head spacer or machine work?

mattromey · 11-19-2009, 09:29 PM

so i just got my block and head back from the shop and was told it might be a good idea to either get a head spacer or machine the pistons both options are about the same price. i had to take .020" off my head and .018" off my block so does anyone have any ideas as to what i should do? head spacer machine work or just put the thing together? i just dont know how close Toyota ran the pistons to the valves.

Thanks
Matt

Bill UK · 11-19-2009, 10:58 PM

Don’t put it back together like that, even if you have enough clearance between the valves and pistons. I’m sure you will have issues locating the timing belt correctly on the sprockets for one thing as the head is lower by .038 thou .Compression ratio will also be increased not a good thing with head gaskets on a Supra. I'm sure someone will give you the correct advice soon. A thicker metal head gasket would be my recommendation.

Bill UK · 11-19-2009, 11:12 PM

Sounds familiar Link

mattromey · 11-20-2009, 11:13 PM

so is there a difference between running a head shim and gasket and just running 2 head gaskets, cause as far as i can tell the head shim looks the same as my head gasket.

cre · 11-21-2009, 01:56 AM

Shim is a single layer and generally compresses less (than a composite that is). Running a shim with a metal HG versus running a thicket metal HG is pretty much the same thing. I *think* the shim would be preferable though in your case. A real thick MHG has a lot of layers and that's a lot of potential for gaps and leaks. A solid copper HG would be the cleanest solution, but I hear longevity is an issue, hence why you really only see them on dedicated race cars.

The question I haven't seen asked or answered is what are you running now and what are your plans? What type of HG do you want to run? If your car is turbo'd are you looking to go to a thicker HG to reduce the CR?

mattromey · 11-21-2009, 02:11 AM

i don't plan on doing to much i was thinking 550cc injectors and a lexus afm and may be running 10 psi and 3in exhaust, other then that it will be stock. oh and i got a full set of forged pistons that will now have to be machined down .020 to be below the deck

cre · 11-21-2009, 02:26 AM

You could see if it would be possible increase the dish of the pistons enough to bring down the CR so you could use a thinner HG and no shim... I don't know if I would though.

Do also keep in mind you need to calculate the new CR after shaving the pistons as the dish will be lessened.

11-19-2009, 09:29 PM	#1
mattromey Stock Join Date: Oct 2009 Location: portland oregon Posts: 12	head spacer or machine work? so i just got my block and head back from the shop and was told it might be a good idea to either get a head spacer or machine the pistons both options are about the same price. i had to take .020" off my head and .018" off my block so does anyone have any ideas as to what i should do? head spacer machine work or just put the thing together? i just dont know how close Toyota ran the pistons to the valves. Thanks Matt

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11-19-2009, 10:58 PM	#2
Bill UK AEM EMS Join Date: Jul 2006 Location: UK Posts: 891	Don’t put it back together like that, even if you have enough clearance between the valves and pistons. I’m sure you will have issues locating the timing belt correctly on the sprockets for one thing as the head is lower by .038 thou .Compression ratio will also be increased not a good thing with head gaskets on a Supra. I'm sure someone will give you the correct advice soon. A thicker metal head gasket would be my recommendation.

11-19-2009, 11:12 PM	#3
Bill UK AEM EMS Join Date: Jul 2006 Location: UK Posts: 891	Sounds familiar Link

11-20-2009, 11:13 PM	#4
mattromey Stock Join Date: Oct 2009 Location: portland oregon Posts: 12	so is there a difference between running a head shim and gasket and just running 2 head gaskets, cause as far as i can tell the head shim looks the same as my head gasket.

11-21-2009, 01:56 AM	#5
cre Toyota Racing Development Join Date: Apr 2007 Posts: 5,038	Shim is a single layer and generally compresses less (than a composite that is). Running a shim with a metal HG versus running a thicket metal HG is pretty much the same thing. I think the shim would be preferable though in your case. A real thick MHG has a lot of layers and that's a lot of potential for gaps and leaks. A solid copper HG would be the cleanest solution, but I hear longevity is an issue, hence why you really only see them on dedicated race cars. The question I haven't seen asked or answered is what are you running now and what are your plans? What type of HG do you want to run? If your car is turbo'd are you looking to go to a thicker HG to reduce the CR?

11-21-2009, 02:11 AM	#6
mattromey Stock Join Date: Oct 2009 Location: portland oregon Posts: 12	i don't plan on doing to much i was thinking 550cc injectors and a lexus afm and may be running 10 psi and 3in exhaust, other then that it will be stock. oh and i got a full set of forged pistons that will now have to be machined down .020 to be below the deck

11-21-2009, 02:26 AM	#7
cre Toyota Racing Development Join Date: Apr 2007 Posts: 5,038	You could see if it would be possible increase the dish of the pistons enough to bring down the CR so you could use a thinner HG and no shim... I don't know if I would though. Do also keep in mind you need to calculate the new CR after shaving the pistons as the dish will be lessened.