924Board.org

[dreamgts]

Hi Guys, I have a query about turbo installation, it is common for someone to fit a turbo in the engine bay, this might even go thru an intercooler too, thus all plumbing has to be made and fabricated in the engine bay.

I have seen an installation at the rear of a car, I was wondering if this would affect the turbo's performance since longer tubes have to be fitted. This is just an idea for a race car/track car only. This though could eliminate the problem of making things fit. I was thinking of lets say fitting a turbo (or 2)unit where the fuel tank lays beneath the car, thus protection can be fabricated for the unit. piping would go into an intercooler which would be fixed at the back just behind where the back seats sit. cooling air for this could be provided by an air duct fabricated on the roof, while fresh air for the air filters could also be aquired by ducts from the rear side windows, I have seen this type of arrangment on what seems to be a 968 and it looks very profesional and racy. I also read that longer piping would affect the forced air temp. that reaches the engine. Doesnt it say somewhere that the cooler the air is the better, I wonder how cool on air one can go, has anyone here ever investigated air temperature difference?? Obviously a fuel cell will have to take place of the original fuel tank which seems to be quite a large unit.

I was also wondering what maximum BHP could be reached with a balanced euro spec 9:3.1(pistons)engine before it goes boom. My concern here is CR. I intend to balance the lower end and fit a race cam, considering that an upgraded clutch is fitted and probably upgraded tube and gearbox which I beleive has to come from a 944 (86 Model is best???? dont know why?) I belive the factory clutch will slip at 210BHP while the tube and gearbox have to be upgraded should this figure of BHP be exceeded,

I am just wondering since at this stage I could make any alterations needed to the engine lower end to reach 250BHP+, once clutch gearbox are sorted out, it seems that some of the Carrera models had the same pistons and lower end as a 924.

I know that some of the above might sound stupid or adventourous, might even sound unecassary to some too, but hey whats wrong in trying something new?

thanks

dreamgts
_________________
2 PORSCHE 924 (CURRENT PROJECTS)
2 CLASSIC CORTINAS (FINISHED)
1 CLASSIC FIAT(FINISHED)
1 CLASSIC FIAT 132 2000CC(JUST PURCHASED)
4 SUV'S
2 SEDANS
1 OPEL PANEL VAN
WIFES SUZUKI ALTO

[owenexile]

Ive Had no expierience with Turbos , but from what i gather , Moving turbo to the back will also cause a massive delay? I could have mistaking all the info ,but please correct me if im wrong?
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924 1982 N/A
For some reason theres always a earth problem somewhere with this car...

[fiat22turbo]

The rear mounted turbo works well on larger engines with a lack of engine bay space. They have more exhaust flow from their 6 or 8 cylinder engines that can spin a small turbo fast enough to generate some meaningful boost. On a 2.0L you'll need to find a very small turbo that would work with that small amount of exhaust flow (exhaust slows down as it cools, BTW)

The biggest cost issue for the rear mounted turbo (aside from all of the mandrel bends and/or mandrel bent piping) is the remote electric oil scavenge pump to pull the oil out of the bottom of the turbocharger. Those are not cheap, nor would you want them to be.

Many find that the extra piping needed for the rear mounted turbo means that they can run little to no intercooling at the 8-9psi they are running on those systems.

Obviously making this work with a CIS system would be difficult due to the extra volume and potential for leaks causing the system to go lean. Same is true for an AFM style EFI system.

Personally, I would mount the turbo on the intake side of the engine (where there is typically more room) like the 924 GTR and 944 turbo did. Then you can use a stock exhaust manifold or a header and run a connecting pipe under the bell-housing to the turbo.

To hold the turbocharger in place, I would build a bracket that bolted to the engine off the alternator mounting ear and the motor mounting ear to relieve stress on the exhaust system. Maybe cross-brace it off the intake manifold brace.

Run a 2.5" or 3" exhaust out of the turbo under the torque tube and more or less out the normal route. Extra heat shielding may be needed, but don't wrap the pipes as they can crack.

One the plus side, the turbocharger tends to act as a muffler and larger exhaust pipes reduce back pressure on the exhaust side of the turbocharger, which helps the exhaust flow, reducing lag. Many of my other turbo cars simply used 2.5" or 3" exhaust with a catalytic converter and a large glass-pack to keep them legal and they aren't annoying to drive everyday.

Case in point, my team's 2.2L turbo equipped Chrysler/Dodge ran a 2.5" exhaust with a single cheap glasspack (or zoomie in hotrod parlence) out the side of the car in front of the rear wheel. We were measured at about 90-92db at 50 feet. The limit at the track was 95db. The car sounded like a diesel put through the Benny Hill treatment, heh.

The oil and water lines can be plumbed in once the turbo is mounted in place. The turbo should be above the oil fill line on the oil pan, and the pan will be tilted away from you making adding the oil drain back much easier to do. Oil feed line (check with the manufacturer for oil flow specs) could be run off the back of the head and many times only needs to be an 1/8" line but many run 1/4" just to be safe. Water lines are similar only reversed with the water feed in the bottom and the return on the top (allows for circulation of the water after the engine is turned off) and can be tee'd into the coolant line for the heater system or the coolant pipe that runs along the engine block.

The air inlet and outlet for the turbo will be easier to reach, creating a shorter run for both and you can more easily add an intercooler if you need to (I would, but then I like boost and I don't like fixing broken motors)

Hope this helps,
_________________
Stefan
1979 924 Carrera GTS (clone-ish)
1988 944 Turbo S (Silver Rose)

[dreamgts]

Thanks Stefan for a detailed explanation. Fitting the turbo at the back was just an idea I took after seeing something similar on a race 968. I think I got carried away by the looks and the idea. I didnt even take advise from my mech here (oops). Since my 924 is totally stripped from the front end and therefore meaning no headlamps. headlamp motors, re locating the radiator overflow tank, alternator ect, I could fit the turbo on the exhaust side of the engine since loads of space seems to be available.This location and the location you mentioned are our original places of mounting the turbo, although to be honest I would prefer a 'BAE" type fabricated manifold and fit the turbo on the exhaust side just to keep the heat on one side, on this side also ( left looking from front of the car) there is no panel between the inner wheel panel and where the same side headlamp assembly and motor used to sit thus theres a big hole for an air duct to be fabricated to cool down turbo and exhaust should these be fitted on the exhaust side of the car. Im still not sure where the intercooler will be fitted though yet. We have decided on a turbo unit that will give power at low revs 1500rpm??, but right now we are looking into some turbo unit specs which will suit me for this idea.

As for the other query I asked about I would like to add that besides euro spec pistons, the lower end will be balanced, my mech says that with a turbo install I could fit a light flywheel too (any danger here?) i will be fitting a race cam to the head besides the turbo. The standard inlet manifold is still to be used for the time being. something better(throttle bodie) will be fitted at a later stage. EFI will be installed too and have decided on Megasquirt 2 as an ECU. We also have a good idea of what injectors to use. An intercooler for this setup will also be fitted, I am still looking into intercooler specs and possibilties. Since I would like to go beyond the 210BHP figure and since the engine is at the moment already dismantled ready to go to the engineers for balancing etc, I was wondering if any other mods to the lower end have to be done in order to achieve figures of 210BHP+ without the engine going boom. As I said my main concern is the CR which is 9:3.1 euro spec, is this too high? Car model is 1979 924NA

I know also that I will have to consider other stuff such as clutch etc since this will slip after or at 210BHP but since certain things will be done in stages I will simply have to keep boost down untill this side of the transplant is achieved.

So if anyone can enlighten me on the above I would appreciate it, believe me I have gone thru the postings many times and still am to find this info.

Also I was thinking of purchasing a donor car for gearbox, tube rear axle(???) disc brakes etc. I have read that either the 944 85 or 86 model would be the best buy any recomendations please.

I have in 2 days contacted 4 sellers who have (donor cars)944's for sale in the Uk which is the cheapest to buy and ship to Malta, unfortunately these are only accepting bids from within the UK. i will have to be patient.

thanks

dreamgts
_________________
2 PORSCHE 924 (CURRENT PROJECTS)
2 CLASSIC CORTINAS (FINISHED)
1 CLASSIC FIAT(FINISHED)
1 CLASSIC FIAT 132 2000CC(JUST PURCHASED)
4 SUV'S
2 SEDANS
1 OPEL PANEL VAN
WIFES SUZUKI ALTO

[ic932]

Hi, I've been reading your post regarding turbo charging your 924. I may be able to help regarding parts.

I'm based here in the UK and often buy 944 parts cars for my own projects. You are right about the 86' models. I have 2 both with 3litre 16V engine conversions.

The parts I have avialable and that you might be interested in are as follows.

- Gearbox 944S. Sronger then the 8v with good ratio's that would suit a turbo application.

- Rear suspension beam complete. 86 turbo. Fitted with stock 944 calipers and discs.

- Torque-tube/gearlinkage and usable clutch kit inc. bellhousing ect. 944S2 so higher clamping force. edit, may not have a 931 bellhousing anymore? Come to think about it you would also need a 931s2 late 82 model flywheel to use these clutches...

- Front turbo hubs/spindles/brembo calipers and discs.

And much more to list.

I have never shipped this sort of weight to Malta before, in fact I've only sent small suff to Malta (SPARKY). But I'm sure it's all palletable.

Regards,
Dave.

[Martijnus]

[Rich H]

Rear mount turbo has been done on smaller engines too in the UK, biggest problem on the 924 is the fuel tank, do you really want a red hot turbo under the tank...!
_________________
1994 Lotus Esprit S4 - Work in progress...
1980 Porsche 924 S2 DITC Turbo - Original spec
1978 Homo-Sapiens - Tired spec
1953 Landrover S1 - Pensioner Spec

[Joes924Racer]

No he want s to of them, Yea dual mounted rear turbos.. cept
its just a 4 banger so it wont work..less you split the exhaust from 4 into
2. Wonder if 2 ex.outs would spin the turbo. Thoughts
_________________
1979 porsche 924 Na
1980 porsche Turbo 931GT Replica
Have u ever driven a turbo.

[ideola]

Fuel tank is in the rear of most vehicles, is it not? And from what I understand, rear mounted setups operate at a fraction of the temp of front mounted setups. A turbo back there wouldn't be any hotter than the exhaust pipe or muffler that is already sitting beneath the gas tank...

The thing to remember about all of this is that the forced induction solution you want MUST be designed as a COMPLETE SYSTEM. There are tons of nay-sayers regarding the rear mounted turbo setups, but there are a lot of guys running them around here that swear by them. The exhaust dynamics at the back of the car are completely different than at the front. You have to select turbine and compressor sizes accordingly, you can't just swap in a turbo designed for a front mount and expect to have good results.

The one company I'm aware of that specializes in this spends a lot of time on each platform fine tuning their setups for a specific application, getting the turbine and compressor sizing just right. So while it is true that the exhaust is cooler at the back of the exhaust tract than at the front, it is still possible to come up with a turbine design that will scavenge what heat is there, and spool up based on your desired characteristics.

Same thing goes for lag. If you have a turbine that spools up at really low RPM, and a properly configured compressor, you can essentially keep the charge tract pressurized from near idle, thus essentially eliminating lag. Of course, the compressor has to be large enough to still perform at adequate efficiency higher in the RPM range so that it doesn't run out of breath. One of the reasons larger compressors aren't used in conventional locations to overcome the low RPM vs. high RPM tradeoffs is because of size constraints. A rear mounted system has nowhere near the same size restrictions as a front mount, so there is much more freedom to select really LARGE turbos that can produce boost over a much wider range of operating scenarios.

Point number 1 is that a rear mounted solution is feasible.
Point number 2 is that a rear mounted solution (like any forced induction application) MUST be designed as a complete system.
Point number 3 is that no one to my knowledge has done this on a 924, so there will undoubtedly be a significant amount of trial and error involved to get such a solution to perform optimally.

This last point is the biggest impediment, as few of us have adequate budget to do the R&D ourselves, and the aforementioned company isn't going to spend the money to R&D something for a worldwide market of...well, let's be realistic...one or two cars.

Just the same, I would love to see this done, as I think once the system was optimized for the 924, it could be the lowest cost and least difficulty for converting an NA to FI.
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erstwhile owner of just about every 924 variant ever made

[Rich H]

Granted, but I'd certainly not be happy with a fuel wrapped turbo... The obvious muffler space has fuel tank on 2 sides - I'd worry about that as the turbo WILL get much hotter than a muffler... turbo is doing work on air and converting heat and pressure (Mostly heat!) and is inefficient (As in less than 100%) the inefficiency will end up as heat...

As long as you manage the heat properly then no problems...

As for the rear mounted turbo as has been mentioned biggest problems will be the length of pipework. Lag will be greater due to the longer pipes, but not that much longer and inter-cooling is unnecessary if you use external pipes for the charge air as it'll cool on the way to the engine
_________________
1994 Lotus Esprit S4 - Work in progress...
1980 Porsche 924 S2 DITC Turbo - Original spec
1978 Homo-Sapiens - Tired spec
1953 Landrover S1 - Pensioner Spec

[Martijnus]

The fact that i've never seen a manufacturer do this stock says enough for me.

It's not efficient.
_________________
"Rule: Turbo's make torque, and torque makes fun." (C. Bell)

924 "50-jahre", 1981.
MSII/extra, LPG, ITB's, 5lug.
To be turbo'ed in a while.
Killed her at the Nurburgring, Porscheless at the moment

[Rich H]

Not the most efficient but a feasible option for an add on. a factory install would keep all the oily/hot/complex bits on one place - under the bonnet/hood. Which is great when working with a factory of designers and an empty engine bay...
_________________
1994 Lotus Esprit S4 - Work in progress...
1980 Porsche 924 S2 DITC Turbo - Original spec
1978 Homo-Sapiens - Tired spec
1953 Landrover S1 - Pensioner Spec

[ideola]

[Martijnus]

[ideola]