[DaveN]

Tks. I'm good for everything being stock as far as the block and head.

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[DaveN]

Flash, any gotcha's as far as the SC being in the way when doing the head gasket? Proper order to remove the least amount of SC hardware without damage maybe?

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[banditsc]

You just need to remove enough to get the timing belt covers off. So removing the brackets that tie into the engine lift bracket should be enough, the SC itself can stay in.

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[rxter]

Had you put a new head gasket on before you installed the SC?

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[flash]

you actually need to remove the main mounting bolts so you can slip the SC forward enough to get the belt cover off. i think i have a write-up - let me try to dig it up tonight

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[banditsc]

I didn't have to and I just did it the other weekend. I did remember one other pieces I had to remove, one of the idler's on the back left side of the SC that is against the cover. Once that and the bracket on the side were off I had no issues with the covers.



I did do the HG shortly after SC, the timing just worked out that way.

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[rxter]

Did you replace your HC with the SC Dave?

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[DaveN]

I did an engine rebuild specifically for the SC, everything was new, new.

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[DaveN]

Well it's taken a while buy my mechanic finally had some time to remove my head <img src="/forum/images/smilies/968/sad.png" class="smilie" alt="" /> Very bad news.

I know I blew my head gasket which is no biggee but then he sent me some pictures and called, cylinder number 1 is scored. He now has to figure out how the best way to fix/replace an Alusil block without the funding some of us have, yea, you know who you are (insert jealous emoticon here <img src="/forum/images/smilies/968/wink.png" class="smilie" alt="" />



The main cause here was a failed Widefire gasket. I had a track day weeks prior and the car ran fantastic but I was going for a top speed run when this happened. He surmises that while the head gasket (and the engine components) will take 10-20 second full on bursts if is always tempered with braking and slowing. Putting the car at 6000+ for over 1-2 minutes with no break pushed the head gasket too far with the heat and pressure. He has been at this for 30 years so I am very confident in his work and diagnosis.



Once we figure out where to go with the rebuild I will never care how fast my car can go again, lesson learned. I was too eager to tell every one with a S/C what the improvement of factory was, lets just say 270 KPH, which is a stupid speed for "fun" driving anyway.



Car is off the road for 2012 now but I will update as we progress with the course of action. Back to Mr. Trusty Toyota, 75 bhp should keep me out of trouble. <img src="/forum/images/smilies/968/sad.png" class="smilie" alt="" />

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[flash]

oof - that looks like detonation



i never considered sustaining that rev point for that long. i've never been able to do that on any track. most tracks are barely that in a full lap, and there is no way to maintain that rpm the whole lap.



if anybody remembers, i designed this as a STREET KIT. i know a lot of people want to track it, and a number of them do. so far this is the first failure of this nature, but i wonder what could have caused the detonation. we have other guys regularly tracking it without issue. are you sure the head was not shaved when the engine was rebuilt? the tuning is right at the edge of the fuel availability, and any increase in compression would mess that up. the wide fire only comes in standard thickness. if they did a clean up of the head surface, coupled with sustained high rpm, you could have run out of fuel.

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[DaveN]

We pulled the records from the shop the head went to and they said the original head was dead flat so they didn't have to do anything but clean it up. No worries about the street kit, normal use and this probably never would have happened. I just decided to plant my foot for a while, stupid me.

I'm no expert so you may have to enlighten me. I only know detonation from the standpoint of using less that recommended octane (93). At full bore if you run out of fuel so you get the same effect?

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[flash]

i just wonder what "clean it up" meant to them. to me, that's take off .002" or so, just to be sure i had a smooth surface. any irregularities could result in lifting. my head was "dead flat" too, but still had irregularities that would have resulted in lifting.



as for the mixture issue, yup. when the mixture goes lean, it reduces the effective octane rating. heat has the same effect.



running 93 octane (90 RON + MON/2) will cause the knock sensors to back off the timing. the problem is that they can only back it off so far. after that, you get detonation. while the kit is tuned to 91 octane (RON + MON/2), i would not consider any such high speed run without running 95 octane (93 RON + MON/2)



the other thing to consider is the effectiveness of the fueling system. if you are going to run extended high rpms, you must be certain that the fuel pump is outputting the maximum volume, and that it is getting to the cylinders. at extended high rpms, the system is going to use every drop of fuel. if there is anything at all less than 100%, you will not have enough fuel to keep things happy.



checking pressure is not good enough. if you closed off the injectors, the pump would still make full "pressure" but not be outputting enough volume. think of it like your garden hose. when you squeeze it off, the pressure increases, but the volume decreases. the same thing can happen in your fuel system.



the fuel filter must be completely clear of any obstructions. the least bit of gunk in there can easily drop your system volume.



the injectors must be completely cleaned, balanced, and up to snuff



i have always said that this kit is at the ragged edge of fueling at the very top. the injectors are maxxed out over 6k rpm. a quick look at the dyno charts shows that the mixture starts to head toward lean again way up top. that isn't a problem normally, and even on the track you don't get there for long, which has so far not shown itself to be a problem. holding it up there though is asking for trouble.



in order to do what you want to do, i think you will also need to change to a colder plug.



before attempting any such run, i would also be sure to have an air/fuel meter installed.





the upside is that the Stage 2 addition kit should address all of this. too late for this engine, but should prevent such things in the future.





feel free to ring me up to discuss any of this.

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[jfrahm]

If you run lean you can have terrible detonation problems.



An engine tuned in reasonably cool weather can also detonate or ping badly on a hot July day. I had to pull out 4 PSI on a boosted Saab for July days. In cool weather I did not even need premium. Heat soak is also a problem, you can boost like crazy on a cool head but when it is cracking hot you get detonation. That is one way a street engine has a lot of wiggle room, lack of sustained boost for most people. Just short squirts.



Water Injection can be a lifesaver, or dialing back boost if you can during hot weather. Maybe try a restrictor plate for those hot months.



It'd be interesting to see the walls and if you also got scuffing. That often comes free with detonation in a motor with short skirts.



-Joel.

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[DaveN]

My walls are a mess so I'm told. I'll post pics when I get home.

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[flash]

ugh - bummer - welcome to the club

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[jfrahm]

I suggest sourcing a low mileage motor with the late rods and tossing it in. If the miles are confirmed reasonably low and it'll pass a cold leakdown test I would not pull the head or replace rod bearings or anything like that. Check the variocam, replace any leaking seals, a couple new belts, and rip it. Some may argue that it'd be better to freshen but if a nice stocker can be found I feel you are more likely to generate new problems when poking around in a perfectly good motor rather than fixing or preventing problems. Plus good labor is very expensive, you may never need a head gasket so why pay to replace one until needed? I do not think a WF head gasket is really any better than stock so I would not go in after a good stocker just to change it out to a widefire.



-Joel.

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[DaveN]

Here's some cylinder photos. It's just a little carbon, come right out with a Scotchbrite right? <img src="/forum/images/smilies/968/wink.png" class="smilie" alt="" />

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[DaveN]

Update. Thanks to banditsc I sourced a block and pistons from DCVinyl in WI. My PM says the pistons were probably shot so I have better get a spare set. Shipping aside (320.00) the cost of the parts was fair and timely. Insurance is off the car for the year now as it's not going anywhere until the fall/winter rebuild. Too bad now that the sun finally came out.

The guy at DCVinyl was also concerned about heat soak changing the hardening of my head and thus making it more prone to warp.....gasp. I didn't know they even hardened Al or that the engine could get hot enough to affect the head casting that way. He recommends having the head sent out for hardness testing. Yikes.

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[Eric_Oz_S2]

I have always been amazed that the 968 injectors could deliver enough fuel for this kit. On my S2, the turbo injectors which flow around 20-30% more than the 968 injectors are at their limit at 6400 rpm. You can see the AFR increase above about 6000rpm. Combination of extended high rpm would lead to intake temps of over 60C (assuming 20C ambient). It is worth fitting a knock counter - I had significant detonation at higher rpm with stock timing and had to pull at least 4 degrees off at higher revs. Even with an intercooler, high octane fuel and the timing retarded, there is still some knock events when using the car on the track (but not that much more than was detected before the supercharger install). It may also be worth fitting an adjustable FPR to get a little more fuel out of the top end.

Does the kit run cooler plugs? The S2 uses a Bosch "5" heat range (WR5DC IIRC)- I think the 968 uses a "7". Perhaps use the S2 plugs?

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[flash]

there is enough fuel to run this kit on the street with the OEM injectors, as long as they are clean and up to snuff, and the fuel pump and regulator are also in top form. yes, it just starts to head in the direction of lean way up top, but it is not a problem. this is a STREET kit though. if it were to be used on the track, and high rpms were to be sustained, or in the case of this failure where sustained high rpms occurred, there needs to be more fuel. it was never intended to do that, and in fact i was pretty clear about no longer needing to go to redline to drive the car fast. i was not anticipating a redline high speed run. i have been pleased that the guys who are out there tracking are having a ball and not having problems, but they are also not holding redline for an extended period.



there is absolutely nothing wrong with 60C intake temps. most engines run at 80C or better. my yukon and the SL550 run closer to 90C in stock trim, as does a stock 968.



an AFPR does not really help, and with this tuning would actually hurt everywhere but up top. in fact, we found that more than about 4lbs in increase in pressure and the volume actually went DOWN, making the mixture leaner up top.



cooler plugs do help, but are not required.



you have to be extremely careful with intercoolers. i continually see people installing turbo intercoolers on centrifugal supercharger setups and really messing things up.



there really is no knocking with this setup. we worked hard on that. i have yet to see a knock sensor triggered when everything is right, though i am not saying that it hasn't happened. it may well be because of the new map and new code though.



the mixture chart is on the website. this was with a tailpipe sensor, which we all know is about a half point lean too

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