Your H1 has about a 5.40 ratio. With a diesel that might limit your
speed, but if it is gas you sould be ok in that range. Building and
engine is an open-ended statement: did you build for torque, high end
horsepower, or what? (basically what cam, and fuel system did you go
for: a mild cam with a smaller carb for torque, or a wilder cam with a
larger carb for high end power?

"h1humr" wrote:

Based on your current level of performance, a set of 4.88’s and 37’s
or 38’s would give you better performance now than with your current
set.  You are going to be running into axle strength limitations with
37 or 38’s if you keep stock axles. Give all of this I would say 4.88
or maybe 5.13’s. I would strongly recommand that you find a 14 bolt
9.5 inch semifloating rear axle (not 10.5 full floater) for your
blazer as they came with 6 lug hubs to in some truck models and it is
about as strong as a Dana 60 but it is limited to a max ratio of 4.88
which would work for you anyway. Another nice thing about the 9.5 is
the wide selection of lockers avalible for it automatic and selectable
and even the stock posi unit is a lot stronger than one that comes in
a 10 bolt rear axle. It is a very wise upgrade for your truck since
you plan to run big rubber and the 9.5 will handle 38’s without any
problem too.