KLR overboost protection

[sawood12]

I am currently running a DPW with standard ECU DME and KLR chips. I've had a couple of occasions where under max boost conditions the boost had cut back. This has only happened in the past on a couple of times on those really cold crisp mornings and i've been told that it's due to the std KLR chip, which assumes a std Single Port Wastegate, under certain conditions can be tricked into thinking it's overboosting due to the speed at which the boost builds up with a DPW especially when the air is cold and so the KLR retards the ignition timing to reduce boost. As I said previously it has happened only when the temperatures are really low until today. It's not particularly cold today and it happened earlier while overtaking. For about 5 mins after the overboost protection would kick in at around 0.2 bar boost but after that everything seemed to reset itself and I could get max boost again (although I didn't want to push it too hard). I've had a look at all the usual vacuum lines and everything looks OK so I don't think i've got a leak anywhere so is this likely to be due to my std KLR chip? Will everyhing be solved once I get round to upgrading to the Promax Level 2 chip and 3 bar FPR?

I've fitted the Promax vacuum line replacement kit but am not 100% convinced about the security of the rubber hoses at each of the connections. Has anyone had any experiance of them popping off and where can I get those spring loaded hose clips (or small jubilee clips) to add a little more security?

 

[Diver944]

ORIGINAL: sawood12
Will everyhing be solved once I get round to upgrading to the Promax Level 2 chip and 3 bar FPR?

Yes - because aftermarket chips do not have overboost protection.

So make sure you have a good auxilliary boost gauge so that you can keep an eye on everything.

I've never had a problem with my puracil vacuum/boost hoses popping off and I've run at 15psi boost (1.05 bar) on track for the past two years

 

[sawood12]

Thanks Paul, it's always good to get a 2nd opinion on these things. I'm halfway through fitting an auxiliary boost gauge - I made a right hash of modifying the 968 cubby hole which i'm going to fit the gauge into so need to fabricate a cover to neaten everything up.

Once I fit the aftermarket chips how much boost can a standard engine take before you need to start thinking about upgrading fuel injectors and pumps and making mods to thinkgs like cylinder head gaskets?

Also how will my car behave at higher levels of boost with it having the smaller K26/6 turbo? Currently i've got my boost level set to 0.8 bar and my Weltmiester traces showed it peaking at 0.8 bar but immediately bleeding down to 0.6 bar at the red line. This says to me that as the wastegate would have cracked at 0.8 bar boost and the pressure bled immediately after the turbo is not capable of delivering anything over 0.8 bar boost. If the turo is capable of delivering a much higher peak boost it would bleed off much more quickly which would make my power delivery much more peaky.

The thing is i'm not necessarily after much more boost than I currenlty have i'm really after the other benefits of aftermarket chips such as reduced lag and better and smoother power delivery across the rev range but I believe that the Promax chips are designed to be run above 1 bar boost - i'm just wondering about the effect on the cars power delivery due to the higher boost levels with my asthmatic K26/6 turbo.

 

[John Sims]

As I understand, it the K26/6 can't flow enough air to maintain boost at higher revs also, because of the relatively small size, it has to compress the air more than a larger turbo, increasing the heat of the charge and hence its efficiency.

With the correct chips you could run as high as 1.2 bar boost on a 26/6 but boost will start deteriorate almost immediately because of the above.

If you are running higher than standard boost the boost protection will cut in on cold days as generally the air is much denser. It probably has little to do with the speed the boost rises and more likely that you are actually boosting above the over boost threshold.

 

[Fen]

The KLR doesn't retard due to boost, it retards due to knock. On a cold day the air is denser therefore the mixture gets leaner and you get knock and then the KLR steps in. If it's doing it more today than normal then I suggest you have poorer fuel in the tank just now than you normally do. I used to run a boost enhancer set to the point where it was OK on Optimax, but would trip the KLR on 95RON quite readily. As John has said you can probably go to about 1.2 bar at an absolute maximum with standard injectors. The K26/6 will lose pressure at high revs simply because it can't maintain the pressure and flow rate it needs to (again as John said), so you will not have anything like 1.2 bar where the injectors have to work the hardest meaning you can push them with more boost lower down the rev range. It is very important that you run only the boost the chips are designed for though as they will not supply enough fuel for increased pressure. You will more than likely lose a head gasket very soon after you increase the boost even if the fuelling is right as yours will be very brittle by now - unless it has already been replaced.

 

[sawood12]

Just what I was worried about - My head gasket doesn't appear to have been replaced according to the cars maintenance history. Having said that i've been thinking about doing a pre-emptive strike on the cylinder head gasket because I would rather control when it is replaced rather than be stranded on the road-side somewhere but it seems to be a pretty pricy job. My specialist disagrees as he is from the school of "if it aint broke don't fix it" but being a Manufacturing Engineer by trade I'm very much a believer in preventative maintenance - I know from experiance it's a philosophy that is cheaper and alot less hassle in the long run.

And while the head is off I suppose it's not a big job to replace the turbo if I can get one off a 250 HP car? I know you don't need to remove the head to replace but I guess all the gubbins that needs to be removed in order to replace will be removed in order to replace the gasket. Oh bloody hell! I'm doing it again! All of a sudden and in the space of two paragraphs i've already spent the best part of £1,500!! Well I do have a budget of £9k to spend on a 2nd car so it looks like it'll be an £7.5k car and the rest on the 944. It's just as Yoda said: "Once you go down the path of the dark side forever will it dominate your destiny"!!

 

[Fen]

I've got a 250 turbo's K26/8 with 3,500 miles on it in the garage, along with an Autothority MAF and a set of ECU's with a Bob Watson remap to run it all at 1 bar (300+bhp) []

 

[Diver944]

ORIGINAL: sawood12

Also how will my car behave at higher levels of boost with it having the smaller K26/6 turbo?

I've been in Phil Rowleys K26/6 car that hit over 25psi boost (1.8 bar) [] whilst we were adjusting a newly setup wastegate and from memory the boost started dropping straight away. The 26/6 simply can't flow a lot of air to maintain a high boost as the revs rise.

The graph below shows the boost level for Phil Kents car at last years Dyno Day. His has a 26/6 but uses the standard wastegate with a boost enhancer. Max boost was just over 0.9 bar at 3600rpm but has dropped to 0.6 bar by the redline.

I don't know what the max boost is that a standard engine and head gasket can hold longterm (providing the AFR is correct) but most 'hearsay' on forums seem to indicate around the 1.2 bar (21psi) mark. The design of the cylinders is quite 'flexible' at the top by the head gasket and high boost can causa quite a bit of movement which will eventually degrade the head gasket or worse.

I'll ask Jon Mitchell about the standard block when I next speak to him. His contacts at Perfect Bore have recently done a lot of analysis on the 944 block, including disecting one to map all the internals. They do claim that my rebuilt block with braced liners will physically be able to withstand 2 bar of boost []

 

[sawood12]

I'm sure i've been told that a std engine and std head gasket is good for 1.2 bar boost but I don't intend to take it anywhere near that level. I was planning on taking it to just over 1 bar as i'm sure Andrew told me the Promax chips need to run above 1 bar boost.

It's interesting to note that 0.1 bar of boost on a mainly standard engine is worth around 23 ish bhp as my car is running at 0.8 bar boost and gets 237.5bhp while Phil Kents car is getting 259.2bhp at 0.9 bar.

Fen - stop putting temptation in my way!!