Most a 3400 has been bored over?

[RacerX11]

By my numbers it would take an overbore of 0.060", and a stroke increase from 84mm to 91mm to get 3.75L (rounding up to 3.8 to give them the benefit of the doubt). I would love to see what rods and pistons they use to make this all fit.

Marty

[3100GAGT]

i heard .050 over. i wanted to go 80 over to be a 3.5L but people told me i would melt the walls.

[Ortie666]

I got a question along these lines.. Couldent you just put diffrent bigger sleeves in, taking in acount mabye having to bore the cast a little?? and do they make a hardcore crank for these engines yet??

[prophiseer]

Sadly, boring a 3400 even 0.060" over brings it to just over 3400cc, since it initially starts out around 3350ish

I think GM got that 3.4 displacement when they also take into account the volume of the dish in the piston, and the volume of the combustion chamber in the head

GM engineer's have always liked to "ruffle" their feathers, I guess you could say


I thought that .055" over on the block was really the largest you could safely go without running into potential problems? And wouldn't you need to lengthen the stroke to see a major difference in displacement on the 60*?

[Superdave]

the max on almost all GM engines is about .060".. probably other manufacturers as well...

[SappySE107]

Sleeves, now you are getting into my kind of project I have been looking at sleeves to make it about 3.7 or 3.8. Given what GM did though to go to 3.9, im not sure how well that bore will work yet. Its not cheap to sleeve the block though.

[prophiseer]

haven't seen the 3-9 block yet; didn't GM stager the cylinders instead of having them sit side-to-side on each bank?

[SappySE107]

No, they are side to side on each bank. They just moved the cylinders back but the spacing between them is the same. The 3400 heads bolt up to a 3900 block but the deck is wider so the head won't cover the whole deck surface. The length is the same though.

[Ortie666]

amazing, so can u use the 3.9 crank? im going to assume its longer.. all im after is 3.6L from a 3.4

[SappySE107]

Nope, its the same as the 3500 from what I saw. Just a bigger bore with the same stroke.

[prophiseer]

I'm a bit confused. So, the deck is wider (valley to front of block) than the 31/34 gen3's? How do they manage that large of a bore size without actually elongating the block itself, if the're side to side? Just to clear this up a bit, you do mean the cylinder placement is like this:

--o---o---o--
----center---
--o---o---o--


as compared to something kinda like this

------o------
--o-------o--
----center---
--o-------o--
------o------


which is the impression I got from some of GM's press releases on the 3900

[CNCguy]

Perhaps this will clear things up some.

3400 is like this:

-o---o---o-
---center---
-o---o---o-

3900 is like this:

-o---o---o-

---center---

-o---o---o-


The bore centerline was moved out 1.5mm and the heads were made wider to compensate. Center to Center is the same from front to rear and the overall length of the engine is the same but the width of the block changed just a little... maybe an 1/8" or so.

When you put the 3400 head on the 3900, the cumbustion chamber is no longer centered over the bore.

[CNCguy]

One other thing... the bore centerline no longer matches the centerline of the crank. IIRC the intersection of the bores is about 1.5mms below the centerline of the crank now.

[prophiseer]

yeah I had heard something like that before, too. That all clears it up, though, I get it. So that practically eliminates 90% of the components from swapping 'tween the motors.

Them shiesty engineering bastards!

[RacerX11]

I think GM got that 3.4 displacement when they also take into account the volume of the dish in the piston, and the volume of the combustion chamber in the head

GM engineer's have always liked to "ruffle" their feathers, I guess you could say

Where do you come up with this stuff? Piston dish and combustion chamber volume have absolutely nothing to do with engine displacement. The 3.4L displacement comes from rounding 3350cc to the nearest tenth of a liter. Has nothing to do with ruffling of feathers.