IcemanG17

As many of you know, I recently bought and built a Chebby LS2.....with minimal "power increasers" other than a better cam it will make at least 520hp-475ftlbs out of a 6.0L engine. The chebby LS series engines have much smaller bore spacing than ours 123mm vs 111.8mm but with a slightly taller deck height allowing more stroke (232mm vs 235mm)....the heads do flow better than a euro 16V 928 head by quite a bit....about 260CFM vs around 212 CFM.....which is nearly identical to the 32V heads....

I was doing research on successful long lasting V8 race engines......the single different "design" difference I see vs our 928 engines is the bottom end....the block & girdle design of our engines appears much weaker than many other designs.....specifically the chebby LS series and the Ford Windsor Y block design.... Looking at how many stroker or high HP 928 engines crack the block webbing it has me thinking that the lower girdle might be a significant weak spot...

Thinking further in theory the "open deck" design could allow for the cylinder bores to vibrate which contributes to the failure as well...however many other high RPM V shaped engines run open decks...so I am not that sure contributes as much as the girdle....

Mike Simard did some research on the girdle and tried to strengthen it....sure I am FAR from an engineer....but looking at the 3 major block parts....the block itself appears stiff to me....the girdle appears like a noodle and the oil pan seems fairly sturdy... I just think that having the crank held by only 1/2 the block seems weak...

The LS and Ford Y all have deep block skirts-web where the crank slips in with plates, sometimes with a 1 piece full circle front main bearing...they also run the bores much deeper into the block

It could also be a combination of issues....the open deck design paired with the longer stroke causing the increased side loading of the unsupported bores which drastically increases the stresses on the already weak block-girdle..... However if side loading due to increased stroke is an issue...why not increase the RPM to gain power....this has NEVER worked in 928's yet....due to oiling issues with heavy rotating mass of the 928 internals...

SO the MILLION $$$ question.... "IF" a new, perhaps billet 928 block was built.......would a stronger lower end help? I think it would....

Of course I am broke and endlessly stuck running stock to near stock 928 engines.....but I can DREAM dammit!!!!

Alan

Better oil control is a required first step for any car that will see prolonged high rpm and high G turns.

Alan

SeanR

Odd, I've always considered the block/girdle to be one of the 928's strengths when compared to a Chevy/Ford engine. I might just learn something here.

TexasDude74

The lower end seems good to me. Chevy came up with a nearly identical bottom end design on their short lived lt5 which has been dry sleeved, wet sleeved, bored, stroked, turbo'ed, injected and blown without ANY block failures, and they've been pushed well past 1500 horses. IF, there is a problem with the 928 bottom end its with the material itself; which means there is no easy solution. If it's a matter of the material being overly brittle as some say, then there is definitely a glass ceiling as far as output goes. However, if it is a heat cycle issue as a few suggest, then all of these engines are destined for fatigue related failures no mstter how much or little power they produce. Going the billet route fixes the problem either way but raises lots of questions. How true to the original design does one stay? Would be tempting to switch to timing chains, close the decks, different water pump, deck height, bore spacing. Where does it end?

hacker-pschorr

Unless you can determine exactly what caused a 928 engine's block / girdle to fail in each instance, this is kind of a pointless topic.

I've seen billet engine blocks blown to smithereens. No engine, no matter how "strong" will fail if the tune is off or something unexpected happens (like a bolt failing, pin coming lose etc...)

Sorry, but in my opinion, 99.9999999% of 928 engine's that suffered a catastrophic failure was caused by some outside force, not an inherent weakness of the parts themselves.

If these blocks were so weak, Todd's twin turbo would have turned to shrapnel the first time he put down over 800hp to the wheels. Yes I'm well aware of certain people who feel those numbers are pure BS. Those individuals have their own issues to deal with.

Am I saying a 928 engine is indestructible at any / all power levels? Don't be silly..... I'm just a bit tired of all these pure speculation threads that can never and will never be proven one way or the other.

LS motors fail at the track all the time, at all power levels. **** happens.

SeanR

Well cupcake, I think that is why he started the thread.

Speedtoys

Any angle we can blame Obama? Just looking for an easy out here...

Lizard928

You'd have better luck blaming someone from germany who's initials are AH.

eijun

What would be better is everyone in Rennlist/928OC/Pelican/Rennsport/ETC ban together and fund a research on it and just build a new engine for the 928.

While keeping our old 928s, we buy some junked 928's (with intact body frame), and install the new engine into it and try to get it near 50/50 balanced with the new engine (all leather interior, nice speakers, comfort stuff etc)

Oh and make it if the belt fails, it wont do so much damage as it does now.

OTR18WHEELER

All I know is, a chubby SB 400 4 bolt main is a strong engine.

xschop

The 928 engine halves are made from different materials resulting in different yield strengths.

17prospective buyer

I never thought the block was weak... shouldn't we focus on fixing the oiling issue? Which blows up more race 928 engines than main bearing catastrophic failure i'm pretty sure.

IcemanG17

Great point............what has blown up more 928 race engines? A couple thoughts

Personally I have blown-seen 7..... 3 for me and 2 for Sean 2 for Dennis of those it was this:

1: 5.0L 32V not blown, but near dead rod bearings causing low oil pressure...stock S4 oiling system (mine)
2: Not assembled correctly from engine #1...doesn't really count (me)
3: 1984 USA 16V classic rod bearing death...well worn engine with lots of oil leaks and crap oil...stock S4 style oiling (1st estate engine)
4: 5.0L 32V properly built, but still near stock S4 oiling system....blew rod bearings in about 10 hours on track (sean)
5: 5.0L 32V stock.....sucked an intake valve from over-rev on stock engine 7k isn't a great idea...this ran a full IJ crank scraper that was damaged (sean)
6: 5.0L 32V.....classic rod bearing, but with accusump? However it did have LOTS of time on track.....50 hours or more?
7: 5.0L 32V...same engine from 6, but had the bad glyco "too tight" rod bearings and died quickly...might have had other assembly issues?

4 died from classic oiling issues, 1 had a mechanical failure of valvetrain from too many RPM....(it was a modified chip with 7000 cut) two had issues with bad parts or assembly

Moving on.....Anderson blew 2 strokers. Obviously professionally built and have dry sump. The 1st went crazy lean and blew after the CF intake failed...This engine had lots of time on it above 500whp....it had cracks in the block.....but ran fine until the intake killed it

Andersons last engine clearly had a parts failure....but I don't think that has been determined 100% yet what the precise failure was.

Don hansen blew his stroker, Louie Ott blew his GT, Sean nearly blew his street S4....I can go on and on about oiling problems

I will have to research the 32V LT5 engine design a bit more

blau928

Interesting notes..

The common cause of death seems to be RPM induced without adequate equipment.........

I wonder why someone would put an RPM limit on a motor at 7K when the rotating assembley is only designed for 6600....? (I'm gonna have to calculate the piston speed and load on this, but it seems like going from 6000 to 7000 would add 45% more load on the rods...) I am surprised that the rods didnt break in that car...

Just from observation, the dry sump seems to be the best cure for the oiling issue, as it removes the excess oil in the heads at high RPM, and keeps the oil pump fed. Whereas in a stock oiling system, the oil is in the head, mist is everywhere, and no oil to the pickup to feed the bearings....

Just a thought...

Lizard928

Brian,

None of those that you list are linked to a weak bottom end.

And as to the oiling deficiencies, there are some weaker spots for sure, but to think that the oiling system is 100% is blame is silly.

Greg Brown told us awhile ago about a 911 variant that had soft bearings (like ours), and when on the track would nuke engines very fast. But once the timing was pulled back a little (not run on the edge like the S4), they lived happily. All because the light knocking that was happening would hammer the bearings to the point of failure. This is the first I have really mentioned this on here. But this needs to be given thought.

A race motor that is held at higher RPMS really should have the injectors MUCH further from the valves to help obtain a more even AFR throughout the combustion chamber. This will help to give a better burn, show less knocks, as well as help to control/reduce some ring flutter (of which the S4 engine is HORRIBLE for).

The intake manifold that I have (99%) completed for my turbo car is using a shower style injector placement for these specific reasons. Along with a vacuum pump to help try to obtain a better ring seal and prevent ring flutter.

Everyone is always chasing after more power out of the engines and for good reason, you want to be faster, especially on the track. And on a street car I will put a MUCH more aggressive tune then I would EVER put on a track car. The VEMS setup that I just put onto Sean's track car with VEMS uses a maximum of 26 deg of advance (stock cams), and above 5k rpm you can clearly see that the intake is a massive restriction. My dyno testing on a stock S4 showed negligible difference on output between 30 deg, and 26 deg. But with 26 deg, there was not even a hint of knocking.

You have had good success with the 16V motors, I feel this is likely that a) their crankcase breathing isnt total gobshiyte, b) stock form run less advance, c) smaller bore diameter is less prone to ring flutter.
There are likely more factors at play, but these are a good portion of them.