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?How to block hot air crossover?

Jack

Well-known member
Joined
Dec 27, 2000
Messages
1,825
Location
Florence, SC (Timmonsville SC)
Corvette
71 War Bonnet Yellow VERT 71 BH Blue CPE (SOLD)
Hey boys & girls:
I'm thinking (hehe mistake one) of COMPLETELY blocking off the hot air crossover through bottom of my 71's 388 sb INTAKE to gain a cooler charge & small performance boost ... what do you think? Winter's fairly mild here in SC. I have a low-rise Non-EGR Weiand aluminum 8004 intake (I'm guessin' it shouldn't matter whether Fe or Al?) and a Qjet on iron GM heads (intake & both heads have the x-over ports). I know other intakes/heads come with no x-over ... also intake gaskets available with no x-over hole. My universal intake gasket set also came w/ two metal inserts. The inserts can be used or not ... they'll restrict flow through a round hole about 1/2" dia. Gasket Instructions say use on one side for year this ... other side for year that etc. I can get other gaskets w/ no x-over hole if that's all there is to it ... dunno if it wouldn't just burn through over time though? I'm also capable of a bit of fabrication ... though I'm not fibbin' here! So, should I block off ... if so How ... and then should it be partial or complete? What's a simple, reversible & reliable way to block it off? For now, heads & intake are off block. Thanks in advance fer yer thoughts on this!
JACK:gap
 
K

KenSny

Guest
Use a gasket with the metal inserts to completely block the crossovers. I do not use a heat riser. I live in Ohio and it's not a problem with warmup. I also used a lifter valley baffle under the intake manifold to reduce the hot oil splash on the bottom to further keep the fuel cooler.
 

vigman

Motor head!!!!
Joined
Feb 13, 2001
Messages
3,471
Location
Valencia, CA,USA
Corvette
88 Convert ( SOLD ) /1973 coupe 4 speed/1964 Vert!
Ken is correct

After time, they will get brittle but it will do the trick.. I would consider another manifold if the block is that important to you like the edlebrock preformer & a holley 650. I getting really tweaked at my Q jet stupid leakin bowls phooey!

Mike
 

Jack

Well-known member
Joined
Dec 27, 2000
Messages
1,825
Location
Florence, SC (Timmonsville SC)
Corvette
71 War Bonnet Yellow VERT 71 BH Blue CPE (SOLD)
KenSny:
Thanks. Are you using a GM baffle like what's rivited to bottom of factory intakes ... or an aftermarket/add-on one ... part number?

Mike:
Thanks. Yea this block, intake & carb are important to my mild buildup ... primarily because they're here & ready to go. Most of the sbc PERFORMERS are pn 2101 or 3701. Like the Weiand 8004, presently those #'s have the crossover too. The AIRGAPS (too tall) don't have it. Dunno 'bout the RPM's. The 8004 & 2101 are very similar in most respects ... some prefer the 8004's slightly different performance envelope ... price too. Holley's are just fine, but for my usage I like the Qjets & Duojets I've had ... so I need the spreadbore flange too (atypical for Holley). I've found good info on how to fix leakers / optimize Qjets. Gonna go out on a limb here, but I'm Guessing most of the low-rise aftermarket sbc spreadbore street intakes did/do have the crossover.

Jack:gap
 
K

KenSny

Guest
No, it does not rivet to the bottom of the intake like some stock ones. See the Summit or Jegs online catalogs and search for lifter valley baffle. There are several different types made.

It seems that if a cylinder head is a "performance" upgrade (Brodix, Dart, etc) rather that a "replacement" upgrade (S/R Torquer) than the head will most likely not have the crossovers. A lot of performance intakes do not have the crossovers.
 

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