Ford Muscle Cars Tech Forum banner

1 - 3 of 3 Posts

·
Registered
Joined
·
183 Posts
Discussion Starter #1
well that post about making higer octane gas was interesting, but it leaves me with another question...

In the manual for a 70 Mach 1 it says a 351C needs 99 octane. Well here in ABQ, NM here we have 91 at the most and usually 90. (So I have been using octane booster for a half tank fill up, but reading that it only raises it .3 seems to be pointless.) Any way, im assuming the 99 octane listed in the manual is research octane, no? Does anyone know how far off 91 R+M/2 is from what it actually needs?
 

·
Premium Member
Joined
·
2,806 Posts
This high altitude cuts the octane requirement down quite a bit. 11.5:1 compression with iron heads can be used with 91 octane pump gas up here. If you have open 2V chambers, knock a point of compression off for 10-10.5:1 compression with 91 pump gas but closed chambers tolerate much more compression with 91 octane up here(11.5:1).
 

·
Registered
Joined
·
1,105 Posts
I think you're okay. My cyclone needs premium, and in 1967 it was somewhere's around 104 octane with its 10.5:1 compression. I can run it on 91 octane with no problem. No pinging or anything. The older gas was dirtier, with more impurities and the higher octane was needed to deal with those two problems. I would try to put in some lead if you can just to help with the valve seats but its not necessary. I believe that the 99 octane figures out to be around 92-94 octane of today. You should be in good shape.
 
1 - 3 of 3 Posts
Top