.040 390 pistons

[George vega]

Looking for suggestions on .040 forged pistons. Would like to keep the compression where I can run pump gas or mix half and half. Thanks

[George vega]

Found some L2291 with coated sides and rings for about 350. Good for 6500+ rpm and 150 shot of nitrous.

[Heo]

Thats what i run, on pumpgas had seen 6500 a few times

[George vega]

The price is good and the only time my car goes over 6500 is when running 1/4 mile. I'll mention them to my machinist and see what he thinks. Thanks

[Heo]

As i se it, yes its a "outdated " design with outdated ringpack
but it will do a good job as a street piston longevity and all that
for that price

[George vega]

I plan on backing from just racing to a strip and strip mode. So im trying to put more reliability in the engine for street use. That's  why I'm thinking of going with these pistons. Yes, they are heavier and as you stated, out dated ring sizes but they're good enough for what I want to do. Thanks

[My427stang]

I like the L2291s, they make a nice little 390 if you don't have serious valve events or valve sizes.  Not a lot of room in the pockets compared to a modern piston.

They do fine though and with a little cut to the deck end up around .004 below

[Heo]

I cut my deck to zero 10.155 i think it was. The streetmaster
intake lined up perfect with 040 headgasket and uncut C4-G
Heads

[George vega]

The deck was cut .020. I do have larger valves but he will modify the pistons to fit and cut my intake for proper fitment if necessary. I'm using my 428 eagle crank and rods. It comes out to about 421 ci I think.

[My427stang]

So, I may have misunderstood the build, but

10.170 block cut .020 = 10.150

Crank (3.98/2)+6.49+1.776=10.256

Those will be .106 above deck.   Are you sure you have the right piston part number?

[George vega]

I may have to use 410 pistons or custom made. Just to clear info on the block. It's  a mirror 105 block, bored .040, and .020 taken off the head surface. Using 428 crank and rods. Yes the pin needs to be lower and maybe cut the top of the pistons. Thanks

[George vega]

I meant raised the pin to lower the piston.

[My427stang]

Give Brent a call, he can hook you up and there won't be any guess work.

Measure your bore, calculate what you need for compression and pin height with him and no labor cutting for valves.  I think you'd be surprised at the difference in cost in the end, and all you do is bolt it together no cutting parts and hope they are strong enough, no digging into a thinner crown for valve reliefs, etc

.

[winr1]

I have a set of those pistons

They are not light as hi dollar pistons but lighter than factory

Mine, with a 3.78 crank are .013 in the hole

Gonna check piston to valve clearance with piston at TDC

See what I come up with subtracting .087 shaved off the top of the piston

This is to see what clearance I would have using a 3.98 crank

EDIT:  the top of the piston to the 1st ring land is .370 IIRC




Ricky.

[CaptCobrajet]

I think there is a Mahle Powerpak for that combo.  It's a nice ring pack, coated, etc..  Very good pistons.

[chilly460]

Autotec sells a 410 piston, it’s their budget line but nicer finish than the speed pros (I’ve had both side by side) and considerably cheaper than typical Ross/Diamond type pieces.

http://racetecpistons.com/

[My427stang]

Autotec sells a 410 piston, it’s their budget line but nicer finish than the speed pros (I’ve had both side by side) and considerably cheaper than typical Ross/Diamond type pieces.

http://racetecpistons.com/

Nice thing about Autotec is you can tweak it a little, instead of having to live with off the shelf.   I certainly wouldn't compare them to Speedpro, other than to say it's a heck of a lot nicer piston.

[George vega]

I'll check on the mahle pistons. Thanks. I think that any truck piston after 68 was actually a 410 piston with the raised pin to lower compression.

[chilly460]

https://www.jegs.com/i/Mahle-Motorsports-Pistons/644/FFE665080F07/10002/-1

[My427stang]

https://www.jegs.com/i/Mahle-Motorsports-Pistons/644/FFE665080F07/10002/-1

If you are sneaky, you can get them 100 bucks cheaper.  I am pretty sure these are listed wrong but the correct FE piston

https://www.amazon.com/Mahle-930264080-Piston-4-080in-3-89in/dp/B06XYPP8R4

I still like the Autotechs, more flexibility than an off the shelf piston, and likely slightly cheaper

[chilly460]

It’d be interesting to have different manufacturers pistons next to each other to compare.  I have a set of the Mahles I bought used at Carlisle, amazing amount of contouring and features in them.  I know there’s a lot to piston Tech I don’t know

[machoneman]

Whoa, at near $100 per piston, that's a lotta Benjamins! Make the old heavy slug TRW's look pretty good!

[George vega]

The Mahler pack is an .030 piston.