[ForcedFirebird]

Originally Posted by 95Grand-Am

3400 rods are not offset, but the pistons wristpin bore is off set in the piston.

I'll want to verify this. Without taking extremely accurate measurements, the wristpins always looked centered to me on the rods.

John,

What's the total width of the big end on those rods?

The 3500 rods are centered.

[betterthanyou]

Yes the wrist pin bore of offset to the thrust side of the piston, not the same thing we are talking about here. All engines are like that.

4.3L Rods have been offset since the first even fire and semi even fire engine was produced. The offset is .100 and was a result of splitting the rod journal to get an even fire motor.

Our engines have individual throws for each cylinder so it was designed right from the start.

[ForcedFirebird]

Originally Posted by betterthanyou

Yes the wrist pin bore of offset to the thrust side of the piston, not the same thing we are talking about here. All engines are like that.

4.3L Rods have been offset since the first even fire and semi even fire engine was produced. The offset is .100 and was a result of splitting the rod journal to get an even fire motor.

Our engines have individual throws for each cylinder so it was designed right from the start.

So the ecen fire SBC's are handled the same way?

It would seem that the meat between the journals would be really thin since each rod pin previously shared two rods. I'm unfimiliar with the new generation SBC's, haven't had one apart in years and it was always Gen1's.

[Driver_10]

This leaves me with few options. Im either going to have to

A. have the crank jounels ground down to 2.100 and purchase conventional 5.7l "5.700" con-rods

OR...

B. special order a set 5.700 con-rods with a custom 2.250 crank-bore.

Either option is going to set me back a K.

Does anyone have any ideas?

[betterthanyou]

Originally Posted by ForcedFirebird

So the ecen fire SBC's are handled the same way?

It would seem that the meat between the journals would be really thin since each rod pin previously shared two rods. I'm unfimiliar with the new generation SBC's, haven't had one apart in years and it was always Gen1's.

Even fire SBC? They have always been that same way.

V8's have no problems since a pair of cylinders share each throw. There are 4 of them offset 90*. There is no meat between each con rod and they are allowed to touch each other and there is only a fe thou left for side play.


The problem arises on the 4.3L since they modeled it after the small block. They kept the bore spacing and cylinder bank offset the same. When you make an odd fire 90* V6 you have no rod offset. But when they make it into an even fire they narrow the bearing journal of each rod and then offset each throw 30*. The narrowing of the journal happens on one side only and gives extra meat between the split throws. So now you have each rod big end separate by about 0.100" this meat is then take out of the con rod big end and bearing.

Buick did things differently. They decided not to narrow the bearing journal and instead moved the rod over towards the counterweight to allow for material between the split lobe. The con rod beam was offset on the con rod big end but this design still requires offsetting the con rod in the cylinder bore and of course on the piston pin. So on the Buick you keep the big bearing cross section but your now offset on the big end and small end of the rod. It have never been an reliability issue. But for all out competition and drag racing, builders go with a forged odd fire crank and live with the vibration of the staggered firing pulses.

[ForcedFirebird]

Ah yes, what was I thinking? The reason ofr the odd fire in the 1st place is the 120* crank throws and 90* bank angle.

John,

What about having the 3500 crank ground to the 327 5.7" rods, or were you looking to keep the larger rod pins? I haven't heard of anybody managing to break a rod pin with the iron cranks, now that you have a forging, I don't see you having problems.

[Driver_10]

Originally Posted by ForcedFirebird

Ah yes, what was I thinking? The reason ofr the odd fire in the 1st place is the 120* crank throws and 90* bank angle.

John,

What about having the 3500 crank ground to the 327 5.7" rods, or were you looking to keep the larger rod pins? I haven't heard of anybody managing to break a rod pin with the iron cranks, now that you have a forging, I don't see you having problems.

I may look into SBC "big pin" con-rods and a reground crank. That seems to be my only viable option. (I believe that thats a 2.150 or a 2.200 crank-bore)

[ForcedFirebird]

Originally Posted by Driver_10

I may look into SBC "big pin" con-rods and a reground crank. That seems to be my only viable option. (I believe that thats a 2.150 or a 2.200 crank-bore)

Sounds good. You can get them on the cheap, Eagle H-beams go for less than $400/set of 8. You will probably just have to shave the big ends equally (both sides) for width.

Here's an ebay site with them less than the Eagles and seem to have a lot of options for length and pin sizes...

http://cgi.ebay.com/ebaymotors/CAT-C...spagenameZWDVW

[project89]

we had a customer build a nitrous motor with a set of ebay rods, he never had an issue with them and there cheap.

im not sure what place he got them from on ebay but i can ask him if u like

they were something liek this 250-300 bucks for the set
http://cgi.ebay.com/ebaymotors/SB-CH...QQcmdZViewItem

[MidnightriderZ24]

heres the best picture i have.. i had to machine mine to fit the 60* crank..
http://s433.photobucket.com/albums/q...00BUILD006.jpg