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Phase 2 under bonnet temperatures.

 
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Dave-M
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Joined: 20 Jan 2006
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Location: Yorkshire, England

PostPosted: Mon Apr 02, 2018 10:52 am    Post subject: Phase 2 under bonnet temperatures. Reply with quote

Phase 2 under bonnet temperatures.

Having just acquired all the bits to do the Cold Air feed to the carbs I got to thinking about the rest of the installation under the bonnet.
As you are probably aware the Phase 2 has a front bulkhead to the engine bay whereas the Phase1 does not.
This means that the Phase 1 has a flow of air through the engine bay, even if it has passed through the radiator first, whereas the Phase 2 does not.
On the Phase 1 air exhausts out through the bottom of the engine bay around the sump and down the transmission tunnel as well but on the Phase 2 this can’t happen as there is no flow into the engine bay.
The under bonnet temperatures on the Phase 2 must be very high and without a cold air feed to the carbs the power of the engine must be reduced significantly.
Have any of you addressed this issue? I have searched the club magazines that I have (not a full set) and looked here on the forum and found nothing.
Here are a couple of pictures of Phase 1 & 2, I know they are not the best but you should get the idea.





Regards, Dave
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Howard Evans
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Joined: 10 Apr 2009
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Location: Crewe

PostPosted: Sat Apr 07, 2018 8:01 pm    Post subject: Phase 2 Underbonnet Temperature Reply with quote

Hello Dave,

I had a severe fuel vaporisation problem with my Phase 2 (1500 PCF and Zenith VN2 carb).

My first step was to ceate an aluminium heatshield which was sandwiched between the Carb and Inlet Manifold with asbestos gaskets - the shield is probably about a foot long and 3" wide, with folded edges to reduce resonance. This gave a minor improvement in driveability but certainly didn't fix the problem.

The second step was to fit a 'summer' thermostat (89 degrees cf. 95 degrees) and this improved things further but not totally. I then decided to get a bit more scientific by thermocoupling the carburettor float chamber and measuring the temperatures that were reached. I can't remember the exact maximium but it was perilously close to point where the fuel flashed off.

I then fitted a 'cooling' fan - plastic from a Crossflow engine, to see if just stirring up the underbonnert air would help things.

Under similar operating conditions the float bowl temperature came down by 5 degrees C and the driveability problem went away.

Hot start, post soak, could still be a problem, so I cut out the dummy air intake grille (on the scuttle) to improve convection, and I also cut away the first 3" of the bonnet seal either side of the latch to encourage air circulation.

Touch wood these together seem to have done the trick!

I must admit that I probably exacerbaterd the problem initially, by fitting an underbonnet reflective insulating pad as my original concern was heat cracking of the gell coat on the bonnet!

Even in the hottest conditions, the bonnet teamperature is now 'stone cold' so I guess the heat has been retained underbonnet as a consequence.

Regards,

Howard
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Dave-M
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Location: Yorkshire, England

PostPosted: Mon Apr 09, 2018 8:43 am    Post subject: under bonnet temps Reply with quote

Hello Howard, Thanks for taking time to reply.
It’s interesting to read how the problems showed and how you dealt with them.

The thermocouple temperature measurements are of particular interest, were the high temps recorded while you were driving the car or during the heat soak period after stopping?

Can I also ask if you have a “cold” air feed to the carb? or does it use under bonnet air and also is your car fitted with a cast iron or a tubular exhaust manifold?

It seems to me that there are two issues here :-

1) When driving the under bonnet temps are high enough to cause a potential problem with fuel vaporisation and cause drive-ability issues.

2) During the heat soak period after driving the temperatures under the bonnet are definitely high enough to cause “hot start” issues.

Following on, here are a few thoughts which may be worth discussing.
Fit a carb cold air system as per lotus elan ie. Mount the air filter in front of the radiator which is then ducted back to an airbox mounted on the carb /s.

Heat wrap the exhaust manifold

Duct a flow of air through the engine bay

Vent the under bonnet through the top of the engine bay to allow excess heat to escape during the heat soak period.

Replace cast iron exhaust manifold with a tubular one. At around 1000 Fahrenheit there is a lot of retained heat in a chunk of cast iron.

Other than the carb cold air system I have still to decide how to tackle the issues so any input at this stage will be a help.

Regards, Dave
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Howard Evans
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Location: Crewe

PostPosted: Mon Apr 09, 2018 12:49 pm    Post subject: Reply with quote

Hello Dave I'm in the us at present. I'll follow up when I get back. regards Howard
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Alan Smith
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Joined: 10 Jan 2016
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Location: Littleborough

PostPosted: Tue Apr 10, 2018 4:44 pm    Post subject: Reply with quote

Hi Dave,
There are certainly a lot of variables here.
You probably already have this one covered, and as a novice, what do I know?
I am thinking that an electric water pump with thermostatic control and timed run-on after the ignition is switched off, would help the overall cooling system plus release a few BHP as a bonus?
It wouldn't help to get the heat out of the engine bay but it would help to get the heat out of the engine quicker and more efficiently, which would be useful in these circumstances?
Regards,
Alan
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Dave-M
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Location: Yorkshire, England

PostPosted: Wed Apr 11, 2018 8:26 am    Post subject: under bonnet temps Reply with quote

Alan, That's a useful idea especially if the rad fans could be linked with the water pump run on period.

It's a fairly expensive solution if using the proprietary Craig Davis? solution but
many modern cars use an auxiliary electric water pump which may be adapted for use in this case.

I'll contact my old mate Google and see what I can find.


Regards Dave
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