Pontiac V8 engine
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An alternative to using the larger chamber heads is to install dished pistons and use any of the smaller chambered performance heads. | An alternative to using the larger chamber heads is to install dished pistons and use any of the smaller chambered performance heads. | ||
| + | ===Studs and guideplates=== | ||
| + | ====The bottleneck stud==== | ||
| + | [[File:Pont stk stud.jpg|thumb|500px|Stock type Pontiac bottleneck stud]]Pontiac heads like the 6X and practically all other heads likely to be used in a performance-orientated build have screw in ''bottleneck'' studs and steel guideplates. There are some exceptions to this, like the Ram Air IV and "Ram Air II" round port heads, which used a straight 7/16" stud with an adjuster nut/lock nut. | ||
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| + | The usual D-port stock arrangement is a "net lash" set-up. Because the stud is 7/16" OD at the bottom, the rocker arm and pivot ball is also made to fit a 7/16" OD stud. The '''top''' of the bottleneck stud is threaded for a 3/8-24 nut, to be torqued to 15 ft/lb to retain the rocker arm. | ||
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| + | Net lash is affected by any of the following: | ||
| + | *Block deck height | ||
| + | *Head deck height | ||
| + | *Head stud boss height | ||
| + | *Rocker arm brand/design | ||
| + | *Cam base circle size | ||
| + | *Lifter design/brand/pushrod seat height | ||
| + | *Valve stem length | ||
| + | *Head gasket thickness | ||
| + | So if any of the above changes are made, the stock Pontiac bottleneck stud/net lash set-up may no longer preload the lifter properly. Unless the studs are changed to allow for an adjustable valve train, different length push rods may be needed to set the lifter preload. For that reason it is always advisable to use straight studs to replace the bottleneck studs. A good replacement is ARP p/n 190-4003 w/hex nuts, or p/n 190-4203 w/12-point nuts. Be aware that there can be clearance issues between the polyloc and valve cover if polylocs are used. Check the clearances carefully; you might be able to use a shorter polyloc. If possible (and the valve cover are so equipped) keep the oil drippers. The oil drippers are a separate piece from the valve covers on the RA II/IV engines. | ||
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| + | While it is not recommended, the bottleneck studs will sometimes work as an adjustable valve train if a stock SBC lock nut is used and the camshaft is very mild. But this does nothing for the inherently weaker design of the bottleneck stud. | ||
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| + | The stock Pontiac guideplates are fine to reuse as long as the pushrod diameter is the same as stock or if the pushrod OD is larger, the holes are tweaked to allow the pushrods to fit without interference. | ||
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| + | ===Rocker arms=== | ||
| + | Most Pontiac engines came with 1.5:1 ratio rockers. Exceptions to this were the Ram Air IV engines, which used 1.65:1 rockers. The 1.65 rockers can be used on any Pontiac head but the push rod guide hole in the head has to be carefully inspected/enlongated at the top of the opening. More on this [ '''here''' | ||
===Valve springs=== | ===Valve springs=== | ||
Cliff Ruggles has said "We use and prefer the Crower 68404 (1.6" installed height) or 68405 (1.7" installed height) for flat hydraulic cams with Pontiac cylinder heads." | Cliff Ruggles has said "We use and prefer the Crower 68404 (1.6" installed height) or 68405 (1.7" installed height) for flat hydraulic cams with Pontiac cylinder heads." | ||
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| + | ===Round port heads=== | ||
| + | [[File:D over rnd pont.jpg|thumb|500px|left|D-port #13 heads above a Ram Air IV head]] | ||
| + | Round port heads were long favored for high performance. But they were scarce (read expensive), and did not flow all that well. | ||
| + | |||
| + | Now that Edelbrock and others have come out with affordable aftermarket aluminum heads, the round port heads are all but ignored by the performance crowd. But to restorers, they are still highly sought after. | ||
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==="Pete's Picks"=== | ==="Pete's Picks"=== | ||
| − | Pete | + | Pete McCarthy did a huge head air flow test that was originally written up in the April and June, 1991 editions of High Performance Pontiac, titled [http://forums.highperformancepontiac.com/70/9029510/the-general-discussion/to-port-or-not-to-port-heads/index.html '''The Ultimate Head: Part I''']. |
;The results<nowiki>:</nowiki> | ;The results<nowiki>:</nowiki> | ||
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