Engine Bay Temperature

[Cater_Racer]

It's evident that some of our problems in re-starting are due to the massive heat build up when the engine is switched off, for the 40 seconds or so during driver changes.

I'm planning to reduce the temperature in the engine bay, by venting the bonnet.

Any ideas or experience would be welcome.

Gerry

 

[944 man]

Is the exhaust manifold wrapped?

 

[Cater_Racer]

No not yet, but it's a b*tch of a job.

 

[zcacogp]

Gerry,

Do you know why these high temperatures are stopping it from re-starting? It sounds like something is wrong, and is exacerbated by the high temperatures.

If this is the case (and the emphasis is on 'if') then surely the better course would be to fix the thing that is wrong?


Oli.

 

[Cater_Racer]

Hi Oli,

I think the crank sensor was partly to blame, it does always re-start now after cranking for 10 seconds. we did some checking at Spa and its v hot under there. So I'm concerned that there are other factors, fuel evaporation, etc. So I'm thinking these issues are all aggravated by high temperatures.

I'm hoping to test at Angelsey (much cheaper than Spa) this week and resolve it. I've got the car going into the body shop to fix the damaged rear wing, thanks to Honda type R driver suffering from brain fade going into the bus stop chicane. So I thought while its in there, bonnet vents?

Gerry

 

[944 man]

Bonnet ventrs are all well and good, but youll never really know what theyre doing. They may let the heat out a little more quickly when youre stationary, but its too late by then.

The best approach has to be preventing heat generation, rather than trying to deal with the heat.

944s have always had high underbonnet temperatures and nothing will get them up like what youre doing. Id suggest buying a cheap temperature sensor so that you have an idea of the still air temperature before you start, enabling you to see what makes a difference and then (assuming tht yours is standard) obtaining a second manifold and some DEI wrap and setting-to...

I know that its a b*tch of a job, but done properly it should drastically lower the engine bay temperatures and more importantly, it should do this by preventing the heat from entering the bay, as opposed to letting out waft out more quickly when its there...

Id also consider adding aluminium heat shields to anything which you suspect is being affected, and maybe foil coating them too. You might be surprised how much heat will be reflected by a piece of cardoard covered in Bacofoil!

 

[944 man]

If you were able to shroud the rear of the radiator, you could keep all of the heat lost through the radiator out of the engine bay (exiting through a large angled vent close to the leading edge of the bonnet). Easier said than done, though.

 

[zcacogp]

Gerry,

I know nothing about bonnet vents, and can offer no advice on whether they would work or not. However it sounds like there is something wrong and the vents would not rectify that which was wrong; they would merely mask the symptoms.

My advice would be to fix the thing that is wrong. Sorry to be so simplistic ... (and it may prove cheaper then installing some ugly bonnet vents!)


Oli.

 

[Neil Haughey]

Definitely get that exhaust manifold and down pipes wrapped. Haven't done either on mine BTA I don't have any hot start problems any more.

 

[George Elliott]

You can see what porsche did when faced with this question Gerry, look at the 968 turbo S and GT bonnets.

The GT had a GT2 style intercooler ducting layout, in at the front, flow thru the cooler, and exit thru the bonnet with a duct.

The turbo S had the pair of NACA ducts approx. above the air filter and close to the cut off snorkel on the n/s of the bonnet.

I'm going to add a guess as the the original problem, the non return valve in the fuel pressure line from the pump at the rear is goosed. You are pressurising the line before starting which takes time.

good luck

george
944t

 

[Cater_Racer]

ORIGINAL: zcacogp

Gerry,

I know nothing about bonnet vents, and can offer no advice on whether they would work or not. However it sounds like there is something wrong and the vents would not rectify that which was wrong; they would merely mask the symptoms.

My advice would be to fix the thing that is wrong. Sorry to be so simplistic ... (and it may prove cheaper then installing some ugly bonnet vents!)


Oli.

I don't think anything is wrong Oli, no road car is designed for race conditions.

If you run at 5000-7000 rpm for 30 minutes, switch the engine off for 40 seconds and then try to re-start it is no wonder it's a bit reluctant.

As Neil & George have pointed out Porsche do modify their cars for racing, I'm following a well trodden path.

I'll probably end up venting the bonnet and wrapping the headers.

 

[zcacogp]

Gerry,

You're right - no road car is designed for race conditions, but cars are designed to run reliably in very, very hot conditions. I recall reading an analysis of the testing in the Mojave Desert that Mercedes does to ensure that their cars perform as the customer expects no matter what the climate. That involved simulating a several-hours-long traffic jam in still air in Death Valley, with ambient temperatures around 130F. Of course, their cars worked perfectly. I can't imagine that Porsche testing is significantly different, as middle eastern dealers wouldn't want to have to explain to their customers that their cars don't work terribly well in the heat ... []

I have no idea what the under-bonnet temperatures would be in such a test, nor how they compare with the temperatures you are getting, but as (the other!) George suggests there are some bits of the fuel system that are designed to maintain fuel pressure when hot, the failure of which will make hot starting difficult. Wrapping and vents are no doubt a good idea, but being sure that all bits of the car fuel and ignition system are as they should be is also a good idea!

I may be wrong ... I know nothing about racing ... these thoughts could be a long way wide of the mark!


Oli.

 

[Cater_Racer]

Oli,

You make is sound as if I'm racing a car that isn't well prepared and has faults.

This is simply not the case.

I have a lightweight race battery, yes it's rated at 700 CCA but its got 10mm connectors, so it's severely compromised in terms of current capability, the starter cable then passes to a FIA approved cut-out switch.

The battery is capable of a few starts maybe 30 seconds of cranking before it gives up, but it's not turning the engine over or providing the voltage that the "Bosch Standard" battery would.

It's the price you pay for meeting the regulations, a lead acid battery is not permitted in the same area as the cockpit, without being fully encased, the red-top gel battery is the only FIA approved battery exception.

That would apply even if it were in the standard location.Mine is on the passenger-side floor, reducing weight and putting lower and between the wheels.

The car starts reliably at all times, it's a Porsche

Even when V. hot, if the engine is switched off for 2 minutes it starts on the button.

It is less energetic if it's only off for 20-40 seconds, just time enough to jump out and belt the next driver in.

It still starts but it takes 5-10 seconds of cranking, and in a race 5 seconds can be the difference between 1st and 10th.

I'm just trying to optimise that process.

If I was prepared to carry the extra 20Kg around I'd put the standard battery in, but it makes a mockery of having taken all the glass out and putting plastic windows in.

 

[944 man]

Gerry, Ive only skimmed, but can you use an auxilliary battery via an Anderson jack? The car will pass all self-starting tests, Id have thought, so it will be down to the series regs.

A solution to a symptom rather than the cause, I admit, but I think that having it as a back-up might be reassuring and itll only had about half a kilo too.

 

[zcacogp]

Gerry,

Not trying to imply that at all, just thinking about the best way to solve your problem!

If all is working as it should be, then the hot starting issue may just be a result of the much harder work you are putting the car to and the extreme engine bay temperatures. However if there is something that isn't working as it should, the symptoms of which are only apparent when trying to start when hot, then it's worth addressing this before trying to reduce those temperatures. I'm not saying there is such a thing wrong, and you seem confident there isn't, so it's probably a non-issue.

You've also now raised the issue of the amount of juice the battery produces, which is something I hadn't considered as being relevant ... !


Oli.

 

[Cater_Racer]

Yes I've been thinking about adding an Anderson Jack.

It's probably a good idea for starting generally saves the poor old gel battery from too much hammer.

The gel battery is about £180 so I want it to last.

The car has always started now I've sorted the obvious things, i spun and stalled it at Spa in the practice and it started ok, just took 10 seconds that's all.

 

[Neil Haughey]

The heat load on the car from racing is nothing like anyone will get driving the thing anywhere in the world on public roads with speed limits. Its actually one of the things I have found most difficult to deal with in this racing lark, more than a couple of times I have felt physically sick and have had to sit in that heat for a minute or two and try and calm down to avoid barfing. The inside of the car is like sitting in an oven even in fairly cool conditions, it is understandable why many racers prefer racing cars to not have a roof even though a roof certainly makes the car safer.

 

[zcacogp]

OK, looks like I am misunderstanding the magnitude of the heat involved!

Apologies. I'll wind my neck in.


Oli.

 

[eddieedmo]

funnily enough my S2 starts best on first touch of key when it has been sat in hot sun ! High fuel pressure I think , could the hot racing conditions be causing much too high a pressure , which is being detected and stopping the car starting until pressure drops ?
Shot in the dark.
Alot of 944 and other older Porsche take a few cranks to build up fuel pressure before they start .

Nick []

 

[944 man]

ORIGINAL: Neil Haughey

The heat load on the car from racing is nothing like anyone will get driving the thing anywhere in the world on public roads with speed limits. Its actually one of the things I have found most difficult to deal with in this racing lark, more than a couple of times I have felt physically sick and have had to sit in that heat for a minute or two and try and calm down to avoid barfing. The inside of the car is like sitting in an oven even in fairly cool conditions, it is understandable why many racers prefer racing cars to not have a roof even though a roof certainly makes the car safer.

Have you considered lining the firewall/bulkhead with reflective insulation, and also on the floor, if its enough to feel through you boots?


Simon