Blue Thunder series 3 does not have a slot in the plenum divider.  I just flowed one of the new intake manifolds, and it averaged 283cfm as cast and shipped.  Four of the ports flowed identical numbers, which is very balanced as dual plane intake manifolds go.  On the older BT series 2 intakes with the slot, there was some turbulence on two ports when flowing with an open spacer, and if you smoothed/cartridge rolled the divider, the flow picked up a few cfm.  The average flow is very close as cast between the BT 2 and BT 3.  (Flowed on SF-600 flow bench)  Joe-JDC.

JDC

Bill.  Good catch on the balancing.  I’m sure that’s not the only thing I missed but that one should have been more obvious than most.  Balancing, degreeing in the camshaft, and center cam journal oiling modifications are performed on all Y builds at this shop.

Lorena, Texas (South of Waco)

Bill.  The 393HP 317 engine got there by way of a 3.810” bore and a 3.480” stroke.  It has 292 sized mains with 2.000” journals.  A 292 crankshaft was used in this instance for the offset grinding.  The 389HP 317 engine got there by way of a 3.830” bore and uses a stock 312 crankshaft (3.44” stroke) that was turned 010X010.  The 312 crankshaft with its larger journal sizes takes a bit larger camshaft to make it competitive with the other 317 engine which has smaller journal sizes.  Bearing speed is the key to some 'free' horsepower if you can capitalize on using the smaller journal sizes.
 
Joe has done a good job in describing the flow differences at the plenum divider between the version (series) 2 and version 3 Blue Thunder intakes.  I’ll add that while the version 2 Blue Thunder intake has been around for several years now, the version 3 intake has only been out for about 3 months.  Visible differences on the version 3 intake are no slot in the plenum divider and some specific casting changes at the rear so that the MSD 8383 billet distributor will clear without modifications.

Lorena, Texas (South of Waco)

In the list of machine shop operations that Ted identified for doing a comprehensive performance y-block Ford engine ‘build’… he included three operations that I'm unfamiliar with HOW to accomplish or best approach.  Additional information would be appreciated.  

1)  'cam tunnel alignment issues being corrected'?  HOW is this done?  Is an 'oversize' cam bearing available that can be line honed to size?  If such a machining operation is undertaken, what camshaft bearing clearance is recommended for a y-block?
2)  'lifter bores being honed'?  What lifter to bore clearance is recommended for a y-block?  Are the existing y-block lifter bores being reamed oversize for the installation of a bronze bushing?
3)  'installing hardened seats for unleaded fuel'?  Frequent practice seems to be installing hardened exhaust seats only… unless the intake seats otherwise need replacement due to other seat wear problems. In installing stainless intake and exhaust valves, is there purpose to installing hardened seats for both the intake and exhaust valves?

THANKS for the help!  

NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York

A good engine rebuild shop should test how freely the cam turns in the block after new bearings are installed. Often they need some skimming with a bearing scraper. 

Charlie.

1. Some of the 312 blocks have cam tunnel bore issues bad enough that it warrants boring the cam tunnels to a 1.813” size and installing a custom cam bearing in which to correct.  The initial check is performed with a solid bar that is machined slightly undersize to the original cam bore diameter and is inserted from each end of the block to determine the directions in which the bore alignment has been compromised.  This is a much better fix rather than having to ‘carve’ on the installed cam bearings in which to get the camshaft into the block.
2. Blocks that have been out in the weather or exposed to moisture requires the lifter bores to be ‘reconditioned’.  Honing is a simple fix for these and targeting for a 0.0015”-0.0017” lifter to bore clearance suffices for most.  To date, I have not had to go so far as do a brass bushing lifter bore repair for the Y engines.  Brass bushing repairs for the lifter bores in BBC engines is pretty common fare though.
3. Hardened seats are typically installed only on the exhaust side but many heads have been reground or worn to the point that installing new intake seats is necessary also.  It's important that the valves are not sitting in a 'sunk in' position in the heads.

Lorena, Texas (South of Waco)

THANKS for your reply to my questions, Ted.  Appreciated!
Regards,


NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York

A thought on the Blue Thunder Plenum slot.  As Ted's  & Joe JDC's testing has confirmed, it's not a desirable feature of the intake, unless the user is going to install an older 3 barrel style carb. So, it's been my experience that aluminum castings can be welded successfully, so why not cut a plate & weld it in with a suitable alloy & eliminate the slot?  


Paul

I agree, a piece of aluminum welded into place, and blended, rolled over to get rid of sharp edges, and it will be a better intake.  I just completed porting my personal BT-3 intake manifold today, and it picked up 40 cfm average.   Joe-JDC

JDC

1) Ted mentioned that SOME 312 blocks are found to have cam tunnel bore alignment inaccuracy.  Since numerous FoMoCo block casting series (five?) from '56 through '60 were used for either 292 or 312 engine production, is there any speculation as to WHY the cam tunnel bore issue is found in 312 produced blocks and not 292 blocks?  

Might the 312 main bearing bores and and cam bearing bores been machined on a particular production machine?
OR
Might the misalignment inaccuracy be tied to block twist (over time) caused by reduced engine block structural integrity brought on by the 312 engine bore being .050 larger than the 292 engine bore?

2) Have the cam tunnel bore issues been found more frequently on some 312 y-block casting series from '56 to '60 than others?  


NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York