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**pjmoreland** · 12-30-2020, 10:08 PM

I have a set of 3998991 heads on my 350, and from what I have read and experienced, these heads are not performance oriented at all. They are low compression and they have small valves. They do, however, seem to make decent low end torque. My plan is to install some Vortec heads I pulled off a 98 GMC at a wrecking yard last weekend. I know you already mentioned the rear end, but I think switching to a 3.73 would be my top priority in your situation. A 3.07 is a pretty extreme highway ratio to have with a 700R4. Switching the gear ratio could really transform the way your truck drives.

12-30-2020, 10:08 PM	#4
pjmoreland Senior Member Join Date: Jan 2005 Location: CA Posts: 5,309	Re: 1972 307 cam selection... HELP! I have a set of 3998991 heads on my 350, and from what I have read and experienced, these heads are not performance oriented at all. They are low compression and they have small valves. They do, however, seem to make decent low end torque. My plan is to install some Vortec heads I pulled off a 98 GMC at a wrecking yard last weekend. I know you already mentioned the rear end, but I think switching to a 3.73 would be my top priority in your situation. A 3.07 is a pretty extreme highway ratio to have with a 700R4. Switching the gear ratio could really transform the way your truck drives.