5.3 LM7 with returnless style fuel system
MagnaCharger MP90 put out 9 psi max before intercooler was installed. closer to 3psi max, after.

I just finished removing the truck's second LM7 and found a broken #7 piston and a few pieces of (something? nothing from #8 broke, chipped, etc) in #8. (SC'ed w/IC for approx. 8000km, SC'ed for approx. 20000km

Motor #1 ended up with a warped valve on #8 and possibly the head. (SC'ed for approx 40,000km, no IC)
Both motors ran the same tune on 8.1L Marine injectors (52# i believe)
Stock Fuel Rails, Stock Fuel pump


Motor #1 has a new set of heads, gaskets, studs, and will be going back in the truck soon. Im starting to think the cause of the damage has been the fuel pump. Now, ive been doing some researching and trying to figure out what would be the best bang for my buck as i dont plan on going higher than 8psi of boost and the engine going back in is still used, but havent had much luck. So far it sounds like an OE Flex Fuel pump would be my best option for my returnless style but im not certain yet. Can anyone help me out here?

Thanks in advance

 

Is your truck flex fuel? What caused your engine to blow? Not enough fuel? Flex pump should be good if not drop in a Walbro 400 or 450 plug and play from what I have heard.

 

If you are killing motors with a MP90 then your tune is way off or you have a fueling issue.

How are you going to get back to 8psi if your setup is maxed at 3?

 

My stock inj and pump from my flex truck was fine at 8 psi

 

What year is the truck?

How was it tuned after the MP90 was installed?

Did you get it re-tuned after the intercooler was installed?

 

My truck is a 2005 gmc 1500 ccsb slt z71. Yes I think it's a fueling issue because of the monster injectors in the stock rails, backed by a stock pump. After WOT for a few seconds, i would imagine those 52# injectors cause the rail pressure to fall flat on its face, causing the back two (farthest cylinders) to lean out. The guy that tuned it for me had his own business that he worked out of his garage doing custom tunes and minor upgrades. I cant remember what program he used but i do remember him saying that he 'turned the fueling way up'....I'm practically illiterate when it comes to the tune.... (also had no intercooler when it was tuned for the SC so I would kind of expect it to run a bit rich now with the IC). I have a wideband and a boost gauge so far. Will be installing a fuel press gauge when I get it all back together. Can't remember what the AFR was but i know it was right around where I wanted it. Which is about 11:1 IIRC, it's been a couple yrs since I've touched this truck :s
So are you guys saying a walbro 255-450 is pretty much a direct replacement? (minor alterations is no problem)

 

I have the "medium/5.3" size pulley on now. Have one smaller that came with it for the 6.0L. If its at 3 now, I'll be happy if I can get it back to 6 or 7 psi without slipping the belt or crank pulley (which I'm probly going to pin today after reading the sticky last night).

 

No my truck is not a flex fuel model. And yes like I said I think the back cylinders were leaning out. My stock exhaust manifolds might be making it hard for the back cylinders to exhaust tho as well.
Any of you guys still using stock exh. manifolds w/ a blower? Up until how much boost/hp would a person be able to stick with the stockers?

 

I just discovered the Kenne Bell Boost-a-pump. Sounds like an awesome idea for the return less style fuel systems. Anyone on here have any experience with it?

 

Forget the Boost a Pumps, it will kill your stock pump in short order. I am assuming you have a non flex fuel truck so get a Walbro 255, as its a easy swap. The rails are not your issue, plenty of people have made allot more power on stock rails. Get a proper pump in place and get it retuned now that you have a intercooler in place. Just don't expect too much from that MP90 as its a small compressor for a 5.3L