924Board.org

kpasko · Joined: 25 Jun 2013 Posts: 35 Location: California

does anyone have thoughts on converting a NA '78 to a turbo? fitment/installation a major pain to add a later 931/944/968 turbo onto the stock NA engine? Not worth the hassle given that I can likely find a donor 931 for under 1k?

thanks for any 2c

K

fiat22turbo · Joined: 18 Jan 2006 Posts: 4040 Location: Portland, OR

Its been done a few times, however you'll destroy the values of two cars in the process given the rarity of 931's on the ground these days.

If you can find a 931, buy it and bring over the parts you want from your 78 and drive the 931. There are a lot of changes under the skin that the 931's received over the NA's, especially the ones older than 79.

home-made turbo conversions made without using factory turbo parts has been done with some success, but they all require a certain amount of fabrication. The two major solutions have been:

1) basically to build a new exhaust manifold to mount the turbo in front of the engine. BAE actually made a kit to do this way back in the day, but they are extremely rare. Most build a log-type manifold or even a header.

2) use the stock exhaust manifold (or even a non-turbo header) and loop the exhaust pipe under the oil pan to mount the turbo on the driver's side of the engine bay, ala 944 turbo. Interesting solution with some compromises.

Either way the stock CIS system (if it is in good working order) can compensate to some extent, many choose to convert to EFI to provide more finite control and free up some horsepower and more easily adapt an intercooler.

An oil cooler and bigger radiator should be installed at the minimum.

The stock Audi-based 4-speed should handle a little extra power, but I'd convert to a 5-speed from a newer 924 non-turbo (or even a 924 turbo/944 NA/944 turbo transaxle and torque tube, which will require a different clutch disc). The stock NA clutch tends to have issues with a lot more power and can slip higher power outputs. The NA clutch isn't cheaply upgraded though.

You may want to look at suspension upgrades as well, there are lots of threads on that, so I'll not rehash it here.
_________________
Stefan
1979 924 Carrera GTS (clone-ish)
1988 944 Turbo S (Silver Rose)

fiat22turbo · Joined: 18 Jan 2006 Posts: 4040 Location: Portland, OR

Raceboy · Joined: 01 Mar 2004 Posts: 2327 Location: Estonia, Europe

I guess my projects are invisible to fiat22turbo,so I'll just put these as a reference here:

http://www.924board.org/viewtopic.php?t=21735

http://www.924board.org/viewtopic.php?t=26946
_________________
'83 924 2.6 16v Turbo, 470hp
'67 911 2.4S hotrod
'90 944 S2 Cabriolet
'78 924 Carrera GT replica
'84 928 S, sold
'91 944 S2, sold
'82 924S/931 "Gulf", sold

'84 924, turbocharged, sold.
http://www.facebook.com/vemsporsche

fiat22turbo · Joined: 18 Jan 2006 Posts: 4040 Location: Portland, OR

No slight intended, I was just going off of the first couple of pages of threads in Performance Upgrades. I thought I included at least one of yours though? Maybe not.
_________________
Stefan
1979 924 Carrera GTS (clone-ish)
1988 944 Turbo S (Silver Rose)

kpasko · Joined: 25 Jun 2013 Posts: 35 Location: California

Thanks for the responses guys.

I love the driver-side mounted turbo...i've already removed my AC system so there's that empty compressor spot over there just waiting for it. I'd definitely have to switch to EFI though...though that's not really a bad thing...

i'm lowered/sways/stiff springs, but still on 4-lug 4-speed, so maybe I'll start with upgrading the suspension bits, going with a 931 header/big valves, and EFI, then maybe I'll be ready for a turbo. Just couldn't help myself asking, as I saw an $800 project 931 avail today...

ps my current goal is for hot-street, not race, fwiw.

Shurick · Joined: 15 May 2005 Posts: 524 Location: Russia, Moscow.

Not sure about 4-speed and how much it can endure. But any performance upgrade to the engine will end up with lack of braking force, I'd consider brakes first, tranny second. And, IIRC, 4-speed used another fuel tank, restricting 5-speed gearbox to just come in place.

As for turbo conversion using stock parts from 931 - it's not worth due to the costs and time. There are much more modern and better performing turbochargers in nowadays, for example. One thing could worth sourcing from the 931 is engine head. It has better flow, better combustion chamber, better cooling, bigger valves. But it's a very rare find.
_________________
WBR, Shurick
'79 931 -- intercooled K26-3060-6.10 turbo @ 1.2 bar, EFI+EDIS, 951S brakes, stripped interior, 951 look.
'86 924S -- R.I.P.
https://www.instagram.com/ru_pacecar/

kpasko · Joined: 25 Jun 2013 Posts: 35 Location: California

Thanks shurick, 5lug susp. upgrade is something I've wanted to do for a while, so maybe a good first mod. What are your thoughts about 931 header v. Port/polish/big-valve mod via European motor works? If I can get a 931 for 800, it could be worth it for header + suspension...but then I'd be tearing into a 931 to mod the 924, which might be a bit backwards...

kpasko · Joined: 25 Jun 2013 Posts: 35 Location: California

Here's the 931 in question, btw

http://sfbay.craigslist.org/eby/cto/4071954355.html

fiat22turbo · Joined: 18 Jan 2006 Posts: 4040 Location: Portland, OR

Brakes aren't needed. the original 931's came with 4-lug brakes.

Only if you're really pushing the car beyond legal road speeds will you see a negative impact of the 4-lug brakes.

There are people who still race their 924's competitively with 4-lug brakes.

Make sure you've got good, sticky tires, fresh fluid, good pads and well adjusted rear drums and you'll be fine.

Now if you want to go to 5-lug to move to Porsche wheels and/or to improve the thermal capacity of the braking system, then by all means. That's a worthwhile change.
_________________
Stefan
1979 924 Carrera GTS (clone-ish)
1988 944 Turbo S (Silver Rose)

Raceboy · Joined: 01 Mar 2004 Posts: 2327 Location: Estonia, Europe

I had 4spd gearbox also behind the turbocharged 2.0 and it held ok, no problems. Gas tank is the same on 4spd cars, at least it was where this 4spd box came from (a '78 euro 924).
_________________
'83 924 2.6 16v Turbo, 470hp
'67 911 2.4S hotrod
'90 944 S2 Cabriolet
'78 924 Carrera GT replica
'84 928 S, sold
'91 944 S2, sold
'82 924S/931 "Gulf", sold

'84 924, turbocharged, sold.
http://www.facebook.com/vemsporsche

Shurick · Joined: 15 May 2005 Posts: 524 Location: Russia, Moscow.

kpasko · Joined: 25 Jun 2013 Posts: 35 Location: California

had a thought...

people mention problems with the 931 head because of exhaust header fitting...if I have access to a parted 931 (which I believe I do) and can get a header, I could get either the same exhaust or something aftermarket and run with that as-is for a while. Then whenever the time/$ comes, I could maybe grab the EFI bits from Ideola, giving me a much nicer headflow, fuel/spark delivery, reliability, etc.

THEN, if I wanted to figure out turbo solutions, things would be a bit more in the realm of reason.

Does this seem like a ridiculous way of going about things?

fiat22turbo · Joined: 18 Jan 2006 Posts: 4040 Location: Portland, OR

You'd have to use the entire engine as is in order to have a drivable car. They also like to crack the top compression rings on the pistons and they are expensive to get, many have the pistons (if they are good) machined to fit NA rings or go with aftermarket forged pistons.

If you put the 931 head on the NA block the compression ratio will be too low. Replacing the pistons with flat tops helps quite a bit, but that isn't cheap either.

The 931 head has fire rings for the exhaust ports and slightly revised intake ports, also the spark plugs are on the driver's side, instead on the passenger side. The intake and exhaust from the NA could be adapted to fit by slotting the mounting holes, etc. but why not use the 931 pieces?

The fuel distributor and plumbing for the 931 is specific to the 931 as are the flywheel, bellhousing, torque tube, transaxle and clutch hydraulics. IF you use the stock 931 exhaust pieces you won't have room to use the stock NA starter and bellhousing, which is why the 931 bellhousing mounts it to the other side and runs it in the opposite direction.

Honestly, you'd be better off just building your own log manifold from cast iron Weld-el's to mount the turbo behind the radiator with the stock motor. This way you can run whatever turbo you can find in the proper size, that is common and easy to repair/replace, etc. you can also not worry about trying to fit all of the 931 pieces into your car and getting them to work, etc.

Just my $0.02

The 931 exhaust manifolds like to crack as do the turbo housings.
_________________
Stefan
1979 924 Carrera GTS (clone-ish)
1988 944 Turbo S (Silver Rose)

kpasko · Joined: 25 Jun 2013 Posts: 35 Location: California

thanks fiat, that definitely sounds like more trouble than its worth. TBH, I'm not a huge purist, so if I'm doing a full engine swap or equivalent, I'd probably consider a TDI before the 931...I'll keep thinkin'