355 Stroker pinging

[96VS355]

Wondering if anyone has any ideas,
I've had my 1996 304 rebuilt as a 355, and I've found it's developed intermittent pinging. On a cold morning it doesn't make a noise, but once it's been running a while, or on a warmer day, you can almost predict it when you step on it. It's round 10-10.5:1 comp with flat tops, Scat stroker kit, mild cam, runs 98 pump, slightly colder NGK plugs, Starr modified bananas with 90mm TB and K&N pod, chipped, thru T5 and 3.45:1 diff.

Now I'm presuming a lot of this is heat related, although the standard temp gauge is still sitting in the same place it was when it was a 304 motor. The block had a minimal rebore and the heads were ported, so I guess that makes the chambers a little closer to the water, plus the extra surface area of a longer stroke length. It has the standard radiator and thermostat, and the old standard cooling fan, and from experience with other 304's I've owned in the past, that normally only operates when the motor's dead cold or when the viscous fluid heats to a point. Now the fan's spending a lot more time on, and hence loading the engine and sapping its power, and possibly also helping it ping. A couple of times also, it's really dropped off in power when it's started to ping, so I assume that the knock sensor's doing its job.

When does it ping? Cam comes on around 2600, and if I go from a light/medium throttle to heavy round then or just after, it'll usually let out a ping or 2, also if I quickly pick the next gear, it has sometimes pinged again the instant my right foot goes down again. It originally ran 320bhp and about 660Nm. Since then my dyno guy's pulled timing out under heavier throttle and higher sensed temp. It did reduce the ping a bit, but it's still there.. and I've lost a few hp and quite a few Nm in the detuning.

It does burn a bit of oil, say about a litre in 2000 kms - which some say is normal for modified engines and about 3 or 4 of the plugs end up with oil making their way up the threads from within the chamber.


Anyone else had this kind of problem with a 355 or stroker in general? Have I given enough info here to be of help? Whilst I get the principles behind how a motor operates, I'm not a mechanic. My wallet wishes I was however.

Cheers

 

[greenfoam]

How is the fuel ratios on it? is the guy at the dyno retuning it or just pulling timing on the dizzy?. If tune and the fuel ratios are good the easiest fix is probably going to a bigger cam to drop the dynamic compression a bit as it must be too high (cams too small for the compression in it)

 

[Immortality]

i think your problem is related to the oil usage, 1 liter for 2000km's seems a lot. oil in the combustion chamber is like reducing fuel octane and can lead to pinging. a rebuild engine shouldn't be using oil except during the "run-in" phase to bed the rings in. then oil usage should be as per any other holden V8. do a compression test, will also indicate if the cam is to small for the static CR.

 

[Morton]

That's what I was thinking. If you've got oil on the plugs and are using a litre that soon, then there's a fair bit of oil in the combustion chamber, and despite the fact that you're running 98 pump fuel, it's going to be effectively around regular unleaded depending on oil consumption. And that's no good with a compression ratio as high as yours

 

[96VS355]

greenfoam, immortality and morton,

Thanks very much for your feedback, my engine builder has queried the air:fuel ratios and the dyno guy has queried the oil, in particular the valve stem seals... so I think the smartest thing to do first is a comp test then go to the dyno guy from there.

The cam in it is a Camtech, now unfortunately while I kinda vaguely get what this all means, that's about it. 112 deg lobe separation, 228 deg duration at 50 thou of lift, with an advertised duration of 273 deg.... just in case anyone has any thoughts on those specs in that kind of motor...

One last thought, the original 304 motor did about 220,000 kms before I did the reconditioning and conversion, and the one thing that is original in the heads are the valves, which were deemed to be ok.. is there any chance that the valve stems can be worn over age and therefore not allowing the seals to seal properly and hence letting excess oil down into the chambers? Does it work that way??

Thanks again for your thoughts, greatly appreciated

 

[greenfoam]

The cams about right so that should be ok, I guess since the motors going to be sucking alot harder than a stock 304 it could be bringing oil past the valve stems. I'm not sure that would cause the pinging but if everything else is fine I guess you need to look at that. I'd like to see a printout of the airfuel ratios if you have one from the dyno, it should be at around 12.5:1 or at least under 13:1 in the areas your having pinging to discount that

 

[96VS355]

OK I'll get that info next time I talk to the dyno guy.. either that or have him check it.

Originally when the motor was first started and dynoed it was given a haltech, the timing was retarded to buggery and fuel was poured into it, the extractors ran red hot even at idle, it seemed to make good power but only dynoed 287bhp and I'd use 1/4 of a 75 litre tank to go about 50 kms if lucky, it idled at 1200rpm, melted leads, O2 sensor wire, etc.

Then my mate put me in touch with another tuner who told me it was best to keep the standard computer and rechip it, so we did, it ran 320bhp and idled with a very slight lope at 850rpm. It had awesome power in heavy foot mode, went like a gun from 2600 to 6000 and felt like it was a walk in the park, but was fantastic on fuel in cruise mode, in fact on the highway, not that much worse than the 304. We took it for a road trip to Melbourne via the hume and it pulled about 9-10 litres per 100km, and it didn't miss a beat.

On the way back we took the Princes Hwy and had a little incident, threw the alternator belt which then derailed the water pump belt. I managed to switch it off as the temp got to about 1/2 on the standard gauge, it vomited about 2 litres of coolant over the ground. I don't know that there is a connection, but it more or less started to ping from roundabout then onwards. I completely drained the fuel tank and lines and changed the plugs when we got back to Sydney because I'd also been forced to use some 95 octane with octane booster due to no 98 being available in country vic.. but it still pinged, so I went back to the dyno guy who detuned it and here we are today...

Cheers again.. I know they say performance cars are always traumatic, but I was hoping that would be due to breaking things like gearboxes and diffs.. both of which have been fine so far, touch wood!!

 

[greenfoam]

Hey you know it could easily be something very simple like just one bad injector do all the plugs look the same?

 

[96VS355]

Cylinders 1, 5, 7, and 8 all have oil around their threads but the colouring around the electrode and the tip of the plug's thread is pretty much the same... at least it was last time.. something else to check this time around...

 

[Immortality]

for the mileage i would have done the valve guides no matter what. they may have been within tolerances but the question is by how much and how much more wear before they aren't within tolerance any more? the fact is that higher RPM's with greater loads (higher lift with heavier valve springs) on the valve train is going to increase the wear rate. getting some K-liners fitted is the best solution, will also ensure a good valve seal.

cooking a motor can stuff the piston rings, although i don't think you got it that hot it is a possibility. a compression test will confirm that anyways. greenfoam is also correct, one dodgy injector causinga lean cylinder can also cause your problems.

the fact that it run good before the overheating incident suggests the original tune was good and the problem lies elsewhere