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81 into 80 931 turbo swap?
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Kenodog  



Joined: 25 Jun 2003
Posts: 2451
Location: Vancouver,B.C.

PostPosted: Tue Jul 01, 2003 5:38 pm    Post subject: 81 into 80 931 turbo swap? Reply with quote

Does anyone know if (A)does a 1981 turbo put out more boost than a 1980?and (B)will a 1981 turbo assy.(turbo,wastegate,ex.man.etc.)directly bolt on to a 1980?I ask this because I have a MINI Cooper intercooler that I am modifying to an air/water unit and will be looking for more BOOOOOST!Safely of course.And because I have somebody nearby with an 81 as a partscar.Turbo and all.Please advise.Thanks
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1981 931, Sabine
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2008 GS500
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dwak  



Joined: 03 Nov 2002
Posts: 840
Location: Eastern Ontario

PostPosted: Tue Jul 01, 2003 10:16 pm    Post subject: Reply with quote

I don't think there's any difference and, if I remember right, there's a little less boost. For more boost, alter the waste gate like John H. etc. Search this site for info, there's quite a bit here somewhere. The dif with the '81 is the electronic timing/flywheel sensor and the intake manifold. There are differences between the north american and euro models as well. Mainly higher compression and lack of polution crap.

dwak
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jl924t  



Joined: 03 Nov 2002
Posts: 214
Location: Surrey, BC Canada

PostPosted: Wed Jul 02, 2003 12:39 am    Post subject: Reply with quote

I have a '81 turbo on my '80 931
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Lizard  



Joined: 03 Nov 2002
Posts: 9379
Location: Abbotsford BC. Canada

PostPosted: Thu Jul 03, 2003 2:31 am    Post subject: Reply with quote

why the 1980 has a bigger turbo =more boost avalible
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epsylon  



Joined: 05 Nov 2002
Posts: 492
Location: South Padre Island, Texas

PostPosted: Thu Jul 03, 2003 2:56 am    Post subject: Reply with quote

is it the size of the blades in the turbo that give the '80s more boost or is it a difference in the wastegate?
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Lizard  



Joined: 03 Nov 2002
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Location: Abbotsford BC. Canada

PostPosted: Thu Jul 03, 2003 3:13 am    Post subject: Reply with quote

I think it is the compressor and compressor housing
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epsylon  



Joined: 05 Nov 2002
Posts: 492
Location: South Padre Island, Texas

PostPosted: Thu Jul 03, 2003 5:22 am    Post subject: Reply with quote

i didn't know that the housing was different between the two. i just thought it was the internals, i read somewhere that the internals of varying k26s were interchangeable to some extent so i just assumed. you learn something new everyday. how much bigger is the '80s turbo compressor?

my next big fix for my 931 is to get the turbo rebuilt. i wonder if it would be worth my while to hunt for an '80s core. instead of using my smaller '82 turbo as the core.
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jl924t  



Joined: 03 Nov 2002
Posts: 214
Location: Surrey, BC Canada

PostPosted: Thu Jul 03, 2003 3:11 pm    Post subject: Reply with quote

When I acquired my car the turbo was siezed. I picked up a '81 unit on ebay put it on while I rebuilt the original. Turned out the housing was cracked on the origional so I kept it for parts. I picked up another unit on ebay which was an '80 unit and had it rebuilt. Now I have to get around to swapping them. The 81 unit has plenty of boost for me but then I may have a different opinion when I feel the performance of the 80 unit. I blew a cylinder today (no compression)so I'm going to take it all apart tonight. Might be a good time to swap turbos while I am at it.
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Lizard  



Joined: 03 Nov 2002
Posts: 9379
Location: Abbotsford BC. Canada

PostPosted: Fri Jul 04, 2003 4:13 am    Post subject: Reply with quote

jl924t wrote:
When I acquired my car the turbo was siezed. I picked up a '81 unit on ebay put it on while I rebuilt the original. Turned out the housing was cracked on the origional so I kept it for parts. I picked up another unit on ebay which was an '80 unit and had it rebuilt. Now I have to get around to swapping them. The 81 unit has plenty of boost for me but then I may have a different opinion when I feel the performance of the 80 unit. I blew a cylinder today (no compression)so I'm going to take it all apart tonight. Might be a good time to swap turbos while I am at it.


aha so your the one who called weissach looken for a piston, hehe it was kind of funny I called an he said that there were 3 people who had called him for engine rebuild parts, so he knew the prices right off the top of his head, the 3 people were you me and lordco, turns out that you can't get the piston through them, try ALPI in surrey and 604-727-6911 he intermitantly buys 931s and might have 1 he could sell you
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jl924t  



Joined: 03 Nov 2002
Posts: 214
Location: Surrey, BC Canada

PostPosted: Fri Jul 04, 2003 6:26 am    Post subject: Reply with quote

No it was not me. I had to replace 1 piston when I first got my car 3 years ago due to a burnt valve. A piece of the valve broke off and rattled around in the cylinder for a while. The previous owner drove it for a week before he parked it. Then he sold the car, cause he was tired of it 2-bitting him to death, and bought a 911. I had a guy at Burnaby Auto Parts get a piston for me but I had to wait a week and I beleive it cost me $325.00. turns out this time that I just blew another head gasket between #1 and #2 cylinder. That's 3 in 4 weeks. The first 2 (blown through first at 9 oclock and the second time at 5 oclock on #4 cylinder) were caused by a loose fuel injector causing a lean condition ( my assumption). I am going to take the wastegate apart to see if all is well. I think it's time to hook up the boost pressure switch or put a block of wood under my throttle pedal. Andrew at Weissach is bringing a new gasket in for me but it won't be here till monday so I found an old good one, if there is such a thing, in my assortment of parts. I will put that on till I need to replace it. Are you looking for a piston? I have a set of 4 pistons NIB, standard bore, that I bought last year. I want to keep them but if you are stuck for one I can lend it to you till yours comes in, if you need it. I also have a set of rods but they are used but look to be in good shape. I have them for spares just in case it blows up real good.
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Lizard  



Joined: 03 Nov 2002
Posts: 9379
Location: Abbotsford BC. Canada

PostPosted: Fri Jul 04, 2003 7:36 am    Post subject: Reply with quote

no that is fine, my friend munkpuppy is buying the 931 from me and I have a spare engine that we are going to rebuild and slap in teh car so he doesn't have to worry about stuff like that.
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bho  



Joined: 03 Nov 2002
Posts: 17
Location: Richmond, B.C.

PostPosted: Wed Jul 09, 2003 3:38 pm    Post subject: Reply with quote

Surprise, surprise. I wasn't aware that there were this many turbos running around Richmond.
I recently had my 81 turbo rebuilt. I also have a spare 80 turbo to directly compare to. The 81 turbo has a smaller AR ratio on the exhaust/turbine side. As a result turbo lag is slightly less with the 81 coming to full boost at about 3000rpm. During the rebuild, a small crack was found on the turbine housing and this was replace. ($400Cdn) Unfortunately, only a 80 housing was available. As a result, full boost now does not come on until 3500 rpm. Side result however is that drivability below 3000 is slightly improved likely as a result of better exhaust breathing.
I am also trying to do an air water intercooler.
Anyone have a spare 81/82 inlet runner. I have a spare 80 runner.
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porschetroy  



Joined: 30 Dec 2002
Posts: 32
Location: Sacramento

PostPosted: Sat Aug 09, 2003 7:14 pm    Post subject: Reply with quote

So bho,

With your larger '80 turbine housing spooling up later, does it seem to make a difference at the top end? Does the power band seem to be any higher in the rpm range? It seems that the exhaust would flow much better.

My '82 931 with the smaller turbine housing and compressor spools up by 3000 rpm but power falls off at 5500 rpm. I am getting ready to have an '80 turbo (larger turbine and compressor) rebuilt to use in my car hoping it will develop more power in the top end. I am also considering using the smaller turbine housing with the larger compressor.
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dwak  



Joined: 03 Nov 2002
Posts: 840
Location: Eastern Ontario

PostPosted: Sun Aug 10, 2003 6:33 am    Post subject: Reply with quote

Wouldn't be easier just to crank up the boost, regardless the unit?

dwak
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porschetroy  



Joined: 30 Dec 2002
Posts: 32
Location: Sacramento

PostPosted: Mon Aug 11, 2003 6:28 pm    Post subject: Reply with quote

Yeah, you could just crank up the boost. But, all turbos are meant to work within a certain range of CFM and pressure levels. Smaller turbos are capable of more pressure but start getting less and less efficient meaning more heat. The same boost pressure from a small turbo as from a large turbo means the air will be a lot hotter which will lead to detonation faster. At this point, I know somebody is going to solve all the problems of the world and say "just install an intercooler". That doesn't change the fact that the boost from a larger turbo operating in its efficiency range will be colder after the intercooler than that of the smaller turbo.

Besides, I think the smaller turbine housing creates a lot of backpressure and limits engine breathing.

I have to rebuild my turbo anyway because it sucks oil and smokes. I might as well try the larger unit. I can always swap the smaller compressor wheel and housing, or turbine housing onto it. The turbine wheels, shaft, and center section are the same whether it uses the large or small housing.

For those who don't want to invest a lot of time and money, the stock '82 turbo does an admirable job. It will easily pump out over 20 psi if you're not careful or if your wastegate fails. I installed a boost line to the top of my wastegate with an adjustable pressure regulator and it works like a charm. It's very consistent unlike trying to restrict the boost signal to the wastegate. I run my daily driver '82 931 at 11 psi boost all the time. On 100+ days, it will ping in 2nd gear at around 5000 rpm if I'm really getting on it. I always run 92 octane. On cold days, I'll turn it up to about 15 psi just for fun. I can tell you that these engines seem to like 13 psi and really come alive. According to my Air/fuel ratio gauge, the CIS does pretty well of enrichening the mixture at all the boost levels I've tried.

As always, have fun. -Troy
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