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Turbo. Targa. Life.
SupraMania Shirt Slinger!
Right, but look at the thickness differences from the 7m and the rb between the WJ and the CYL. The Rb has more surface area there, AND larger water jackets, thus removing more heat.
Isn't there anyone out there that has any data on the water flow in the water jackets? Is it possible the water pump impeller is cavitating leaving the water still as a lake in the water jackets especially at the rear of the engine where Major flow is needed the most? Or has this gone uninvestigated for years as to a solution to SOME bhg's? I believe it is and one reason is the gurgling sound in the heater. If the impeller had an anti-cavitation plate on it, it would be pumping water like a mofo and instantly flush any air out of the tubing system and all this talk about parking your car pointing to the stars to bleed the air from the coolant wouldnt exist.
I'm not sure what effect heat would have on the gasket - I suspect that overheating would cause your head to warp before it blew the gasket.
I haven't torn down an engine with a BHG yet that couldn't be attributed easily to either lack of torque (usually) or detonation from too much boost (occasionally), and I've helped tear apart a fair number of engines.
I haven't torn down an engine with a BHG yet that couldn't be attributed easily to either lack of torque (usually) or detonation from too much boost (occasionally), and I've helped tear apart a fair number of engines.
well from what i know and have bean told byt many people is this
the pitch/angle the bolt's/stud's go in
lack of turq
crappy gasket withc is better now go for the black one withc si the new toyota desigh
remmber we have poor cooling system after shut done in the 7m whiel runing it is fine thou as any motor remmber that boiling you hear when you shut donw you car after a hard run poor flow
it just the head cools at to many diffent rates
all so thorwing tones of boost inot it pulling to much fule = detionation as well bad gas ect ect ect
the pitch/angle the bolt's/stud's go in
lack of turq
crappy gasket withc is better now go for the black one withc si the new toyota desigh
remmber we have poor cooling system after shut done in the 7m whiel runing it is fine thou as any motor remmber that boiling you hear when you shut donw you car after a hard run poor flow
it just the head cools at to many diffent rates
all so thorwing tones of boost inot it pulling to much fule = detionation as well bad gas ect ect ect
the fact that toyota has used the same m block for 30 odd years could be a big factor in the design problems of the 7m. I mean think about it the block when first produced in the 60's had a bore of 75mm and a stroke of 75mm then the 2M was stroked (to 85 mm/3.35 in) for 2.3 L (2253 cc) then the 3m got a new head and the 4m was bored out to 80 mm (3.15 in) to create the 2.6 L (2563 cc) then the 5m was Bored again to 83.1 mm (3.27 inches) in the 2.8 L (2759 cc) and got a new head the 6m was stroked to 91 mm (3.58 in) to create the 3.0 L (2954 cc) and the the 7m got a new head. All this tells me is toyota didn't design the 7m for heavey duty abuse from high boost applacations unlike a 1/2 jz engine.By the time the 7m came along the orignal square design of the m had been long since ruined and toyota was doing what any profitable car company does and milking every last cent out a classic design and you can't hate them for that when so many others do it ford 302 chevy 350 ect...I personally beleive its a combo of problems that lead to a bhg cylender wall thinkness or lack off,coolent design flaws,and toyota under torquing the heads was just the straw that broke the camels back. It sounds like i'm bassing the 7m i know butyou have to keep in mind with modifications what where not factory exceptable for cost reasons the 7m can be a great powerplant
most that i've seen occur in #6. Isn't their more heat back there from the egr? Lots more heat? I just figured it was low tqe on bolts and tons of heat on #6.
First of all, they don't all blow. In fact, of the dozen or so that are mine or known personally through immediate relatives, I have seen one go. And it was an intentional tuning error by me.
This caused some premature failure. The rest is tuning and poor building.
Yep. Being low on coolant causes a cavity near 5 and 6 according to Toyota. Not necessarily a local shitty dealer who doesn't know, but Toyota themselves. This was covered on another site a few years back.
Most of the time, at least what I read on the internet, the BHG is a symptom of another problem. Overheating is damn good way to lose the headgasket on an iron block/aluminum head engine. The head warps, and it damages the gasket as a side effect. This is why Toyota redid block designs on many models, including 4Runners, Celicas, and Supras.
This caused some premature failure. The rest is tuning and poor building.
I didn't see it mentioned, but the extra heat behind cylinder 6 due to the EGR could be super-heating the already hot coolant back there (and if you get a DROP low, that's room for steam expansion) guess what? You get a little warpage back there, and cylinder 6 says 'Good night, folks!'
Also, I saw a thread a while back on a possible water passage that could be in the block, but not in the head, back by #6.
http://www.supraforums.com/forum/showthread.php?t=318284&highlight=drill+head+passage
Also, I saw a thread a while back on a possible water passage that could be in the block, but not in the head, back by #6.
http://www.supraforums.com/forum/showthread.php?t=318284&highlight=drill+head+passage
EDM Supras dont have EGR and still, we all get BHG in #6 cylinder, so don't blame it all on EGR.
This is what I see as a common sense happening (it don't mean it's so), the block and head being dissimilar metals NEED to expand and contract at close to the same rate (the thermostats number one job). If for any reason the head or block in what ever area gets starved of coolant then the aluminum is going to rapidly expand faster than the cast iron. This would rapidly cause the gasket to rip, since the side against the head is growing like a mofo and the cast iron side isn’t. I saw the pics of reigns that showed a blow out and agree crappy construction, but this could have been originally caused by a rip or tear from the different expansion rates. In the time I have been a member of this awesome site I’ve seen folks also complain their aftermarket gaskets blew too. So one might assume that if someone were to tally up the BHG's people reported on this site alone since it's inception we might see it could be just the stock crappy gasket construction, OR it might be the stock flow of water just isn't removing heat from way back there thus causing dissimilar expansion rates thus destroying the gasket seal and warping (bowing) of the head. So the questions I've asked is any one out there using any type of forced water pump and NOT had a BHG?
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drumminforev
Guest
Ok, so now that we have all this discussion of #6 cavitation and this and that....who has a solution?
Here's an example of what I believe a Supra Water Pump Needs. I made this exact pump myself a few years ago for my 440 using a MP Alu pump, all I did was weld a plate on it just like the Milodon in the pic. It's easy to make yourself as you can see from the pic I added. I dont have a cooling problem currently but if someone does I am sure this could help solve it. I will be uising a pump off my old BHG'd motor to make a mock up soon to show as an example.
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EGR will not do it.
Funny thing about that EGR. People delete it saying it only goes in the one cylinder because of the mounting, then turn around and install a front facing manifold and say it will distribute to all the cylinders, even though the layout is the same. Go figure about Supra people.
I have never seen a blown headgasket on a 7M that didn't have another problem that led to it. I saw a Cressida once, same story, back at 5 and 6. And as it turns out, he had a coolant leak for some time, and that is where the cavity and hotspot forms.
The composite gasket is used to compensate for the movement of the dissimilar metals. Manufacturers often use that type of gasket as a metal one clamped down extra tight requires costly machining.
Funny thing about that EGR. People delete it saying it only goes in the one cylinder because of the mounting, then turn around and install a front facing manifold and say it will distribute to all the cylinders, even though the layout is the same. Go figure about Supra people.
I have never seen a blown headgasket on a 7M that didn't have another problem that led to it. I saw a Cressida once, same story, back at 5 and 6. And as it turns out, he had a coolant leak for some time, and that is where the cavity and hotspot forms.
The composite gasket is used to compensate for the movement of the dissimilar metals. Manufacturers often use that type of gasket as a metal one clamped down extra tight requires costly machining.
It's easy to see that the clamping force put on the stock headgasket in the areas it is very narrow (between the cylinders and the water jackets), is insufficent for the high cylinder pressures that can occur under boost. More head bolt torque helps, but doesn't fix the problem that the composite gasket deforms too easily in the spots it is not wide enough. The other problem is that the stock gasket erodes around the coolant passages making it weaker and weaker over time. Since the metal headgasket is much more difficult to deform, plus it is always used with higher quality head bolts/studs at a higher torque, it pretty much solves the headgasket issues the 7m has. I've seen way too many 7m bhg's on completely stock engines (some with with under 100k miles) that were always well taken care of for me to think it's always user error. If it's that easy for it to happen, it's a design flaw. Engines should be able to handle small cooling system problems, that will happen in normal operation at some point on almost every engine.
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drumminforev
Guest
If you can download the pic and blow it up you'll see a metal plate welded onto the stock impeller making it able to pump some major water through your system. I've had this type of pump on all my vehicles for years and never once had a cooling issue. On a 68 dodge van I had installed a very built 360 in, I welded the plate onto the impeller and it solved my heat issues caused by the engine being inside a square box 4 feet back from the front of the van. I've also seen folks with Panteras solve their cooling issues with this type of mod since they pump their water from the back of the car way up to the front where the radiator is located. Panteras have always had cooling issues cause of how far they need to force the water to the radiators.
A real mystery for me is why the intake side cooling passages on the block do not match up with the holes in the head gasket. Even more bizzare, the single passage in the block is partially covered by the separator between the two holes in the head gasket??
It would seem the HG would be a lot stronger if they did match up since those two holes in the gasket make it look like swiss cheese.
It would seem the HG would be a lot stronger if they did match up since those two holes in the gasket make it look like swiss cheese.
As far as blowing, one fact is that the HG's were undertorqued from the factory, I believe around 50 lbs, which is VERY low. And if they blew awhile after, it's due to the lack of maintenance or the car has overheated a few too many times.
-Matt
-Matt