last i heard lbz were crack around 600ish vs the 700-800 lb7 were lasting too.. dont know the excats on that...
LB7: Pistons ?
- Thread starter TrentNell
- Start date
last i heard lbz were crack around 600ish vs the 700-800 lb7 were lasting too.. dont know the excats on that...
You can't put a HP number on the piston failures. There are guys running over 600 hp with no problems, and there are guys cracking them at 500 hp. I had cut LBZs in my rebuild and they ran over 700 hp without a problem, but they were only in for about 4500 miles.
I'm not exactly sure what hp I was at with the stock LB7 longblock but in the fall of 2006 I ran a best of 11.53 @ 117.63mph on fuel only in the 1/4 mile with a race weight of 6600#. That motor had about 110k miles on it and about 300 combined 1/4 mile passes and hooks sled pulling. When I pulled that motor out ever rod was bent so I got my monies worth out of it.
good to know what did the pistons look like
i am still seeing that not many have cracked a lb7 piston and if you know of someone that has what were the conditions high egt ect ?
good to know what did the pistons look like
I cracked a stock lly/lb7 piston on 500hp tune seeing some serious egt's though in the dunes . When it let loose I wasnt on it like normal either . I was at 1700 , but only for a few seconds and boom . Really felt like I had weakend them previously from high egt's . It let loose at a time you wouldnt have expected it to .
I think it is random . I did the same to a motor for 45,000 miles with no issue and pushed a head gasket . Everything looked good inside . Put in new motor in and it only lasted 12,000 and cracked a piston . Go figure . Random ......
New motor in truck now has guys delipped LLY's in it . 7 of them are my old pistons . A little worried about the heat cycling the other 7 have seen , but sometimes $$ plays a role in our builds . You have to go with what you can with $$ as a factor sometimes . I made the choice to take the risk .
Many say delipp and I have a few other guys I know that say it isnt cracking from center out , and that it is cracking from wrist pin in . They said dont delipp it wont help . You will always have many different opinions and you just have to go with your gut . My gut said delipp . I did it and am happy with it so far . Only way to find out is to try something new . I know I can crack a lipped piston already on only a 500hp tune . So this was the right thing to do in my opinion .
I really believe it is heat cycling making them weak or just a random flawed piston out of the bunch . Time will tell if delipping helps them last better with same heat cycling .
You have to go in a direction . I went with delipping them now . I know I can crack a stock lipped piston . Thats known already . So why not go with something new and see if they give up like lipped one did .
Time will tell with the delipped ones in it now . All is good so far .
In the past I had stated I thought the bottom end torque felt like less , I was wrong it is still as good as before . It was my cracked intercooler making it lazy down low blowing off boost at leak . Feels as good as ever now with new intercooler . Same power as before with lip on .
I would delipp if it was mine .
I don't know hardly anything when it comes to pistons.... My buddy gave me one and said it came out of a very fast duramax that likes a ridiculous amount of nitrous . Any idea if this is cut/coated/delipped or any of that stuff previously mentioned? It looks pretty interesting and has seen better days.
. Any idea if this is cut/coated/delipped or any of that stuff previously mentioned? It looks pretty interesting and has seen better days.Attachments
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thanks for the info john i know how long it takes to type up some of these post :hug: ,and your poast brings us back to the argument at hand does the need for this mod go away with egt's in the 1250 deg range . i am not saying this is a worthless mod and truth be known i will probably cut my piston but as you said john my gut is telling me that this is caused from a high egt situation as with your truck . if i had the money i would try the stock pistons till they blew just to find out .
super diesel
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This is a good point about the heat. However, I don't know if my experiences play into it, but at my elevation (6000+ most the time), I can see some huge EGTs (1800-2000+ briefly sometimes by accident) while going through the mountain passes. I know I ignored the EGT gauge many, many times when I shouldn't have. None of my stock LB7 pistons cracked (luckly). Now I'm running Guys cut pistons (non-coated) and I've had good luck for the last 9 months and about 10K with the same treatment. Not saying that there not going to, just I've been lucky maybe? Just throwing this up so we can get some ideas of what's happening here.
i think we are on the same page i also live and tow at high elevation 4500 ft is home base and i tow in 8000 ft not counting D/A, all the time going through the mountains and the 1150-1250 deg egt's i stated are with a track proven 620 hp tune runing truck only of course , wich is why the twins were chosen nothing else would do the job . and i am the same as you just deciding what is the cause of this . and wonder why people with twins are not craking pistons in lbz and newer trucks ? unless they have and i dont know about it . i know how many times this has been gone over not trying to beat a dead horse but is the real answer egt reduction all along ? with pistons anyway .
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what were your egt's like with that kind of power ? we are debating on the link between egt's and piston failure , there seem to be alot of twinned trucks running the lbz/lmm's pretty hard without failure yet unless you know of some one ? and if thats true for the lmm/lbz why not lb7
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I was streetracing the night before and saw extreme EGTs. Didnt look but I was 130+mph and my gauge was freakin out at me.... Id say 1700º or so.
I'll be able to say more of what caused my cracked piston soon but it was on a 540+hp motor with 150 or so passes and daily driving like I stole it. Stock LB7/LLY pistons. Ever since i got faster than 12.8s the EGTs haven't been over 1400*; prior to the Cheetah and injector my EGTs were higher (buried an 1800* gauge a few times but not for long). Mine also failed when I was being easier than ever on it. I'll post more in the next week or so when I tear the motor down.
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high timing tune ? i am shure injectors helped alot . i could knock my egts's down to about the same with a single with enough timing ? nothing negative from my response just collecting data .
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The highest timing I ran with the bigger injectors was 26* and that was only from 3250RPM and above. When you only have a 1960 PW you don't need much timing to get your fuel shot in.
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cant say if that would be considered high or not , on a my 2800 pw tune now i dont ever go above 28 deg . but on a 3250 pw i have went as high as 35 deg timing @ 3700 rpm tested but never ran at track . egt's were good but timing scared me