Methods for decreasing injector duration?

[V7 SLR]

Last time V7 was tested on the rollers it was showing 200bhp at a little under 8000rpm but the injector duration was showing 97%. Now that V7's head is fully DVA'd I'm ging to need to feed it more fuel.

 

Option A)

 

I understand the correct way to do this is to replace the injectors with uprated ones. Normally they're very expensive but I've found a set of 430cc/min ones at a little over £100, but as the standard ones are only 235-248cc/min (depending on who measures them) I'm worried that I won't be able to control them adequately at idle. They will need VERY small duration times from the M3DK. Anyone know if this'll be OK? This would be the most elegant solution for increased fuel delivery.

 

Apparently idle's the thing that could suffer with too big injectors. replacements in the order of 330cc/min would be best but they're not the same impedance, and anyway, I can get the 430cc/min ones (which are of the correct impedance) very cheaply. I use the car mainly for touring, so not having the car fluff at idle or low revs is important. As is emmissions as I'm going to have to MoT is this year. I have a Cat, but dumping a lot of unburnt fuel into it won't help the emmissions reading.

 

Option B)

 

Leaving my current injectors in place, I could increase the fuel pressure from it's current 3 bar to 4 or 4.5 bar. This is likely to give me enough extra fuel delivery to compensate for my increased airflow. The problem with this is the standard fuel rail does not have an adjustable FPR. Caterham supply an alternative rail which can attach to an adjustable FPR but the angle at which the FPR comes off this rail is such that it interfers with the throttle bodies. I've heard that this alternative fuel rail is to enable the 1.6K supersport map to be used with the 1.8K supersport engine.

 

I could fit this fuel rail the other way round. Then the angle of the FPR would actually be in my favour, but the hose that feeds fuel to the rail would have to connect to the rail at the front of the engine rather than the back... so I'd need a new hose set... blah blah blah blah. Bloody complex.

 

 

So, advice please. Injectors or increased fuel pressure?

[oilyhands]

Depends where you are going in the future..

 

I'd go for the bigger injectors, the M3DK has a function which will re-calculate the injector modulation times across the map if you resize your injectors, its under 'Additional settings', menu item 'injector scaling', it takes into account and netss off the injector latency time before adjusting the injector times, then adds it back so it will be pretty accurate provided you know the correct flow rates for the old and new injectors.

 

Oily

[EFA]

Nigel,

 

Increase your fuel pressure with the std injectors.

 

Fat Arn

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[V7 SLR]

Two answers. Two different opinions. OK... thanks for that. Confirms that I must have weighed up the arguements well enough. wink.gif

 

Can either of you please answer whether the larger injectors will bugger up my idle, low speed running and/or emmissions at idle?

 

To answer Oily: I don't want to go any further than Mick Smith. If I can retain my current crank and rods and keep the limiter at 8000rpm yet still achieve 220 - 225bhp I'd be happy.

 

I'm happy enough that I can map for the new injectors, and have seen how the M3DK can do this (great bit of kit) and I'm booked into a session at Emerald on 25th May, but it's whether it will be possible to open the injectors for a sufficiently short period to enable good idle, low speed running and emmissions at idle.

 

If I go for the seemingly-simple "increase fuel pressure" method, where can I get the appropriate fuel hoses from to implement it? I'm going to have to turn the fuel rail around which means the feed-pipe connects to the rail near to the front of the engine, rather than the current location at the back of the engine. Mike Bees indicated in an email to me some time ago that the thread for this fuel pipe is non-standard. I'd certainly need to replace this hose for a longer one.

 

The increase fuel pressure method appears simpler, and would certinaly be cheaper... but I want to do it right. I'd need to reduce my injecotr duration quite a bit. Running at 97% at the moment (OK, only at full tilt, but even so...) isn't a good idea. I need to compensate for the fabby head job my good friend has done for me, plus reduce the duration at full tilt to something more acceptable...

 

... I think.

[Rob Walker]

Nigel pay attention I wrote to you and told you where to get a set of 4 X 380cc/m high impedance injectors for £50 which work a treat. No problem with the idle either. Would you rather pay £100 for injectors that are far too big ?

 

Rob

 

Edited by - Rob walker on 29 Mar 2002 14:31:33

[V7 SLR]

Rob, I agree with you but I was a little uncertain by your advice to get them checked out by a Bosch dealer (or words to that effect). Those that I've been offered were brand new, but as you say, a bit big.

 

So, with your suggestion, I now have 3 options.

 

Cheers. smile.gif

[V7 SLR]

I've just been talking to Mick Smith who has taken Rob's advice and confirmed that it is the right move. We've managed to ascertain that the M3DK should easily be able to control the large 430cc/min injectors, and coupled with the fact that I'd reached 97% duration at 200bhp I should be seeking to reduce the duration at 200bhp, let alone as the bhp rises towards my goal of about 225bhp.

 

So, bigger injectors it is then.

 

Which ones though..??.. Rob's 380's at 50 quid plus postage, plus reconditioning (at 12 quid per injector plus postage) or 430's at 108 all in..?? Chap that's offered to source me the 430's said I may be able to borrow his current set, so I think I'll do that first.

 

Thanks to all for A&G. I wasn't trying to ignore your advice Rob, but I had to work through all the possible tiny options in my head. FWIW I finally decided against the fuel pressure increase on the grounds that I don't know what fuel pump I have and whether I'd actually benefit from an increase.

 

 

[Mike Bees]

You need to establish which fuel pump you have irrespective of how you choose to deliver the extra fuel. The 'stock' K-series one (19gm/s) is marginal on a VHPD engine.

 

430 cc/min sounds awfully big to me FWIW. There was a bloke on www.racecar.co.uk selling Lotus Carlton injectors (high impedance, 380cc/min) at 100ukp a set some time ago. Supposedly 'brand new', although the ones I bought don't look it.

 

Mike

[V7 SLR]

No-one selling Lotus Carlton injectors now Mike, but Rob has told me where I can get similar fare from and Mick Smith has successfully gone down that route. I've got the opportunity to borrow a set of 430's so I try them first then decide a more permanent course of action.

 

Caterham say that the JPE, the SLR and the R500 all use the same fuel pump. They say the pump as it comes from Rover has an assembly kit replaced (I guess this is the pumping mech) for an uprated one. No-one could quote me flow numbers but they said the part was 70 quid.... but I've apparently already got it. That was the best piece of news I've heard for a while. smile.gif