Vortec L31 cylinder head
m (→Upgrading and Compatibility) |
(Minor clean up; add text; format links) |
||
| Line 2: | Line 2: | ||
==Overview== | ==Overview== | ||
| − | The L31 Chevy Vortec cylinder head is the best flowing production head for the Gen I SBC engine. They are made of cast iron, have 64cc combustion | + | The L31 Chevy Vortec cylinder head is the best flowing production head for the Gen I SBC engine. They are made of cast iron, have 170cc nominal intake runners, and 64cc nominal combustion chamber volume (actual volumes may vary due to production tolerances and/or modifications done previously, so volumes, especially the combustion chamber volume, has to be determined by measuring, or "CC'ing" the chamber). |
Because of the superior port and combustion chamber designs, total timing requirements for maximum power is 4-6 degrees less than the earlier non fast burn heads. | Because of the superior port and combustion chamber designs, total timing requirements for maximum power is 4-6 degrees less than the earlier non fast burn heads. | ||
| Line 50: | Line 50: | ||
==Upgrading and Compatibility== | ==Upgrading and Compatibility== | ||
| − | The L31 Vortec head will bolt directly onto Gen 1 small block | + | The L31 Vortec head will bolt directly onto Gen 1 small block Chevrolets. They will also obviously work on L31 engines (sometimes referred to as Gen1+). They are not compatible with Gen2 (LT1 or LT4) engines. They are also not compatible with any of the current LS engines. |
| − | There are however, some inherent costs associated in swapping | + | There are however, some inherent costs associated in swapping 1995-back heads with L31 Vortec heads. Here is a list of items to be purchased and/or labor associated with the upgrade: |
* L31 heads (and required hardware like springs, valves, retainers, valve keepers, etc) | * L31 heads (and required hardware like springs, valves, retainers, valve keepers, etc) | ||
| − | * Center bolt style valve covers | + | * Center bolt style valve covers if the heads used previously were perimeter style |
| − | ** Note: | + | ** Note: [http://www.crankshaftcoalition.com/wiki/Vortec_L31_cylinder_head#Small_port_Vortec_head_p.2Fn_25534351_.28bare.29_and_p.2Fn_25534421_.28assembled.29 GMPP small and large port Vortec heads] and other aftermarket Vortec heads accept either perimeter or center bolt valve covers |
| + | *Self aligning rocker arms | ||
* Valve cover gaskets | * Valve cover gaskets | ||
| − | * Vortec specific intake manifold | + | * Vortec specific intake manifold. While some aftermarket heads have both 12 and 8 bolt intake bolt patterns, the height of the Vortec ports require a tall, "raised port" type early intake manifold (along with porting/port work to the intake manifold and/or head), to even come close to fitting correctly |
* Vortec specific intake manifold gasket | * Vortec specific intake manifold gasket | ||
* Vortec specific intake manifold bolts | * Vortec specific intake manifold bolts | ||
| − | * Head bolts (required | + | * Head bolts (required only if the original head bolts are either missing or unusable for some reason) |
| − | * Head gaskets ( | + | * Head gaskets ([http://www.crankshaftcoalition.com/wiki/Head_gasket#Re-using_head_gaskets generally required] any time heads are re-installed) |
| − | * Grinding down valve guides to | + | * Grinding down valve guides or the use of different retainers and springs, or ghetto grinding the stock retainers, etc., to work with a camshaft having somewhere around 0.480" or more valve lift. NOTE: The clearance between the retainer and the seal has to be checked during the engine mock up phase of the build to determine exactly what the clearance is with the cam, retainer, valve stem seal, valve locks and rocker arm/rocker arm ratio used. |
==Valves== | ==Valves== | ||
| − | Vortec heads come equipped with valves having a 30 degree back cut to help flow. Unlike previous SBC valves, Vortec valves have just one groove for the keepers instead of two grooves (one for the keepers, the | + | Vortec heads come equipped with valves having a 30 degree back cut to help flow. Unlike previous SBC valves, Vortec valves have just one groove for the keepers instead of two grooves (earlier valves had one groove for the keepers, the second (lower) groove was for the oil control O-ring); Vortec heads use a positive-type valve stem oil seal and do not use the tin oil shield seen for years on SBC heads, nor do Vortec heads use exhaust valve rotators. |
==Valve springs== | ==Valve springs== | ||
| Line 73: | Line 74: | ||
The stock springs are not suited for high performance use. There are several replacements for the stock springs, among the best is the beehive spring and retainer combination from Comp Cams, originally designed for the LSx engine series. There are two part numbers for the different spring rates: | The stock springs are not suited for high performance use. There are several replacements for the stock springs, among the best is the beehive spring and retainer combination from Comp Cams, originally designed for the LSx engine series. There are two part numbers for the different spring rates: | ||
| − | + | *'''[http://www.compcams.com/WhatsNew/NewsDetails.aspx?ListHistoryID=164462240 26915]'''- 105 pounds at 1.8" installed height; 293 pounds at 1.2" (according to Competition Products catalog info); spring rate 313 lbs./in (according to Summit Racing catalog info) | |
| − | + | *'''[http://www.compcams.com/WhatsNew/NewsDetails.aspx?ListHistoryID=1166393320 26918]'''- 125 pounds at 1.8" installed height; 367 pounds at 1.15" | |
==Valve spring retainers== | ==Valve spring retainers== | ||
| Line 85: | Line 86: | ||
==Rocker arm studs== | ==Rocker arm studs== | ||
| − | Production L31 Vortec heads come with pressed in studs. For high performance and/or solid lifter applications, screw in studs are highly recommended. The pressed studs can be pinned, but this is a stop-gap measure that should be done only in cases where the spring pressures/engine RPM/lobe intensity will not be excessive and the budget is limited. Otherwise use ARP #070-134-7221 M8 x 1.25 studs or the equivalent. Unless the builder is well versed in doing this type of work | + | Production L31 Vortec heads come with pressed in studs. For high performance and/or solid lifter applications, screw in studs are highly recommended. The pressed studs can be pinned, but this is a stop-gap measure that should be done only in cases where the spring pressures/engine RPM/lobe intensity will not be excessive and the budget is limited. Otherwise use ARP #070-134-7221 M8 x 1.25 studs or the equivalent. Unless the builder is well versed in doing this type of work, i.e. drilling straight, correctly located holes and tapping them, this is better left to a professional machinist/machine shop. |
Guide plates can also be installed at this time if desired. If not, non shouldered studs can be used instead of studs having shoulders and a hex for tightening (this type of stud is tightened by "double nutting"). | Guide plates can also be installed at this time if desired. If not, non shouldered studs can be used instead of studs having shoulders and a hex for tightening (this type of stud is tightened by "double nutting"). | ||
==Exhaust seats== | ==Exhaust seats== | ||
| − | Not long after the L31 Vortec head was introduced, there was much made of the supposed difference in flow between the Vortec heads that came with the hardened exhaust seat inserts as opposed to the heads that had induction hardened seats. This was largely due to an incorrect, though oft-repeated statement made by a car magazine that said in essence the 906 head was to be avoided because of the exhaust seat insert being vastly inferior to the heads with induction hardened exhaust seats. | + | Not long after the L31 Vortec head was introduced, there was much made of the supposed difference in flow between the Vortec heads that came with the hardened exhaust seat inserts as opposed to the heads that had induction hardened seats. This was largely due to an incorrect, though oft-repeated statement made by a car magazine that said in essence the c/n 906 head was to be avoided because of the exhaust seat insert being vastly inferior to the heads with induction hardened exhaust seats. |
| − | Despite this having been being dispelled any number of times, it still surfaces now and then. But like is often the case, there's a grain of truth to this. On c/n 906 Vortec heads having the hardened exhaust seat insert (not all 906 heads used the insert), there ''can'' be a lip made by the seat where it's pressed into the head. If there's a lip it can be blended and smoothed to improve the flow using nothing more than a Dremel. This is a common procedure that's often done in performance builds- regardless of whether the seats are inserts or induction hardened or unhardened. And also on the 906 heads having the insert, the seat was machined with a single angle instead of a three angle seat as seen on Vortec heads having the induction hardened exhaust seat. The wider seat was used to better transfer heat from the valve into the head/cooling system. Three angle valve seats are the norm these days, done routinely by almost every machine shop. So if the seats are reground during a valve job, the single angle seat can be made into a three angle seat without a problem. | + | Despite this having been being dispelled any number of times, it still surfaces now and then. But like is often the case, there's a grain of truth to this. On c/n 906 Vortec heads having the hardened exhaust seat insert (not all c/n 906 heads used the insert), there ''can'' be a lip made by the seat where it's pressed into the head. If there's a lip it can be blended and smoothed to improve the flow using nothing more than a Dremel. This is a common procedure that's often done in performance builds- regardless of whether the seats are inserts or induction hardened or unhardened. And also on the c/n 906 heads having the insert, the seat was machined with a single angle instead of a three angle seat as seen on Vortec heads having the induction hardened exhaust seat. The wider seat was used to better transfer heat from the valve into the head/cooling system. Three angle valve seats are the norm these days, done routinely by almost every machine shop. So if the seats are reground during a valve job, the single angle seat can be made into a three angle seat without a problem. |
| − | So both the c/n 906 and c/n 062 heads have virtually the | + | So both the c/n 906 and c/n 062 heads have virtually the same performance potential. In fact c/n 906 heads having the hardened inserts are actually preferred by some performance engine builders, mainly for marine applications. Later production c/n 906 heads stopped using exhaust seat inserts and at some point, all Vortec head exhaust seats were induction hardened. |
Your Privacy Choices