Porsche Enthusiasts Club Forum

Further to what Ive already said about mixing big turbos and higher compression, which simply wont all bolt together and work with the original fuel/ignition control - buy a Knocklink!

Even if you dont integrate it (which you should really), you can place the box in your line of sight and itll warn you of big end destroying detonation that you almost certainly wouldnt feel or hear.

Wes,

I used to enjoy 924.org until one of the members tried to stitch me up, no one there believed me until he stitched a whole load of them up on mass about a year later... I tried to warn them.

With the 924 turbo, number 4 gets hot simply because it is the last one to get a bit of the cooling cherry from the waterpump.

The factory guys involved in the CGT endurance racing at the time told me they modified the blocks to have a shallower waterway across the whole block, making it only as deep as the second compression ring goes down the bore at BDC. This increased the flow of coolant in the important part of the waterjacket across all four cylinders. A cool side effect is that it also made the blocks more rigid.

I also know that Porsche motorsport had Inconel exhaust valves for the CGTS and CGTR motoros that were very exotic for the day.

Thermal management is key.

A couple of things I should also say.

Intercooling on the 924 Turbo
Badge panel mounted 944 Turbo intercooler is a good route.

Cutting holes in the front bumper or using the 924 Turbo nose vents.
There is a reason that Porsche only provided a small slit air intake to cool the 944 turbo with its venturi duct behind it.
Having a air entry to the intercooler for cooling, followed by a venturi to guide the air into the intercooler was to to maximise the cooling effect of the air following over it.
At 80, 100, or 150 miles per hour (for example) the air going through the entry in the 944 turbo front bumper is moving at that very same speed.
Without an entry duct with a venturi shape the air becomes turbulent, can flow around the intercooler rather than through it, and to an extent will be moving at the same speed as the car.
With the ducting, the air entering the front bumper is promoted to expand, causing it to slow down by an 8th of its original speed by the time it hits the intercooler, its flow in not turbulent and it is forced through the intercooler.
The slower speed of the air actually makes it easier for the air to flow through the intercooler, in direct contact with it, maximising the cooling effect.

If you have the same intercooler, but with a big intake collector on the front (such as a big hole in the bumper, or a larger entry collector, the airflow will go up, even if you still force the air through the intercooler with a duct, the airflow speed will be much higher. This will cause the air passing through the fins of the intercooler to be faster, more turbulent and forming a boundary layer over the surface of the fins, which will drastically reduce cooling to the intercooler, which may be counter intuitive to what you would expect.

The other thing about intercooling, an intercooler like the 944 turbo gets all of its efficiency not from the surface area of fins when you are on boost, but from its thermal mass, its a big heavy aluminium lump, which acts as a heat soak while you are on boost, soaking up massive volumes of energy (heat), which is then released over a longer period of time than your on boost for.

Think about it, if you have 300 BHP, and you are driving the car hard, unless it is on a very complicated hill climb circuit, it will be able to get from a standstill to its maximum speed (especially on a 924 turbo) in a very short space of time. However, even if used on Silverstone GP circuit, more time is spent off boost, or at maximum speed, than is spent on boost. This is even more so when you have modified the performance, because it will get to terminal velocity much more quickly.

This means that your intercooler will be constantly releasing heat the whole time, at a pretty constant rate when you are on or off boost. Whereas a lot of people think it will be releasing heat more when it is on boost than when it is off boost.

If the car was a dedicated sprint/hill climb car, you would probably want a large front mounted intercooler, with the ratio of thermal mass to surface area much more in favour of surface area, simply because you will be on boost more of the time than off of boost. So the key will be getting rid of heat almost as quickly as it is absorbed... However, put this type of intercooler on a fast road car, you will effectively get less performance, because thermal mass absorbs heat much more quickly than surface area can release heat.

The way of thinking of it is as follows... A big lump of aluminium can absorb heat faster than a large volume of air... The tick is to have enough thermal mass to absorb heat when on the duty cycle at a constant rate, with the maximum of cooling before you get into diminishing returns, while having enough surface area to release that heat when on the duty cycle and between the duty cycle.

Some serious calculations can predict this for you, but sometimes it is just quicker to use the car in the way it will be used (track, road etc) and monitor pre and post intercooler temperatures as well as intercooler core temperature away from the fins (such as a lump of aluminium with a temperature probe mounted in it on the end tank. Then you can see how well the intercooler is absorbing heat, if the intercooler is become heat soaked, and how quickly it is able to cool down again.. Then if you find it is heat soaking to soon, you need more thermal mass, if it is not cooling quickly enough between boost events (on average) then you need more surface area or improve cooling.

This is something dyno time can not tell you, a powerful car on the dyno might be slow on the road because of this very issue.

I mentioned this because Carrera was talking about his front mounted intercooler and it is worth mentioning that this could be done in a right way or a wrong way.

Its also valid to mention that so many people get 944 turbo badge panels vented to be like a 924 turbo one, or they use a 924 turbo one, or they even fit a aftermarket scoop one.. Unless the airflow through the vents, along with the 944 turbo standard bumper one, is managed properly, you will get a far less efficient intercooler.

Another good example is intercooler boost pipes, many people change these for stainless steel, mild steel, plastic or rubber items... This is not a great idea, thermal mass again is key.. Use a heavier aluminium pipe is a good thing to do, as it will increase thermal mass and mop up even more boost heat.

Another problem is polished boost pipes, again, bad.. Polishing reduces the surface area of the pipes, a sanded pipe with a texture could have twice the surface area of one that is polished, which means it could have twice the ability to release heat back into the engine bay.. this does also mean it has twice the surface area to soak up engine bay heat, but when on the move, especially with a vented bonnet to release engine bay heat, this is not a problem.

Which brings me onto bonnet vents.

In a modified 944 or 924 turbo, the engine bay temperatures can rise much higher than a standard car, with the only exit for heat being under the car (around the under tray) or through the gaps in the bonnet, or being inducted by the engine intake.

Also at speed, the pressure within the engine bay can become high, which is good for ram induction, but not great for airflow through radiators, oil coolers and intercoolers. Also because the pressurised air will be hot, it is not good for power anyway.

The airflow being forced under the car also reduces ground effect and stability at speed.

Another issue is when the car is stationary, all that heat soaked in the turbo housing, exhaust manifolds, radiator and intercooler will release into the engine bay.. On our 3.2 engines we have found with one which is quite highly tuned to around 700 ft-lbs of torque that the engine bay heat when coming to a halt in the pits was enough to melt or deform nylon tubing in the vacuum management circuit.

The solution to this is to use bonnet vents of exactly the right size (too big is as bad as too small) of a design to pull air from the engine bay at the speeds the car is likely to spend most of its performance life at. Over the last year we have done a lot of research into this and have had some real success improving engine bay airflow characteristics, which improve intercooling, radiator cooling and even core engine temperatures while also making an improvement to promote more airflow over the car and less under it.

Anyway, my main point is.. think about your intercooling and the big picture, it will make a real difference to how fast your car will be on the road or track.

In answer to Carrera's post on how much boost to run with his setup, he could go as far as 1.2 bar of boost from experience, but I would probably recommend 1 bar is safe as has already been said.

With forged pistons and some detonation monitoring and avoidance I would say he could run much higher

Hi Jon, on another thread for the 944 turbo you set out a series of mods to hit 300bhp and then the jump to 400bhp. Is there a similar route with the 924 turbo? A series of must haves and the target bhp achieved if that route is followed.

In my case

Head refurbished
Fuel system refurbished and working well (metering head, WUR, injectors etc)
FMIC - installed
S1 + 951 hybrid turbo - to be sourced, refurbed and installed
Stock waste gate - checked and OK
Removed centre exhaust silencer, straight through rear box
MBC - installed
Boost gauge and AFR - installed
EFI - on the back burner for the short term

The next steps...........?

Dump valve - is it really needed as I will be loosing the recirculating valve on the stock S1 turbo?
Warmer cam?
Vernier pulley?
I have a refurbed WUR on the car and an adjustable 'bolt', just needs putting together and tuning
?
?

I need to decide on the piston route over the weekend and get them ordered asap due to lead times for supply. The choices are-

Stock Mahle pistons - circa £1100 (my engine builders personal choice)
Diamond forged pistons with coatings - circa £600 plus postage and import duty - here
JE or similar forged - no idea of spec or prices at this point

Also do I buy the 87, 87.5 or 88mm? I have 3 spare blocks so oversizing one to near its maximum 88mm is no issue

With the turbo you are thinking of, I think you will be limited to around 320 bhp in my own opinion, maybe a bit less, it can change from build to build and spec to spec.

Fuel injectors, metering head and other parts will also limit you, but lower than the turbo. I might recommend an early 928 fuel metering head, connected to 8 injectors in the intake, one set in the normal location, another set further up almost at the plenham or on the opposite side of the plenham, this will create its own charge cooling effect and push the fuelling limitations further into the power league.

Ignition wise, there would need to be a little bit of development to find the ignition timing that works best in each mode, on boost, off boost, on load, off load, and rpm levels.. once this has been found, then the distributor re-curved to provide the best ignition curve to compromise and get you into the right ball park.

I would also recommend an improved FMIC as works with the 944 turbo.

You will also need a better exhaust system, from the head through to the tailpipe to get much beyond 300 to 340 bhp...

Wastegate will need to be a 924 dual port version, such as a modified tial.

Pistons, I would go with JE and have a few custom tweaks designed into them.

Conrods, I would probably recommend some H-section ones from a good source, I think the standard ones would not be my personal recommendation beyond about 290 bhp, they will go further, but for how long.

Bore, I would stay as close to standard as any of your blocks will allow, that way if you have a disaster then there is scope to repair it or go one size up.

Intake manifold, I would not trust this to make power very high up, would recommend something better is fabricated.

At the stage you are at now, I would recommend that there is the chance that you can go in several directions, I would recommend choosing your route carefully, you have the chance to go in several directions, which will be pivotal in the future of the performance delivery of your car.

So, how much power would you like sir?

At this moment in time with what I currently have to play with, and the fact a working car is better than no car, north of 200bhp would put a smile on my face, however I'd be really, really happy with a reliable 240ish bhp which is in line with a CGTS, which of course ran the 928 fuel dizzy you speak of. Of course this happiness is often short lived once you have driven it for some time and the power hunger pang starts to bite again. I have studied the CGTS and club sport set up which at 1.1 bar was good for 300bhp. Getting north of 250bhp is not on my radar for the current stage of tune I am working towards, however once my car is back on the road I would start the process towards the next level of tune. Then further copying of the CGTS and the upgrades you mention would be on the cards.

I spoke with my engine builder earlier and he didn't seem too excited about JE pistons. But then you only know what you know and he favours the OEM Mahle. I want to order a set on Monday/Tuesday to avoid further engine build delay. So some pointers on brand and spec would be appreciated.

It may be the case I start another engine build once this car is on the back on the road with a wilder set from the outset and aiming for 300 bhp from the start.

I would have to recommend you follow your engine builders advice with pistons even though I do not agree. Simply put, if you use a piston he does not like, anything that happens to that engine will be down to the pistons. To an extent, if this happened I might not blame him. Anything less would be like asking Jamie Olivia to make dinner following Delia Smiths cook book

Any advice on benefits of adjustable WUR and RPM controlled CSV http://930wur.com/?

I think every CIS Equipped car should have an adjustable WUR especially as they age so you can maintain the correct system and control pressures

An adjustable WUR Will also allow you to move your fuel curve up and down the load range, other tweaks allow further manipulation

Controlled CSV is handy and easy to do, ideally weld a boss for a second CSV into the intake before the throttle body for good mixing, use a 1 bar pressure switch, a rpm trigger and wot switch with a little logic so it only happens when you need it

Another cool device is plumbing a electronic fuel injector between the system and controll pressure lines with a variable pulse width generator with a control knob to set altered pressure or hooked to a map sensor to alter pressure relative to intake air pressure can provide additional fuelling, we have done this for years to 924 turbos, Carrera GTs 911 turbos and even turbo 928s with a great deal of success. Used to be one of my secret weapons in tuning CIS Turbo cars, but now the market has shrunk, the cat can be let out the bag!

I remember this now or at least i think i do. You had done loads of development work on the 924 NA head, adding material etc. and that guy tried to palm a free head from you, secretly aiming to copy it, then probably sell copies?

I applaud anyone having a go at running the CIS to the max - I was going the same route until I plucked up the courage to have a go at a standalone. I even got hold of a brand new never used fuel distributor metering head.
There seems to have been lots of different approaches over the years. I think the Mercedes 450 V8 fuel distributor also works well for the 8 injector approach.
If you're gunning for 240-250hp to start with Steve, the standard system will support it with some adjustment.
As Jon has said, above that you really need the 8 line fuel distributor or a method of supplementary fuelling. That electronic fuel injector with variable pulse width sounds like the best route to me.
There was a guy who ran a similar system a few years back with 2 large electronic injectors running with CIS through a fuel controller. He also had some kind of piggyback for the distributor so he could control the amount of timing retard on-boost. Along with this he ran ARP con-rod bolts, ARP headstuds and forged Mahle 87mm VW flat tops. His head and block were machined to a fine finish with a 2mm copper headgasket fitted. All this allowed him to run 2 bar boost with no issues. With his K26/K27 hybrid, custom inlet, and a decent intercooler he was probably making more than 400hp.

Going back to pistons - if I was replacing my own or needed to buy a set I would buy forged. I understand what you're saying Jon about going with what the builder is comfortable with but at the end of the day it's a lot of money for OEM cast pistons and it's not his money. Any piston will die of course with detonation but at least the forged variety run cooler to start with. I just can't see the logic in paying more for cast. The only reason I'm staying with mine is because they're mint and hopefully I can stay away from detonation with the standalone. Also, I can't afford to change to forged at the moment.

You really should get your own 924 Turbo done Jon, your ideas and plans on tuning are exciting to read.

Wes, you remember right.

I have so many projects I should do it breaks my heart, we do not have enough time in the day for them, to be honest we do not even have time for a lot of customers projects and are changing the way we deal with them.

But I will get a 924 Turbo project underway this year, it may be a winter thing, or it may start a little sooner.

But I also need to get my 944 Turbo cup and 968 Turbo S sorted as well, not to mention restoring my 964, continuing my Boxster turbo project (I was SO tempted to just put a 944 turbo engine into it!!) and last year I inherited my fathers car, which sorely needs restoring and love... Not enough hours in the day... Especially when customer care needs to be my biggest concern.

Yeah, I bet it is hard getting round to doing your own cars when you're trying to run a business.
That's a nice line-up of cars - in particular the holy Turbo trinity of 924,944,968!

I had someone on 924.org recommend reversing the coolant flow and using an electric pump instead of the standard one. Do you think this would be possible without causing other issues? The idea was to cool the head first and so raise the detonation threshold.

The other method I've seen is having the coolant exit at the rear core plug, go through a second rad then into the rear of the head where it would exit at the front and go straight to the rad. This obviously loses the bypass and thermostat. I am wary of getting rid of the thermostat because as I understand it, it helps pressurise the system and raises the boiling point.

I have a feeling I'll probably be satisfied with 300hp. With my low 7.5:1 CR, 951 cooler and K26/K27 along with the standalone management, how much boost do you think I'll need to run to achieve 300?

Is it worth doing anything with the head? Are there any easy mods worth doing or is it better to leave it standard?

The important thing to remember is...

The coolant enters the front of the block and exits the front of the head.

The head is a big aluminium block, which has an awesome capacity to absorb heat

The head is thermally coupled to the block via conductivity through the head gasket, coolant and head fasteners.

There are coolant pathways through the head gasket not just through the back of the block into the head, but also through the the entire length of the head gasket. The hole size is restricted to promote correct coolant flow between head and block along its entire length with slightly more of it traveling the length of the block and back across the length of the head, but along the way combining with the minority which will be flowing directly up through from the block via the small waterways that join the two.

Even without flow you will get thermal conductivity through these small waterways.

In effect, what happens is that there will not be a massive difference between the two ends of the block and the two ends of the head. Although there will be a difference, with a magnatude dependent on the level of tune of the engine. Which can be addressed through head gasket modification and altering the quantity of coolant flowing through the waterpump, which can be done by altering the dimension of the waterpump pulley.

To be honest, I do not think for one moment you will have a problem with the thermal management of the 924 turbo engine in almost any performance level. There are also uprated radiators that you can choose from, such as switching to a 944 radiator, or even one of the uprated ones available for the 944. and then you can switch to dual cooling fans, again from the 944 range.

But then there is how you tune the engine, which can make a massive difference to the amount of heat you need to manage. I think one of the problems that 924 turbo owners have had in the past is with ignition. This is often underestimated or even distrusted like witchcraft and so ignored or "left be".. But with experimentation you can find where your ignition is bet suited timing wise, and therefore mechanically map the ignition to provide a good aproximation of where you want your timing in each load, boost and rpm site.. More often than not, tuners of old school ignition systems will tell a distributor company "this is what I have, please modify the ignition curve to what I need", the distributor companies will follow this request, in exchange for the tuners "green" and he will get what he has asked for, when in fact he needs to be much more specific, and treat the decision of ignition timing to be performed after the engine build, after running in and just like a mapable system, when he is actually tuning the car.. Not only this, but he needs to accept he might not be right first time.. the problem is, most people at that stage loose patience and want to go go go and enjoy the car.. All this results in poor performance and a whole load of energy being converted into heat, which needs to be managed.

300 bhp, from previous experience, you should be able to hit this with about 1.2 to 1.4 bar of boost, dependent of course on the rest of your package. Exhaust will be critical to getting the power you want, as will other metrics of your build.

A good example is the work that we have done with 944 turbos. I mention them because we have tuned far more 944 turbos than I like to think of. Anyway, the cars we modify with 295 BHP and the ones we modify with 420 bhp, have something in common, apart from being the same used standard 2.5 engines, they all run around 1.2 bar of boost. The difference is in the support hardware, intercoolers, fueling, exhaust, turbo specification and ignition. To get one of the 300 BHP examples up to 400 bhp, without the support hardware, if possible and safe, would probably take twice the amount of boost. But the right support hardware makes the extra power come to the party without needing more boost. Thats the key.. And to be honest, the thermal situation with a 250 bhp or 420 bhp 944 turbo, they are probably the same, or it is even possible that the 420 bhp car has to deal with less thermal management, because the power has been made through efficiency improvements, and that is the key.

Properly tuned, with the right kit, your 924 turbo will make 300 bhp with less wasted energy turned into heat to deal with than a 220 mildly tuned one.

I would not worry about the head, I would worry more about your strategy with the intake manifold and intake pipework, that will probably make the biggest difference to power.

Found some old photos of Joakim's engine set-up from Sweden. These are from 2003. Engine now makes 400hp+...


JE forged pistons - relevant to Steve's decision-making methinks.


Shows new inlet/plenum. It's now running ITB's.


Shows custom log exhaust manifold flange and GT30 turbo.


Shows large 44.5mm inlet, 37.5mm exhaust valves. Head was worked by some "legend" in Sweden. It was milled 10 degrees and the ports altered. Head has a longer duration cam and uses a stock gasket punched out allowing the use of "pyramid rings" in the block to seal combustion pressure - 80's F1 tech.





Figures from first dyno run back in 2003.