Originally Posted by 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.

Originally Posted by Rob Edwards

Seems to me that a large piece of the pie in engine failures (other than just plain metallurgic failures) is a combination of poor oil control and insufficient control over ignition timing and fueling. Which both boil down to preventing detonation.

Sharktuner, Alpha N, VEMS, megasquirt, Link, etc, are amazing tools, I have to imagine that the the initial buy-in on any of these systems would save their costs many times over in preventing or at least prolonging the on-track lifespans of these motors.

Originally Posted by Rob Edwards

For race tuning, I agree 100%! I am barely competent to do a safe street tune with the ST2 and SP (where 'safe' = no knocks anywhere on the map), but on track the margins are so much smaller. At least I'm willing to know what I do'nt know, and the motor we're planning for the white Zombie is certainly not going to be tuned by me.

Originally Posted by Lizard928

Richard,

There are many articles on this, I challenge you to do your own research, your own tests, and draw your own conclusions.

That being said, for the intercept angle of the injector to the airstream. It should never exceed 45 deg, but is best to be shot straight into the runner therefor being straight in line with the airflow to achieve the best atomization.

Having the injector far away from the valve can hurt idle quality especially with big lumpy cams/low vacuum (less than 14" Hg). However there are definite gains to be had from this. Moving the injector farther away from the valve allows more time for the air/fuel to atomize properly and remain in suspension when air velocity comes up at high rpm. This should improve peak power but-because of poor low-rpm velocity-at the expense of idle quality especially with injectors larger than 96#.
Some engines have seen 50+ hp gains just from moving the injectors further away from the valves because of the more consistent AFR in the chamber, and better atomization.

As for my intake. I made my runners vertical, 90 deg straight up. I could have angled them at 15 deg to match the one wall on the S4 intake port. But I chose vertical, and then modified the port where the injector notch is to achieve a more vertical port. My total runner length is closer to 7.5", and the injector sits above the port looking straight down the middle into it. I'm running 60# injectors btw, which did achieve a very nice idle on a stock S4 intake manifold. Keep in mind, this intake is designed around my own theory (which hasnt been fully tested, but will be soon!), for maximum HP with boost on a 5.0L motor.

Originally Posted by IcemanG17

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...

Originally Posted by Mike Simard

Aside from the brittle material, the 928 design is very good and had features that are superior to the old American pushrod v8s.

The cracking seen in the main webbing is real though and feel that I've greatly reduced (I nearly say eliminate) the chance of that ever happening in my own engine but nobody else at all seems to care.

The reason for any V engine cracking there is detonation forces.
(the friction welding TBF failures in autos are a different story)
I consider fastener design the most misunderstood part of engine building and that's key to why I don't worry about my block cracking. I make special head and main studs and use a girdle over the bottom of the engine that must look pointless to everyone else. I know the direction of forces seen when things go wrong and that's what dictates the design.

I've made bunches of head studs and am making more now but nobody ever wants the mains.

These threads always seem to bring up chevy and ford fanbois and they spout about durability (and cheapness) but I've seen plenty of them fail. When I go racing there's typically a vette motor that fails every time but yet we have to hear about them being bulletproof in these threads.

It's an ironic case of mass perception, in daily driver cars, most consumers that buy a Honda feel that they are so smart and if it breaks down it's something that happens even to the best sometimes. if they buy a Ford, it gets taken back to the dealer for minor stuff becasue it's a damn POS!

And so it goes with Porsche and Chevy engines

Originally Posted by Mike Simard

Aside from the brittle material, the 928 design is very good and had features that are superior to the old American pushrod v8s.

The cracking seen in the main webbing is real though and feel that I've greatly reduced (I nearly say eliminate) the chance of that ever happening in my own engine but nobody else at all seems to care.

The reason for any V engine cracking there is detonation forces.
(the friction welding TBF failures in autos are a different story)
I consider fastener design the most misunderstood part of engine building and that's key to why I don't worry about my block cracking. I make special head and main studs and use a girdle over the bottom of the engine that must look pointless to everyone else. I know the direction of forces seen when things go wrong and that's what dictates the design.

I've made bunches of head studs and am making more now but nobody ever wants the mains.

These threads always seem to bring up chevy and ford fanbois and they spout about durability (and cheapness) but I've seen plenty of them fail. When I go racing there's typically a vette motor that fails every time but yet we have to hear about them being bulletproof in these threads.

It's an ironic case of mass perception, in daily driver cars, most consumers that buy a Honda feel that they are so smart and if it breaks down it's something that happens even to the best sometimes. if they buy a Ford, it gets taken back to the dealer for minor stuff becasue it's a damn POS!

And so it goes with Porsche and Chevy engines