Blowing head gasket due to excessive timing?

Hello,

i had to tune a drag car this week which made 2300whp on 50psi of boost running on pure methanol. The head is sealed using fire rings and a copper gasket, the car pushed the head gasket out, broke the fire rings and made a hole in the head. we replaced the head, pushed the car 4 times on the dyno and again the same thing happened. What i would like to ask could this be due to advancing the timing excessively or is it a machinist fault due to incorrect sizing of the ring?

car is running 55 psi on pure vp M5 methanol i have my timing around 21 degrees from 6000 up to 8000 rpm lambda 0.66 egts around 640 up to 680 degrees c

It's caused by the peak cylinder pressure exceeding the ability of the sealing to contain it.

Normal practice is to adjust the timing to achieve peak torque at each rpm, or to just short of the point where detonation is detected, whichever comes first. What did you do to establish the timing you're using?

I haven't used the fuel, but while it does have some excellent properties, it does, as I understand it, work best with very rich mixtures - could you be running insufficiently rich?

It is also tolerant of very high boost and/or compresson ratios, but could you be pushing it too far?

My timing is right on my mbt and i have seen that increasing 2 more degrees of timing helped in reducing the egt’s, i took a look at the top surface of the pistons but i cannot find any signs of knock. Regarding the fuel mixture, i am targeting my mixture based on my egt’s they are held constant through the whole run between 640 and 680 so it shouldnt require extra enrichment.

correct me if i am wrong

thanks

As I said, haven't used the fuel (that I recall).

However, doing some checking suggests that there are some problems using that as 'the' tool for setting the mixture - the primary one being where it's placed, as there are numerous factors affecting the accuracy. That said, the consensus seems to be you're running way too hot, with a max' around 600C being a more common area, and some suggesting as low as 540C. There is a lot of info' from guys on-line who have been using this for years.

I'm rather confused at why you are using that, EGT, rather than lambda and the actual engine's torque to establish the fuelling - seems you have a set idea of what it "should" be rather than giving it what it actually needs?

What the vehicle is being used for may also be a factor - if you're doing sand hillclimbs you're going to be putting a lot more heat into the engine than if doing 1/8th mile sprints.

The reason the EGT changed as you changed the timing was mostly down to more heat energy being lost in the expansion process and piston/head/cylinders walls. Conversely, with late timing, there is less energy lost in expansion and so more passes out the exhaust - in extreme cases it may still be burning as it passes the valves, as can often be seen in methanol fuelled drag, and other series, cars at night. It's another reason it isn't a good idea to make EGT the primary fuelling guide, as the late burning fuel may also be due to slower burning excessively rich mixtures.