Just buttoned everything up today - swapped ina 99 vortec L31 from my 350 sbc. same trans/TC but had to buy a new flex plate cos rear crank mount was narower.

I also noticed the old sbc had a big flange on trans side of crank on outsie but L31 had nothing.
Anyway hoped down to oreillys - gave them car year and the flex plate had a big weight on the one side.

Anyways - there is a vibration esp when in drive.. car has almost zero power, I have to half throttle t move it up small hill.

I triple checked plug wires, car fired up immediately actually. as about 6 degrees off initial timing only.


A: could the weight on the flex plate be the wrong type? ie do I need a neutral flexplate?

I would have thought the flexplates would be the same for a 350, esp since they have the same blocks..

this was from a 99 suburban or something - 4L60 trans iirc.

and what could be causing the power loss? I did grind off 1mm of the governor as per a tutorial I found to make the shifts later -

I did install this same trans/TC in my sbc and it ran fine. Checked fluid levels few times after first short drive - all good in motor and trans,

quite stumped. was hoping to go on long trip today - guess not

 

far as i can tell, the 350 uses a neutral flex [ate and the 400 has a large weight welded on it.. like the one given to me by oreilleys so clearly the wrong one! that explains the vibrations. will return/swap it 2moro.

Will that also explain the power loss??

 

The 1-pc-rear-main-seal crank in ANY small block from 86 up, including the L31, requires the rearmost bit of internal balance weight to be mounted externally, on the flex plate or flywheel. So no, you do not need a neutral-balanced flex plate for that; and in fact you will most likely be unable to find such a one that will fit your crank because there's no such thing in the real world.

And of course, that doesn't account for lack of power.

Sounds more like you have 2 plug wires swapped. I'd verify that they are in the correct order around the dist cap REAL carefully to start with, especially #5 & #7, no matter how many times you've "checked" them so far. I'd suggest instead of "checking" that you take them all off completely, and put them all back one at a time with great care and attention to detail.

 

ok will do thanks! yes the power loss isnt related to the balance issue, perhaps it is something else.. ok on the flex plate.

if i installed the flex plate wrong way around would this cause problems? I looked at the one from my sbc and saw a slight rise on the centre part where thebolt holes are and installed it the same way.. I THINK it was with the rise towards trans, i think..

 

double checked everything todayon engine side. whining noise coming from trans tc. guess I'll have to pull it and check..