Aero Mods Thread: Stage 1: Grill Blocks VS Intake Air Temps
 

Hi All,

I recently added a scan gauge II before doing a 500+ mile trip for work to get a base line feel for what my water temps and IAT (intake air temps) are prior to doing some aero mods in the search for higher MPGs.

From my casual observations (outside temp upper 20's)...

My coolant temps varied from a low of 188 to a max of about 197 with the "norm" being about 190 (Since I most likely have a 190 thermostat).

Test conditions :

Speed set at 68 MPH for 65 and 70 mph speed limits ...then speed set at 55 for 2 lane roads (55 mph limits) and 60 MPH for 55 MPH roads NOT 2 lane....Slower speeds were done at speed limit....chosen speeds were for repeatability purposes....No hypermilling.... just set speeds).

Can't really "go slow" for added mpg's since work runs are timed and must be done on a schedule hence the set speeds.

Now for the mods....

For starters, I decided to block the upper grill, the lower grill, and the side vents (I think that is what they are called)....I did leave the "corner" section of the lower grill opening (passenger side) open for intercooler airflow / cooling.

I did leave the lower most center opening open tho for radiator airflow (the center opening on the black chin spoiler piece).

I used cardboard and blue painters tape for clean removals and will fashion better looking grill blocks (also removable should the need arise) if the tests prove positive...

The following night I ran the same route for work (AFTER aero modding) and these were my findings....

outside temps Upper 20's low 30's...
Coolant temps...seemed to hover about the same as before BUT I did note a high of about 207 degrees (THAT had me a little worried but admittedly maybe up the same hill before it could have been the same but I just didn't notice the temp before since I also had to pay at lease some attention to driving!

Anyways, water coolant temps didn't really didn't concern me too much BUT IAT's on the other hand DID change somewhat more drastically...

BEFORE partial blocking of the air intake to the intercooler, I roughly noted that under low boost conditions (say 2 to 3 lbs boost) the IAT was roughly 20 degrees higher than ambient....Moderate boost.....say 5 to 7 lbs boost
IAT was about 30 degrees higher than ambient....High temp that I saw was in the 90s...

After partial blocking of the intake to the intercooler....the temps seemed to be about 30 to 40 degrees higher than ambient at the LOW side with temps going into the triple digits sometimes on the high side !....

Partial blocking seemed to definitely affect engine IATs more than coolant temps.

With that my questions are :

1) Does injection pump timing vary with IATs ? If so (and I assume it does)
how much does say a 10 degree increase in IAT, affect fuel mileage
due to timing changes?...Ill assume increased IATs affect fuel mileage
in a bad way... (I didn't specifically ask about coolant temps because the temps really did not seem to change much if at all)

2) I have heard of "vented" fender skirts that allow air behind the intercooler to be vented into the wheelwell therefore allowing more cooling air to pass through the intercooler itself thus lowering IATs....
While the increased airflow, should lower IATs (and in theory may help better pump timing and fuel economy) does the increased airflow through the wheel wells help or hinder good aerodynamics more so than potential gains through better (i.e. lower) IAT's?

3) is there any way to log data in real time in a cost effective manner?...The reason I ask is because my looking at the gauges is sometimes tedious and my findings are often based on just what I see at the time and or can remember....real data that is computer logged for post trip evaluation would be best and more comprehensive.

OK....so now for the results...

My standard "work run" typically yielded fuel mileage in the 50 to low 51 MPG area....

The first tank AFTER aero modding (grill blocks) yielded 52.56 MPGS!
(OK only 1 tank so far but I'll be doing 2 more runs later this week....Hopefully the painters tape survives the bad weather tonight and I can try 2 more runs for mileage readings (I suppose I could duct tape over it to help but I'm cheap!....HA).

Future mods I'll try....Comments welcome and encouraged....

1) Air dam...Car is pretty low now and factory seems to have blocked off
most everything I can see hanging in the wind with the factory spoiler but nothing ventured nothing gained right? Also, has anybody tried any of the aero parts off ebay?....
I was looking at this one (shame it has the cut out in the middle....I would have preferred smooth....also I don't know if this is lower than the factory spoiler...the ebay one is just up front whereas the factory tucks under the car and may be just as low to the ground)...

ebay.com/itm/FIT-FOR-99-0...lWl0QM&vxp=mtr]FIT FOR 99 0 lWl0QM vxp mtr |

2) Side skirts (maybe hinged even to flex up when high centering)...
Was thinking of welding some bolts on to the "lip" running the length of the car (the lip factory jacks jack from) and bolting on some plastic or rubber skirting....If I go to the ground I may put a hinge system on to allow the side skirt to ride up rather than wear away altho it will still wear over time)...

would side skirts be best mounted on the factory lip or would further outboard be better (like on the ebay link below.....too bad about the cut out tho...

I was eying these off eBay as well.. ebay.com/itm/1999-2004-Vo...1%26rkt%3D1%26]1999 2004 Vo 1 rkt 1 |

3) Trailer Tail (well I guess it should wagon tail but will model after tractor trailer "trailer tail").

4) Belly Pan (yes I put this last since it is probably the hardest for me since the car is low to the ground....If only I had a lift!).

5) Pizza Pans - I already did this on a set of steelies BUT I want to do it on my set of avus rims....lighter weight has to help right?!

Thanks in advance for any and all help / comments

Andrew

PS - I know this is more of a TDI thing BUT aero doesn't go over as well on the VW forums as they would here! ;-)

I had to modify the links above because I haven't posted much yet BUT I have been reading bunches !....definitely a cool place to learn stuff!

Sooo long post :-) Welcome to the forum, by the way!. I must admit I just skimmed through it, but, at least, I can answer this:
For logging purpose I use GPS capable smartphone, Torque Pro app and cheap OBD 2 bluetooth adaptor. Circa $20 alltogether. When kids finally fall asleep, i will write more.

1)Cummins has stated 1%loss per 10°f above 60°f IAT. This is due to false boost, more volume and less mass hot air is expanded it takes more space
Check with the Manufacturer for min opening for a Winter Front as a starting point. Then work down from there.
Timing adjustment gas yes, newer diesels IDK ??? What are you driving?
3)data log. I ran across one on AutoSpeed - Technology, Efficiency, Performance but can't find the direct link this morning

He drives a 2003 Vw jetta tdi...

I Called Cummins today they told me that the temperature the intake grid intake air heaters turn off~ 45°f should be used as a min IAT for effective efficient combustion. Ambant permitting maximum IAT of 60°f. Virginia doesn't seem like the kind of place you have to worry too much about Sub-Zero intake air temperatures like I do in Montana so your automatic shutters can work off a high limit type switch. Variable opening shutters would be optimum.

Hi

Thanks for the great info regarding cummins and intake
temps...i'd imagine similar numbers should apply to most diesels including the tdi.

I've been more closely monitoring my intake air temps vs Ambient temps by purchasing a cheap outdoor digital thermometer from tractor supply and I was surprised to see how much difference there was between ambient and intake temp....and the temps are pretty cool....low 30s at night.

With that I may open up the grill area I blocked off on front of the intercooler....perhaps the added Cooling air would more than offset any aero losses of the partially blocked grill.

I have been thinking of venting the passenger side fender liner....ie...putting in a vent in the fender liner would effectively let cooling air through the intercooler since in jettas there is a definite vent and ductwork from the bumper cover to the intercooler but no defined exit after the intercooler....opening up the area behind there should promote airflow through the intercooler but will introduce additional airflow into the wheelwell....

Do you think additional airflow into the wheel wells would negatively affect aerodynamics and mileage?

If not would venting both fender liners be beneficial?

Fwiw Jettas have belly pans and side skirts in the engine compartment that greatly enclose the engine compartment....ive read that the purpose is to retain engine temps....redice noise...and keep the engine cleaner...i guess gender venting may not be in line with all this but I am looking for maximum fuel mileage.

Thanks for you great info and insights

Andrew