I need some help from all you smart guys.I got a chevy 350 bored .30 over with a small dome piston. I want to install a set of GM Vortec heads. What thickness should I use on the head gasket? I was told that a regular Felpro (.20 thickness) would do fine. Well, like most of you, I hate to throw money away.Any help will be greatly appreciated!!

 

Not tosure about the smart guy thing but I think you need to consider what compression you want. What size dome is it and what size are the valve reliefs. Has the block been decked? The 350 stroke is stock (3.48) correct? Also I am gussing your compression is getting fairly high so we will might need to consider the camshaft specs to calculate a dynamic compression ratio.

 

Thanks for the reply. The lift of the camis .460. The blockhas beendecked. The piston dome is small. I don't know how to measure it. I did do what I could with a steel ruler and got just under 1/8th inch. I figured that I would have to run high test in it because of the dome and the vortec heads. I'm not sure what sizethe valve reliefs are. How do I get that info? They are stock cast iron vortec heads casting 906, nothing fancy. any help will be welcomed. Thanks.....

 

If you have a 0 deck height a .025 compressed head gasket thickness a piston that equates to a 0 volume(which I doubt) and the 64 cc chamber of a vortec head. You will have a compression ration of around 11.5 to 1 put that together with a mild cam and you will have a dynamic compression ratio where you will need race gas or will need to retard the timing to run pump gas. To find the piston volume you need the specs from the manufacturer, the cam card has spec you use to calculate the dynamic compression. The deck height is 9.025 stock 9.0 is considered 0 deck height. the more its decked the more compression you can have. Find the deck height, piston and cam specs and we can help you out alot better.

 

Ok got a hold of the builder.Pistons are Speed Pro Z8KH618CP30, cam is Lunati 00017 (Advertised Duration 290/290, Lift .460/.460) all from summit, and I was wrong about the deck height. He said that he didn't touch it. He wanted to keepit on pump gas. I've got 100 lb springs in my vortec heads. Will this be a problem?He also told me that compression ratio should be between 9.5 and 10.5..........He seamed to know what he was talking about. Does this soud right toyou?I hate being so ignorant to all of this, but I'm glad that I can talk to someone that knows. Thanks for your time and patients with me...........

 

I had trouble finding some of the info and havnt had time to double check it but using this calculator for compression http://www.csgnetwork.com/compcalc.htmland a .020 head gasket, 4.03 bore, .025 deck and the piston spec I get 10.93 compression which is some what verified by the piston manufacturers site http://www.21cgt.com/FMWebCatalog/default.htm(fill in the blanks you will get to the part #) they show a 10.72 cr. I used a simple calculator for the dynamic compression ratio http://www.wallaceracing.com/dynamic-cr.phpusing the cam card http://www.lunatipower.com/Product.a...84&gid=245gave the info below:
Static compression ratio of 10.92:1.
Effective stroke is 3.18 inches.
Your dynamic compression ratio is 9.76:1 .
Your dynamic cranking pressure is 205.23 PSI.
Your dynamic boost compression ratio, reflecting static c.r., cam timing, altitude, and boost of PSI is 9.76 :1.
V/P (Volume to Pressure Index) is 200
My gut reation is that it is kindof high for pump gas but I need to verify the numbers when i get the chance...

 

Griff, thanks so much. Youmade you caoculationswith a .020 compressed thickness head gasket. Could I go with a thicker gasket and reduce thar ratio? When I pulled the heads there was a .041 compressed thickness on it. It was a felpro 1003. It is a lock wirering type. My heads aren't set up for this style but I'm sure that there are other ones out there. That would make since if the builder was trying to geep it on pump gas. What do you think? Would I be OK on pump gas if I go with somthing that is .041? Thanks

 

Double check with the piston manufactureer to see if the pistons are suitable for the vortec head. The head gasket change will lower it to probably around 10.5. What does your engine builder think you will need to run foroctane, maybe he has experience with this combo the tighter quench may actually work better for detonation resistance thanincreasing the head gasket thickness.

 

I will Call him again. I want to Thank you for sharing your welth of knowlege with me. Thanks to all on this sight.