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#1
10-12-2005, 10:31 PM
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Head Gaskets: To Mill or not to Mill?
I'm contemplating doing the (leaky) head gaskets on my '92 pearl. Assuming the heads aren't warped and are perfectly flat, is it a good idea to machine them or not? I've been told that machining increases the compression ratio, putting greater strain on the bottom end, and causing excessive oil consumption and/or engine failure. The engine has 160k but has been well maintained, runs fine (except for the head gasket issues), and uses no oil at this point.
I'm aware the 'ideal' solution would be to replace the engine with a nice low-mileage unit, or do a complete rebuild, etc, etc... 
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#2
10-13-2005, 08:25 AM
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According to Subaru, the max head milling allowed is (0.30mm) 0.0118"
With a bore of (96.9mm) 3.815" that only takes away .809304 cid. Since our engines are 202.46 cid, at the stock 10 to 1 compression ratio that gives 20.246 cid in the head and head gasket volume. Dropping the head volume down to 19.436696 only raises the compression ratio to 10.416379to 1. And would slightly retard the timing. I believe a bump in compression is a good power builder, and that our engines can handle it, but a thinner head gasket might be better. Tom
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www.svxfiles.com The first SuperCharged SVX,  the first 4.44 gears, the first equal length headers, the first phenolic spacers, the first Class Glass fiberglass hood, the first with 4, 4.44s in his driveway  Fiberglass Hood thread My locker 4.44 Swap link Last edited by svxfiles; 10-13-2005 at 08:34 AM.
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#3
10-13-2005, 08:56 AM
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The eg33 block has a grinding limit of 0.016".
Milling that off the block loses 1.0973616 cid. With both the heads and the block milled to the factory max that gives 18.339335 combustion cid, or an 11.039658 to 1 compression ratio, with the stock head gaskets! The maximum overbore allowed by Subaru is 0.020". This would give 204.453 cid. Not a huge differance. Cut the compression goes up to 11.148332 to 1. Every little bit helps.
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www.svxfiles.com The first SuperCharged SVX, the first 4.44 gears, the first equal length headers, the first phenolic spacers, the first Class Glass fiberglass hood, the first with 4, 4.44s in his driveway Fiberglass Hood thread My locker 4.44 Swap link
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#4
10-13-2005, 10:35 AM
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So, how would milling the block and heads affect the non-interference (valve and block only, exhaust and intake valves can interfere) characteristic of the engine. Also , do you think there would be a problem with an intake cam with 8mm lift instead of 7mm.
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____________________________________________ 95 LS-i Red, 31,xxx; bone stock for now; Daily Driver 94 LS-i Emerald Pearl, 106,xxx,; 246 whp; Tomyx snorkus and HKS Cold air intake; PWR aluminum radiator, silicone hoses; Inline thermostat; enhanced coolant routing; external power steering and oil coolers; Phenolic intake manifold spacers; 2004 WRX 5 speed transmission; ACT Clutch Kit, Heavy Duty Pressure Plate, Lightweight flywheel, performance disc; Group N motor mounts; ‘07 WRX 4-pot front calipers, cryo-treated slotted Tribeca rotors; Hawk HPS ferro-carbon pads; Frozenrotor rear slotted rotors; SS brake lines, Axxis Ultimate pads; Rota Torque 17x8 wheels; 245/40-17 Bridgestone RE01-R's; Koni inserts with Ground Control coilovers, Eibach springs; K-Mac camber/caster adjustable strut mounts; Urethane swaybar bushings; Bontrager rear sway bar; Urethane differential bushing; Custom Whiteline adjustable rear lateral links; Outlaw Engineering forged underdrive pulley; custom grind Web intake and exhaust cams (11 mm lift, 250° duration); solid lifters; CP custom aluminum forged 11 to 1 pistons, Brian Crower coated SS intake & exhaust valves; Brian Crower upgraded springs w/ titanium retainers; NGK sparkplugs; RallyBob (Bob Legere) ported and polished cylinder heads; Eagle H-beam rods; ACL Bearings; Cometic Head gaskets; ARP head studs & fasteners; Hydra Nemesis EMS; Wideband O2 sensor; 740cc Injectors; Walbro 255lph fuel pump; Upgraded WRX starter; Equal length SS headers (3 into 1); dual Magnaflow cat converters; 2 into 1 into 2 SS exhaust with Bullet muffler; OT Fiberglass hood; Oil pressure gauge; Programmable shift light, 2017 Subaru Forester XT, metallic dark gray, 29,xxx 2005 Porsche 911 Turbo S Cabrio, 24,xxx 2006 Subaru Outback LL Bean, 166,xxx sold 92 LSL Dark Teal, Smallcar Shift Kit - sold
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#5
10-13-2005, 10:42 AM
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Get the heads milled.... With a leaky HG you can easy overheat the engine with air pockets in the coolant. This will warp the head if it not already. I did not mill the heads on my old when doing the HG and payed the price of wasting my time
Mill the head and get a thicker HG to keep the engine at stock specs... Maybe one of the copper ones that talk is floating around aboutTom
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#6
10-13-2005, 10:59 AM
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Quote:
Thats 0.70mm combined, and Subaru would not allow that if it made our engine an interference engine, rather than a non-interference engine. The second question is harder to answer. If you are only installing a higher lift cam, without shaving the head and/or block, then sure 8mm will be fine. The pistons have valve reliefs, and the valves do not go strait up and down, they are at an angle to the piston, making their vertical travel less than 1 extra mm. Of course, if you take your engine apart, you can check the clearances with clay. If anyone does this, please report back to the rest of us. Thanks, Tom
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www.svxfiles.com The first SuperCharged SVX, the first 4.44 gears, the first equal length headers, the first phenolic spacers, the first Class Glass fiberglass hood, the first with 4, 4.44s in his driveway Fiberglass Hood thread My locker 4.44 Swap link
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#7
10-13-2005, 11:21 AM
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I also realize that the intake valves will not yet be fully open when the piston is at TDC, so the question is really academic, unless you break a timing belt.
__________________
____________________________________________ 95 LS-i Red, 31,xxx; bone stock for now; Daily Driver 94 LS-i Emerald Pearl, 106,xxx,; 246 whp; Tomyx snorkus and HKS Cold air intake; PWR aluminum radiator, silicone hoses; Inline thermostat; enhanced coolant routing; external power steering and oil coolers; Phenolic intake manifold spacers; 2004 WRX 5 speed transmission; ACT Clutch Kit, Heavy Duty Pressure Plate, Lightweight flywheel, performance disc; Group N motor mounts; ‘07 WRX 4-pot front calipers, cryo-treated slotted Tribeca rotors; Hawk HPS ferro-carbon pads; Frozenrotor rear slotted rotors; SS brake lines, Axxis Ultimate pads; Rota Torque 17x8 wheels; 245/40-17 Bridgestone RE01-R's; Koni inserts with Ground Control coilovers, Eibach springs; K-Mac camber/caster adjustable strut mounts; Urethane swaybar bushings; Bontrager rear sway bar; Urethane differential bushing; Custom Whiteline adjustable rear lateral links; Outlaw Engineering forged underdrive pulley; custom grind Web intake and exhaust cams (11 mm lift, 250° duration); solid lifters; CP custom aluminum forged 11 to 1 pistons, Brian Crower coated SS intake & exhaust valves; Brian Crower upgraded springs w/ titanium retainers; NGK sparkplugs; RallyBob (Bob Legere) ported and polished cylinder heads; Eagle H-beam rods; ACL Bearings; Cometic Head gaskets; ARP head studs & fasteners; Hydra Nemesis EMS; Wideband O2 sensor; 740cc Injectors; Walbro 255lph fuel pump; Upgraded WRX starter; Equal length SS headers (3 into 1); dual Magnaflow cat converters; 2 into 1 into 2 SS exhaust with Bullet muffler; OT Fiberglass hood; Oil pressure gauge; Programmable shift light, 2017 Subaru Forester XT, metallic dark gray, 29,xxx 2005 Porsche 911 Turbo S Cabrio, 24,xxx 2006 Subaru Outback LL Bean, 166,xxx sold 92 LSL Dark Teal, Smallcar Shift Kit - sold
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#8
10-13-2005, 11:47 AM
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Shotgun, your signature lists an ECU tune stage 2V4.
Do you have it installed yet?
__________________
www.svxfiles.com The first SuperCharged SVX, the first 4.44 gears, the first equal length headers, the first phenolic spacers, the first Class Glass fiberglass hood, the first with 4, 4.44s in his driveway Fiberglass Hood thread My locker 4.44 Swap link
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#9
10-13-2005, 11:55 AM
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Yes. I do. Even had it out on the track. I haven't noticed that much difference with the Stage1v4. They both really change the character of the SVX throttle response. However, with some upcoming mods to improve breathing and installation of an Impreza FPR, I think the Stage 2 chip has a lot more potential.
Can you take a look at my thread in this forum concerning error codes. Wondering if you had some thoughts on that.
__________________
____________________________________________ 95 LS-i Red, 31,xxx; bone stock for now; Daily Driver 94 LS-i Emerald Pearl, 106,xxx,; 246 whp; Tomyx snorkus and HKS Cold air intake; PWR aluminum radiator, silicone hoses; Inline thermostat; enhanced coolant routing; external power steering and oil coolers; Phenolic intake manifold spacers; 2004 WRX 5 speed transmission; ACT Clutch Kit, Heavy Duty Pressure Plate, Lightweight flywheel, performance disc; Group N motor mounts; ‘07 WRX 4-pot front calipers, cryo-treated slotted Tribeca rotors; Hawk HPS ferro-carbon pads; Frozenrotor rear slotted rotors; SS brake lines, Axxis Ultimate pads; Rota Torque 17x8 wheels; 245/40-17 Bridgestone RE01-R's; Koni inserts with Ground Control coilovers, Eibach springs; K-Mac camber/caster adjustable strut mounts; Urethane swaybar bushings; Bontrager rear sway bar; Urethane differential bushing; Custom Whiteline adjustable rear lateral links; Outlaw Engineering forged underdrive pulley; custom grind Web intake and exhaust cams (11 mm lift, 250° duration); solid lifters; CP custom aluminum forged 11 to 1 pistons, Brian Crower coated SS intake & exhaust valves; Brian Crower upgraded springs w/ titanium retainers; NGK sparkplugs; RallyBob (Bob Legere) ported and polished cylinder heads; Eagle H-beam rods; ACL Bearings; Cometic Head gaskets; ARP head studs & fasteners; Hydra Nemesis EMS; Wideband O2 sensor; 740cc Injectors; Walbro 255lph fuel pump; Upgraded WRX starter; Equal length SS headers (3 into 1); dual Magnaflow cat converters; 2 into 1 into 2 SS exhaust with Bullet muffler; OT Fiberglass hood; Oil pressure gauge; Programmable shift light, 2017 Subaru Forester XT, metallic dark gray, 29,xxx 2005 Porsche 911 Turbo S Cabrio, 24,xxx 2006 Subaru Outback LL Bean, 166,xxx sold 92 LSL Dark Teal, Smallcar Shift Kit - sold
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#10
10-13-2005, 12:04 PM
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I got one from Michael, but do not yet have a Z32 maf. I am hoping for a big differance, as I am maxing out my stock maf, I believe.
8psi will do that!
__________________
www.svxfiles.com The first SuperCharged SVX, the first 4.44 gears, the first equal length headers, the first phenolic spacers, the first Class Glass fiberglass hood, the first with 4, 4.44s in his driveway Fiberglass Hood thread My locker 4.44 Swap link
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