2000StreetRod
Moderator Emeritus
- Joined
- May 26, 2009
- Messages
- 10,597
- Reaction score
- 334
- City, State
- Greenville, SC
- Year, Model & Trim Level
- 00 Sport FI, 03 Ltd V8
perform more testing
I suggest you perform more testing before swapping the engine.
Was the throttle plate wide open when you checked the compression?
Did you let the engine rotate long enough for five compression strokes on the cylinder being checked?
Did the engine overheat before the rebuild? How did you determine that both head gaskets were blown?
You mentioned that the original exhaust manifold ports did not match the head ports and that the heads were ported and polished. If the head exhaust ports were enlarged then they wouldn't match the exhaust manifold ports. If the original manifolds would not bolt to the heads that indicates that the heads, manifolds, or both were warped. A reputable shop should have checked the heads for cracks and warp before porting and polishing them. Milling severely warped heads to make them flat may not be adequate because the combustion chambers might have different volumes. That would result in different compression ratios and imbalanced power pulses.
Normally an SOHC V6 with less than 200K miles should not need boring and oversize pistons for good compression. If your compression test results are accurate, I suspect the problem is incorrect camshaft timing or leaking compression chambers (improper piston ring installation, warped heads, valves not seating, etc).
I suggest you perform more testing before swapping the engine.
Was the throttle plate wide open when you checked the compression?
Did you let the engine rotate long enough for five compression strokes on the cylinder being checked?
Did the engine overheat before the rebuild? How did you determine that both head gaskets were blown?
You mentioned that the original exhaust manifold ports did not match the head ports and that the heads were ported and polished. If the head exhaust ports were enlarged then they wouldn't match the exhaust manifold ports. If the original manifolds would not bolt to the heads that indicates that the heads, manifolds, or both were warped. A reputable shop should have checked the heads for cracks and warp before porting and polishing them. Milling severely warped heads to make them flat may not be adequate because the combustion chambers might have different volumes. That would result in different compression ratios and imbalanced power pulses.
Normally an SOHC V6 with less than 200K miles should not need boring and oversize pistons for good compression. If your compression test results are accurate, I suspect the problem is incorrect camshaft timing or leaking compression chambers (improper piston ring installation, warped heads, valves not seating, etc).
