924Board.org

[Fasteddie313]

I suggest this as the first stage of tune for a 931 and believe it will accomplish about 300chp.. I kinda skipped some of this going to “stage next” with my build but will backtrack a bit.. This should serve as a predecessor to “stage next” where things get rediculous..



1. Replace head gasket with choice of OEM or MLS and replace head studs with ARP.

Just do it.. Refresh your gaskets..
I don’t personally buy into the head studs torquing procedure of loosening them and then retightening them..
I would progressively torque from the middle outwards in a cross tightening pattern, in many small stages increasing torque, and do the same after a few heat cycles, and probably every time I have my valve cover off..



2. Find a used 951 turbocharger and graft it’s compressor onto your 931 turbocharger.. Include a new k26 rebuild kit from eBay if you wish..
(Required for my intercooler install to get rid of the 931 compressor housing)
If you have a 2664 compressor their is an Audi comp housing that will work on it, I also have one sitting..

Balancing is not absolutely needed because these weren’t even balanced brand new from Porsche..
The parts are pretty well independently balanced as they are, and is the way it was done when new..

Just take the compressor side off of the one and put it onto the other, probably with the comp side piston, rings, and backplate too, because they can be different..
Tighten the shaft nut very tight and use locktight on it.. Don’t mark it and try to lign it up, just make it tight..

Send it to a shop if you wish but I have found shops to be less than friendly about wanting to modify things..
In my experience they act like it’s rocket science and talk to you like a child..

I would build it myself first before sending it to a shop for balancing if you wish..
IDK.. I just don’t trust them to be honest and actually want to use your parts..

When taking turbochargers apart DO NOT try pulling the comp wheel off of the shaft..
DO punch the shaft all the way through the turbo, after removing the nut, in order to remove the compressor wheel..
Tap tap tap it out the other side.. Obviously remove turbine housing first..
Comes right out..

Turbochargers are definitely NOT rocket science once you get inside of them, they are actually very simple..


Installing a new turbocharger to the car is a whole other ball of worms, getting the housings clocked correctly to mate to the rigid mounts, and cross tightening everything in..

I would install with loose housings and cross tighten to the manifold and block and housings all at the same time so it will clock it’s housings in to perfectly match the angles of the engine..
Tighten what you can on the housings while bolted to the engine after getting it all aligned to the manifold and block mount, then remove it again to finish tightening the housings, then finally install it permanently..
Just use your logic to cross tighten it to where it pulls itself all together into its perfect position..



3. Copy my intercooler install..
Or copy anyone else’s, but I can’t vouch for how well they work, how much original equipment you will have to loose, or how easy/hard they are to accomplish..

I’m not going to jump on anyone else’s IC and say they suck, or why would you want to lose your headlights, or why would you want to cut all that, or add all that weight, why would you want anything but a front mount, etc..

I LOVE mine..
Here it is.. Cheap ass huge eBay China intercooler with almost no cutting and keeping all other original accessories..
But NO AC! Will not work the same with AC..

Everyone has different opinions on their intercoolers and what they do them the way they do and whatever..
I like mine the best so I’ll recommend mine, because I know it works, and I like to keep everything else very original..

Maybe I’m blinded by something, because to date no one else has yet copied this intercooler, which I don’t understand, but whatever..
Probably having to change the turbo.. But it works soooo good..


These 27x9x4 universal intercoolers you can find on eBay fit and maximize frontal area..


But they may be overkill..
I hypothesize that these slightly smaller 27x7x2.5 intercoolers will also fit superbly and make the install a little easier..



Having 2.5” in/outs would leave more room and not require 2.5-3” 90 adaptor elbows..

I think they are about the same size except they have a 2” thick core instead of a 3” thick core, and have 2.5” nipples instead of 3” nipples..

I can attest that the 3” model does fit like a glove.. 2.5” model just might be a bit easier, but I’d still go with the 3” as I know it fits remarkably well and looks amazing..
The 2.5 might not end up as nicely flush afterwords..

It will require you to hack just a bit off of the back side of the tow hook and shave a small amount of the sheet metal where the nipples go out the sides..

IC plumbing ends up looking like this...
Note, I have since upgraded and/or changed many of these hoses and clamps, but the concept is still the same..


I did eventually find it more tidy to use a 2.5”-3” 90 elbow reducer on both sides, rather than the straight reducer and elbow pipe shown on the right in the pic..

On the left where their is an open spot by the hammer head, use a long 90 hard pipe from the 90 reducer off of the intercooler to shoot up to lower charge tube.. Cut to length..

Make a temp sensor bung HERE like this..



Drill a hole in the pipe and weld a 3/8 NPT bung over it, install sensor..
3/8 NPT coupling from hardware store cut in half makes a good bung..

Steel piping because cheap/easy.. You don’t need stainless.. Not rocket science..

The curvy 2” hose from the compressor to the 2”-2.5” adaptor pipe in the middle of the crossmember is from a..
Gates RAD hose 21216
For a lot of Ford 5.0s from 83-96
Cut about where these red lines are..


Clearance for this curvy gates hose requires shortening one steering rack bolt and removing some unnecessary material from a tab on the engine block..
You will see.. It’s not hard..

IC mounting is accomplished like this..





upload a photo

Longer bottom radiator bolts, with spacers, and a piece of 90 degree angle iron..
Rad bolts go through spacers and angle iron and IC bolts top top of angle iron..
Leave angle iron long on the oil cooler side, straighten the mount on the oil cooler, and bolt oil cooler mount also to the same piece of angle iron..

Makes for an extremely stiff and sturdy mount, but you will now be able to feel the rad fans vibration more than before because it is so stiff..

Bottom of the radiator swings back a couple inches, remount the top of the radiator on the front side of its mount rather than the back side..
Swap top mount over first, swing bottom back, pretty easy..



IC comes out looking beautifully flush like this...
In this first pic you can see where the tow hook boxed section needs some removal for the IC to slip behind it..



As if it were meant to be..

Overall very minimally invasive, keep your pop up lights, original windshield washer tank, basically everything is left OEM and operational..
It works with the original oil cooler and lines too, but hard banjo ends of lines need just a little rebending to clear over the top of the compressor housing..

Install a BOV if you wish, anywhere you wish, to atmosphere or recirculating, or not at all..
I prefer my BOV to atmosphere and would probably put it under the car right after the turbo if I was doing it again.. Credit to Cedric for that idea..

Now, after installing a wideband, you can turn up to around 15-17 psi on a stock US fuel system.. Just watch your AFRs and you can turn it up untill your AFR gets to the high 11s and stop there..
Easy 15psi, probably a bit more..

To enjoy excellent AFR control, run leaner for more power, and turn up to the max of what a US fuel distributor can provide, proceed to step #4..

But otherwise congratulations!!
With a serious intercooler your 931 engine is now damn near bulletproof, and 15psi is pretty darn fast!! You won’t be getting smoked by minivans anymore..

Bulletproof as in 13.5 AFR at 10 psi would be dangerous on a non-intercooled engine, but with a good intercooler it’ll be fine..
931s blow up in my opinion because they don’t have intercoolers, so even being just a bit out of tune could damage them severely.. An intercooler is like a huge safety net, not only can you run leaner on purpose but screwing up a bit and going lean a couple times won’t make your engine explode as it would without an intercooler..

Just the intercooler alone at the same PSI will add noticeable power..
And next in step 4, just raising your AFR from 10.5 to 11.5, safely because now you have an intercooler, will also gain noticeable power.. Even without turning the boost up at all..

I think I run about 13.0 AFR at my OEM spring pressure, it’s fine.. Without an intercooler I wouldn’t try that..
Spring pressure is like.. Light load..

No cooling issues whatsoever with stock rad and stock rad fans!
Adding an intercooler is like adding another radiator.. Engine runs MUCH cooler..

Recommended cooling mods:
Bypass heater core or create another circuit around it with 2 Tees for better coolant flow from back of head..
Install lower temp thermostat..
Control rad fans to lower temp accordingly either with lower temp thermo switch on rad or control with megasquirt against your coolant temp..

Stock rad and fans are beasts and work just fine..


4. Buy a microsquirt and load it with frankencis firmware to control your frequency valve. Install and wire required sensors..

RPM signal to green distributor wire..
3 or 4 bar map sensor.. Get a good one..
Wideband O2 sensor wired appropriately after controller..
That’s all you REALLY need.. Add the following if you want..
TPS (ask about big bore s1 TB with TPS)
IAT/MAT
control rad fans
Coolant temp
Any sensor you can imagine for logging purposes..

Ask me for tuning help when you get there..

Basically with your VE map all at 100s tune your old AFR screw to get your idle you want, and never touch it again..
The rest, just adjust your VE map to give you whatever AFR you want at any RPM/loads you want..
I think I run about 14.7 all the way to 100 kpa, drop to about 13 by 120 kpa (0.2 bar of boost) and then to 11.0-11.5 AFR from about 150kpa (0.5 bar) all the way up to the moon..

When tuning boost I like to first tune for about 10.5 AFR, and once I get that dialed in pretty well, lean it out to the mid to low 11s..
Better to start on the rich side to be safe and lean it out from there, rather than start from lean which may be dangerous..

Whatever VE you end up at for say 14.7 at 100 kpa, put another 20 VE points into it for your 120 kpa row, see what that gets you, and then remove VE from there to get you up to 13 AFR..
Whatever you get from there, add 20 to it for your 150 kpa row (or whatever your spring pressure is) see what that gets you, and then remove some from there to get you the AFR you want.

Then tune for 200 kpa the same way, or 175, then 225, whatever you want and as high as you want to go untill your frequency valve duty cycle gets close to 100%, because that’s going to be where it just will not flow any more fuel..

You’ll feel a good bit more power in the mid 11 AFR range than you will in the mid 10s, so just being able to tune leaner will get you more power, and with being able to increase your FV duty all the way to 100, you will be able to flow more fuel for more boost than a stock system otherwise would..

Your WUR will no longer matter at all..
You can leave it as it is and let it control your warmup (beware of tuning before the WUR has warmed up because it will be another variable), or you could simply replace your WUR with a needle valve to give a constant control pressure, and tune all of your warmup with your megasquirt..
You could possibly also just remove the bimetallic strip from your WUR, to remove its warmup function, and tune it all from your megasquirt.
You should also probably remove the boost line to your WUR, and just tune your boost in your megasquirt, to remove that variable..
You may want to raise or lower your control pressure to get you closer to 50% duty cycle at say 13.0 AFR @ your spring pressure, to give you more room to add more fuel on top..

You will just have to see what you get and adjust from there..
It would probably be best to just set your megasquirt to copy exactly what the original lambda system used to do, and adjust from there..
It’s all pretty easy and very stable.. CIS gives quite a stable AFR and then you just move it a bit with the frequency valve control..

Tune it to max out your fuel flow by upping boost to probably around 18psi while raising freq valve duty cycle.. Small increments..

Aim for like 10.5 AFR and as you get good at it and more confident in your tune increase it to around 11.0-11.8 AFR..

Be able to make nice logs of everything for further tuning review..


You can’t watch 10 gauges/sensors at a time in the real world, but your logs CAN, and you can go back and look at them to see exactly what is happening in all aspects so you can tune from there..


If anyone ever gets this far we will work on it more then..


5. Have a very fast and reliable 931, and try not to kill yourself (especially in the wet)..
It’ll RIP!!

These are all quite simply accomplished with some research but I will edit this OP and further extrapolate starting now..

Pretty darn easy..

I keep getting comments on this recipe so I might as well outline it..



6. At this time if you STILL want more, you could proceed to STAGE 1.5 and take over your ignition with your megasquirt also, and enjoy complete ignition timing control for a bit more power..

7. If you STILL want more before or after step 6 you could use your megasquirt to transition into full EFI if you wish, or move to STAGE NEXT with a V8 fuel distributor, either way giving you more fuel capability than your engine could ever use..
Either will give you anti-lag capability, full fuel cut, 2 step, etc..

For extra credit points, have your megasquirt spray a wet shot of nitrous just for fun

Do whatever you want, spray some meth too..
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80 Turbo - Slightly Modified

[924RACR]

Nice!

I'd be worried about an unbalanced turbo, but if it's working for you, it may simply be an issue of longevity...
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[Cedric]

[Fasteddie313]

I guess it just depends on how diy you are..

Old parts are balanced separately, new units are balanced as an assembly..
Old parts can be mixed and matched and keep what balancing they have, not new parts..

Yeah ok sure balance it.. If your paying a shop $800 or so to build you a turbo then balancing makes sense while your there..

But if you already have your 931 turbo, and can pick up a /6 951 turbo for $150, and a rebuild kit for $50, then your building your own turbo for like $200..

Send it out to be balanced for like $300?
And so the shop can tell you it’s all junk and want ridiculous money to build you a new turbine piston and rebore your bearing housing that is not really needed..

Or take the chance on it lunching itself..
And you buy another used /6 for $150 for a new comp wheel and housing if it gets lunched..
Worst case you also have to buy another 931 turbo or basically almost any other k26 to scavenge a new turbine wheel/shaft for around $150-$200 (that a shop will try charging you like $500 for), if not less, another bearings kit for $50, and build another complete turbo for around $350-$400 if you completely ruin one..

Your gonna have to screw up pretty bad to ever hurt a bearing housing or turbine housing..

MAYBE if your gonna buy a big expensive compressor like a k27 or something, that you would really lose out if it got lunched, then yeah maybe have a shop do it..

But for a 931 turbo with a cheap scavenged compressor from something else cheap?
I say DIY and skip the shop altogether..

https://www.ebay.com/itm/162140843766?hash=item25c058eef6:g:qHEAAOSwdzVXjTJB

As far as I know these old KKK turbos were never even balanced when new back in the late 70s-early 80s...


Still working on this OP..
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80 Turbo - Slightly Modified

[Rasta Monsta]

[Fasteddie313]

Idk.. Don’t want to argue a small detail..

I guess is said that incorrectly..
Modern balancing is assembly balancing, old parts are all balanced separately and therefore retain their balance when moved..

To me it’s not even a big deal to blow a turbo.. Don’t care..
I’ve build like 4 of them, and only had a problem with one I tried indexing because I couldn’t get the indexing and nut torque both right, so my nut backed off and I lunched one comp wheel..
My fist one I built.. I’ve learned more since then..

Don’t care, built a bigger one for like $150, torqued the crap out of the nut and locktighted it.. and the rest of them..

I have been far overspoiling my latest one, trying to blow it up.. Probably 130,000-140,000 RPM
Wastegate basically clamped right shut.. Won’t make any more boost.. Can’t blow it up..

I’m not trying to make it last 100k miles.. Planned on replacing it again before I even had it built..

Looking to build a bigger one again.. (WTB big compressor)
We’ll see what it looks like when I take it apart..

Doesn’t smoke on startup or anything.. No smoke ever..
Sounds like the shops can hardly even accomplish that..

Want to hear another kicker?
Lunching that comp wheel also bent my shaft a bit..
Put it in some V blocks on a dial indicator and straightened it myself..
Doesn’t blow up for some crazy reason..
Imagine that..
Self straightened, “unbalanced”, home made turbo of Audi, 931, and 951 parts, spooled to the moon, doesn’t blow up, doesn’t even smoke, will only make up to like 23-25psi, makes a little more when it’s cold out..

:shrugs:
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80 Turbo - Slightly Modified

[Rasta Monsta]

[jacobroufa]

I really appreciate the breakdown here of pre- and post- frankencis. Still on the fence about IC approach for my 931 but this is very compelling...
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1980 Porsche 931
1981 Porsche 924 Weissach

[Cedric]

Great write up, its good inspiration for people that's thinking about IC mods. My solution was inspired by yours since it can be made to look full original from the top, and fairly manageable modding to make it work, but i made it a little bit different due to reasons. And stayed with my CIS completely stock, which seems to limit it to about 245 hp. More would be fun, but these cars get seriously quick at that power, bet its a riot at a bunch more boost.

Replacing the HG is a good idea, mine was original and started deteriorating and was leaking water straight through the gasket layers into the cylinders=not fun..
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1980 924 Turbo
www.instagram.com/garagecedric/

[Fasteddie313]

Hey Cedric, would some $$ get that lower charge tube printing faster?
Probably should make atleast 3..

I also have a tunable US fuel distributor with most of the frequency valve setup for you if you want it..
Known working and will bolt right on.. Just add a microsquirt..
Will tune exactly the same way as my V8 one, except it doesn’t need any other external DPR controller, but won’t do complete fuel cut..
(I’ll talk someone into trying it eventually)
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80 Turbo - Slightly Modified

[Fasteddie313]

THIS is where I get that “300HP” # from..
That everyone freaks out about when I say it..
Btw...

[Mike9311]

Quite the opposite

You are clearly intelligent and you possess something a bit more rare.... you are free minded

In other words you let your mind take your conscious intelligence and let it wander unconsciously

Its where innovation comes from

Keep it up!
_________________
1980 931 since 1989
1981 Ideola 931 Club Sport
1982 931 Entwicklungsfahrzeug
1979 924 NA ohne 650 mit 471
1982 931 Red Resurrection - 951 IC
1982 931 parts car / resurrection?
1980 924 NA (R&D lightweight)
1982 931 wana-be GTR race car

[Carrera RSR]

You say your US fuel dizzy is pushing 438cc/min? But doesn’t the injectors top out circa 360cc/min??
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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

[Fasteddie313]

[Carrera RSR]