Diffuser anyone?

[Mike]

Working with my friends at Spectrum PowderWorks to create a rear diffuser. This is just a mock up and slight modifications are still being made. Look for titanium mounting hardware and some slight adjustments to curvature and length. Cleans up airflow by closing off the rear underbelly. What are your thoughts? Suggestions are welcome.

We also came up with an internal plate mount that cleans up the rear of the car while still offering good airflow out of the right side rear exit.

 

[Mike]

Negative comments are welcome as well. Just trying to gauge if there is any interest before finalizing a design and making up a few of them. The cost should be very reasonable too. Another option for those not wanting a full diffuser is an underbelly pan that tidy's up airflow underneath and cleans up the looks of the back underside of the car. Thoughts?

 

[Larry L.]

What effect, if any, might/does sealing the area under the engine have on venting hot air from the engine compartment?

I like the concept.

Could you take a photo or two of the diffuser under better lighting conditions? 'Hard to get a very clear idea of what the thing actually looks like in the photos above, Mike.


('Might also be good to know what a wind tunnel session would reveal regarding the effect the diffuser would have on the car's stability 'at speed'. [There goes the budget! lol!])

 

[Mike]

Larry, I knew when I got home and looked at the photos we had made a mistake shooting it direct sunlight. I have a couple photos from inside the shop I'll dig up.

Regarding heat, if anything I believe it would help or at least have no adverse effects. Without it, I believe there is a lot of turbulence back there that probably reduces airflow through the side vents and out the rear vents. The front of the diffuser mounts to the cross member so the oil pan is still uncovered and get's airflow across the bottom.

A wind tunnel could be rented but the prices might go up just a little lol. That said, with the reduced underbelly turbulence, slight low pressure area being created, and the rudder like affect, it should make it more stable.

I'll test all aspects of your concerns when we have it finished and let you know

 

[Kevin L]

Michael,

Looks good and changes the back of the car a lot. This is completely a shot in the dark and without aero data it s probably not able to be answered, but does it need to curve up more in the back?

Any interference with the rear clam opening? I assume that is what the gap is for.

Super cool project
Kevin

 

[Mike]

Kevin, we were talking about raising it up slightly to close the gap. We may try but there is lots of transaxle pieces that hang down making it a challenge. We will try try to do that and no, there are no issues with the clam shell being opened. I think another change will be to slightly smooth out the curve on the outside fin to more closely match the bottom of the clamshell profile. I have some pics of that as well. I have to go run some errands but when I return, I will post up several more pictures from inside the shop that maybe can better show how it looks. Keep the suggestions coming thanks!

 

[Mike]

PS honestly when we first hung it on there, I was not sure I liked it. Now, looking at the back of the car without it, it looks incomplete or as if it's not fully assembled. It really does clean up the back underside appearance.

 

[Mark]

Mike, it has been a pleasure to work on your car. I really enjoy building period aero bits. I've built several diffusers mostly fitted to Lotus cars. It doesn't really require a wind tunnel to achieve positive results when fitting a diffuser. A few basic principles need to be understood. First, the angle that the veins exit the rear of the car need to be between 8 and 10 degrees. More angle can be added to the rear of the diffuser the more the veins extend beyond the rear of the car. I like to extend the veins 8-10" beyond the body spoiler or wing if applicable. The basic idea is to create a low pressure "slippery" under surface. As faster air can pass under the car more quickly then the air flowing over the top of the car a low pressure situation is created creating down force. The more "junk" there is under the car to create turbulence the more the pressure increases interrupting the desired low pressure and down force.

In regards to the engine cooling being affected... Here are my thoughts. By using a trellis or open means of attaching the rear of the diffuser to the chassis air is still allowed to enter the upper air panel openings and flow though and out without interruption and more importantly without turbulence. My money is on cooler running temps.

This is a really good article on diffusers
Diffusers | Engineering basics | Aerodynamics | Racecar Engineering

I'll post some pictures detailing the fab in a bit.

 

[Seymour Snerd]

...Just trying to gauge if there is any interest before finalizing a design and making up a few of them. The cost should be very reasonable too. Another option for those not wanting a full diffuser is an underbelly pan that tidy's up airflow underneath and cleans up the looks of the back underside of the car. Thoughts?

I guess I'm not entirely clear on the motivation in this instance. What problem is this trying to solve (especially in the context of "it's an accurate replica of an early-60s-design race car)?. Or to put it more generally, what are the "features and benefits" and/or the "value proposition?". Oh, and the price? That matters too....

(BTW, Mark, you mean "vanes", not "veins". I nearly fainted before I figured out what you were talking about. )

 

[Mark]

(BTW, Mark, you mean "vanes", not "veins". I nearly fainted before I figured out what you were talking about. )

Haha..... No, I mean "vein" like a branching passage, forming framework for the passage of fluid or air. I'm not refering to a stailizing fin but rather a structure to channel and direct air.

The value, if you're into performance is to create a better handling car while embelishing the "race car" looks. If you're more of a purist than maybe it's not for you. I'm thinking alot of the GT40 replicar guys are having some fun with their toys. Canards and diffusers were done long ago on several vintage works cars.

 

[Mark]

A few more pictures that I took.

 

[Seymour Snerd]

Canards and diffusers were done long ago on several vintage works cars.

GT40s: canards yes, diffusers no.

Price?

 

[Larry L.]

Okaaaaay, just from a VISUAL ASTHETICS standpoint ('have no idea as to the effect on 'functionality'), I'd like to see THREE vanes on each side vs. the present two. IMO that would look much better...'more balanced...'more purposeful...'more NASTY! (There's nothing really adverse about the way the unit looks now, I just think it would look better with 3 vanes per side.)

Be advised 'purists' are likely to put a bounty on you for this regardless!

 

[Mike]

Thanks Mark for stepping in. I think as some of you figured, I'm a stickler for attention to detail. I have found Marks work to be up to my standard which says at least a little.

Alan my friend, please help me keep this thread on a positive note. Thank you my brother.

 

[Rich E.]

I personally like it. Gives it a modern yet retro look. Especially when its balanced out with a set of canards or maybe a front splitter. If only it would clear the luggage boxes on my MKII.....:cry:

 

[Mike]

I think if Mark had a Mk II to play with, he could come up with something

 

[Seymour Snerd]

Alan my friend, please help me keep this thread on a positive note. Thank you my brother.

Michael my friend/brother: you said "Negative comments are welcome as well." But, so far, I'm unaware of having made one. I could probably come up with one if you want....:laugh:

I did ask a couple questions because I truly was not sure what was your proposal as to why I would want one. Now I understand the proposition is that I need more rear downforce and I need my rear end "cleaned up" (really? right here in public? ). Thank you for answering.

As to downforce, is your proposal that this is needed for street cars, or is it intended more for track use? Regardless, is a diffuser without splitter and full length veins (thank you Mark) really a good idea for a GT40? Is a splitter envisioned as well? If so how well will that work with our current flat tubs? Or do we work in veins there as well? There is, after all 4+ inches to work with, not to mention adjustable shocks......


(BTW, heads up: being in Sales sucks sometimes).

 

[Mike]

I'll defer to Mark on pricing as he is the fabricator. I'm not in it to make a buck but rather just to pass on the info for those interested. For me, my car is a weekend street car/garage queen. My priorities are aesthetic in nature provided they don't hinder performance or reliability. In this case I think there may be a side affect in that these may actually aid in cooling at the same time while looking great.

 

[Seymour Snerd]

...there may be a side affect in that these may actually aid in cooling at the same time while looking great.

I've wondered about that because (IIRC) the Mk IIIs (or was it Mk VIs?, or....) had largely closed undertrays beneath the engine and I always wondered why. IAE given the Mk II FE cars' notorious problems with exhaust header proximity to fiberglass, etc., I shied away from the idea for P2160. Even in the case of the Mk Is, I suspect the cooling advantage will turn into a disadvantage when not moving, since paths for convection would be blocked. Of course, why would you not be moving....?

 

[Larry L.]

Mike:

What is the purpose of the 3 holes ( small/medium/large) drilled into the outside vanes?