Intake manifold
From Crankshaft Coalition Wiki
(→Notched plenum divider vs. spacer vs. single plane) |
(→Small block Chevy intake bolt patterns) |
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[[File:429 CJ Q JET INTAKE 2.jpg|thumb|left|300px|429 Ford factory Q-jet cast iron intake]] <br style="clear:both"/> | [[File:429 CJ Q JET INTAKE 2.jpg|thumb|left|300px|429 Ford factory Q-jet cast iron intake]] <br style="clear:both"/> | ||
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| + | ==Small block Chevy intake bolt patterns== | ||
| + | From 1955 until about 1986, all SBC engines had the same 12-bolt intake bolt pattern. In about 1987, GM changed the center 4 bolts to 72 degrees. This was used (except on Corvette aluminum heads, which retained the early bolt pattern) until the 8-bolt Vortec head bolt pattern took over in about 1996. | ||
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| + | The early intake can be made to fit later 72 degree heads by slotting the bolt holes and fabricating (or buying) shims to correct the angles (same with using the later intake (both TBI and TPI intakes from F-bodies (Camaro/Firebird) with the early cylinder heads and 87-91 Corvette aluminum heads). [http://www.persh.org/pickup/TBI%20Intake%20Manifold.htm '''Using a stock TBI Intake Manifold'''] and [http://www.hotrodders.com/forum/sbc-87-cast-iron-heads-vs-older-intake-55-86-a-175547.html#post1250079 '''this Hotrodders forum thread'''] has the details. | ||
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| + | Neither of the earlier intake bolt patterns are compatible with the Vortec 8-bolt cylinder head (with the exception of some performance intake manifolds e.g. Edelbrock Victor Jr. if used with the Vortec head after redrilling - some aftermarket Vortec heads will have a dual bolt pattern which do not support the traditional SBC intake manifold), nor can a Vortec intake be used on either of the earlier bolt pattern heads. | ||
==Types of intakes== | ==Types of intakes== | ||
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Only because the Chevy V8 uses the intake bottom to seal the lifter valley is this considered to be an improvement. Other engine that use a separate plate to cover the lifter valley have had "air gap" intakes all along. But with the SBC engine, especially if using Vortec or aftermarket heads that lack a heat crossover beneath the plenum, the engine may tend to be cold-blooded until the intake comes up to temperature from engine heat. | Only because the Chevy V8 uses the intake bottom to seal the lifter valley is this considered to be an improvement. Other engine that use a separate plate to cover the lifter valley have had "air gap" intakes all along. But with the SBC engine, especially if using Vortec or aftermarket heads that lack a heat crossover beneath the plenum, the engine may tend to be cold-blooded until the intake comes up to temperature from engine heat. | ||
| − | That means the Edelbrock Air-Gap intake will require a longer warm-up. In cold weather this can lead to | + | That means the Edelbrock Air-Gap intake will require a longer warm-up. In cold weather this can lead to drivability problems, almost like a tunnel ram. The air/fuel mixture- if tuned for a fully warmed up engine- will be lean until the engine is up to temp. This can be compensated for by the choke, but if using the choke, spirited driving is out until the choke is fully open. |
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| − | As far as cutting the RPM like the AG, because the carb height and runners are basically the same between the two intakes, that mod will make their top end output equal for all intents and purposes. Not saying that's the thing to do in every case- just saying that | + | As far as cutting the RPM like the AG, because the carb height and runners are basically the same between the two intakes, that mod will make their top end output equal for all intents and purposes. Not saying that's the thing to do in every case- just saying that ''if'' the same powerband as the AG is wanted, it can be had by notching the divider. For the right engine and vehicle combo (low gears, higher stall speed, light weight, more track than street, etc.) notching the plenum (or adding an open spacer) can help more than it hurts. |
===Single plane vacuum loss=== | ===Single plane vacuum loss=== | ||
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*[http://www.hotrodders.com/forum/carb-spacer-163755.html Carb spacer] thread on Hotrodders forum. | *[http://www.hotrodders.com/forum/carb-spacer-163755.html Carb spacer] thread on Hotrodders forum. | ||
*[http://cms.nhra.com/dragster/1999/issue05/racing_technology.html Racing Technology Tuning with carburetor spacers] from NHRA.com | *[http://cms.nhra.com/dragster/1999/issue05/racing_technology.html Racing Technology Tuning with carburetor spacers] from NHRA.com | ||
| + | * Here's a dyno flog by Car Craft involving 23 different intake manifolds..... | ||
| + | *[http://www.carcraft.com/techarticles/1309_dual_plane_intake_manifold_comparisons/viewall.html] | ||
==Marine intakes== | ==Marine intakes== | ||
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[[File:VORTEC INTAKE BOLTS.jpg|thumb|left|]] <br style="clear:both"/> | [[File:VORTEC INTAKE BOLTS.jpg|thumb|left|]] <br style="clear:both"/> | ||
| − | + | ==Using early intake on later (non Vortec) heads== | |
On the 1986-back heads and intakes, the center four bolts were the same angle as the other bolts. 1987-up use a different 72 degree angle except for Corvette aluminum heads. To compensate, spacer/washers can be made or [http://www.holley.com/90748.asp '''bought'''] to allow the intake to fit. | On the 1986-back heads and intakes, the center four bolts were the same angle as the other bolts. 1987-up use a different 72 degree angle except for Corvette aluminum heads. To compensate, spacer/washers can be made or [http://www.holley.com/90748.asp '''bought'''] to allow the intake to fit. | ||
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