Need more P/V clearance in a BB mopar

GallopinGhost · 04-18-2018, 03:40 PM

Having trouble finding enough P/V clearance. Hope someone here can give some advice. It’s a 70 dodge 383 for stock. Iron heads. Pistons are flat top without valve reliefs. Short block is finished, cam installed. I'm using a spare cylinder head to make measurements so I can give directions to the cylinder head builder so he can finish the heads.

I’m shooting for at a minimum .025/.060 when done. Right now I have .040/.057. To get that number, I’m comparing valve drop numbers from my heads to the new one at the cylinder guys shop. I'm setting valves at hot lash setting of .008” , solid lifters. The new heads haven’t been decked yet, although the valve job is done. Heads are at 88 cc now, min. spec is 79.5. It should take 0.040 to get the chambers to min. spec. I’ve moved the cam around to find the sweet spot for the intake clearance, it’s at 4 degrees retarded now. I‘m thinking of decking the heads 0.020 and sinking the valves 0.010/0.025. It seems to be a juggling act between sinking valves, how much to cut the cylinder deck, and or change gaskets. I’d like to keep the current spec gasket, which is a steel shim .021”

I hope I've explained that clearly enough, this is my first time building a stocker engine. I guess the question is what kills power more, sinking valves or losing compression ?

Glenn Briglio · 04-18-2018, 04:30 PM

Degree the cam where the engine will like it to be. Then live with the loss in compression to get desired piston to valve cleaance. Ie don't mill heads as much.

GTX JOHN · 04-18-2018, 05:23 PM

Maybe sink the valves a little bit and or angle mill the heads.
FelPro 1009 Gasket will give you a extra .020 to .022.

I prefer to make heads near spec and use deck and gasket
on Big Block Mopar stuff to make them more universal for different shortblocks.

ss3011 · 04-18-2018, 10:44 PM

What method did you use to figure out your clearance ? Clay with full valve springs , or dial indicator with a light checking spring ?

Larry Hill · 04-19-2018, 07:33 AM

Use more deck clearance and keep the gasket thin. You will need about .035 '' total to keep pistons from contacting head. Have P/V clearance through the range of adjustment, so you can roll the cam forward or backwards without bending stuff. Exhaust valve will like to make contact in split overlap.

Glenn Briglio · 04-19-2018, 08:17 AM

Having the correct cam timing is more important then losing a half a point of compression.

GallopinGhost · 04-19-2018, 08:19 AM

Checking springs, with an indicator on the retainer

I've already moved the cam around to give me the most intake clearance, which has been the biggest problem, and still have around twice that amount of exhaust clearance.

Piston is .010 in the hole, spec is .004. I'm leaning on leaving the valves alone and using whatever gasket gives me the clearance needed. Those 2 together should give me the .035 Larry mentioned.

In hindsight, I should have gotten a smaller cam so I could keep some compression........

04-18-2018, 03:40 PM	#1
GallopinGhost Member Join Date: Jun 2010 Location: VA Posts: 230 Likes: 23 Liked 21 Times in 13 Posts	Need more P/V clearance in a BB mopar Having trouble finding enough P/V clearance. Hope someone here can give some advice. It’s a 70 dodge 383 for stock. Iron heads. Pistons are flat top without valve reliefs. Short block is finished, cam installed. I'm using a spare cylinder head to make measurements so I can give directions to the cylinder head builder so he can finish the heads. I’m shooting for at a minimum .025/.060 when done. Right now I have .040/.057. To get that number, I’m comparing valve drop numbers from my heads to the new one at the cylinder guys shop. I'm setting valves at hot lash setting of .008” , solid lifters. The new heads haven’t been decked yet, although the valve job is done. Heads are at 88 cc now, min. spec is 79.5. It should take 0.040 to get the chambers to min. spec. I’ve moved the cam around to find the sweet spot for the intake clearance, it’s at 4 degrees retarded now. I‘m thinking of decking the heads 0.020 and sinking the valves 0.010/0.025. It seems to be a juggling act between sinking valves, how much to cut the cylinder deck, and or change gaskets. I’d like to keep the current spec gasket, which is a steel shim .021” I hope I've explained that clearly enough, this is my first time building a stocker engine. I guess the question is what kills power more, sinking valves or losing compression ? __________________ Brian Carpenter Stock 1358

04-18-2018, 04:30 PM	#2
Glenn Briglio VIP Member Join Date: Nov 2002 Location: Massapequa Park,NY Posts: 1,281 Likes: 1,890 Liked 969 Times in 307 Posts	Re: Need more P/V clearance in a BB mopar Degree the cam where the engine will like it to be. Then live with the loss in compression to get desired piston to valve cleaance. Ie don't mill heads as much. __________________ 1989 Camaro Iroc-Z I/SA B&B Auto Machine Shop.

04-18-2018, 05:23 PM	#3
GTX JOHN VIP Member Join Date: Jun 2009 Location: Boulder City, Nevada 89005 Posts: 2,727 Likes: 2,780 Liked 2,460 Times in 693 Posts	Re: Need more P/V clearance in a BB mopar Maybe sink the valves a little bit and or angle mill the heads. FelPro 1009 Gasket will give you a extra .020 to .022. I prefer to make heads near spec and use deck and gasket on Big Block Mopar stuff to make them more universal for different shortblocks. __________________ John Irving 741 Stock 741 Super Stock Last edited by GTX JOHN; 04-19-2018 at 12:59 AM.

04-18-2018, 10:44 PM	#4
ss3011 Senior Member Join Date: Feb 2002 Location: Southeast Michigan Posts: 909 Likes: 70 Liked 239 Times in 114 Posts	Re: Need more P/V clearance in a BB mopar What method did you use to figure out your clearance ? Clay with full valve springs , or dial indicator with a light checking spring ?

04-19-2018, 07:33 AM	#5
Larry Hill Live Reporter Join Date: Oct 2004 Location: Hickory, Ky Posts: 10,627 Likes: 1,917 Liked 10,676 Times in 2,220 Posts	Re: Need more P/V clearance in a BB mopar Use more deck clearance and keep the gasket thin. You will need about .035 '' total to keep pistons from contacting head. Have P/V clearance through the range of adjustment, so you can roll the cam forward or backwards without bending stuff. Exhaust valve will like to make contact in split overlap. __________________ IHM Used Parts https://ihmusedparts.com 888-821-1817

04-19-2018, 08:17 AM	#6
Glenn Briglio VIP Member Join Date: Nov 2002 Location: Massapequa Park,NY Posts: 1,281 Likes: 1,890 Liked 969 Times in 307 Posts	Re: Need more P/V clearance in a BB mopar Having the correct cam timing is more important then losing a half a point of compression. __________________ 1989 Camaro Iroc-Z I/SA B&B Auto Machine Shop.

04-19-2018, 08:19 AM	#7
GallopinGhost Member Join Date: Jun 2010 Location: VA Posts: 230 Likes: 23 Liked 21 Times in 13 Posts	Re: Need more P/V clearance in a BB mopar Checking springs, with an indicator on the retainer I've already moved the cam around to give me the most intake clearance, which has been the biggest problem, and still have around twice that amount of exhaust clearance. Piston is .010 in the hole, spec is .004. I'm leaning on leaving the valves alone and using whatever gasket gives me the clearance needed. Those 2 together should give me the .035 Larry mentioned. In hindsight, I should have gotten a smaller cam so I could keep some compression........ __________________ Brian Carpenter Stock 1358