226 head on a 254 flat six; better gas mileage?

[M6ride]

As I under it a 226 head on a 254 would increase the compression.

But, would this INCREASE or DECREASE the AVG gas mileage, changing nothing else?

And, why??

Thanks

 

[Fred]

Increasing compression increases efficiancy. You get more power from the same amount of fuel (all other factors being equal, i.e. same cam & both iron heads etc.).

 

[flatford6]

Watch out for preignition problems from head gaskets extending into the combustion chamber when putting 226 heads on 254 engines. If you use the 226 head gasket with this combination the gasket will extend unsupported over the bores. If you use the 254 gaskets with the 226 head, an about 1 inch section extends into the combustion chamber. It will get hot due to lack of heat conduction under a hard load and act as a glow plug. It will cause backfiring or popping back through the carburator under hard loads. If the beading around the combustion chamber is not supported by both the head and deck, it is also more likely to blow or burn through to a water jacket or outside the engine. If you can get a head gasket with sheet metal on both sides and composition material inside, the offending section could be lifted up and rolled back and the soft material could be cut back and then the bead rolled back into position to where it would not extend into the combustion chamber. McCord gaskets are made like this. I dont know if McCord is still in business. A 226 head on a 254 will gain you almost 1 point cr increase, almost exactly the same as a 254 head milled .060 inch.

 

[Fred]

I don't see a problem with a 226 head on a 254 motor with a 254 head gasket.

 

[flatford6]

If you plan to just putt-putt around you will probably not have too much trouble from a 226 head on a 254 block using a 254 gasket. Under a hard load it will preignite, and or blow out. The bead around the combustion chamber is to increase sealing pressure at that point and if the bead is hanging out into the chamber, sealing is impaired. It would be even worse with the composition style gaskets with soft material on both sides. Flipping the head over with the chamber side up and setting the gasket on it will show where the problem is. That is how I found it. This is with the H model 226 head . Using the earlier G model with machined recess for the piston would probably not gain anything as you would lose the quench area over the pistons. Anyway, a one point gain in compression would probably net you about 4 percent power gain and a somewhat better percentage gain in mileage. Incidently, most of these heads measure about 1.89 inches from the bottom surface to the tops of the head bolt bosses from the factory. After 50+ years, many of them have already been milled , some quite a bit or several times. Always check valve to head clearance before and after milling.

 

[Fred]

I agree if you have any part of the head gasket not supported on both sides by the block and head you will have problems. It has been a while since I inspected a 226 and 254 head side by side so I could be remembering wrong. What I remember is the combustion chamber outline (if you took a rubbing of the head) was basically the same. The 254 head had a much deeper area over and around the valves, but not narrower that the 226; thus no problems. Am I remembering wrong? If you have a picture of a 254 gasket sitting on a 226 head, please post it. Thanks, Fred.