Underbonnet air temps (2) Louvre effects
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[QUOTE=Daim;1524305
In my head and in my opinion, IF Jaguar had seen the need to fit some louvers, like on the E-Type, they would have done so. They did it to the XKR, they fitted side exits on other models. So IF there was any need, Jaguar wouldn't have gone through all the effort to model an engine bay and bonnet, with such sleek lines and good air flow.
Certain parts can be modified, but I doubt to be really honest, that the louvers do anything, than "bling" and, when raining, let more water into the engine bay and therefore a higher liklyhood of getting some electrical gubbins to go wrong. They seem to work when parked, but that is an expensive way of just popping the bonnet for a little while...[/QUOTE]
Daim
I agree with your points, but I highly doubt that Jaguar (at that time, late 1960s) did any serious research into under-bonnet air flow on the XJS. They did a considerable amount on the exterior airflow, that is a fact.
I tended to look at the Ford era cooling slots on later models as proof that louvres are a good idea, though it might just be marketing, as you indicate!
Greg
In my head and in my opinion, IF Jaguar had seen the need to fit some louvers, like on the E-Type, they would have done so. They did it to the XKR, they fitted side exits on other models. So IF there was any need, Jaguar wouldn't have gone through all the effort to model an engine bay and bonnet, with such sleek lines and good air flow.
Certain parts can be modified, but I doubt to be really honest, that the louvers do anything, than "bling" and, when raining, let more water into the engine bay and therefore a higher liklyhood of getting some electrical gubbins to go wrong. They seem to work when parked, but that is an expensive way of just popping the bonnet for a little while...[/QUOTE]
Daim
I agree with your points, but I highly doubt that Jaguar (at that time, late 1960s) did any serious research into under-bonnet air flow on the XJS. They did a considerable amount on the exterior airflow, that is a fact.
I tended to look at the Ford era cooling slots on later models as proof that louvres are a good idea, though it might just be marketing, as you indicate!
Greg
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Well, it's better to know now than to spend money and be disappointed. And there's still the substantial cool-down benefit.
It's possible that louvers in the hood altering that airflow to allow circulation at the top and rear of the engine is as significant as the venting.
It's possible that louvers in the hood altering that airflow to allow circulation at the top and rear of the engine is as significant as the venting.
Agreed. If money were no object, I would get them done; and it is quite possible, given the undoubted temp gauge and aircon efficiency benefit I am certain about, that even though the under bonnet air temps are not that much lower, that is because heat is getting out of the radiator stack more efficiently that with a non-louvred bonnet.
This theory is slightly born out by the fact that, if I switch on the main electric fan (even though it is not needed as water temps do not require it) under bonnet air temps rocket up by 10 degrees very quickly. This can only be caused by the fans pulling more heat from the radiator, and therefore cooling the coolant more than required - which the thermostats would compensate for by closing a touch! So maybe not necessary!
Greg
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Guys, yesterday I wrote as my conclusion: "I estimate that, given equivalent ambient air temps, the louvres reduce underbonnet air temps by more that 7 degrees and coolant temps by 5 or 6 C. Tomorrow I shall prove it by closing off the holes with cardboard."
Turns out this was a bit optimistic, as today in 35 c temps at midday, I taped up the holes with cardboard and did a test at various speeds: simulated traffic stops, shutdown test etc. Mother in Law wrote down the numbers. Then I tore off the cardboard taped-on hole covers and repeated the tests; so as good a comparison as is possible to do, I think.
Well, holes uncovered made an average of 3 C air temp reductions across the range of test speeds I used, which were 50 KPH, 70 KPH, 90 KPH, and 110 KPH. I was pretty surprised it was not more, but that was it.
So a big question whether it would be worth the bother and expense of louvres and painting the bonnet for such a reduction.
Just shows to take nothing for granted. I am sure the aircon benefitted though, and also that the temp gauge needle was definitely half an N lower with holes open; even so, nothing the car cannot handle without the holes. Top hose temps and cam cover temps immediately after shutdown were 86C and 90 C respectively, so well within the normal temp range.
So a definite benefit, but not as great as I had thought and hoped.
Greg
Turns out this was a bit optimistic, as today in 35 c temps at midday, I taped up the holes with cardboard and did a test at various speeds: simulated traffic stops, shutdown test etc. Mother in Law wrote down the numbers. Then I tore off the cardboard taped-on hole covers and repeated the tests; so as good a comparison as is possible to do, I think.
Well, holes uncovered made an average of 3 C air temp reductions across the range of test speeds I used, which were 50 KPH, 70 KPH, 90 KPH, and 110 KPH. I was pretty surprised it was not more, but that was it.
So a big question whether it would be worth the bother and expense of louvres and painting the bonnet for such a reduction.
Just shows to take nothing for granted. I am sure the aircon benefitted though, and also that the temp gauge needle was definitely half an N lower with holes open; even so, nothing the car cannot handle without the holes. Top hose temps and cam cover temps immediately after shutdown were 86C and 90 C respectively, so well within the normal temp range.
So a definite benefit, but not as great as I had thought and hoped.
Greg
I'm curious if your test isn't as conclusive as it might seem. There might be a aero/thermodynamic difference between a square hole in your hood, versus a set of proper louvers. It's possible that at any speed, the air flow is sweeping over the open square and might be creating a pressure situation that holds heat in the engine bay rather let it escape.
Additionally, JigJag's suggestion of an undertray, could make hood/bonnet louvers radically more effective by directing airflow upward toward the louvers.
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Greg,
I know this is on the wrong side of the pond:
https://www.summitracing.com/parts/sum-476001
But if you could find something similar that is this inexpensive, you could simulate more accurately how louvers would perform.
I know this is on the wrong side of the pond:
https://www.summitracing.com/parts/sum-476001
But if you could find something similar that is this inexpensive, you could simulate more accurately how louvers would perform.
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Greg next time you go for a run in the holey bonnet would you tape a slack piece of duct tape across the bonnet holes and tell us what they do at idle with the fan on and off and at speed? For science.
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a little more confusion, 2015 Mercedes, maybe M/B dont know what there doing???!!!
i looked into the hood openings, and they do catch rain etc. from going down onto motor.
looks as tho they have ducts going forward, maybe to catch hot air from radiator!
owner not around ,if i see him,might take alook /pic.
i looked into the hood openings, and they do catch rain etc. from going down onto motor.
looks as tho they have ducts going forward, maybe to catch hot air from radiator!
owner not around ,if i see him,might take alook /pic.
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@ Greg
Cheers for your second post! That really was my thought.
In my head and in my opinion, IF Jaguar had seen the need to fit some louvers, like on the E-Type, they would have done so. They did it to the XKR, they fitted side exits on other models. So IF there was any need, Jaguar wouldn't have gone through all the effort to model an engine bay and bonnet, with such sleek lines and good air flow.
Certain parts can be modified, but I doubt to be really honest, that the louvers do anything, than "bling" and, when raining, let more water into the engine bay and therefore a higher liklyhood of getting some electrical gubbins to go wrong. They seem to work when parked, but that is an expensive way of just popping the bonnet for a little while...
Cheers for your second post! That really was my thought.
In my head and in my opinion, IF Jaguar had seen the need to fit some louvers, like on the E-Type, they would have done so. They did it to the XKR, they fitted side exits on other models. So IF there was any need, Jaguar wouldn't have gone through all the effort to model an engine bay and bonnet, with such sleek lines and good air flow.
Certain parts can be modified, but I doubt to be really honest, that the louvers do anything, than "bling" and, when raining, let more water into the engine bay and therefore a higher liklyhood of getting some electrical gubbins to go wrong. They seem to work when parked, but that is an expensive way of just popping the bonnet for a little while...
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