Hot Rods Can dome pistons be mill to flat tops.

Bought a 406 CI small block looking at making it a Blower motor. I know i can get by with flat tops if I.'m careful with the boost. It has dome pistons in it. Can the domes be milled off to flat top them which i can do with the mill at work just dont know if they have been hardness treated that would be removed with milling. I know I can buy new dish pistons but like doing thing that not every body can do.

 

Short answer is probably not. If the head on the inside is recessed uder the dome for sure not. No heat treating to worry about. For the cost of piston failure buy the correct stuff.

 

What piston are they?

 

With a 76cc head and a flat top, a 400 is still going to have way too much compression(still over 10:1) to run any kind of forced induction. Your going to need a dished piston to achieve the correct compression, and going from a dome to a dish with these pistons isn't likely.

 

I doubt it... I would be amazed if there were enough material to machine away, and still leave enough for the head of the piston. On top of machining it flat, you need to machine valve reliefs in them, otherwise your valves will hit. I'm guessing the valve reliefs would brek through. Also, keep in mind that when you remove that much material, you're removing weight... so if it's balanced now, it will need to be balanced again. Of course, this is true for piston replacement as well.

 

All depends on what fuel you run and how good you are at setting things up. There are a couple guys in town with "street cars" that run over 10:1 and somethig like 10-15psi... on E85. (one is a SBC, makes over 1,000 hp)
I, personally, would error on the side of caution and stay around 9:1 with 5-10 psi if it's in a hot rod. Look neat, sound good, and still make plenty of power to get you in trouble in a hurry.

 

First thing is that if these pistons have already been run in this motor then cutting the dome off will not change valve pocket to valve clearence(think about it).Second, if these are forged pistons and there hasnt been any machine work inside to reduce weight, then the tops can be machined, because all forgeings are material heavy on the tops and material is removed, less for domes and more for flattops. 10.5 C/R is fine if you are planing to run alcohol.

 

If they aren't hollow domes, or recessed underneath they can be cut, you don't have to worry about the hardness. But before cutting you need to see if can find a number on them (usually on the underside of the piston somewhere) that can help tell who they are made by, then you can find out if they can be cut (and how much), or not.

 

I have shaved a couple of thousandths off of the correct piston to adjust compression before. I don't know of anyone who makes a domed piston that can be milled flat. The piston weight would be horrendous.

A set of blower pistons is not that expensive when it comes to making you engine functional. I like to keep my static compression in the 8:1 range but a lot of the fellas will disagree with that. I think that there are a lot of ideas that I use when building a blower motor that many would not agree with, my biggest grief with blower motors is that many of them are not blower motors at all that are naturally aspirated motors and the blower was an after thought.

 

Thanks for the input new ones it will be. Don't know what brand they are have'nt tore it apart yet. It came out of a late model dirt car and is build right just needs freshen up.

 

You haven't said if the pistons were forged or hypereutectic. If they're hypereutectic, it won't work for long.

If you mill the dome off hollow domed pistons, they won't work for long.

If you run flat top pistons, you'll have a LOT of compression for a blower and it probably won't last for long.

I think I'd buy the right piston for the blower and just do the job once (hopefully).

 

You caught me....

 

2 things here I want to point out.
1- this is not a engine build to quess at, you need to know several calculations and have a real plan here, or you will fail and it could very well be VERY expensive failure.
2- This engine from a late model dirt tracker might have some SERIOUS squeeze or compression, 14:1 or more!. To make things worse the cam will not be ideal by any means with the supercharger.

All that said, you need to pull the heads and C.C. a combustion chamber. You also need to see how far the pistons are now in or out of the hole or knowing the current deck height. You will also need to know the rod legnth to order new pistons. Order NEW pistons for your intent and purpose of your build. No crying in Baseball, and no cutting corners with a blower engine- be real here unless you have boat loads of money to burn.

Another thing, these heads may have been angled milled, and if so you will be hard pressed to get compression in a useable range even with dished pistons. Not trying to bust balls, but make you think and in the long run- help you.

You will more than likely need to rebalance the rotating ***embly with the new slugs. The weight of the current piston versus the new pistons will confirm or deny that. You will also need to verify valve to piston during mock-up. You might need to change oil pans as well, best of luck, TR

 

Looks like i need to rethink a few things on this one. back to drawing board. So any and all help will be welcomed.

 

You seem like a nice level headed new guy, and that's a welcome change. Any way we can help friend!!!

Some of us stayed at a Holiday Inn Express last night, and some of us actually do this for a living, all the best, TR

 

If the pistons are solid dome, you can mill them flat no problem. I didnt see where it said this is a dirt late model motor, but if thats correct, TR is right about the cam, its a non-starter for a blower motor, will almost certianly be on a 105-108 lsa, wont work worth a **** in a blown motor. You will be pushing lots of fuel out of the pipes, and it will be way down on power.
I would think the compression ratio is gonna be real high too, ESPECIALLY if was running in a 2bbl cl*** or any other sort of inlet restriction.

 

As mostly said above, you really need a set of blower pistons to do it right. The blower pistons have a slightly thicker dome / dish area to better cope with the extra heat you'll get even with modest heat. In the long run it's cheap insurance.

 

It came out of a late model dirt car and is build right just needs freshen up.[/QUOTE]


Here you go George, post # 10, TR

 

It was a alcohol engine. I'm not the smartes one out there but dont care to stick my neck out to try things. What about O ringing the block heard different things about it

 

What about O ringing the block heard different things about it
If you are talking a mild / moderate street engine, you don't need to "O" ring the block. On a 400 it might cause more issues that it might prevent.

 

The serious question here is --What do you plan to do with the motor??? race it? or street?

 

Would like to do both with it race a little then street also. Already have 6-71 blower set up with crabs

 

Severeral veriables to consider here. 1. Piston material 2. If the pistons was originally meant for blown or turbo engines 3. If piston is a hollow or solid dome forging.
PM me if you would like for more tech advise.

 

You may want to get that checked out.

 

I wonder if they got into the blower.................

 

What can i say never could spell. Heard crabs are hard to get rid of. Carbs got it right this time may be.

 

Crabs are easy to get rid of

1) shave half your ***** off
2) set the other half on fire
3) when they make a break for it----stab them with an icepic

 

Have the carbs already been modified for blower use?

 

They came with the blower that was on a running motor so I'm guess they are.

 

Here you go George, post # 10, TR[/QUOTE]
Thanks TR. Milling the domes off is not gonna get you where you need to be, and the pistons in that motor will probably be hollow dome. Non-starter. You are going to need dish tops and a new cam.