Dyno Run/AFR/Fuel Pump

[scam75]

Morning everyone

After my latest upgrade session I got the old girl on a dyno yesterday. List of current mods is in my signature. She made 290 bhp with boost peaking at 17 psi. I've got to be happy with that I think and seems about right for the mods I have.

Only concern was a slight leaning at full boost when the AFR touched 12.8 to 1. How does that compare with other cars around the same power output? The guy at the rolling road reckoned it was a bit lean and asked how old the fuel pump was. On finding out it was 22 years old he suggested a new one would be a good place to start! The injectors were serviced about 3 years ago so I think I'll swap out the pump and filter first and see how that goes.

I think I've heard that the standard pump when healthy is good for about 350 bhp so I don't think I need a motorsport one. Al has a brand new one for a 911, does anyone know if it's the same pump?

Cheers

Stuart

 

[Lowtimer]

Is that 290 bhp at the wheels, or a calculated flywheel figure adding back the coast down drag?

 

[Ewan]

With my aim of 320 bhp (approximate) JMG suggested an upgraded fuel pump was a good idea, as the up cost over a straight replacement was not a lot. The thought of fuel starvation and the consequential pop was enough to make me agree! A fairly cheap upgrade for peace of mind, so for me, a no brainer.

By the way, your Dyno run was more successful than mine! A weak spring in the waste gate restricted mine to 12 psi, so we only got 258 bhp. But when this is fixed and we go back to Dyno on Friday we should be able to run at the planned 18 psi (peaking at 20) and this should up us towards the aim figure. Time will tell.

 

[scam75]

ORIGINAL: Lowtimer

Is that 290 bhp at the wheels, or a calculated flywheel figure adding back the coast down drag?

Hi LT

290 bhp at the wheels.

Stuart

 

[robwright]

Stuart running a modest 15 psi my AFR will dip as low as 10 when the foot is buried in the carpet. Not good for fuel economy I know but comforting to know I have plenty of fuel to keep the combustion temperatures down. It also means I have plenty in reserve should I wish to go higher in the future []

 

[Lowtimer]

290 at the wheels is pretty good, I'd say. Probably 340 at the flywheel and therefore the sort of territory where I would not be wanting to rely on a 22 year old standard fuel pump.

 

[scam75]

ORIGINAL: Ewan

With my aim of 320 bhp (approximate) JMG suggested an upgraded fuel pump was a good idea, as the up cost over a straight replacement was not a lot. The thought of fuel starvation and the consequential pop was enough to make me agree! A fairly cheap upgrade for peace of mind, so for me, a no brainer.

By the way, your Dyno run was more successful than mine! A weak spring in the waste gate restricted mine to 12 psi, so we only got 258 bhp. But when this is fixed and we go back to Dyno on Friday we should be able to run at the planned 18 psi (peaking at 20) and this should up us towards the aim figure. Time will tell.

My run certainly seems more successful, I should really be well pleased everything considered. I think I've got as many horses out mine as I could expect for minimal lay out. The next few horses will be more expensive. I may just leave them in the stable!

I hope you get your waste gate sorted soon and round up those missing horses!

Stuart

 

[scam75]

ORIGINAL: Lowtimer

290 at the wheels is pretty good, I'd say. Probably 340 at the flywheel and therefore the sort of territory where I would not be wanting to rely on a 22 year old standard fuel pump.

Thanks LT. I have to agree on that. A fuel pump is number 1 priority.

On trawling the interweb it appears that my AFR isn't a concern. Some american chaps are running 13 and 14 to one and seem to think 12.7 is super safe? Interested to hear what some of our home grown learned people think.

Stuart

 

[GPF]

ORIGINAL: scam75

ORIGINAL: Lowtimer

290 at the wheels is pretty good, I'd say. Probably 340 at the flywheel and therefore the sort of territory where I would not be wanting to rely on a 22 year old standard fuel pump.

Thanks LT. I have to agree on that. A fuel pump is number 1 priority.

On trawling the interweb it appears that my AFR isn't a concern. Some american chaps are running 13 and 14 to one and seem to think 12.7 is super safe? Interested to hear what some of our home grown learned people think.

Stuart

Hi Stuart,

Firstly, congrats on a good result - although I think the dyno you took it to must be one of the more optimistic ones if it's 290 at the wheels.

However, as for the AFR, I don't know where you found the 13 to 14 refs but they are talking absolute crap.

At 17 psi you need to be in the low 12's at highest.

What FQS is your DME set at? You may be able to add a little more fuel there - depending on what it is already set to, and which version of the ProMax chips you have.

Oh, and Rob - running with AFR of 10 would worry me a lot - with all that extra fuel you could be washing the bores and damaging the engine.

Don't want to be negative, but better safe than sorry........

 

[pauly]

ORIGINAL: scam75

On trawling the interweb it appears that my AFR isn't a concern. Some american chaps are running 13 and 14 to one and seem to think 12.7 is super safe? Interested to hear what some of our home grown learned people think.

Stuart

High 11's I would have thought, what injectors are you using ?.

 

[robwright]

ORIGINAL: GPF

Oh, and Rob - running with AFR of 10 would worry me a lot - with all that extra fuel you could be washing the bores and damaging the engine.

Don't want to be negative, but better safe than sorry........

Sorry mate I should have been a little more specific. What I should have said was CAN dip as low as 10.9 or something but not stay there. Generally it will settle around the 11.5-11.9 mark.

 

[scam75]

ORIGINAL: GPF



Hi Stuart,

Firstly, congrats on a good result - although I think the dyno you took it to must be one of the more optimistic ones if it's 290 at the wheels.

However, as for the AFR, I don't know where you found the 13 to 14 refs but they are talking absolute crap.

At 17 psi you need to be in the low 12's at highest.

What FQS is your DME set at? You may be able to add a little more fuel there - depending on what it is already set to, and which version of the ProMax chips you have.

I think it's actually flywheel power after looking at the print out again! [&:]

I don't know what the fuel quality setting is at. Where can I check this?

The box for the chips only says Porsche 944TS on it. No version number.

Standard injectors Pauly, although they were serviced about 3 years ago.

Stuart

 

[pauly]

ORIGINAL: scam75

Standard injectors Pauly, although they were serviced about 3 years ago.

Stuart

Time for some 55's probably.

 

[GPF]

The FQS is set using a little rotary switch which pokes through the casing on the DME itself - you might have noticed it when you fitted the chip?

The promax chips generally use this to scale the fuel globally, together with the Impedance Adapter(IA) and Region Coding Plug(RCP) to select which one of the 3 sets of maps are actually in use.

These combinations changed over time so you really need to know which chips you actually have.

Were there no instructions with the chips?

 

[pauly]

Not sure about earlier versions but I understand the later promax chips use the FQS to accomodate a DPW and/or 55lb injectors, why not ask promax ?.

 

[GPF]

They started out using the FQS to select std injectors v 55's and/or +3% +6% etc.

The different maps, selected with combinations of the IA & RCP plugs, were for different boost levels.

This was up to the SciVision maf - don't know about more recent versions, but at one point there were different chips for AFM/MAP/MAF.

Not that this really helps Stuart - good job he went to the dyno and therefore has a good idea where the fuelling ended up!!

 

[pauly]

ORIGINAL: GPF


The different maps, selected with combinations of the IA & RCP plugs, were for different boost levels.

Without digging out the paperwork I think on later cars one of those takes the standard lambda signal out.

 

[Diver944]

Hi Stuart, they are good figures but you're right it is definitely much leaner than is healthy for the engine at high revs. Ideally you should be between 11 and 12:1 on full boost, 11.5:1 is just about perfect. Do you have a copy of the chart showing the AFR through the rev range?

If you are lean everywhere then it simply means you are running too much boost for the programming on that chipset and should simply turn it down a psi or two. If you are only lean at high revs but okay further down then it could well be that the old pump is running out of breath and can't keep up supplying 3 bar at the fuel rail when the injectors are wide open.

If you just move the FQS switch without finding out the real reason you could end up being ok at high revs but then being really rich lower down which will lose you low down power, increase the spool up time and maybe even give you bore wash as mentioned

Here is a chart from Ed's car a few years ago at a similar power level. After 4000 rpm he is pretty much spot on []

 

[robwright]

Guys I have asked this question before but thought I wouild ask it again. What are yout thoughts about the max boost you should run with standard head gasket and injectors? I have been previously advised 15 PSI with standard injectors but would really love to have a go at higher than this.

 

[pauly]

How old are the head gasket and injectors ?.