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Adapting a V8 Intake Manifold from Another Engine
In some cases a manifold originally intended for a different engine may be adapter or modified. Some will require spacers under the intake port flange either to adapt the bolt pattern, add height for a taller deck, or both. The spacer can also adapt the intake flange angle somewhat, but the math to do this is not as simple as it appears. Engines with separate valley covers (Chrysler RB) are easier to adapt than engines with integral valley covers (Chevrolet SB). The manifold being adapted must have the correct size and shape intake port, or slightly smaller. In no instance may the manifold port overlap the head flange, but must have free flow into the intake port at all points although it may be somewhat smaller.
The bore pitch (the center-to-center distance between adjacent cylinders in the same bank) must be similar. Gross differences will cause a fatal mis-alignment on three of the four ports in each bank.
There is no fixed maximum bore pitch difference that an adaptation will tolerate, since thicker walled castings, large pitch distances and large port areas obviously can ”hide” a larger error.
The preferred method is to center the inner cylinder pairs (3 & 4 and 5 & 6) of the manifold on the heads. This “averages out” the difference in bore pitch, so that the alignment error of each of the paired inner cylinders is ½ of the bore pitch difference.
An example: if the manifold’s bore pitch is 4.800” (Chrysler B) and the Buick 430 heads are 4.750” the difference is .050”; let’s call this the “pitch error”. The 3 & 4 and 5 & 6 inner cylinders will be off by .025” from ideal. The outer cylinders will inherit this error, and add their own pitch error of .050” for a total of .075” each for cylinders 1, 2, 7, & 8.
This is preferable to perfect alignment at one end, where each successive cylinder is cumulatively worse. Not only is the maximum error much greater, but the range of mis-alignment between all cylinders is much greater: 0-.150” or .150”, compared to .025”-.075” or .050”, making for potential mixture bias problems: |
Cylinder pair | Preferred “centered” method | “From one end” method |
1, 2 | .075” pitch error | .000” pitch error |
3, 4 | .025” pitch error | .050” pitch error |
5, 6 | .025” pitch error | .100” pitch error |
7, 8 | .075” pitch error | .150” pitch error |
For a manifold comparison, subtract the pitch distance from any engine in the Table below from the pitch distance of your subject engine (doesn’t matter if the result is a negative number). The outer four cylinders (1, 2, 7, 8) will mis-align by 1.5 × the pitch error, and the center four cylinders (3, 4, 5, 6) will mis-align by .5 × the pitch error.
Here is a table of the most common automotive V8 engines, ranked by bore pitch, along with their intake port configuration.
V8 Bore center distances |
Engine | Size | Bore pitch | Ports |
Ford modular OHC | 4.6, 5.4 | 3.937” | 00-00 |
Buick, Rover SB | 215, 300, 340, 350 | 4.24” | 0-00-0 |
Olds, Pontiac SB | 215 | 00-00 |
Dodge hemi & poly | 241, 259, 270, 315, 325 | 4.1875” | 0-0-0-0 |
DeSoto hemi | 276, 291, 330, 341, 345 | 4.3125” | 0-0-0-0 |
Ford 335 | 221, 260, 289, 302, 351, 400 | 4.38” | 0-0-0-0 |
Chevrolet SB | 265, 283, 302, 307, 327, 350, 400 | 4.40” | 00-00 |
Chrysler poly A | 277, 301, 303, 318, 326 | 4.46” | 0-0-0-0 |
Chrysler LA | 273, 318, 340, 360 | 00-00 |
Studebaker | 224, 233, 259, 289, 304.5 | 4.50” | 00-00 |
Cadillac *-1966 | 331, 365, 390, 429 | 4.5625” | 00-00 |
Chrysler hemi & poly | 301, 331, 354, 392 | 4.5625” | 0-0-0-0 |
Pontiac | 287, 326, 347, 350, 370, 389, 400, 421, 428, 455 | 4.62” | 00-00 |
Oldmobile | 330, 350, 400, 425, 455 | 4.625” | 00-00 |
Ford FE | 332, 352, 360, 390, 401, 410, 427, 428 | 4.63” | 0-0-0-0 |
Rambler *-1965 | 250, 287, 327 | 4.75” | 00-00 |
AMC 1966-* | 290, 304, 343, 360, 390, 401 | 4.75” | 00-00 |
Buick | 400, 430, 455 | 4.75” | 00-00 |
Buick nailhead | 264, 322, 364, 401, 425 | 4.75”? | 0-00-0 |
Chrysler B/RB | 350, 361, 383, 413, 426, 440 | 4.80” | 00-00 |
Chrysler RB hemi | 426 | 0-0-0-0 |
Chevrolet W | 348, 409, 427 | 4.84” | 00-00 |
Chevrolet BB | 366, 396, 402, 427, 454 | 00-00 |
Ford MEL | 383, 410, 430, 462 | 4.90” | 00-00 |
Ford 385 | 332, 352, 360, 390, 401, 410, 427, 428 | 4.90” | 0-0-0-0 |
Cadillac 1967-* | 368, 425, 472, 500 | 5.00” | 00-00 |
Packard | 368, 425, 472, 500 | 5.125” | 00-00 |
After a comparison of pitches has narrowed the potential manifold selection, the next variable that must be addressed is the port configuration. There are only three possible layouts: two identical pairs (shown in the Table above as “00-00”), four individual ports with equal separation (0-0-0-0), or 1-2-1 (0-00-0) which is unique to older Buicks. Except under extremely unusual circumstances where the transition between the manifold flange and the head port will be several inches long, the port layout must match.
In addition, Ford cylinder banks are arranged so that the passenger’s side is ahead of the driver’s side (closer to the front of the engine), which is the reverse of most other brands. Except for manifolds with separated banks such as Hilborn, this cannot be changed without major surgery.
The Ford Y-block (239, 256, 272, 292, 312) is a special case, since its ports are arranged in pairs (1 & 3, 5 & 7, 2 & 4, 6 & 8), but they are stacked vertically unlike any other common engine. I’m not sure if the larger but similar Lincoln and H-D truck Y-block engines (279, 302, 317, 332, 341, 368) share this design.
The number and position of manifold bolts is not critical, in some cases filling the existing threaded hole with a stud or bolt may be useful.
Water flow must be examined carefully. In some cases, the manifold is the only transfer between banks and must be retained. |
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