3400 block and 2.8 DIS crank make a 3L rev monster?

donk_316 · Post by **donk_316** » Tue Nov 30, 2004 9:07 pm

Well...

This topic came up over MSN between Shaun and I.

Could you use 6" rods instead of the 5.7" rods and use 3.1 or 3400 pistons?

Aftermarket 6" SBC rods arent expensive at all...and this would stick with my "being different" motor build.

2.8 stroke- 2.992"
3.1/ 3.4/ 3100/ 3400 stroke- 3.312"

Diff of 0.32".... so the increase in rod length would eat 0.30 leaving 0.02 to be either having the piston down the hole or made up with a custom moved pin piston.

3400 bore- 3.622"
http://60degreev6.com/modules.php?op=mo ... =15&page=1

The Dark Side of Will · Wed Dec 01, 2004 8:44 pm

Bad math.
The stroke difference accounts for 0.16", not 0.32".
I looked at things once, and with the bore punched out to 93 MM and using Northstar pistons, the 76mm crank would require 6.050" conrods. So yes, pushing the pin up far enough to use 6" rods in a 3.0 or a 3.1 destroker is quite possible.

I'm going to build up a TDC like this sometime...

The Dark Side of Will · Wed Dec 01, 2004 8:46 pm

Bad math.
The stroke difference accounts for 0.16", not 0.32".
I looked at things once, and with the bore punched out to 93 MM and using Northstar pistons, the 76mm crank would require 6.050" conrods. So yes, pushing the pin up far enough to use 6" rods in a 3.0 or a 3.1 destroker is quite possible.

I'm going to build up a TDC like this sometime...

Shaun41178(2) · Post by **Shaun41178(2)** » Wed Dec 01, 2004 9:31 pm

I remember you saying it was .16 before but dont' remember why.

I thought it would be .32 as simple subtraction tells me that.

How is it .16?

Thanks.

2.8 · Post by **2.8** » Thu Dec 02, 2004 3:34 am

Shaun41178(2) wrote:How is it .16?

The piston goes up the hole 0.16" further and then down the hole 0.16" further, for a total travel of 0.32" further.

2.8

Shaun41178(2) · Post by **Shaun41178(2)** » Thu Dec 02, 2004 1:17 pm

2.8 wrote:
Shaun41178(2) wrote:How is it .16?
The piston goes up the hole 0.16" further and then down the hole 0.16" further, for a total travel of 0.32" further.

2.8

Ahh ok gotcha on that aspect.

When using a 6 inch rod though and a 2.8 crank, you dont' change the stroke at all you just move the piston .3 higher up in the bore. so if you used a 2.8 piston on a 6 inch rod your piston would now sit .3 higher in the bore at TDC.

So what we have to do is find a way to move the piston pin down on the piston. This is accomplished on a 3.1/3.4 piston. We need to try and bring the distance of the piston at TDC back to where it would be at on a 2.8 with 5.7 rods

Compression height on a 2.8 HO pistons for iron heads is 1.599 CH for a gen 2 3.1 piston is 1.45. CH for a 3100 is 1.47 and the CH height for a 3400 is 1.46

Difference with a 3.1 piston is .149 in CH from a 2.8 iron head piston.

Someone else do the math for me but where does this put the piston at in comparison to the Deck Height in relation to the old 5.7 rod and 2.8 piston? Almost seems to me the 3.1 piston would still be sitting .15 higher in teh bore at TDC

by doing all of this I am prob just confusing myself more. I never did well in Math. Alg 2 I was a B- student so its not my strong point.

Data taken from this on 60 degree

Code:

Application Dish/Dome C/H
2.8 LO 0 cc's 1.578
2.8 HO 0 cc's 1.599
3.1 12 cc's 1.450
3.4 8 cc's 1.457
2.8 Gen2 21.2 cc's 1.608
3.1 Gen2 26.4 cc's 1.450
3100 24.5 cc's 1.470
3400 27 cc's 1.460
TDC 5 cc's 1.457
DOHC 5 cc's 1.457

Head Chamber size
Gen1 48.5 cc's
Gen2 26.4 cc's
Gen3 26.4 cc's
TDC 54.0 cc's
DOHC 51.5 cc's

Misc: Gen2 stock head gasket: 0.060
Gen1 stock head gasket: 0.040

_________________

Shaun41178(2) · Post by **Shaun41178(2)** » Wed Dec 08, 2004 10:34 pm

The Dark Side of Will · Wed Dec 08, 2004 10:46 pm

I think the deck height of a V6/60 is 224mm (8.818")

So with a 76mm crank, 6" rods and zero deck pistons, the pistons would need a 1.322 CH (33.58mm). This is easily done. The factory N* compression height is 32mm, and there's room to move the pin up a little bit in that piston.

If you knock the CH down to 1.164 (29.58mm), then you can fit a 6" rod with an 84mm crank, but that's getting to be a pretty minimal CH, especially for forced induction...

Shaun41178(2) · Post by **Shaun41178(2)** » Wed Dec 08, 2004 11:26 pm

those these pistons prob wouldnt' even work then huh.

It looks like in the pic that the CH is 1.242

Like these pistons would sit too deep in the block whereas the 3.1 pistons would sit too high.

Correct?
[/img]

The Dark Side of Will · Wed Dec 08, 2004 11:39 pm

That's correct...

Who in the hell made those pistons and for what? With 76 crank and 6" rod, they'd be 0.079 in the hole... with 84 crank and 6" rods, they'd be 0.078 out of the hole... WTF?

Shaun41178(2) · Post by **Shaun41178(2)** » Fri Dec 10, 2004 4:57 pm

so you would need a rod that is 6.079 inches long to have 0 deck height? Thats correct right?

I am starting to consider this for my alum block build.

6 inch rods are cheap, already forged, and should hold up to high rpm better then the stock forged.

I want to say I need a crank dia of 2.1247 as thats what GM says. Ones I see on ebay doing some research many have a 2.100. I am sure this makes a difference or the seller is rounding off the numbers to make it easy.

Also anyone know the weight of a stock rod?

Shaun41178(2) · Post by **Shaun41178(2)** » Fri Dec 10, 2004 5:27 pm

meh the more research I do on this the less I want to do it.

The cost doesn't really outweigh the benefits of it. quite a bit of machine work would need to be done on the rods to get them to work which just adds to the cost. Almost after everythign is said and done, it would almost cost as much as a set of performance rods specifically made to the v6 journal and pistons specs. And those arent' all that cheap.

stock rods shotpeened and polished should be good enough for me anyways.

The Dark Side of Will · Fri Dec 10, 2004 7:33 pm

Are you saying that the GM spec for inside the rod is 2.1247? What I have says 1.9987-1.9994. The bore in the rod may be 2.1247, but that's the journal size PLUS twice the thickness of the bearing insert.

The V6 and early, small journal Chevies have the same size journals... Should just need to have the big end narrowed, and whatever has to be done to get the wrist pins to work.

A 6" rod should be plenty economical; a 6.079" rod would cost...

Shaun41178(2) · Post by **Shaun41178(2)** » Fri Dec 10, 2004 10:35 pm

yea its 2.147 or whatnot. Thats prob without the bearing in it. Its straight from the GM performance parts catalog

So I guess I need a 2 inch bore with the bearings. large journal must be 2.1 and small must be 2.0.

I see them for around $200+ on ebay. With that would require custom pistons, even more money. Not really worth it for my power goals.

The Dark Side of Will · Fri Dec 10, 2004 10:38 pm

L99 conrods are 5.940", which would get those 1.242 pistons down to 0.18 out of the hole... but the L99 is a late engine with 2.100 rod journals.

Where did those pistons come from anyway? What was their original intended application? What's the bore? 3.598? That'll give you 4 thou of clearance on a completely virgin block...

Shaun41178(2) · Post by **Shaun41178(2)** » Fri Dec 10, 2004 11:03 pm

THey were on the 60 degree board in the mall section. Some custom pistons someone had and was trying to sell. I thought about getting them, but I saw the CH and knew they wouldnt' work so I passed. yea they have a stock bore pretty much.

This is such a ghetto idea. But maybe one could use oversized bearings to bring the rod journal bore diameter down? I am sure you could get the clearences close but its prob not a good idea.

The Dark Side of Will · Fri Dec 10, 2004 11:33 pm

Yeah, people use bearing spacers to put standard Chevy cranks into 400 blocks, but those are main bearings... I don't think the rod bearings would be a good idea... that's reciprocating weight that doesn't contribute to the strength of anything...

donk_316 · Post by **donk_316** » Tue Dec 14, 2004 4:24 pm

ok so why not just go with a set of 60 degree rods on a 2.8 crank with custom pistons. Would be alot easier then custom machined rods.

Still benefiting from the destroked motor and same rod ratio as a 2.8

2.8 crank with 5.7 rods is a 1.9 r/s ratio
2.8 crank with 6 rods is a 2 r/s ratio
Not a huge difference to warrant the kinda expense we are talking.

This motor with worked 3400 heads would =>fucking<= scream easily to 7000 rpm... maybe farther assuming the rods are worked stockers with ARP bolts.

Bolt on a 3500 open plenum, 65mm TB (480cfm) and my turbo. My god.... I have wood.

Shaun! Wanna hog out some 3400 heads for me? ZOOM!

The Dark Side of Will · Wed Dec 15, 2004 7:54 pm

Because 6" rods are by definition cooler than 5.7" rods.

And because narrowing the rods is really not that hard. Especially for individuals like myself who have access to a machine shop. Small journal 6" rods are readily available.

And the fact that every little bit helps. The increase from 1.9 to 2.0 isn't as beneficial as an increase from 1.6 to 1.7, but it is still an increase and is still beneficial.

Post by **eHoward** » Wed Dec 15, 2004 8:09 pm

A little birdie tells me that 1.75 is the ideal rod to stroke ratio.