Thread: 406 rebuild question

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I have a 406, which just bit it last week. We haven't torn it down yet to see the damage. But, the general consensus is that I broke a skirt on #4. The guy who built it left that cylinder a little loose. Hopefully there isn't too much damage.

The motor has 200cc Sportsman II heads, 72cc & 2.02/1.60 valves, Forged flat tops, 1.6:1 rockers, MSD with HEI, Edelbrock Air Gap intake, RV cam, with 770 Holley, and good fuel delivery.

I need to know some good combos if I have to go +40 or even +60. Also what size would it be if I had to go to +60.

Any info would be great, and I already checked Ryan's page, not any combos close to what I have.

Thanks

+ 0.060" = 413.

Assuming that the piston is 0.030" in the hole and 5 cc's of valve reliefs in the piston, compression ratio will be 10.1:1 and that might be a little iffy with a "RV" type cam if it has a short intake closing point. Matter of fact, I suspect it's been rattling from excessive cylinder pressure all along.

Thanks for the info. Any cam sugestions for the rebuild? or site where a guy could get some knownledge. I am new to this, and am willing to learn. I really don't like depending on others for eveything.
Thanks again.

I agree with Techinspector1. I think your cylinder pressure was pretty high with the short duration cam and you've been detonating the engine. I just calculated your compression ratio as follows:
4.155 Bore
3.75 stroke
72 cc combustion chamber
0.039'' head gasket
0.010 deck
-5 cc valve relief
10.457:1 Compression ratio. Thats pretty high with iron heads and pump gas, especially with the small cam.

If you go to a 0.060 overbore I'd recommend you fill the block with block filler up to the bottom of the freeze plugs so you will have enough strength in the block for that overbore size.

Suggestion: Cam the engine just like it was a big block Chevy. Most of the cam info for SB Chevy's are for the 350. The 400 type will handle a lot more cam than the 350 will. A good choice for a street 406 would be something in the 230 degrees @ 0.050". Maybe 235-240 degrees on the exhaust side. You can drive it every day and it will still make good power.

Have fun

Thanks that is very helpful. Maybe I will look for a 400 block, instead of boring this one any bigger, keep it a 406.

Another option I have is to build a 350, I have 3 blocks to work with, all stock 4 bolt cast#3970010. With my heads, intake and carb any ideas for a good combo to make some big power. I checked Ryan's page and only one combo made good power with anything close to what I have, combo #26.

http://www.ryanscarpage.50megs.com/combos4.html

What do you guys think? I would like 400HP and about the same torque. It would save me some money if I can use some of the pieces I already have.

Thanks

say "good bye"to that block

block filler is for dragsters you could go .060 over 412ci.on the 70-72 4 bolt main blocks .i did .they seem to be heavier&definetly are of higher nickel content.the stock short con.rods will take more compression and make more torque. yes you had too much compression.comp cam dual energy cams emphesize on the weak exhaust port flow of stock engines.good for big inch small blocks.hope your heads didn't get wacked too hard good luck

Filling the lower part of the block has shown a cooler running engine. I've done it on several 406's on the street and it works. It also stabilizes the cylinder wall and helps keep ring seal. It also makes the 4-bolt blocks stronger.

grouting the block is fine,as long as your heads have been drilled for steam holes,but 406 s are notorious known for
trying to run hot,a good aluminum radiator
with a good'puller fan'works best,also,you will need to get an oil cooler,keep the temp low,your oil WILL break down faster
with the heat and bye bye 406,seen it happen a couple of times to those who thought they knew 400s....

Originally posted by dirtyplumber
say "good bye"to that block

Which block the 406 or the 350? Why?