My rolling road session...

[macaroni]

I went to Racepower motorsport in Kent to have my carbs set up properly and see what power the engine was making.
Their place is a bit ramshackle, but they know their stuff and have an old boy working there who is good with carbs.

All the levels were checked by me beforehand, as was the compression pressures. This gave me some concern as the 4 cylinders read as follows, from the gearbox end: 140, 130, 135, 150. Whilst consistent, they seem strangely low. I checked my 205gti engine at the same time and had 4 readings in the 190s.

Anyway, the initial power reading was 101bhp at the flywheel. I know all the arguments about measured wheel/calculated fly figures, but these are what I had to work with. It was running quite weak at the top end and the air correctors were changed from 210 to 200 to give a nice air/fuel ratio of 13 all the way from 2500rpm - 7000rpm. The carbs were also balanced, which helped the idle and the popping out of the exhaust.
The ignition timing was then checked and max advance was 32degrees BTDC, which seemed fine.

All this messing around gave a final power figure of 106bhp @ fly. This seems very low and the consensus seemed to be that the cam timing could be out and the compression needs looking at.

The car drives better, with less stuttering at low revs and a strong pull up to an indicated 5500rpm. WHat the RR session did highlight, was how far out the rev counter is. At a measured 3000 rpm, the gauge said 2500rpm, but at the revs in this picture (6740, giving a top speed of 137mph!!) the rev counter read less than 6000rpm!! So I shall be keeping to a rev limit of about 5000rpm on the clocks from now on.




So, a worthwhile session, but I'm a bit distraught as to where my misses horses have gone!

Any ideas?

[Anders Dinsen]

So, a worthwhile session, but I'm a bit distraught as to where my misses horses have gone

Sorry to hear that, Tony - But nice to hear that you found a good place to do the job. Yes, compression... wear, valves not sealing etc... Cam could be off, but why? What was the max torque produced by the engine?

Is that photo showing the power curve? If so, I would have expected the cam to top off later and have a flatter curve on the top as what you have looks more like the curve a standard cam would produce...

[macaroni]

Can't remember the torque figure, I'll find out later and post it.

I have no tangible evidence that a Holbay cam is being used, only a comment from SCU that it was part of their "pseudo-S" kit. It may well be a standard cam. Would that rev to almost 7000rpm?

I guess a mid-term plan of action would be to have the head off, skim it, 3 angle valve seats and send the cam off to Holbay for a regrind.

[Anders Dinsen]

Can't remember the torque figure, I'll find out later and post it.

I have no tangible evidence that a Holbay cam is being used, only a comment from SCU that it was part of their "pseudo-S" kit. It may well be a standard cam. Would that rev to almost 7000rpm?

I hear a few people complain they can't get their engines above 4000 rpm. If their rev counters are as much off as yours it may actually mean that they are talking 5000, but there's still a good way to 7k. So... probably not.

I've got some photos of my Holbay and a standard cam I got on eBay - it should be possible to tell one from the other:

Holbay lobes:
http://gallery.dinsen.net/v/biler/Murena/technical/engine/DSCF0005.JPG.html
http://gallery.dinsen.net/v/biler/Murena/technical/engine/DSCF0008.JPG.html

Std cam:
http://gallery.dinsen.net/v/biler/Murena/technical/engine/DSC_0325.JPG.html

I guess a mid-term plan of action would be to have the head off, skim it, 3 angle valve seats and send the cam off to Holbay for a regrind.

That sounds like an excellent plan. May I suggest you also have polishing done on the ports to remove the worst edges and improve the airflow.

[macaroni]

You may, but porting is very expensive. Donations gratefully received!

Thanks for the pics, I'll refer to them when I remove the cam cover.

[JV]

WHat the RR session did highlight, was how far out the rev counter is. At a measured 3000 rpm, the gauge said 2500rpm, but at the revs in this picture (6740, giving a top speed of 137mph!!) the rev counter read less than 6000rpm!! So I shall be keeping to a rev limit of about 5000rpm on the clocks from now on.

After reading your message I have looked at my rev counter this weekend.
At 120 km/h the gauge said exactly 3000 rpm. However, it should be 3550 according to the instruction booklet (33,79 km/h at 1000 rpm). So that is also almost 20% too low!

Any idea what could be the reason for that?

Jan

[Anders Dinsen]

Any idea what could be the reason for that?

I thinks it's tolerances in the rev counter electronics.

Converting a frequency to a current isn't a straight forward task, and the counters have probably either never been calibrated, or have gone out of calibration. I've never looked at the actual circuit used in this particular rev counter. If there's anyone out there with a spare which they are ready to take apart, I could help doing some reverse engineering to find a way to improve the readings.

- Anders

[Lennart Sorth]

20% sounds "about right" in the way that this is what I hear from almost all owners - I have never heard about an original one that was reading to high. Always 10-20% too low.

Maybe some of the lucky Murena (and Bagheera?) owners who had their cars from new can shed a bit of light on this ?

/Lennart

[roy4matra]

What the RR session did highlight, was how far out the rev counter is. At a measured 3000 rpm, the gauge said 2500rpm, but at the revs in this picture (6740, giving a top speed of 137mph!!) the rev counter read less than 6000rpm!! So I shall be keeping to a rev limit of about 5000rpm on the clocks from now on.

I have had my car from new and have said on many occasions that the rev. counters in ALL Murena read low.  In my experience they are all like this and have been from new, so were probably calibrated incorrectly in the beginning.  I have stated a figure of approx. 500 rpm low at 6000 rpm (which is not far from what you have found) and I did mention this to you Antony in one of our recent discussions.  I have also stated on numerous occasions that the Murena speedos are more accurate than many cars, so they have the reverse set up to most - accurate speed and inaccurate revs!

Roy

[macaroni]

Cheers Roy.

Any ideas on the low power and the power curve?

Antony

[macaroni]

Some results:

after resetting the valve clearances which were all too tight, about 0.004" (0.1mm), the compression has become much more consistent at 150 for all 4 cylinders. Still too low, but better than before.

Next job is to re-check the compression after squirting some oil into the cylinders to ascertain whether the rings or the valves are to blame for the low values.

The car did seem more lively during the subsequent test drive, but that is entirely subjective.

[Anders Dinsen]

The car did seem more lively during the subsequent test drive, but that is entirely subjective.

Absolutely not, Murena's react to TLC

I haven't heard about the trick with the oil before, how does it work?

I hope to get time to check compression over the weekend on mine too, then you will have some numbers to compare with.

[macaroni]

I haven't heard about the trick with the oil before, how does it work?

I hope to get time to check compression over the weekend on mine too, then you will have some numbers to compare with.

That would be very useful information, or it could be very depressing for me!!

After checking the compression figures once, squirt A LITTLE oil into the cylinders and take the readings again. If the compression goes up, then the rings are leaking compression. The oil effectively deals the rings better. If it doesn't change, there is no sealing to be done. Any low compression can then be attributed to the valves not sealing properly.

[Anders Dinsen]

Thanks for the tip - I have never done a compression test on any engine before, so I don't know what to expect Googling on the subject, 150 psi doesn't really sound too bad to me. And as it is consistent, chances are that it is good now? Let's see what I come up with. I could be in for a surprise too!

[macaroni]

Don't forget to give it full throttle whilst cranking, and to unplug your coil lead from the distributor cap so the engine doesn't start.