406 build

Paul P · Posted: Fri Feb 15, 2013 11:15 am Post subject:

Is that number down the hole and is it .015" not .15"? If it is .15 with a 72cc head you'll have 6.6:1 compression...

With the reading at .015" it is 8:1.

The measurement needs to be taken at the piston edge where there is no dish.

cmarr6 · Posted: Fri Feb 15, 2013 11:38 am Post subject:

I just went and measured again to make sure and it is .15 not
.015. I measured at the wall of the cylinder down to the first ring. I am confused. My machinst told me these pistons are exactly like the stock pistons except .30 over. Same size dish and everything. The bottom end is completely stock. Rods, crank, everything. How is it that the stock 400 with 76cc heads had a compression ratio of 8.5:1 and I get a CR of 6.6:1 with 72cc heads? I didn't do anything except bore it .30. Shouldn't I be getting similar numbers to the stock numbers?

cmarr6 · Posted: Fri Feb 15, 2013 2:01 pm Post subject:

I called the machinist and found the part# of the pistons. They are Silvolite 1443's. Looked them up on line and it said compression height is 1.54 and had a compression ratio listed as 8.5:1. Will these be okay to use? If it's listed as 8.5:1 in stock configuration can I use a smaller chambered head than the stock 76cc head and increase compression? or would I be better off replacing the pistons with something with less dish and and higher compression height?

af2 · Posted: Fri Feb 15, 2013 7:58 pm Post subject:

clay · Posted: Sat Feb 16, 2013 1:20 am Post subject:

I agree with exactly what has been said. However you have the cylinder volume at t.d.c. which is basically all you need. Finding out how far the piston is down in the hole is nice if you are after everything but unless you are going to tear it back down and deck the block if necessary what you've got is what you've got. Now that you have the t.d.c. volume it's just basic math. Add the total volumes at b.d.c. (swept volume using bore and stroke + your t.d.c. volume + gasket + chamber) then divide by the total volume at t.d.c. (everything previous - swept volume). This should give your compression ratio. Then play with different chamber sizes and different gasket thicknesses to come up with what you want. I would shoot for the 9 - 1 range for 87 octane or in the upper 9's to low 10 - 1 range if you want to run premium. Clay

cmarr6 · Posted: Sat Feb 16, 2013 7:49 am Post subject:

It says on the silvolite web site that the dish it a .15 inch dish, so if I am getting .15 down to the piston, the top of the ridge around the dish should be even with the top of the deck, right. That is what I assume you mean by the "top of the piston". It difficult to tell because there is the dish, then the ridge around the dish and then it angles at about a 45 d. angle down to the cylinder wall. So If I have to measure the top of the piston, would that be the top of the ridge around the dish? Sorry for sounding so stupid about all of this but It is the first time doing this and I want to learn how to do it correctly. Thanks for being patient with me. I will take the volume I have, and do the math and see what I come up with. What is the typical thickness of head gaskets? And what type of head gasket should I use if I go with aluminum heads? anything special? or just a regular head gasket? Thanks again for the help.

clay · Posted: Sat Feb 16, 2013 8:46 pm Post subject:

Yes, you measure to the ring or ridge located between the dish in the center and the chamfer around the outside of the piston. You have several gasket choices. There is a gasket that has a copper wire inside the fire ring (metal ring on the gasket at the bore edge) for aluminum that won't put an indention in the heads. Standard gaskets have a steel wire inside that will indent aluminum heads but will seal better for nitrous or forced induction. These are commonly 0.039" thick compressed. You can get a 0.051" thick version but I don't think you need it. I can't remember the volume - you should be able to find it on felpro's website I would think. Also available is a 0.015" thick steel shim gasket either coated or uncoated. You can also get a MLS (multi layer steel shim) gasket in about any thickness you want but the downside is they aren't cheap. I would look at the Felpro performance gaskets instead of the regular gaskets. They have a silicone beads around the coolant passages and I just like them. Most important is to retorque even they advertise them as not needing it. You can do it before you fire it though. Just torque and let them sit for a day then loosen and retorque. I'll usually do this twice. Clay

dawg · Posted: Sun Feb 17, 2013 3:17 pm Post subject:

one important thing not to overlook is the head gasket on the 406.
I blew mine 2 yrs ago and decided to get a good head gasket.
400 engines have a habit of blowing head gasket between 3 and 5
and 4and 6.
Felpro PermaTorque MLS 1143 is about the only fix.
a good write up is here:
http://www.flickr.com/photos/406vette/5499673214/in/set-72157623991273645
I wish I knew about this when I built my 406!

Paul P · Posted: Mon Feb 18, 2013 1:10 pm Post subject:

I have had good luck with the Fel Pro copper ring 1010s Never any problems.

cmarr6 · Posted: Tue Jul 01, 2014 9:34 am Post subject:

Okay, after a lot of research, reading, thinking, learning about all this, I have decided to tear apart the bottom end and start over!!!!! Decided to go with stock crank, 5.7 scat rods, Speed Pro hyper pistons, either flat top or 12.5 cc dish. I'm leaning toward the flat tops. Will have to run some premium gas, but that's okay. Will get some aluminum heads with appropriate size chambers to keep compression down and deter detonation. Similar to the one Big Dave said he built in a previous post.
I got the Vizard book and have been reading trying to soak up the info.
Since I already have the cam(summit 1103), and I think it's a little undersized, I thought I would just go with 1.6 rockers to increase lift a little. How's this combo sound. Any concerns or other things I should be thinking about?

Paul P · Posted: Tue Jul 01, 2014 10:19 am Post subject:

Hypers will limit your build for future upgrades but I guess with a cast crank having its own limits it should be ok. Forged is the way to go though piston wise. I did the same thing with my first 406 I had KB128 hypers and then bailed that idea and went with some Ross forged pistons. They never let me down.
Paul

cmarr6 · Posted: Tue Jul 01, 2014 11:58 am Post subject:

I don't forsee any future upgrades to this motor. Just a streetcar. If I ever wanted to get serious and do some racing I would definitely start new and I really want to move up to LS motors in the future. This will more than likely be my last Gen 1 motor.

squeeezer · Posted: Tue Jul 01, 2014 1:33 pm Post subject:

My camaro (I sold it) had 11:1 with flat tops and 68cc chambers
It had a bigger solid flat tappet can in it that bled off just enough cylinder pressure
Ran on premium pump all day long and made 515 lbs torque
Use this as 1 example
11:1 would be the absolute max for an aluminum headed gen 1 SBC
L's motors can handle more,you have a 400 .....use it