MAK­ING SLANT SIX SENSE, PART 2

WE SWAP THE STOCK 1-BAR­REL FOR A HOL­LEY 2-BAR­REL CAR­BU­RE­TOR ON A BONE-STOCK SLANT SIX. NOW OUR SIX-IN-A-ROW HAS MORE GO FOR TO­DAY’S TRAF­FIC FLOW!

Mopar Muscle - - Contents - BY DAN FOLEY • PHO­TOS BY THE AUTHOR

Swap­ping the stock 1-bar­rel for a Hol­ley 2-bar­rel carb on a bone-stock Slant Six

In our last in­stall­ment, we proved the old-re­li­able Slant Six in bone-stock form isn’t any­where near the per­for­mance stan­dards of a mod­ern sixor four-cylin­der en­gine. When we put our 1966 Dart GT on the road two and a half years ago af­ter a 20-year hi­ber­na­tion, we re­al­ized just how slug­gish the old lean­ing tower of power was in this day and age.

If you missed Part 1, we added Per­for­mance Dis­trib­u­tors Tri-power elec­tronic ig­ni­tion and Livewires ig­ni­tion wires, which jolted-up its per­for­mance sig­nif­i­cantly. Then we dyno tested TTI’S new 2 1/2-inch ex­haust, and it also upped the per­for­mance to the tune of 9 rwhp and 10 lb-ft. Those two bolt-ons helped our Dart be a more com­pat­i­ble driver, but it’s still not enough per­for­mance in to­day’s world. To­tal out­put on the chas­sis dyno was still a pal­try 71 hp and 119 lb-ft of torque. We needed more.

Our plan for our early A-body is a re­li­able daily driver in our (rapidly ap­proach­ing) re­tire­ment years. We want to be that “old guy driv­ing a Dodge Dart.” But we don’t want to be that old-timer hold­ing up traf­fic, be­cause we don’t have the per­for­mance to go and flow on to­day’s roads, which are jammed with im­pa­tient driv­ers. Be­fore we get to the 1- to 2-bar­rel con­ver­sion, fu­ture plans for the lean­ing tower of power will be a cam and cylin­der head swap. The camshaft will be of the smooth idle type to broaden the power band from idle to 5,000 rpm. The stock cylin­der head will be ported and .080 inch re­moved from its deck. We thought

swap­ping to this Hol­ley 350 two-bar­rel might be too much for a stone-stocker, but the Slant Six will be ready to breathe in the added air­flow when we per­form the cam and head swap.

So here we’re ex­plor­ing new ter­ri­tory by bolt­ing on a big Hol­ley 350-cfm two-bar­rel in­stead of the Su­per Slant Six, Carter BBD two-bar­rel with 260 cfm. We fig­ured since the TTI 2 1/2-inch ex­haust is get­ting the flow out, the Of­fen­hauser four-bar­rel in­take fit­ted with the Hol­ley two-bar­rel would get the flow in more ef­fec­tively for more power. Our the­ory is the six-in-arow will go bet­ter with a two-bar­rel than a small four-bar­rel Hol­ley 390 or Edel­brock 500 cfm. There’s no wait­ing for the sec­on­daries to kick in.

We think this is a very worth­while up­grade for the Slant Six en­thu­si­ast. Just be sure to have a high-flow ex­haust and strong ig­ni­tion be­fore plan­ning to per­form this in­take/carb swap. Also, we need to men­tion, gas mileage has im­proved. The tilted en­gine must be get­ting the right amount of the air­flow in and out to make it in­her­ently more ef­fi­cient. All the per­for­mance parts needed for this one- to two­bar­rel ad­ven­ture are avail­able through Sum­mit Rac­ing. The restora­tion sup­plies

were from East­wood. Now our cool-look­ing Slant Six is the star on cruise night when we open the hood. Fol­low along and see how to add 26 per­cent more go to a six-in-a-row.

We think this is a very worth­while up­grade for the Slant Six en­thu­si­ast. Just be sure to have a high-flow ex­haust and strong ig­ni­tion be­fore plan­ning to per­form this in­take/carb swap.

We de­cided a two-bar­rel car­bu­re­tor like this Hol­ley 350 cfm would per­form bet­ter on our stone-stock six over a small four-bar­rel Hol­ley 390 or an Edel­brock 500. We in­tend to daily drive the Dart in our re­tire­ment years and chose this elec­tric choke Hol­ley Street Avenger 2300-se­ries two-bar­rel (PN HLY-0-80350, $373.95).

In the pre­vi­ous episode, our ’66 Dart’s orig­i­nal Slant Six im­proved its get-upand-go from Per­for­mance Dis­trib­u­tors elec­tronic ig­ni­tion and TTI’S un­re­stric­tive 2 1/2-inch ex­haust. For this ad­ven­ture, the stock Hol­ley one-bar­rel, a 150cfm choker, will be re­placed with a bet­ter-in­hal­ing Hol­ley two-bar­rel 350-cfm car­bu­re­tor. The re­sults were bet­ter than we ex­pected. We found out that even a bone-stock Slant Six en­joys freer breath­ing.

We’ve been test­ing and us­ing K&N X-stream air clean­ers since their in­tro­duc­tion in the late ’90s with great re­sults. K&N’S 11-inch X-stream Air­flow as­sem­bly (PN KNN-66-3110, $137.99) will pro­vide un­re­stric­tive breath­ing, fit with the fac­tory air con­di­tion­ing com­pres­sor, and un­der the Dart’s low hood.

This Sum­mit Rac­ing 1-inch-thick two-bar­rel car­bu­re­tor adapter plate (PN SUM-G1406, $53.99) al­lows use of a Hol­ley 2300-se­ries type two-bar­rel car­bu­re­tor on a square-bore four-bar­rel in­take man­i­fold. Three Hol­ley 2300-se­ries two-bar­rel carbs were stan­dard equip­ment on our beloved 340 and 440 Six Pack en­gines. Our 225 Slant Six only needs a Two Pack.

In­stead of swap­ping to a 40-some­thingyear-old fac­tory Su­per Slant Six two-bar­rel in­take man­i­fold and car­bu­re­tor, we chose this proven, tried-and-true Of­fen­hauser four-bar­rel man­i­fold (PN OFY5270LK, Sum­mit, $357.99). This cool Offy in­take bolts up to the fac­tory ex­haust man­i­fold, al­low­ing us con­tin­ued use of the 2 1/2-inch TTI Ex­haust bolted to the stock man­i­fold.

When we re­moved the in­take/ex­haust man­i­fold as­sem­bly, we dis­cov­ered the ex­haust man­i­fold was cracked right where it was once re­paired/welded. The ’60s Slant Six ex­haust man­i­folds were no­to­ri­ous for crack­ing. Luck­ily, we knew of a parts car nearby, a 1972 Dart, and were able to get the needed man­i­fold.

Or if you’re handy and have the tools, like us, you can use a cut­ting wheel, car­bide bit, and sand­ing rolls to open up the car­bu­re­tor base area. To pro­mote good air­flow ve­loc­ity, we rolled the roof of all the run­ner en­trances and blended the outer sec­tions of the four holes to help di­rect air­flow to­ward the outer cylin­ders (1, 2, 5, 6).

Mount­ing the two-bar­rel adapter plate into po­si­tion showed a ma­jor re­stric­tion un­der­neath from the four holes for a four-bar­rel car­bu­re­tor. An ad­van­tage of run­ning a two-bar­rel on a four-bar­rel in­take is the two ven­turi holes will be cen­tered bet­ter to the in­take’s run­ners. A ma­chine shop can cut away the four holes and turn it into an open plenum­type in­take.

Af­ter ex­tract­ing the bolts, IDM also steel-shot blasted and tapped the threads for the three bolt­holes in the man­i­fold. Your author smoothed-down ex­ces­sive cast­ing flash us­ing his die-grinder equipped with sand­ing rolls. Us­ing a sand­ing block, we resur­faced the gas­ket area where the man­i­folds bolt to­gether.

No­tice the top of our Dart’s 1966 thin­ner-look­ing ex­haust man­i­fold (shown up­per). Ma’ Mopar beefed-up the Slant’s ex­haust man­i­fold in 1970. They made it a thicker cast­ing with ex­tra re­in­force­ment ribs (shown lower) to strengthen it and pre­vent the crack­ing is­sue of the ’60s Slant Six ex­haust man­i­fold.

Now, af­ter our hand­i­work there’s no longer air­flow in­ter­fer­ence un­der the two-bar­rel adapter plate. The two nos­trils will now have un­re­stric­tive air­flow!

The three bolts hold­ing the man­i­folds to­gether broke off in­side the ex­haust man­i­fold. We tried soak­ing the bolts with pen­e­trat­ing oil for three days, but they still snapped. Our lo­cal ma­chine shop (IDM Speed and Ma­chine, Mana­hawkin, New Jersey) ex­tracted the bolts for us.

Also, at IDM the flange area was resur­faced to re­move pits for good gas­ket seal. We smoothed-out all the port en­trances, go­ing an inch into each port.

No­tice the ex­haust port exit also re­ceived the sand­ing roll treat­ment. We welded the heat riser shaft to keep it in the open po­si­tion for best ex­haust flow. The Slant Six man­i­fold has longer port run­ners for su­pe­rior flow com­pared to the other straight six’s of the time.

First, the 13-nuts were pro­gres­sively tight­ened (2, 5, 10, 15, 20 ft-lb) from the mid­dle to the out­side of the in­take/ ex­haust man­i­fold as­sem­bly. Then, the three bolts that were fin­ger-tight hold­ing the man­i­folds to­gether were se­cured to 18 ft-lb. High-temp an­ti­seize was uti­lized on the threads of all the fas­ten­ers. Next, seen here, is one of the four screws be­ing tight­ened to hold-down the four-bar­rel adapter plate.

At first we tried us­ing the com­bi­na­tion of the stock throt­tle ca­ble with a four­bar­rel bracket we had lay­ing around. The Lokar trans kick­down ca­ble and bracket worked well and looks great. Us­ing the stock throt­tle ca­ble made for ex­ces­sive gas pedal travel (an ex­tra inch) to ob­tain full throt­tle. At that, we or­dered the Lokar throt­tle ca­ble giv­ing us the right ra­tio for the throt­tle and kick­down ca­ble to func­tion prop­erly.

The new 350-cfm Hol­ley Street Avenger is mounted with the fuel bowl for­ward and the throt­tle lever on the left side. The throt­tle lever faced rear­ward on the stock one-bar­rel. This ne­ces­si­tates the use of af­ter­mar­ket throt­tle and kick­down brack­ets/ca­bles.

Here the Hol­ley 2-bbl adapter is mounted, and the pen­cil is point­ing at the in­cluded ta­pered head screw. This screw needs to be in­stalled in the left/ front hole for ac­cel­er­a­tor pump clear­ance. The tan-col­ored two-bar­rel carb gas­ket is the same Fel-pro gas­ket (FEL-60124, $4.99) listed for the 340 or 440 Six Pack Hol­ley car­bu­re­tors.

With the three-bolts fin­ger-tight, we were able to move the man­i­folds around enough to see if they were square to the edge of the ruler. The man­i­folds met up square ex­cept for the amount re­moved (.015) from resur­fac­ing the ex­haust man­i­fold flange. See the or­ange washer? There are 10 of those tri­an­gu­lar-shaped wash­ers to help evenly se­cure the two man­i­folds to the cylin­der head dur­ing as­sem­bly.

We cleaned up the side of the block with East­wood’s Pre Paint­ing Prep be­fore paint­ing. East­wood’s High-temp Ce­ramic En­gine Paint is the most durable en­gine paint we know of. For our ap­pli­ca­tion, we used Chrysler Red (PN 51621ZP, $31.99 quart) and their Urethane Ac­ti­va­tor (PN 21854Z, $14.99) for added dura­bil­ity and gloss.

While we were at it, the starter and these two brack­ets were cleaned and prepped with the Pre. East­wood’s 2K Ce­ramic Un­der­hood Black (PN 14147Z, $22.99) has two-part spray gun tech­nol­ogy, and it’s as close as it gets to pow­der­coat­ing. We used the Aluma Blast (PN 10109Z, $12.99) on the starter’s hous­ing for that ex­tra de­tailed look.

The thick Rem­flex gas­ket lined up well with all the ports. No need to gas­ket match the ports or gas­ket it­self. For Slants with pit­ted and/or warped flanges, this thick (.125 inch) gas­ket can pre­vent leaks that the other thin­ner gas­kets can’t.

Mock as­sem­bly showed us there wasn’t quite enough hood clear­ance us­ing the 1-inch-thick Sum­mit two-bar­rel carb adapter (left) with the K&N X-stream air cleaner in place. Us­ing the Hol­ley 3/4-inch-thick two-bar­rel adapter plate (PN HLY-17-90, $106.95), there was just enough clear­ance to close the hood.

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