Maximum to shave off the head

ianstaley · 06-20-2013, 08:16 PM

Quote:

Originally Posted by icey756

I already have .011 of an inch off my 7mgte head. I was wondering how much in total can be shaved off before running into problems?

I wouldn't quote me on this but I have had some experience of shaving the heads on another car that I turboed some years ago. I had a BMW 730 which was a NA carburetor model of some 3.0L. I turboed it using parts from a scraped 745 turbo. Now the 730 normally ran @ 10.5 to 1 and after shaving the head it was brought down to 8.5 to 1 which the engineers that did the job said was risky as there wasn't a lot of meat on the head. Even though the head had not blown a gasket it was warped (ally head). The result was that 3 months after the job was done it blew the HG.

So I would seriously check out the engine has it had a BHG before, if it has I would not be overly enthusiastic in using the head again as you may remove too much that can't be taken up with a thicker gasket.

I would imagine that the factory Comp ratio would be about 8 or 8.5 to 1 MAX. Hope that helps.

icey756 · 06-21-2013, 02:05 AM

I have no idea what those numbers even mean. I'm not doing this to increase/decrease my compression. I just want to know if taking more off the head will compromise it. I bought the car with a BHG and replaced it with a felpro gasket. I now have the engine out because I got the car totally repainted. I wanted to do a MHG since the engine was out and it was convenient. I shaved the block and gave it new bearings and rings. I just want to know how much more I can take off the head if I have .011 off of it already. Along with that, the block has .006 of an inch off. I bought a 1.4mm Titan MHG. Is everything still going to be ok if the machine shop takes off another .006 or so off the head?

cre · 06-21-2013, 11:07 PM

CR isn't the issue and can be accounted for with a thicker MHG or in the worst case an added shim. As for the maximum allowable cut, I'm certain I posted it here in the past but I'm having trouble finding it and I can't find my notes on it. I'll let you know if I do locate the info.

ianstaley · 06-22-2013, 10:27 AM

Ah okay, thought you were going turbo sorry. I think that taking a few though shouldn't be a problem , however, there is always one isn't there, the MK3 is a non interference engine but I am thinking that take too much off it could become an interference engine, make sure the company that is doing the shaving can tell you if the valves will interfere, hit the pistons, just incase the timing belt breaks.

cre · 06-23-2013, 05:05 PM

Coming from Ian, I'd take this as gospel: "20 thousandths" So you'd be effectively doubling the height the piston crown extends past the deck in a clean, stock engine. Then you will want to account for it with your head gasket selection.

http://www.supramania.com/forums/sho...ness-selection

icey756 · 06-23-2013, 07:32 PM

The only problem is that Ive already had the gasket for a while and it's a 1.4mm. Will that still work ok without running into any problems?

06-21-2013, 02:05 AM	#2
icey756 3" Exhaust Join Date: Jun 2011 Location: Wisconsin Posts: 177	I have no idea what those numbers even mean. I'm not doing this to increase/decrease my compression. I just want to know if taking more off the head will compromise it. I bought the car with a BHG and replaced it with a felpro gasket. I now have the engine out because I got the car totally repainted. I wanted to do a MHG since the engine was out and it was convenient. I shaved the block and gave it new bearings and rings. I just want to know how much more I can take off the head if I have .011 off of it already. Along with that, the block has .006 of an inch off. I bought a 1.4mm Titan MHG. Is everything still going to be ok if the machine shop takes off another .006 or so off the head? __________________ 1988 7M-GTE Manual Turbo, Godspeed IC, Stock HG Torque to 90FP W/ Arp bolts, Silicon water hose kit, silicon vacuum hoses, Godspeed radiator, 2 12" electric fans.

06-21-2013, 11:07 PM	#3
cre Toyota Racing Development Join Date: Apr 2007 Posts: 5,038	CR isn't the issue and can be accounted for with a thicker MHG or in the worst case an added shim. As for the maximum allowable cut, I'm certain I posted it here in the past but I'm having trouble finding it and I can't find my notes on it. I'll let you know if I do locate the info. __________________ If something breaks or you need to contact a member of the administration please post HERE. Unless it's a private or administration matter please post it on the forum. It benefits no one else if car related questions aren't posted for future users and takes away from the time I'm able to spend helping on the rest of the forum. If you're so inclined I'm always more than happy to accept tips via PayPal. Tip Jar --->

06-22-2013, 10:27 AM	#4
ianstaley Stock Join Date: Nov 2008 Location: Pontefrac Posts: 24	Ah okay, thought you were going turbo sorry. I think that taking a few though shouldn't be a problem , however, there is always one isn't there, the MK3 is a non interference engine but I am thinking that take too much off it could become an interference engine, make sure the company that is doing the shaving can tell you if the valves will interfere, hit the pistons, just incase the timing belt breaks. __________________ Bored old git that loves his toyota's I have two one a Supra MK3 with a targa top the other is a brit Camry V6.

06-23-2013, 05:05 PM	#5
cre Toyota Racing Development Join Date: Apr 2007 Posts: 5,038	Coming from Ian, I'd take this as gospel: "20 thousandths" So you'd be effectively doubling the height the piston crown extends past the deck in a clean, stock engine. Then you will want to account for it with your head gasket selection. http://www.supramania.com/forums/sho...ness-selection __________________ If something breaks or you need to contact a member of the administration please post HERE. Unless it's a private or administration matter please post it on the forum. It benefits no one else if car related questions aren't posted for future users and takes away from the time I'm able to spend helping on the rest of the forum. If you're so inclined I'm always more than happy to accept tips via PayPal. Tip Jar --->

06-23-2013, 07:32 PM	#6
icey756 3" Exhaust Join Date: Jun 2011 Location: Wisconsin Posts: 177	The only problem is that Ive already had the gasket for a while and it's a 1.4mm. Will that still work ok without running into any problems? __________________ 1988 7M-GTE Manual Turbo, Godspeed IC, Stock HG Torque to 90FP W/ Arp bolts, Silicon water hose kit, silicon vacuum hoses, Godspeed radiator, 2 12" electric fans.

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