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931 Exhaust Manifold Discussion LHD/RHD
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Mike9311  



Joined: 14 Dec 2004
Posts: 1102
Location: Chicago-ish

PostPosted: Thu Dec 03, 2020 12:19 am    Post subject: 931 Exhaust Manifold Discussion LHD/RHD Reply with quote

Per Cedric's advice

Exhaust manifold design discussion. This can be ongoing and when time permits. Its straightforward for me to get general outer flange locations in space. If it were me alone, I would optimize the rest. Maybe even a quick change setup for 3 or 4 bolt flanges, individual runners, etc.


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1982 931 Entwicklungsfahrzeug
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924RACR  



Joined: 29 Jul 2001
Posts: 8421
Location: Royal Oak, MI, USA

PostPosted: Thu Dec 03, 2020 2:22 am    Post subject: Reply with quote

Very interested to hear Cedric's report on flow characteristics of the RHD vs. LHD setup.

The more drop-in for stock replacement of cracked original manifolds, the easier to sell a larger volume. Then again, if you're in there that far, maybe as long as the rest of the hookups (well, as many as possible) to stock plumbing are least affected, maybe a newer upgrade option might be better.

After all, just as the manifold itself is prone to cracking, so too ends up the exhaust housing is cracked and needing replacement...

I am interested/curious; while my turbo is recently refreshed and upgraded, my manifold is still cracked and a limitation, which will only get worse as I keep cranking the boost. At this point, only the manifold, downpipe, and oiling ports are stock hookups...
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Mike9311  



Joined: 14 Dec 2004
Posts: 1102
Location: Chicago-ish

PostPosted: Thu Dec 03, 2020 5:12 am    Post subject: Reply with quote

I have a few pics saved in a manifold folder for sometime. I always imagined something like this from AMS. I am looking for another similar one I saw for a VW

Maybe even using a v-band to 3 or 4 bolt adapter as part of the package. V-band would be niiiiice for anyone who has done a turbo swap in situ


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1980 931 since 1989
1981 Ideola 931 Club Sport
1982 931 Entwicklungsfahrzeug
1979 924 NA M650 Herausnehmbares Dach
1982 931 Red Resurrection - 951 IC
1982 931 parts car / resurrection?
1980 924 NA (R&D lightweight)
1982 931 wana-be GTR race car
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Fasteddie313  



Joined: 29 Sep 2013
Posts: 2223
Location: MI

PostPosted: Thu Dec 03, 2020 10:04 am    Post subject: Reply with quote

How optimal is the rhd manifold and pics??

Really though I think they can be welded fine..
Don’t preheat with a torch, use a kiln like a blacksmith and heat the whole thing stupid hot.. Problem solved..
Bury in dry sand to cool slowly..

For a cast manifold, I think the lhd 931 manifolds are quite optimal, minus the cracking situation..
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Carrera RSR  



Joined: 08 Jan 2010
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Location: Somerset, UK

PostPosted: Thu Dec 03, 2020 6:27 pm    Post subject: Reply with quote

RHD ...... there are 4 part number updates......iirc this is the 3rd. I believe it relates to the fire rings being introduced. I have never used a fire ring between the manifold + turbo. Just renewed the gaskets each time.




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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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Last edited by Carrera RSR on Thu Dec 03, 2020 6:30 pm; edited 1 time in total
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Cédric  



Joined: 27 Aug 2004
Posts: 2114
Location: Sweden

PostPosted: Thu Dec 03, 2020 6:27 pm    Post subject: Reply with quote

I wish we had someone to do a TMF calculation, that would be great to see where the weaknesses are when it heats and cools down..

If this project where to go through and to make the outcome better from an economical perspective making it fairly standard so the guys running these cars in historic rallying etc can buy them would be very helpful. They are used to a different level of money, hence why stuff cost like they do. And maybe team up with some suppliers like mittlemotor and see if they are interested to buy some of them.

Remember the Swedish guy ( i uploaded pics here during the build) who built a very serious FIA homologated 924 Rally GTS replica and casting all the necessary parts needed? He still thought that was a good deal compared to buying a ford escort rally car for example. Theres money in that buissness

Anyway, regading the LHD and RHD, i will post some data later when im back att my computer. The difference is not big, but the RHD manifold reduces the knock sensitivity in cylinder nr 4 in a good way, and some other small differences i will show later. If I only had an .stl of the internal manifold volumes i could make the simulation much better
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Mike9311  



Joined: 14 Dec 2004
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PostPosted: Fri Dec 04, 2020 3:55 am    Post subject: Reply with quote

I have to see what I can do

It sounds like sticking to stock-ish is the better idea here given the possible use cases across the board

I totally remember that Swedish guy doing all the casting. That was an awesome build

Need to get a hold of a RHD manifold at least temporarily
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1980 931 since 1989
1981 Ideola 931 Club Sport
1982 931 Entwicklungsfahrzeug
1979 924 NA M650 Herausnehmbares Dach
1982 931 Red Resurrection - 951 IC
1982 931 parts car / resurrection?
1980 924 NA (R&D lightweight)
1982 931 wana-be GTR race car
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Cédric  



Joined: 27 Aug 2004
Posts: 2114
Location: Sweden

PostPosted: Fri Dec 04, 2020 5:18 am    Post subject: Reply with quote

OK guys, heres some nerdy stuff. The software im using is the one used by more or less all OEMs out there. I worked with it for years at my previous job. HOWEVER, since i have so little data, the 931 model is much simpler than the models I used to work with, but anyway still a detailed mode compared to anyhting that has ever been done on a 931 engine.

Heres some nerdy data, i only did one full load transient simulation in this analysis. Its my 8,5CR 2670 s2 engine, timing curve have s2 shape, probably to aggressive for this boost, so that power level would probably not be possible to reach, depending on temperature.

This is how a model looks like, built up by cutting every pipe and part into parts, and the filling them with all sorts of information, maps, heat transfer data, combustion data, etc etc



This is for cylinder four, the one we know might run hotter than the others.

As you can see it runs leaner with the UK manifold, but thats not necessarily a problem, as we can see further on.



Here you can see the knock index, its very general, since i cant do any detailed predictive combustion simulation due to lack of data. So its more of a general number, the higher the larger the probability of detonation. As you can see, as soon as the boost comes on the UK manifold actually have less risk of detonation, due to the reduced residual gases in cylinder 4 mostly.


Here you can see the residual exhausts in cylinder 4, more is worse and increase the risk of detonation.


Heres the power, not alot of difference, maybe 3,5 at most. Maybe it could take a tiny bit more timing with the uk manifold on boost, which would make the differens a tiny bit larger.


Everything from combustion to gas exchange is calculated for every fraction of crank angle, so all data is available if you want to get nerdy.


Volumetric efficiency bewteen the runs, its a transient run, so numbers might change compared to a static running points due to heat building up in the material.
[img]https://rejsa.nu/im/user/1552/2020-12-03-20-02-57_voleff.png [/img]

If you are really serious you could also get detailed heat transfer data for valves, cylinders, piston etc,


Conclusion, once its on boost the UK design isnt so bad after all, acually preferable in some areas. Mostly due to the hot cylinder 4 going from the worst when it comes to residual gases (with the std manifold) to being the best (with the uk manifold obviously), and hence the total knock risk goes down a little bit, ad the pumping work is slightly better.
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Mike9311  



Joined: 14 Dec 2004
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PostPosted: Fri Dec 04, 2020 7:53 am    Post subject: Reply with quote

Cedric that's awesome stuff, thank you

I just looked at a LHD and cyl 4 does not have direct exposure to the wastegate feed. It shares it with cyl 3 and the others

Based on the pictures, since I don't have a RHD manifold, it looks like cyl 4 also feeds right to the wastegate?

Ultimately, what I want to know is if the wastegate flange is in the same location for both manifolds? Essentially, can one bolt in a RHD manifold into a LHD car? I feel like this has been answered in the distant past elsewhere here

EDIT: I'm wrong! 4 goes all the way to around 1 as does 2-3. Wastegate is fed from up front.
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1980 931 since 1989
1981 Ideola 931 Club Sport
1982 931 Entwicklungsfahrzeug
1979 924 NA M650 Herausnehmbares Dach
1982 931 Red Resurrection - 951 IC
1982 931 parts car / resurrection?
1980 924 NA (R&D lightweight)
1982 931 wana-be GTR race car


Last edited by Mike9311 on Fri Dec 04, 2020 9:43 am; edited 1 time in total
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Fasteddie313  



Joined: 29 Sep 2013
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PostPosted: Fri Dec 04, 2020 9:08 am    Post subject: Reply with quote

Cedric, is that accounting for the WG being open, or closed, or half open..??
Flow through the turbo or flow while dumping waste?
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Carrera RSR  



Joined: 08 Jan 2010
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PostPosted: Fri Dec 04, 2020 8:50 pm    Post subject: Reply with quote

So the 'UK' is good for something.......

Off to buy as many RHD turbo manifolds as I can.......already have 3, 2 on engines and one spare just in case
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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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Cédric  



Joined: 27 Aug 2004
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PostPosted: Fri Dec 04, 2020 10:20 pm    Post subject: Reply with quote

Fasteddie313 wrote:
Cedric, is that accounting for the WG being open, or closed, or half open..??
Flow through the turbo or flow while dumping waste?


Yes of course, the WG is targeting 1 bar boost, at full power max RPM about 46% of the flow goes through the WG.

Steve, I actually did these probably a year ago, when I had some plans on maybe buying a UK manifold due to the lack of uncracked std manifolds. As you know, 931 parts is something you have to hoard in good time before you need them, if you want to get stuff for a reasonable price

The one i have is repaired by a pro, but after a couple of years there are signs that if maybe wont last forever.
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morghen  



Joined: 21 Jan 2005
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PostPosted: Fri Dec 04, 2020 10:23 pm    Post subject: Reply with quote

My red GTS wannabe had an UK engine, so the RHD manifold.
Cool
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Mike9311  



Joined: 14 Dec 2004
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PostPosted: Sat Dec 05, 2020 3:51 am    Post subject: Reply with quote

I don't stand a chance over here

Its like buying stock too late when everyone knows its the stock to buy

Edit: This also seems to explain why Steve has never seen cracking
Personally I have issues with all the bracing on the LHD drive manifold. It has nowhere to go when cycling
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1980 931 since 1989
1981 Ideola 931 Club Sport
1982 931 Entwicklungsfahrzeug
1979 924 NA M650 Herausnehmbares Dach
1982 931 Red Resurrection - 951 IC
1982 931 parts car / resurrection?
1980 924 NA (R&D lightweight)
1982 931 wana-be GTR race car
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MOTANUL  



Joined: 19 Nov 2018
Posts: 157
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PostPosted: Sat Dec 05, 2020 5:10 am    Post subject: Reply with quote

mine was cracked.
Now I hope it stays craked free.


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