D15 series 1 compression ratio

Shawnba67 · Jul 26, 2021

I am rebuilding a gas 149 the data books show the factory compression ration of 7.75 to 1 the kit Im looking at shows 7.5 to 1. I dont want less power, more wouldnt be needed but I do want to run cheap pump gas and start well. Wiull I even notice the small difference in CR? The head did get slightly milled with the valve job

DrAllis · Jul 26, 2021

I've seen D-17 engines listed at 7.2 to 1 and 7.25 to 1. I see yours was rated at 7.75 to 1 according to Nebraska Test data #795 and that is as official as it gets. Milling the head does nothing on an AC head as it is flat. Valve protrusion can effect the actual compression. It will be OK fine with everything new and fresh.

D15 series 1 compression ratio

Shawnba67

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DrAllis

Well-known Member

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