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Skankin · 01-02-2001, 11:55 AM

I think they're a GREAT street head too... the smaller ports & runners provide some nice flow velocity and low to mid torque.

The stock castings aren't machined too well, so there's some nice gains with a bit of work. A streetable 325FWHP would be quite reasonable (Jeff's making more, but I presume he's running HIGH compression, and making that power at a fairly high RPM... 6000 or so?).

Here's the best source of info: http://www.geocities.com/MotorCity/Pit/5755/gt40p.html

I recommend bare heads ($200), and doing a bowl blend and exhaust runner cleanup yourself. Then a 0.030" mill for 10:1 compression, and a good valve job.

I think spending a little extra for the manley race flow valves ($195) is worth it (OEM=$75).

A crane 2030/2031 cam kit is a great, budget, streetable match ($205 including springs etc).

You definitely need an intake to take advantage of the heads breathing though.

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'89.5 5L LX, hatch, Medium Canyon Red, 155K Km (No winters), 5sp, 3.08, GT interior, a/c, Alpine CD, K/N, Crane PS91, Walbro 190 LPH, March Pulleys, Mr. Gasket 180 therm (HP balanced), 3 core rad, MarkVIII fan, Variflow controller, Polygraphite front bushings, FMS-5300B springs, 6 KYB's, 73mm Calipers, Maximum Motorsport 4pt chassis brace, Western Motorsport Racing's Sub-frame connectors. Re-ringed bottom end, conv. motor mounts, melling oil pump, FMS-C50 waterpump, GT40P heads (blended, polli

01-02-2001, 11:55 AM	#3
Skankin Registered Member Join Date: Dec 1998 Location: London, Ontario, Canada Posts: 1,349	I think they're a GREAT street head too... the smaller ports & runners provide some nice flow velocity and low to mid torque. The stock castings aren't machined too well, so there's some nice gains with a bit of work. A streetable 325FWHP would be quite reasonable (Jeff's making more, but I presume he's running HIGH compression, and making that power at a fairly high RPM... 6000 or so?). Here's the best source of info: http://www.geocities.com/MotorCity/Pit/5755/gt40p.html I recommend bare heads ($200), and doing a bowl blend and exhaust runner cleanup yourself. Then a 0.030" mill for 10:1 compression, and a good valve job. I think spending a little extra for the manley race flow valves ($195) is worth it (OEM=$75). A crane 2030/2031 cam kit is a great, budget, streetable match ($205 including springs etc). You definitely need an intake to take advantage of the heads breathing though. ------------------ '89.5 5L LX, hatch, Medium Canyon Red, 155K Km (No winters), 5sp, 3.08, GT interior, a/c, Alpine CD, K/N, Crane PS91, Walbro 190 LPH, March Pulleys, Mr. Gasket 180 therm (HP balanced), 3 core rad, MarkVIII fan, Variflow controller, Polygraphite front bushings, FMS-5300B springs, 6 KYB's, 73mm Calipers, Maximum Motorsport 4pt chassis brace, Western Motorsport Racing's Sub-frame connectors. Re-ringed bottom end, conv. motor mounts, melling oil pump, FMS-C50 waterpump, GT40P heads (blended, polli