corvette engines/ problem ?

[rkvette]

it seems all the engines-ls7/ls9 that have a problem, it's#7 cylinder !! this comes from the corvette sites.. now hearing about impala ss v8/ls4 with problem ,again number 7 cylinder !! some people think its from long intake length ? no facts, just speculation.. what do you guys think ? rkvette

[0rion]

#7 has been an issue with all the LSx engines...even the LS1's. Doesn't take much reading to figure out that if a cylinder lets go there's a pretty good chance it's #7. Most will say it's due to the air feeding 7-8 more air than the front 6 and leaning them out. I've read a bunch of explanations as to why it happens but couldn't tell you for sure if any of them are 100% correct or if it's just a combination of all of them.

[sunsetorangess]

From what iv seen its a Combo deal
J

[Marc 85Z28]

Ever notice how the #7 piston ringlands always let go on engines that run lean with the LS6 style coolant crossover and rear plugs, but never with the LS1 crossover?

[shady milkman]

the issue is actually a combo thing like sunset said. 1. it is the fact that the air hits the back of the intake manifold and stalls..air that isnt in motion and causes pressure changes which alter the density of the air ..so the rear cylinders get denser air than the others. 2. is the design of our fuel rail. any contaminates in the fuel that make it past the filter will hit and collect at the end of the rail right above #7. this is why it is a good idea to go to a gm dealership ( i know) and have them do a fuel injector cleaning as #7 is known to clog.
on top of that #7 is spraying the same amount as all the others..this is why a lot of hi po builds will put their fattest injector on #7 and the next on #5 (i don't quite know why they do 5 over 8..)
i know it is also possible to scew the injector's fueling ..so you could command over 100% fueling on certain cylinders....i dont know if 98-02 f-bodys have that option or if it is only available on later models

so as you can see...#7 gets more air than the others..so it runs leaner as is..on top of that you add a injector that 1. tends to get clogged faster than others 2. is spraying the same amount of fuel in as if the air was the same as the others ..and you get major lean condition (especially for tunes that are running pretty lean as is) and you get problems

[psychowette]

I wouldnt be surprised if the initial intake design wasn't as perfect as hoped for. I do recall reading how the LTX engines were extremely starved for air in the rear cylinders perhaps they overengineered the lsx manifolds to fix that.

[LSXZ28]

Ever notice how the #7 piston ringlands always let go on engines that run lean with the LS6 style coolant crossover and rear plugs, but never with the LS1 crossover?

Bingo! Back two cylinders run hotter = detonation...

[shady milkman]

I wouldnt be surprised if the initial intake design wasn't as perfect as hoped for. I do recall reading how the LTX engines were extremely starved for air in the rear cylinders perhaps they overengineered the lsx manifolds to fix that.

yeah i think that is the case ..but mind you they have had 12 years to fix it if it was truly a issue...i think it is one of those cases were the cons dont come close to outweighing the pros.

[spordee1]

Would anyone consider commenting on the quality of the LS3 intake and whether replacing it with the FAST 102 will in their opinion improve the situation.
I am planning a 600hp build and have not made the final decision on the intake. So this could be very crucial.

[shady milkman]

Would anyone consider commenting on the quality of the LS3 intake and whether replacing it with the FAST 102 will in their opinion improve the situation.
I am planning a 600hp build and have not made the final decision on the intake. So this could be very crucial.

no i dont see it improving the situation as the fast castings are heavily based on gm's intake design..i would make sure with a hi-po build like that you have the steam tubes on both the back and the front (unsure of the layout of the ls3 in regards to the valley cover and such) I would also make sure and put your fattest injectors on 7,5,8,6 (in that order personally) and if possible change the injectors on the 7 and 5 to spray 105-110% more than the rest to prevent the lean condition if you are really worried about it (shoot frost a pm and ask if that option is available in terms of our PCMs etc)

good luck on your build if you are trying for 600 to the floor with the ls3

[spordee1]

I really appreciate the info, as you know these builds are incredibly expensive.
Knowledge up front can address situations that could crap the whole works.
thx.

[SOMbitch]

When my 346 was pulled for the 403 swap I was very surprised to see.......you guessed it a broken ringland on #7. I lucked out and thete was not so much as a scratch on the head. Car ran fine with no issues so I was shocked. I had TFS 220 heads so there was no rear coolant crossover. It was matched with a FAST 90/90.

I spoke with Erik Koenig who built my shortblock about this and he offered no definitive explanation. I tend to think it is due to many of the factors above combined instead of one single thing. I have no proof of this but it also seem to me to occur more with the FAST intake....

I'll post pics next week when I pick up the old motor and start pulling it apart.....

[shady milkman]

i hate you and your 403 swap ...........*jealous* i want those heads too

[SOMbitch]

i hate you and your 403 swap ...........*jealous* i want those heads too

Haha my bank account hates me too