Sevenman's TVR (was SAAB) Blog

January 29, 2006

Where has my boost gone?

Filed under: Saab — Administrator @ 1:48 pm

The car has stopped producing huge amounts of boost. It boosts smoothly to the broken yellow/red section of the gauge and that’s it.

All hoses have been checked and were fine. The car had no problems on Wednesday when I last drove it hard.

What could have gone wrong this time ?


January 26, 2006

Crankcase breather one-way valve

Filed under: Saab — Administrator @ 5:11 pm

I now know the function of the one-way valve that was replaced yesterday, so shall share the information here.

Nasty gasses build up in the crankcase. Instead of venting to the atmosphere these are fed into the inlet manifold where they can be burnt. I guess this is more environmentally friendly.

In a normally aspirated car this is fine since the manifold is always below atmospheric pressure. However in a turbocharged car the manifold can be at high pressure when the turbo is boosting before returning to low-pressure when the throttle is released.

The one-way valve lets gas flow from crankcase to manifold and not the other way. Should the valve fail completely then the crankcase could become pressurised. From reading posts on Saabscene it looks like this pressurisation can force oil out of the filler pipe and generally do very bad things.

Was probably worth changing then :)

January 25, 2006

New DI Cassette

Filed under: Saab — Administrator @ 11:42 am

I have just returned from WMSS and my car sports a shiny new DI cassette.

Upon arrival a number of tests were performed on various bits of the vacuum system. The one-way walve on the crankcase breather hose was found to be faulty. Apparently this is bad although and they explained why but I am still not sure it makes sense.

Everything else was found to be ok, although they strongly advised me to change the dump valve for a more substantial version. Elkparts sell Forge valves so I may well be purchasing one soon.

The DI was then swapped for a new unit, new plugs fitted, and I took the car for a drive.

Found a nice bit of dual-carriageway and proceeded to evaluate the performance. The car felt good with possibly more boost higher up. Very hard to tell though as everything goes by so quickly.

On return to WMSS (after getting lost) I purchased the parts. They said I could return the DI cassette if I felt it made no difference.

Car felt good on the drive home. MPG at 70mph seemed improved over recent drives. Perhaps this is a placebo effect or maybe a new DI helps?

Still got my brakes to sort out – have had a recommendation for Black Diamond disks so shall check those out.

January 16, 2006

More Dyno Analysis

Filed under: Saab — Administrator @ 12:40 pm

Having spoken to one of the guys who tested my car I have more information to add. It seems that analysing these plots is more complex than I had thought.

1) The Dyno

The performance figures were definitely measured at the wheels – they didn’t do a deceleration run.

Their rolling road is one of the newest and most sophisticated in the UK.

The single-roller design is more efficient that dual rollers. This reduces the amount of transmission loss.

The transmission loss is exponential with revs. At low revs the losses are small, so at 3000rpm there is only a few lbft difference between wheel and flywheel torque. This would agree with my peak torque being close to that achieved by Scaero (see Saabscene thread).

HLM have one of the largest cooling fans used in UK dynos. Combined with it being a cold day this should allow a high-power run.

2) Comparison

Comparison between results from different dynos on different days is difficult.

Power isn’t solely limited to boost – Air to Fuel ratio is an important factor and needs to be known for both.

The most powerful point for the engine isn’t necessarily when boost is higher, but when the turbo is working at its most efficient speeds.

Due to the cold ambient air temp and very big fan, the intake air temp may have been dense and cold, therefore allowing more advanced timing and high power with less boost.

Perhaps if the intake was warmer, greater boost would be needed for the power? I am not sure what my engine would do in the situation.

3) Where to go from here

One of the dyno testers felt they detected a misfire, however the other tester didn’t and I haven’t noticed it. The DI casette is 8 years and 110k miles old. The car is currently booked in with WMSS next week to take it for a test drive. I am now not sure if I should still go ahead with this or wait until March when I intend to have a service and other work done.

January 13, 2006

Fixing problem

Filed under: Saab — Administrator @ 10:00 am

The car is now booked in at WMSS towards the end of January. Hopefully they will be able to diagnose the problem and fix it.

I have recieved a suggestion of removing the DI casette, stretching the springs and giving it a clean before reassembling with some silicon grease around the boots and springs. Might give this a go at the weekend if I find some grease and spare time.

January 11, 2006

Dyno analysis

Filed under: Saab — Administrator @ 2:52 pm

Following debate on Saabscene, it seems likely that my car isn’t producing as much power as I thought it was.

The thread here contains more info. It looks like the dyno figures may well have been adjusted to flywheel rather than being wheel measurements.

This matches my peak torque at 1.4 bar boost to similar flywheel figures from equally modified Saabs, and a peak power of 243bhp would be about right with the 0.75 bar boost at 6000rpm.

This of course leaves me with a problem – I am not getting full boost through the rev-range, leaving me with reduced power. Hopefully a solution will be found…

January 10, 2006

Rolling Road Results

Filed under: Saab — Administrator @ 9:30 am

The Aero had its first outing on a rolling road yesterday.

It performed well, although apparently there is a misfire at the top-end of the rev range. I don’t really want to splash out on a new DI cassette now so that may wait a few months. It was recommended that I try the BCR8 spark plugs instead of the 7 in warmer weather and for track use.

The person doing the testing hadn’t heard of Speedparts before, but seemed happy with the chip mapping – apparently the air to fuel ratio is where it should be and fairly steady.

Power at the wheels – 243bhp seems about right, I guess this would be 285 ish at flywheel. Torque is a high 427nm (315lbft) – If this scales in the same manner as the bhp that would make 360lbft. Seems possible considering the 1.41 bar of boost.

Dyno Plot - Wheel measurements

January 3, 2006

Rolling Road

Filed under: Saab — Administrator @ 10:03 am

The car is now booked for a rolling road session next week.

This should let me know the power, torque, boost and air-fuel ratio throughout the rev-range.

This will all be done at Chip Tuning, in Bromsgrove,

Results will be posted next week.

January 2, 2006

Headlamp problems

Filed under: Saab — Administrator @ 10:07 am

Whilst driving home last night I found my headlamps didn’t work properly.

The driving lights (which are always on) were fine, and these are close to dipped-beam brightness so it is possible to drive on them.

The next switch setting is sidelights, and this worked fine.

The final setting is dipped-beam and this didn’t work – neither did full-beam or flashing full-beam.

There were no errors on the dashboard pictogram so I was fairly sure it wasn’t simultaneous bulb failure.

Following a quick search on Saabscene I found many posts on faulty solder joints in headlamp relays.

These are easily located in the right of the engine compartment under a clear cover.

I removed the orange and red relays, then pried the covers off with a selection of small screwdrivers.

The solder joints looked ok and I tested them all with a multimeter – no problems there.

I re-inserted the relays, tested the lights, and all looks fine.

With the problem now gone, no further testing took place – however I am worried it may return at some incovenient time.

The other potential cause could the the headlight switch, but I shall have to wait and see what happens.

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