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TimK 07-27-2016 06:31 PM

DIY upper & lower partial grill blocks - 2005 330Ci convertible
Hi all,

New to the site but thought I'd share my progress on my 330i soft top - I've just made partial upper and lower grill blocks today and fitted them. It seems to me that the size of the grills and amount of air going through the grills is much more than needed for the climate here and heat generated by the engine.

I live in the North of England and have owned the 330i for about a year, I do sometimes get the roof down despite the British weather! It's a sweet car to drive, and having owned Diesels before it I love the 3 litre 6 cylinder straight 6 engine, hardly too eco friendly but it is fairly economical for the type of engine - 30+ mpg US on a highway trip.

It's a sound car, I have done lots of preventative maintenance to keep it running well, replacing the MAF sensor, eliminating air leaks (famous E46 BMW problem), new vanos seals, using premium tyres (Continental), premium fuel, it's been remapped to gain a few bhp and advance the timing slightly for mpg.

Being a facelift 330 it has a 6 speed gearbox and turns 2500rpm at 70mph, not too bad.

I recently tweaked the wheel alignment and changed the front and rear toe to close to zero, I have not done enough miles before doing the grill block to know how much difference changing the toe made, maybe 1mpg at highway (motorway) speeds - it was about 0.5 degrees toe in on the front and 0.7 on the rear, now close to zero at both ends but slightly toe in at the rear for stability.

Sadly I can't see much more low hanging fruit to mod the aero on the car - the underside seems well optimised, I don't want to change the looks or driving experience, and I don't want to block the brake ducts for insurance reasons/safety.

Anyhow, here are some pictures of the car and grill blocks:

Pose shot of the car, freshly waxed:

Upper grill block (about 65% block, with air duct added for intake)

Lower (about 70% block)

I made the upper block and duct from hardboard covered in Gorilla tape (fancy duck tape), and the lower block from cardboard covered in agricultural black film. Oh and some cable ties to hold them in place and more Gorilla tape to fix the blocks and round off the air vent for the intake.

For the upper block I made an air channel to feed the air intake at the top of the kidney grills. I had noticed when the engine had only been driven a few miles, the throttle response was better than if driven a bit longer. I also noticed inlet air temps a bit high after driving for a while - 110F when cruising at 65mph on a 70F day, along with some pinging from the engine. Since pinging will cause the car to pull timing I figure cooler air is best for my engine to optimise econony.

I wanted to keep some airflow to the radiator and aircon condensor, which sits right in front of the radiator, and into the engine bay to avoid plastic and rubber parts deteriorating too much, the exhaust manifolds sit to the side of the engine and give out quite some heat.

If I drive in a relaxed manner on the highway at 65-70mph using cruise control (in gear/ no coasting), with the occasional blast to overtake, I can NEVER hit 33mpg US, typically it is 30-31mpg US. The OBC is very accurate it seems for mpg. If I can achieve 33mpg US with these mods with my typical highway driving style then I will be happy - this is a milestone for me as it is 40mpg in UK measurements, so to achieve this from a 3 litre gasoline will make me very happy.

I have an Andoid head unit with a bluetooth OBD dongle, running torque, so can keep an eye on coolant temps and intake temps. I have also set an alarm on Torque, so if the coolant ever goes over 212F it will shout at me through the stereo - normal max. temperature is 205F and the car won't let it rise more than a couple of degrees before the fans coming on slowly.

A quick drive after fitting the grill blocks at highway speeds gave a couple more mpg more than I would normally expect to get, driving at 65-70mph, in two directions. I will know more about how well the grill blocks help with mpg in the next week as I drive some more on the highway.

I did some steady speed mpg testing at 40-55mph before the grill block, so I will repeat this to see if I can measure an improvement - at higher highway speeds of 60-75mph the benefit should be more of course.

Hope you find this interesting, be good to know what you think of this.


mcrews 07-27-2016 06:48 PM

I didn't notice if you had increased the psi in the tires. Typically 40-44psi will get you a couple of mpgs.

TimK 07-27-2016 07:00 PM

Thanks! Crikey you read quickly.

I tried 45psi in the rear tyres but got excessive centre wear on the tyres, so I'm back down to 40psi - factory unladen pressure. The 45psi was in between the unladen and fully laden pressures which are somewhere about 50psi. I think the Continental Sport Contact 5s I am running don't respond too well to higher pressures due to this experience.

The fronts are at 36psi, the factory figure. I am worried about adverse wear if I go above the unladen factory numbers as happened on the rear. The car has a near 50:50 weight distribution (something like 48F, 52R) so I don't think the front tyres are being punished too much and would benefit a great deal from higher pressures.

I am going to go for the Michelin Pilot Sport 4 tyres next, which have a slightly better EU fuel economy rating than the Continentals, and have won some performance tyre tests for their grip, and should have better wear too. These tyres might gain 1mpg or so on the highway.

TimK 07-27-2016 07:02 PM

Nice to see you enjoy a large gasoline engine too!

mcrews 07-27-2016 07:27 PM


Originally Posted by TimK (Post 519445)
Nice to see you enjoy a large gasoline engine too!

👍👍👍👍👍👍👍👍:thumbup::thumbup::thumbup::thumbup::thumb up:

mcrews 07-27-2016 07:28 PM

The trick for me was the underbelly pan, grill block and taller tires!

And driving below 65.....����

Xist 07-27-2016 11:16 PM

TimK 07-28-2016 07:31 AM

Thanks, I've made an album and linked to the pictures in it now, so they appear larger.

TimK 08-03-2016 03:22 PM

I did some testing last week, on my local 2 way test road, I did testing at 40-55mph. Same tyre pressures as last time, and same brand of fuel.

The results show a calculated gain of 0.5mpg in the testing, however, it was gusty today so that may have showed less gains then there would be in better weather conditions.

However, I did a 30 mile run on a familiar road cruising at 65mph, and with the occasional moment at 70-ish mph to overtake quickly. The result was 40mpg UK, 33mpg US, which means I reached my goal on that day. There was wind around though so I'll reserve judgement, however the wind direction was across me, so not a tail or headwind.

So the initial results at high speeds look good, I would expect to get 31-32mpg US normally in those conditions, so it's possible I've gained 1.5-2mpg at highway speeds with the partial grill blocks and achieved my goal of 40mpg UK.

There is less wind noise at the front so I think drag is reduced to some degree.

I will see what happens next time I go on a run to see if the mpg contiues to be a couple higher than normal.

MobilOne 08-05-2016 01:34 AM

Sweet Ride!!

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