MatraSport Forum

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.

(http://i18.photobucket.com/albums/b120/macaroni12/Image009-2.jpg)


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

Any ideas?

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...

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.

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


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.

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.

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

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

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

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

Cheers Roy.

Any ideas on the low power and the power curve?

Antony

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.

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.

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.

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! ;)

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.

And what ever you do DON'T put too much oil in the cylinder!!

What a job... the sun was BOILING me and these plug holes are so painfully deep and inaccessible. Just getting the stud on the meter into the hole and screwed in was nearly impossible!

So after three cylinders with the same value (and no indications of any problems) I quit, but good news for you, Antony, is that I got a consistent reading of 160 psi on those three. Your 150 and my 160 could just be the difference between our instruments (mine is *not* a quality instrument!)

I'll go make lunch now and celebrate that I've got a good engine. I hope I won't have any nightmares tonight about the fourth cylinder having a "gremlin" inside or anything! ;D

- Anders

Well done and thanks for the effort. I found that after the first plug was done, and I had my eye in, the rest were easy.

150/160 seems fairly consistent.

Unless your 4th one is below 100...

You must have very long eyes! ;D


Shhhhhhh :-X

Hello after long time  ;)

I don't know the ratio between Psi and Atm, but know that good engine have to be more than 12 Atm - mine is at 14 Atm  ;) bad compression (shabby engine) is less than 9 Atm. So if you know the ratio Psi vs. Atm you have better imagine what is good and what isn't.

And my first measurement was 6 Atm at 1st, 5 Atm at 2nd, 5 Atm at 3rd and 6 Atm at 4th - I was close to infarct  ;D yes the reason was that I forgot to give full throttle  ;D

Hi Michal, good to hear from you, what has been keeping you away? :)

Try this link:

http://www.google.com/search?q=14+atm+to+psi (http://www.google.com/search?q=14+atm+to+psi)

(When will Google get a coffee machine feature?)

I don't know if you have all of the values, but if you do you can calculate what the compession should be.........
http://www.csgnetwork.com/compcalc.html (http://www.csgnetwork.com/compcalc.html)

Lot of troubles, work, etc. So something is new (Simca 8 1200) something has been sold (Honda CBR600F3), wife has gone, new girlfriend came, me and my friends we are preparing the trip to Chernobyl (You know this damaged nuclear plant in Ukraine?)... just "normal" life ;)

Well it means that my engine has 205 Psi (Mr.Dobes told me, that it's nearly new :) ) and 160 Psi is 10,9 Atm what isn't bad too. The compression makes the power of the car...

So my 150psi = 10.2atm, so that isn't too bad, but I suspect if it was nearer the 190 psi it should be I would find some of missing horses.

I hope your new girlfriend is as pretty as your wife.
I like the way you mentioned the Simca and bike before your relationships - good man!

Hi to all,

Just to sneak a little,

On my 2.2ti with 8:1 piston comp. around 150psi on each
Chrysler said that lower limit is 100psi, under that no burning

This is not as easy as it looks like, you know - I loved her and if you asked me if I would prefer her or my cars, I would say her, but she made it different way - she did found another man (of course, that was what I couldn't accept) and as the reason she told me, that she was unhappy. If she will be the woman for life she would speak about it with me and would try to find a way for both of us, but she didn't make it fair. And I don't want to risk that one day, when I'll be old and ill, she will left me because will be unhappy...  :-\
My "new girlfriend" has much different character and I feel that she is much better one for me.
Btw: my wife also has a new relationship - older man who doesn't have any hobbies, but company and lot of money...  :(

This is Maria (she likes older cars as I do ;) ):
(http://sweb.cz/Belmondo27/Maru%C5%A1ka.JPG)
(http://sweb.cz/Belmondo27/marus.JPG)

Nice car!  ;D

Wheres the car, i dont see a car!!!