Read­ers’ Tech Q&A

Hot Rod - - Contents - Mar­lan Davis

I have a 1978 Cut­lass Supreme with a 260 V8. It was re­built a few years back, but I don’t think it was done very well. It has a rod knock now. I don’t know which way to go: re­build this one again (they want $2,800 to re­build it), or up­grade to some­thing with a lit­tle more get up and go. If I re­place it with a used en­gine, what newer-year Oldsmo­bile would bolt di­rectly in? What size would work best?

There’s no re­place­ment for dis­place­ment. Al­ways get the largest en­gine you can af­ford. That’s my motto, so com­ing from a HOT ROD per­for­mance per­spec­tive, I wouldn’t waste time or money on a stock 260 re­build when com­plete Olds 1980–1889 307, 1964–1967 330, 1968–1980 350, and even 1977–1979 403 small-blocks are di­rect bolt-ins for a 260 (they all have the same ex­ter­nal

di­men­sions). Search­ing on­line, I see you can get an in­ex­pen­sive stock re­built Olds 350 long-block for $1,695 plus a re­fund­able $400 core-charge from out­fits like Re­built Crate En­gines. A base­line mild 350 per­for­mance ver­sion goes for $3,299.95.

If search­ing the wreck­ing yard, the most com­mon larger-dis­place­ment Olds en­gines of sim­i­lar or later vin­tage to yours would be a 307 or a 350 (be sure it’s an Olds 350 gas en­gine “VIN-R”—there were scads of Olds diesel 350s made dur­ing this pe­riod). The 403s were only made for three years, so they’re rel­a­tively rare, but you never know, it might be your lucky day.

Whether used or re­built, Olds ex­perts like Mon­dello and Dick Miller say you need to pay at­ten­tion to the fol­low­ing items when swap­ping Olds mo­tors:

• Olds en­gines are ex­ter­nally bal­anced. Fl­ex­plates were in­di­vid­u­ally bal­anced at the fac­tory, so try to grab the orig­i­nal flex­plate with your new en­gine. The larger the dis­place­ment, the greater the amount of flex­plate un­bal­ance, so your orig­i­nal 260 flex­plate may cause a slight vi­bra­tion if used on the larger en­gines. Many re­place­ment fl­ex­plates are uni­ver­sal, mean­ing not ideally bal­anced for the in­di­vid­ual mo­tor, re­gard­less of dis­place­ment.

• Mon­dello’s ex­perts say 260 and 307 har­monic bal­ancers in­ter­change. Ditto for 350 and 403 bal­ancers. But don’t use a 350/403 bal­ancer on a 260/307—or vice versa.

• Ac­ces­sory drives, pul­leys, and wa­ter-pump snout lengths may vary on dif­fer­ent mod­els. If nec­es­sary, trans­fer these items as a com­plete, matched set, from the old en­gine to the new en­gine. Block and head ac­ces­so­ry­mount bolt holes never changed.

• De­pend­ing on the model, you may need to

trans­fer the oil pan and oil-pump pickup.

• A 260 in­take man­i­fold only fits a 260

be­cause of port-size dif­fer­ences. There

Norm Bran­des 02] The num­bers or let­ters on the front of the block near the oil fill tube are one way to ID an Olds. If the large digit fol­low­ing the smaller cast­ing num­ber is a let­ter, you have a big-block; a large num­ber or num­ber/let­ter is for a small block. Cast­ing No. 390925, ID E, tells you this block is a 1966–1967 big-block 400. Mon­dello’s Oldsmo­bile V8 Tech­ni­cal Ref­er­ence Man­ual, Vol. 3 ($26) is full of hard­core data and en­gine-build­ing tips like this.

01] A big-block Olds V8 like this hot rod­ded 455 also bolts in place of small-block Olds en­gine, but they’re slightly taller and wider, so check en­gine-bay clear­ances. Big-block Olds en­gine-swap head­ers for a GM 1977-and-later A/G-bod­ied in­ter­me­di­ate chas­sis are avail­able from Mon­dello and Dick Miller.

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