The development of the 400 V8 led to a significant design flaw that remained with the engine throughout its production life. With a longer stroke, the compression ratio became excessively high with the 351-2V heads and flat top pistons. Ford engineers reduced the compression ratio by using a piston with a compression height that was too short and this led to an excessive deck clearance of 0.067" compared to a 351-2V at 0.035" . In 1971, this method of reducing compression was sufficient due to the higher octane leaded fuels. However, once lower octane unleaded fuels became used the excessive deck clearance lead to problems with detonation. For 1975, Ford dealt with this problem by decreasing the compression ratio further with a larger 15cc piston dish and reducing ignition timing. However, the 400 V8 obtained a reputation for being prone to detonation. Although Ford did not make a piston to correct this, TMeyer Inc worked with Keith Black pistons to make a 400 piston that increases the compression ratio and gives the piston a "zero deck" deck clearance.