3 out of 6 cylinders do not like 12.5:1 compression

[neilca]

I have built a 2.4 liter 12.5:1 compression, 46 mm throttle body, DC70m cam engine. We were tuning it this weekend at Little Talladega when things started to go down hill. I checked compression at home to find 3 cylinders with 0 compression. Initial teardown indicates blown head gaskets. I was using stock head studs and stock torque requirements. Obviously this is not adequate. Where should I go from here to seal these cylinders?

[fred cook]

Are the tops of the cylinders cut for head gaskets? If not, something to consider. Also, you could add a shim under each cylinder to lower compression marginally. I assume that you had measured compression on each cylinder earlier. If so, were the 3 blown cylinders higher than the other 3? Were the blown cylinders all on the same bank? Was the deck height set the same for all cylinders? All questions that should be answered before attempting to reseal the engine!

[fred cook]

At 12.5 cr, I assume that you are using twin plug ignition. What were you using for timing advance? Also, are you certain that all plugs were firing?

[neilca]

The cylinders were grooved for the O ring head gaskets. I am running twin plugs with a max advance of 30 degrees. The cylinders that where blown are 3, 4, and 6. I have yet to pull the engine and the heads so more info to come.

[fred cook]

Originally Posted by neilca

The cylinders were grooved for the O ring head gaskets. I am running twin plugs with a max advance of 30 degrees. The cylinders that where blown are 3, 4, and 6. I have yet to pull the engine and the heads so more info to come.

When you get it all back together, try a max advance of 24-25 degrees. That should put the engine right on the "sweet spot". Twin plug ignition seems to work best when set about 9-10 degrees less than single plug. Consider that the less advance you use, the less negative work the engine will have to overcome, thus making more horsepower.

[John at J&S]

Check out our SafeGuard knock controller.

[Eagledriver]

Too much advance for twin plug.

[Raceboy]

If you track the car, just use E85, you will make more power and engine runs much cooler, also you pretty much never encounter detonation with NA.
If it is not available, just buy a barrel of denaturated ethanol and mix 15% of regular gas into it.
Here we can buy ethanol for 1.20€/litre in 200l barrels.

[neilca]

Originally Posted by Raceboy

If you track the car, just use E85, you will make more power and engine runs much cooler, also you pretty much never encounter detonation with NA.
If it is not available, just buy a barrel of denaturated ethanol and mix 15% of regular gas into it.
Here we can buy ethanol for 1.20€/litre in 200l barrels.

That is an interesting thought to use ethanol.

I pulled the engine apart last night. No signs of detonation. But I did have 5 blown head gaskets, one so bad it burned through the steel liner. I am using birels. I checked the torque of the head studs prior to disassembly and they were all loose. I suspect the studs were loaded past the yield strength causing the blown head gaskets. I will post pictures later.

[Lapkritis]

Re: E85. Not as easy as just putting this fuel in. The lower energy potential of the fuel relative to gasoline means you need to adjust the mixture to add more fuel for the same HP output. Once you have the mixture adjusted correctly for e85 you can run more advance.

[Eagledriver]

Still think it was the advance. So much advance put all the energy into lifting the heads instead of turning the crank.

[neilca]

I have no problem backing off the timing, but I need to figure out how to keep these cylinders sealed. Do you think stock studs and torque will keep them sealed if I back off the timing? I have noticed the back two cylinders faired the worse. Is there a way to get additional cooling to the rear?

I am intrigued by the E85 fuel for the cooling effect. I am running a Megasquirt 3 engine management so I can adjust for just about anything. One concern is my aluminum fuel surge tank. What will E85 do to that?

Lots of questions for now

[fred cook]

Get hold of Henry Schmidt at Supertec. They offer a set of very high quality studs designed specifically for performance engines. He also sells a set of repro 906 air diverters to go around the cylinders. He should also be able to advise you on the best sealing process for your cylinders/heads. Nice guy and very helpful. One of the top 3-4 engine pros here on the board.

[fred cook]

Check your heads for valve leakage by closing the valves and filling the combustion chamber with ethylene glycol (antifreeze). If a valve is leaking, you will see a wet stain in the intake or exhaust ports.

[neilca]

Henry has already said I was nuts to try 12.5:1. He suggested 10.5:1. I was rereading some of his previous posts on the subject and I was struck by his statement that with a mag case you should try to avoid creating heat rather than trying to take the heat away after the fact. I now know what that means. I am considering dropping the compression to a more reasonable level.

[356RS]

On the photo of #4, 5, & 6, it looks like there was no spark plugs in the left side holes? Carbon build up in the plug holes. Right side plug holes with clean threads? Were the left side plug holes caped off? Or is this a camera angle deal? Just curious.

[neilca]

Camera angle. All the plugs were in place

[fred cook]

The fact that one cylinder survived the ordeal indicates to me that the pressures are right on the "edge" of being too much. You could try adding a base shim on the cylinders to increase the deck height slightly and also back down the timing to around 23-25 degrees. Also, if your engine management is sophisticated enough, map cylinders 3 and 6 for a bit more fuel for cooling purposes. Might be just enough relief to let the engine survive! By the way, did you check the compression pressures in each cylinder? Also, did you CC the combustion chambers? If a couple of the heads have a bit more volume, put those two on cylinders 3 and 6. Good luck!

[Walt Fricke]

Neilca - how certain are you that the cylinder bases were true, that the cylinders were the same height, and that the heads were all cut to the same depth. Maybe the cylinders which did seal were a hair taller, effectively, and also prevented the right seal on the others?

[neilca]

Walt I checked those things prior to assembly. I have a marble table and height gauge for measuring such things. I used a straight edge on the spigots.