rod to stroke

[butchville]

i'm fixing to rebuild a 3.4 dohc was pondering the idea of 4.3 ford pistons on a .83 overbore an 6 inch rods the pistons are stock 4v per head forged in the speed pro piston cataloge any thoughts just a idea>

[v6h.o.]

i've gone through the whole sealed power piston catalog and havnt really found anything from another application that will have the right Compression Height for 6inch rods...

[Anonymous]

You mean .083 overbore, and Gm says that .060 is the biggest safe bore to the block.

[RacerX11]

0.083" will work.

Marty

[Anonymous]

This site says that .080 is risky, and that's enough discouragement for me. And since he is building the motor to performance spec, I'll assume he'll bump compression, or run boost. Wicth IMO would make this .080 bore even more risky, maybe even dangerous.

http://60degreev6.com/modules.php?op=modload&name=DOHC&file=index&req=viewarticle&artid=8&page=1

But yah, it will work and go together, just not last very long...Especially if you are running 260+hp at 7,000rpm.

[RacerX11]

If you check your block for core shift before boring, there shouldn't be a problem. The difference between a 0.083" overbore and the "magical" safe limit of 0.060" is so small (11-1/2 thousanths wall thickness difference) that you won't significantly impact the durability of the engine.

I'll let you know next spring how my 0.120" overbore 3.1 block likes boost. It seemed to handle the high compression and high rpm beatings just fine for 3 years.

Why do you say only 260HP at 7000rpm? Don't think he can hit 400HP @ 8000rpm like you?

Marty

[Anonymous]

I said 260+, and I was just assuming that he wasn't building the motor nearly as much as we will be. Anyone can hit 400, it just takes some knowledge, money, and time.

[butchville]

but do i have a advantage by using 6" rods

[Anonymous]

but do i have a advantage by using 6" rods

I don't now if you'll be able to get away with 6" rods, it depends on your pistons. Hopefully the custom ones won't run into clearence issues due to them being cut for the 6.0" rods. IMO, you'd probably save a lot of money and time by just sticking with factory 5.7s. How much of a build is this?

[SappySE107]

Well, it depends on who you listen to. Some say the higher the ratio, the better. I prefer the 1.72-1.75:1 ratio as ideal theory...probably because that makes our stock ratio perfect. Either way, you will want to research this and come to your own conclusion.

http://60degreev6.com/modules.php?op=modload&name=Sections&file=index&req=viewarticle&artid=18&page=1

If there is anything I haven't put on that page that needs to be, let me know.

[butchville]

i'm working on a 6-71 gmc blower to a 3.4 dohc with 40 psi boost on top end blower driven by the cam belt

[SappySE107]

If you are serious...im gonna laugh my ass off.

[butchville]

i'm serious the bugcatcher is going to be straight ahead blow excess pressure off with electric valve at idle an use boost computer to close valve inrefference to rpm should be different also the big blower wont biuld heat like overdriving a small one may use propane as fuel for octane rating an cooling effect should burn a rising sun or too.

[SappySE107]

Did you research the flow chart on that supercharger? The cam belt spins at half speed so its not going to do you any good to drive a SC off that. In fact, its bad for the cam belt to begin with (which would be custom length for the SC as well).

[Anonymous]

IMO a 6-71 might be a wee bit of overkill...

I'd use a M90, maybe a 112.