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

[The Dark Side of Will]

Yeah, your math is right.

Who makes a 5.9" rod??

[Shaun41178(2)]

I can only assume they are custom. 5.9 inchers seems odd to me as well.

They appear to be custom though.

Looks like someone can do something here with these. might be worth a shot?

hell who knows.

[crzyone]

Will, are you saying with a 2.8 crank and forged flat top pistons the tdc would have 8.5-1 comp? Is this with stock rods or the 6" rods?

That would make building a turbo tdc pretty damn easy. I'm assuming thats with stock pin and deck height?

I was thinking about building the motor for NA power, but I have my turbo just sitting there, I could get an easy 300-350hp out of this thing.

Thanks!

[The Dark Side of Will]

The block deck height is 224mm (8.818"). The 2.8 crank throw is 76mm/2 (1.496"). With a 6" rod, that would require a compression height of 1.322" (not stock) in order to achieve a zero deck piston.

With an overbore to 93mm, a chamber volume of 54cc's, for the sake of argument an 0.040" head gasket and 4cc valve reliefs, the engine would have ~9:1 compression... Looks like you'd need a smidgen of a dish or teensy bit bigger valve reliefs to get down to 8.5:1. Without the overbore it would probably be down around 8.5:1

I would advise AGAINST having a piston with lower compression height made, as that would open up your quench height and screw up your combustion characteristics. IMO, one of the biggest reasons for building a 3.0/3.1 this way is the very high rod ratio an accompanying detonation resistance. I'd hate to see someone build one of these engines and then fuck away all that detonation resistance by building it with 0.080 quench....

[crzyone]

Thanks Will


If I go to a company and say I need a set of forged pistons for a 3.4dohc bored 30 over and I need 8.5-1 comp, will they know what I need or would I have to tell them dimensions?

Thanks again
Levi

[The Dark Side of Will]

You'll probably have to give them the dimensions I spelled out above. You may have to send them a sample from which to work and spell out what changes you need made to it.

I'm going with flat tops because they're cheaper and I'll just live with whatever the compression ends up being, since it's going to be 9:1 or less. If you can deal with that, we can go in together and get two sets. We might find a place that can cut us a price break for orders of more than one set.

I'm thinking a pair of DSM or TGP T25's shouldn't be working too hard making 350-400 RWHP and would still be reasonably responsive...

Before I spec piston dimensions, I'd like to get my hands on a set of rods. That way I could get an estimate of piston weight from the piston mfg I was planning on using, then talk to the rod mfg about rod stretch at my planned redline, then spec the compression height of the pistons for PERFECT quench at redline.

[The Dark Side of Will]

Thinking about it some more... the thickness of a custom copper head gasket could also be used as a tool to fine tune quench characteristics...

[crzyone]

Tell me when you are looking at getting forged pistons and I will go in with you. Should be cheaper for 2 of us. I will keep my motor stock till then. Are you going to use the 2.8 crank and 6" rods?

[The Dark Side of Will]

Yes. 2.8 crank and 6" rods.

[Shaun41178(2)]

if you were going to use a 3.1 crank there are Hyper pistons on the market that you could use for a 3.4 iron head pushrod that would prob give you compression around 8.7:1 or so.

It has a dish of around 10 cc's and with a 52 cc head chamber on a 3.4 that works out to about the stock compression ratio of a 3.4 iron head motor.

Yea its not forged but they are stronger then cast.

[The Dark Side of Will]

I got to thinking about this some more today...

With 6" rods and a 76 mm crank, the pistons would need 1.322 CH to come out zero decked.

With 6.125" rods and a 76 mm crank, the pistons would need 1.197 CH to come out zero decked.

I believe that this is workable for non-forced induction applications, but I'll have to talk to a piston MFG about it.

If that's workable, then an 84mm crank with 6" rods and 1.164 CH might be doable as well.


Why go to a 6.125" rod on a 76mm crank when we already know that the 6" rod will work?
Hot rodding at its best... If some is good, then more must be better.

[Shaun41178(2)]

compression height is getting very minimal. You do need somewhat of a ringland area or the rings will burn

[The Dark Side of Will]

Yeah, that's what I was thinking, but I'd like to talk to someone about it...

[The Dark Side of Will]

Bump.

Getting my credit card paid off... Looking at getting rods within a couple of months. Anyone else still in?

[Shaun41178(2)]

I might have been. Maybe still. Problem is finding a good boat anchor dis crank. they are getting pretty rare.

However I will prob just stick to the 3.1 crank and pistons since I have both and both are new.

[The Dark Side of Will]

Bump.

Had an idea for a quick/dirty build that gets better mileage AND makes better power than my 2.hate. This info was VERY handy. Where did you find it all? I'd like to add it to the Tech Articles thread.
Can you find similar info for 3900's and both 94mm and 99mm 3500s? Thanks.

Also, a 2.8 crank with 5.850 rods would take a piston comp height of 1.472 for zero deck. A 3.4 PR or TDC piston would be .015 in the hole. A 3400 piston would be about .012 in the hole.

Eagle makes 5.850" conrods for the 2.000 main journal diameter. They're over $600 for a set of 8, but they're off the shelf.

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:

Code: Select all

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

_________________

[The Dark Side of Will]

I think the dish volumes for 3.1 and 3.4 iron head pistons are swapped in the data above.
I think the 3.4 has a 12 cc dish and the 3.1 has an 8 cc dish. That puts 3.1 compression at 9.0 and 3.4 compression at 9.1.
With the dishes as listed, 3.1 would have 8.5 comp and 3.4 would have 9.6 comp.

[Kohburn]

I thought the 3.4 was listed as 9.1:1

[The Dark Side of Will]

test

Why the F@#$ do I get a 404 when I try to post what I actually wrote?

[The Dark Side of Will]

This thread lists the chamber volume for 3500 heads (presumably early 3500 with 94 mm bore) at 32cc.
http://60degreev6.com/forum/showthread. ... 463&page=2