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

[Geezer914]

Check a Haynes manual for diagrams of the engine tin.

[wonkipop]

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

i don't run them on mine - have not had them for 35 years at least.
went missing when SS heat exchangers went on back in 80s.

they are there to "try" and direct the exhausted cooling air out the back of car.
stop it pooling under car (and in particular the area where the fuel pump is).
instead with the guides it pools under the trunk and around the gearbox.
this only happens when the car is sitting still in traffic idling.
the rest of the time that air gets pulled out when the car is on the move,
guides or no guides.

they save the speedo and clutch cables from frying. i have mine wrapped in a foil insulation. as far as i am concerned with the guides you are just frying the same cables further back along their length.

the important tins are the ones higher up and curved around the cylinder fins like splitters.

the 914 has an inbuilt problem. called mid engined.
standard VWs don't. the lower guides do something on a VW because that exhausted cooling air gets squirted straight out the back of the car.

so long as you have good sealing around the engine bay tin apron the lower guides are not in my opinion necessary.

others will say they are.

[914werke]

so long as you have good sealing around the engine bay tin apron the lower guides are not in my opinion necessary.

others will say they are.

Including VW/Porsche engineers. (IMG:style_emoticons/default/happy11.gif)

[wonkipop]

so long as you have good sealing around the engine bay tin apron the lower guides are not in my opinion necessary.

others will say they are.

Including VW/Porsche engineers. (IMG:style_emoticons/default/happy11.gif)

don't disagree. but its the why of the engineers putting the guides in that might be of interest.

i know what you are saying.

what i observe is that sitting still idling the flanks of my car get very hot.
that exhausted cooling air goes straight down without the guides.
and then tends to collect in the zones around the edge of the engine.
like where the fuel pump is.
the tops of the rear wheel wells and the trunk floor.

back in the 90s i recall doing a comparison with a mate of mine who had a 73 2.0 with the guides. i was curious about it then and thought i should get hold of some guides.
the difference we found was his trunk floor got hotter than mine. the tops of the rear wheel wells and fenders got about as hot. and the flanks on the side of the car did not get as hot.

the guides do something. don't disagree. they guide the air to an area the original engineers thought was less negative to the fuel line and pump.
but they don't guide the air out from under the car. it still pools in a big heated bubble under the trunk.

the guides are an adaption of an element that definitely did do something on rear engined VWs. on a standard VW they guide the air right out from under the car completely. its a little bit of a different problem in the same engine in the mid mount location. and if you ask me the same engineers never really cracked it.

the heated air pooling under the car only happens when you have the car sitting still in traffic. its not a problem when the car is moving.

[rhodyguy]

They really stiffen up/help support the heat exchangers. Just puny 8mm ex studs and nuts and a rear hanger makes for a good sized unconnected space. They provide some cover for the pushrod tubes too. Pretty sure the bean counters would have omitted the WAGs if the engineers would have let them.

[wonkipop]

They really stiffen up/help support the heat exchangers. Just puny 8mm ex studs and nuts and a rear hanger makes for a good sized unconnected space. They provide some cover for the pushrod tubes too. Pretty sure the bean counters would have omitted the WAGs if the engineers would have let them.

maybe.

but the heat exchangers are hung at both ends so there is no twisting.
its really just a span and the heat exchangers are plenty stiff enough as a bridge element. don't think they are stressing the head studs.

consider your standard VW. the whole exhaust system is cantilevered off the head studs.
muffler and all. (admittedly not anywhere near the length but it is just hung there).
no muffler hanger. (IMG:style_emoticons/default/biggrin.gif) (IMG:style_emoticons/default/biggrin.gif)

those acclaimed engineers were definitely struggling with something on the 914 and they did not crack it from day 1 - good as they were. i give you the little rubber flaps that hang down either side just in front of the engine bay. not on early cars. they definitely do do something and not while the car is standing still either. heated cooling air exhaust was not fully cracked and maybe never fully cracked on a 914. (IMG:style_emoticons/default/biggrin.gif) (IMG:style_emoticons/default/biggrin.gif)
the whole thing is pretty hairy when you think about it - jamming an engine that was designed to go in the rear end of a car and sticking it in the middle. at least they did a better job of it than all the italian supercar manufacturers back then who stuck substandard sized radiators into the pencil noses of their over engined wedges!. (IMG:style_emoticons/default/biggrin.gif)

[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!

[rhodyguy]

Don’t sit idling in the drive thru at the burger joint. Park-n-walk. Then the car won’t smell like French fries. Our DD has never had fast food (or slow food, coffee, stinking lattes, etc) inside of it. Water and gum only.

[930cabman]

I don't run them on my 2056, never overheats.

230 is the max oil temp I have seen and this is extended periods over 80mph. If I cut it back to 70 mph the temp drops to 200

[rhodyguy]

What’s the upside to not using them? A few bucks? Losing a few ounces of original weight? New ones are reasonable $. Nice used originals? Dirt cheap.

[wonkipop]

What’s the upside to not using them? A few bucks? Losing a few ounces of original weight? New ones are reasonable $. Nice used originals? Dirt cheap.

one of the more amusing aspects of those warm air guides is not something any of us with our fuel injected cars would have need to notice.

but if you were one of the lucky european owners of the plucky little twin carb 1.8 that went in the 74/75 small engine cars you got a standard low pressure mechanical fuel pump - which in a type 4 engine is in the strangest location.

check the photos (from haynes manual).



(IMG:style_emoticons/default/biggrin.gif)

would not have given a bus or a 411/412 owner the slightest bit of trouble tucked there.
the warm air guides are sending the hot cooling exhaust towards the other end of the engine.

but i'm betting the euro 1.8s had a fuel vaporisation problem worse than anything the fuel injected cars ever had. cause i reckon those VW and porsche engineers might have had one too many beers when they thought that one up. (IMG:style_emoticons/default/biggrin.gif) (IMG:style_emoticons/default/biggrin.gif)

on the other hand in a standard type 4 rear engined car the oil filter basks in the beautiful hot air flow of both the exhausted engine air and the oil cooler. gets a double barrelled dose.

(IMG:style_emoticons/default/biggrin.gif) (IMG:style_emoticons/default/biggrin.gif) (IMG:style_emoticons/default/biggrin.gif) (IMG:style_emoticons/default/biggrin.gif)

but honestly if i could get hold of a set of warm air guides i'd probably stick them on just to stop things getting hot around the fuel pump when i'm sitting stuck in traffic because i do think that is a bit of a problem and i have noticed it. but not sure they really do much else.

[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).

[rhodyguy]

How did 912s become part of the conversation? The HEs for them are a fraction of the length compared to 914 HE’s. The unsecured portion is dinky. Looks like they rot just as nicely.

[wonkipop]

How did 912s become part of the conversation? The HEs for them are a fraction of the length compared to 914 HE’s. The unsecured portion is dinky. Looks like they rot just as nicely.

talking about the warm air guides. does not have them. its just blowing it straight down.
same as a 911.

the question my friend is what do the warm air guides do on a 914.
i know what they do on a standard VW. been around them for 40+ years.

what i am hearing here is the engineers put them on so they must be right.
as far as i can tell the engineers struggled to get the 914 right when it came to heating problems under the car. no matter what they did. (IMG:style_emoticons/default/biggrin.gif) (IMG:style_emoticons/default/biggrin.gif)

[rhodyguy]

I don’t think the exhaust systems have much in common. Comparing apples and oranges.

[wonkipop]

I don’t think the exhaust systems have much in common. Comparing apples and oranges.

are you talking combustion exhaust or exhausting heated cooling air? (IMG:style_emoticons/default/beerchug.gif)

[87m491]

[/quote]

maybe.

but the heat exchangers are hung at both ends so there is no twisting.
its really just a span and the heat exchangers are plenty stiff enough as a bridge element. don't think they are stressing the head studs.

consider your standard VW. the whole exhaust system is cantilevered off the head studs.
muffler and all. (admittedly not anywhere near the length but it is just hung there).
no muffler hanger. (IMG:style_emoticons/default/biggrin.gif) (IMG:style_emoticons/default/biggrin.gif)


[/quote]

Data point, in dropping my system last week I found there was no rear muffler/HE hanger installed on my car and indeed the whole system was held up with lust the 8 exhaust manifold nuts and studs! (no lower tins) I can say the muffler was pretty rock solid before removal and some how 7 of the 8 manifold nuts came off and the one stud that followed the nut out left a very clean helicoil behind so it will be reused. Very surprised given the weight and leverage on the HE's. Probably why I can't even begin to get the manifold gaskets to budge!