Cast pistons or forged in 400HP 360 magnum?

Which pistons would you use in this build? And what brand name?

Uhh, only cast pistons out there are going to be stock replacements, and they are probably going to sit a mile in the hole, not what you want from a performance build. If you plan to run nitrous or boost, go forged. If it's just a street/strip motor without boost/nitrous, I would go with a set of hyper pistons.

I will not run nitrous and there will be no boost. The block is going to be bored 30 over and I plan on using the stock crank and rods, after they are resized. Plan on using a set of EQ heads.

Even a stock piston for a magnum engine is going to be a hypereutectic cast alloy. But any of the hyper eutectic pistons from Keith Black or Speed Pro will do the trick for a 400HP motor.

If I was going to be happy with 400 HP and knew I would never upgrade then the factory magnum pistons would be fine the factory crate motors made 400 with them, however, a set of KB 107s might be cheaper, they would work better and be stronger. 400 hp from the motor you are talking about is a cake walk.

How would you build this motor? Be brand specific so I can get this on order from Summit. Give all details on how you would make 400 HP. Thanks

KB107 pistons and aftermarket heads will get you there. Block decked so pistons are zero-deck.

Other than that, research the build on the MP 360ci/380hp crate engines. One of the mopar mags put a good carb on top of one a few years ago, tuned the carb and distributor, did a dyno run and got a little over 400hp out of it.

theres 100 ways to skin a cat


http://www.geocities.com/alwest_83/dyno

heres a couple

If it was my motor I would use the EQ heads you mentioned. Just spend 5 minutes in each port smoothing down rough spots and transition areas, use the GM 3100V6 springs. Get an eddy airgap intake. Use the KB107 pistons in as small of an overbore as your block will clean up. Zero deck them and use the felpro .039 thick head gasket. I would get the SCAT I beam rods, you would amost spend as much resizeing and buying ARP bolts for yours. The comp 280 magnum cam is mild enough for every day driving and works great with magnum heads. Personaly I would use a Thermo-quad but a 750 holley or eddy of your choice would be ok. Other than that stuff you can get a standard overhaul kit for the gaskets, rings, bearings, and oil pump. Get the best headers that fit your budget.

This combo should be good for about 425hp. If you really think you want to knock off 25 hp don't touch the heads with a grinder and get a comp magnum 270 cam.

if you're starting with a mag motor, instead of using a flat tappet cam like the 280H, I'd look at the comp XR265HR cam, or a custom ground roller cam with 218-226@.050 duration on the intake and the same to +6 degrees on the exhaust, and about .318" lobe lift max...

I do agree with patrick about the roller cam if you are useing a 89 or newer block, go roller cam and re-use the factory roller lifters and the comp XR265HR cam.

Yeh I'm either going to get the KB107's or the Speed Pro's from Summit. I'm going to be using a Eddy Air Gap and the Holley 750 3310 carb. Since this is on a budget, I'll probably use the rockers of my cracked magnum heads on the EQ heads. These heads allow a cam with a .550 lift. I don't mind having an aggresive cam, but I'm going to go with a Comp Cam and tell them my application and get a custom grind. As far as headers, again on a budget...I'll probably go with the Flowtech headers in black ($129 brand new).

Anyone know if Summit has a sale or coupon right now or coming up? Because I plan to buy a few things from them and show around e-bag for other parts to save money rather than buying from the machine shop.

Lastly, are the KB107 with a .30 bore on Summit? I've looked and they have three sets of pistons for a 360 maggie with a .30 bore, but the product # is not KB107. They may just have differnt product #'s? If someone knows for could you post a link or the part #? Also would the extra money spent on KB pistons be worth it over the Speed Pros?

Thanks Moparts! Tomorrow the engine will be bored over and the project will be underway!

Summit has them
http://store.summitracing.com/partdetail.asp?part=UEM%2DKB107030%2D8&autoview=sku
In stock too. For $200 you can't get a better piston, speed pros tend to be heavy. You will have trouble not makeing 425 hp with this motor depending on your cam choice really. Are you going flat tappet or roller?

Dave thanks for the link. I've got a question in regards to those pistons. When I clicked applications it does not say it is for a Magnum motor.

LA & magnum short blocks are essentially the same.

They will fit a magnum motor with LA rings.

Spoke with a tech rep with KB and he said you have to use a magnum piston in a magnum motor. The connection rods are different between the 2 motors. He said to use the KB 372030-8 set from Summit. What type and brand of rings should I use?

Isn't the only significant difference between the two the fact that the small end of the Magnum rods are 1" wide and the LA rods wider? Lots of the KB pistons require that the little end of the rod be machined down to 1", or that aftermarket rods be used.

Clair

bullcrap. the only real difference between the LA and mag rods are the mag rods are narrower on the little end (1" for the magnum, IIRC). you can't fit a piston designed for a magnum rod on an LA rod w/o narrowing the little end, but you can put an piston designed for an LA rod on a magnum rod. heck, most aftermarket rods are narrower than LA rods
on the little end (and pretty much the same as a mag rod), because the same forgings are used for SBC apps.

a KB362, designed for mag rods will give ~1.2 points less compression than a KB107

Yeah I call bull pukey!

You talked to a chevy rep at KB. I used a set of the 107s in a 360 mag and it was great.

you are correct on the lower compression ratio.