| Home  Blogs Help Search Login Register  
« previous next »
Pages: 1 2 [3] Print
Author Topic: What is EWP?  (Read 16342 times)
Anders Dinsen
Administrator
YaBB God
*****
Posts: 2823



WWW
« Reply #30 on: May 11, 2007, 03:02:38 pm »

Hi Roy

Your your valuable input on this subject is very much appreciated!

Regarding ignition, I have been referring to Des Hammils book on the subject of tuning distributor ignition systems. He points out that it is important to get the static idle advance correct AS WELL as the total advance. I understand that total advance is a dangerous thing to play with, but with care it should be possible to go beoynd the factory numbers. As Hammil points out, the car manufacturer had to ensure that the car would be able to run on many different kinds of conditions (including fuel octane numbers) - we can be more careful. I think you agree on this, Roy?

Macaroni had his dizzy set up for something around 35 degrees total advance with a professional tuner, which is a safe number according to Des Hammils suggestions for hemispherical combustion chambers. If we look at the ignition maps at http://www.technikhomepage.de/kfz/elektrik/verteiler.html (which I have verified to be according to the workshop manual, whether they are according to actualy distributors I don't know of course), we will find that the total centrifugal advance on the 2.2 dizzy is 13 degrees (cam), corresponding to 26 degrees on the crank.

Thus with an unmodified dizzy, we can go up to 14 degrees static ignition and still be within the 35 degrees total advance. Whether that is safe to do with a given engine on a given fuel type will have to be carefully verified of course - Hammil discusses fast road cars as well as racers, and while pinking and even a bit of detonation may be okay on the latter (where people tend to rebuild their engines routinely), I think most Murena owners will be playing the safe game. I know, I will Cheesy

Hammil gives instructions for limiting the total advance of the distributor, though. It is a relatively simple mechanical modification. The difficult part is to get the tuning right - and you will always be "on your own" when you start modifying things. It's not a thing you "just" do.

Hammil claims that a 290-300 degree cam like the Holbay should run about 12-16 degrees static advance, depending on the actual engine. The 2.2 Murena engine may require less? Increasing the idle above 1000 rpm will however increase the effecitve idle advance (by simple centrifugal advance), so it may not be necessary to advance it at all on a given setup, but that's another story.

Thanks for the tip of lubricating the distributor - that was a service item I would have missed! It is extremely valuable to have this kind of advice passed on from an experienced person like you.

As always, your input is extremely valued, Roy.

- Anders Cool

PS: Your performance numbers on the Holbay cam with the single carburettor setup should impress a few people. With that cam, I beleive that the exhaust manifold is much more important to its performance than the inlet.
Logged

'82 Murena 2.2 prep 142
'01 Grand Espace 24v
'08 Smart Fortwo 0,8 cdi
roy4matra
YaBB God
*****
Posts: 873



« Reply #31 on: May 13, 2007, 11:58:08 am »

Regarding ignition, I have been referring to Des Hammils book on the subject of tuning distributor ignition systems. He points out that it is important to get the static idle advance correct AS WELL as the total advance.

Yes but unless you start modifying the distributor, one has a direct bearing on the other.  Most people are not going to start modifying distributors and owing to liability legislation I would only recommend the manufacturers specs.  If you change the static timing position you change the overall advance too.  For most people the static advance is 10 degrees BTDC and the distributor will add up to another 24 degrees with throttle and higher revs. giving 34 degrees total advance, which is close enough to that 35 degrees limit.

The other problem is getting accurate figures.  The only figures I have seen for the 2.2 were actually for the Tagora version of the 2.2 (code 9N2) not the Murena 2.2 (code X5N2) which has a different distributor with 'altered timing characteristics' according to the publicity.  I have written to Bosch stating the two different distributor numbers and asking if they can supply details of the actual differences but so far have not received any reply.

Without these details, all you can do is try one on a rolling road, and check it's setup and even tune it ideally for that specific car, but as mass produced cars all tend to be slightly different it is not safe to assume what you do to one is good for all.  In fact setting up a car on a rolling road is usually the best way to get the ideal for any particular car and can often benefit all round.  However, as you say, fuel also varies and you have to allow a little for that with a road car.

This is possibly why some peolpe claim they can run a 2.2 Murena on normal low-leaded (95 octane) when I have found mine will simply not run on it.  It must have 98 octane to run properly.  A little pre-ignition (pinking) may be acceptable occasionally but detonation - never!  Since most cannot distinquish between the two it is best to have neither.


Quote
Thanks for the tip of lubricating the distributor - that was a service item I would have missed!

I had a kit car in last week with a Triumph Vitesse (6 cyl. 2 litre) engine in it, and the distributor was rusty and seized through lack of oil, so the advance could not work, so it reminded me that people have forgotten about this important item!


Quote
PS: Your performance numbers on the Holbay cam with the single carburettor setup should impress a few people. With that cam, I beleive that the exhaust manifold is much more important to its performance than the inlet.

That was a good example of setting up on a rolling road to get the best for that particular engine but it was also a few years ago when we had proper (leaded) fuel!  I don't know what it is now.

Actually both manifolds are important as shown by another club member who did not have the cooling system plumbed in to the downdraught inlet manifold, and the car was not pleasant to drive during the warming up phase; but the tuned exhaust certainly is more important with a modified cam.
Logged

Pages: 1 2 [3] Print 
« previous next »
Jump to: