What type of gas to use?

[Dan-MI]

I've got a 72 GT that must have been a very early 72 since the owners manual says 71 GT. It says use 98 research octane low lead fuel. My question is: is it acceptable to run lead free in a 72 low compression engine or should I use a lead replacement additive? Also, what does a 98 research octane translate into octane on the current pumps?

[namba209]

I'm gonna guess here, but if you have not replaced the engine or the PO didn't and it is in fact an original engine, it's probably a hi-comp motor and will require the highest octane you can get at the pumps. You may have one of the later built in 71 GTs that still had the hi-copmp motors, lucky you.

[kwilford]

Originally Posted by namba209 I'm gonna guess here, but if you have not replaced the engine or the PO didn't and it is in fact an original engine, it's probably a hi-comp motor and will require the highest octane you can get at the pumps. You may have one of the later built in 71 GT's that still had the hi-comp motors, lucky you.

Not likely, since even my '71 GT (built in October 1970) had the low compression pistons.

As for fuel, this has been discussed ad nauseum in a prior thread (or two). After 1970, GM recommended regular, low or non-lead fuel for all Opels. In truth, the non-hardened valve seats didn't like the lack of lead much, even after '74 when they went to flame-hardened seats (which were also susceptible to cracking). But for a "daily driver", or even more for a "garage queen", un-leaded gasoline is fine, although a bit of lead-additive every so often wouldn't hurt. When the head is off someday for a valve job, have hardened seat inserts installed.

As for Premium versus Regular, if you are not experiencing detonation (pinging) with regular, it is fine. If you don't drive it much, the extra cost of Premium isn't a lot, and does allow you to advance your timing a bit, thereby getting better mileage and a bit better performance (but ONLY if you optimize the ignition timing to take advantage of the higher octane).

JM2CW

[RallyBob]

Originally Posted by kwilford ...even after '74 when they went to flame-hardened seats (which were also susceptible to cracking).

They went to hardened seats when the head design changed to the '12 bolt' style. This was in late '72, though officially it was a '73 changeover.

Bob