The only V8 that I know Toyota to make is a DOHC 32-valve unit, which I understand to be too sophisticated for NASCAR's tastes. So did Toyota take a great leap backward and clone the Chevy small-block V8, or do they run their own engines with a weight penalty?
That's a little complicated...
The block must be iron, and
cast by the manufacturer...
With the heads built to spec,
and modified to spec, using
the spec applied for by the
Manufacturer, and approved
by NASCAR (they all have
different limitations)...
The big teams do the cylinder
bore themselves, and all parts
need NASCAR approval..
That posed a problem for Toyota
as there were no foundries in Japan
that could cast an iron block..
Unlike the other teams, Toyota
teams get finished engines from
the manufacturer, and now they are
going to ship finished chassis as well..
One of the reasons Toyotas was fast last
year was NASCAR allowed them to use
an advanced head design the others were
not a allowed to use until this year..
NASCAR said that it would be unfair to have
Toyota design a head to the old spec for a single season..
and NONE of the engines are "stock engines" made by Chevy/Ford/Dodge/Toyota
(maybe a couple of the parts are, but most of them are custom made)
They are ALL specialty built for the teams.
Just like the cars aren't based on rear wheel drive models
(other than the Dodge Charger)
NA$CAR gives the teams a set of rules,
that they must follow to get the engines to pass inspection
these are all "specialty built" cars, engines, suspensions,
which bear almost NO resemblance to a real car.
NA$CAR has to do this
to make the cars safer
(street cars and engines aren't built to run safely at 190 MPH)