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Engine        Valves             Chambers        Springs

2.5              33.2 x 28.0        28.5cc’s           Single Conical

2.7              33.2 x 28.0        29.5cc’s           Single Conical

3.2              37.0 x 32.4         35.0cc’s           Single Conical

3.4 996      37.0 x 32.4         35.5cc’s           Single Conical

3.4 987      40.2 x 34.4        41.0cc’s           Dual Straight Intakes                                                                                                                                        Single Conical Exhaust

3.6             40.2 x 34.4          41.0cc’s          Dual Straight Intakes                                                                                                                                         Single Conical Exhaust

3.8              40.2 x 34.4         42.0cc’s          Dual Straight Intakes                                                                                                                                       Single Conical Exhaust

X51            40.2 x 34.4          39.5cc’s           Dual Straight Intakes                                                                                                                                       Single Conical Exhaust

Cracks?        Click here for more info about cracked M96 996 cylinder heads.

2.5                Occasionally occur in the spark plug wells

2.7                Occasionally occur in the spark plug wells on 5 chain models

3.2                Occasionally occur in the spark plug wells on 5 chain models.                                                            Can occur in secondary air ports on 2003-2006 model 3 chain heads

3.4 996        Very common in spark plug wells. The most common location radiates out                                   toward an exhaust valve guide bore. Click here to see pictures of this crack.

3.4 987        Deep inside the secondary air passage. Symptoms are steam out tailpipe. Can be diagnosed by removing exhaust manifold and pressurizing coolant system.

3.6               Deep inside the secondary air passage. Symptoms are steam out tailpipe. Can be diagnosed by removing exhaust manifold and pressurizing coolant system.

3.8               Deep inside the secondary air passage. Symptoms are steam out tailpipe. Can be diagnosed by removing exhaust manifold and pressurizing coolant system.

X51               None observed to date. Will update if we see one.

 

Failures?     None of the M96/M97 heads are prone to blown head gaskets. We’ve only                           seen it on three pairs of severely overheated heads. Sometimes related to improper coolant purge which causes air pockets in heads.

2.5                 Occasional broken valve spring, possibly/probably related to abuse and/or                                     hydraulic follower malfunction.

2.7                 Occasional broken valve spring, possibly/probably related to abuse and/or                                     hydraulic follower malfunction.

3.2                  Occasional broken valve spring, possibly/probably related to abuse and/or                                   hydraulic follower malfunction.

3.4 996         Occasional broken valve spring, possibly/probably related to abuse and/or                                     hydraulic follower malfunction.

3.4 987        Occasional dropped O.E. intake and exhaust valve seats, and fretted intake keeper  grooves.  Dropped seat risk is significant for street cars and high for track cars. Risk is very high on heads that receive a valve job on O.E. seats.

3.6                Occasional dropped O.E. intake and exhaust valve seat, and fretted intake keeper grooves.  Dropped seat risk is significant for street cars and high for track cars. Risk is very high on heads that receive a valve job on O.E. seats.

3.8                None observed to date, but deemed at risk of dropped seats due to design similarity  to 3.6 and 3.4 987. Elevated risk on heads that receive a valve job on O.E. seats.

X51               Dropped intake & exhaust valve seats, and severely fretted keeper grooves. These heads use very heavy intake valves with a wide margin and flat face. Despite the significant increase in valve weight, they use the same valve spring pack as the standard 3.8.

Guide Wear?

2.5                     None to moderate, depending on maintenance regimen and use, ie.                                              mild street or aggressive street/track.

2.7                     None to moderate, depending on maintenance regimen and use, ie.                                              mild street or aggressive street/track..

3.2                    None to moderate, depending on maintenance regimen and use, ie.                                              mild street or aggressive street/track.

3.4 996            None to moderate, depending on maintenance regimen and use, ie.                                              mild street or aggressive street/track.

3.4 987           Severe intake. Significant exhaust

3.6                   Severe intake. Significant exhaust

3.8                    Severe intake. Significant exhaust

X51                   Severe intake. Significant exhaust

All valve stems: 6mm with 3 keeper grooves

All keepers are floating type, meaning the tips butt for rotation.

All valve angles: 45*

Dual springs are non-interference type

All springs use round wire

All retainers are steel and impressive in design and quality.

All seats exhibit zero wear characteristics.

All heads have very rigid decks. We have never seen two of any model warp in excess of .005”

All models use Euro style valve stem seals

Hoffman Automotive Machine

1461 Greensboro Hwy.

Watkinsville, GA 30677    706 769 3783