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Project black 924 :)
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WEASEL149  



Joined: 19 Aug 2005
Posts: 592
Location: UK, Sheffield

PostPosted: Wed Sep 16, 2015 7:16 am    Post subject: Reply with quote

Raceboy wrote:
That was my guess. The rods are quite heavy and could not cope with the hugely increased tensile loads. I have never dared to rev the 924 engine past 7k on regular basis...


It begs the question then... if you want to rev up to 7500rpm with a hotter cam in a max effort turbo engine, is it worth buying ARP bolts for stock rods, or just buying new and lighter rods with their own corresponding ARP bolts?

This is the first time my faith in the stock rods has been shaken a little.
Maybe stock rods with full prep/shot peen lightened to 815g with ARP bolts would hold up better?

It's definitely rev related failure rather than boost. It's a diesel engine so designed for high compression...
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DutchPug  



Joined: 27 Jul 2008
Posts: 94
Location: the Netherlands

PostPosted: Wed Sep 16, 2015 8:29 am    Post subject: Reply with quote

Yes could very well be rpm related. But at two bar it did not hold up long, just a few hundred km and have the rev limit since i have the cam. Perhaps just a coincidence. I do intend to shift just before the limiter basically everytime i floor it, meaning i took it to 7000 - 7200 rpm a lot. It's just too much fun

Think in any case it is not sensible running high rpm with the stock rods... but if the turbo comes on boost late... you want te stretch the power-band as much as possible.

Maybe some more clues appear when taking the engine apart.

Anybody know some off the shelve forged pistons for the NA?
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WEASEL149  



Joined: 19 Aug 2005
Posts: 592
Location: UK, Sheffield

PostPosted: Wed Sep 16, 2015 9:28 am    Post subject: Reply with quote

Only pistons I can think of that would be almost 'off the shelf' would be Mahle VW flat tops at 87mm.
These need 22mm small end bushings or rods with 22mm small end.
Would have to check where that would leave you though with compression ratio. Can't remember off the top of my head.

Raceboy - didn't 'Racing' run 2bars with essentially a stock bottom end apart from pistons?
I think he kept stock cam though so probably didn't rev beyond 6500rpm.
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Raceboy  



Joined: 01 Mar 2004
Posts: 2292
Location: Estonia, Europe

PostPosted: Wed Sep 16, 2015 4:00 pm    Post subject: Reply with quote

Jesper (Racing) did rev the engine to 7000 and occasionally to 7200 but the K27 turbo he used did not pump as much air at 2bar as Pieters Garrett and he did not use E85 _> made less power too.
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Last edited by Raceboy on Wed Sep 16, 2015 7:50 pm; edited 2 times in total
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CÚdric  



Joined: 27 Aug 2004
Posts: 1684
Location: Sweden

PostPosted: Wed Sep 16, 2015 4:31 pm    Post subject: Reply with quote

It could well be a combination of peak cylinder pressures and revs. Its easy to get extremely high pcp with E85 and high boost/aggressive timing since its not knocking. But i would have guessed the head gasket would have gone before it got to bad. But its hard to know if you cant measure it.

Stock rods are very heavy, the verdi rods that Joakim.s uses is approx almost half the weight of the stock ones. And that engine have had its fare share of beating around 7500rpm and high power figures. So it seems to work well.

BTW, great decision to continue with the 924 engine, this is one of my favorite threads! Have you logged any performance figures? 100-200 ?
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morghen  



Joined: 21 Jan 2005
Posts: 7808
Location: Romania

PostPosted: Wed Sep 16, 2015 4:47 pm    Post subject: Reply with quote

Maybe it was just a coincidence? Could it be that that rod had a fabrication defect or has had a harsh life and now you've put it up to the test?
One incident does not confirm anything IMO.

Perhaps lightened and why not stregthened stock rods would hold to 2bar and 7200RPM. Is your valve train factory?
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CÚdric  



Joined: 27 Aug 2004
Posts: 1684
Location: Sweden

PostPosted: Wed Sep 16, 2015 5:01 pm    Post subject: Reply with quote

That is of course an important factor, could as well be just a coincidence, it could have held up for a year aswell, 1 engine is a small statistical sample

Getting lighter forged pistons+balancing of the bottom end will help aswell. Maybe shotpeen+polish the stock rods if you want to be on the safe side?
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931 twinturbo  



Joined: 20 Jun 2007
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PostPosted: Tue Oct 18, 2016 2:55 am    Post subject: Reply with quote

Any updates?
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mikeycrum14  



Joined: 19 Jan 2017
Posts: 112
Location: Juneau, Wisconsin

PostPosted: Fri Feb 03, 2017 9:08 am    Post subject: Total Newbie Reply with quote

Looking for performance upgrades on my NA 924. the engine is bone stock. five speed trans and a Stage 3 racing clutch (apparently). Looking to upgrade the engine cheaply and safely without ruining reliability. Ive heard about upgrading to EFI from the CIS. What would that entail? any suggestions on upgrades. minimal car knowledge (first car).
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DutchPug  



Joined: 27 Jul 2008
Posts: 94
Location: the Netherlands

PostPosted: Sat Mar 04, 2017 9:43 pm    Post subject: Reply with quote

Update...; No time for this car. Have not even touched it since.

Have a spare engine and ordered billet connecting rods 4 months back, should be here soon. Still looking for pistons.

The idea is to make a stronger engine and upgrade both the intake and exhaust manifolds. But, don't hold your breath on updates
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