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Discussion Starter #1
I finally decided to take my engine apart and replace the stock head gasket with a MHG
I personally didn’t have a fail on the head gasket, not sure how many times the previous owner did.
I’m the second owner
While I’m at it I’m replacing the 30-year-old valve springs, just had to head resurface and I am lapping the valves My question is how can I check the head to make sure that is still within specs and not too much material has been removed And what would be the correct head gasket ? Would thicker be better ?


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You'll need a way to precisely measure the distance between the deck and cam cover surface of the head. OEM measurement is 116mm.

Should also check the block to see if it's been resurfaced. Same deal with the measuring tool here, height from the main bearing saddle to block deck is 198.5mm OEM.

What ever is taken off from those two measurements would get added to the head gasket thickness to maintain factory clearances and compression.
 

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Discussion Starter #3
Just what I was looking for thank you very much


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Not a good reference, as all manufactured items have a +/- tolerance, and without taking a pre-machining measurement, there is no way to tell for sure.
My currant block was machined .020" by a guy in an old reputable shop, who did excellent work for me for years, and after it came back, it was still taller than that 198.5mm.

But guess what, it doesn't matter at all. your deck height is constantly changing as carbon build up accumulates, and your compression rises.

The critical part is front to back being the same on both the head & block.
A tilt will do two things, it will jack compression ratio from one end, to the other, and screw the cam being parallel with the crank.
 

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Discussion Starter #5
One of the biggest questions is to determine which head gasket thickness should I get

On a forced induction engine the lower the compression the better, would getting a thicker head gasket say 2 mm would that be better than 1 mm or 1.2 or 1.4 ?


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It's a good practice to check the surface of the head for warpage with a straight edge and a feeler gauge as described in the online manual. Here. After you've hand lapped your valves you need to check the lash because it's going to change. You might have to play musical chairs with your adjusting shims to get them all in spec. It's good to have some spares. A metal head gasket requires absolute flat clean and parallel surfaces. Be certain that the aluminum cover on the front of the block was shaved at the same time the block was otherwise there will be step there. I'm using a standard head gasket and a 0.020 metal shim gasket underneath it on the block sprayed with Permatex copper spray on the bottom only. I haven't had any issues after 6 years and 25K miles. I pulled a picture down from eBay to illustrate where to look when purchasing a head from someone. Underneath the thermostat housing is an extension of the head casting that is rounded on an uncut block (see circle in photo). The more a head is cut, the more a flat appears where it was rounded. Other things to be wary of are heads that have been overheated and the aluminum softened. One way to check is to torque the camshaft cap bolts to spec on the exhaust side. If the torque wrench won't achieve specification and keep turning stripping the threads in the hole, then the metal is soft. (This happened to me.) Most everyone has to replace a exhaust manifold stud sooner or later. I used a Helicoil repair kit and standard studs. Don't reuse exhaust manifold nuts or they will work loose. New Toyota ones grip the stud because they are split on the end and crushed smaller than the stud itself. About the only Fel-Pro gasket I use is their exhaust manifold gasket. It's beefy and seals well.

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One of the biggest questions is to determine which head gasket thickness should I get

On a forced induction engine the lower the compression the better, would getting a thicker head gasket say 2 mm would that be better than 1 mm or 1.2 or 1.4 ?


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Depends on your intended use for the car, as well as available fuel type, tuning capability of your ecu, power level desired, etc. I'm a fan of higher compression, personally. I want as crisp of throttle response as I can get, and the only reason I even bother with a turbo is because I live at 6500' elevation, smaller engines are basically pointless at this altitude without boost.

Now, if you're running stock-ish power levels, a bit of extra compression shouldn't be a problem, provided that you run a quality fuel. If you're going to be running high levels of ethanol, have fun with the compression, alcohol is pretty great in the right application.

If you're limited to fuel grades below 91 octane, or intend to go chasing big power on pump gas, I'd say keep the compression modest, near stock, or even a bit below. It'll be a bit of a dog down low but will tolerate more boost pressure. Just kinda depends on preference for where you want your power.

Side note, glad to see some solid advice in this thread, you guys beat me to the precautionary advice, and THEN some! :)
 

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Discussion Starter #8
Thanks guys

So . The car is a ‘89 I’m second owner Got it 6 years ago with 114k miles
Suspension got done Tein coilovers
BBK and wheels
Now for the engine
I went from stock CT26 6 psi to 9 psi
With the correct down pipe and full cat back exhaust. ( Blitz Nur spec ) I had the car dyno
with 317hp to the wheels
From there a used Garrett T4 P-Trim
60 trim compressor and .68 a/r running at 14 psi. All on stock HG, injectors, and clutch ( not a great idea lol ). But I do have afpr with the bigger fuel Pump , I’m also running a Maft-Pro Car was running great till the turbo seals started to leak oil

So my project took me from just replacing the seals or even maybe the turbo to now ....... Oil filter relocation kit with a bigger cooler , MHG ( I know it was just a matter of time ) also replacing 30year old valve springs Just Cut valve seats, lap valves and new top end gaskets
I’m also think on new BC stage 2 cams replacing injectors to 550cc

I will be running pump gas but my goal is about 20psi for now lol Saying for now because when I bought the car I was happy with going from 6 to 10psi lol

Eventually I might switch to a standalone unit
But for now. The Maft-Pro was working

So with that goal in mind what do you guys think the thickness of my head gasket should be ??

And if anyone knows what change do I need to make to Maft-Pro to go from stock cams to BC cams ?


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I will be running pump gas but my goal is about 20psi for now
But for now. The Maft-Pro was working
Unless you've managed to get the Maft-Pro to control timing these two above are a bad idea. Skip the cams and invest in a full standalone ECU instead, you'll get far better returns than trying to mickey-mouse a piggyback to do what you really need done.

If you insist on cutting corners, get a 2mm HG. The extra thickness will give you an ever-so slight margin of safety when you push past the safe usefulness of the Maft-Pro.
 

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Discussion Starter #10
You Are 100% right.

And I will get the standalone unit ( not sure which one ) but since half of my engine is torn apart and almost out of the engine bay
I want to build the motor and still keep it at the 12 to 14 psi I was running before turbo seals.

I was even contemplating pistons, rods and oil pump. again since engine is out. I still have to replace Clutch But thinking ahead
Is 2 mm MHG still good for the next step ?


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And I will get the standalone unit ( not sure which one )
AEM Series 2 PnP from Driftmotion for simplicity and the fact that almost every tuner will tune AEM. Has user friendly tuning software but is no longer supported by AEM.

ECU Master gets a nod but with the recommendation of making a new engine harness instead of dealing with the jumper harness used in the PnP application. I swear every problem thread I see on that ECU is related to the PnP adapter. Tuning software is not very user friendly and the customer service is terrible. The programming was done by a software engineer and the user interface reflects that. Any inquiry into the software and many of the seemingly arbitrary values given results in being referred to as an idiot.

If you're ok with spending a bit more money, the Pro EFI 128 is a great unit with more features than you will likely ever use but you'll at least have room for growth. You, like many others, appear to be inflicted with the "more power" disease, so the extra features my ultimately become of use to you.

I was even contemplating pistons, rods and oil pump. again since engine is out.
Do it now or do it after your piston ring lands end up in the oil pan or bounced around in the cylinders before making an expensive exit through the exhaust.

Rods can safely be used to right around 600hp with the ARP bolts upgrade. Your next step from there will be chinese rods which have been shown to hold 900whp. Just get them from a reputable "manufacturer" like Eagle and have your machine shop balance them to you pistons and crank. Last set I messed with had a variance of 29 grams between lightest rod and heaviest rod. That difference is pretty significant at 6000rpm.

Checking the oil pump is never a bad idea and replacing it if it's worn out is a necessity. Shimming the relief valve usually isn't a bad idea either. I also recommend replacing the piston squirter bolts while you're there since they are a spring actuated device and springs tend to wear out over time, especially at elevated temperatures like what they see. With a quality set of forged pistons and a good tune you can even get away with deleting the squirters so the oil all goes to where you need it most: the bearings.

If
Is 2 mm MHG still good for the next step ?
If you're building it properly, no. Unless you've had that much material removed that you need that thick of a gasket. It won't necessarily hurt it, but your response will be a bit slower than a properly setup motor. I'd usually wait until you have the complete motor ready to assemble before figuring out the gasket thickness.

I want to build the motor and still keep it at the 12 to 14 psi I was running before turbo seals.
Running a built 7M at near stock power levels is perfectly fine. Running a stock 7M at double the factory power level leads to burning money like a hippy burning weed at woodstock.
 
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