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Wrist Pin height?

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Old Apr 10, 2011 | 09:11 PM
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Default Wrist Pin height?

I was shotting the breeze at the local tuner last week and I mentioned I was thinking about a 408 for a winter build. He mentioned that a 390 would be a better idea because of the wrist pin height on a 408. (Yes, he said 390. I've never heard of it.)

Someone inform me of what he may be referring to on these two different builds? He said something about how the wrist pin is too high on the 408 pistons.
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Old Apr 10, 2011 | 09:20 PM
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Too high up in the piston, ie short compression height.
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Old Apr 10, 2011 | 09:23 PM
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Hmm... Can you change it with different pistons and shorter CR's?

The 390 would be a 4" bore and 3.90" stroke LS2/LQ9/4, right?
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Old Apr 10, 2011 | 09:29 PM
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Originally Posted by bayer-z28
Hmm... Can you change it with different pistons and shorter CR's?

What's this 390 build I heard of? 4" x 4" is a 408, IIRC. Honed LS2 is a 370, I think. So it would be a 4" bore and 3.90 stroke, right?
3.90" stroke crank rather than 4" gets you roughly 392ci. Callies sells 3.90" cranks and I know Probe makes shelf pistons (pn 14512), not sure who else.
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Old Apr 10, 2011 | 10:03 PM
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^ Tach better/ higher w the shorter crank?? I could do some 59 or 61cc heads for an n/a build and maybe get a set of 72's for boost to drop it down, right? Depending on valve relief size. Should be a stout platform for boost then.

I'd like to use my 243 heads on it for NA and eventually when I get the money for boost, I'll pick up some larger cc heads for it. I'd like to stay cathedral on them so I can still use my 102 on it.

Last edited by bayer-z28; Apr 10, 2011 at 10:09 PM.
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Old Apr 10, 2011 | 11:46 PM
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Originally Posted by bayer-z28
^ Tach better/ higher w the shorter crank?? I could do some 59 or 61cc heads for an n/a build and maybe get a set of 72's for boost to drop it down, right? Depending on valve relief size. Should be a stout platform for boost then.

I'd like to use my 243 heads on it for NA and eventually when I get the money for boost, I'll pick up some larger cc heads for it. I'd like to stay cathedral on them so I can still use my 102 on it.
I don't know about "tach better". There are thousands of these engines out there that run well with a 4.00" crank, so I really don't think the 3.90" crank is necessary. I'd stick with the 4.00" crank and enjoy the extra displacement.
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Old Apr 11, 2011 | 12:02 AM
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We're able to have much thicker ring lands with 3.800" crankshaft, we debur the bottom of the bores however 3.800/3.825 will clear with no clearacing using compstar H beam rods.

I've seen plenty of 408 pistons tweek the top ring land with boost. I've had one customer replace his 408 with 390 using a PT88, made more power. I'm not advocating the power gain, it definatly didn't loose power.

I have a line of exclusive pistons made by CP-Carrillo, 1.200" compression height.

Last edited by AES Racing; Apr 13, 2011 at 01:15 AM.
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Old Apr 11, 2011 | 07:53 AM
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^ That's what I was wondering. I thought I remembered hearing him say something abotu the rings. But it was so out of left field that I didn't remember it easily.
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Old Apr 11, 2011 | 09:50 AM
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Originally Posted by AES Racing
I've seen plenty of 408 pistons tweek the top ring land with boost. I've had one customer replace his 408 with 390 using a PT88, made more power. I'm not advocating the power gain, it definatly didn't loose power.
What kind of power are you talking about here?
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Old Apr 11, 2011 | 04:34 PM
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^ I dunno about him, but I was thinking of 650rw for a goal. There's gonna be a track close to where I'm moving, so I may end up with a drag car.
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Old Apr 11, 2011 | 04:35 PM
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Originally Posted by KCS
What kind of power are you talking about here?
Around 1200hp (engine),

408 I believe combination was making 990rwhp @19psi
with 390 same combination made 1050rwhp @17psi

https://ls1tech.com/forums/forced-in...ugh-4l80e.html
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Old Apr 11, 2011 | 07:28 PM
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Wow... Reeeaalllllly!! VERY interesting!!

Last edited by bayer-z28; Apr 11, 2011 at 07:42 PM.
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Old Apr 11, 2011 | 10:15 PM
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Originally Posted by AES Racing
Around 1200hp (engine),

408 I believe combination was making 990rwhp @19psi
with 390 same combination made 1050rwhp @17psi

https://ls1tech.com/forums/forced-in...ugh-4l80e.html
I'm gonna take a wild guess here, but did LME build the 408 and you guys build the 390?
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Old Apr 12, 2011 | 08:52 AM
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Originally Posted by KCS
I'm gonna take a wild guess here, but did LME build the 408 and you guys build the 390?
No. LME did not build the 408".
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Old Apr 12, 2011 | 09:17 AM
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I was looking at an LME 408 a couple years ago, but found the finished cost to be WAY out of my range. The long block was reasonably priced, but add in everything else needed also. (fuel system, turbo(s), tune, induction, rear end etc etc)
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Old Apr 12, 2011 | 01:29 PM
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Originally Posted by Bryan@LME
No. LME did not build the 408".
Oh okay, just asking. Have you ever seen pistons get "tweaked" on these 4" stroke deals?
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Old Apr 12, 2011 | 06:34 PM
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I have seen pistons "tweaked" a lot even on stock stroke deals so no special piston can save an engine or the pistons themselves from the tuner! Still I do like the lower stroke taller piston turbo / blower only deal AES is doing.

We used to do a lot of 3.900 strokes for the same reason but there's not a lot of pistons available except customs. This deal from AES is nice as they already have the right pistons there sitting on the shelf.
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Old Apr 13, 2011 | 03:14 PM
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Originally Posted by racer7088
I have seen pistons "tweaked" a lot even on stock stroke deals so no special piston can save an engine or the pistons themselves from the tuner! Still I do like the lower stroke taller piston turbo / blower only deal AES is doing.

We used to do a lot of 3.900 strokes for the same reason but there's not a lot of pistons available except customs. This deal from AES is nice as they already have the right pistons there sitting on the shelf.
This is exactly what I have seen as well. The shorter stroke & taller CH piston is ultimately stronger. However we are making 2700+HP with a 1.110" CH. and have not had any "tweaked" pistons as of yet. Not to say detonation would not make that happen to any piston..
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Old Apr 13, 2011 | 06:30 PM
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Originally Posted by Bryan@LME
This is exactly what I have seen as well. The shorter stroke & taller CH piston is ultimately stronger. However we are making 2700+HP with a 1.110" CH. and have not had any "tweaked" pistons as of yet. Not to say detonation would not make that happen to any piston..
I agree Bryan as even the shelf Wiseco's can put up with a LOT!

There's some extra safety margin in the taller pistons like AES has here but for most apps the Wiseco shelf stuff works great for us.

Something extremely wacky crazy big hp I certainly don't ever mind more CH though of course!
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Old Apr 23, 2011 | 08:50 PM
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^^ I'm gonna bump this as I have another question.. Are there any pistons that would be as good with a 4.125" stroke? (as the 3.900" stroke ones in question)

I've got a thing for a perfect square, if I can get it I'd be happy, but if there are other factors at play, I won't worry about it.
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