Big bumper or small? (VW Golf Mk2)

[G2TDI]

Originally Posted by MetroMPG

... added 88 lbs to the stock motorcycle, which only weighed 231 lbs to begin with ...



The stock bike can get 114 mpg (US). The faired (and re-geared) one can get over 200 mpg (US), despite the 88 extra pounds.

I think what is a tad misleading on this one is:

A) The weight of the driver is excluded making the difference (in %) somewhat different.

B) The changed position of the driver has a major affect, meaning what would the improvement have been with ONLY changed driving position without the added aero (and weight) parts?

[G2TDI]

Originally Posted by lunarhighway

i think the main reason for the bifferent bumper is that the golf was a long running model that needed a new face... aerodinamically it might incorporate more of an airdam than the original "clasic" configuration, but with the adition of an airdam i think both setups will likely be comparable. the main thing indeed would be a front undertray.

Oh yes no doubt they were mainly going for cosmetic "improvements" or updates, and maybe weighed in safety improvements and some aero values?

But yeah that's what I have thought too, that with a lower spoiler and closing/smoothing out some of the holes, the smaller bumper (with less weight) should be equivalent if not better option.

Originally Posted by lunarhighway

also with a front undertray a very low airdam might not be needed. aerodynamic modern cars often have a raised airdam in the center, alowing a more smooth transition to the undertray, rather than be harch to the air. so if you go for modern aero, the old bumper might give you more freedom, while the "modern" bumper has the 'low tech' airdam function build in (vs more advanced undertray)... on the other hand, you can't be sure untill you test it that with a relative rough underside, a classic airdam isn't better than a partial undertray... or that perhaps the plastic airdam provides easier undertray attachment...

I'd want to say I agree, but I have a feeling I am too green on some of the terms you use to say yes or no care to add some pics of what you mean? as you can tell I love illustrations

Originally Posted by lunarhighway

the advantages of the newer bumper might be better crash protection, to a small degree... and also cosmetic protection (the lower metal work might dent but the plastic might not on a minor impact, and if it's destroyed it can be replaced)... not fe related, but something to take into account perhaps.

Yes most def there is better safety on the newer one. I don't have any worries about cosmetic damage, that lower valance can be bolted off/on and is cheap and easy to get new, so no worries, been there done that in the past on these vehicles.

Yes the big bumper does crack relatively easy a pain in colder climates both due to temp and snow and ice that can hit is (been there done that too!) but currently fortunately I don't have to deal with such any more here in California.

[G2TDI]

Btw here is a couple of similar projects:

Operation Project weight loss (56k+) - TDIClub Forums
VWvortex Forums: Build: A New mk2 Rally Shell for mid 2009

With end result on one of them being this:



Unlike these I am not looking to race anything so I am not going to use any race cage or wide tires, but there are some things such as empty/light weight I am very much looking to do like these. Both of these are also TDIs btw!

[COcyclist]

Welcome to Ecomodder. It's always nice to have another TDI on board. I think your choice comes down to personal preference or what you think looks the best. In my opinion the difference in bumpers will be hard to measure in mpg gains. The big gain will be if you can get a diesel to work in a Mk II chassis with the right gearing. That is going to be a job.

I have removed probably 100 lbs from my car by taking out the spare, back seat when not needed and swapping the muffler for a straight pipe. My aero mods so far weigh almost nothing, foam and coroplast and folded mirrors.

Edit- I see you know what you are in for with the engine swap

[G2TDI]

Originally Posted by COcyclist

Welcome to Ecomodder. It's always nice to have another TDI on board.

Thank you, and while yes we do have a TDI and some plain old VW diesels right now, we've had in the past a number of the various setups 1.5D, 1.6D, 1.9TD, 1.9TDI AHU&ALH, the topic at hand that project car doesn't exist just yet not even the shell , well it's "out there somewhere"

Originally Posted by COcyclist

I think your choice comes down to personal preference or what you think looks the best. In my opinion the difference in bumpers will be hard to measure in mpg gains. The big gain will be if you can get a diesel to work in a Mk II chassis with the right gearing. That is going to be a job.

Yes it is a personal choice, and I am just trying to see pros and cons for various options one of the major crossroads I'm at is to decide which style I'd go for I've had both mid 80's Mk2 as well as late 80's-early 90's Mk2 Diesel and Gasoline (AWD) versions before, so I am familiar with them. The transmission is no big deal there's endless of options with going either with an 020 or cable shifted 02A, I'd prefer a TDI transmission myself. But we will see. TDIs into the Mk2s had been done over and over again so that's nothing new really.

Originally Posted by COcyclist

I have removed probably 100 lbs from my car by taking out the spare, back seat when not needed and swapping the muffler for a straight pipe. My aero mods so far weigh almost nothing, foam and coroplast and folded mirrors.

I want to remove several hundred pounds (100lbs is only like 45kg so that's not much) but then again I am willing to sacrifice most comfort things most people wouldn't want to be without including windows not being open-able etc.

Originally Posted by COcyclist

Edit- I see you know what you are in for with the engine swap

That part I'm not too afraid of actually

[lunarhighway]

what i meant by the center cutout is something like this



or this

this is the 2010 bluemotion so it should have the best aero this this generation

even cars without an undertray sometimes have an "airdam" that's lower at the sides that in the center.

this is mainly to deflect air away from the front wheels, but also to allow more air under the car. also notice the curve of the bumper, it seems as if all air that can't be felected sideways is allowed under the car in this area

one reference i read to this was in the aero developement on the opel calibra with a 0.26Cd where it was found raising the center of the bumper lowered the Cd, but this car also had an undertray.

this can be a bit confusing as there's also reports of big airdams reducing drag, so ultimately it'll depend on getting the size right for your car, but if you can make the bottom of the car a bit more aerodynamic with a small undertray under the bumper and perhaps the engine this could make a difference.

an undertray also makes the car more quite and keeps the engine clean, so nothing but advantages.

perhaps it's also interesting to note the small dams the mercedes in the top picture has in front of the tires. these are quite common in current cars and are said to help stability and aerodynaimcs... gains aren't huge, but a difference can be felt, and they're really easy to make. but getting the size right is a different matter. and oversizing kan kill fe

from observations on production cars it seems a safe dimention for a non lowered car is to leave them 1/6th of the total wheel hight above the ground.
this is a rough avarage of what i've measured on different cars.
on production cars they often only cover the inner half of the tire (perhaps as this is also the with covered by the bumper), but sometimes extend past the tire inward to shield the suspention and inner wheel well.

but perhaps i digress from the original subject to far here

[geeteethree]

An EM thread I can have some input into
I run a 1990 big bumper Golf Mk2, which I have been attempting to improve aerodynamically. No ABA testing, but I have seen MPG improvements.

I run an engine undertray, stock VW part (well mine is SEAT) as fitted to later diesel models. Fits perfectly to the subframes, as well as blocking most of the wheel well gaps too. I will post a pic if my post count ever gets above 5

I have also installed a partial grille block, having refrained from a full block due to air cooling demands of my turbocharged engine, but all air that does pass through the grille is directed to the intercooler, oil cooler and radiator.

Also note that the rear underbody between the fuel tank and the rear valance/bumper is somewhat of a parachute, and where I'll be tackling next. Some Mk3 VR6s utilised a plastic panel there.

Look forward to seeing your progress

Kind Regards
Grant

[G2TDI]

Originally Posted by lunarhighway

what i meant by the center cutout is something like this



or this

this is the 2010 bluemotion so it should have the best aero this this generation

OK Thanks, yeah that is the Mk6 front end, though the Mk6 is only a facelift of the Mk5.

As for best aero, I personally have my doubts that new cars have the best aero, just look at some of the hybrid cars (Priuses etc) they seem to look "odd" in the public's eyes, cause they are different cause they put more focus on aero than your avg car. I believe there are so many other factors manufacturers take into account such as cost, look, safety, sound, weight. While some of those go hand-in-hand with aero others might not (i.e. safety).

But thank you for your input! I am all for as much input on this subject as possible!

[G2TDI]

Originally Posted by geeteethree

An EM thread I can have some input into
I run a 1990 big bumper Golf Mk2, which I have been attempting to improve aerodynamically. No ABA testing, but I have seen MPG improvements.

I have had a couple of what I believe to be the heaviest Mk2 Golfs ever made, the Golf Country, they had metal cover under the engine, heavy though!

I assume yours are plastic, do you have pictures? I am not convinced NA got these plastic covers on the Mk2, have to check, partially because diesels in Mk2 era was not very common in the US.

[geeteethree]

Originally Posted by G2TDI

I have had a couple of what I believe to be the heaviest Mk2 Golfs ever made, the Golf Country, they had metal cover under the engine, heavy though!

I assume yours are plastic, do you have pictures? I am not convinced NA got these plastic covers on the Mk2, have to check, partially because diesels in Mk2 era was not very common in the US.

The one I used is from a '95 SEAT Toledo, but are also found on Mk3 Golfs. There is a good thread on the subject with part numbers on ClubGTI

Happy hunting
Grant