Boost enhancer?

[JM1962]

I recently bought a 1990 944 Turbo with the intention of restoring it to its former glory. It has a few desirable extras fitted which include a KW coilovers, full Haywood and Scott exhaust and the Promax level 2 kit which has a dual port wastegate and manual boost control, 3 bar FPR and a different dump valve.

Since purchase I have removed the head overhauled it and replaced all the belts. I did the head because the belts were 10 years old and there was a large oil leak from the cam tower so a good time to do the head as well. Now its all back together and running great. When it comes on boost it is absolutely immense. The problem is the lag is also immense. The question is with the Promax kit fitted would it still benefit from a boost enhancer to help reduce the lag a little. I am a turbo novice so any advice appreciated.

 

[944 man]

The Lindsey Racing boost enhancer works on a subsystem that you have removed to fit the manual boost controller, I believe.

 

[Lowtimer]

No, because the dual port wastegate that you have as part of your Promax Level 2 kit already does everything that the boost enhancer does, and more.
The boost enhancer is just a clever way of tricking the original wastegate into behaving better. The DP wastegate eliminates the need for it.

If you think the lag on your car is excessive then it is possible, even likely, that you have quite a lot of leaks here and there in the induction and boost control systems. It is vitally important for all these to be chased down and eliminated, otherwise you are in danger of running the engine lean and blowing it up. Checking this involves pressuring the system and eliminating every leak. The last one I had was around the idle stabilisation valve, which was a new one. The folk at Promax are expert at finding and eliminating 944T air leaks and can do so far more quickly and easily than I can, so I have them specifically test and check the whole system every time they see the car - usually once or twice a year. This is something that from experience I don't trust all Porsche specialists to get right - most of them spend most of their time working on normally aspirated cars. You need someone who lives and breathes turbos: there are a few of them around.

Another possibility is that the turbo bearings are not in the greatest condition, and it's not spooling up as easily as it should.

On my car there is solid boost by 2700 RPM, accelerating in third or fourth gear. So the actual boost threshold is very significantly reduced from where it was in the factory setup (which is why the mapping has to be so different).
However, the 26/8 turbocharger is inherently a big heavy lump of rotating metal and it does take a while wind up to full chat so these cars will always have a softer throttle response than you would get with a modern lightweight VG turbo.

A fairly small capacity highly turbocharged engine with a fixed geometry turbocharger is necessarily going to have a steep ramp of power onrush once it passes the boost threshold. Even if you eliminated all actual lag, you would still be experiencing a very steep set of torgue and power curves around the boost threshold.

The transition from full throttle off boost at 2500 rpm (around 65 bhp) to 3500 rpm on-boost (around 180 bhp) is always going to feel very different from the way a normally aspirated car picks up.

By the way, you are using good quality high octane fuel, I hope? The Level 2 map is set up for either 97 or 98 octane as a minimum (can't remember which) and if it is not run on the right fuel the car will be pulling back the timing during the boost transition which will not make it feel great. The cars can be run safely on ordinary petrol if you need to get to the next fuelling point and stay off boost, but they really need good fuel to be run properly.

 

[JM1962]

Thank you for the replies. I will do my best to check for leaks although having had everything in bits I fairly sure all the hoses and connections are good. It may be what I'm experiencing is a normal amount of lag, I just haven't driven any other cars (apart from more modern turbo diesels) to have the experience to know. I will check to see when the boost kicks in on full throttle.

 

[Lowtimer]

ORIGINAL: JM1962
I will do my best to check for leaks although having had everything in bits I fairly sure all the hoses and connections are good.

Honest opinion?

That isn't good enough for safe operation. It *must* be leaktight and the only way to know that is proper pressure testing.
The issue is not the boost lag, it is the near certainty that running lean will destroy your engine if it happens on boost. Your overboost protection is disabled and (unless you have one you haven't mentioned) you are running without an AFR warning system. You *have* to have it set up just right.

 

[944 man]

*KnockLink*

 

[924nutter]

I would have thought that an air leak in the high pressure side of the inlet tract, i.e. after the turbo and after the air mass has been metered would lead to rich mixture on boost, but you are right that running lean will not do the engine any good. Everything else being equal, of course, off boost the leak out can also be a leak in, and that is where lean running can ocur in my opinion. Here's how I see it; The ecu takes the air mass measuremet and opens the injectors according to the air mass that has been measured. (+rpm v load etc) If you then blow the HP air out through a leak or suck in extra air, the engine doesn't know. Either way not best practice. Also if you have an air leak how can you overboost?

 

[944 man]

Are you sure that the wastegate is closed: properly closed until such time as it needs to open? An infrared thermometer can be useful for detecting this, but itd be easier if someone has experience checking rather than working it al out for yourself.

How would a Turbo owner go about pressurising their plumbing? Im guessing (the easy part): high pressure air and a regulator set to about 18psi, but how do you intruduce the air and where?

 

[924nutter]

Disconnect the turbo outlet pipe and fit an adapter? Blank the inlet pipe off at the turbo and pressurise via the boost control line with a Tee adapter, which will keep the boost control line in the circuit? The hard part that I can't solve off the top of my head is to isolate the manifold from the head because two pairs of valves will be shut, (coming up on compression, and going down on the pwer stroke) and one inlet valve will be shut on the cylinder that is on its exhaust stroke, but then again an engine in good order with good leak down sealing will just pressurise the cylinder, so maybe it can be done that way. Then its good old soapy water around all the joints and look for bubbles. I don't know, just off the top of my head...

 

[CarreraRSR]

My 5p's worth is all is fine and your not used to old school turbo lag especially if your used to driving low down torquey modern diesels. If you really are in doubt take it to a recommended specialist and get it checked out. A leak down test and/or rolling road session will soon tell you if its set up right.

 

[simkin911]

I have owned a few Turbos. The best of the bunch had the Promax stage 2 kit. The lag was practically non-existent. It was a lovely drive and in regret parting with it (although I am happy with my 968). I loved the sound of the H&S exhaust too. Something isn't right with your kit / set-up.

Interestingly, an earlier turbo i owned had been modified at a cost of £2700 by RPM and churned out 310bhp. The lag and then subsequent power delivery was hugely entertaining but not great for day to day use. It was written off last year on a wet roundabout. Again, expensive kit but there was something not right with it.

Good luck tracking down the issue.

 

[edh]

Your setup really should be great fron 3k rpm ish. What sort of revs does boost really kick in?

The only time I found an issue with a well sorted turbo was first gear pulling onto roundabouts. Boost in higher gears is pretty instant.

 

[Eldavo]

Fwiw I fitted a vacuum manifold made by the guy on Rennlist and it has a spare test port that can be used to pressurise the system.

Well worth replacing the vacuum lines with decent silicon ones too.

 

[JM1962]

I will do some investigation on the road and see when the boost kicks in. It may be there is nothing wrong. The last turbo petrol engine I drove was a Sierra Cosworth over 20 years ago.

Just to add I bought the car with the Promax kit already fitted. I was unaware that fitting this kit does away with overboost protection which seems a little worrying.

 

[Lowtimer]

All 944s running higher than standard boost do away with the factory overboost protection, otherwise you wouldn't be able to run higher than standard boost.

 

[ChasR]

I guess if you were that worried about the overboost protection missing you could always get an electronic boost controller to pput your mind at ease.

 

[Lowtimer]

Someone asked earlier about how to pressure-test the plumbing. Here's a video showing how it can be done. I haven't done it myself but I think it's broadly the same method that the folk at Promax use when they inspect and maintain my car. If you don't have access to regulated compressed air then just use a tyre valve instead of the air connector used in the video, then it can be pumped up with an ordinary foot pump.

http://www.youtube.com/watch?v=AL3jbcrqY8g&feature=player_embedded

If it holds pressure, then obviously no leaks. If pressure seeps away then it's a case of listening for the hiss, and possibly brushing on soapy water to find bubbles just as you would with a leaking tyre.

 

[924nutter]

Well I'm sorry and all that but for me with some mechanical sympathy I would never put positive pressure on parts of the inlet tract designed to work under manifold depression, especially as somewhere on the crankcase vent there should be a flame trap, there certaily is on the 924T, and it just seems like bad practise to blow some of the accumulated gunge back into the crankcase. Even if there isn't you will blow the residue in the pipe back into the sump, and I ask if this is good practice? I don't know if the 944t has a flame trap so please help me expand my knowledge base, but anyone thinking that this method could be cross pollenated on to say a 924T or anything else with a flame trap in the vent line, would blow crap back into the sump. Not withstandiing that the pipes on the vacuum reservior only seem to be held in by the vacuum and you could blow the pipe off. If you suspect an air leak then it is just as easy to connect up an old domestic vacuum cleaner in a similar manner in the drepression side of the tract, and listen for leaks, perhaps simply by comparing the tone of the motor with the suction hose covered to the tone you get when you connect it into the fanimold. Any lowering of the tone indicates an ingress of air. No not my preferred method at all. With all due respct and apologies.

 

[JM1962]

ORIGINAL: Lowtimer

All 944s running higher than standard boost do away with the factory overboost protection, otherwise you wouldn't be able to run higher than standard boost.

True, but I would have thought the overboost protection could be set higher.

Anyway, it seems I may be worrying about nothing. At 70mph in 4th at around 3200rpm the stock boost gauge reads 0.4 bar, if I floor it the boost gauge responds immediately going over 1 bar eventually to the top of the scale at 2 bar the acceleration follows a little behind. My understanding is maximum boost is about 1.2 bar with the Promax kit so I should get an aftermarket gauge.

Thanks for the video link. I may give that a try when I get chance to fiddle again.

 

[Lowtimer]

The Promax Level 2 fuelling maps cope with up to 1.2 bar but what boost you actually get depends what the boost controller is set to (and, if it's a manual boost controller, that will vary slightly according to ambient atmospheric conditions). There are various switches to set one of a range of maps which are appropriate to different boost levels and other variables such as what injectors you have and what your fuel pressure is set to.

Do you know who installed and set up the equipment on your car? Ideally it was actually done at Promax, but some people install the kits as DIY. If it were mine I would call Promax, see if what they can tell me about the car and get them to check it over to make sure it's all still as it should be.

It is a good idea to get a decent boost gauge fitted. It is also a good idea to get a wideband AFR gauge fitted with any tuned 944 Turbo.

The way the factory overboost protection works means it can't operate on a car with the cycling valve out of service and its functions replaced by a manual or electronic boost controller operating a dual-port wastegate. On your car the cycling valve will have been removed. Basically if you want to work things the Porsche way you'll have to revert to a standard setup (which is easy enough, should you wish to do so, but you will get a lot more turbo lag and a lot less performance than with the equipment you have, providing it is all in good order and properly set up).