Fuel requirements for 1974 TR6: Classic Cars forum: Classic Motorsports Magazine

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Sept. 6, 2008 3:47 p.m. amalachowski None

I have a 1974 TR6 that I had covered for a while. I was planning to start it up. I want to know what is the fuel requirements for this vehicle. I was wondering what the recommended octane was and if it uses leaded or unleaded gasoline. Thanks Alex
Sept. 9, 2008 12:59 a.m. Daryl New Reader

When it was built we were all using leaded gas, which I don't think is available anymore in N. America. As far as the octane rating, that would depend on what the factory recommended back then. If you can't find that you should be safe with 92 or better, depending on your compression ratio. You may be alright at a lower octane, but better to start high if you can't get a definate answer. I am not familiar with the TR6s, but depending on how it was built, it will probably need to have some hardened seats for the valves installed at some point. Is it a cast iron or aluminum head? If it is aluminum, you may be alright for a while....
Sept. 10, 2008 6:03 a.m. bravenrace HalfDork

I'm pretty sure that if the engine is stock, all you need is regular 87 octane. Those engines had pretty low compression (around 8.5:1, IIRC) to meet US emissions standards.
Sept. 10, 2008 6:51 a.m. André Rousseau Reader

My 2L GT6 hates anything under 91.

Stock she was 9.5:1, but I did redo her with .060 pistons so she could be a touch higher.

Still got decent fuel milage on my last road trip.

A.
Sept. 10, 2008 8:09 a.m. bravenrace HalfDork

Your GT6 is a '68, which would have significantly higher compression than a '74 TR6.
Sept. 10, 2008 9:03 a.m. mattmacklind PowerDork

My 71 BGT, rebuilt 60 over, runs on lower octane just fine. Rarely it will run on a bit, but I suspect an ignition problem as opposed to an octane issue.

I don't know what the compresion ratio is, likely around 9:1. I put in the hardened valve seats and all but I don't have an "unleaded head" as they say.
Sept. 10, 2008 11:26 a.m. OFracing New Reader

Here's a reference site for Spitfires and GT6. All kinds of valuable info. mike http://www.triumphspitfire.com/Ref.html
Sept. 10, 2008 5:17 p.m. Jack SuperDork

Regular. My 9.25:1 compression TR4 Engine (in my TR3) will run on it, as long as the timing is not advanced more than a few degrees beyond stock. Your lower compression TR6 will be fine.

All that said, I would start running it on high test, 91 or higher, and work down, to be sure it's not going to detonate.

Jack