Slight Power Dip just before redline

There are variable length intake runners that increase power in the 5500+ rpm range. A malfunction in this system might cause the symptoms you describe. MY 575M certainly does not have that problem and it will bounce the engine off the rev limiter if you are not quick with the shifts in lower gears.

If it is supposedly common in 550s, that is strange, because I have never heard of it in this forum.

Brian or any of you pros: how about an educated opinion on cause and potential fix?

Taz
Terry Phillips

 

Right, what Terry said. Also check that your muffler valves are operational.

 

Barry- Good thought on the pneumatic exhaust valves. On the Maranellos and SAs, the valves are fail close. On later cars like the 599, they are fail open. We know the rpm for opening on the 575M is 2720 rpm and 64% throttle, but on the 550, the workshop manual say so to make sure the valves are open at WOT and 5000 rpm.

Those valves would certainly have a choking effect on high rpm power, especially if one of the vacuum tubes has a leak and it takes more revs to open the valves.

Taz
Terry Phillips

 

The was a guy on here named Stephens. He did a lot of well thought out and recorded tuning on his 550. He had his own dyno and carefully documented changes. He commented on that. You should look up his old posts and read the entire series.

 

All the above suggestions are very valid and should be looked into. We have also seen a large number of 456, 550 and just recently 575 with the ruber and plastic fuel cups that the fuel pump sit in come apart and plug the pump inlet. this would first begin to show up at high RPM high load. Just a suggestion and further diagnosis is adviseable including the easy items listed above. Good luck

 

I second the fuel pump scenario, it certainly was the case with my car

Tarek

 

Here are the threads started by Stephen, who owned two 550s.

http://www.ferrarichat.com/forum/showthread.php?t=47640&highlight=550+tuning

http://www.ferrarichat.com/forum/showthread.php?t=20023&highlight=550+tuning

Way before my time.

Taz
Terry Phillips

 

Its not a fuel pump problem. Power would not come back.


As I recall Stephens found it a common problem on the dyno. If I recall he traced it to the operation of the valve joining the plenum chambers. But it was a few years since I read all that.

 

Opening your exhaust valves will not cause that problem. They would have been fully open in the 3000-4000 rpm range at WOT in any case.

Reading Stephen's articles, he thought the solenoid valve Brian mentioned was moving the intake runners too late (at too high an rpm), and causing a rich condition in the rev range you noted. The early Motronic ECU was having a hard time leaning the mixture quickly enough, resulting in the bog or slump you noted. The Motronic ECU eventually caught up, leaned the mixture, and the result was a strong surge to redline.

The variable length intake runners are one of the reasons the Maranellos could produce so much torque and power low in the rev range, like a Tesstarossa, and still be a screamer producing big horsepower at the 7500 rpm redline.

The next evolution of the V12, the Enzo, used VVT in addition to the variable length intake runners, and power made another big jump to 650 hp. Add direct injection and commensurate higher compression and higher rev limits to the next generation V12 and we should be in the 700+ hp range for the normally aspirated V12s. The V8s are already at 560 hp in the direct injected 458.

Taz
Terry Phillips

 

When I read Stephens articles it made sense on the surface but I own a 550. My problem is spinning tires and the redline from 4000-7500 comes in the blink of an eye. Since I have a streetcar I just can't break the law enough to notice anything but smooth operation as I go past 5000rpm to redline. Maybe I could feel an issue on a track with sticky tires. Any other owners felt a blip at the seat of the pants from this plenum actuator thing?

 

Right, and this applies to aftermarket mufflers without valves also.

Perhaps doppioexpresso frequently disconnects his battery with the cut off switch and notices this slight dip before the ECU has a chance to relearn what it forgot (see picture below )

Right Terry, the variable length intake runners coupled with the muffler valves. This is why I've kept my stock muffler valves functional and haven't considered an aftermarket system without valves. Now if your Novitec system only had valves, Terry.......

Over the past two and a half years, I've saved both Stephen and Brian's threads detailing their work and findings on this subject. There's a wealth of information there!

Barry
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Marc- Moving between generations of Motronic ECUs is very difficult. There were only two Motronic ECUs for non-US cars, one for cars with, and one for cars without, catalysts, as near as I can tell. The Motronic ECU was doing two things to cause the problem: it provided the signal to vary the intake runner length and it should have leaned the mixture more quickly.

http://www.ricambiamerica.com/parts_catalogs.php?M=FE&P=&V=diag&I=312

I do not know if any of the aftermarket ECU upgrade companies can help or not.

Taz
Terry Phillips

 

Sorry, I meant fuel filter

Tarek

 

What about starting with the connections to the bypass valve? Is that valve working?

 

I would have to agree with others that the dip in power you are noticing comes from the change over from the variable length intake plenum. Its a vacuum operated pump that sits right behind the plenum. As for the car feeling stronger as you go up in gears, it could be from the gear ratios. A 550s gearing is at .94:1 in 5th gear making that its strongest gear. I'm impressed how sensitive you are to power changes.

 

No, he is talking about the solenoid valve that pneumatically controls intake runner length.

Taz
Terry Phillips

 

Right. As Terry said, that valve should be checked for proper function.

During the Pocono Raceway event this past Sunday and Monday, I brought this subject up to the tuning specialist at Classic Coach who was up at the track with us. He said he would like to dyno my car (Dynojet Research) as he replaced my center resonator with straight pipes a year and a half ago. He also suggested remapping my ECU to hasten the intake runner length change and to lean the fuel mixture more quickly.

I return from Pocono to see this discussion moving in the same direction. I'll send my tech Stephen's research posted elsewhere in this Forum and see what he has to say about it.

Barry
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I have not found anyone local who can tune a 5.2 motronic ferrari. If classic coach can tune ask him what he can do for someone living on the left coast. With vettes people do mild mail-order tunes and maybe another alternative is a second set of tuned ECU's which would be my preferrence and then a way I could look at the output data to let him look back at it to make sure it is OK. Racing vettes in SCCA , aggressive tunes have also caused cars to lean out and blow up.

 

reading the graph I don't understand what is happening. Also the WSM does not say that the ECU leans out the mixture. It could be that the act of allowing more air flow leans the mixture and increases the power thusly. If that is the case then you don't have to remap the ECU. You could mechanically or electronically trigger the valve at any RPM you want just like we trigger our nitrous oxide systems to come in at specific RPM's totally independant of the ecu.

 

FBB,

The graph shows the comparative length of the runners through the RPM range. From what I can gather, the runners are longest at ~2,200 RPM when the valve is 30% open.

As far as remapping the ECU, I'll see him again on Friday. I need a new oil pressure sender again. This one lasted about a year and a half. I'll ask him what he's been able to do with 550s in the past.

Barry

 

Perhaps that's what he meant. I'll question him more on Friday.