Intake manifold
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==Overview== | ==Overview== | ||
| − | + | Basically the intake manifold connects the carburetor or throttle body to the intake ports of the cylinder head and in some cases like the small block and big block Chevy engine, it seals the lifter valley and provides a means of mounting the distributor and water neck. | |
| − | But that is just the tip of the iceberg. The intake manifold design has a lot to do with how the engine will perform and | + | But that is just the tip of the iceberg. The intake manifold design has a lot to do with how the engine will perform and can radically influence the engine output and the shape of the power band. Matching the intake type to the engine and vehicle specs is an important part of making a balanced combination, and the choice of what intake best suits the circumstances should not be taken lightly. |
==History== | ==History== | ||
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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. |
<br style="clear:both"/> | <br style="clear:both"/> | ||
| − | 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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===Notched plenum divider vs. spacer vs. single plane=== | ===Notched plenum divider vs. spacer vs. single plane=== | ||
| − | The 1" x 3" notched plenum divider of the RPM AG falls in between an intact plenum divider of a dual plane and an open spacer on a dual plane. It allows ''some'' of the benefits of a single plane, but w/o all of the downsides. It has been observed that using an Edelbrock C3B- with its cut out for the secondary throttle blade of the Holley 3 barrel extended out to a little over 3.5"- it performs right in between an open spacer and no spacer or "notched" divider of a dual plane. This also seems to be the trend w/the Edelbrock RPM vs. RPM Air Gap. | + | The 1" x 3" notched plenum divider of the RPM AG falls in between an intact plenum divider of a dual plane and an open spacer on a dual plane. It allows ''some'' of the benefits of a single plane, but w/o all of the downsides. It has been observed that using an Edelbrock C3B- with its cut out for the secondary throttle blade of the Holley 3 barrel extended out to a little over 3.5"- it performs right in between an open spacer and no spacer or "notched" divider of a dual plane. This also seems to be the trend w/the Edelbrock RPM vs. RPM Air Gap. An unmodified C3B is shown below, left. An RPM AG below, right. |
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| + | [[file:CB3_003.jpg|400px|left]][[file:Rpm_7501_air-gap.jpg|400px|right]] <br style="clear:both"/> | ||
An open spacer on a dual plane will increase plenum volume- something that a notched plenum doesn't do, and this is part of the reason why an open spacer/dual plane often falls in between an open plenum and a standard dual plane without an open spacer in performance. Also there's no added carb height when using a notched plenum divider like there is using a spacer. The added height of the spacer can help allow the air/fuel to make the turn into the runners with less deflection of the A/F stream when it hits the plenum floor at high rpm. | An open spacer on a dual plane will increase plenum volume- something that a notched plenum doesn't do, and this is part of the reason why an open spacer/dual plane often falls in between an open plenum and a standard dual plane without an open spacer in performance. Also there's no added carb height when using a notched plenum divider like there is using a spacer. The added height of the spacer can help allow the air/fuel to make the turn into the runners with less deflection of the A/F stream when it hits the plenum floor at high rpm. | ||
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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. | ||
Photos and text on using [http://www.summitracing.com/parts/PFS-52112/ spacers from Professional Products] is [http://webcache.googleusercontent.com/search?q=cache:bcfaJAnphjUJ:www.persh.org/pickup/TBI%2520Intake%2520Manifold.htm+&cd=1&hl=en&ct=clnk&gl=us&client=firefox-a '''here''']. | Photos and text on using [http://www.summitracing.com/parts/PFS-52112/ spacers from Professional Products] is [http://webcache.googleusercontent.com/search?q=cache:bcfaJAnphjUJ:www.persh.org/pickup/TBI%2520Intake%2520Manifold.htm+&cd=1&hl=en&ct=clnk&gl=us&client=firefox-a '''here''']. | ||
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| + | ==Using an early style intake on an aftermarket Vortec-type head== | ||
| + | Many aftermarket Vortec style heads feature dual bolt patterns allowing the use of the early 12-bolt intakes. This has a very limited use. | ||
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| + | Because of the height of the Vortec intake port, only the single plane 'raised port' race intakes have enough height to actually mate to the Vortec port- but even then the ports may be too wide or have other port fitment issues. The commonly available dual plane intakes do not have enough metal above the port to be ported to match the Vortec port, w/o having a vacuum leak or razor thin sealing surfaces above the ports. | ||
==Gaskets== | ==Gaskets== | ||
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