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My 924 Turbo, finally out on the road !
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CÚdric  



Joined: 27 Aug 2004
Posts: 1746
Location: Sweden

PostPosted: Wed Oct 08, 2014 9:41 pm    Post subject: Reply with quote

Carrera RSR wrote:
Your current turbo is an S2 spec is it not? It's using the #4 turbine and not the #6 used by a RoW series 1. (Tries not to start a confusing turbo spec argument!!). RoW S1 was K26 2470 6.10, Row S2 was K26 2660 4.10 although some replacement turbos appear to be K26 2664 4.10 and were fitted retrospectively to both S1 and S2 cars, certainly some I have found. I'm now running the same 2664 compressor wheel but with #6 turbine as used on the CGT's. My head certainly hurt a lot in trying to determine the various historical RoW versus US specs of original and replacement turbos.

The 2664 compressor should feel better then the previous 2660 even if the same 4.10 turbine housing was used on your car I guess

Sorry if this comes across as a challenge to your information. It's not meant to be. Its a minefield of info out there. We have a turbo specialist in the UK who believes that the S2 spec 2660/4 with 4.10 turbine provides better performance than than the original S1 spec. Agree with the 2470 compressor, not so sure with the 4.10 turbine.


No challenging here, I was just a little fuzzy with the explanation..

It is from my S1 engine, but you are correct that it is the 2664 and #4 turbine. It is a refubished turbo by a swedish company according to the tag, probably where the turbo got this spec. the S1 engine I had also had some S2 uppgrades such as ex.maniold and turbo de aeration up to the head, which is a little odd.

There was definitely more top end after the turbo swap, but lost more than I expected low down. I have an almost brand new #6/2470 in a box, where I would take the turbine from if I need in the future. But it doesnt seem so necessary according to the character of the dyno runs, so i will try to hit the 200whp nex time but with this turbo. I just cant afford to lose more HP down low, due to the slowest curves at our tracks
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morghen  



Joined: 21 Jan 2005
Posts: 7874
Location: Romania

PostPosted: Thu Oct 09, 2014 4:17 am    Post subject: Reply with quote

You can compensate by running more advance on low boost.
When i first installed the K27 hybrid the car was slow off boost and fast on boost. The 937 DITC fixes that by advancing the ignition off boost and the character is more balanced now, similar to stock but of course more power at the top end.
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Carrera RSR  



Joined: 08 Jan 2010
Posts: 1582
Location: Somerset, UK

PostPosted: Thu Oct 09, 2014 6:15 am    Post subject: Reply with quote

You can also give your engine a little more low end boost by advancing the cam 1/2 or full tooth depending on where it sits currently with a vernier pulley. Due to a couple of head skims mine was 1/2 tooth retarded. Great for top end. Not good for getting on boost early. Its now a 1/2 tooth advanced. Full boost and punch in the back by 2750rpm now but I'm changing up a gear at 5500rpm as it goes flat up top. Personally I'd rather have more bottom end and not rev its bits off!!
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1980 931 - forged pistons, Piper cam, CGT turbo, 951 ducted FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife LSD
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Rasta Monsta  



Joined: 12 Jul 2006
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PostPosted: Thu Oct 09, 2014 7:47 am    Post subject: Reply with quote

Key to 931 happiness: more compression, less boost.
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Carrera RSR  



Joined: 08 Jan 2010
Posts: 1582
Location: Somerset, UK

PostPosted: Thu Oct 09, 2014 9:13 am    Post subject: Reply with quote

Rasta Monsta wrote:
happiness: more compression, less boost.


Is that a 'pick two' options only?!

Oooops. Running more compression and boost than a stock S1. Looks like my happiness may be short lived!!
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1980 931 - forged pistons, Piper cam, CGT turbo, 951 ducted FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife LSD
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WEASEL149  



Joined: 19 Aug 2005
Posts: 595
Location: UK, Sheffield

PostPosted: Sat Oct 11, 2014 4:30 am    Post subject: Reply with quote

Rasta Monsta wrote:
Key to 931 happiness: more than 8.0:1 compression, and at least 2 bars boost.


Yes, I have to agree Rasta
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morghen  



Joined: 21 Jan 2005
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PostPosted: Sat Oct 11, 2014 7:45 am    Post subject: Reply with quote

haha, way cool
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Euro924S2  



Joined: 06 Mar 2008
Posts: 165
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PostPosted: Tue Oct 14, 2014 7:56 am    Post subject: Reply with quote

Really interesting stuff Cedric - thank you for posting your results and being as methodical as possible. Dyno comparisons between cars is a mine field but it's always helpful to see other people charts.

When comparing your chart to mine from a few years back (supercharged 931 engine) you get the same problem with torque falling off at rpm above 4.5k. This seems systemic throughout the 924 models and the common theme seems to be the cam profile. Your hp graph certainly starts to drop off after 5k as a result of your torque so I wonder if retarding the cam a touch would bring your power up at the top end whilst accepting a further sacrifice at the lower end - I guess it depends where you drive your car most of the time.

I'm going to start a separate post about cam timing in a minute to save de-railing your thread too much!!!

Cheers, John.
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UK spec '83 N/A with 931 motor with Eaton MP62 'charger @ 15psi. EFI - 565cc inj. Standalone Adaptronic ECU. 951 FMIC. Ally rad. Twin throttle. Recirc valve. Custom manifolds and CAI. 232bhp
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Rasta Monsta  



Joined: 12 Jul 2006
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PostPosted: Tue Oct 14, 2014 2:42 pm    Post subject: Reply with quote

Carrera RSR wrote:
Oooops. Running more compression and boost than a stock S1. Looks like my happiness may be short lived!!


Nah, I'm running 9:1 and about 10PSI. Car is very fast, and boost is nothing compared to modern hot rod turbos.
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CÚdric  



Joined: 27 Aug 2004
Posts: 1746
Location: Sweden

PostPosted: Tue Oct 14, 2014 5:24 pm    Post subject: Reply with quote

Euro924S2 wrote:
Really interesting stuff Cedric - thank you for posting your results and being as methodical as possible. Dyno comparisons between cars is a mine field but it's always helpful to see other people charts.

When comparing your chart to mine from a few years back (supercharged 931 engine) you get the same problem with torque falling off at rpm above 4.5k. This seems systemic throughout the 924 models and the common theme seems to be the cam profile. Your hp graph certainly starts to drop off after 5k as a result of your torque so I wonder if retarding the cam a touch would bring your power up at the top end whilst accepting a further sacrifice at the lower end - I guess it depends where you drive your car most of the time.

I'm going to start a separate post about cam timing in a minute to save de-railing your thread too much!!!

Cheers, John.


Yup, it is always very tricky. Especially when comparing roller dyno data to other roller dyno data or, or to my hub dyno data. Comparing betwwen two hub dynos would probably be the least painful since you can run them at the exact same way. And you have excluded tyres/strapping etc.

Yeah, there is a drop of in tourque, but pretty small since the power curve is rising pretty good all the way to the redline. thus it pulls very nicely all the way. Maybe not the most efficient, but fun. I cant really afford to lose anything down low, some corners on track are already a little bit frustrating, I have to go just to low in 3rd gear. Instead I will try to lift the curve a bit all the way form where I reach max boost. It will probably result in a little flatter power curve at the top since the compressor will reach the outer end of the map and start loose efficiency. And the turbine housing will probably start to build up some back pressure. But at this power level the turbo is obviously a tiny bit to big, there is no practical reason to have an even steeper power curve...
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gegge  



Joined: 27 Jul 2007
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PostPosted: Tue Oct 14, 2014 6:02 pm    Post subject: Reply with quote

When the torque is dropping it is all related to the choked flowcapacity of the head and not the cam. The turbo use as we know a good NA cam and by turbostandards that is hot.

A mild DYI portjob and advancing the standard cam slightly could solve both topend power and lowend responce.

My 10 cents.
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Carl Fredrik Torkildsen

924 turbo -81 Carrera GT clone LSD Coilovers
924 -85 DP kit, BBS RS, M030 and tuned engine
924s -86 Black on black with low ET "Phonies"
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Euro924S2  



Joined: 06 Mar 2008
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PostPosted: Wed Oct 15, 2014 5:33 am    Post subject: Reply with quote

Thanks both. I see how it could be the head Gregg but the NA shows very similar dyno characteristics despite being a poorer flowing head and having smaller valves IIRC?!?
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gegge  



Joined: 27 Jul 2007
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PostPosted: Thu Oct 16, 2014 1:21 am    Post subject: Reply with quote

Sorry for the OT:

I have a good ported 931 head showing +170cfm and a 924 head not far behind. The 931 starts with ~140cfm and 924 slighty less. The 924 has got larger short radius and the 931 better pressure recovery due to the combustion chamber. Similar results in the end. Why? Because both use 40mm inlet valves.

The related VW 8v conter- & crossflows does show the same caracteristics from 40mm inlets - from stock 140 up to ported 170cfm. A 270 cam in a stock head will result in 140hp and a 300 cam in a ported 170hp. Give or take...

Going turbo and adding boost just multiplies the output numbers, but be careful with a hotter cam since there are so many other factors in the equation: overlap, LSA, backpressure, manifold & hotside.

Supercharging is different to turbocharging of course, but if you want better performance above 5000rpm - start with the head and let it breathe.
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924 -85 DP kit, BBS RS, M030 and tuned engine
924s -86 Black on black with low ET "Phonies"
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CÚdric  



Joined: 27 Aug 2004
Posts: 1746
Location: Sweden

PostPosted: Wed Oct 22, 2014 9:31 pm    Post subject: Reply with quote

NIce with some performance discussions, even though they are slightly offT. There has been way to little of that on this board for a while

This seems to take shape as my thread for oncoming tuning, since we now have a little kid (2months old) I┤m not planning to go driving that much next year. Instead I will try and get some hours here and there in the garage. And as I will be on parental leave from april to october (thank god I live in sweden ) I will have time to think about car stuff

The car is in storage all winter so I will go with planning and buying instead of garage time.

I started out with buying a second hand J&S safegurad unit, it is and active knock control device, seems to have a really good reputation. So I hope it will replace my XS knock lite permanently. Will be a good safety net and tool when I start playing around.

http://www.jandssafeguard.com/


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fiat22turbo  



Joined: 18 Jan 2006
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Location: Portland, OR

PostPosted: Thu Oct 23, 2014 10:43 am    Post subject: Reply with quote

I have one of those in my 951S
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