The 1947 - Present Chevrolet & GMC Truck Message Board Network - View Single Post

BigBlocksRule · 10-15-2010, 08:08 AM

10.2 is high for pump gas with iron heads unless you have a big, choppy cam or a computer to pull timing when you need it. You can have the shop unshroud the valves out to the gasket line and add "eyebrows" to the tops of the bores to help it breathe and bring your compression down a bit. I'd shoot for the high 9's, around 9.75 and even then it'll be iffy. If you ever take it to the coast, you'll ping like crazy due to the changes in barometric pressure. Most shops shoot for 9:1, so you're a bit on the high side. You can also have a bit of the domes milled off to help, too. As long as you're building a higher compression mill, you really should consider using those 781's you bought...

10-15-2010, 08:08 AM	#57
BigBlocksRule Registered User Join Date: Jun 2008 Location: Lubbock, TX Posts: 2,047	Re: 350 to 454 swap...is it worth it? 10.2 is high for pump gas with iron heads unless you have a big, choppy cam or a computer to pull timing when you need it. You can have the shop unshroud the valves out to the gasket line and add "eyebrows" to the tops of the bores to help it breathe and bring your compression down a bit. I'd shoot for the high 9's, around 9.75 and even then it'll be iffy. If you ever take it to the coast, you'll ping like crazy due to the changes in barometric pressure. Most shops shoot for 9:1, so you're a bit on the high side. You can also have a bit of the domes milled off to help, too. As long as you're building a higher compression mill, you really should consider using those 781's you bought...