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931 Track / DE Car Reliability
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L Cubed  



Joined: 01 Dec 2013
Posts: 11
Location: AL/GA border

PostPosted: Thu Dec 12, 2013 12:15 am    Post subject: Reply with quote

Thanks for the responses!

For me this car would be as fiat22turbo mentioned "unless they enjoy tinkering and have a spare car to drive". This statement is quite accurate if we add weekend track days. For myself, I want a project to tinker on that I can race. What I don't want is something that is down for months after each track day just to get it running well enough for the second race.

I don't mind spending some time and some money to upgrade the engine to get to this point, especially since I want EFI +Ignition control and newer turbo tech to reach near the 250 hp level.

So I have another question for those that haved raced: What was the most common/frequent failure that either happened at the track or didn't let you run at the track?[/quote]
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ideola  



Joined: 01 Oct 2004
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PostPosted: Thu Dec 12, 2013 1:53 am    Post subject: Reply with quote

IMHO, 200-250 BHP from a 931 motor is not high strung, even with CIS. After all, the Carrera GT had 210 from the factory. Just mimicking that kind of build (8.5:1 pistons, intercooler, 12 PSI boost, and appropriate timing control) is not hard at all.

Add in a boost controller, a water meth kit, and take the boost up to 15-17 psi, and you should be approaching 250BHP. Of course, a more efficient turbo would be a big help with longevity and reliability. Achieving 250 BHP should be no problem, even with CIS. Depending on what you plan to do with the car, you might have the option of programmable ignition, and better yet, full EFI / engine management, which will allow you to tune for optimum power without having to resort to all-out boost.

Weight-wise, getting to 2200# would be quite a challenge, particularly for anything that would be remotely streetable. My Club Sport project has been reasonably stripped (although not 10/10ths), and is still only net ~250# lighter than factory-listed curb weight. I'm not sure where I could find another 300#, to be frank.

The bigger issue, in my opinion, is reliability. Achieving reliability is NOT cheap, whether in stock form or somewhat tuned. The mistake most people make with these cars is that they look at the initial acquisition cost as an indicator of how much should be reasonably spent overall. Big mistake. To build a high performing AND reliable car will EASILY cost you 3x to 4x the purchase price you are considering, and that's just replacing with OEM components. Add in any of the aftermarket performance stuff, and it adds up really quick.

I agree with Cedric's point earlier about reliability being an indicator of the care and skill of the mechanic!

I hate to say it (because I love the 931), but a 951 might be a more reasonable starting point to achieve your goals. Newer by 10 years; fewer NLA parts; wider availability of performance mods; more modern engine management; and on and on. The 951 is not as rare as the 931 (especially at the track, given the Spec44 and 944Cup series), but not as common as the Miata. Might fit the bill...although initial acquisition cost might be more. I don't see any point in messing about with the stock 2.5L normally aspirated motor (or variants). VERY expensive to milk more power.
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ideola  



Joined: 01 Oct 2004
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Location: Woodstock IL

PostPosted: Thu Dec 12, 2013 2:14 am    Post subject: Reply with quote

Also, regarding the "frequent failure" question, while I don't have track experience directly, I can tell you that from what I've witnessed, and from my extensive experience with daily drivers, it's sometimes the most mundane things that fail.

- Suspension components suffer a lot of abuse on the track. Make sure the bearings and bushings are all refreshed, and consider sticking with steel trailing arms and a-arm, which will bend rather than break like aluminum, and can be strengthened with creative welding if necessary.

- Replace the alternator, the starter, and rebuild the main wiring loom that connects them to the battery. The most common failure I've had that's left me stranded is the alternator. It has failed on EVERY single car I've had. So I just replace them immediately now.

- Replace ALL hoses. Period.

- Consider the 944 radiator setup with a lower t-stat/temp switch combo, especially on the 931. Replace the water pump and the expansion tank cap. Use 60:40 water to coolant with water wetter.

The bottom end is fairly bullet proof on the 2.0L. The biggest problem is keeping the 931 cool, hence the cooling system overhaul recommendations. Failure on the track of any of the cooling components will cause a myriad of problems elsewhere, so don't overlook how important it is.
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Carrera RSR  



Joined: 08 Jan 2010
Posts: 1973
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PostPosted: Thu Dec 12, 2013 3:18 am    Post subject: Reply with quote

I said mine was highly strung due the continuing saga of shake down fixes. Cooling being the number 1 continuing process of elimination this year. Everything had been replaced and/or upgraded. It now has no cooling issues. The only issue is now I have bypassed the cabin heater I am now freezing. But at least the engine is safe.

If the OP is planning on EFI, standalone ecu, modern turbo and IC the why stop at 250bhp? This is the limit for a stock CIS system. With everything upgraded then 350bhp should be the target.

Also agree with Dan, there are cheaper options than modding a 931. I could have bought a CGT!!
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L Cubed  



Joined: 01 Dec 2013
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Location: AL/GA border

PostPosted: Thu Dec 12, 2013 3:41 am    Post subject: Reply with quote

Carrera RSR wrote:
Also agree with Dan, there are cheaper options than modding a 931. I could have bought a CGT!!


Carrera RSR what other cars are you thinking of? I haven't seen a CGT for sale in the states near me (south east).

A quick search of some classifieds shows 951s in the $7-12K which was kind of my anticipated budget for the build outside of consumables. The issue is I was planning on doing it in stages over a few years to spread the money out. If I had the cash on hand to do that I would definitely be looking into although the FOES service cost worries me on those 2.5L motors. While this isn't a budget build, I am trying to budget the costs over time to maximize my bang for buck.



Ok, what if I were to do the following in preparing the car do you guys think I would end up with a fun reliable track car that can drive to and from events?

Starting with a running 931
-Refresh old engine wiring - EFI + Ignition control
-Refresh old fueling/remove CIS - EFI and fuel pump upgrade
-Update cooling - 944/951 radiator & thermostat
-Replace any broken exhaust piping
-Add 951 intercooler
-Add boost controller - electronic control with EFI
-Replace worn out hoses
-Replace alternator/starter
-Replace old shocks/springs - 944 spec kit from Paragon or Ground Control kit + new bars 275 lb/in spring + 28mm t-bars
-Replace bushings with delrin/polyurethane components
-Add grippy tires - BFG Rivals
-Lightly strip interior of carpet, sound deadening and back seats to reduce weight

I think, from what you guys have posted and previous research, that this should give me a useable 200hp and 2500lb weight which should provide the thrill I am looking for while having an excellent tool for bettering my and my wife's driving/racing skills.
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morghen  



Joined: 21 Jan 2005
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PostPosted: Thu Dec 12, 2013 3:42 am    Post subject: Reply with quote

Carrera RSR wrote:
I could have bought a CGT!!


+1
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WEASEL149  



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

PostPosted: Thu Dec 12, 2013 4:08 am    Post subject: Reply with quote

Carrera RSR wrote:
I could have bought a CGT!!


CGT's are nice but your car would annihilate one on the track.

951's are great if you buy a good one. Buy a nail and you'll wish you had bought a 931... and yes, there are many bad 951's out there.
951's also have bottom-end oiling issues, particularly on track. Personally I'd baffle the sump for track use regardless of car.

A standard 931 with 250hp would be VERY highly strung - no charge cooling.

Add better rad, charge cooling and full engine management and 250hp would be child's play and reliable.
Removing the CIS means less inlet restriction, so the turbo doesn't have to work as hard to produce the same boost, so the standard turbo has a bit more headroom for boost without running off the map.

You'll have a lot of fun with 250hp and moderate lightening of the car.

A modern turbo will get you into the big power league but I think 350hp and longterm reliability comes with it's own set of challenges, but is possible no doubt.
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Carrera RSR  



Joined: 08 Jan 2010
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PostPosted: Thu Dec 12, 2013 4:57 am    Post subject: Reply with quote

For some multi discipline motorsport or reliability rallies I'd consider a 924S or 944/944S2 http://forums.tipec.net/viewtopic.php?f=25&t=15340. Less power potential but far more reliable to abuse subject to the base car purchased. Only issue with 944's is they are heavier than a 924. But lots of performance part options new and used.
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WEASEL149  



Joined: 19 Aug 2005
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PostPosted: Thu Dec 12, 2013 9:18 am    Post subject: Reply with quote

ideola wrote:
The mistake most people make with these cars is that they look at the initial acquisition cost as an indicator of how much should be reasonably spent overall. Big mistake. To build a high performing AND reliable car will EASILY cost you 3x to 4x the purchase price you are considering, and that's just replacing with OEM components. Add in any of the aftermarket performance stuff, and it adds up really quick.


Agree with this 100%. I never understood this mentality. I have the opposite mentality of "This car was cheap. That leaves me much more money to tune and improve!".
A Porsche Turbo deserves the TLC and money, regardless of it's worth IMO.
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CÚdric  



Joined: 27 Aug 2004
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PostPosted: Thu Dec 12, 2013 5:09 pm    Post subject: Reply with quote

Regarding money, I mean its nothing magic, its like any other car. If you want to play around with roll cage, EFI etc almost all of the costs are more or less the same, regardless of car.

What I like with my CIS 931 is the simplicity and robustness. Few and simple parts make it simple to work with. Thats the drawbaack of the alu 944 engine, way to over complicated for what you get, have you ever looked down under the bonnet of a 951 .. Although there are lots of power that can be achieved in those its a steep evil spiral, they are much heavier, so you need much bigger brakes and larger tyres that eats up at a faster rate etc etc..

If I raced endurance racing though I would chose one of the n/a engine instead, much easier to get thing to hold up. A 944s2 woulb be a decent choice.

Ive had one bolt come lose that holds the intake, that was in the carusel on the ring, unbelivable bumpy. Lost all boost of course, but an easy fix.

The cooling fan switch broke, and the thermostat was dodgy at the same time. To bad it was 40C and a track day, had to run with heating on to be able to run the car. Changed those and didnt have any problems with cooling whatsoever.

Otherwise after the dial in period to get AFR right (swapping out some parts like clutch etc) and so on nothing engine wise has troubled me. A worn out cam shaft, but I missed checking the play when I bought the engine, Judging by the sound before and after a correct adjustment it was definietly not correct earlier...Lazy misstake
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Dutch924-racer  



Joined: 23 Jul 2007
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PostPosted: Thu Dec 12, 2013 5:50 pm    Post subject: Reply with quote

I have had a 944 for track use, but the 931 is so much more fun !

Here some of my video's:

http://www.youtube.com/user/931turboracer?feature=watch
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L Cubed  



Joined: 01 Dec 2013
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PostPosted: Fri Dec 13, 2013 6:40 am    Post subject: Reply with quote

Dutch924-racer, would you mind tossing out a few numbers on the average operating cost to track the 944 compared to the 931?

I like the vids and website by the way. Have you run into any problems tracking the 931 after you upgraded the suspension and rebuilt the motor?

Thanks
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L Cubed  



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PostPosted: Sun Dec 15, 2013 4:45 am    Post subject: Reply with quote

So what would the be recommended car if I dropped the power requirement, between a 924 NA, 931, 944 NA? I am asking this because I have found quite a few more 924 NA and 944 NA near me for cheaper and I wouldn't be opposed to turbo'ing a 924 NA
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Fifty50Plus  



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PostPosted: Sun Dec 15, 2013 5:04 am    Post subject: Reply with quote

My suggestion is to check out what type of track driving is available to you (car club driving events, SCCA type racing, enduros, drag, hill climb, solo, etc). And then pick a car type that will fit within their rules.
Building a Frankenstein may be fun (and expensive) but you may not be allowed to play with it at a lot of venues.
Go with a basic reliable FACTORY DESIGNED car and focus on enhancing it within the local rules and your budget.
Just as a data point (and Ian and Vaughan can check in if they wish), a really cheap weekend at an SCCA race for me is between $500 - $700 on average but depends on mass quantities consumed

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L Cubed  



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PostPosted: Sun Dec 15, 2013 7:08 am    Post subject: Reply with quote

I live near Road Atlanta and Barber Motorsports Park. There are also two SCCA regions that I am between for autocross. So I have autocross, lapping, driver's education and some NASA Time Trials available to me which are the type of events I am interested in. I like racing against the clock and testing my engineering skills in combination with my driving skills which is what I did designing Formula SAE cars in college. This is also why I don't want to just get a miata.

Basically if I find a 931 in the right shape for a decent price near me I probably get that because then I don't have to swap over to 5-lug stuff. If I can't find one I was curious which would be a better replacement a 924 or 944. I am leaning towards a 924 because of relative ease of adding power compared to the 944 by turboing it and not having to deal with the extra weight or timing belt issues of the 944.
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