M5 vs GTR / Heat Soak

[Protious]

Originally Posted by nugent

grills are blind, nonfunctional.

Really? Mine actually spew out heat.. I think?

[nugent]

Originally Posted by Protious

Really? Mine actually spew out heat.. I think?

are we talking chrome side grilles or something else?

[DrEd]

Originally Posted by Simon H

If you look under the bonnet, you will see that the engine compartment, is sealed with a rubber seal all the way round. There are no vents at all for any heat to escape, it must be like a pressure cooker under there, with all the heat just sat there. The turbos are on top of the engine compounding the problem. I wonder if running without a bonnet [purely for a test purpose] would see heat soak eradicated ?, surely some strategically placed vents, or other airflow measures would help. Over here, i dont think its a major problem, as we dont have prolonged periods of hot weather.

The vents are at the front of the wheel arches and below the front sub-frame. Air passing over the inter and oil coolers, passes below the engine bay and also into the wheel arches, the former being the primary escape route, assisted by directed airflow as vehicle road speed increases, the latter I presume, may have some brake cooling effect. Let's not forget however, that this is a nigh-on two tonne car and whilst a GT-R is not exactly anorexic, it simply is not as heavily burdened or inertia bound as the less focussed F10 M5 is. That the M5 can square toe-to-toe with the GT-R, albeit only in a straight line, is praise indeed.

In the UK where straight roads, nevermind dry ones, are in less abundance, it only adds weight (ha!) to the GT-R's corner. I love my M5, don't get me wrong, but I've got my hands dirty, learned about some of the oily bits and more empirically, have found its limits.

Ed.

[Protious]

Yeah, you're right - I guess I thought the side vents were actual vents as well.

[Simon H]

Originally Posted by DrEd

The vents are at the front of the wheel arches and below the front sub-frame. Air passing over the inter and oil coolers, passes below the engine bay and also into the wheel arches, the former being the primary escape route, assisted by directed airflow as vehicle road speed increases, the latter I presume, may have some brake cooling effect. Let's not forget however, that this is a nigh-on two tonne car and whilst a GT-R is not exactly anorexic, it simply is not as heavily burdened or inertia bound as the less focussed F10 M5 is. That the M5 can square toe-to-toe with the GT-R, albeit only in a straight line, is praise indeed.

In the UK where straight roads, nevermind dry ones, are in less abundance, it only adds weight (ha!) to the GT-R's corner. I love my M5, don't get me wrong, but I've got my hands dirty, learned about some of the oily bits and more empirically, have found its limits.

Ed.

Ed,
I can understand the points about the airflow through the wheel arches, and over the intercoolers and oil coolers, and under the subframe, but if hot air rises, and the engine compartment is sealed, would the hot stagnant air not just sit there, on top of the engine area, as it has nowhere to go ?. Are you hankering after a GT-R Ed ?.

[Protious]

Well, "the video was too dark". Maybe next time then I guess, GTR's don't like admit that they lose to us in a strait line!

Time to invest in my own GoPro!

[DrEd]

Originally Posted by Simon H

Ed,
I can understand the points about the airflow through the wheel arches, and over the intercoolers and oil coolers, and under the subframe, but if hot air rises, and the engine compartment is sealed, would the hot stagnant air not just sit there, on top of the engine area, as it has nowhere to go ?. Are you hankering after a GT-R Ed ?.

Simon, I see your point - there is literally nowhere in the upper engine bay for warm air to escape and thus allow cooler air to flow in continuously, allowing heat exchange with the components you previously described.

I can only assume that the dedicated heat exchangers themselves (radiator - coolant, oil cooler - oil, intercoolers - charge air) were intended to be sufficient in their capacity as to keep the engine within an operating envelope over a range of conditions. It's unfortunate and I have to say, a little disappointing, that some owners are finding the limits of this range.

I can see how my comments on the GT-R might have read. It's a car whose abilities I do respect. But - and it's a big butt (!) - it's not really a car I could see myself in

[dhirm5]

Originally Posted by DrEd

I can only assume that the dedicated heat exchangers themselves (radiator - coolant, oil cooler - oil, intercoolers - charge air) were intended to be sufficient in their capacity as to keep the engine within an operating envelope over a range of conditions.

^ This.

Originally Posted by DrEd

It's unfortunate and I have to say, a little disappointing, that some owners are finding the limits of this range.

Generally agree, but let's not forget the OP said it was 107F outside. That's well outside of the normal operating temperature of a car - it will work at the temp, but racing in that temp just doesn't make sense - the M5 is not a race car. It's a very fast super-saloon - fast enough so it can run with the best of the world's super sedans, but it's not going to win in all conditions against the likes of the GTR.

[richard in NC]

The one question if both the M5 and GTR are turbocharged, how is the GTR better at heat disapation?

Also interestingly, the ///M folks in Austin were quite proud of the M5/M6 cooling to prevent that.

[s62]

Originally Posted by richard in NC

The one question if both the M5 and GTR are turbocharged, how is the GTR better at heat dissipation?

GT-R's chief engineer explained that the distance from the front tire edge to the fender was designed to work with aerodynamics of the front to pull air from the engine bay, thereby keeping temperatures at check. Then people go and put spacers for looks

[Northern X5M]

Originally Posted by nugent

so could you just hose down the engine bay to help with cooling? not as a daily thing but on track days between run sessions. i typically just open up the bonnet.

It would be interesting to see what ambient tap water does to a red hot engine.

[DrEd]

Originally Posted by dhirm5

Generally agree, but let's not forget the OP said it was 107F outside. That's well outside of the normal operating temperature of a car - it will work at the temp, but racing in that temp just doesn't make sense - the M5 is not a race car. It's a very fast super-saloon - fast enough so it can run with the best of the world's super sedans, but it's not going to win in all conditions against the likes of the GTR.

I've got to back-track a little here and suggest that Simon H was bang on. If the F10 M5 had bonnet vents (I'm Scottish btw - Hood vents in US vernacular!) then heat soak would indeed be LESS of an issue. 107F or 42C, I have to remind myself, is exceptionally warm, however the GT-R coped better. There are obviously a multitude of reasons for this, to which the layman will seldom be privy, but the fact remains that a vehicle of similar engine configuration to the F10 was less affected.

As far as I can remember, no M5 has ever had bonnet/hood louvres, a la AM Vantage V12 or even E92 M3 - and I'd suggest that Motorsport Division, or at least their marketing department, were keen to maintain that tradition. Style over substance unfortunately. Slightly ironic given that the E92 M3 has one real and one 'dummy' nostril, yet as it is N/A, has far fewer heat dissipation issues - and is the first mass produced M3 thus adorned.

Ed.

[Rob///M5]

Originally Posted by richard in NC

The one question if both the M5 and GTR are turbocharged, how is the GTR better at heat disapation?

Also interestingly, the ///M folks in Austin were quite proud of the M5/M6 cooling to prevent that.

Are you joking? The M5/M6 cars were in limp mode every lap at COTA. A complete embarrassment, if you ask me.

[Simon H]

I owned a TT RS a couple of years ago, and this car had very similar heat soak problems. It had a sealed engine bay, with no air outlet vents/bonnet hood louvres. The single turbo was at the back of the engine, very nearly touching the bulkhead and very little space, with again, nowhere for the heat to go. One of the slight mods at the time, was to remove the rear rubber seal, that ran along the top of the bulkhead, creating a slight space for heat to escape. I actually tried this mod, and was surprised at just how much heat was escaping through the slight gap created. Im positive some strategically placed venting would have a great effect on this problem.

[richard in NC]

Originally Posted by Rob///M5

Are you joking? The M5/M6 cars were in limp mode every lap at COTA. A complete embarrassment, if you ask me.

This issue seemed to be more of a M-DCT issue, dropping into D1. But a few seconds later I could always go back into manual shifting for another lap.

But yes, during the premier, the engineer talked about the air flow they created thru the V for the turbos. See http://sirsnapsalot.smugmug.com/Cars...hB35&lb=1&s=XL
For a picture during the discussion.
I did not have a chance to discuss the issue with him during the track day.

[Rob///M5]

Originally Posted by richard in NC

This issue seemed to be more of a M-DCT issue, dropping into D1. But a few seconds later I could always go back into manual shifting for another lap.

But yes, during the premier, the engineer talked about the air flow they created thru the V for the turbos. See http://sirsnapsalot.smugmug.com/Cars...hB35&lb=1&s=XL
For a picture during the discussion.
I did not have a chance to discuss the issue with him during the track day.

The effect was that you lost control of the transmission, I seriously doubt that was the cause.