240SX exhaust temperature

[Eagle7]

I didn't get the exhaust temps during the dyno runs... didn't have time to get the mychron out of my uncles car.
I plan on getting a few rev runs in the garage with the different plugs and different timing, and see about temps.
I am running a pacesetter header into 2.5" through a Summit straight-thru muffler(where the Cat used to be), and then 2.25 pipe the rest of the way back.
MAF is good, Injen intake, no leaks anywhere
[/b]

If you really have 2K degree exhaust your header will be cherry red - very clearly noticable.

I've forgotten, did you check the other runners? How do they compare?

[mgp240]

Other tubes read within 100F
I am looking into the readings though, I'm not sure what TC the mychron is set up to take as an input... (I don't think the difference would be a 500F one)
After a race they header is slightly red, but not glowing (carbon steel melts at ~2600F ??)
Mike

[kthomas]

Headers will look normal after a race, and during operation at part throttle. Only at WOT or heavy load will they be bright red/orange. They will return to a normal color within seconds of the throttle being lifted. If your headers are still red after a race, you got real problems.

[Ron Earp]

Is there any malfunction on this particular car that could cause the spark in this one cylinder to be severely retarded? This would cause a lot of heat and can easily burn an exhaust valve.

Clearly if it uses a dizzy this would not be possible since it'd affect all cylinders the same. But could it be possible with a crank fired ignition system? Just a stab in the dark here as not much is adding up here.

Ron

[slickS14]

I would also think ignition timing with header primaries being "red" or fuel pump not keeping up under load at RPMs. Check your wiring/ground/connections to the pump because that can greatly affect the pump operation as well. Something else worth checking is your camshaft timing components. If the oil pressure activated chain tensioner is not working properly it will be changing your cam timing at different RPMs which in turn changes your combustion/fuel/spark/power...just a thought. I had a chain tensioner blow a plug out that looks similar to a freeze plug once and experienced similar problems. I had fun trying to diagnose until I went to the dyno chasing other ideas and found the problem. I bought a new one from Nissan and had the plug tig welded in place and have had no more issues. Ofcourse I fished the old plug out of the oil pan.... Good Luck. Your best bet is to make friends with a dyno owner!

[mgp240]

I'm not sure what TC the mychron is set up to take as an input... (I don't think the difference would be a 500F one)
[/b]

Well, with the propper TC (purchased from Pegasus, and made by Aim Sports) the temps are in the 1300F range 6 inches from the head at 5k rpm no-load rev for about 1 minute in the garage. So, in a way, I was right... it wasn't a 500F difference... it was a 700F difference. After all that fiasco I may have finally learned to purchase the correct tools and parts for the job instead of trying to make do with what's around (but probably not... look at the signature)
Now the real issue. I started looking into this because I blew a relatively young engine up in the same way that I had blown up a junkyard motor the year before.
I still have NO IDEA why I would be breaking/melting #3 exhaust valve!
I'll be racing this weekend with the mychron installed, so maybe I'll find something then.
Thanks for all your help... even though it turned out that my exhaust is running normal temps, I still got quite a bit of useful info from this thread.

Mike

[John Herman]

...I still have NO IDEA why I would be breaking/melting #3 exhaust valve! ...
[/b]

Now that the temp thing is resolved. The likely culprit is valve float. The fact it was the same cylinder could be dumb luck (1 in 4). First, any over reving? Be honest. Over reving on downshifts is easy to do. Get a memory tach to check yourself. Second, if the head was redone, the valves moved up into the head, reducing the preload on the springs. So, you need to be sure your head is setup correctly. First, use new springs and have them checked for preload, or inspect your used springs CAREFULLY and have them checked for the correct load at installed height (the value should be in the service manual, something like 85# @ 1.5" for example only as I don't know about your engine specifically.) Then check the installed height of ALL the springs in the cylinder head. You'd be surprised how far off they will be (.010-.035" depending on how old the head was or how aggressive the machine shop was). If the preload is not correct, you are losing rpm capability on your engine. Check for any "bad" lifters, (cracks, scores). Once that is set, another thing to look at is oil viscosity. Don't run too low of one, or get too fancy at this point. When I went to the 30W Redline oil (and I actually tried 40W and their blends as well), I started having all kinds of problems. I now use Mobil One Delvac 15W-45 (the stuff for diesels). I've heard Rotella is very good as well. If you're worried about dino oil, change it every weekend. The reason for the oil concern is you could be aerating the oil, which messes with the lifters, causing them to bleed down and "drop" the valves onto the seats. (Sort of like getting air in your brake lines.) Also, make sure your windage tray/oil pan are up to snuff to eliminate oil pickup/aeration problems. I never found an Accusump was effective enough for me to band-aid the issues. Once I fixed all this, my valve problems significantly reduced. Good luck. This is a frustrating and EXPENSIVE problem to have....I know.

[mgp240]

As for the over-rev... the first engine, yes. The recent blow up, I didn't over-rev. I had the light set to 6100, and it usually comes on between 6000 and 6100. I also found out that my tach is actually reading a little high from the dyno and the mychron. (tach reads 6100, actually 5950)
I have pics of the head and block from the June disaster... here is the head pic, reduced enough to fit it on here.

[attachmentid=649]

[Eagle7]

Wow!