Tuesday, August 08, 2006

More mapping

Car has been working great, bar at cruise from 3000-4000rpm. This area is quite important to our Ring trip! Althought I guess all driving will done at 4500-5000 in 5th.

This area directly relates to an area where the TH7 drops torque (see above)...I have been fighting this area for a while on the jets, but its not the jets, its the bloody ignition. The cam needs and likes a shed of advance from 1000-3000, but then it can't take the advance through to 4000 and needs retarding from 3000-4000.

I have created a funny map that has really cleaned up this area, its still a bit flat but the engine is smoother with it now. Since I lightned the flywheel this problem has come into play...It relies on torque and power in higher gears but the power is only weak at these rpm and torque actually falls from 3000-4000!

Much improved.


VitesseEFi said...

Hi Dave,

Would have thought that the torque dip at 4000 for TH7 indicates poor filling/trapping at that point giving lower charge density and flame speed. This being the case (?) more advance at 4000 would help I would have thought - even if you have to back it off again above that.

Don't know where that set of curves comes from but they will only be valid for particular inlet and exhaust configs and presumably, at full throttle. Are they representative of your exhaust and inlet setups?

Passenger plus laptop would be highly useful for tweaking!


David Powell said...

Nick its a well known torque glitch on this cam, Andy V racer fitted 3D ignition to attempt to cure this area I think.

It can't take more advance as it runs like **** with more advance from 3000-4000, hense I retarded it and its a BIG improvement. The car drives in a superior fashion to the distributor in all RPM's.

I have done 10hrs of road testing this week and tried over 40map variations on the motorway and A-roads, this map is the one that appears to give me the best performance.

The map works well at wide open and also gives me good cruise and drives like a kitten in town, progresses well has strong power at all TPS and RPM, within the constrains of 33mm choked carbs and race-cam, lightened flywheel etc, works well slowly behind traffic, it works well in my opinion. It is the basis of over 2months road testing. Life became much harder after fitting a pretty light flywheel.

David Powell said...

P.S yes a rolling road session would be useful.

Actually this MAP is a what I'd class as a safe one, I made this to cruise well at high rpm and get me safely to Nurburgring, hense its quite linear in some ranges as the engine will be doing 1600miles at high speed. The dissy is linear in the that respect and did a good job.

I had some ping and roughness in this area 3000-4000 carrying on with my lower advance in a straight up fashion..., ONLY at cruise KPA - MP when the throttle was near closed and as a result I tested 5 more retarded maps in this area and ended up with an advance dip in the 30-KPA-40KPA-50KPA areas which smoothed things right out.

I understand the requirement for more advance in poor filling situations... My plates are virtually closed at these cruising speeds (3000-4500 in 5th gear)

The problem goes away completely at WOT throttle or 50% open in these ranges -it just runs like a sack at cruise in this area when you increase advance at low TP areas of the map...So my map is backwards to what you would expect in this area? Its backwards to what I expect too, but it works.

I understand that poor filling needs more advance etc as this is used in the low-end areas, if you retard the 30-40-50KPA areas in the 1000-2500area the engine runs poorly compared to the higher figures.

You would expect to have to run more advance before the cam comes on...yes...but in the 3000-4000 area where it looses torque it won't take the advance without the performance going very much downward.

This is only at a light throttle load...Its quite baffling as the mixture is fine in this area, if you scale the map more like the stock distributor, ie the same'ish numbers from 100WOT-30KPAclosed the engine is happy, like it was before on a dissy, as soon as you start ramping in low TP advance it goes bad!