piston quench requirements

[matmaster]

I have posted a similar question and did not get an answer. Perhaps nobody in this forum knows for sure, but I'll ask again. In my experience building high compression (10-11:1)street V-8 engines, I always carefully set up the deck height/ head gasket combination to acheive a quench height of 0.035 to 0.040". The literature on V-8's is explicit about this particular elemnt of combustion chamber design. In his book "Racing Engine Preparation", Wadell Wilson explains how quench height is crucial to supressing detonation in the combustion chamber and racers have been chasing the best quench height for decades. Wilson claims that optimal quench is 0.035 but the benefits of piston quench are lost if the quench height is allowed to exceed 0.060". Now, fast forward to the Mitsubishi 4G63: The Mitsu engineers certainly designed quench into the piston/combustion chamber combination on this engine. However, the 4G63 has at least 0.060" clearance between piston top and quench area. Most available head gaskets are in the 0.050 - 0.060" range, if coupled with a block/piston combo that puts the piston tops below the block deck, this would lead to a larger area. Does anyone have any specific knowledge in this area? Anyone ever experimented with more or less quench height? There might be some power to be gained by optimizing the quench height.

 

[anconover]

As posted in the other thread, these arent V8 motors with 11:1 CR. Adding the thicker headgasket will lower compression a little. You wont have any problems. And do you know that your head was NEVER resurfaced? If it was resurfaced, youd need to know how much to calculate all this. But really, if the valves arent hitting pistons, dont worry about it.

Ive never heard of people complaining, or machining/choosing a headgasket for an ideal quench. It seems like a v8 thing to me. Its usually checking to make sure you have proper valve clearance, and if your real anal, using measurements to calculate your actual CR.

 

[Maglin]

Matmaster... I do have been wondering about the quench height on the 4G63... I'm in the process of building my forged 2.0 and later on the 2.3 and I'm thinking of decking the block .020 to make up for the added quench of the cometic HG that I'm going to be running. Cause if you can increase detonation threshold you can increase potential power output with the given components...

And as for the "Well it just works so don't bother" attitude that is SOOO common on these boards... Usually people are not shooting for the stars for their HP figures and don't really need to pay close attention to these critual things. This is part of blueprinting a motor. You make everything perfect and a combination that works fluidly together... A lot of people run a gigantic FMIC to compensate for the added quench.. They don't know it but that is what they are doing as lower intake charge temps also lower the pre-ignition threathold... I'm going to get with JAM and see what they would suggest.. I hope they will give me some info instead of just tring to get me to buy their motor... My block is going in next week for a .040 bore, Main Line Hone, and a decking.. So you have brought this up at a good time... I was just about to say screw it and kept it close to stock.. I'll look into the quench height this week and post back what I find that other known shops have done that work...

 

[matmaster]

Maglin, that would be great if you can get some advice. I have personally built an engine (Ford 351C) with a thicker head gasket and LOWER compression than before. The engine pinged like mad. I found out later (and fixed the problem) that I had pretty much negated the quench area by going over 0.070". That was a very good lesson for me.

The head gaskets available for the 4G63 are pretty thick, around 0.050". To get the optimal quench of 0.040" would require having the pistons stick out of the block by about 0.010". This would not be a problem except the compression ratio may start getting too high. It would probably not be too difficult to remove material from the combustion chamber to compensate for this. Of course, milling the head gives less to work with, but show me a used head that isn't warped :thumbdown .

The 4G63 I am assembling is right at zero deck height. I am putting the thinner 0.051 Cometic gasket in. After cc'ing the head and pistons I am at 9.01:1 compression. That is with 8.5:1 Ross pistons. I wish I could get a thinner head gasket to get the quench height back in line with what I think it should be.

 

[sunflashx]

Ive never heard of people complaining, or machining/choosing a headgasket for an ideal quench. It seems like a v8 thing to me. Its usually checking to make sure you have proper valve clearance, and if your real anal, using measurements to calculate your actual CR.

I chose a .036 thick Cometic headgasket to acquire a optimal quench area. The pistons I used theoretically should take advantage of the quench area. My pistons sat .005 in the hole. The next step down was a .030 thick gasket and that was too tight for my comfort.

Marco spec 2.4L Pistons w/ Quench area:
http://www.utdsm.org/gallery/view_photo.php?set_albumName=album13&id=DSCF0066