Bore and Stroke

[Bliggida]

Anyone ever checked with a professional machinist, or internal engine parts company to see what the limits are for a 3.8L to be bored and stroked.
If so, please list which company or with whom you spoke with.

Do not reply if your brothers' girlfriends' Sisters' Cousin, on his mother's side who knows this guy who is friends with a mechanic told you it was xxx.

Looking for these bore possibilites:
3.83, 3.86, 3.925
And these stroke possibilities:
3.67, 3.92, 4.045 (or 4" even)

[Arctc Wolf]

I have heard that 8.83 bore is max for ours because of water jackets and cylinder wall thickness issues. stroke, I haven't figured out yet since I don't know block height or compression height of our pistons.

[Bliggida]

Block deck heighth is 216.5mm.

If by cylinder compression of the pistons you mean the deck clearance. That's 0.57mm.

If you are just asking compression ratio 9.4:1 but I don't see how that would affect anything, so maybe I'm misunderstanding you.

Askin' the distance between the piston at TDC and the heads (valves)?

[SLOWBRAEATER]

mine is bored .030

[Arctc Wolf]

I mean that there's a height of the pistons from the wrist pin that helps 2 figure out how much more stroke you can run. compression heights such as 1.5, 1.25, 1.125, ect. That deck height doesn't seem right. That's 8.523 inches tall. we have a 5.7 inch rod, plus 1/2 stroke length=7.4 inches. with a piston at tdc, no deck clearance, we have 1.123 inches for piston compression height. That's minimum for piston compression height w/o sacrificing the piston rings. basically you can only play w/ the rod and stroke ratio to make more displacement. Rod angularity will kill high rpm potential, since too much rpm and too much angularity means overly stressed rod bolts and mains and can cause catastrophic engine failure. Unless u can somehow bolt on a custom block spacer between the block and heads, u can't up the stroke very much.

[ April 01, 2003: Message edited by: Arctc Wolf ]</p>

[Bliggida]

I got those numbers directly from GM specs catalog. May be odd, but I believe it to be correct.

Your point makes sense, and that's what I thought you were talking about.

However the RPM issue really isn't an issue I don't feel.
A) How many years has Hot Rod Magazine (and the like) made 415+ci small blocks rev at 8,000???
and B) a car that makes 200 horsepower and revs to 7000 is still going to lose to a car that has 300 horsepower and revs to 5000.

according to the "MVMA Specifications" I have the following numbers...
Bore 96.5mm
Stroke 86.36mm
Bore Spacing (C/L to C/L) 107.0mm
Cylinder Block Deck Height 216.5mm
Cylinder Block Length 396mm
Deck Clearance (above block) 0.57mm
Cylinder Head Volume CM3 62.9mm (3.81 inches)
Head Gasket Thickness (compressed) 1.5mm
Minimum Combustion Chamber Total Volume 75.675 (4.168)

Sorry if the wording sounds off, that's what GM lists those things as. Not mine. Dunno if those numbers will help.

Block weighs 120 pounds, and the heads are 29.3 pounds. Total weight fully dressed but dry, with manual tranny is 454 pounds. Not too bad.

[Slow-N-ugly]

Are you looking for a stroker crank?

Bore isnt much good, basicly good for rebuilds and I would think we could go atleast .40 but I dont know.

Artic wolf are you sure we can go "8.83 bore is max"
Thats a big honkn' hole man, I would think under 4.0 max. And "1/2 stroke length" nope its got to be around 3.25 I would think.

[Arctc Wolf]

oops, i meant 3.83". if you go 3.83 bore on a stock crank, you'll hit 4.0 liters I think. My main worry is that you'll hit a water jacket inside the block, and then u need a new block. also, cylinder head and combustion chamber volumes don't mean nething when looking at bore/stroke specs, it only matters when ur messin w/ compression. what do u mean by deck clearance? is that how much depth between the piston and top part of the block when the piston is at TDC?

[67-03 RIP]

I would probably be careful going over .040 regardless unless you check bore thickness. Bores that aren't centered totally (core shift) could give you a problem. Probably any potential stroking (of any benefit)would require a special piston because of where the wrist pin is located. For example, putting 400 cranks in a 350 to make a 383 requires different pistons than the stock 350 wrist pin height. Don't know what the aftermarket is like for the 3.8, but there might not be the availability of those cool things like 6 inch rods, out of the box stroker cranks and pistons. Of course everything could be custom made to spec - simply hold out wallet while bending over at the waist...

Fun idea though!

Ron

[Bliggida]

If I do this (if it's worth it) I will of course be running aftermarket rotating assembly. So of course pistons will be changed out.

As for deck clearance. I feel the same as you Artic Wolf, I think that is what GM is trying to say. Why they have to be different in wording I have no clue. But, I think we are both reading them right.

The stroker 3.8L will be based on making 1HP per cubic inch. That's about the only time a bore and stroke is worth it anyway. Compression will be sky-high too.

If it can be done, I'll spend the money it'll cost for custom work. If not, then I'll look elswhere. Maybe start with a 4.3L block? (doubt it)

Just still in the planning stages, no sense getting all hopped on it if not possible.

[Arctc Wolf]

i don't think it'll be worth it. way too much custom work. also, it seems that GM has stroked it out as much as it can already, unless u wanna go maybe up to .2 bigger, maybe up to .3. it's not very much, and you won't see much of a gain out of it. perhaps if this was done to a sc'd or turbo'd motor, you'll see some decent gains from it. you can easily get 1 hp per inch from our motor w/ basic bolt-on's and a cam. head's will make it more than 1 hp per inch. perhaps lower compression would give us more deck clearance to fit an even longer stroke in there, or improve the rod:stroke ratio w/ a slightly longer rod.

[Bliggida]

Stock stroke. Hmmm, up the compression goes then! Power will go up another 8 percent. Maybe I should look at a 4.3L V6. Stuff that in there. That way instead of 231 cubic inches, I could be making 321 cubic inches. 5 Liter V6. Hell yeah. But no, by that time I will have hopefully scored an SS. But Hot Rod tested a Vortech blown 4.3L and make 500 horsepower before puking a gasket. It was bad-@$$.

[00swartz]

check with www.merkelengines.com