FrankR
Web Wheeler
Reged: 02/01/04
Posts: 10224
Loc: Columbia, SC
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Re: 3.0 rebuild
08/13/08 02:16 PM
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Quote:
Ever port or polish the heads or other head work?
Yes - I gasket-matched the lower intake and blower discharge plenum.... you could do the same with the upper and lower intake flanges. I also cleaned up any casting seams in the intake and exhaust ports. I first gasket-matched the exhaust manifolds to the gasket - then cut an anti-reversion step into the exhaust manifolds and polished the exhaust manifold inlets as far as I could reach with a die grinder.... the idea was to improve exhaust gas scavenging. Your guess is as good as mine if there's any benefit, but it only takes some time and effort to try it.
The exhaust ports are already larger than the exhaust valves, so I doubt there's much benefit in doing much more than a light polish job. You could try opening up the exhaust ports in the heads to match the gasket, but if you do, you'd better do the same (at least) to the manifolds or you'll have a restriction.
AFAIK, there are no larger valves available for the SOHC heads. You should examine the valve guides to see if any have dropped - fairly common with exhaust guides in the 3.0L. The new style replacement guides have a retainer ring.
There another cam/piston combination I didn't mention - using the 8.9:1 piston with the Diamante cam, but rolling the cam forward to regain some low end. That's similar to what I've done in my engine (but with 9:1 custom pistons), but spun 3 main bearings on the break-in when the oil pump relief valve stuck open. In the few miles before the engine went south, my butt dyno told me there was a definite improvement in the low end.... but that's all I know until I build another engine and get it on the dyno.
The Diamante cams have 4° more duration, so if they're rolled forward to recover DCR and low end performance with the 8.9:1 pistons, there's a good chance they may also extend the top end a little.
Frank
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'89 G-Raider Supercharged 3.0L, MegaSquirt 2, lockup A/T, 2.5" exhaust, 155k, Cibie H4s/Oscar SCs, Hella Micro DE fogs, Cobra CB, Superwinch hubs, LSD rear/Aussie Locker front, Bilsteins, 165A alt., Lifeline AGM, Rust-Oleum
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