93 Octane necessary??
Laughing Gas
Joined: Apr 2001
Posts: 1,191
Likes: 4
From: West Union, OH USA
Did you get the engine or truck from this guy telling you this?
There was only one version of 351m to my knowledge. All low compression. Cars may have had a slightly different cam, but not much different. All stock 351m-400 engines had around 8:1 compression.
Unless this guy owned the truck and is the one who had it built, it sounds like he doesnt know what he's talking about.
Most "flat top" pistons for these engines dont actually increase the compression any appreciable amount. To my knowledge they would have to have been custom pistons or ones from Tim Meyers. The options are very limited.
An engine with this low of compression would run on low octane fuel without a problem. Cam and timing would be your variables.
Buying high octane is a waste of money.
My 71 429 that was "built at a race shop" runs fine on 87 octane.
There was only one version of 351m to my knowledge. All low compression. Cars may have had a slightly different cam, but not much different. All stock 351m-400 engines had around 8:1 compression.
Unless this guy owned the truck and is the one who had it built, it sounds like he doesnt know what he's talking about.
Most "flat top" pistons for these engines dont actually increase the compression any appreciable amount. To my knowledge they would have to have been custom pistons or ones from Tim Meyers. The options are very limited.
An engine with this low of compression would run on low octane fuel without a problem. Cam and timing would be your variables.
Buying high octane is a waste of money.
My 71 429 that was "built at a race shop" runs fine on 87 octane.
Lead Driver
Joined: Oct 2018
Posts: 7,879
Likes: 2,368
If you build a 351 or 400 up enough to make power your weak bottom end will be even shorter lived than it was to begin with. you're right on the flat tops I did it once. upgraded everything, I turned a dog 400 into a new dog 400.
Low compression is still low compression. run whatever fuel you want it's not going to matter much.
Low compression is still low compression. run whatever fuel you want it's not going to matter much.
Mountain Pass
Joined: May 2006
Posts: 217
Likes: 5
true, it won't precisely reveal CR. but PSI results of 150 vs 220 would give you a rough idea where the CR is.
Grumpy goat
Joined: May 2017
Posts: 3,058
Likes: 594
Not buying it. But even if that was so, it's not a close enough figure for what he needs. A point of compression can mean the difference between 87 and 91 octane requirements.
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