Ilja_hamburg

Hi

At first sorry fore my bad englisch
I read this board since a longe time an i nearly learn all about 3,1 tuning

At the moment i search fore forget pistons to get a higher kompression!
Can some help me? I canīt find some and forget fiero pistons are to high

Any internet link?

thanks .....


PS: nearly every v6 tuner in germany knows dave10second

bl85c

iTrader: (2)

If you're just looking to raise the compression you don't need forgings, there's many combinations of OEM pistons, cylinder heads and gaskets that will raise the compression. Browse around on www.kb-silvolite.com, they have replacement pistons listed for about every american engine ever made.

If you're looking for forgings you're pretty much limited to what the fiero store has, or having custom forgings made. Try searching www.60degreev6.com for more info. You might even find someone that has a used set of forgings they're willing to sell.

firstfirebird

iTrader: (3)

No dice . I'm an avid member there, and jump on any kind of good deals comming through .

If you want to raise compression, have a machine shop shave the heads and intake manifold.

If you have good fabrication skills, you can use FWD aluminum heads and intake manifold from a 3400, but you will need a way to control spark because there is no room for a distributor with the 3400 top end.

The 3400 heads can be worked to give you about 11 or 12:1 compression, how much are you looking for, and how much octane in your gas?

https://www.thirdgen.org/forums/v6/4...ts-hybrid.html

Ilja_hamburg

at first thanks

I look fore a 10-11:1 kompression
And the fuel in germany have "super benzin" 95 octan "super plus" and 100 octan
The 3400 heads are a nice idea but other pistons are easier! And i have allready spent so muth time in port my heads now!
shave the heads also a very good idea! How many must i cut ore shave from the heads?
and i cant find some pistons on the quick on kb-silvolite

bl85c

iTrader: (2)

Wow, 100 octane from pump gas? That's considered race gas here in america.

Pistons #1463, 1478, 1486, 1492, 1496, 3409, 3420, 3439, 3459, 3477 and 3483 are all designed for 60 degree v6's, of those only #1486, 1496, 3459 and 3477 will fit your engine without modification. A 'c' after the part # means the piston skirt has been coated with a friction reducer and an 'h' means it's made of hypereutectic alloy.

You should keep the pistons you have (#1486) because they have the smallest dish of all 3.1L pistons. Have the block milled down .0165" to give it a neutral deck height (with an excellent .04" quench height) and have the heads milled down to 40cc's to give you 9.8:1 compression, which is safe with iorn heads and 95 octane.

If you want higher compression you can have 2.8L pistons milled to fit, but that would neccecitate the use of higher octane gas and possibly aluminum heads to keep detonation down.

P.S. Your machinist can measure how much to cut the heads for you, and have them cut the same amount off the lower intake manifold otherwise it won't seal correctly.

Ilja_hamburg

thats very interesting and helpfull thx
is it possible to milled a piston without to distroy it?
I think i try to use 2,8 pistons und hope the iron heads work
to drive 100 octan is no problem in germany

firstfirebird

iTrader: (3)

2.8 pistons on a 3.1 crank will make the pistons collide with the head. The .3" differance in the crank was made up by placing the wristpin higher on the piston in the 3.1.

You can get a 3500 crank that has larger journals for the rods, and offset grind it to give you a little more compression.

Also, don't get stuck on keeping your iron heads, just because they are ported.

Look how much better the aluminum heads are than the iron heads...












And here are aluminum heads after porting...





And unshrouding the valves (3400 heads)...



You can't get that with iron heads, even ported. You have a much better starting point with the aluminum heads.

bl85c

iTrader: (2)

Not if he has the piston crown milled down like I said. He would only need to mill them down .133" to give it a neutral deck height.

If you do choose to use 2.8L pistons you should use #1478 because it has a slightly thicker crown. Using piston #1478 without milling the block or the cylinder heads would give you 10.4:1 compression and save money in the process. The downside is that the crown will be slightly thinner and there will be less material between the piston crown and the top ring, however later piston designs also use thinner crowns so it's not a concern.

Aluminum cylinder heads would definately be the better choice because they can tolerate a full compression point higher than iron can and stock aluminum heads can outflow fully ported iron ones, but to you they might not be worth the effort to retrofit. To really get an idea of how much compression you could get away with I need to know what your cam specs are because cam timing has a huge effect on cylinder filling and the dynamic compression (the compression the engine actually sees in operation). You can guess what the engine will tolerate based on the mechanical compression, but dynamic is much more accurate.

Ilja_hamburg

thanks i will by the 1478 and try it :-)

firstfirebird

iTrader: (3)

You ar giving wrong information. The 3.1 has a .317" longer stroke than the 2.8. If you put 2.8 pistons on a 3.1 crank (they both use the same rods) the piston will extend out of the block by quite a bit. The 3.1 piston stops .095" below the deck, and the gasket is .040" compressed height. This means you have .135" above a 3.1 piston to hit the heads, and adding .317" is too much, even if you used .060" compressed height gaskets from a FWD. You would have to shave at least .082" off the top of a 2.8 piston for it to be even with the head, plus .040" for quench, giving you .122" total to remove. This might be OK to do with a forged piston, but I wouldn't recommend doing it with a cast product, especially because ring lands have been known to break even in stock form.

The Fiero store sells modified Ford Cosworth forged pistons, if you do go shaving them down, I recommend you get these.

Ilja_hamburg

oki thanks i will try it :-)

bl85c

iTrader: (2)

firstfirebird, when you do the math correctly piston #1478 is exactly .1325" above the deck.
Radius of 3.307" stroke + 5.7" rod length + 1.599" compression height = 8.9525" piston height at TDC; 8.820" deck height - 8.9525" piston height = .1325" above deck so he would need to mill it ~.133" to give it a neutral deck height.
You don't use the full stroke to figure piston height since only half the crank's travel is upward, so at TDC the 3.1L crank is only .1585" higher than the 2.8L crank. Im' not doing this to be rude, just make sure your math is right. By the way, your 3.4/3500 hybrid looks sweet! Can't wait to see it done!

llja_hamburg, you can go whichever route you want, but the most cost effecive way would be to mill the 2.8L pistons.

Ilja_hamburg

thanks a lot @bl85c and @firstfirebird
I tray today to mill down an normal 2,8 piston frome an older engin and it works...but ist very few rest material
In the next days i think about if i try it whit forget pistons ore whit the 1478 an milling the block

one question left
www.fierostore.com there they sell forget 2.8 pistons but they are 9,5-1 so i must mill more?! and i think the is a point where its to muth ore?

firstfirebird

iTrader: (3)

You don't have to butter me up to tell me "I saw we Todd did"! I don't know where my head was during these calculations, but for some reason I was thinking in diameter, not raidius

If 3100 gaskets were used (from say a 1995 FWD 3.1), then at a .060" compressed thickness (RWD iron head gaskets are .040" compressed thickness), then you wouldn't have to mill the pistons at all. This would also give a good quench at just over .040".

Thanks lb85c for the correction. I have been number crunching a ton since this build, and I guess I got confused confused for a minute.

bl85c

iTrader: (2)

Just one problem with using .06" gaskets though, it would have an unusable 14.7:1 compression. Amazing how just an extra .1325" can change the compression.

bl85c

iTrader: (2)

I don't know the specs on those pistons, but you would have to mill them more since they have a higher compression height (and possibly a thinner crown...) so milling them for use with a 3.1L crank is questionable. There is a point where you can mill it too much, the thinnest the crown should be is ~.150" for any performance engine. If you plan on turbocharging or nitrous later it should be at least ~.250" thick.

Ilja_hamburg

.150" is no problem! at the moment i test at a 2,8 piston and they have after mill about .210"

firstfirebird

iTrader: (3)

Well the stock iron heads gaskets are .040" compressed height so .060" compressed height will give you LESS compression.

Have you ever used the CR Calculator at 60degreeV6.com?

Link (click here)

bl85c

iTrader: (2)

Building it this way would give a 14.7:1 compression. I have used 60degreev6.com's calculator, but I preffer kb-silvolite.com's c/r calculator because it's much more accurate.

firstfirebird

iTrader: (3)

You said the problem with using .060 gaskets is the compression would be too high. Also, the 3500 head gaskets have a 3.8" bore and .060" compressed height, they will lower it a little.

bl85c

iTrader: (2)

Have you done the math? .06" gaskets on a 3.1L with un-milled 2.8L pistons will give 14.7:1 compression.

I'm not suggesting that .06" gaskets alone will raise the compression (obviously not), I'm saying building it the way you suggested on post #14 without milling the pistons will. I should've clarified what I said on #15.

firstfirebird

iTrader: (3)

Gotcha . I'm not fimiliar with the 2.8 piston part numbers, where did you compile that list from?

bl85c

iTrader: (2)

It's kb-silvolite.com's list of gm pistons.