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Johntom
Joined: 30 Aug 2011
Posts: 18
Location: South Yorkshire
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 Posted: Mon Sep 19, 2011 9:53 pm Post subject: Turbo choice ? |
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Hi
I have a 1981 series 2 with a smokey turbo ( K26 2470 R6-10) and have the chance to buy a rebuilt unit (2660 Ga4-10) from another series 2.
Is the 2660 better in terms of performance, or should I rebuild the 2470 or (if possible) is it better to combine parts of the 2 units?
I don't want to particularly modify the engine, i just want to get the best performance from it and wondered what option would be best, or any other alternatives ? |
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9xx
Joined: 18 Jun 2006
Posts: 627
Location: Jarvenpaa, Finland
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Johntom
Joined: 30 Aug 2011
Posts: 18
Location: South Yorkshire
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| Posted: Mon Sep 19, 2011 10:46 pm Post subject: |
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Hi
It smokes above 3000rpm. Ps I have emailed you about your eBay ad! |
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9xx
Joined: 18 Jun 2006
Posts: 627
Location: Jarvenpaa, Finland
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| Posted: Mon Sep 19, 2011 11:07 pm Post subject: |
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Lots of turbo information here: http://www.924board.org/viewtopic.php?t=33955
Johntom, I sent you PM.
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Mikko
All gone: 931 '82 Alpine White, original option "220" G31 with LSD + 3 x 944 |
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WEASEL149
Joined: 19 Aug 2005
Posts: 595
Location: UK, Sheffield
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| Posted: Mon Sep 19, 2011 11:44 pm Post subject: Re: Turbo choice ? |
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| Johntom wrote: | Hi
I have a 1981 series 2 with a smokey turbo ( K26 2470 R6-10) and have the chance to buy a rebuilt unit (2660 Ga4-10) from another series 2.
Is the 2660 better in terms of performance, or should I rebuild the 2470 or (if possible) is it better to combine parts of the 2 units?
I don't want to particularly modify the engine, i just want to get the best performance from it and wondered what option would be best, or any other alternatives ? |
If you're not wanting to modify the engine then if it was me I'd buy the rebuilt turbo and fit it as it is.
The 2660ga4-10 is what your S2 should have anyway. The smaller 4-10 exhaust housing will give you quicker turbo spool-up - less lag, which you may prefer.
The other option is to buy the rebuilt turbo then swap the exhaust housing (6-10) from your old 2470 onto it. I wouldn't really recommend this as apparently the compressor on the 2660 is only good for around 200hp and so the 6-10 is overkill. This would give you basically the same turbo as the Carrera GT and does reduce back pressure.
I can't really see the point in doing the second option though if you want to keep the car stock.
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1979 UK 932 |
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Johntom
Joined: 30 Aug 2011
Posts: 18
Location: South Yorkshire
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| Posted: Tue Sep 20, 2011 3:44 am Post subject: |
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Hi and thanks for the advice
So if I swapped the exhaust housings as described, would the performance and acceleration be noticably better than just fitting the 2660, or wouldn't it be worth the effort on a standard engine ?
Also what would the next stage be for the engine to increase the bhp nearer to 200bhp ie k&n filter, re worked cylinder head etc ? |
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ideola
Joined: 01 Oct 2004
Posts: 15550
Location: Spring Lake MI
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| Posted: Tue Sep 20, 2011 4:06 am Post subject: |
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| Johntom wrote: | | Also what would the next stage be for the engine to increase the bhp nearer to 200bhp ie k&n filter, re worked cylinder head etc ? |
K&N won't do jack squat except let more dirt into your intake.
Big Valve head will help it flow more, but I don't yet have numbers to quantify the HP gain. I am really hoping to dyno four cars this winter: GEBLASN, my 81 bone stock US-Spec 931, the new 941 motor, the new Club Sport motor, and the bone stock 937. The numbers from GEBLASN and the 937 should provide a really good baseline of factory configured cars.
The 941 has stock valves in the head, but has been aggressively ported and polished, with port matching on the intake, plus a Stage1 Integral Cam profile. It has a K26 2470 R6-10 S1 turbo charger, with all ceramic coated exhaust to the cat, with a 1-bar spring (by accident) in the wastegate. I'll be replacing that with a stock US-spec S1 wastegate spring and installing an in-cockpit boost controller. This engine also has 8.7:1 custom pistons with my long rod setup (increased rod length by 6mm). So it should be at least as hot as a stock Euro spec, if not a touch better.
The Club Sport has a 2.2L stroker, custom pistons, full windage dual scraper, 8.0:1 CR pistons, big valve head, Stage1 Integral Cam, and a CGT-spec 6-10 hot side mated to a K26 2470 S1 cold side. I will also be running a stock S1 wastegate spring with an in-cockpit boost controller. So I am hopeful to approach, if not eclipse the factory 937 output with that setup. Non-intercooled.
Intercoolers and water injection are still on the table for both the 941 and the Club Sport once I have a baseline.
That said, the quickest path to 200 BHP in your situation will be upping the boost and adding an intercooler or water injection to suppress detonation. Headwork and cam will help, but so far we have no definitive evidence as to exactly what impact they have on overall power. If you want a sure bet, just add an intercooler and boost controller. You should be at 175BHP already with ROW spec, so getting another 25 BHP shouldn't be hard, especially if you can intercool, without having to do extensive engine mods.
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erstwhile owner of just about every 924 variant ever made |
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Raceboy
Joined: 01 Mar 2004
Posts: 2327
Location: Estonia, Europe
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| Posted: Tue Sep 20, 2011 5:36 am Post subject: |
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The best way to get more power from any 931 engine is to install intercooler, better turbo and programmable EFI. I wouldn't worry about anything else (cams, valves etc) before these things have been done.
Compared to regular 924 head, 931 one is far better in terms of port shape and I managed to get around 245hp/320 Nm from bone-stock Euro 924 engine (with 9.3:1 CR) by using just IHI turbo from Hyundai Terracan 2.9 diesel, 951 intercooler and VEMS programmable EFI. Of course, after a while stock clutch started slipping and I bought SPEC Stage III+.
On 931, when you get to around 300 controlled hp (I mean, NOT with stock CIS and tired distributor), you should start thinking about better piston rings as stock ones are not exactly optimum for boost (too thin) or better pistons and head studs.
BTW, 931 pistons can be machined to accept 924 NA rings that are far more beefier and withstand boost much better. And are cheaper too. I've seen 931 pistons machined this way, these have worked like a charm.
_________________
'83 924 2.6 16v Turbo, 470hp
'67 911 2.4S hotrod
'90 944 S2 Cabriolet
'78 924 Carrera GT replica
'84 928 S, sold
'91 944 S2, sold
'82 924S/931 "Gulf", sold 
'84 924, turbocharged, sold.
http://www.facebook.com/vemsporsche |
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WEASEL149
Joined: 19 Aug 2005
Posts: 595
Location: UK, Sheffield
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| Posted: Tue Sep 20, 2011 8:47 am Post subject: |
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| Johntom wrote: | Hi and thanks for the advice
So if I swapped the exhaust housings as described, would the performance and acceleration be noticably better than just fitting the 2660, or wouldn't it be worth the effort on a standard engine ?
Also what would the next stage be for the engine to increase the bhp nearer to 200bhp ie k&n filter, re worked cylinder head etc ? |
Don't bother with K&N - as Ideola says, they're a waste of money on a mild-tuned engine and not as effective at filtration. The original air filters aren't actually that bad with regard to flow.
Swapping the housing on its own, you probably wouldn't notice much difference. The main reason for swapping it is to reduce back pressure and therefore heat in the exhaust manifold and exhaust ports. This would only be worth doing if you plan on intercooling and increasing the boost SIGNIFICANTLY (say 1bar).
You will actually notice a difference though when you swap the turbo for the rebuilt one with the smaller exhaust housing.
The turbo will spin up approximately 6-800rpm sooner than with your old 2470 because the exhaust gas speed through the smaller housing is greater (even though there is more back pressure created).
A lot of people prefer this improved throttle response in a road car and this was Porsche's aim with the S2 turbo.
From what I've read on here the 4-10 is fine up to around 200hp.
It all depends on how far you want to go with the car and how much work you want to do on it (plus how much money you want to spend).
Fitting an intercooler is the first mod I would do but takes a bit of thinking out and fabrication to fit a front mount. This alone will give you a small power increase without increasing boost, and increase reliability due to cooler inlet temperatures.
You could then get rid of the smaller primary exhaust silencer and fit a straight section of pipe instead. Along with a decent 'straight-through' rear silencer this can give up to 10hp.
After that you'd need to fit a boost controller. You could increase boost to the same level as the Carrera GT without risking reliability and this would probably see you comfortably past the 200hp mark.
Without boost increase with the other mods you're probably looking at 190hp.
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1979 UK 932 |
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stevekat
Joined: 19 Jan 2008
Posts: 719
Location: Los Angeles, CA
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| Posted: Tue Sep 20, 2011 3:30 pm Post subject: |
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Go with the turbo that provides better throttle response. Unless you are on the track predominantly, I think the real world effect of better response, and drivability shall provide the greatest satisfaction, regardless of peak horsepower. Nothing is worse in these cars than waiting for them to come on the pipe (from a start from a light in normal driving, or when accelerating from slow speed.) Having boost come on earlier and reducing bog, and having better responsiveness is far more important than modest peak hp difference, at least in my opinion.
_________________
"Never get out of the boat. Absolutely goddamn right. Unless you are goin' all the way."
Gone to new home: '81 924T, US version, CGT Intercooler, UTCIS-PT, Euro DITC, Greddy Trust MBC, Forged Fuchs Flat Dish 6's, Factory Recaro's.
Last edited by stevekat on Wed Sep 21, 2011 1:35 am; edited 1 time in total |
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WEASEL149
Joined: 19 Aug 2005
Posts: 595
Location: UK, Sheffield
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| Posted: Tue Sep 20, 2011 11:56 pm Post subject: |
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| Raceboy wrote: | The best way to get more power from any 931 engine is to install intercooler, better turbo and programmable EFI. I wouldn't worry about anything else (cams, valves etc) before these things have been done.
Compared to regular 924 head, 931 one is far better in terms of port shape and I managed to get around 245hp/320 Nm from bone-stock Euro 924 engine (with 9.3:1 CR) by using just IHI turbo from Hyundai Terracan 2.9 diesel, 951 intercooler and VEMS programmable EFI. Of course, after a while stock clutch started slipping and I bought SPEC Stage III+.
On 931, when you get to around 300 controlled hp (I mean, NOT with stock CIS and tired distributor), you should start thinking about better piston rings as stock ones are not exactly optimum for boost (too thin) or better pistons and head studs.
BTW, 931 pistons can be machined to accept 924 NA rings that are far more beefier and withstand boost much better. And are cheaper too. I've seen 931 pistons machined this way, these have worked like a charm. |
If you are interested in hiking the power a lot, then I agree with Raceboy on intercooler, better turbo and programmable engine management. That's the route I'm taking - not the easiest but you do learn a lot along the way.
Don't know if I'll make it to 300hp (I would like to) but that's an interesting fact I didn't know about machining the pistons for NA rings.
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1979 UK 932 |
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Johntom
Joined: 30 Aug 2011
Posts: 18
Location: South Yorkshire
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| Posted: Wed Sep 21, 2011 7:43 pm Post subject: |
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Hi thanks for the advice, I will fit the 2660 when it arrives then think about intercooling.
I know this has been discussed many times (and I've read as many posts as I can about it) but is a front mount a better option than trying to fabricate a Gt replicar top mount? Would a front mount introduce more lag, but have cooler air ? |
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Raceboy
Joined: 01 Mar 2004
Posts: 2327
Location: Estonia, Europe
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| Posted: Wed Sep 21, 2011 7:57 pm Post subject: |
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| Johntom wrote: | | Would a front mount introduce more lag, but have cooler air ? |
Front mount is far better and when built even remotely properly, you won't feel the difference in response.
Find an intercooler with vertical core and run the piping from down to up, not from the sides which makes the piping insanely long.
_________________
'83 924 2.6 16v Turbo, 470hp
'67 911 2.4S hotrod
'90 944 S2 Cabriolet
'78 924 Carrera GT replica
'84 928 S, sold
'91 944 S2, sold
'82 924S/931 "Gulf", sold
'84 924, turbocharged, sold.
http://www.facebook.com/vemsporsche |
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Johntom
Joined: 30 Aug 2011
Posts: 18
Location: South Yorkshire
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| Posted: Thu Nov 03, 2011 4:15 am Post subject: Turbo priming after replacement |
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Hi all
I have finally replaced the turbo and reassembled the car. Having filled with oil how do I prime the turbo? The Haynes says remove the spark plugs and then 'remove the plugs from the manifold pressure limiting switch' where is this as the book gives no other reference to it ? |
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flosho
Joined: 01 Jul 2004
Posts: 3160
Location: Eau Claire, Wisconsin
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| Posted: Thu Nov 03, 2011 12:38 pm Post subject: Re: Turbo priming after replacement |
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| Johntom wrote: | Hi all
I have finally replaced the turbo and reassembled the car. Having filled with oil how do I prime the turbo? The Haynes says remove the spark plugs and then 'remove the plugs from the manifold pressure limiting switch' where is this as the book gives no other reference to it ? |
Sounds like the haybes is referencing the overboost switch which is the plug on the upper charge tube, it has two connections going to it.
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[This Space For Rent] |
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