Modified 944 turbo - taking in too much hot air?

[JamesO]

I have actually logged the intake temps with a cone filter behind the bonnet catch and yes the temperature does indeed rise when moving slowly but once at speed it's back down to near ambient. I relocated the filter behind the headlamp mostly due to water being thrown up off the crank pulley causing problems soaking the filter during very heavy down pours. your issue could be the inlet temperature sensor becoming heat soaked in the hot engine bay causing the ecu to pull back the timing as it thinks the air is hotter than it is.

 

[Masher]

ORIGINAL: JamesO

I have actually logged the intake temps with a cone filter behind the bonnet catch and yes the temperature does indeed rise when moving slowly but once at speed it's back down to near ambient. I relocated the filter behind the headlamp mostly due to water being thrown up off the crank pulley causing problems soaking the filter during very heavy down pours. your issue could be the inlet temperature sensor becoming heat soaked in the hot engine bay causing the ecu to pull back the timing as it thinks the air is hotter than it is.

Is this something easy to test? Alternatively, is this something easy to insulate and therefore ensure it is not occurring?

The effect was apparent after 4 to 5 laps of Bedford so we're talking 20 miles of hard driving (starting with a warm car).

Thanks
Mick

 

[944Turbo]

Am I correct in thinking you have a lux front rather than a turbo S2 shape? If so I wonder if they ducted the incoming air to the IC - there is a reasonably elaborate duct with sealing strips around it on a factory turbo if you haven't got it then you will lose a lot of the efficiency of the IC which wont help!

 

[Masher]

Correct - my car was a 944 NA. The front end is now mock 924GT with the fixed lights and 4 vents in the badge panel. The IC is behind these vents. I would need to check how air gets to the IC but I assume it simply comes in those holes and straight onto the IC. There is also a large bonnet scoop over the turbo like the 924GT but on the passenger side in this instance.

A picture of the 944 Turbo set up would be interesting if someone has one.

The symptoms of the IC not working effectively are....?

Also, what liquid does an IC use and where is the tank for it? Does it use the same plumbing as the engine and therefore the same header tank (again, showing my ignorance... but I'll get there with your help).

Cheers
Mick

 

[edh]

The intercooler uses air to cool the intake air. Tony makes a good point about the ducting being important. The turbo intercooler is usually fed from a thin oval vent above the numberplate & there have been some suggestions from Jon Mitchell that adding the 924 turbo grills is actually counterproductive on a turbo front end.

I think I used to see heat soak of the IC on my turbo after 20-30 mins on track when it was hot. Your problem comes very quickly - after only a few laps.

Ducting behind the intercooler is also a possibility worth exploring - with a big hole in the bonnet (low pressure area) to help suck air through the intercooler.

 

[edh]

a good pic here

note that Rick's car was using a filter in the same position - behind the IC

 

[edh]

And a pic showing an intercooler venting through ducting (OK a 924 turbo, but a 951 Intercooler IIRC)

 

[944 man]

ORIGINAL: Masher

...my car was a 944 NA. The front end is now mock 924GT with the fixed lights and 4 vents in the badge panel. The IC is behind these vents. I would need to check how air gets to the IC but I assume it simply comes in those holes and straight onto the IC. There is also a large bonnet scoop over the turbo like the 924GT but on the passenger side in this instance...

This leads me to believe that your issue is with charge temperatures rather than inlet temperatures!

 

[Masher]

ORIGINAL: 944 man

ORIGINAL: Masher

...my car was a 944 NA. The front end is now mock 924GT with the fixed lights and 4 vents in the badge panel. The IC is behind these vents. I would need to check how air gets to the IC but I assume it simply comes in those holes and straight onto the IC. There is also a large bonnet scoop over the turbo like the 924GT but on the passenger side in this instance...

This leads me to believe that your issue is with charge temperatures rather than inlet temperatures!

Again, sorry for ignorance but what are charge temperatures?

For interest, the IC positioning on my car looks like the ones in edh's first picture but with the air coming straight through the slots in the badge panel rather than being brought in below and funnelled up onto the inter cooler. Personally, I am wondering if the slots in the badge panel and the bonnet scoop are between them trapping warm air rather than allowing it to flow cold in the front and warm out the back. Having said that, Porsche thought this a good idea for the 924GT...

Looking again at the air filter positioning, I cannot just flip the j boot over since the thing attached to it (dump valve?) needs to be mounted next to the header tank to feed into the big pipe above it. Reversing the j boot would, at a minimum, complicate this procedure by requiring a considerable extra length of pipe to bring the two pieces back together (one now exiting on the left with the other requiring input on the right).

I cannot help thinking this issue has been overcome before since several turbos have the air filter in the wing but for my car it will clearly require a significantly different j boot (in fact more like an L boot than a j boot) which also provides attachment for the dump valve (?) next to the header tank. Anyone know a good mechanic near Ware?

Thanks for your help and patience guys.
Mick.

 

[barks944]

Heres my datalog from bedford. 951 with K26/6 hybrid running 1 bar boost. The peak temperatures are actually after power runs as the turbo heat soaks the manifold a bit. My IAT sensor is in the plenum chamber. Sorry its quite large! My intercooler is a stock stage 1 intercooler. Modifed intercooler pipes and air filter behind headlight. After a good pull temps are about ~40C.

 

[944 man]

I will sum it up another way: the temperature of the air that enters your engine is affected by two things. The first one is the ambient temperature and this can be influenced locally by the under bonnet temperature generally or by the filter/inlet being in th path of the hot air leaving the intercooler. The second is the the amount of heat added by forced induction compression and heat soak from the turbocharger and the amount of this heat which ios them lost by passing the inlet chrage through an intercooler or charge cooler. These act as heat exchangers with the waste heat being passed either to water with a CC or to air with an IC.

You have an intercooler and it needs two things to work properly. It has to be able to pass the cooling air freely and it needs an adequate supply of cooling air.

This is where I believe that your car is poorly engineered. Disregard the 931 style vents in the badge panel. They werent designed to work with an intercooler and they dont, whether it is behind there or not. Porsche spent a lot of time ensuring that the 951 intercooler was supplied with sufficient air cool the charge and they did this with a large inlet in the new PU and a good deal of ducting.

Without this and with only four cosmetic vents in the badge panel I cant see how your car can control its inlet temperature and I suspect that it will eat itself if you continue.

 

[944 man]

Its a nice bit of fabrication Ed, but it will probably be more difficult whilst I still have a slam panel...[] Ideally mated to a 968 Turbo RS bonnet duct.

 

[924nutter]

Here's a thing. What exactly does the scoop do? Scoop air I shouldn't wonder, so it will increase underbonnet airflow which has to go somewhere, and it will take the path that the intercooler air would take on its exit path so maybe the scoop is back pressuring the I.C. reducing its efficiency, especially as if, has been previousy mentioned by 944 man, you have made air flow into the I.C. less efficient by having the 924 front vents Tape over the scoop inlet and try a couple of runs, just to eliminate that possibility.
In answer to your other question, charge coolers, i.e. water/air use water or water+water wetter in a closed loop around a much smaller heat exchanger becasue water is so much denser than air its thermal capacity is higher so will cool better and allow smaller heat exchanger. The down side is all the extra plumbing, the need for a recirculation pump and a radiator to cool the water.

 

[944 man]

34: 951.575.133.01 Air duct

40: 951.575.131.00 Air duct

 

[Masher]

ORIGINAL: 944 man

I will sum it up another way: the temperature of the air that enters your engine is affected by two things. The first one is the ambient temperature and this can be influenced locally by the under bonnet temperature generally or by the filter/inlet being in th path of the hot air leaving the intercooler. The second is the the amount of heat added by forced induction compression and heat soak from the turbocharger and the amount of this heat which ios them lost by passing the inlet chrage through an intercooler or charge cooler. These act as heat exchangers with the waste heat being passed either to water with a CC or to air with an IC.

You have an intercooler and it needs two things to work properly. It has to be able to pass the cooling air freely and it needs an adequate supply of cooling air.

This is where I believe that your car is poorly engineered. Disregard the 931 style vents in the badge panel. They werent designed to work with an intercooler and they dont, whether it is behind there or not. Porsche spent a lot of time ensuring that the 951 intercooler was supplied with sufficient air cool the charge and they did this with a large inlet in the new PU and a good deal of ducting.

Without this and with only four cosmetic vents in the badge panel I cant see how your car can control its inlet temperature and I suspect that it will eat itself if you continue.

Happy to take an opinion but whilst I am no mechanical genius, the guy who built the engine has a strong reputation and clearly hasn't gained that without reason. The difficulty with modified cars is the difficulty communicating what has changed and the interactions between these changes. Always tough to ask for a diagnosis on a forum without others necessarily having the benefit of seeing the car.

Just looked at the intercooler:
6 inches in size top to bottom and at a 20 degree angle to the vertical facing downward with air fed through 3 inch slots 1 to 3 inches from it's face. It is enclosed at the top and sides but there is a gap between it's void and the lower valence intake for the radiator. Clearly fairly open at the back. Strikes me a good air flow onto it will result. Could be wrong. Would the ducting on a factory turbo be guiding air from a lower intake up onto the intercooler i.e. the intake and face of the intercooler are offset with the intercooler higher than the air inlet? Just a guess. If your thought is to 'force' air through the intercooler i.e. create a positive pressure then additional ducting could assist in this respect by narrowing in the sides of the IC space on my car.

I also note an additional radiator is fitted to the front offside of the car - I believe this is directly cooling the engine oil looking at the plumbing connecting just below the oil filter. This will, at least, help with engine cooling and certainly the temperature gauge does not think the engine itself is running hot.

As 924nutter has suggested, i too wonder whether the scoop and the front air intake are working against one another effectively trapping warm air under the bonnet. Since a standard turbo needs no bonnet scoop I don't see a necessity for mine to have one. I'll try taping it up (I'm guessing I'll need strong tape to withstand 120+mph!). Trouble is you need a track day to play around since you cannot possibly generate the temperatures on the road.

Again thanks for the input.
Mike

 

[944 man]

I did struggle for a term that I was happy with and engineering seemed to be the most appropriate, although I realsie that it can be easily misunderstood.. The fact remains though, that he might have built a fantastic engine but using a 931 badge panel to supply a 951 intercooler shows that his strengths dont lay in this particular field.

 

[Masher]

If you were to look for a solution, what would you be thinking? Turbo front valance and ducting? I am assuming a Turbo front valance will fit an 86 car.
Cheers
Mick

 

[944 man]

Assuming it is this, then Id be looking for a 951 style GRP 'PU' which will fit your existing badge panel and wings and which will be similar to the OEM part enabling you to utilise the OEM air ducts with as little expedient adaption as possible.

Id probably speak to Kein or Alex at EMC because i] they have fitted these to scores of cars including many Turbos (along with the earlier pattern wings in GRP to match) ii] they understand exactly what you need to do.

Of course, it may be possible to adapt the exisitng 937 panel by adding an inlet where the 951 PU has one and fabricating a duct with aluinium sheet and a pop riveter.

 

[TTM]

It is still unclear to me if this blue car is running a std 944T intercooler or something else.

Post pictures.

 

[Masher]

I am pretty certain this car has a standard turbo and intercooler though fitted into the shell of a 1996 NA car (principally, the IC is located in exactly the same position as in a fartory turbo car). Photo does not specifically show the IC but shows the general engine bay layout. The original 2.5L engine has been bored and sleeved to 2.8L with upgraded pistons and rods.

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With respect to the air flow over the front of the car, this gives some idea:

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Cheers
Mick