JCI mounts LS1 centre alignment?

[Boy from Oz]

I'm attempting to install a GM IRS diff. It has about a 60mm pinion offset and I am wondering whether a JCI mounts LS1 has the tailshaft running offset from the centreline of the vehicle which might address the diff offset to some extent. I thought I read somewhere that it does!

[VinhZXT]

The original drive line is offset to the passenger side by 3/4" relative to the center line of the 2 frame rails. On my LS1 swap where I made my own mounts that's where I put the motor. However I also install JCI mounts on my friend's LS1 swap and I didn't bother to measure where the motor sit. I can check the measurement and get back with you later on. I did 120MPH plus on my friend's LS1 Z with JCI mounts and there was no vibration at all. So I think the driveline has to be very close to the original driveline.

[Pop N Wood]

Pretty sure the JCI mounts are offset to the US passenger's side. So if the GM diff is offset to that side you should be good.

 

You also know the diff and motor don't have to be centered on each other to be OK. As long as they are parallel and the total offset (left right plus up down) is within reason there will be minimal vibration.

[Boy from Oz]

Vinh - I would appreciate it if you could confirm there is an offset and the actual measurement. I will contact JCI as well.

 

...and the total offset (left right plus up down) is within reason ...

 

Can you give a value?

 

The original donor car setup is a two-piece shaft with a CV located in the middle. The service manual sets the vertical alignment to zero with very little tolerance for both shafts but states nothing about the horizontal setting. I'm guessing that's because there is no horizontal adjustment and vertically it's implying more about ride height rather than tailshaft alignment.

[Pop N Wood]

Most articles say you want 3 to 5 degrees of static alignment. So figure the total offset can't be more than say 7% of your driveshaft length

(i.e. 0.07*DSLength). That works out to 4 degrees of driveshaft angle.

[Boy from Oz]

Most articles say you want 3 to 5 degrees of static alignment. So figure the total offset can't be more than say 7% of your driveshaft length

(i.e. 0.07*DSLength). That works out to 4 degrees of driveshaft angle.

 

Do you have a specific reference for this information? Thanks.

 

John (JCI) advised that his mounts are offset 25mm (1").

 

If I use the formula above, 0.07 x DS length [0.07 x 20.75" (530mm) = 1.5" (37mm)] and add the 1" (25mm) then a diff with a pinion offset of 2.4" (60mm), i.e. the GM diff, should be okay centrally mounted.

 

20.75" = http://forums.hybridz.org/showthread.php?t=94188

[VinhZXT]

JCI mount engine placement:

From the left frame rail to the center of the crank pulley bolt = 13"

From the right frame rail to the center of the crank pulley bolt = 12 1/4"

The center of the crank pulley bolt is 1/2 " below the frame rails.

 

I didn't have a chance to measure the drive shaft relative to the various points of the body and frame. Will do it next time when I have the car on the lift.

 

Vinh

[Boy from Oz]

Mea culpa, mea culpa.

 

I have remeasured the offset and it is 33mm not 60mm, so there is no problem at all. Must still be excited about Casey Stoner's Moto GP world title and not thinking too clearly. Thanks for the earlier comments. This GM diff is looking better and better all the time.