I wonder, does John routinely offer pre-machined examples for those with milled heads? While quite a bit of latitude likely exists, providing head thickness & gasket specs. when ordering would make for a more perfect seal.



Also, I wonder why the riser block-off area isn't recessed/machined to accept the raised gasket section, since a flat/unbowed seal area would seem desirable? I assume no one makes a flat gasket?

6 VOLTS/POS. GRD. NW INDIANA

Here are pics of a Blue Thunder with a welded up exhaust heat riser ports and the Mummert intake as provided with no heat riser passage.  Welding up the port in the BT intake eliminates the need for putting shim stock at the gasket to block the port and also allows the intake manifold gasket itself to sit more square with the mating surfaces and not bow the intake up in the middle.

  Blue Thunder Intake

  Mummert Aluminum 4V intake

Lorena, Texas (South of Waco)

Paul.  The Blue Thunder intakes do have the heat crossover capability if it’s deemed that is a must.  But I’ll reiterate that once an engine is fully heated, that exhaust crossover is a detriment to performance and especially if the exhaust flow continues to be restricted to force exhaust through the intake manifold.  In a perfect world, there would be a valve on each side of the intake to close that channel once the engine is heated but that would be more of an issue than the oem flapper valves in one side of the exhaust that helps to force heated exhaust through the intake manifold.  Those flapper valves are an issue all by themselves after they get some age on them.  If the heated flapper valve isn’t closing properly on the exhaust when it’s cold, then the full benefit of the exhaust crossover passage during engine warmup is not being capitalized on anyhow.

 

But now to touch upon the chokes.  The 60’s 292 intakes do not have a provision in the intake manifold for choke coil heating.  The heat source for the choke came from the exhaust manifold instead.  I have some ECZ-B 4V intakes here that also do not have the choke tube going through the intake so I’ll assume that many of these came off of the big trucks.

 

Many of the Sixties Ford V8’s used the exhaust manifolds for the automatic choke heat source.  The exhaust manifolds had a cast chamber in which air could pass through to be heated before entering the tube going to the carburetor.  My ’61 Fairlane with a 292 had an insulated and covered tube going over the passenger side valve cover for the choke.  My ’62 Convertible with a G code 406 had a similar cloth covered tube going over the drivers side valve cover to provide hot air for the choke.  Electric choke coils are a way of life now for carbureted engines.

 

Here’s a picture of the FE 3X2 setup with the automatic choke pulling heated air from the drivers side exhaust manifold.

 

Lorena, Texas (South of Waco)

This discussion hasn't even touched on the heat issue for the choke itself. In cold situations, the choke will not open properly without a heat source. The only alternative is to convert to a manual choke or an electric choke setup. Some like the electrics, others don't. I realize that in Texas or California this isn't an issue, but up North it is..

Paul

Carb or intake heat is still a good idea in the frozen North when it's 20 degrees or less. But then nobody I know is driving his or her 55 year old Y-block in the winter. EXCEPT Hoosier's Ranchero, and he runs a "B" intake with heat in that. He does, however, Disable the blower for snow and ice. Mine stays in the garage.

Frank/Rebop

Bristol, In ( by Elkhart) 

From a performance standpoint on a fully heated engine, any additional heating of the intake manifold is a detriment.  For a carbureted engine that only gets driven 5-10 miles at a time, then the exhaust crossover within the intake manifold has its place in the grand scheme of things.  For an engine that sees a majority of miles each time it runs, the exhaust crossover is not needed.

 

The oem’s went out of their way to reduce carburetor icing and hesitation issues as the engine was transitioning from cold to hot.  Once the engine is fully heat soaked, then any additional heating of the manifold under the carburetor tends to create other problems and was cause for some additional ignition controls to further retard the ignition timing under high heat situations.  The Seventies saw a variety of thermostatically controlled valves and a myriad of vacuum lines to work out the warm-up issues with carburetors.

 

The crossover exhaust ports in the intake manifolds along with the temperature controlled flapper valves in the exhaust were the early fix for carb icing and cold carburetor choke/hesitation issues.  In the late Sixties and thru the Seventies, duct work from the outside of the exhaust manifold to the air cleaner inlet in conjunction with vacuum controlled flapper valves supplemented the exhaust crossovers.  This allowed warm or heated air to actually flow into the top side of the carb in addition to the heating that was taking place in the intake manifold below the carburetor.  All this was done to solve that icing issue at the carb just during the warmup period.  Once fuel injection went from throttle body design to port injection, then the additional heat from the exhaust during engine warmup was able to be removed from the engines.

 

And that’s the short version.

Lorena, Texas (South of Waco)

Most modern engines have multi-port fuel injection which do not require the additional heat.

I know for a fact that TBI GM vehicles still used a heat passage into the early 90s and when modifying those particular engines, retaining that feature is generally desirable for street performance. Though since they are still efi, much of the ill effect can be tuned out pretty easily.


Lawrenceville, GA

Ted,



Pardon my ignorance, but I'm curious whether most all more modern cylinder heads (and the performance-oriented manifolds made for them) are missing the Y-Block's heat riser system? If this is something that was found to be non-essential and thus phased out over the years, I can certainly understand why it was not incorporated into John's design. I had only assumed that the restricted, non-flowing riser passage in my '55 manifold was still providing just enough heat to enable good cold weather performance, as I do routinely drive in sub-freezing dry weather without any hint of warmup stumble.

Still, it would seem to me that bare aluminum directly exposed to super-heated exhaust would likely conduct more heat to the manifold body than when the riser port is blocked (with steel shim material) under the gasket, and thus insulated from the manifold (routine/typical performance setup). Though a very minor issue, it would still be interesting to see a back-to-back dyno HP comparison between blocked & unblocked risers using John's manifold, assuming a small difference in fuel charge temp. would register?

6 VOLTS/POS. GRD. NW INDIANA

Daniel.  The nice thing about John’s intake is the exhaust port does not need to be blocked.  The blocked port is built into the manifold casting so don’t look for any heat from the crossover port at the heads being significant with either a blocked or open gasket.  I’ve welded the ports in the Blue Thunder intakes ‘shut’ so the same could be accomplished.  Without a flow path under the manifold, there’s not much exhaust heat at the intake gasket actually heating the intake manifold itself.  Once an engine is fully heated, the crossover port can be considered a detriment but in cool weather, it does reduce the propensity for carburetor icing while the engine itself is transitioning from cold to hot.  And that's assuming the flapper valve on the exhaust pipe is working correctly to force additional exhaust across the engine through the exhaust passage in the intake manifold.

If you'll look at the Edelbrock Air Gap dual plane intake lineup, there are no heat risers on those either.  And there are none on most single plane intakes regardless of manufacturer.  Eliminating the heat riser passages is a standard item on performance orientated intake manifolds.

Lorena, Texas (South of Waco)

It just occurred to me that a standard intake gasket would likely expose the part of John's manifold that blocks the riser port to enough direct exhaust heat to warm up the entire intake considerably. The stock '55 configuration I'm running now has 5 gaskets under the carb, and the restricted truck-type intake gasket plus deleting the flapper valve likely has my '55 manifold not a lot hotter (?).

6 VOLTS/POS. GRD. NW INDIANA