Can some explain why #7 hole is always giving people problems. The more detail the better

EXP. if its a lean issue why not just install a little large injector in that hole?

Ricky

 

dam good question i have prolems in 7 all the time

 

Although #7 & #8 get the most air & run a bit more lean, #7 is also the warmest spot in the motor. Learned this the hard way when I lost cylinder #5 & #7 to overheating. The overheat was my fault, but, it also revealed the hot spot. Under normal conditions, I think it's as much a cooling system issue as it is a lean issue. Am told that stock set-ups have 3 to 5% more fuel @ #7 & #8. Don't know for sure & even if this is true, it doesn't help the hot spot. The area around #7 holds the most heat according to my experience.

 

Race teams run the coolant crossover at the back of the motor to help with this. I do not think its so much a lean condition as a its a hot spot like stated above.

 

You know........, I wondered if that would help back there. Thanks for the information.

 

At WOT and high RPM (when the sizable column of air entering the intake has the most speed, momentum, and energy) air rushing thru the entrance of the LSx style manifold has the easiest time negotiating the turn in the #7 intake runner at the rear of the manifold. Hell, I even notice that when I clean the porting chips from the FAST intakes with pressurized air (from the front of the intake) that the air is blasting out of the #7 manifold runner which just makes sense with the layout of that manifold design. A slightly larger injector would be a great idea and would help the motor make a little more power and run safer IMO. I will try to get O2 readings in every primary pipe of the header next time I happen to be on the engine dyno....I would guess the exhaust temps are up in that hole due to a slightly leaner mixture. Number 8 is in the rear as well obviously and gets it's fair share of air as well, but its not as heavy as the air exiting #7....again, simply due to the location and layout of the typical LSx manifold.

At least this is my take on the situation....

Tony M.

 

See the reason I was looking at another customers intake carb stuff and made me think about all the problems I have read over the years about thank cylinder giving poeple troubles. Lot of good information thank yall. (texasterm)

Ricky

 

A few people have gotten trash in their #7 injector and posted about it, but I think over-all it is a heat related problem.
I posted a picture of the #7 intake runner in this thread to show how it probably flows less air than the others.
https://ls1tech.com/forums/pcm-diagnostics-tuning/498726-misfire-7-removed-cats-help-please.html

 

I have to agree, the rear cylinders is going to get more air than the front cylinder at high flow rates. Mainly because there is more pressure at the rear of the intake than the front because of the ram effect.
Tony, next time you are doing some Dyno testing, try to install a pressure gage at the front, and one at the rear of the intake and see what the differential is. I think that is where you will find your answer.

 

I have never seen test results, but it would be very interesting to learn what each intake port flows with LS6 or FAST intake attached.

 

great idea,if i had the means of testing it i would be doing it right now

 

If the problem is related to hot spots in the coolant passages, why not run Evans coolant, NPG? Its supposed to fix just that issue.

Andrew

 

Read here:
https://ls1tech.com/forums/advanced-engineering-tech/483588-7-piston-failure-fix.html

 

cyl # 7 & 8 allways run hotter, its in the back, ask any drag racer who's blown an engine, 7&8 will show signs of high heat, any V8...

 

No one is disputing that #7 & #8 run hotter or that higher air flow to #7 & #8 are part of the problem. The best solutions I've seen are to connect the coolant vents on the heads @ the rear & to add a bit more fuel @ 7 & 8. I haven't had any trouble w/ #8, only #7 & #5.


What is Evans coolant NPG? Please explain how it can help the problem.

 

This link will explain it better then I ever could:

http://www.evanscooling.com/main21.htm

From the looks of it, NPG solves the exact problem that is being discussed. The formation of isolated hot spots, which creates hot spots in the cumbustion chamber, which in turn causes detonation and ultimately damage to parts.

Andrew

 

Thanks for the information. Looks like a great product.


General note: Evans cannot be used w/ electric water pumps. Confirmed @ Thunder racing's web site.

 

so if you are to add more fuel to 7 and 8 for cooling purposes what would the % be over the rest of the injectors?

 

I am not sure that this can be answered in such simple terms. The proper way to take care of this issue is have an injection system that allows individual fuel and timing trims for each cylinder. Then you would have a wideband in each header tube and monitor what is happening. Then based on testing you would adjust the trims in the lean cylinders so they will equal out. The trim level may also not be constant at all RPM level. I have no doubt that at certain RPM and load cylinder 7 gets more than its share of fuel.

So the proper solution is not to simply add xx% to the whole fuel table.

Andrew

 

I bet this is due to the fact that Evans requires a higher volume pump. For the same reason underdrive pulleys are not recommended.

I am using it in my LSx powered RX7 and so far it has worked well. Then again I am not on the ragged edge.

Andrew