924Board.org

[mads_gedebuk]

Hi all

While i'm waiting for my new workshop to be finished i'm starting to plan the performance upgrades i want to be done on my 931.
The goal is to make 300whp and 1100kg.

This is not a budget build(i want it to be done right) but i don't want it to get all crazy so i guess there are room for decent turbo, internals and ecu.

I'm an aircraft technician and F16 crew chief but are currently studying mechanical engineering at university. I have(well soon again) a well equipped workshop with lathe, mill, MIG and TIG.

The build limits so far:

LHD
Stock G31
EFI
Internal wastegate
Stock turbo location
FMIC placed in front lower valance(maybe air/water)
No A/C
96 octane
Street legal(Denmark)



Please only post proven ideas as i wrote, this is not a budget build, but i will not be making a test mule for the Internets enjoyment

Looking forward to hear your ideas or just linkt to build post that send me in the right direction.


/Mads

www.bruunsgarage.dk
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931 Current status: bits and pieces

[morghen]

What do you want to use the car for? Or is it just an exercise to see a number on a dyno plot?

I used a K27/k26 hybrid turbo that gave a dramatic and impressive power delivery on the 2L S2 engine.
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https://www.the924.com

[mads_gedebuk]

[morghen]

Right, then HX35 +VEMS but I think its a very tight squeeze in the stock location...perhaps move it forward a bit...you need to do a custom manifold to benefit from the new turbo anyway.

Regarding the K27 hybrid, how similar? the different wheels and compressors make a world of difference...as well as the turbine you used and the amount of advance you run off and on boost.
I ran the smallest inlet K27 compressor and wheel with the #6 turbine and the ECU from a Carrera GT, that was quite a bit of difference to the normal turbine, car drove 265km/h but you needed to ride the boost wave to be effective.
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https://www.the924.com

[Carrera RSR]

Hi Mads

One proven result for reliable 300+RWHP is a full GTS motor from Mittelmotor in Germany. Uses forged pistons 8.0:1 CR, MLS HG + ARP studs, their own head design, warmer cam, K26 26xx 6.10 turbo, GTS fuel metering and CIS..... NO EFi , GTS intake manifold, FMIC in front of the radiator, stock waste gate but circa 1.4bar I believe, stock waste gate can be made in to adjustable dual port, NO standalone ECU just a programable electronic distributor

https://www.mittelmotor.de/cms/en/4-10-rennsport

Vid of engine build and car. https://www.youtube.com/watch?v=STVYcsejP5c&t=4s

Car runs in FIA Historique racing with circa 395bhp (crank?). Came 6th or 7th behind their own 914/6 and 911 Carrera RSR's at Nurburgring last year. So proven results. Won't be cheap but looks and retains original parts and look

If I knew then what I know now, my money would be spent on their motor versus the £5k on my engine rebuild and further £2-3k on other performance enhancements under the bonnet.

Steve
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1980 931 - forged pistons, Piper cam, K27/26 3257 6.10 hybrid turbo, 951 FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife
Now www.924board.org/viewtopic.php?t=34690
Then www.924board.org/viewtopic.php?t=31252

[Carrera RSR]

Or drop in a 2.2 5 pot AAN Audi motor for 400+bhp

https://youtu.be/UbBow08jRjY
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1980 931 - forged pistons, Piper cam, K27/26 3257 6.10 hybrid turbo, 951 FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife
Now www.924board.org/viewtopic.php?t=34690
Then www.924board.org/viewtopic.php?t=31252

[Cedric]

Sorry, but mittlemotors numbers are not correct, the 26xx wheels just can't flow that much, they seem to use very large corrections on the dyno numbers aswell, anyway, not a discussion for this space. Though they obviously make good power, but it isn't exactly the most simple or cheap solution.

According to my simulations a Mitsubishi td07 #7 combined with a 19t compressor should make a really nice responsive turbo for 300-340hp. The mitsus are very well regarded among us who works with this. Would try to keep it on the exhaust side for minimal exhaust manifold volume. Preferably twin scroll. Though td05 is a beter choice they are much harder to come by.

It's possible on the stock manifold aswell as Joakim has proved with almost 400hp on it,but not optimal, I think his rewelded manifold with garret flange is for sale btw, maybe the turbo aswell, would be close to bolt on.

Add a light port and cam to your list, will make it easier to get the power at the top end.
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1980 924 Turbo
www.instagram.com/garagecedric/

[Cedric]

If you can find one a TD05 16g Twin scroll turbo would be my preferred weapon of choice. The TD05 have larger wheels and better efficiency than the 04s, at a higher price point though. A well proven turbo for these kinds of power levels.

Making it twin scroll would be a preferred solution for an engine like ours with fixed cam timing. Then you will have good separation between the banks, thus low levels of residual gases in the cylinders, this will make it possible to go for much more aggressive timing. And also make it possible to use far more aggressive cams when it comes to overlap and exhaust duration. This was shown on Joakims engine, which ran much better with the TS manfold and had much lower EGTs. Its the one in the video below. Though a log TS manifold would most likely made similar results, and is much easier to build.

https://www.youtube.com/watch?v=Maae0lF1mXs

I made some simulations in the 931 model on the twin scroll subject, but i dont have the data in front of me now, i think the trends were similar to this mag tests, that was disregarding any cam or timing poissibilities.

http://dsportmag.com/the-tech/twin-scroll-vs-single-scroll-turbo-test-the-great-divide/

I would keep the standard intake manifold, not worth the work to build a different one, its pretty ok in std form

Here you can see the IC im putting in my car, it was in Joakims car before, he ran 400hp with this one, even though its not at all an optimum design, it shows there ais lots of room up front for a pretty big one.

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1980 924 Turbo
www.instagram.com/garagecedric/

[924RACR]

I'm actually planning to build/mod a new intake, at some point... I have a stock 931 intake we cut the top of the plenum from. I plan to build a new plenum on the runners with the throttle up front, like the GTS, to fit well with the 951 FMIC I want to graft in.

Shouldn't be too bad, just a bunch of aluminum welding, not having to remake the runners/mounting flange...

I don't plan the turbo swap and exhaust change, at least not yet, still stock CIS for a while, so not the same power targets, however.

I've got plenty of much more powerful cars available to me, no need to make a mess of my one fun little street car to make numbers!
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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[mads_gedebuk]

I knew about the twin scroll so was already moving toward that direction so i guess i'm still going with the HX35...

CIS is out of the question. There are no support locally and i don't want to spend half of the building time trying to compensate for an outdated system.

AAN is also a no go, due to Danish tax. If the engine is swapped the guvernment see the car as it has lost its identity so import tax have to be paid... like 25k$

What have people done to the internals. I have been through the forum and can see that people try all sorts of combination, but what need to be done on it?

Obviously pistons but which? and how about compression ratio?
Then how about rods? are the std. forged rods adequate?
Head work? cam? solid lifters, big valves...?

I guess the list goes on...

I just want to make a good build sheet made, so i have something to work from so i can start to acquire some of the key parts.
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931 Current status: bits and pieces

[mads_gedebuk]

Great idea about using the runners of the original intake manifold... I guess it could be done to resemble the CGTR intake.

I also have an aluminum foundry at home so considerate casting one myself but i would be a lot of work to get it right due to shrinkage and such plus the core would be a nightmare to make.

My daily is a 2006 Mercedes S500 so want my 931 to be the complete opposite. The S500 is really lazy and detached but obviously fast.

My turbo have to be involved but faster than the Merc therefore 1100kg and 300whp.
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931 Current status: bits and pieces

[Cedric]

Why anyone would chose a HX35 for such an application over a TD05 is puzzling.

Rods seems to hold up, at least if you keep RPMS sensible. Joakim has Verdi rods, almost half the weight of the std ones, at a cost though, i wouldnt for a 300hp car.

Forged pistons is definitely a good thing to have here, people run JE, CP, Omega etc

Is it a track car or street car? Makes a massive difference.

Dont forget about radiatior and oil cooler upgrade, which you most likely would want.
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1980 924 Turbo
www.instagram.com/garagecedric/

[mads_gedebuk]

As i wrote the car is just for hooning around and occasionally trackdays i like to think of it as a hot rod style 924.

It will have fibreglass panels, plastic windows and roll cage but just because i think it is cool and enjoy the engineering that goes into making it.

Concerning cooling i plan on shifting to an aluminum radiator and larger oil cooler.

Great to hear that the stock rods can are proven to hold up to that power figures!
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931 Current status: bits and pieces

[Lau Christophersen]

Hi Mads.
The internals in my engine is standard rebuild 924 N/A block with pistons, just milled 2mm down, and then the standard 931 rebuild head on top.

CR = around 8,3:1.

Then I bought a VEMS EFI setup with wasted spark from Peep(Raceboy on this forum) from Estonia.

The turbo will be placed on the drivers side of the engine, ot is a turbo from a 2,9 CRDi engine. (Cheap, maybe i will chanhe it later).

Then an alu flywheel and a pressure plate from a 911 together with a custom made friction plate. The weight of the cluth assembly is around 40 % less than original.
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76 924 (PARTS)
77 924 (PARTS)
77 924 converted to 924S
77 928
79 931
79 931(PARTS).
79 931 Carrera GT look (PARTS).
79 931 with VEMS and opgrades
81 928S +30 cm widebody kit
82 924 (SOLD)
83 928S
86 944
86 944 (S2(SOLD))
89 944 S2 (SOLD)

[Cedric]

If you feel rich you can buy a GTS manifold from sweden for about 18k sek ex VAT from our rally friends

I would wait with the manifold though, far down on the list.

If i remember it I will run different intake runner length in my simulation model and you will see how we can move around the power curve. I think i have a mitsu 300hp 931 model already set up
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1980 924 Turbo
www.instagram.com/garagecedric/