortly be coming to life and I've used cream jobbies in this. Nick. Link to comment Share on other sites More sharing options...
EFA Posted July 7, 2004 Share Posted July 7, 2004 You are correct Nick. Bosch Cream will be fine at 3 bar in a 208. Ex Fat Arnie Hauling Less Lard.... Link to comment Share on other sites More sharing options...
Harry Flatters Posted July 7, 2004 Share Posted July 7, 2004 Alba 7 - Yes the 'cream' injectors (at 50 psi) are the correct ones to use on the SBD208 setup. *arrowright*Harry Flatters *arrowright* AKA Steve Mell of Su77on Se7ens and Surrey Joint AO Link to comment Share on other sites More sharing options...
F355GTS Posted July 7, 2004 Author Share Posted July 7, 2004 Thanks for the responses so far, Can I assume I have a JPE pump? is it the only one that would/ could have been fitted? how easy is it to identify if I remove it from the tank? Mark Link to comment Share on other sites More sharing options...
I reply to every thread Posted July 7, 2004 Share Posted July 7, 2004 Cream? - I'd say they were kinda beige Link to comment Share on other sites More sharing options...
EFA Posted July 7, 2004 Share Posted July 7, 2004 "Can I assume I have a JPE pump? " Unless your car was a JPE it is unlikely. I no longer have the info to confirm. I do no of cars up at 225-230 bbhp using the std K pump if that helps. If you can maintain the fuel pressure when the duty cycle is high then your pump has the flow rate to do the job. Ex Fat Arnie Hauling Less Lard.... Link to comment Share on other sites More sharing options...
F355GTS Posted July 7, 2004 Author Share Posted July 7, 2004 Arnie The fuel pressure seems to be OK running at 70psi (4.7bar) everybody tells me this is high? so I assume the pump is working OK although perhaps I need to strip the pump and make sure the pickup is clean and replace the in line filter just for good measure. Could my problems be with the pressure regulator? are these adjustable? or does one buy units of a specific pressure? Mark Link to comment Share on other sites More sharing options...
EFA Posted July 7, 2004 Share Posted July 7, 2004 Mark, 70psi is very high. I am now thinking that as the duty cycle increases, the pressure likley drops as theer is not the flow rate to maintain it. This is probably why Steve is blaming the injectors. What BHP are you aiming at? Ex Fat Arnie Hauling Less Lard.... Link to comment Share on other sites More sharing options...
F355GTS Posted July 7, 2004 Author Share Posted July 7, 2004 Arnie I was told it produced a strong 218BHP on the dyno (and it was implied that this would translate into around 235 on a rolling road?) engine was built and dynoed by Bob Jones in Manchester. Is it possible to calculate what I should be getting at 7.6k if I'm getting 207BHP at 6.7k? if I carry up the trace from the rr it would suggest this would be around 235/240BHP Mark Link to comment Share on other sites More sharing options...
Peter Carmichael Posted July 7, 2004 Share Posted July 7, 2004 There appear to be some funny numbers flying around here. I haven't done much work with the injectors in question, so I will just be talking from the point of view of theory. The Bosch 744 injectors have a rated flow rate of 214.4cc/min (or 20.4-20.7lbs/hr if you prefer) at 2.5 bar. A quick rule of thumb is to take maximum horsepower required per injector and divide by 2 to get the required lbs/hr flow rate figure. Rule of thumb suggests these injectors are good for 40 or so horsepower each. Max hp=160 for 4 injectors. As another check, injector tables list the most optimistic rating for these injectors at 46hp/injector at 95% duty. This implies a brake specific fuel consumption of 45% which is about as good as you can get. With an engine fuelled for significant cooling of the charge with 12:1 air:fuel ratio BSFC would be closer to 50%. 260 horsepower has been mentioned. For 744s to deliver this at 95% duty and 50% BSFC, would require the flow rate to increase by a factor of 65/46=1.41x. The fuel pressure needs to be increased by the square of this factor. 1.41^2=2x The net result of this is that for 260bhp from these injectors you need to run 5 bar fuel pressure. I'd generally class 5 bar fuel pressure as a bodge, beacuse of all the consequences for the current draw by the pump, load on the wiring and effects on pump longevity. You can redesign the entire fuel delivery system to cope, or you can rely on over-capacity in the existing setup; fuses may blow, wiring may get a bit warm, pumps may not last as long as you'd like. It is also worth pointing out that there is considerable optimism in using 45% BSFC as the basis for calculations. Working with a realistic BSFC of 50%, the required fuel pressure becomes in excess of 6.2 bar. All the comments about 5 bar are applicable for >6bar only more so. Fuel pressure increases of this magnitude are no substitute for correctly sizing the injectors in the first place. Link to comment Share on other sites More sharing options...
Peter Carmichael Posted July 7, 2004 Share Posted July 7, 2004 Mark, To calculate peak power potential, given a rev potential... Take the peak torque figure... Multiply by .89... Multiply by your target rpm and divide by 5252..... If you are still constrained by mechanical strength from opening up the engine to its full power potential revs you may get a few more than this. Link to comment Share on other sites More sharing options...
Peter Carmichael Posted July 7, 2004 Share Posted July 7, 2004 At 50% BSFC, maximum power potential of those injectors at 4.7bar is 226bhp @95% duty cycle. If the engine has a peak torque of 175lbft, you could see a 226bhp @ 7600rpm peak. If the engine still hasn't peaked it will be important for you to have more capacity in the injectors. Even if an ignition-cut rev limiter cuts in shortly after, you still need to be fuelling correctly for the following few hundred rpm. Link to comment Share on other sites More sharing options...
EFA Posted July 7, 2004 Share Posted July 7, 2004 Peter, While I see the logic of your calculations, I have seen several engines running 744 cream injectors at <5 bar which likley gave or exceeded 260bhp. Ex Fat Arnie Hauling Less Lard.... Link to comment Share on other sites More sharing options...
Peter Carmichael Posted July 7, 2004 Share Posted July 7, 2004 Well we are just getting to the bottom of your bull**** power claims then, aren't we 😬 😬 Like I said, my posting is all about theory and good practice. If results have been achieved that exceed these numbers, then good luck to them... Link to comment Share on other sites More sharing options...
Alba 7 Posted July 7, 2004 Share Posted July 7, 2004 Arnie / Steve - Thanks for the confirmation. Aves - I ken what you mean but beige nearly always has 'Austin Allegro' and 'hearing aid' associated with it Nick. Link to comment Share on other sites More sharing options...
EFA Posted July 7, 2004 Share Posted July 7, 2004 .......or Steve Walkers R300 *tongue* Peter, It would be unkind of me to quote your comments after driving K2RUM (with crema injectors) at Brooklands after Curborough then 🤔 🤔 🤔 Using your predictive power calculation quoted earlier my present spec would seem good for 310bhp! Like I say, the theory is flawed! Ex Fat Arnie Hauling Less Lard.... Link to comment Share on other sites More sharing options...
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