Q: I am in the process of building a circle track vehicle. I purchased a Chevy 383 four-bolt main and equipped it with a Dart Iron Eagle top-end kit (DRT-01110002) and an Eagle Street and Strip rotating assembly (ESP-B13005E030). With a compression ratio of around 10.9:1, can I run on pump gas or do I need racing fuel?
From: Robert • Stockton, CA
A: There are some simple guidelines to stick to when it comes to choosing the right fuel for your racer. If you’re running iron heads, then anything above a 9.8:1 compression ratio will require more than pump gas. On the flip side, aluminum heads can support up to a 10.5:1 ratio on pump gas. Since your engine is equipped with iron heads and has a 10:9:1 compression ratio, you’ll need to run race fuel.
So then why does a bone-stock LS3 run fine on pump gas (even 91 octane) at 10.7:1? Accuracy of the fuel injection system? Better cooling? Something else?
Just seems odd that 10.5:1 is so often quoted on this site as being the upper limit for pump gas, when factory engines are going beyond. I think a deep dive into your reasoning behind this statement is in order.
Because its an Al head