Shock cooling

[JHerscher]

I understand that it is a good idea to have cooling ducts to ones shocks. (I don't remember where I heard this...probably "They" said it!)

Anyway, it seems to me to be a smart thing. My rear shocks, particularly the one directly aft of the exhaust manifold, are exposed to quite a bit of engine bay heat which in my mind must be playing with their performance over the course of a session.

How, and indeed, are you cooling your shocks?

I'm considering a 3" NACA duct in the engine cover 2" or so in front of the rear shocks. FWIW the car is a RF01 FC which has the NACA ducts in front of the engine cover. Is that sufficient? I'm thinking no.

Anyone done a similar duct? If so, what was the difference?

Other ideas? Put a heat shield in front of the shock in question? Duct some of the air from the main bodywork duct and forget about it?

Don't even bother?

Thanks
John

[Neil_Roberts]

Here comes one of my fundamental principles: Don't guess when you can know.

The first clue to overheated dampers is handling that degrades after the first few laps, and stays bad. Overheated springs will lower the ride height, worsening bottoming after the first few laps. Combined with overheated dampers, that produces a more bouncy ride.

Your damper manufacturer or builder should be able to tell you how hot is too hot. A temperature label or a thermocouple to a logger will tell you what your operating conditions are. If you are over the limit, then carefully ducted airflow that fully envelops the item to be cooled is the most effective solution. Adding a simple inlet upstream of the damper will only mix a tiny bit of cooler air in with the much larger mass flow of air going through the engine bay.

[EricP]

DaveW will have a lot to say on this. I’m following his lead after I found that even with shielded, baffled, and mildly ducted (NACA doesn’t really work) dampers, they still got too hot. From Dave I’ve learned that your exit flow from body work might be more important than your scoops bringing air in. I’m probably not saying it right but that’s the idea...

[DaveW]

DaveW will have a lot to say on this. I’m following his lead after I found that even with shielded, baffled, and mildly ducted (NACA doesn’t really work) dampers, they still got too hot. From Dave I’ve learned that your exit flow from body work might be more important than your scoops bringing air in. I’m probably not saying it right but that’s the idea...

You've got it right. And how hot is too hot is what Neil said. When the damping goes away after some running, something needs to be done.

On my rear dampers, we (Penske and I) went to lower viscosity fluid along with no-bleed pistons and essentially duplicated the good cool performance on the old setup at 180F with the new setup. This means the damping is controlled more by force (deflecting shims) than viscosity through bleeds. I do have a dedicated shock scoop and a vent tunnel on the tail, but before the valving mods it wasn't enough - now it is.

Vent tunnel below:

[Rick Kirchner]

I bought a 2" naca duct years ago but never installed it. What I did do is wrap the cans in gold foil, and using the two unused holes in the bellhousing, made a small vertical dam out of jabroc and covered it with goid foil. The hope (as I have no real data) was to force the hot air off the header to go upward and out the slot in the '94 engine cover, or to go low out the bottom side cover. I suppose it's a draggy way of doing it.

[DaveW]

I bought a 2" naca duct years ago but never installed it. What I did do is wrap the cans in gold foil, and using the two unused holes in the bellhousing, made a small vertical dam out of jabroc and covered it with goid foil. The hope (as I have no real data) was to force the hot air off the header to go upward and out the slot in the '94 engine cover, or to go low out the bottom side cover. I suppose it's a draggy way of doing it.

IMO, wrapping the shocks is not a good idea. Wrapping traps the heat generated inside the shock (damping generates heat) and they will eventually get to be warmer than they would unwrapped no matter what airflow or ducting you have.

[924RACR]

I'd have a bit of concern merely wrapping the shocks in insulation (realizing this isn't exactly what Rich is saying); after all, the shocks themselves are a heat source. Protection from other heat sources, yes, but cooling air flow just as important.

I've heard my car's original setup - SE1/DB1, with the rears sandwiched between two other heat sources, the oil tank and the engine - was horrible for heat soak on the rears. All in the name of drag...

In my current rear suspension setup, the rears are laying down low almost parallel to the frame rails at the back of the car. Lots of easy access to the exit air path out of the body, but on the RHS is the exhaust, which runs out back; IR pics of the rear of the car have highlighted how warm that shock gets compared to the other side. So I added a heat shield on standoffs to kill off radiant heat transfer from the exhaust (damn bike motors!). Though the car has not yet been so perfectly dialed-in to hone in on if that made an improvement - and haven't had any IR pics since.

Just some thoughts...

[Rick Kirchner]

I had considered a polished stainless heat shield - on the mid 90s VDs, that might as well be a thinwall tube with the ends closed and access for the oil tube.

The gold tape, from a reflective standpoint, seemed simpler.

I'd think a lot of instrumentation would be needed for a good answer. Wither thermocouples, heat tape, or a IR camera that's calibrated.

[DaveW]

Photos attached. The scoop feeds cool air into the opening in the heat shield. There is also an AL plate under the shocks which attaches to the upper heat shield that you can see to shield them from transmission heat. This all forms a loose box in an attempt to route cooler air around the shocks.