[Formulajones]

Originally Posted by Skip Fix

We tried doing a 0.100 down deck to lower compression on a 455 in the late 80s to lower CR down to 10:1 . Ran good but had to have race gas or was a rattling fool!

Yeah that starts to get into more technical things like mixture motion and poor combustion. Lots of things at play here whether something will live and work on pump gas or not. But you already know that.

One of the 455's built for dad's car was .030 over and zero decked with a flat top piston. Ran a set of #12 heads that were milled quite a bit (.030 if I remember right) and I believe compression cam out around 12:1. It had tight quench with just the .038 head gasket.

Ran a solid flat tappet cam from Ultradyne. Can't remember the specs off hand but it was healthy (in a box here somewhere)

Anyway, that thing would pump 195-205 cold, had a bunch of cylinder pressure. But on the street I could get away with running 94 Sunoco pump gas. I'd just run the total timing down to 30-32 degrees. Alot of that was due to good quench, keeping engine temps in check, etc.....but I will admit it's not for everyone, it was a finicky engine and the tune had to be spot on.
At the track we mixed a 1/2 tank of 110 race gas and I'd bump the timing up to about 34-36 degrees. It was a decent running combo.

Did this to keep the street driving costs to a minimum because he did drive it on the street a bunch. Drove it for about 4-5 years like that and it survived fine.

This was the engine that pushed me and my father to stick to strictly pump gas builds and learned that we didn't have to sacrifice power in doing so. As we tend to drive the cars more than race them, the whole mixing fuels thing just became way too much trouble and was getting more and more expensive. It's much easier, and more convenient, not to mention a hell of a lot cheaper, to just be able to roll into any gas station and fill the car and be on my way without worrying about how the engine will react or dinkering with the tune. Especially when towns are 100 miles apart in the middle of the desert. Not like I can carry that much fuel with me.

These days many of us have learned how to build higher compression engines and run fine on pump gas with all kinds of tricks we didn't know 30 years ago. I now run an 11:1 iron headed engine as a daily driver on 91 octane pump gas and it loves 36-38 degrees of timing. Don't even have to band aid it.