Clearance Question????????

[splitdecision71]

I recently bought a 421sbc that came with Brodix 11x superspec heads. They had been milled approx .051 to get a 58.5cc chamber. Heads had 2.08/1.60 valves. The block was decked to .0000. It has the diamond pistons specifically for the Brodix heads and they are 8cc dome. I have my own set of 11x that im putting on and my question is will there be any issues? Mine originally were 67cc and milled .018 to get to 64cc. Mine also have 2.100/1.625 valves. Logic tells me I will be ok on the clearance but im afraid the bigger valves may be an issue. Any thoughts on what im trying to do? Thanks in advance.

[prairiehotrodder]

i'd say this is a crystal ball type question and nobody has one. You will have to check and measure.
Brian

[Newold1]

Depends on the valve relief sizes in the pistons. You will have to find and answer your own question. Clay the piston and check for clearance issues!

[mag2555]

Yup, its clay or balls of Aluminum foil time.

[groberts101]

I recently bought a 421sbc that came with Brodix 11x superspec heads. They had been milled approx .051 to get a 58.5cc chamber. Heads had 2.08/1.60 valves. The block was decked to .0000. It has the diamond pistons specifically for the Brodix heads and they are 8cc dome. I have my own set of 11x that im putting on and my question is will there be any issues? Mine originally were 67cc and milled .018 to get to 64cc. Mine also have 2.100/1.625 valves. Logic tells me I will be ok on the clearance but im afraid the bigger valves may be an issue. Any thoughts on what im trying to do? Thanks in advance.

Unless you were already riding on the edge of disaster with previous clearances I highly doubt losing .010" of radial clearance at any given point withing the existing valve notch would create an issue. The bigger concern would be clearance loss from the slightly larger valve potentially sitting a bit higher on its seat compared to the previous heads smaller valve/seat/valvejob geometry.

Assuming similar valve lengths it should be easy enough to measure and compare valve tip heights or simply lay a straightedge across both chambers to compare valve head heights. If you gained clearance in the right direction I'd not even waste time claying them up. On the other hand.. always nice to know safety margin is left over should you decide to change cams in the future. Doesn't preclude having to check the new cams clearances.. just gives clues as to what lattitude you have available when choosing another stick with more aggressive spec's is all.

[splitdecision71]

Thanks every one for your responses. I will check everything to be on the safe side. I was just thinking the substantially bigger chambers in my heads would be more than enough clearance being that the others were good. I am just anxious to get the motor together and that is not a smart move. It could cost me dearly. Thanks again!

[Newold1]

In the same designed and built head, nominal surfacing off deck to lower cc's with respect to chamber size makes no big difference in location of equal valves only the height of the valve open and closed with respect to the top of the piston. Large decking removal will slightly shift the in and out of the valve location though which can obviously affect piston valve relief and valve heights open.

[6.50camaro]

The biggest issue is are you using the same cam installed at the same centerline? Dan

[splitdecision71]

The biggest issue is are you using the same cam installed at the same centerline? Dan

Same cam, my heads and jesel rockers are different. Thanks for reminding me of that. He had 1.6/1.5 and my heads have 1.65 and 1.60. Something more I need to consider!

[Mark O'Neal]

Most everyone has gone to a 2.200 intake and a 1.8 or 1.9 exhaust cutter at this point....so I doubt you'll have an issue.

But, as Bob McPhearson once said; "The price of progress is trouble."

[splitdecision71]

Most everyone has gone to a 2.200 intake and a 1.8 or 1.9 exhaust cutter at this point....so I doubt you'll have an issue.

But, as Bob McPhearson once said; "The price of progress is trouble."

Thanks for your input. Im confident its going to be ok but Im going to double check.

[af2]

Most everyone has gone to a 2.200 intake and a 1.8 or 1.9 exhaust cutter at this point....so I doubt you'll have an issue.

But, as Bob McPhearson once said; "The price of progress is trouble."

Thanks for your input. Im confident its going to be ok but Im going to double check.

10fore and 10aft. Checking I was at 12 degrees closest! To get it correct without the clay Bullshit!

[splitdecision71]

Most everyone has gone to a 2.200 intake and a 1.8 or 1.9 exhaust cutter at this point....so I doubt you'll have an issue.

But, as Bob McPhearson once said; "The price of progress is trouble."

Thanks for your input. Im confident its going to be ok but Im going to double check.

10fore and 10aft. Checking I was at 12 degrees closest! To get it correct without the clay Bullshit!

Forgive me but can you elaborate on what your saying please? I have been a mechanic for a long time and put many engines together but they were stock engines that I didnt have to worry about. But I have never done my own race engine that is this precise. Thanks, James

[splitdecision71]

Ok gentleman, I picked up some clay to measure the P2V clearance. Plan on doing it in the next day or two. The question I have now is the guy I bought the motor from gave me some new copper head gaskets for the motor and told me they were .040. I have never used that type of gasket. Is there anything I need to know like use them or not? Do they compress like a normal gasket?

[Mark O'Neal]

Thanks for your input. Im confident its going to be ok but Im going to double check.

10fore and 10aft. Checking I was at 12 degrees closest! To get it correct without the clay Bullshit!

Forgive me but can you elaborate on what your saying please? I have been a mechanic for a long time and put many engines together but they were stock engines that I didnt have to worry about. But I have never done my own race engine that is this precise. Thanks, James

The closest the valve gets to the piston is at about 5 before and 5 after split overlap. Since no cam company has had that number since Harold died...just use the clay method and skip the math.