[general]

I have a 1985 gmc 454 dually it is all stock and I dont have a book on it. you guys have better answers than books!, anyways I need to tune this rig for pulling would like to know initial timing, total timing and at what rpm should all advance be in? would timing be set differently if on a street machine? same rig different question what size headers and exhaust pipes would be good for performance? am thinking about adding a centrifical blower later.

[ September 09, 2002: Message edited by: general ]</p>

[4 Jaw Chuck]

If your going to add a blower I would just put in a good quality header with moderately sized 2 1/4 pipes. You'll pick up some power and economy and add some flow in preparation for the blower. A win win proposition.

[KULTULZ]

Your timing is going to be controled by the ECM (except initial advance). You would have to buy a custom PROM to alter the timing curve and fuel curve.

[general]

4 jaw chuck. i'm a little confused are you saying I can get the primary tube size in 2 & 1/4 for a 454.

Kultulz my 1985 came with an HEI. would you have any other info?

[4 Jaw Chuck]

General, you would have to see what is available before deciding on a certain model. My suggestion is running a header tube diameter (from the port) of 1 5/8" leading to a header collector with a 2 1/4" diameter outlet with a dual exhaust system 2 1/4" diameter out the back. It's small but for a nearly stock engine equipped with a mild blower boost the flow would be high and driveability would be excellent.

[KULTULZ]

[quote]Kultulz my 1985 came with an HEI. would you have any other info?<hr></blockquote>

The timing events (as well as fuel curve) is programed into the vehicle ECM/PCM. You can buy a custom PROM chip to insert into the ECM to get the performance you want.

One such vendor is Hyper-Tech. I don't know that they have anything for the 454. You may have to check several vendors to find exactly what you need for your application.