The 355 'spider' idle stumbling problem is solved!!!!

Oz, I think your work and efforts are definitely in the right direction. It is great to have a 355 owner like you who is making worthwhile contributions, which show potential for increasing the performance level above OEM.

I look forward to your future posts concerning this aspect of redesign.

We have given alot of consideration of using the front trunk compartment for something other than Schedoni luggage...lol

 

So when are you going to start selling the shields for those of us who do not like to make our own things. I'll buy a set.

Great work

 

No, I did not check both sides.

I am fairly sure that the 348 uses a different pattern of turning on the fans than does the 355, however...so the right side for 348's may be less of an issue (then again, what the heck, maybe it would be spot on clever to use shrouds on both sides).

For instance, the 355 has a coolant temp sensor on the left side radiator, whereas the 348 has it on the upper right side.

Don't both models have a temp sensor on the lower right side oil radiator, though?

 

Yes, that flapping would nicely complement broken exhaust valves

Seriously that is a great idea, somehow hinge Goth's shroud on the top. Or just make it out of something kinda flimsy like rubber (again just attached at the top). Not sure on durability though...

 

Yeah, rubber cut in Goth's design pattern, but with slits cut out in rectangle shapes (except for the top side of each rectangle in order to act as a hinge). Leather? Neoprene? Alcantara?
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For the first time in a long time a thread that is heading in the right direction!
Goth has a terrific idea and changes to his original design are not being taken as an insult but mearly ideas to take his design a step further. Doesnt get better than this!

Goth,

Tape 3" yellow yarn tuffts to the side of the drivers door every few inches and have someone drive along side you on the hywy. and take a photo. I am worried that the ram effect will be greatly reduced. If it is, the air will also be stalling out for the engine intake.
The rad. capacity of the 355 is plenty good that I do not think you will see it on the gauge when driving in town.

Dave

 

Actually it doesn't work to ram fill a closed air box unless there is a restricted flow through outlet. Study the mid 80's to 90's Formula Atlantic cold air intake. In the Pro Spec race series we had a dickens of a time finding a way to produce ram effect and it took some pretty creative "venting" of a closed air box to gain a positive pressure in that area. It builds a pressure front as you propose but the air intake is a very limited "outlet" (1/2 of the engine displacement as it is being fed by both sides) compared to the available ram air. Build even the slightest pressure front and the laminar flow hugging the door skin is destroyed and any ram effect that there might have been is gone. Many good articles are on the Net regarding restrictions when working with NACA duct applications.

I could be completely wrong with this application. I spent so much time trying to get cold air intake boxes to work in the past that I think its worth checking with and without the mod to verify. It would be a shame to loose any positive pressure to the engine intake.

Dave

 

I am looking for just about anything to do to get out of posting on that M#@*Fing 355 valve guide blackhole thread...lol.....so lets get it on with some sub-sonic air intake stuff.

I really need to watch my comments about the things which, IMO, suck on the 355....things are really not that bad for a street car. Having only worked on race cars, my views(when it comes to the 355) are out of touch with what's acceptable and within the boundries for normal road going vehicles.

Having said that, it is my opinion the 355 air intake as a complete system(from ouside air inlet to head intake port) can be improved such that some fairly decent hp/torque gains can be realized.....some without modification to the ems proper, and others which would require the complete removal of the OEM unit. Later we can discuss how to design/modify the intake(using velocity, density, and pressure differentials) for the best performance throughtout the whole rpm range.

Oz, I am a little puzzled about the air reversion at the LH radiator. I know you indicated this was in fact what was happening when vehicle is stopped, but is this the case at say 3-5mph?

As you know the only way air moves thru this set-up is due to the pressure differential across the radiator.....the fan is supposed to produce a sufficient low pressure area not only at its' diameter, but that low pressure area should extend further into the wheel well area. If that were the case those areas of the radiator which are not within the fans radius would still be exposed to the low pressure area thereby eliminating the reversion.
When the vehicle is stopped there is no high pressure wave at the frontal area of the radiator, and as the fan attempts to create a low pressure area the volume of air taken in exceeds the evacuation capacity of the wheel well.
At speed this condition may go away....do you have a DMDPG? They are fairly cheap and you will be able to measure the pressures...static and dynamic.

If you removed your block-off plates and removed you wheel well liner are you still getting that reversion?

 

Oz, thanks for the detailed reply. I do not doubt you for one second concerning the reversion. I know it took some real thinking to translate your observations into a cure. I may be asking a stupid question, but why wouldn't the RH side(same fan,radiator,intake air inlet-5.2Motronic) also not effect the sensors?

Your observations have also led to some very interesting flow characteristics which go way beyond the idling problem. I am wondering how much of the naca duct properties are present in the door scoop design, pressure differentials in wheel housing/engine bay, and what role the wheel arch guards/undertray are playing in air evacuation at those areas. I know the CH grille may aid in cooling, but it also appears to reduce the high pressure build up. The design(cosmetic small holes) of this grille severly limits its ability, but is still a great improvement over the non-vented type.....no rear grille at all works the best, but that is not cosmetically acceptable.

In our quest to build a reliable super hp engine we must also look at the cooling system. Having done primarly nothing but air cooled engines, I will be the first to admit I am struggling with this type coolant system.

I do know a few things but am needing alot of help. IMO, 175-185 degrees seems to be a very conservative operating temp. The ONLY things I want to keep as cool as possible are the fuel and intake air......the engine proper I like it HOT. To achieve a hot engine without hotspots is difficult.....I want, coolant flow from heads down to cylinder, even heat distribution to all cylinders, and coolant flow as consistant as possible throughout the rpm range. In approaching all of this I am forced to look at the coolant pump, coolant passages, and even the coolant itself. The hotter I can safely run the engine the less cooling is needed(I know this sounds a little strange).
Depending on final operating temps it may be possible to run a single highly efficient copper/brass(with silver solder) radiator. If this is possible then the air flow at the door scoop becomes even more critical.

This is all developement work and nothing so far is set in stone. I am very open to any and all suggestions/comments.

Again Oz, great work.......I really appreciate it!!!!!

BTW, the DMDPG is Magnehelic Differential Pressure Guage...you can use a water manometer, but it is awkward and clumsey.

 

Got it Oz.....in my haste I flew right by the word "abrupt", must be a low pressure area in my brain....lol

 

I'm goinjg to go out and get some flexible BLACK rubber today and make a "Goth shield" for my LH radiator. There are no less than 5 F355s here in Seattle all with check engine light problems and all with Tubi exhausts and some with Hyperflows. My car was the guinnea pig to try to stabilize the engine idle and stabilize the decel engine smoothness. What seems to work is installing the stock muffler, the engine is much smoother but still stumbles at idle occaisionally but I hadn't correlated that with the effect discussed herein. According to the current theory here in Seattle, is that the Over area Tubi and Hyperflows create misses on decel and idle that dump raw fuel into the CATS and burn them up, thus the Check Engine Lights. I'm now wondering how much of this CAT deterioration is related to these fan induced stumbles. By the way we are going to run an experiment of installing choke washers behind the CATs with the Tubi muffler installed to reproduce the factory aera match. I only mention this incase there are other people out there experiencing CAT deterioration with the Tubi Mufflers in addition to these idle stumbles.

 

By the way my LH fan is blowing fuses - What rating and value of Capacitor should be installed across the fan circuit to avoid voltage spikes?

 

Dave, I think a metal oxide varistor might be a better item to use...but I am not an EE...I just know we used them on the power supplies of our surgical lights to reduce voltage surges. http://www.littelfuse.com/metal_oxide_varistor.html

I know our friend JH has 40 amp fast acting fuses on his 355 with no problems, some service dept must have did that to correct the same issue prior to his aquiring the car. Littlefuse, does make slo-blo fuses up to 30 amps, but I wonder if the only reason Ferrari chose 30 amp fast acting fuses is to account for the voltage surge/spike when it starts...so if you use a slo-acting fuse, you may need to use a lower rating...something closer to the actual current draw of the motor...perhaps a 20 amp slo-blo? Might try to read the specs on the side of the fan motor.

http://www.littelfuse.com/cgi-bin/r.cgi/en/prod_series.html?SeriesID=3184&LFSESSION=Z5YpYlmTTN

 

"So at least the cause of the known idle stumble has been identified and there is no doubt about that !"

I do not believe the cause is the air temp going into the engine, I still believe it is a disruption of the airflow when the fan kicks on. Adding a couple of inches to thecenter of the fin is not enough to get away from the reversion you speak about but it does eliminate the idle issue. When I speak about adding length I refer to eliminating the radius cut back and just bringing the fin out even with the outer edges. The fan reversion extends well beyond that point as you have pointed out.

Even if the fin mod. fixes the idle problem, you have brought to light an issue that has performance written all over it.

Yes, I am thinking too much but this is one part of a much bigger picture.

 

The air mass in front of the radiator at the intake of my 348 spider with the left fan on when hot caused non-cold air to blow forward at the edges, but I wouldn't call it "hot" air.



(that's more what comes out of my keyboard)

 

In the age we now live in there is a plethora of probes and sensors for just about anything and everything you care to monitor. Air temp probes,flow and pressure sensors can be placed from air inlet all the way to inlet ports on the cylinder head if one has spares modified to accept them. This takes all the guess work out, and makes data collection factual/real time for analysis.

One of the reasons I am interested in the electonic dash offered in another thread is that it may be possible to add additional info in real time.
Not only can you monitor exh. gas temps, but intake air temps,ems closed/open loop modes, A/F ratios, manifold vacuum,fuel injector on/off, or whatever data one considers useful. BTW, AFR and ems mode monitoring devices are easy to build and very inexpensive.

Oz, your test procedure for checking "air disruption vs abrupt temp change" should work. Look forward to your findings. BTW, are your rear grille mods going to be done before or after the 360 header mods....lol

 

Goth,

I am not sure it is worth the effort. Your shields have changed the airflow enough to accomplish the goal.

As I stated earlier, there were some 355 Spiders that upon delivery from FNA to the dealership, died when the fan would kick on. In 2 instances I had to cut a small half moon shape of cardboard and sandwich it with black duct tape to change the shape of the fin to a straight edge so the car would idle when the buyer came to see it. This was done before even the PDI and a pop rivet fix waited until the car could fit into the service schedule.
Thinking back, I think I only had to address it on 355 Spiders and at that, only 97's. Most would just bobble when the fan kicked on but a few would die.
I don’t think there is enough mixture swing programmed into the ECU regarding intake air temp. I think that is a very small trim adjustment.

Either way, your fix works and there is no reason to go through the effort to prove it, I believe you. I just think you have identified a much larger problem area with your research than just a bobbling idle.

For years now I have been working on a race car running a highly moded 348 drive train and 355 doors and rear bodywork. I have an EFI injection system with a detailed data collection system that has long pointed to a problem with the air intake charge while at speed vs. dyno. There is a large amount of HP / torque that has gone missing while at moderate speeds on the track.
Intake air density / temp and fuel temp has long been an area that I have been working on with the 355 as I know there is a good deal of performance (for both street and race cars) left on the table due to this.
An interesting side note in that direction is the addition of a Challenge grill shows a massive increase in the amount of brake dust covering the engine after a hard run with a 355. Here I am trying to get rid of engine bay heat by putting on a Challenge grill all to end up with brake heated air being drawn across the headers and all of this straight up to the aluminum air filter housings that capture every bit of the heat. Totally counter productive. I then took the wheel well and cut out all of the louvers and replaced them with chicken wire to keep stones out of the radiator in an effort to increase the airflow going out the wheel well. That didn’t work well but did lessen the amount of brake dust on the engine so it was a step in the right direction. As the car had been dropped so low I had problems with the shift cables on the 348 trans bottoming out and scraping so I fabed a 1/8" thick "belly pan" out of T6 aluminum with titanium rub blocks off a Groupe 6 car. This again changed the pattern of the brake dust found on the engine after a run.
I have been working on a cooler intake air charge for the street going 355's for a long time and this race car has shown me how the smallest changes to airflow effect the strangest things. Spend $1K on a Challenge grill all to have it provide super heated air to the outside of a heat sink aluminum filter housing not to mention drawing it across a nice aluminum fuel filter.

What this boils down to is you have identified an area I had given little thought to in my quest for the answers to this problem. You bet, I have spent way too much time on this but there is much to be gained when the answer is found. For decades I have been taping yarn on the race cars and taking photos while at speed in a quest to aid engine and oil cooling. I have hundreds of photos of Rolands F-40 driving down the highway covered in yarn to learn what the top side outlet radiator air was doing. The car was impossible to drive on a hot day for more than 20 mins. Lets just say all it accomplished was to super heat the driver of the car and provided little to no down force as configured. Two 1/2 inch tall x 3"s long tabs taped to the front hood fixed the airflow but looked terrible. Yes, the smallest changes will change many things on a street going 355.

Sorry for the ramble but I wanted you to better understand why I am "way over thinking" this issue. I think you are on to something big, just not the end all fix for a poor idle. That has been done with duct tape and cardboard.
The quest for answers is still ongoing as I have yet to find a 355 owner that thinks a snorkel from a F-5000 / Can-Am car is a nice cosmetic addition to the car.

Dave