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Head swap
https://slantsix.org/forum/viewtopic.php?t=37517		 Page 1 of 1
Author:  itlldo1 [ Fri Oct 16, 2009 3:45 am ]
Post subject:  Head swap
I've searched the forum on this topic. From what I've read there are no issues swapping a head (tube style from a '69) to a 78 non hydraulic block is that correct? I purchased a 69 complete motor that I'd like to have cleaned and honed and whatever other machine work needs to be done for my rebuild and use the reworked head from my '78 motor. Are there any other issues? I notice that the '69 engine is rated at 140 hp, and the 78 was rated at 90. Since they both have the same bore, stroke and valve sizes I'm assuming the difference was the cam and valve timing. If that is a valid assumption, then I should have a slight warmer motor than using the '78 block correct? Thanks-Mike
Author:  dakight [ Fri Oct 16, 2009 4:41 am ]
Post subject: 
My understanding is that the heads are interchangeable. There are some differences in the valve train but no "show stoppers."

The horsepower difference comes mainly from a change in the way it was measured; there is no real difference in the power generated by the engine. In the mid 70s all manufacturers began reporting "net" where previously they had been reporting gross numbers. I was thinking that the 225 produced 101 net HP so you may have a 198 there, but I'm not sure and at 4:30 AM i'm not especially inclined to look it up. :lol:
Author:  66aCUDA [ Fri Oct 16, 2009 5:29 am ]
Post subject: 
I think the Smog equipment also choked the engine down in the late 70's and 80's.
Yep your head will work no problems.
Frank
Author:  Aggressive Ted [ Fri Oct 16, 2009 9:21 am ]
Post subject: 
itlldo1,

I am running the 78 head on a 74 block. I swapped over the valve train from the old head. I have been running it for 3 years now. The 78 head helps to keep the engine real clean. Click on the red link below my name if you want to see what it looks like. Once the picture comes up, double click for full screen slide show mode. It looks that clean right now after 50,000+ miles.
Author:  Krooser [ Fri Oct 16, 2009 6:41 pm ]
Post subject: 
Early engines used SAE guidelines for measuring HP... later engines use a different set of guidelines and measurements.
Author:  SlantSixDan [ Fri Oct 16, 2009 10:43 pm ]
Post subject: 
Early and late (and latest) horsepower ratings were/are SAE standards. See this post for some detail. There is no problem putting a '69 head on a '78 block. It'll allow a wider range of spark plug options, but won't in and of itself improve horsepower.
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