KB Pistons

F

Finallall

Member
Joined
Oct 6, 2008
What do you guys think about these? Will they rase my compression? The specks are:

Bore (in) 3.820 in.
Bore (mm) 97.028mm
Piston Style Dish, with no valve reliefs
Piston Material Hypereutectic aluminum
Compression Distance (in) 1.805 in.
Wrist Pin Style Press-fit
Pin Diameter (in) 0.940 in.
Piston Ring Thickness 5/64 in. x 5/64 in. x 3/16 in.
Quantity Sold as a set of 6.
Notes 3.050 in. diameter, 0.205 in. deep recessed piston head.


Keith Black/KB Pistons 1740H-020 - Keith Black Hypereutectic Pistons - Overview - SummitRacing.com
 
From their own website:
Make BUICK
Engine Type V6
Liter 3.8
CID 231
Engine Size 3.8L/231
Beginning Year 1977
Ending Year 1987
Engine Family GM V6
Application Notes Non-turbo engine VIN code A. Replacement for original equipment numbers 1394558, 1249538, 12157377, 25501423, 25518053, or 25527178. Not intended for racing applications.

I say no they will not increase your comp ratio. Because they are replacements for an OE application
 
Application Notes Non-turbo engine VIN code A. Replacement for original equipment numbers 1394558, 1249538, 12157377, 25501423, 25518053, or 25527178. Not intended for racing applications.
Click to expand...
good eye warwagon
 
If you're running NA you could raise the compression ratio by going with the early 3.0 L FWD engines piston. You'd get between 9 and 9.5 out of it unless you cut the heads and block. If you're running turbo then go ahead and get some JE or one of the other makers. They have some nice stuff and Aj and I've been looking at a set of Probes for the 4.1's we're building. Found a set that should yeild about 9.2 with a 4" bore. We are using 6.65" long rods though.
 
I heard the 3.0 pistons will give you more like 12:1 compression and will interfier with the valves needing valve reliefs cut. 350 pistons are the ones I want.
 
Finallall said:
I heard the 3.0 pistons will give you more like 12:1 compression and will interfier with the valves needing valve reliefs cut. 350 pistons are the ones I want.
Click to expand...

indeed, turbokinetic has compared them....apparently the rods for the 3.0 FWD are longer than the 3.8's, but using these rods with the 3.8's crank would cause the pistons to stick out of the heads and push the heads off;
im not sure which combo wouldve had too low of a CR and too high of a CR, he compared LK9 high deck block stuff with LG3 FWD 3.8 SFI engine, theres a LN7 3.0 MFI engine with lower deck, different pistons 9something CR, so basically theres a specific combination thats going to cause you to have the 12 CR, a combo thats going to be 6something, a combo that the piston will exit the cylinder sleeves' lower edge (3.8 piston/3.8 rod/3.0 crank in 3.0 block), a combo that'll put the piston out of the block deck...
 
CamoDeafie said:
indeed, turbokinetic has compared them....apparently the rods for the 3.0 FWD are longer than the 3.8's, but using these rods with the 3.8's crank would cause the pistons to stick out of the heads and push the heads off;
im not sure which combo wouldve had too low of a CR and too high of a CR, he compared LK9 high deck block stuff with LG3 FWD 3.8 SFI engine, theres a LN7 3.0 MFI engine with lower deck, different pistons 9something CR, so basically theres a specific combination thats going to cause you to have the 12 CR, a combo thats going to be 6something, a combo that the piston will exit the cylinder sleeves' lower edge (3.8 piston/3.8 rod/3.0 crank in 3.0 block), a combo that'll put the piston out of the block deck...
Click to expand...

Aj and I have been playing with rods and pistons to see what would give the best combo. We're both using 6.65" long rods Which lower the total height of the piston quite a bit. We've gone from a pin height of 1.825" down to 1.17" to increase dwell time of the piston for better charging if the cylinder. I've also looked at using the 3.0 early rod. It reduced the pin height to 1.45" and the 93-95 3800 piston can be used to get the right heights for the pistons. If you just substitute the early 3.0 piston in place of the 3.8 piston then you end up with a slightly higher piston which fits and increases comp ration less than a point. It must be the 83-85 piston only though.
 
Now when you say the 3.0l piston is this the flat top one or a domed piston. Also what is the exact increase in CR?

Thanks Charlief1
 
It's less than 10:1 but I'd have to look it up again. I'll see if I can find the exact info for you later.
 
its a flat top; theres no domed 3.0 piston i know of, according to SIlvolite, the 1982-1987 (?!) LK9 piston is flat top; the 1985-1988 LN7 MFI has a DISHED piston; the LK9 is a high deck block, CR is 8.45:1 for 1982 and 83, 84-85 8.40:1 according to wikipedia, and for the low deck block, CR with the dished piston is 9.0:1 or so..the compression height of the LK9 piston is 1.808, the LN7 piston is 1.805, .003 difference, dont know about the deck height differences though, but TUrbokinetic found that for the LK9 engine, the block shares the deck height measurement as the LG3 3.8s, presumably similar to a RWD 3.8 evenfire (as they shared the majority of the casting, only bellhousing differences for FWD vs RWD) but have shorter cylinder sleeves at the bottom of the bores...he and I dont know about the LN7's though...I had the idea of going to LN7 block for a 3.0 build using LK9 pistons to see if the CR can be bumped up..tho it sounds like the 350 pistons for the buick 350 would do a good job as well? hmm something to consider.
Im also curious about variety of pistons in regards to the Buick V6s :)
 
Those pistons are for a 4" bore, not a 3.8" bore. They will fit a 4.1 but not the 3.8. If you're interested I'll take them off your hands. They're basically what I've been looking for for the long rods I have.

How the heck did you find them? I search fairly regular and never saw them.
 
the guy must have posted them wrong.:confused: i have not recived them yet im still waiting for him to ship it.:mad:
 
They use a .927 wrist pin and have a 4.000 Bore size with a 1.120 comp,height

How did you miss this in the add. These will give you an 10.85:1 compression. I just did the math and they won't work for me. Way to high a compression. I'm gonna bet these are for a Stage II engine.
 
When you get them in I may still be able to use them so don't be too discouraged. See if you can take a better pic of the top of the piston so I can see how deep the valve pockets are. That will be the deciding factor. I may be able to have the top machined to lower the compression ratio for my 4.1. Thanks Matt.
 
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