3ltr twincam engine, coming together
02-15-2013, 01:08 AM
#226
Drifting
Thread Starter
Sean - What you have accomplished with these cars is amazing and inspiring. Thanks for sharing your projects here. I have read everyone of your threads. 
According to Cometic, this kind of damage is the result of head lift/flex that overworks the seal boss and then a fatigue fracture occurs and starts to propagate. Some refer to this a "chomping". I think the math will show that head/block flex is the greatest at cylinders 2 and 3. I do think that ARP studs and higher torque will help some but that much of what occurs is the result of high peak cylinder pressure (22psi) and the large bore size in our motors. I have been researching this extensively for my own build. Fatigue failure is fairly repeatable and thus the consistency you have experienced.
Also, I believe in general that HG failures on cylinder 4 are more related to detonation (4 getting the least cooling) rather than flex. Obviously detonation has not been an issue for your car with relatively low CR and E85.
According to Cometic, this kind of damage is the result of head lift/flex that overworks the seal boss and then a fatigue fracture occurs and starts to propagate. Some refer to this a "chomping". I think the math will show that head/block flex is the greatest at cylinders 2 and 3. I do think that ARP studs and higher torque will help some but that much of what occurs is the result of high peak cylinder pressure (22psi) and the large bore size in our motors. I have been researching this extensively for my own build. Fatigue failure is fairly repeatable and thus the consistency you have experienced.
Also, I believe in general that HG failures on cylinder 4 are more related to detonation (4 getting the least cooling) rather than flex. Obviously detonation has not been an issue for your car with relatively low CR and E85.
I have had better luck with filling the block, however, I pulled the head 3/4 through the season last year and saw the thin gasket on the bottom side starting to split. Mine was dead center of the bore. Right where the gasket is embossed.
I am going to see if cometic will do a gasket for me without the embossing. Or see if I could get away with deleting the lower thin gasket and just copper spray the thick one.
I am going to see if cometic will do a gasket for me without the embossing. Or see if I could get away with deleting the lower thin gasket and just copper spray the thick one.
Im with you here. changing a headgasket is a walk in the park and changing it every 2 seasons doesnt worry me. Even gives me a chance to check hoses and even the bores ones the head is removed. One think i did notice with using E85 is that it leaves more carbon deposit behind(in the inlet track and pistons) compared to premium unleaded. When we use to use just premium the valves would remain clean. I might start to run premium every so often to keep it clean.
02-15-2013, 01:39 AM
#227
Race Car
I have thought about using a solid copper gasket with o-ring and receiver grooves for a few years now. I just havnt committed to a platform to invest in it yet. I will be doing a new block with flanged sleeves that will have enough meat to install an o-ring. This will allow me the flexibility to have receiver grooves in both my 8v and 16v heads.
I used to use copper gaskets exclusively on the pro mod engines bitd. Yes they have some coolant seal issues, however, a heavy copper spray generally did the trick.
If the 8v engine didn't run so darn good I think I'd already have done it.
Hard to give up on a good thing.
IMO I don't mind doing a HG once or twice a season. With v band headers it's a 2-3 hr deal.
I used to use copper gaskets exclusively on the pro mod engines bitd. Yes they have some coolant seal issues, however, a heavy copper spray generally did the trick.
If the 8v engine didn't run so darn good I think I'd already have done it.
Hard to give up on a good thing.
IMO I don't mind doing a HG once or twice a season. With v band headers it's a 2-3 hr deal.
02-15-2013, 11:15 AM
#228
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A couple of thoughts on this -
The assumption that cylinder 4 gets the least cooling is actually wrong. In fact cylinder 4 gets the lowest temp cooling in the head. Cooling the head is more important than cooling the block, much greater surface area exposed to the combustion chamber on a continual basis. Hot spots that help cause detonation/preignition are located in the cylinder head and not the cylinder walls.
The head casting is pretty thin in many areas - adding more clamping force may cause localized flexing and uneven clamping force, so increasing the tension on a head stud is not a guaranteed solution. Some time ago I posted some pics of a sectioned head - you would be surprised how thin it is around the stud holes!
The typical variation in casting goes a long way to explain why some 944 engines never have a head gasket problem and some have continual issues even at stock boost.
The assumption that cylinder 4 gets the least cooling is actually wrong. In fact cylinder 4 gets the lowest temp cooling in the head. Cooling the head is more important than cooling the block, much greater surface area exposed to the combustion chamber on a continual basis. Hot spots that help cause detonation/preignition are located in the cylinder head and not the cylinder walls.
The head casting is pretty thin in many areas - adding more clamping force may cause localized flexing and uneven clamping force, so increasing the tension on a head stud is not a guaranteed solution. Some time ago I posted some pics of a sectioned head - you would be surprised how thin it is around the stud holes!
The typical variation in casting goes a long way to explain why some 944 engines never have a head gasket problem and some have continual issues even at stock boost.
02-15-2013, 11:58 AM
#229
A couple of thoughts on this -
The assumption that cylinder 4 gets the least cooling is actually wrong. In fact cylinder 4 gets the lowest temp cooling in the head. Cooling the head is more important than cooling the block, much greater surface area exposed to the combustion chamber on a continual basis. Hot spots that help cause detonation/preignition are located in the cylinder head and not the cylinder walls.
The head casting is pretty thin in many areas - adding more clamping force may cause localized flexing and uneven clamping force, so increasing the tension on a head stud is not a guaranteed solution. Some time ago I posted some pics of a sectioned head - you would be surprised how thin it is around the stud holes!
The typical variation in casting goes a long way to explain why some 944 engines never have a head gasket problem and some have continual issues even at stock boost.
The assumption that cylinder 4 gets the least cooling is actually wrong. In fact cylinder 4 gets the lowest temp cooling in the head. Cooling the head is more important than cooling the block, much greater surface area exposed to the combustion chamber on a continual basis. Hot spots that help cause detonation/preignition are located in the cylinder head and not the cylinder walls.
The head casting is pretty thin in many areas - adding more clamping force may cause localized flexing and uneven clamping force, so increasing the tension on a head stud is not a guaranteed solution. Some time ago I posted some pics of a sectioned head - you would be surprised how thin it is around the stud holes!
The typical variation in casting goes a long way to explain why some 944 engines never have a head gasket problem and some have continual issues even at stock boost.
I wonder, is there a difference in E85 peak cylinder pressure compared to 93?
02-15-2013, 02:04 PM
#230
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The 8v is famous for the #4 cylinder failure. I have not seen the same in the 16v head. The 16v head looks like it is stronger (except for cracking at the spark plugs!).
The cylinder pressure profile with the E85 will be quite a bit different because you can run a lot more ignition timing. With 93 you have to retard the ignition timing to prevent detonation and that means a less 'peaky' pressure profile.
The cylinder pressure profile with the E85 will be quite a bit different because you can run a lot more ignition timing. With 93 you have to retard the ignition timing to prevent detonation and that means a less 'peaky' pressure profile.
02-15-2013, 04:56 PM
#231
Rennlist Member
So would there be a different tq clamping force for larger headstuds? More, less, same?
08-05-2013, 10:14 PM
#232
Drifting
Thread Starter
Thought about time for an update, The car has been running very strong. Daily driven and mostly on E85 (95% of the time, only when we go on a holiday and cannot get E85 do i switch back to 98 octane). The engine has now done 35,000kms (21,000 miles). Daily boost is set to 1.5bar (22psi) but rarely would i use that for any extended amount of time on the road. Its too fast and exceeds the speed limit too quickly. So far we have competed in 9 supersprints and 9 motokhanas
Before the beginning of this season we decided to remove the head to inspect the headgasket and bores. The headgasket looked good with the sealing rings of the cometic spring steel still intact. The bores (running Wossner pistons) were still in perfect shape. On goes a new Cometic gasket gasket and we will push out the use again to see what it can take.
The only other modification we have made is another catch can, more for cometic reasons. I annealed some 2mm alloy sheet and shaped it like a can, welded together with AN fittings. Looks much neater.
Regards
Sean
Before the beginning of this season we decided to remove the head to inspect the headgasket and bores. The headgasket looked good with the sealing rings of the cometic spring steel still intact. The bores (running Wossner pistons) were still in perfect shape. On goes a new Cometic gasket gasket and we will push out the use again to see what it can take.
The only other modification we have made is another catch can, more for cometic reasons. I annealed some 2mm alloy sheet and shaped it like a can, welded together with AN fittings. Looks much neater.
Regards
Sean
08-06-2013, 07:33 AM
#236
Drifting
Thread Starter
Thanks guys,
Bas,
The rear hose connects to the air oil separator , the middle hose to the cam cover and the front hose connects back to the J pipe.
The manifold and cam cover are painted with wrinkle finish black.
http://www.vhtpaint.com/products/wrinkleplus/
Its quite resilient for a spray can paint
Regards
Sean
Bas,
The rear hose connects to the air oil separator , the middle hose to the cam cover and the front hose connects back to the J pipe.
The manifold and cam cover are painted with wrinkle finish black.
http://www.vhtpaint.com/products/wrinkleplus/
Its quite resilient for a spray can paint
Regards
Sean
08-06-2013, 08:26 AM
#237
Three Wheelin'
Hi Sean,
Thanks for letting me know! How did you get the hose connect to the camcover? As i'm very busy with my own build i'm just gathering info
And for the connected to the "j-pipe", it's boosted, so doesn't that get the airpressure in your catchtank? Or is it connected differently?
And thanks for the spraypaint tip! I've been looking for this for my inlet as well!
Grtz,
Bas
Thanks for letting me know! How did you get the hose connect to the camcover? As i'm very busy with my own build i'm just gathering info
And for the connected to the "j-pipe", it's boosted, so doesn't that get the airpressure in your catchtank? Or is it connected differently?
And thanks for the spraypaint tip! I've been looking for this for my inlet as well!
Grtz,
Bas
08-07-2013, 03:38 AM
#240
Three Wheelin'
And now for the next question; do you really notice the catchcan in the car? Is it sucking up the oil and sucking it back into the intake? And does is relieve the pressure in the crankcase?