Lower heat shield question Options

[technicalninja]

I've got the beginnings of a performance T4.
I bought a decent 73 2.0 core complete from 914Sixer.
I got a set of 1.8 SSI aftermarket heat exchangers from another member that are also pretty nice.

What I am missing is the bottom tins that go between the heat exchangers and the engine case.

Anytime folks put dedicated headers on a T4 these are left off...

How important are they?

I'm thinking "not much" but I would like insight from others.

Thanks

Rick

[technicalninja]

Awesome replies!

Already altered my thought process...

One I had from the start involves operation at speed.

Because the tins create a reverse cavity to the direction of airflow, at speed...
The airflow under the car should create a low-pressure area at the rear exit of the lower tins and actually increase airflow through the cooling system.

The fact that the tins should ALSO be thought of as bracing for the stupid long exhaust system is just GRAVY that I flat assed over-looked...
These attach to the outer shells. Might rattle like a bitch without them.

This is a street car so being able to handle heat directly under the engine WILL be important. "Mc Donalds drive through test" will be one of its targets.

Sure, it probably will not be a huge difference and I should be able to put the car through it's preliminary resurrection but I'm leaning "requirement" now and maybe "improving" as well.

Hey Wonki, your post regarding vapor lock with the T4 in another thread started a whole new line of thinking for me...
Has anyone tried "after-cooling" with a timed fan to improve heat soak issues with the 914?
Seems stupid simple to me. It would need to feed the magnesium housing.
Lots of stuff used aftercooling systems which actually tended to work quite well...
You need just enough air to overcome "stagnate" to vastly improve cooling after shut down.

Thanks for the replies again!

[wonkipop]

Awesome replies!

Already altered my thought process...

One I had from the start involves operation at speed.

Because the tins create a reverse cavity to the direction of airflow, at speed...
The airflow under the car should create a low-pressure area at the rear exit of the lower tins and actually increase airflow through the cooling system.

The fact that the tins should ALSO be thought of as bracing for the stupid long exhaust system is just GRAVY that I flat assed over-looked...
These attach to the outer shells. Might rattle like a bitch without them.

This is a street car so being able to handle heat directly under the engine WILL be important. "Mc Donalds drive through test" will be one of its targets.

Sure, it probably will not be a huge difference and I should be able to put the car through it's preliminary resurrection but I'm leaning "requirement" now and maybe "improving" as well.

Hey Wonki, your post regarding vapor lock with the T4 in another thread started a whole new line of thinking for me...
Has anyone tried "after-cooling" with a timed fan to improve heat soak issues with the 914?
Seems stupid simple to me. It would need to feed the magnesium housing.
Lots of stuff used aftercooling systems which actually tended to work quite well...
You need just enough air to overcome "stagnate" to vastly improve cooling after shut down.

Thanks for the replies again!

i honestly do avoid driving my 914 in heavy traffic on super hot days in aus anyway. (IMG:style_emoticons/default/biggrin.gif)
apart from anything else i can't stand driving with the roof on and the sun is like an oxy torch down here - all you industrial age buggers stripped the southern hemisphere of ozone and we get skin cancer at the drop of a hat and all our women age before their time. (IMG:style_emoticons/default/biggrin.gif) (IMG:style_emoticons/default/biggrin.gif) (IMG:style_emoticons/default/biggrin.gif)

i think the warm air guides help out in situations where you could get bubbles of hot air forming in those forward cavities of the lower engine bay. i have noticed it get very hot there on warm summer days in australia. but not in winter. and it only happens when the car is standing still but running and there is no breeze around.

i still think the german engineers were a little over optimistic thinking they could kind of squirt the air out the back. its a long way from the engine to the back bumper on a 914. (IMG:style_emoticons/default/biggrin.gif) (IMG:style_emoticons/default/biggrin.gif) but they were doing the best the could with what is kind of basically a parts bin mid engined car when it comes to the mechanicals. they had to reverse the direction of the cooling air as it comes out of the bottom of the engine. the original application which is what the engine was designed for is all the other way around in terms of pushing that waste air out.

[87m491]

[quote name='wonkipop' date='Dec 9 2023, 07:13 PM'

i still think the german engineers were a little over optimistic thinking they could kind of squirt the air out the back. its a long way from the engine to the back bumper on a 914. (IMG:style_emoticons/default/biggrin.gif) (IMG:style_emoticons/default/biggrin.gif) but they were doing the best the could with what is kind of basically a parts bin mid engined car when it comes to the mechanicals. they had to reverse the direction of the cooling air as it comes out of the bottom of the engine. the original application which is what the engine was designed for is all the other way around in terms of pushing that waste air out.
[/quote]

Hard to say but I was pretty surprised to find my trunk floor was too hot to touch after just a 10 minute drive this summer. The heat shield for the muffler is in place. I now know why the insulating layer(s) came standard back there. That said my car does not have the lower tins. When I get them I can compare.

[wonkipop]

[quote name='87m491' date='Dec 10 2023, 08:35 AM' post='3117136']
[quote name='wonkipop' date='Dec 9 2023, 07:13 PM'

i still think the german engineers were a little over optimistic thinking they could kind of squirt the air out the back. its a long way from the engine to the back bumper on a 914. (IMG:style_emoticons/default/biggrin.gif) (IMG:style_emoticons/default/biggrin.gif) but they were doing the best the could with what is kind of basically a parts bin mid engined car when it comes to the mechanicals. they had to reverse the direction of the cooling air as it comes out of the bottom of the engine. the original application which is what the engine was designed for is all the other way around in terms of pushing that waste air out.
[/quote]

Hard to say but I was pretty surprised to find my trunk floor was too hot to touch after just a 10 minute drive this summer. The heat shield for the muffler is in place. I now know why the insulating layer(s) came standard back there. That said my car does not have the lower tins. When I get them I can compare.
[/quote]

be interested to know. report back after the install. (IMG:style_emoticons/default/beerchug.gif)

i realise there is a second source for heat being trapped under the car. the heater dump valves on the heat exchangers. dumps into the forward section of engine bay underside and gets the flanks feeling pretty hot on my car in summer. i suspect the rubber flaps in front of the engine bay that the engineers came up in the later cars are there to help extract heated air from the dump valves in that area rather than influence the warm air being directed out of the engine.

very easy to see why VW had the guides in their conventional rear engined cars.
the area in front of the engine where the gearbox is was a big cavity that could fill with a bubble of heated air. this is where they located the fuel pump in both the twin carb and EFI versions of the type 4. the fuel pump would have been vulnerable to vaporization problems - particularly in the carb version with a low pressure mech fuel pump.
not to mention the starter and solonoid.




interestingly the 912E with type 4 engine did not seem to have warm air guides.
this seems to be porsche's practice not to have them. similar to a 911.
hard to know for sure but every 912E i could find pictures of did not have the guides.
but there are some suspicious tabs on the HEs?




given the 914 was plagued with vapor lock problems until they moved the fuel pump and also given the old hot start problem - the guides were an attempt to try and get that hot air out from under the car but they never really worked it out fully. properly. the guides certainly protect the clutch and speedo cables and probably assist in not adding more heated air to the forward cavities underneath that the heater dump valves were already pumping in in abundance when you were not running the heater. (Which is me most of the time down here in aus, i rarely have the heater on even in winter).