This will be the last video (maybe) from this event. It's After the Narrows, 73 miles into the 90 mile course, where I damaged the exhaust pipes.


__________________
George
90 S4 Grand Prix White (Murf #5 - 210 mph top speed)
94 GTS 5-Speed Midnight Blue
06 Cayenne S Havanna/Sand Beige (PASM)
http://928.jorj7.com (http://928.jorj7.com/)

 

Yea....but higher volume IC means a higher volume of heat can be removed. You could put an IC in the size of a deck of playing cards and you're still going to get high water discharge temps.

One concern is his IC is getting heat soaked, larger one can help alleviate that without having any other negative side effects. It's hardly the same as reinventing the wheel with a different intake. Cost wise it isn't even close.

You're seriously going to tell me if we took Todd's car above, installed an IC half that size or smaller nothing would change?

I meant to ask what is the current pump setup. That is another option for "low hanging fruit" to make the whole system more efficient.

This has the potential of disrupting his aero, which George pointed out he's trying to avoid.

I also thought he said he's spraying the heat exchangers or is he only spraying the radiator? If he's only spraying the radiator then yes, this is an area to improve upon, spray the heat exhangers too. It's amazing how fast temps drop when you spray some ambient temp water on the exchangers.

One idea we talked about on a local supercharged race car, is move the heat exchanger to the back under the bumper cover. Lots of room for a large cooler and will also increase the fluid capacity with the longer runs. Some different ways to get air routed through them without drastically changing the outward aero of the car.

There's a couple other ideas I sent to George via PM that Todd and I have been working on for my car. Not quite ready for prime time discussion.

 

..a cooling circuit that literally runs through a tank of ice. I bet it would nearly last the duration of the run. I’ve always wanted to do this on my car just for the sake of futzing around. Have a custom tank in the spare wheel well plumbed into my intercooler circuit and a simple valve to change coolant source at the drag strip...when the ice is gone it’s more coolant capacity. Crazy’?.....I’ve seen a 928 with an AC evaporator installed an intercooler tank.

 

We watched the first two videos this evening. Crap that's fast. What's crazy is how slow 170-ish seems after flying along at 210+ for 10s of seconds. It's also a reminder of how violently bumpy the smoothest road is at fractional mach speeds.

I note that at 200+ the front end doesn't seem very-well controlled. There's quite a bit of up/down 'ringing' movement after bumps and a couple of times it yaws side-to-side. That in particular is pucker-ish for me with my ancient aero degree. Maybe the yaw was you reaching for your coffee

Probably not though. Nevertheless, it looks to me like another few tens of pounds of front down force would make the super-high-speed sections a bit less wobbly.

I assume that access to wind tunnels, even scaled down for use with scale models, is not on the horizon?

 

Considering this is what the garage looked like the week before the race:



I don't think it's priority or in the budget (confirmed by the wife)...

__________________
George
90 S4 Grand Prix White (Murf #5 - 210 mph top speed)
94 GTS 5-Speed Midnight Blue
06 Cayenne S Havanna/Sand Beige (PASM)
http://928.jorj7.com (http://928.jorj7.com/)

 

There's two ways in which an intercooler can be too small. First, it can be too small in the sense of flow area and pressure loss: the charge pressure can drop too much between the inlet and outlet. Second, the temperature difference between coolant outlet and charge outlet can be too large. If the pressure loss is small and if the charge outlet and coolant outlet have almost the same temperature, intercooler size is not the bottleneck. Something else is the bottleneck. Prescribing a larger intercooler in that situation ignores basic rules of thermodynamics.

The thermal inertia is an issue to consider for street cars that just accelerate for a couple of seconds and then coast. However, in this ORR race car, the system will be close to the thermal equilibrium, so heat soaking issues are second order. The system will be heat soaked close to its thermal equilibrium during this sort of a run.

Although this is not rocket science, it's still science, even if it's of the high-school variety. The current bottleneck in George's system isn't the intercooler size if the coolant outlet is at 190F+ temperature. The bottleneck is that heat isn't being removed from the intercooler.

Why isn't heat being removed from the intercooler? The simplest possibility is that the coolant circuit is engineered poorly to have the pump sucking from the intercooler coolant outlet. If the pump sucks from there, that's going to lower the pressure. So close to the boiling point, the fluid will boil, pump will cavitate, and water flow will slow to a trickle. At least one pump needs to be sucking the coldest coolant from the heat exchanger outlet (or the reservoir, if the reservoir is after the heat exchanger and before the intercooler in the flow path).

I have no idea what would happen in that other system with 944 A2A intercooler converted to A2W intercooler if the intercooler size would be cut in half in terms of the length of the charge flow passages. It depends on what the temperature difference between the charge outlet and coolant outlet is now, and what it would be "half-sized".

 

I agree 100% the root-problem is the inability to remove heat from the intercooler coolant.

The car is making 500+ rwhp at guessing 10+ psi, which we know is typical and expected from a MURF supercharger kit, so the intercooler itself is not causing a restriction to the engine making hp.

The 190+ degree coolant temps shows that heat is being removed from the air charge by the intercooler.

Therefore, again, the real root-cause issue is the inability to remove heat from the coolant.

With all that said, the very first thing I would do is measure the coolant flow/volume thru the system. Find-out online what the ballpark/reasonable flow-rate should be given the hp, etc.

Let's assume it's less than expected, one can check if the system is completely bled and has no air pockets - just like bleeding the 928 engine coolant. Look how that relatively simple system overheats when not bled of air correctly.

Let's assume now you have excellent coolant flow where you can water your neighbor's lawn across the street with its output. So now is the question of air-flow thru the coolant radiator(s).

Jean-Louis on his racecar has his tranny cooler mounted up behind his rear bumper with a small fan on it, and it works perfectly. Taking that and Erik's idea, mount a heat-exchanger in the back with heavy-duty fans blowing thru (..or pulling thru) it like Todd has or had on one of his cars.

The combination of proper coolant-flow thru a heat-exchager, and propr air-flow thru it to remove heat, and you're all set.

Instead of running fans on the back, maybe you can concept-wise rig up a P-51 underbelly air scoop to provide air-flow thru the heat exchanger. High-pressure in the front, and low-pressure behind to push and pull the air thru the heat exchanger without stalling the air flow. BTW, I believe that was for the P-51's oil cooler.

 

I agree with Swaybar on the thermodynamics of the situation.

For a street car, the fan idea is pretty good. Think about sitting in traffic, for example.

For this ORR race car, however, I don’t think fans are a good idea. It’s like an airplane at 200mph+, and airplane engines don’t have many fans — just the big one! There’s already a big pressure differential available at 200mph+ speed from the velocity head.

 

I appreciate you all trying to solve my problem, and have heard a couple of ideas that may work. I have already bought a larger heat exchanger for the intercooler a couple of years ago. I'll have to customize it to fit, and since I didn't need it until now, it's been on the back burner. (In the garage photo it's in a box to the right of the tool chest). I plan to replace the one in the passenger fender with the new one. The space in the rear bumper is already filled with two fuel coolers and some other fuel related items. Getting a larger pump or second pump might help, since I'm using the one that came with the original Murf kit and have increased the length of hose and number of heat exchangers. A larger intercooler might help, but since I was working with the idea of removing heat from the coolant I've been focusing on the heat exchangers. Also I not very familiar with what choices are out there, so Erik/Todd might have the info I need. I have also thought of adding a "ice bucket" to the circuit. This seems to be a common solution for 1/4 mile and 1 mile events. I would have a switch that controls when it was utilized, so I could only bring it in when I was on the Timing Straight. I was thinking of putting where the rear AC is currently mounted (since it's not used). This area should allow easy access to fill with ice, but would require a separate pump and longer hoses to connect to the current system.

__________________
George
90 S4 Grand Prix White (Murf #5 - 210 mph top speed)
94 GTS 5-Speed Midnight Blue
06 Cayenne S Havanna/Sand Beige (PASM)
http://928.jorj7.com (http://928.jorj7.com/)

 

http://www.lingenfelter.com/forum_li...esting-results

 

You never know: there might be an Aero student that needs a thesis topic.

A question:

What looks to me like the front end bouncing... is it just the front end? Or is the rear in 'sync' with the front?

Or, in other words, is the ride height change more-or-less the same front and rear? Or is it a differential ride height change?

The former is 'interesting' at those speeds. The latter, the faster one goes, can lead to bad things depending upon how front and rear down force or lift changes as a result.

 

Both the front and back are going up and down, the camera is trying to compensate for the motion, so it doesn't reflect what the motion is really like. For the most part it's pretty stable, but severe bumps or winds can upset the balance.

__________________
George
90 S4 Grand Prix White (Murf #5 - 210 mph top speed)
94 GTS 5-Speed Midnight Blue
06 Cayenne S Havanna/Sand Beige (PASM)
http://928.jorj7.com (http://928.jorj7.com/)

 

Ok. So my 'brown pants' moments from watching the videos are camera induced.

I don't want to see you pull a 'Webber'

 

What shocks /springs are you using?

 

Regarding cooling the charge...

Consider changing the spray pattern/direction of the injected water to "forward" so it has more time to spread out and evaporate before hitting the intercooler. It takes 672 Kilocalories of energy to evaporate a gram of water and the more time that water has in the cooling air column the greater evaporative effect it can have. The dry air of that race location should be taken advantage of to its fullest extent. Plus its an inexpensive modification!

Congratulations on your achievements thus far, I have enjoyed your videos immensely and the vicarious thrills!



>