keep it original or swap head?

[maverickhead]

I've got a '75 Maverick 200 w/about 89k on it. I drive it weekly and it's all stock. The head gasket is beginning to seep oil(otherwise, the engine is fine). I've got another 200 that's a '78. Should I just replace the gasket & reinstall the '75 head or would the '78 head be a little better(since it's gotta come apart anyhoo)? Not doing any head work, but the 200 under the '78 head is tired, so if it'll get me a few hp or a a little more mpg, I'm all ears.

 

[JackFish]

I'd get the '78 head milled because the original head will be on an original steel shim gasket.
Unless you can find one of those gaskets, you will have to use a modern composite gasket.
The new ones are thicker and the compression ratio will decrease without milling the head.
Probably should mill at least .050 off to maintain the stock ratio, and a little more will bump it up, which is a good thing.

 

[MPGmustang]

+1 to Jack

The higher compression IIRC should bump HP, and possibly low end TQ. Aim for a 8.9 for 9.0 CR. unless you want to do the cam while your at it then go for a 9.3 CR.

the only real difference between heads is the size of the log, I think the valves are the same size stock.

GL and have fun!

Richard

 

[CZLN6]

Howdy Mavhead and All:

The significant difference between a "75 casting and a '78 casting is the size of the intake valves. '75= 1.69". '78= 1.75". Another iffy differecne may be hardened valves seats on both intake and exhaust. The '75 will most likely have harneded seats on the exhaust. The '78 will, most likely, have hardened seats on both intake and exhaust. Carb hole diameter, intake tract volume and chamber sizes should be the same. The increase in valve size alone is not significant.

In addition to the need for milling to compensate for the difference in thickness of the head gaskets, I'd suggest that you add a performance valve job to the '78 head that includes, at least a three angle valve seat, a back cut-on the intake valves and a little pocket porting, basically to smooth the transition from machined to cast surfaces.

FYI- You stock '75 CR is rated at 8:1. So long as your milling the head I'd suggest (1) that you mill .025" to compensate for the gasket differences and (2) another .050" to get the CR closer to 9:1, for a total mill cut of .075". The increase in CR along with the performance valve job will improve both economy and performance.

What carb, distributor and transmission are you using? Are you planning an future upgrades or modifications?

Adios, David

 

[Explorer]

This more of a question than suggestion. Isn't it bad policy to bump the compression on rings with almost 90K miles on them?

 

[maverickhead]

The car runs the stock duraspark, stock 1bbl carb and a 3 speed manual w/ 2.79 gears. The only other possible upgrades I can see would be a 3.00 gear and MAYBE a header & better exhaust, but only if a good used header comes up at the right time. This car is a driver and gets about 22-23 mpg around here (hilly terrain, but still lots of 55-65 mph driving).