273/235 Gas/Octane Requirements

[65 Dartman]

My oldest son (who lives in the Netherlands) will eventually be getting the 65 4 speed Barracuda I have. The motor that's in it - 273 2 barrel - has no oil pressure so I located a true 273/235 10 plus compression ratio motor which is in the process of being rebuilt. He asked about gas octane needed for this motor. He stated they have 95 and 98 octane there in the Netherlands but apparently might be measured differently there. He did say there is a higher octane (100) he saw in Germany but not available in the Netherlands. I don't know and he can't confirm but I suspect his 95 might be equivalent to our 87 and his 98 to our 91. I told him this motor with the 10 plus compression ration will need at least our 93 octane to be happy. Told him maybe an octane booster might have to be used or lower the compression of the motor or set up the timing differently or maybe use a warmed over 318 that would run good on his 98 octane. Thoughts?

 

[SSVDP]

I haven't checked on the Euro fuel in about a dozen years but if I remember correctly their regular is almost same as our mid- grade. But I think the 318 is a good idea.

 

[toolmanmike]

I never had any problems with 93 octane. Those closed chamber 273 heads are pretty efficient.

 

[Jim Lusk]

I couldn't tell you why, but back in the 1980s the 340 that was in my GTS (stock 73 short block, 8.5:1) would ping on the mid-grade at the time. The 340 that is in it now (.030 1970 with TRW 10.5 pistons) never pinged on the modern premium, which is rated lower than the old mid-grade. Fuel mileage was lower, though...

Anyway, the point is that something changed and I just don't put any stock in the number on the pump as compared to decades ago...

 

[clinteg]

If the right cam is chosen and he adjusts the timing correctly, he could probably run whatever is equivalent to 91 over there with 10+ CR. Now I don't know if you mean slightly over 10:1 or closer to 11 or 12 to 1. I can't claim to run pump gas yet but my motor is being built with 10.8:1 to run pump gas with iron W2's. But we had the cam custom ground so my dynamic CR is 8:1. Plan is to back off the timing for pump gas and advance it with race fuel at the track. So if the motor is being rebuilt right now, I'd check into that cam.

 

[65 Dartman]

The motor that's in the process of being rebuilt is a 66 273/235 motor that had a published compression ration of I think 10.5 to 1. I say the compression ratio is 10 plus as I'm using the Fel Pro gaskets rather than the stock steel gaskets. I ordered the cam from Racer Brown. We discussed at length the motor (original 273/235), transmission (4 speed), rear end gears (currently 7.25 3.23 non-SG but will be upgraded to an 8.75 with 3.23SG), headers or stock exhaust manifolds (no header), how the car was going to be used - cruiser, race or combination (cruiser). Also told him the car will be going to the Netherlands where quite a few roads speed limit is but 80 KPH (50MPH). I can't put my hands on the cam card right at the moment but it's similar to a stock 65/66 273/235 cam. My son said if it'll run on our 93 premium it should be OK on their 98 premium.