Aerodynamics on a 245 for 200mph standing mile?

Thanks! Sorry I'm such a 'puter dunce. If you're so inspired, there is a really nice professional shot of Mutt at the finish line at Ohio taken by our track photog. Maybe if I Email it to you you could post it up (I think I still have your address).

Those shots are actually from the first time I ever drove the truck after the initial build-up. Me and my buddy - the guy I'm building the Volvo for - took it to the drag strip just so I could drive it and get a feel for it with the M-B engine and manual trans. It wasn't quick but wasn't built to be. Anyhow, that's the reason for the shoe polish numbers on the windshield. My ECTA/SCTA number is the 5678 on the door and the class is F/DT - F engine class (roughly 2-3 liters) and D/T is Diesel Truck, based off the car gas classes.

Best speed to date is 129.6083. That's with a near-stock turbo w/just clipped compressor fins. I have a big turbo ready to go on and I'll get on that ASAP. I'm real close to the fastest F/DT in the country though someone ran a bit faster at El Mirage last year. I don't know who that was but it's fun to have someone to chase! Depending on what he's running, I MAY have the fastest OM617 Mercedes (based on actual timed measurement) in North America. Or maybe not......

Dan

Here ya go Dan.

ecomodder FTW:



It's called a "Kammback," you can google that and find a lot. And you might want to use stronger materials than cardboard and duct tape if you're shooting for 200mph

That wing on that Stagea is more of a spoiler and meant for down force. The Kammback actually slopes down and inward (you're creating a teardrop taper on the back of the car). Some German scientist (named Kamm) figured that you don't have to create an entire tear drop shape to get the benefits of drag reduction.

You want a sharp cutoff so that the airflow doesn't try to curve around the back of the car and create all that wake turbulence. You'll notice cars like the corvette and GT40 have a sharp cutoff at the back of the car, same thing on cars like the Prius and Volt...

Nonhog - thanks for posting the pics. Sorry for the threadjack but it DOES show the aero enhancements that I'm allowed. As mentioned, very class specific, evidently not a worry for the OP.

Dan

383Mazda said:

ecomodder FTW:

It's called a "Kammback," you can google that and find a lot. And you might want to use stronger materials than cardboard and duct tape if you're shooting for 200mph

That wing on that Stagea is more of a spoiler and meant for down force. The Kammback actually slopes down and inward (you're creating a teardrop taper on the back of the car). Some German scientist (named Kamm) figured that you don't have to create an entire tear drop shape to get the benefits of drag reduction.

You want a sharp cutoff so that the airflow doesn't try to curve around the back of the car and create all that wake turbulence. You'll notice cars like the corvette and GT40 have a sharp cutoff at the back of the car, same thing on cars like the Prius and Volt...

Click to expand...

This is what I'm going to try and now I know the term for it too
I'm thinking of making a shorter fixed part for road use(legal reasons and trunk usability) and an attachable extension for events. Thin sheet metal for starters. I have to do the fixed part in one part to make it move with trunk lid. Or three parts to have only roof part move with the lid.

I was in the assumption too that type of wing used on Stagea is meant for downforce because of the angle.

I'll start doing stuff as soon as I get 245 back on the road after winter. Which is in a couple weeks.

As far as I know, my car has the fastest RWD-Volvo standing mile speed in Finland. There are several faster FWD-Volvos, fastest being 855 with "just" 335km/h/209.75mph. But this isn't a contest, just for the kicks

Dan Stokes said:

Sorry for the threadjack but it DOES show the aero enhancements that I'm allowed. As mentioned, very class specific, evidently not a worry for the OP.

Dan

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You've removed rear bumper. Diffusor isn't allowed, but you can remove bodyparts for better airflow?

Lankku said:

You've removed rear bumper. Diffusor isn't allowed, but you can remove bodyparts for better airflow?

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Interesting. The rear bumper was not standard equipment on that truck. You could order a bumper or install an aftermarket unit (more common on the full size trucks - you often see a diamond plate bumper) but they were often shipped from the factory without a rear bumper. I'm not sure it's an aero enhancement but it probably is. Bottom line is that I didn't remove the rear bumper - it was never there either when I got the truck or when the former owner got it.

Mutt has been a race truck for a LONG time - probably at least 15 years, maybe 20 - and ran at Maxton with one of several small block Chevys. The last SBC was a 327 which tossed its cookies at the last Maxton meet and I got the truck from the owner (a friend of mine) and he got my old Camaro which Keith Turk now owns. So I pulled the dregs of the Chevy out and built the truck from there. Still plenty more I want to do to it including reworking the cage and other improvements.

As mentioned, the D/T classes are based off the SCTA Gas classes and therefore some of the rules are not intuitive. One of the things that makes a vehicle such that runs in "Gas" is an engine swap so my swap is actually one of the changes they look for to see if it's really appropriate for the class. The rules do allow a stock Diesel equipped truck if I chose to - I've run the Dodge just for fun (117.8 MPH.).

Dan

so other than pushing the huge frontal area of that thing though the air, your two largest sources of drag will be 1. from compacting the air that travels under the car and dragging that same air along the ground.and 2. as has been mentioned before-the drag induced by the separation of airflow at the rear of the car. the lip spoiler you made should be a very good start at the front but it needs to be as low as you can make it. the trailing edge extensions that you are talking about making will help with the surface it is mounted on(top), but you need to address the sides and bottom as well. if you can run a diffuser on the bottom it will help. it doesnt need to be that long either,you can get good results with a short diffuser that has a parabolic cross section. if you can some kind of vortex generator on the sides of the car would probably be one of the few things you can do. http://airtab.com ? If you wanted to get really crazy take out the rear side and back windows and build a duct to get a bunch of air in through the sides and straight out the back k

bongo:
I shoud have stated in the first post that I won't be going crazy on the body mods. Would've been easier before body was repaired and painted a year ago. At this point it is a street car first and everything else second. For example I want to keep the trunk usable. So no to removing windows. But to anyone else wondering these things, go for it I'll consider bigger changes if I won't get the results I want.

I have earlier thought of making a removable extension to the front lip/air dam or doing a new altogether. Though current height is just barely good for driving around without scraping in every corner and bump. Extension has to be installed on site, so buying a jack that fits under the car and lifts high enough is also on the list. If it isn't broken, I'm driving there and back

What about bottoms of the sideskirts? Shoud I make a small edge downwards to prevent air getting out from under the car?

Just bought a 10Hz GPS receiver and will be buying full version of Harry's lap timer or/and Racechrono for logging speeds. Those will be adequate. VBOX is good but cheapest version is too expensive for my taste. Just have to look for suitable start and end points in the track profile in the app or side of the track.

If you look at my air dam you can see a strip of rubber along the bottom just so I don't scrape the track. They get REALLY angry if you scrape the track! I got that rubber strip at a local supplier who provides stuff like that to local businesses and it wasn't terribly expensive (seems like I remember $25). Probably is someone near you who does this, too.

Second trick: The lower the better. Mutt got so low I couldn't load the old boy on the trailer so I went with RideTech ShockWaves, basically a combined air spring and shock absorber. Mine are only on the front though you could do all 4 corners. So now when I want to load I just pump up the front and drive on. When I get him unloaded at the track I just lower the front back to where I want it which is the rubber about 1 1/2" off the track. Works great and if I had a fast car that I want to run both on the street and on the track it's the way I'd go for sure. IIRC, there are several options for the shocks but given my application I just went with the standard deal.

EDIT: Bottom line is that for LSR the lower the better and if you can find an easy way to change ride height at the venue that's really the way to go.

Dan

Tire sidewall is pretty tough stuff, priced right, and comes with a forward curved lip.

Redwood Chair said:

Tire sidewall is pretty tough stuff, priced right, and comes with a forward curved lip.

Click to expand...

And that works, too.

Dan

Neat car!

Check out the pan on this Porsche.








What do you think of "votex generators" on the tail end?





I think I'll put them on the roof of my race car.

http://www.airtab.com/

Hi, I was thinking about the "pressurised" engine bay & ways to vent it.
Would there be any advantage in cutting a hole or holes through the cowl/bulkhead in the area under the bonnet to vent out through the air vents at the base of the windscreen?
I don't mean just leaving a hole but tidying the whole thing up so the air was properly ducted & the fresh air vent access was re-routed.
Would the low pressure area at the base of the windscreen be sufficient to help draw out the hot air or would the air coming out be too messy on the windscreen for a d/d? This would remain stock looking on the outside at least.
I understand what you are saying about not doing any body mods, but if it would provide an advantage it could be incorporated when doing other mods or repairs in that area.
On my 240 the cowl/bulkhead joint is pretty rusty & will need attention.
Any thoughts?

K9 240 said:

Hi, I was thinking about the "pressurised" engine bay & ways to vent it.
Would there be any advantage in cutting a hole or holes through the cowl/bulkhead in the area under the bonnet to vent out through the air vents at the base of the windscreen?
I don't mean just leaving a hole but tidying the whole thing up so the air was properly ducted & the fresh air vent access was re-routed.
Would the low pressure area at the base of the windscreen be sufficient to help draw out the hot air or would the air coming out be too messy on the windscreen for a d/d? This would remain stock looking on the outside at least.
I understand what you are saying about not doing any body mods, but if it would provide an advantage it could be incorporated when doing other mods or repairs in that area.
On my 240 the cowl/bulkhead joint is pretty rusty & will need attention.
Any thoughts?

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I've seen the rear of the hood spaced up a tad (like maybe 1/2"/13mm) but I have no clue if that's effective. Again, not legal in my class (I saw this on a street car) but I guess it could work. The guy just made a couple of wedges that went between the hood and the hinge flat.

Dan

Hi Dan
Yeah - I know what you mean, but I've never been a fan of that look - looks like the bonnet doesn't shut properly to me.
Having said that, due to the aforementioned rust issues, I had to remove the rubber sealing strip that goes along the cowl/bulkhead join so I guess I've got a similar gap!
Tim

K9 240 said:

Hi Dan
Yeah - I know what you mean, but I've never been a fan of that look - looks like the bonnet doesn't shut properly to me.
Having said that, due to the aforementioned rust issues, I had to remove the rubber sealing strip that goes along the cowl/bulkhead join so I guess I've got a similar gap!
Tim

Click to expand...

It's one of those things you could install at the track and see if it works without any permanent changes to the car. Might be worth a try just to see what happens. It would be interesting to see a couple of back-to-back runs with and without. Like I said, no clue if that works or not.

Dan

Don't oil your hood hinges and let nature take it's course.

Redwood Chair said:

Tire sidewall is pretty tough stuff, priced right, and comes with a forward curved lip.

Click to expand...

Not a bad idea, except it looks better on a Rat I think I might source plastic hard enough not to bend due to air pressure. Or just make a 3-4cm(~1.4") high extra part. Either way it has to be removable. Cant drive to many places with a front end that low.

K9 240 said:

Hi, I was thinking about the "pressurised" engine bay & ways to vent it.
Would there be any advantage in cutting a hole or holes through the cowl/bulkhead in the area under the bonnet to vent out through the air vents at the base of the windscreen?
I don't mean just leaving a hole but tidying the whole thing up so the air was properly ducted & the fresh air vent access was re-routed.
Would the low pressure area at the base of the windscreen be sufficient to help draw out the hot air or would the air coming out be too messy on the windscreen for a d/d? This would remain stock looking on the outside at least.
I understand what you are saying about not doing any body mods, but if it would provide an advantage it could be incorporated when doing other mods or repairs in that area.
On my 240 the cowl/bulkhead joint is pretty rusty & will need attention.
Any thoughts?

Click to expand...

Cabin air intake would have to be sealed and moved elsewhere to prevent that air from coming inside. It would also be a serious safety issue, as would lifting the rear of the hood. If anything goes badly enough wrong, fluids, smoke and fire will be over the windscreen and inside the sideskirts(if cabin air intake is sealed).

To my understanding there is an overpressure area under the windscreen. That's why air flows so well inside even without using blower. I have seen floating hoods being used. In those cases air pressure in the engine bay lifts the rear of the hood when it is higher than air pressure on the hood. But air coming out of the engine bay right under the windscreen would mess with the airflow and that's why front of the hood is better place for venting.

I'll be thinking vortex generators if results with coming changes aren't enough.

I've done first plans for flat bottom years ago but did abondon those and haven't had the interest to make it since. Let's see what happens during the spring. First standing mile event is in the end of May if weather is good enough.

Dan Stokes:
Air suspension or similar could be a possibility if budget would allow and I would not already have adjustable shocks all round. And front coilovers with spring rates to suit also random driving on track, just with less boost than standing mile. And I'll be going back from HX55 to K31 too in the name of usability.

Lankku said:

Dan Stokes:
Air suspension or similar could be a possibility if budget would allow and I would not already have adjustable shocks all round. And front coilovers with spring rates to suit also random driving on track, just with less boost than standing mile. And I'll be going back from HX55 to K31 too in the name of usability.

Click to expand...

I really like my ShockWaves and they weren't megabucks though I don't recall the price off the top of my head. They're REALLY nicely made. My only issue was that the rotating air inlet fittings they provided leaked so the front end didn't hold it's position. I replaced them with fittings from our local Parker store and all was well. So if you get to that point I'd recommend them. RideTech is a sponsor on one of the other forums I hang out on and one of their guys (Ryan) has even taken the time and interest to be one of our regular posters so I feel like I have an actual connection at the company.

Anyhow, it IS an option.

Dan

Dan Stokes said:

Interesting. The rear bumper was not standard equipment on that truck. You could order a bumper or install an aftermarket unit (more common on the full size trucks - you often see a diamond plate bumper) but they were often shipped from the factory without a rear bumper. I'm not sure it's an aero enhancement but it probably is. Bottom line is that I didn't remove the rear bumper - it was never there either when I got the truck or when the former owner got it.

Click to expand...

Correct. Trucks were that way for a long time, especially imports. Some trucks came with cute little rubber bumpers on the sheet metal because of Japanese interpretations of the law. (Datsun or Toyota dealer, I forget...)

Back to the wagon:

The nose being slightly lower helps with the undercar pressure and drag, and the pans help a bunch.
The rear axle area is very bad for drag. A pan under the axle or from front of axle halfway back will help.
The transmission area is also bad, but if you do a pan under it, make sure you aren't trapping air from the front.
Engine pans should be open behind the crossmember.
Block off the grill and test cooling (for high speeds). If enough air gets in from the under bumper area, leave the grille blocked. If you need more area, remove some of the blockage at the lower grille area.

DON'T make the air dam as low as it will go. There is a tradeoff between drag and downforce, and you want some flow in the front or else it will come in around the wheels and sides. Skirts are for keeping air out, not in (unless you are attempting a venturi car).

The rear top lip spoiler curving up is a good idea, the side plates mentioned earlier will help, and I have no opinion on the "flow generators", since they look like drag to me.

If you remove the rear seal on the hood and hide a washer under each rear bolt hole (between hood/bonnet and hinge, closest to windshield) it will raise the gap just enough.

If I get time to actually look at a 245 with all this in mind, I'll run the ideas by Drew, down in NASCAR-land. His job is to make brick-shaped cars win. (not quite as brick-shaped as ours, but go back to the 70s and 80s, and they are square)