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931 stock boost levels /safe boost levels on stock internals
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Carrera RSR  



Joined: 08 Jan 2010
Posts: 2309
Location: Somerset, UK

PostPosted: Wed Nov 23, 2022 5:42 am    Post subject: Reply with quote

For simplicity I'd stick with stock turbo and sandwich a FMIC to the rad.

FYI the 951 IC is not a big issue for a body guy. Took my guy 2 days in between other jobs and cost me £500 labour not including painting. But you will have other mods to do plumbing it in and added costs.

Later 951 turbos have water cooled centres. Not needed if your using high quality oils and consider warm ups/cools downs.
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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
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Carrera RSR  



Joined: 08 Jan 2010
Posts: 2309
Location: Somerset, UK

PostPosted: Wed Nov 23, 2022 5:44 am    Post subject: Reply with quote

MikeDanger wrote:
Still have too much fuel at WOT at full boost (13psi)


Turn up the boost and use the available fuel
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MikeDanger  



Joined: 21 Nov 2002
Posts: 770
Location: Denver

PostPosted: Fri Nov 25, 2022 7:16 am    Post subject: Reply with quote

Carrera RSR wrote:
MikeDanger wrote:
Still have too much fuel at WOT at full boost (13psi)


Turn up the boost and use the available fuel


ive thought about that, but A I don't want to push my luck (at least until my 951 is ready for battle) and B it actually pulls pretty good as is.(well untill it goes too) rich
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MikeDanger  



Joined: 21 Nov 2002
Posts: 770
Location: Denver

PostPosted: Fri Nov 25, 2022 7:31 am    Post subject: Reply with quote

here: https://www.924board.org/viewtopic.php?t=44906&start=0&postdays=0&postorder=asc&highlight=

here is the IC I used https://www.ebay.com/itm/133635760063?hash=item1f1d4fdfbf:g:HlYAAOSwwwVf~iFf&amdata=enc%3AAQAHAAAA4Pk8X4XbR%2FuFgM%2BJVieBiSxzFAIFa2E28BthShgmmxK4TWKCSTRUTDs25h4quyvUXFz6GxA5zvwdqlhA0kAhvG6V8sZI2Z0MeV7%2Fyi8wla7FHfi7E2gz3q21cD0v6YlNbkv6u81yoL6tr1XKtjeJWF8lj4tlmOuWjnPDevlvicAyUsIVK9Q5yoeNPMZ%2FgQWCFoNwatKGP%2BJfKKQb%2Ff%2BYZgNn%2BGYgKMVNO2f5ot31qLI1OdQqSyPlz5zvx4S9m%2BgfVjMwBLn%2F1EmWnXBfnfJeCBj6JaJYsrIZ%2By4lSC%2FtQxAN%7Ctkp%3ABk9SR-zMzbiVYQ (alt+w)
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Beartooth  



Joined: 05 Apr 2022
Posts: 213
Location: Roberts, MT

PostPosted: Fri Nov 25, 2022 12:59 pm    Post subject: Reply with quote

Two reasons I can see why the 931 wasn't intercooled: one was keeping cost under control (given the limited numbers and how many parts are particular to the 931, it couldn't have been a big profit-maker), and the other was to keep it from outshining the 911. I wouldn't say an intercooler is something Porsche absolutely should have done, just that it's hard not to look at it and see how much an intercooler and perhaps bigger turbo bring to the table. My ultimate build would be an updated turbo (twin-scroll would be awesome) and manifold, intercooler, and a longer rod and forged piston setup with around 9:1 compression. Possibly offset grinding the crank to stroke out to 2.2L would make sense, and head work is probably the other place where there are big gains to be had. The trouble there is there's not much middle ground between a typical port and polish and going full custom like the head Mike9311 is working on.

Anyway, my goal would be, rather than pursuing big numbers, just get over the 200 HP mark and make it reliable, responsive, and fairly simple. I'm not quite sure how much compression you could get away with at 200HP, but I'd think with an intercooler, forged pistons, and knock detection, 9:1 should be workable and would make it much snappier off-boost, especially compared to the S1 with 7.5:1... Of course, if I wanted more power, I'd be doing about the same things, except somewhat lower compression. I don't have any personal experience with trying to push the envelope by cranking the boost, but based on everything I've read, lowering compression may not buy that much margin depending on how it's done. The open-chamber emissions heads of the 70's often knocked or detonated more easily than much smaller closed-chamber heads of the 60s despite significantly lower compression. Apparently, the loss of a quenching effect was the reason. A lot of what allows modern motors (both boosted and NA) to run significantly more compression than you could get away with in the past is the combustion chamber design.

My idea for an intercooler would be to fit it under the vent between the right strut tower and battery. You'd have to rework the firewall so you could use the empty space between it and the battery - I don't think you could fit an adequate IC in the space as-is - but with custom end tanks and some baffling to direct airflow through the core, I think it could work well. I do think you'd want to put an electric fan in: not one big enough to keep the IC fully fed, but just to keep it from heat soaking while sitting still. I'm not sure how much flow that vent generates though. Maybe I'm counting too much on it, but I'd hope that once you got up to 30 MPH or so it'd be giving you enough flow. I do have to say that I've seen some setups with the IC in that area, on top of the motor and between the turbo and firewall, that appear next to if not worthless to me. Without a directed flow of fresh air, anything under the hood is going to get little cooling, and without that you may not even be cooling the charge air. I will say that for big power, a front IC is probably the only way to go. Even if that vent gets good flow at speed, it's not that big, and even making the best of it you might have to be flying to get enough air, and maybe not even then. That said, for what I have in mind, the advantages might outweigh the disadvantages. The big advantage would be simplified plumbing: the less ducting the air has to flow through, the less parasitic losses, and also you'd have quicker response. Could be particularly important with CIS, since the longer intake track is, the more A/F transients you're going to get no matter what you do. EFI would theoretically give you the ability to compensate, but you'd still have the longer path for the pressure wave to transit.

One last thought I've had is to experiment with water/alcohol injection. It seems like it wouldn't be hard to rig up a solenoid to open a bleed on the wastegate line and have it set to open when you trigger the water/alcohol injection. Many experts (Corky Bell, for one) poo-poo that idea, and there aren't many scenarios where you'd prefer it over a proper IC setup, but done right, it could allow you to push as much boost as you want until you start blowing head gaskets and such. You could use a cheap on-off setup and just use it close to peak HP, or you could go more elaborate: there are controllers that can be set to modulate the flow based on RPM and boost. There are good reasons some people recommend against it - and having a boost juice tank to fill is probably the least of them - but done right, and depending on one's driving style, it could give all the benefit of an IC for cheaper and without all the cutting and fabrication a proper IC calls for. There's a lot of no-man's-land in terms of tuning, but that's true of an IC setup anyway; get it tuned right and keep the boost juice topped up, and you should never have a problem. In particular, I think the results would be much better than a mediocre IC setup.
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Cedric  



Joined: 27 Aug 2004
Posts: 2617
Location: Sweden

PostPosted: Fri Nov 25, 2022 5:41 pm    Post subject: Reply with quote

Water/meth is quite widely used, not just in this part of the car world:) ideola had it on one of his 931, it absolutely works no doubt about that, the effects have been known since 80years IC is safer though, since without EFI it's harder to include safety strategies like a flow meter for example.
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morghen  



Joined: 21 Jan 2005
Posts: 8889
Location: Romania

PostPosted: Fri Nov 25, 2022 6:57 pm    Post subject: Reply with quote

I'm running ethanol+water injection on my supercharged 924NA.
I'm using fairly little amounts to just mitigate the temperatures during hot summer days but the effect is noticeable.
Any boosted application benefits from some form of cooling and increasing the oxygen levels in the combustion chamber.
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kondzi  



Joined: 02 Jul 2018
Posts: 485
Location: Poland/EU

PostPosted: Sat Nov 26, 2022 2:41 am    Post subject: Reply with quote

Slow down guys

TARGET 220HP +/- 20HP at crank

To do list:
- proper knock detection
- EBC with line to the top of the WG
- ignition management with retard when (almost) knocking
- Sandwitched FMIC
- Stock turbo or newer type (like Mitsubishi TD04) with integrated WG and BlowOff or just with BlowOff, depending on what is there in my car.
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'89 951 US
'88 Mustang 5.0 LX Convertible (factory specs)
'84 911 Carrera 3.2 RoW (factory specs)
'81 931 RoW (TBD)
'81 Ford Capri 2.8i (factory specs)
'79 Ford Capri 2.9 (heavily modded)
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Cedric  



Joined: 27 Aug 2004
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PostPosted: Sat Nov 26, 2022 3:04 am    Post subject: Reply with quote

Sounds good, i would add the alternative to buy a cheap audi turbocharger and take the compressor from(and put on your current turbo) if you find it to much of a struggle to fit the piping to the original one.
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Carrera RSR  



Joined: 08 Jan 2010
Posts: 2309
Location: Somerset, UK

PostPosted: Sat Nov 26, 2022 6:05 am    Post subject: Reply with quote

Beartooth wrote:
Two reasons I can see why the 931 wasn't intercooled: one was keeping cost under control (given the limited numbers and how many parts are particular to the 931, it couldn't have been a big profit-maker), and the other was to keep it from outshining the 911. I wouldn't say an intercooler is something Porsche absolutely should have done, just that it's hard not to look at it and see how much an intercooler and perhaps bigger turbo bring to the table. My ultimate build would be an updated turbo (twin-scroll would be awesome) and manifold, intercooler, and a longer rod and forged piston setup with around 9:1 compression. Possibly offset grinding the crank to stroke out to 2.2L would make sense, and head work is probably the other place where there are big gains to be had. The trouble there is there's not much middle ground between a typical port and polish and going full custom like the head Mike9311 is working on.

Anyway, my goal would be, rather than pursuing big numbers, just get over the 200 HP mark and make it reliable, responsive, and fairly simple. I'm not quite sure how much compression you could get away with at 200HP, but I'd think with an intercooler, forged pistons, and knock detection, 9:1 should be workable and would make it much snappier off-boost, especially compared to the S1 with 7.5:1... Of course, if I wanted more power, I'd be doing about the same things, except somewhat lower compression. I don't have any personal experience with trying to push the envelope by cranking the boost, but based on everything I've read, lowering compression may not buy that much margin depending on how it's done. The open-chamber emissions heads of the 70's often knocked or detonated more easily than much smaller closed-chamber heads of the 60s despite significantly lower compression. Apparently, the loss of a quenching effect was the reason. A lot of what allows modern motors (both boosted and NA) to run significantly more compression than you could get away with in the past is the combustion chamber design.

My idea for an intercooler would be to fit it under the vent between the right strut tower and battery. You'd have to rework the firewall so you could use the empty space between it and the battery - I don't think you could fit an adequate IC in the space as-is - but with custom end tanks and some baffling to direct airflow through the core, I think it could work well. I do think you'd want to put an electric fan in: not one big enough to keep the IC fully fed, but just to keep it from heat soaking while sitting still. I'm not sure how much flow that vent generates though. Maybe I'm counting too much on it, but I'd hope that once you got up to 30 MPH or so it'd be giving you enough flow. I do have to say that I've seen some setups with the IC in that area, on top of the motor and between the turbo and firewall, that appear next to if not worthless to me. Without a directed flow of fresh air, anything under the hood is going to get little cooling, and without that you may not even be cooling the charge air. I will say that for big power, a front IC is probably the only way to go. Even if that vent gets good flow at speed, it's not that big, and even making the best of it you might have to be flying to get enough air, and maybe not even then. That said, for what I have in mind, the advantages might outweigh the disadvantages. The big advantage would be simplified plumbing: the less ducting the air has to flow through, the less parasitic losses, and also you'd have quicker response. Could be particularly important with CIS, since the longer intake track is, the more A/F transients you're going to get no matter what you do. EFI would theoretically give you the ability to compensate, but you'd still have the longer path for the pressure wave to transit.

One last thought I've had is to experiment with water/alcohol injection. It seems like it wouldn't be hard to rig up a solenoid to open a bleed on the wastegate line and have it set to open when you trigger the water/alcohol injection. Many experts (Corky Bell, for one) poo-poo that idea, and there aren't many scenarios where you'd prefer it over a proper IC setup, but done right, it could allow you to push as much boost as you want until you start blowing head gaskets and such. You could use a cheap on-off setup and just use it close to peak HP, or you could go more elaborate: there are controllers that can be set to modulate the flow based on RPM and boost. There are good reasons some people recommend against it - and having a boost juice tank to fill is probably the least of them - but done right, and depending on one's driving style, it could give all the benefit of an IC for cheaper and without all the cutting and fabrication a proper IC calls for. There's a lot of no-man's-land in terms of tuning, but that's true of an IC setup anyway; get it tuned right and keep the boost juice topped up, and you should never have a problem. In particular, I think the results would be much better than a mediocre IC setup.


Personal experience/opinion, I think 9.0:1CR would be too high and limit ignition and boost too much, unless not looking to boost too high. 8.0 - 8.2:1 would be my preference for higher boost over 1.0bar. I'm currently running nearer 8.5:1 with 1.1bar. I have gone as high as 1.4bar briefly. This still gives a snappy off boost throttle response

I'd also avoid and air or water cooled IC anywhere near the turbo/manifold with the heat I have experienced. The gains will be negated buy high heat soak. FMIC is the way to go. My 951 IC maintains +6-8deg C above ambient. Pre IC temps have been over 100degC.
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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
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Beartooth  



Joined: 05 Apr 2022
Posts: 213
Location: Roberts, MT

PostPosted: Sat Nov 26, 2022 8:42 am    Post subject: Reply with quote

I'd agree, anything over 1 bar, or probably even close, would require less than 9:1 compression. My thought would be to keep boost levels close to stock - around .8 max, maybe closer to .7 (10 PSI). Most of the gains would be from density gains thanks to the IC, a better flowing head, being able to run more reasonable A/F ratios thanks to knock detection, and other refinements. I'm not sure how well my idea for the IC would work, but it wouldn't work without ensuring that the IC could only be fed air from the hood scoop, and a fan to keep exhaust heat from reversing the flow and heating the IC when the car is stopped. You'd probably hit some limits in terms of airflow to the IC if you were trying to push a lot of boost, but like I said, I'd be looking more for moderate gains. An air-water IC would solve the tradeoff of keeping the intake track short but limited cooling air vs. plenty of air but a long intake track, it's just that it adds so much complexity and more components to go wrong. I'd go with air-air every time unless I hit a wall, but can understand why someone would go that direction.

One thing's for sure, there are many different approaches, and which is "best" depends on budget, driving style, power goals - a lot of factors. My thinking is along the same lines as Kondzi: make some refinements and modernize it, which should give you an easy 20% increase without really pushing the envelope. And in my case, I'd rather have the benefits of more compression than the ability to push a lot of boost. With unlimited time and resources, we'd all probably come up with a different setup, and what proves to be "best" might be more a matter of preference than anything else.
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Carrera RSR  



Joined: 08 Jan 2010
Posts: 2309
Location: Somerset, UK

PostPosted: Sat Nov 26, 2022 8:19 pm    Post subject: Reply with quote

Unlike say Sierra/Escort Cosworth development, where you have a well trodden path by many tuning companies and consumers with proven dyno results, the 931 community is full of varied plans + budgets + executions, some with results, many without, so the route to a solution is fraught with head scratching with trial and errors. There's a few on this board with strong knowledge and experiences and happy to share knowledge, use them and thank them. There's quite a bit of internet hearsay and myth to wade through. Also watch out for the RoW versus US spec's potholes which can give you the wrong understanding or specs.

Whilst some may say more power is better. From my experience anything over 200bhp est crank brings these cars alive. It enhances the fun, noise and theatre of 80's turbo lag. 220ish is perfect for the twisties. Sure you may want more for straightaways or drag strips. But for fun mountain/canyon/country roads, this is perfect.
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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
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Mike9311  



Joined: 14 Dec 2004
Posts: 1678
Location: Chicago-ish

PostPosted: Sun Nov 27, 2022 1:45 am    Post subject: Reply with quote

Carrrera, I've been reading this thread and I can tell you are older.

You have stated a lot of interesting and thought provoking words of wisdom that should be taken to heart by anyone currently building a 924

No need to be on the bleeding edge. Just pull the reigns back and bit and enjoy
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1982 931 Entwicklungsfahrzeug
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kondzi  



Joined: 02 Jul 2018
Posts: 485
Location: Poland/EU

PostPosted: Sun Nov 27, 2022 2:19 am    Post subject: Reply with quote

Mike9311 wrote:
Carrrera, I've been reading this thread and I can tell you are older.


ROTFL

Cedric wrote:
buy a cheap audi turbocharger and take the compressor from(and put on your current turbo) if you find it to much of a struggle to fit the piping to the original one

Which exactly?
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'89 951 US
'88 Mustang 5.0 LX Convertible (factory specs)
'84 911 Carrera 3.2 RoW (factory specs)
'81 931 RoW (TBD)
'81 Ford Capri 2.8i (factory specs)
'79 Ford Capri 2.9 (heavily modded)
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jacobroufa  



Joined: 18 Nov 2016
Posts: 531
Location: Belvidere, IL

PostPosted: Sun Nov 27, 2022 2:41 am    Post subject: Reply with quote

Konrad, here's a picture of the housing I have waiting to do a FMIC install. I got it from Ed (FastEddie) on the board after he upgraded to a larger turbo; this is the one he used for the first iteration of his FMIC setup, using the method Cedric suggests to clock the housing to be facing downward.

https://photos.app.goo.gl/eDqfG7uzCvCxdYG69

Housing cast number: 5326 101 50 71 1821 226
Plate numbers:
Kund.-NR. 035 145703L
Grosse K26
Atl.-NR. 88 403 2130
AUSF.-NR. 5326 970 6411

Hope this helps!
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