MY 2005 TL Owners Manual states the following on page 172:

Fuel Recommendation:
"Your vehicle is designed to operate on premium unleaded gasoline with
a pump octane of 91 or higher.  If this octane grade is unavailable,
regular unleaded gasoline with a pump octane of 86 or higher may be
used temporarily.  The use of regular unleaded gasoline can cause
metallic knocking noises in the engine and will result in decreased
engine performance.  The long-term use of regular-grade gasoline can
lead to engine damage.

We recommend quality gasolines containing detergent additives that
help prevent fuel system and engine deposits.

In addition, in order to maintain good performance, fuel economy, and
emissions control, we strongly recommend, in areas where it is
available, the use of gasoline that does NOT contain manganese-based
fuel additives such as MMT."

Continues relative to impact to performance,  You can use fuel  with
up to a 10% ethanol content.  Methanol is not to be used.

The TL engine is a high compression engine and even with knock
sensors, etc., trying to limit detonation through timing adjustments,
enriching the mixture temporarily, and so forth, detonation can hole a
piston in fractions of a second.  Using lower octane fuels is not
worth the risk.  The cost difference between regular 87 octane fuel
and 91 or higher over the life of the car is minimal compared to the
cost of an engine rebuilt/replacement.

I think it goes without saying that if you have to put regular in for
some reason, drive the engine VERY gently and get some premium into
the tank as soon as possible and drive gently until a full tank of
premium can be obtained.

I have seen some stations in the USA now offering only two grades of
fuel, 87 and 91, much like Europe.  I hope we can switch to a two
grade system here and stop paying for the extra octane grades we don't
need in the cars.

Paul

If you want to run regular, you might want to consider an Accord V6 or I4.
They all run regular.