Advantage of MFI over SFI on 98 GMC 5.7

[FOG]

Can someone explain the advantages, or dis-advantages of changing to MFI.
I have a 97 GMC C1500 with a 5.7.

[bwood]

I'm going to assume you mean the updated "spider" for the Vortecs. I just did this on my 98 305 while replacing the engine. There area really in no performance to be had other than better idle and smoother performance. When I pulled my old style out, it was broken in a few spots (tabs that hold the poppets in) and a few of them look like they hadn't been firing very well. If you are concidering replacing the spider for maintenance (like bad injectors) I would definitely upgrade as it is the same price as the old style. Also remember the older style can be repaired with new injectors and poppets. I'm thinking it would cost around $80 per injector to rebuild, so if you had to replace 5 bad injectors, it should cover the cost of the upgrade. I paid $365 wholesale @ NAPA for mine and it was a Delphi unit in a NAPA box.

Here is a shot of the newer style:
http://www.gmpartsdirect.com/results...ber=PK93441235

If you are talking about stepping up the marine manifold for the Vortecs, there is performance to be had with different injector setups, fuel pressures, etc. I have seen the cost of these start @ $800ish and I believe the manifolds are all cast iron. This upgrade would be best on an engine making 400+ hp. The factory Vortec V8 injection is said to be capable of supporting up to 400hp with computer mods/programming.

Here is a post with a lot of good info and pics (40+ pages) for the marine setup:
http://www.pacificp.com/forum/viewtopic.php?t=317

[FOG]

Thanks for the reply. I don't have any problems yet, but I just wanted to see if there was something to gain (performance or mileage) with the new MFI setup.

Based on your response, I will just wait until I do start having problems and change it over then.

[Scott68-93-97]

what new mfi setup?????? you mean mpfi (multi point) sfi is mpfi that just means you have an injector for each cylinder instead of something like tbi where you have 2 injectors for the entire motor at the throttle body, sfi stands for sequential which means the injectors fire in the order of the firing order with the plugs instead of bank firing like other mpfi's that fire 4 at a time repeatidly, like early tpi is a bank fire type mpfi, sequential systems get a lot better fuel economy, now a days all mpfi's or mpi's as your calling it are sfi, bank firing is a thing of the past now! I have 135,000 on my 97 vortec 350 and have never had an issue, run a cleaner every 20,000 or so and you wont have an issue my pop has been at chevy 35 years and he says the stock setup is great as long as you maintain it like you should, performance wise other mpfi's could hurt your power band and fuel economy I wouldnt do anything to it except a prgrammer maybe and they have an inline harness to advance the timing from idle at a stop so you get a better low end grunt from these trucks other than that dont touch you will do more damage than good