My own experience on #4. I managed to blow #4 twice within a month of each other in the name of science.

I was playing around trying to see what the max my setup would handle..... +20psi, 91 octane, aftermarket turbo.

AFR's were near perfect (actually slightly rich). I was able to see a spike on EGT's on #4 both times it let go............... both gaskets let go at the same location........You can clearly see that #4 was being heavily pounded on throughout the entire circumference of the ring...........

On a side note. I was able to drop my EGT's with Lindseys intake by 50 degrees at various driving modes......

 

alex,
your observation is correct , Run a colder plug in number 4 it will help with your situation.

 

Would it be wise to mix ranges of the plugs? What would be the reason for predetonation in the #4 cylinder - intake restriction or something else?

 

Cylinder bore and head hot spots , is the usual culprits.
Mixing ranges will not harm anything but it will help the no 4 handle the temps on low octane gas. which is very sensitivity to temp changes , unlike race gas that gives you a high ceiling to play with where this is concerned.

 

High post count only means you ain't got no life besides the net and when posters run out of arguments on the 951 board they resort to insults and threats , like "I am going to get you banned". The posters with a balanced ,unemotional and fact based attitude are definitly in the minority.

Now , 1600 -1700 deg egt's are a no go IMO . New VAG cars have Egt sensor as standard equipment (some even wideband!) and I have never been able to reach those temps even with ignorant tuning . In my experience serious engine damage would occur before that.

 

I sure hope they don't change the rules....

 

also, the fact that our motors have an open deck desing might have something to do with so many blown head gaskets..

 

Chris,

The n/a air cooled guys are crying in gt3 as strange things are happening so ther was talk about restrictors , adding weight and moving the 16v turbocars up

 

I have heard that crying….
Give me a break, do I whine that they weigh as much as 300-400 lbs less? Besides – how many 16v turbos are there out there?
I’ll go with the restrictor if they match my weight….!
PCA set up an advisory committee for 2006 that ‘may’ make a rules change suggestion for 2007.

A good question is where will they bump the 16v? to GT-2? That’s a NA class, so will the 16v get bumped to GT-1? Give me a break, 2.6l 16v 4cyl vs a lighter upto 3.8l 6 cyl???

One class in all of PCA racing that might be considered favorable to 944s and they want to change the rules….

Chris White

 

What is driving this ,is the sudden surge ( apparent surge or poss future wave)
of 911TT coming into gt3 and gt4. so the 944T's are being caught out in this and it did not help when Roy Chong pegged the rest of the field in gt3

 

sounds like this thread is getting off topic...

 

I AGREE !
Chris if you want start a thread on this in the racing section !

 

A Wayne,

Thanks for your techincal input and the kind remark. Though I am not a professional in this industry, I struggle my way through the mechanical process and most of the time find a solution. I have taken night classes and almost have an AS degree in Automotive Technology, a couple of ASE certs and a smog license. Just one of my hobbies.

Chris White,

As usual your input is valuable. I do understand the above point and in my efforts I have tried two methods to minimize this process. 1. I had 1 step colder than stock spark plugs, which I removed. My hope was to aid in a more complete burn and thus reduce temps inside the cat (possible source of Nox). Before my Nox problem, I installed colder iridium plugs with the small tip to aid in preventing knock. Also because my output is more than 100 hp over stock. And 2. By retarding timing, the combustion has more time for a complete burn before it get sent out the exhaust.

Your other points are great information. The more excited the gas molecules, the faster they expand, the quicker spool. This is a great edge. I had my exhaust ceramic coated to aid with this. However with my application, just for the street, I need to pass smog.

 

why doesnt someone just buy some frieking cumbustion temp sensors that go near the end of the sparkplug and find out!

 

you mean (cylinder head temperture) CHT's? I think it would be interesting to log CHT vs. egt data especially on cylinder #4