Excellent thread topic
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I have loved the 924 Turbo my whole career. Has the potential to be a real monster.
Would you like to benefit from millions of pounds of development to tune your 924 Turbo?, well, that has already been done for you.
Take a look at the 944 Turbo, Porsche took everything they learned from the 924 Turbo, Carrera GT/S/R and fixed a few problems and pushed technology forward some. But as with any evolution, some mutations happened which brought about new problems.
Apply some of these developments to a 924 Turbo, along with the benefit of 30 years further developments in technology and you can turn a 924 turbo into a very competent contender to run rings around even a mildly tuned 944 Turbo.
The first step in advising a spec, would be to ask the budget, you can achieve anything with the right budget. The second question would be the intended use for the car... A very different approach is taken to modifying a car for track or race, compared with a car for the road or fast road.
Probably a good place to start is to outline what I would like to do with one of my less loved of my two 924 Turbo's, which I may do earlier rather than later. If someone does what I am planning, I don't mind, I would just like a little credit for the ideas, which in many cases are the result of over 20 years of pondering. Much of my ideas are based on value for money, as well as performance and also flexibility.
One problem with the 924 Turbo, that Porsche as a company suffered for, was cracked exhaust manifolds. In the 944 Turbo they chose to relocate the turbo to the other side of the engine bay, allowing the use of longer primaries than the 924 turbos stubby primaries.
What I plan on doing is just what Porsche did with the 944 turbo, relocate the turbo to the other side of the engine bay, geometrically to exactly the same location as the 944 turbo and even using a 944 Turbo crossover for roughly 80% of this part of the exhaust. This has many benefits.
One benefit is the ability to use from a wide range of Turbo's developed for the 944 turbo, from the original k26/6 (plentiful and cheap) through to many hybrids, as well as everything that has been learned about the turbo for a 944 turbo over the years, the knowledge learned from tuning 944 turbos can be scaled to the 924 turbo application.
The other benefit is being able to use a complete 944 turbo exhaust system, the back section has always worked, but with this layout you could use a complete 944 turbo exhaust and even the likes of a fabspeed 3.0 inch exhaust system. Not to mention using a wastegate designed for a 944 turbo, such as a tial 38 or 46 with the 944 adaptions.
For the head to the 944 crossover to lead to the turbo, it should be quite easy to either custom fabricate primaries and collectors to either work with a complete 944 turbo crossover, or modify it where it goes from 2 to 1, to mate to custom manifolds or even perhaps the disposable (if damaged or crack) 924 NA exhaust manifold, which could at least be used for initial development to check the viability of the idea.
One other benefit of the turbo in this location is that it makes servicing or replacement of the turbo much more simple than the 924 layout. Especially handy in development of a car.
Lastly the crossover pipe design pre turbo has benefits of exhaust flow being more continuous rather than pulsed, which is not just kinder to a turbo, but allow more to be scavenged from the thermodynamics of the turbo, as well as causing more of an extraction effect on the exhaust ports prior to valve opening. The longer the runners for a turbo, as long as heat is retained in the exhaust charge, the better... there are no real drawbacks.
Now if you are going to benefit from this relocated turbo, with the alternator put back in the same location as the 924 NA, and as many are already doing, you use the 944 turbo intercooler, in the 944 turbo location, then it is not a bad idea to use the 944 pipe layout too and from the intercooler, which then allows the use of off the peg upgrades to intercooler and pipes.
Modifying the 924 turbo intake, to have its throttle body, again a 944 turbo one, to the same location as the 944 turbo physically in the engine bay will allow you to see the benefits again of the 944 turbo evolution, it is an elegant solution, reduces sharp bends to a minimum. Redesign of the intake manifold, to provide nice long runners and a tapered plenham chamber will be a nice improvement.
Next, I would possibly recommend the complete ditching of CIS injection, we have mastered it over the years, using modifications to the WUR and fuel metering head, along with electronic adjustable fuel pressures via the WUR plumbing, can allow a certain amount of fuel curve adjustment, which can be boost sensitive. However, why not benefit from something that is cheap and completely reverse engineered. A 944 turbo DME and KLR combo with maps completely changed to make them 2.0 924 turbo specific, perhaps hand in hand with a MAF sensor replacement of the 944 turbo airflow meter and the addition of a map sensor to bring in boost sensitivity and three dimensional mapping.
You could say use a complete stand alone system, but to be honest, for my own application, I am completely familiar with the DME and KLR software, which has already been and is being modified for flexibility, supporting a 924 turbo with it, will just require a fuel rail being fabricated, the flywheel modified. Combine this with the cheap available 944 turbo DME and KLR ecu's, and you have knock detection, EFI reliability and most of all for me, 30 years of development of the ecu and software.
Just like a 944 turbo, the pre turbo intake would include a dump valve.
Add to this the knock monitoring equipment we have for the 944 turbo, for safely narrowing the safety margin between safe and detonation limits, with individual cylinder knock sensing and automatic individual cylinder retard and re-advance following an event, you can run more boost than normally safe.. this will also work with CIS, which we have been doing on 930 turbo's for a while now as well as EFI on 944, 964-2, 993 and 996 turbo's.
Transmission wise, I think I will be going for a hybrid transmission, 944 Turbo hardened 1st and 2nd, 944 S2 LSD diff in a pre 85 housing, allowing the use of the standard 944 NA rear beam and transmission crossmember. The snail shells are getting hard to get parts for, and the 944 transmission is more user friendly.. another evolution to take advantage of
Engine wise, the modifications to the 24 turbo head would be minimal, the bottom end would be given a good blueprinting and treated to a set of H-section con rods and custom forged pistons with nickel ceramic coated bores.
The cast iron block of the 924, mated to the 924 turbo head, will make for an extremely strong bottom end, which if kept away from detonation will allow some massive boost pressures to be used without issues. And before anyone starts, boost pressures do not cause head gasket failure, detonation does... manage ignition and fuelling with detonation detection and the sky is almost the limit with power.
Budget for this will not be massive, all experimental, but a guy needs a hobby.
I say this setup will work well.. We will find out later in the year
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