260 CID Engine Detail

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General Information

Note: The information contained in all of the "Engine Detail" sections should be read before proceeding with modifications, etc., because some information that applies to all engines, or all small blocks or all big blocks, might not be duplicated in every section.


4 BBL Modification
If you want to use a 4 BBL on this engine, you must change the heads to 5A castings as found on 307 Olds motors. If you mill them .030-.040, then you'll gain back compression. Then you can bolt on the Edelbrock Olds performer intake. A set of Mondello heat riser plugs installed in these heads will make more power. Just drill a 1/4" hole in each plug to get back just enough carb heat. The Mondello 15-100 cam works great in those little 260's.

The heads on the 260 are designed for the 260's small displacement. So, in order to increase torque (I'm assuming) the intake runners are 1/2 the size of conventional runners. Unfortunately the way the accomplished this was to fill the bottom half of the runner with material - BIG flow stopper! Not to mention a good spot for fuel to puddle.

Being undaunted by this (plus I had already purchased the intake and carb) I went forward with the installation. What I found was that the 260 required me to do a LOT of tuning to the carb to keep it from bogging out of the hole.

I had the motor tied to a TH-350 and 3.42's. After getting the carb staightened out, had to rejet and fiddle with secondary opening rate, the combo ran noticibly different. Part throttle was very similar (slightly stronger) but where the big difference was, was in the top end. I had put an "RV" type cam in it, PAW special, and it definitly liked the 4 barrel over the 2 barrel. Unfortunately never had the car to the strip either before conversion or after, but it did make a very marked improvement. Gas milage was about the same for both combos as long as I kept my foot out of it (aprox. 17mpg).

[ Thanks to Scott Woodworth, Todd Daenzer for this information ]

Buildup Examples


Tuning / Power Boost

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