tdc OFFSET

[Slim shady]

I know this is an old question but here goes.
I just put a 6.5 with 18.5:1 pistons and ported heads together and Spring loaded waste gate controller. I have been looking for the TDC offset,. I know the factroy setting is 0.00 to -.55 but I have also heard that the phaser gear sets run -1.70 to -1.90 as the TDC offset.
Right now I am running -1.40 and it seems a little loud as far as rattle. When I set it back to the factory setting at -.55 it is real quite but doesn't seem to have the throttle response. Any ideas? I have a MAC Master tech and have rest the TDC offset so I don't need to know how to do it, I just need some input on what others have run their TDC offset at.

Thanks

[nvmtnlion]

The common school of thought is to run at about -1.92 for performance or -1.5 for towing. I am going to set mine at -1.5 when I get my new timing set since the higher settings come with more clatter.

[Slim shady]

I have tried the -1.90 setting but since I have 4.10 gear sets at highway speed I am running around 2600 rp, at 75 miles an hour at it seemed quite loud . I figured the 18.5 :1 pistons would make it rattle a little less. It starts hard when the TDC offset is at the factory setting to. I will keep an eye on the responses but I will try the -1.50 setting and see how it is. I noticed boost goes down when I use the higher TDC offset. Ran it at 0.00 for about one day and 15 psi of constant boost under load wasn't uncommon up untill around 2200 rpm.

[rjschoolcraft]

I ran -1.94 on stock compression and run that now with my new 18:1 engine. Can't tell any difference in sound at all. The dyno data shows the performance gain...

And, oh... I tow a lot!

[Cowracer]

RJ,

Does yours have a 'rattle' (for lack of a better term) at around 2500 rpm when lightly loaded (coasting or maintaining speed)

I like the 1.94 setting on mine, except for that rattle. It just noticable to enough to drive me nuts.

Tim

[Slim shady]

I have a C2500 8600 gvw with a Mt8 five speed that I just converted to a single Mass flywheel. Yes I had to put the balance weight in the trans because mine didn't have it. So that I can clear things up I also have The 4" exhaust by Pinnacle.
Now to answer your question I do have a very distinct sharp rattle at around 2200 to 2500 Rpm under light load. When I accelerate and just get up to the shift point at around 2200 it gets real pronounced. This is part of the reason I was asking for others opinions about there TDC offset. When I ran the factory offset it was extremely quite at 1500 to 2000 rpm but got just a little louder at around 2500 rpm
I just don't want to fry my new pistons, even though they are ceramic tops :}. I don't want to go thru this rebuild and expense again any time soon. I spent right around $4000 including the trans and I had the block from an old motor I parted out and it needed a sleeved cylinder and to be bored out.

[rjschoolcraft]

Mine always did/does that...no matter what the timing was/is

[Slim shady]

So you think the sharp rattle is not an issue at that rpm? I am just a little gun shy that is all.

[rjschoolcraft]

The rattle only occurs with small APP commanded fuel flow... Therefore, the cylinder pressures are much lower than when under power and things are much quieter. Don't see an issue...

[Slim shady]

Thanks
Never thought about that, you are right, and under a load it really didn't seem that loud. I am glad I joined this site. Thanks again, I am going to play with it a little and see where my truck runs best.

Hopefully the smoking at cold start will get better, I can lay down some heavy cover with it now.