Intake manifold

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==Overview==
 
==Overview==
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The intake manifold is an important part of the induction system. Basically it 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.
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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.
  
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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 an radically influence 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.
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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==
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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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Professional Products makes a knock-off of this design also, called the Typhoon, p/n 52021 for satin finish.
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[[File:Typhoon 52021.jpg|thumb|300px|Typhoon p/n 52021]]
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[[File:Typhoon 52021.jpg|thumb|300px|left|Typhoon p/n 52021]] <br style="clear:both"/>
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Professional Products makes a manifold of this design also, called the Typhoon, p/n 52021 for satin finish. Ad copy on the various Professional Products intake manifolds can be read [http://www.professional-products.com/manifoldsProductSBchevy.php here].
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===Air gap===
 
===Air gap===
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The so-called "air gap" intake concept has been around since the late '40s-early '50s. It has been used by various auto makers through the years, like Pontiac, as original equipment. Air can circulate beneath the plenum; the plenum is separated from the hot motor oil being splashed onto the bottom of the intake where it seals the lifter valley.]]
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[[File:Rpm 7501 air-gap.jpg|thumb|400px|left|Edelbrock SBC RPM Air-Gap intake. Air can circulate beneath the plenum; plenum is separated from the hot motor oil being splashed onto the bottom of the intake where it seals the lifter valley.]]
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The so-called "air gap" intake concept has been around since the late '40s-early '50s. It has been used by various auto makers through the years, like Pontiac, as original equipment. Air can circulate beneath the plenum; the plenum is separated from the hot motor oil being splashed onto the bottom of the intake where it seals the lifter valley.  
  
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Only because the Chevy V8 uses the intake bottom to seal the lifter valley is this called to attention. Other engine that use a separate plate to cover the lifter valley have had "air gap" intakes all along.
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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.
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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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[[File:Rpm 7501 air-gap.jpg|thumb|400px|left|Edelbrock SBC RPM Air-Gap intake. Air can circulate beneath the plenum; plenum is separated from the hot motor oil being splashed onto the bottom of the intake where it seals the lifter valley.]] <br style="clear:both"/>
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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 ''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.
  
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The Edelbrock Air-Gap intakes will require a longer warm-up. In cold weather this can lead to driveability 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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===Single plane vacuum loss===
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A single plane intake will have about 4 in/Hg less vacuum than a dual plane due to the design, all else being equal. Obviously this is not written in stone; other factors like carb size and cam specs will have a large effect on the amount of vacuum the engine has.
  
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===Single plane===
 
 
{|
 
{|
 
|[[File:WEIAND 7546 001.jpg|thumb|450px|center|Weiand single plane p/n 7546.]]  
 
|[[File:WEIAND 7546 001.jpg|thumb|450px|center|Weiand single plane p/n 7546.]]  
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==Carb spacers==
 
==Carb spacers==
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Carb spacers in their various designs are often used as a tuning aid and for helping to make power in the range where it's needed.
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===Open spacer===
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Tend to boost output in the upper range and will increase plenum volume. On an intake like the Edelbrock RPM (non Air Gap) dual plane intake, using an open 1" spacer will let the intake make identical power to the cut down plenum divider of the Air Gap.
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===Divided spacer===
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These will retain the dual plenum low-to-midrange benefits while possibly raising the power peak. Tends to make the runners seem longer.
 
   
 
   
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[[File:CARB SPACERS WOOD Q-JET 001.jpg|thumb|300px|left|Pair of homemade spacers.]]
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[[File:CARB SPACERS WOOD Q-JET single.jpg|thumb|300px|left|Spacer made specifically to fit the Pontiac Performer intake. Spacer is upside down.]]
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<br style="clear:both"/>
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===Notched plenum divider vs. spacer vs. single plane===
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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"/>
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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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===Also see:===
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*[http://www.hotrodders.com/forum/carb-spacer-163755.html Carb spacer] thread on Hotrodders forum.
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*[http://cms.nhra.com/dragster/1999/issue05/racing_technology.html Racing Technology Tuning with carburetor spacers] from NHRA.com
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* Here's a dyno flog by Car Craft involving 23 different intake manifolds.....
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*[http://www.carcraft.com/techarticles/1309_dual_plane_intake_manifold_comparisons/viewall.html]
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==Marine intakes==
 
==Marine intakes==
 
[[File:VORTEC ALUM INTAKE VOLVO PN 3856270.jpg|thumb|300px|left|Volvo Penta p/n 3856270 marine intake with brass water crossover/thermostat port.]]
 
[[File:VORTEC ALUM INTAKE VOLVO PN 3856270.jpg|thumb|300px|left|Volvo Penta p/n 3856270 marine intake with brass water crossover/thermostat port.]]
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==Fasteners==
 
==Fasteners==
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===Vortec heads===
 
L30/L31 Vortec engines use fasteners made specifically for the plastic Vortec intake and intake gasket. To prevent over torquing the fasteners and crushing the intake gaskets, the bolts come with a longer shank having a non threaded bottom portion so as to bottom out before the gasket or intake sealing flange/bolt hole is compromised. Below the OEM bolt is on the left, an ARP bolt, right:
 
L30/L31 Vortec engines use fasteners made specifically for the plastic Vortec intake and intake gasket. To prevent over torquing the fasteners and crushing the intake gaskets, the bolts come with a longer shank having a non threaded bottom portion so as to bottom out before the gasket or intake sealing flange/bolt hole is compromised. Below the OEM bolt is on the left, an ARP bolt, right:
  
 
[[File:VORTEC INTAKE BOLTS.jpg|thumb|left|]] <br style="clear:both"/>
 
[[File:VORTEC INTAKE BOLTS.jpg|thumb|left|]] <br style="clear:both"/>
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==Using early intake on later (non Vortec) heads==
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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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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==
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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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==Intake installation==
 
==Intake installation==
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Generally speaking, using RTV on intake gaskets acts as a lubricant until it's set up; using it alone can let the gaskets slip out of position when tightened. Most gasket makers caution against using RTV, especially on the side of the gasket that has an RTV bead applied at the time of manufacture. Instead of using RTV over the entire gasket surface, use weatherstripping cement or Gasgacinch on one side of the gasket to hold the gasket in place. Nothing is used on the other side.
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Generally speaking, using RTV on intake gaskets acts as a lubricant until it's set up; using it alone can let the gaskets slip out of position when tightened. Most gasket makers caution against using RTV, especially on the side of the gasket that has an RTV bead applied at the time of manufacture. Instead of using RTV over the entire gasket surface, use [http://3mcollision.com/3m-super-weatherstrip-and-gasket-adhesive-08002-yellow.html 3-M weatherstripping cement] or [http://www.summitracing.com/parts/EDL-9300/ Gasgacinch] on one side of the gasket to hold the gasket in place. These are able to hold a gasket in position almost immediately if applied by the directions. Nothing is needed on the other side in most cases, although a light application of RTV (following the directions for skim time) or one of the non-hardening sealers mentioned above can be used around the water crossovers on ''both'' sides of the gaskets, in conjunction with the cement.
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Some prefer to use [http://www.permatex.com/products/automotive/automotive_gasketing/gasket_sealants/Permatex_Super_300_Form-A-Gasket_Sealant.htm Permatex 300] or [http://www.permatex.com/products/Automotive/automotive_gasketing/gasket_sealants/auto_Permatex_Aviation_Form-A-Gasket_No_3_Sealant_a.htm Permatex Aviation] non-hardening sealers.
  
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{{Note1}}A light application of RTV (following the directions for skim time) around the water crossovers can be used in conjunction with the cement.  
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{{Note1}} A couple cut off bolts or studs can be used to position the gasket perfectly, remove before installing the intake.
  
 
RTV should be used on the ends of a Chevy intake instead of the cork or rubber seals supplied with many gasket sets. Apply a 1/4" thick bead of RTV across the seal surface at each end of the block. If using an O2 sensor be sure to use sensor safe RTV.
 
RTV should be used on the ends of a Chevy intake instead of the cork or rubber seals supplied with many gasket sets. Apply a 1/4" thick bead of RTV across the seal surface at each end of the block. If using an O2 sensor be sure to use sensor safe RTV.
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[[File:Heat shield rivets.jpg]] <br style="clear:both"/>
 
[[File:Heat shield rivets.jpg]] <br style="clear:both"/>
  
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==References==
  
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{{Develop1}}
 
[[Category:Engine]]
 
[[Category:Engine]]
 
[[Category:Carburetors]]
 
[[Category:Carburetors]]
 
[[Category:undeveloped articles]]
 
[[Category:undeveloped articles]]
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[[Category:Undeveloped Engine articles]]
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[[Category:Undeveloped Carburetors articles]]

Latest revision as of 03:46, 15 January 2015

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