destroked 3400?

[Wulfgeist]

Hi! new to the forum and looking for advice on an idea i had. Is it possible to put a 2.8 crank into a 3400 block? I am looking to create a higher revving engine by utilizing long rod theory as well as the improved flow of the gen3 heads. From what i understand in order to build a race type motor you need a large bore, short stroke and long rods. this is what this motor would be used for. By the way shall the article on Colin's car in grm, got me to thinking about this.

thanks for any help!

[Guest]

It can be done. I see 6 inch SBC rods on ebay for cheap all the time and are forged as well. Only thing you will need custom are the pistons. I don't know how to go about figuring out compression height nor or dish volume.

Although you might be able to get away with 6 inch rods and then use 3.1 pistons. I heard someone mention that one time. since you are adding .3 inch stroke to the rod, and are subtracting .32 from teh crank, it might work out to do it that way.

It would be able to spin to 7500 rpm no problem but you will need a heavy duty valvetrain and probably a big cam to take advantage of the higher rpms. The cam prob wont' be streetable then or have a horrible idle. Stock computer might not be able to handle it so a aftermarket computer would be needed. Which adds even more to the cost. Maybe an agressive regrind on the cam and then a reprogram of the idle speed if thats possible. It might idle at 1300 or so but the sacrifice for performance could be worth it.

DOnt' know of anyone that has really done it and then reported on it.

SHaun

[Wulfgeist]

I'm not so sure about the 3.1 pistons, since the 3.4 has a larger bore.

[v6h.o.]

you can use a set of narrowed 6inch rods for a Small Journal SBC.

you will need a set of custom pistons for the engine. you will have to raise the piston wrist pin location IIRC 0.150 inch (stock 5.7 inch rod, long 6inch rod is .300 inch longer, half distance =.150.) however check the math on the compression height and deck height.

this has been disscused before (3000 engine, 2.8L crank in a 3400 block) alot of people agree that its best to keep the larger displacement.

[Guest]

My bad. I mean 3.4 pistons. just a typo.

I want to say the 3.4 pistons have a higher pin hight then a 2.8 piston.

So like I said. you take .32 off of the stroke by going to a 2.8 crank. WHich means if you use stock 5.7 rods the pistons woudl then be at a height .32 below the deck surface. that is if we assume deck height is zero. However when you add 6 inch rods you now have the piston back .30 closer to the deck height. Which means you lost a total of .02 inches by going to 6 inch rods and keepign the 3.4 pistons.

I might be wrong and if this is a bad idea then someone chime in but it almost makes sense to me.

But yea, unless you have a cam and a valvetrain able to support 7500 hp it isn't worth it to destroke it. You need more rpm to make hp to help offset the loss of low end torque.

I think this would be better suited for a 3.4 DOHC engine wear it can breathe really well at that rpm anyways.

[blk92z34getrag]

7500 hp

[donk_316]

he means RPM not HP

[Guest]

Your correct. I am a tool.

[Chris88CL]

So theoretically I could run the 3400 block, 2.8L crank with tha 6" SBC rods and have a SLIGHTLY lower compression ratio using the 3400 pistons?
Does anyone make forged aftermarket pistons for the 3400 yet?

[TurboZ24]

The rod to stroke ratio (which is already pretty high on the 2.8/3.1/3.4) isn't really going to be a factor in getting the 3400 to rev high, it's more the valve train and the intake/exhaust setup. I rev mine to 7500+ all the time with no problems, but I also have a roller mechanical valve train and extensively ported heads.

As for Forged pistons, you can get them from any custom piston company (I got some from Ross), but no one seems to have the correct wrist pins in stock (and no companies will sell them except with the cast pistons), so I had to have some made.

[GPXSS]

Your correct. I am a tool.

and a bad speller