Nick M Posted November 8, 2002 Share Posted November 8, 2002 I've just sent my car off to have the mapping sorted and the person doing the mapping made a comment that the injectors were, at some points running around 96% duty cycle (which seems too high to me) so he'd had to increase the fuel pressure to compensate. Having gone back through the archives it seems that anything over 95% is getting a bit iffy but that there *may* be some advantages to a long duty cycle. The basic engine spec is as follows : 1.6 16v Vauxhall Corsa GSi engine SBD tapered throttle body conversion Bosch Cream injectors Fuel pressure - initially 50psi Power output - should be around 185bhp at about 8,000rpm I'm now wondering if I need to go up to the Bosch Green injectors and accept that they may be a bit over the top at low fuel requirements. What about the Peco injectors - anyone tried them ? Any comments or suggestions would be welcome. Or if I've missed out any vital info just shout. Link to comment Share on other sites More sharing options...
oilyhands Posted November 8, 2002 Share Posted November 8, 2002 96% is too high, a safe maximum would be 85-90%, the injector capacity is purely down to its flow rate at any given pressure, granted the Picos have a slight faster open/shut time but the difference is small. Increases in pressure only increase the flow by the aquare root of the increased pressure. I'm sure that there are many injectors which are closer to your requirements than the greens, the stock K series injectors (common to the K and the C20XE) flow enough for 220BHP at 3.5 bar (235CC/min) and are easy to find, you wont have granularity problems with those and if your ECU software is any goo you should be able to re-scale the map if you know the old injector capacity. Oily Link to comment Share on other sites More sharing options...
Nick M Posted November 8, 2002 Author Share Posted November 8, 2002 Thanks Oily, Forgot to mention it's running on an MBE 967 ECU with the Easimap 5 software so I would hope that's capable of dealing with an injector change. Link to comment Share on other sites More sharing options...
Matt Seabrook Posted November 8, 2002 Share Posted November 8, 2002 Hi Nick I am surprised that you are running such a high duty cycle on these injectors if they are the 2000cc Vx cream injectors @ 50psi what is the duty cycle at 60psi. SBD recon that these injectors are good for 235bhp. Are you running sequential or batch fired injection? Link to comment Share on other sites More sharing options...
Nick M Posted November 8, 2002 Author Share Posted November 8, 2002 Batched. I was surprised at the duty cycle as well - I know the fuel pressure needed with the 185bhp SBD kit is about 15psi higher than the others either side of it (one produces 164bhp but runs 35psi fuel pressure on Cream injectors, the other 200bhp with Green ones at 35psi) so I assumed this was to compensate for the injectors. But the main reason for the query was reading some of Chelspeed and Arnie's comments that they'd run 250bhp engines (or more) with these injectors without any problems which made me wonder why my ickle engine producing a mere 185bhp was struggling with them. Maybe they're duff injectors, but I had them checked. I'm just wary of running components at or near their limits and would rather build in a margin of safety than risk running them flat out and damaging the engine somehow. Link to comment Share on other sites More sharing options...
Matt Seabrook Posted November 8, 2002 Share Posted November 8, 2002 Nick I run Green injectors on my engine (yep I know its a Zetec but it makes 210bhp min) @40psi and they only run 75% d/c at peak. Great for when I go for more power but I think they would be over kill for you. I’m with you though about running things at the max not a good idea. Thinking about it though the cream injectors on the Vx engine as standard are running sequential and are producing 150+ Bhp so running batch fire 185bhp should be easy. Something is not right. All the best Matt Link to comment Share on other sites More sharing options...
Nick M Posted November 8, 2002 Author Share Posted November 8, 2002 Bingo - just not sure what at the moment !! Could be I had the static fuel pressure set too low to begin with and Rob has merely brought it up to where it should have been, but if it's running at much over 50psi then something's not quite right. Looking at prices of the Magnetti Marelli "Pico" injectors - GBP64 plus the dreaded in the UK - be interesting to see what they cost here in the US !! Link to comment Share on other sites More sharing options...
Matt Seabrook Posted November 8, 2002 Share Posted November 8, 2002 Only thing I can see with the peco injectory is they are a lot shorter so you will also need to do something with your fuel rail. Matt Link to comment Share on other sites More sharing options...
Matt Seabrook Posted November 8, 2002 Share Posted November 8, 2002 Just a thought and a bit of a long shot is your fuel pump up to the job in hand if it is running out of steam it may not be an injector fault. Fuel pressure may not be the problem may be fuel delivery (I.e. quantity). Matt Link to comment Share on other sites More sharing options...
Nick M Posted November 8, 2002 Author Share Posted November 8, 2002 Fuel pump shouldn't be an issue - can't remember it's exact specs but it should be more than up to the job in hand. As for the shorter injectors, yes, this may be an issue but I think that's going to be one of those things that you can't really tell until you try and put it all back together. Suffice it to say that a bespoke fuel rail wouldn't be beyond the realms of possibility. Link to comment Share on other sites More sharing options...
Matt Seabrook Posted November 8, 2002 Share Posted November 8, 2002 Good luck mate let us know how you get on. Matt Link to comment Share on other sites More sharing options...
Nick M Posted November 8, 2002 Author Share Posted November 8, 2002 Cheers Should know the score on Monday as it will be fully mapped by then. Might even have a better idea of how much power the thing is producing too !! Then on Thursday it's being taken away to be containerised and shipped over here to the US for 12 months !! Roll on Septic-baiting at the local drag strip !! Link to comment Share on other sites More sharing options...
Matt Seabrook Posted November 8, 2002 Share Posted November 8, 2002 You will have to let us know a little ond 4 cyl goes against those tank-engined yanks 😬 Link to comment Share on other sites More sharing options...
Nick M Posted November 8, 2002 Author Share Posted November 8, 2002 Oh don't worry, I will !! Should annoy quite a few cars out here if it runs mid 13 second 1/4 miles 😬 Link to comment Share on other sites More sharing options...
Matt Seabrook Posted November 8, 2002 Share Posted November 8, 2002 Should think that will be on the cards mine run 13.9 @ 105mph on road tyres 630kg and a bog s. mt75 gearbox. With the right box tyres and lookin at your avitar you car is about 550kg aprox. 13.5 sec is on the cards. Happy blating yank tanks 😬 Link to comment Share on other sites More sharing options...
Nick M Posted November 9, 2002 Author Share Posted November 9, 2002 Yep, probably weighs something around the 540-550kg mark. Although the driver does rather knacker the power to weight ratio !! 😳 With 13" rims with ACB10s I reckon it should be quite quick. May even invest in a pair of proper drag racing slicks, just for a laugh 😬 Link to comment Share on other sites More sharing options...
EFA Posted November 9, 2002 Share Posted November 9, 2002 Cream Injectors of the type fitted to the XE 16V are good for 280bhp if the fuel pressure is set appropiately. The statement that "Increases in pressure only increase the flow by the square root of the increased pressure." is absoultely correct. If at 45psi and a 90% duty cycle the cream injectors are good for 235bhp (they are) then increasing the pressure to 65psi will yield a power figure of 282bhp. The above of course assumes that power increases in a linear fashion with fuel charge - I believe this to be the case, based upon the theories of Brake Specific Fuel Consumption. There are of course many other factors which infuence the max power relative to flow rate, including the mapping - mapping rich for margin of safety will require a higher flow rate, thermodynamics of the combustion - an engine which runs cool will require less fuel to produce the same amount of horsepower as a warmer engine - and piston area which is why there is no direct correlation between displacement, RPM and BHP. Nick - if you are concerned as to your fuel pressure effecting power, then measure your fuel pressure at the rail when running high RPM/load. Any drop here will have a serious effect on output. It should remain stable - i.e +/- 0.5psi Fat Arn Visit the K2 RUM website See the Lotus Seven Club 4 Counties Area Website here Link to comment Share on other sites More sharing options...
Nick M Posted November 10, 2002 Author Share Posted November 10, 2002 Thanks Arnie - think the final top end mapping is being done on Monday so I'll ask them to check the fuel pressure at the top end under load. I'll also ask them to confirm what the fuel pressure is as well - I've a feeling the problem of high duty cycles is largely a product of the initial fuel pressure being too low - I'm guessing even 5psi would make quite a difference to the time the injector needs to remain open. Link to comment Share on other sites More sharing options...
Chelspeed Posted November 10, 2002 Share Posted November 10, 2002 My SBD engine was rated at 252bhp (but exactly what it made who knows) it ran cream injectors at 60psi. Today an SBD 252bhp engine would be supplied with green injectors at 50 psi. To me that infers the creams were marginal at this level. Unless of course you ran huge fuel pressures or have injectors like Arnies that can run 103% duty cycle. I now run yellow pico's. On the dyno last year the duty cycle reached 94% so we upped the fuel pressure from 50 to 60psi which dropped it down below 90%, forget the exact number. But be careful, the duty cycle doesn't stay constant. Lots of other things affect it, if volts fall a correction curve will increase duty cycle to compensate, if water temp is cold, if air temp is cold, again duty cycle will be increased. So it doesn't take long for duty cycle to get pushed up and exceed 100% then you're in the doodoo big style. This is what caused my ECU problems this summer, something, probably brushes on the alternator, caused the volts to drop at high revs, the correction curve pushed duty cycle up, when it hit 100% the ECU said enough and ctrl-alt-delete'd. Link to comment Share on other sites More sharing options...
Nick M Posted November 10, 2002 Author Share Posted November 10, 2002 Thanks for the warning !!! *goes off to buy some new injectors....* Link to comment Share on other sites More sharing options...
edmandsd Posted November 10, 2002 Share Posted November 10, 2002 I recently changed my 4 370cc/min injectors (Similar to Cossie greens) for Cossie Grey's as the duty cycle was up to 93% at 5 bar fuel pressure ! In retrospect maybe I should have gone for the Cossie Blues which were somewhere in between the Green's and Grey's. Home of BDR700 Edited by - edmandsd on 10 Nov 2002 16:38:28 Link to comment Share on other sites More sharing options...
V7 SLR Posted November 11, 2002 Share Posted November 11, 2002 I changed Rover whites (I think 270cc/min) for Saab reds (around 330 cc/min - possibly a bit oversized). The Rover whites should give me around 220bhp but at 200bhp I was seeing duty cycle of 96%. The Saab reds were down to mid 80's% at slightly more power. Worcs L7 club joint AO.//Membership No. 4379//Azure Blue SLR No. 0077//Se7ens List Tours Link to comment Share on other sites More sharing options...
Rob Walker Posted November 11, 2002 Share Posted November 11, 2002 Nig the big red SAAB`s are 380cc/m at 3 bar. Edited by - Rob walker on 11 Nov 2002 17:33:59 Link to comment Share on other sites More sharing options...
V7 SLR Posted November 11, 2002 Share Posted November 11, 2002 Is 4 bar the Caterham standard? If so, that explains why the injectors are a bit larger than I probably need. Granularity is marginal at idle where they either run rich (which will bugger up my MoT emmissions) or switch off altogether if you try to lower their switched-on-time any more. For the MoT I'm thinking again of raising the fuel pressure and reverting to my original injectors. I can see an occasion where 2 maps might be required... one for everyday running on the big RED's and one for MoT time on the little WHITE's. Worcs L7 club joint AO.//Membership No. 4379//Azure Blue SLR No. 0077//Se7ens List Tours Link to comment Share on other sites More sharing options...
scooby dooby doo Posted November 11, 2002 Share Posted November 11, 2002 V7, What were/are your thoughts on deciding between the Rover injectors at a higer pressure and the Saab ones at a lower pressure 🤔 Why chose one or the other 🤔 HOOPY 500 kg R706KGU Link to comment Share on other sites More sharing options...
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