I can't find a definition for quench height... any ideas?

 

...

 

it has to do with the space between the block and head. A good way to look at it is the thickness of the head gasket and deck clearance combined.

 

http://www.chevyhiperformance.com/te...ide/index.html

 

Quench height is defined as the distance (static) between the piston deck (flat part) and cylinder head deck surface (flat part) at Top Dead Centre (TDC.) Quench isn't a spec that's normally discussed except in some high-performance engine builds, or when you're trying to maximise fuel availability by minimising Octane Number Requirement (ONR) - referring to "pump octane," or Anti-Knock Index (AKI.)

Quench height (hereafter "quench") is slightly lower in operation, due to flexion in the gudgeon pin/wrist pin and crankshaft, and the elasticity of the piston and connecting rod. This usually works out to .003-.004", tops.

The effect of "proper quench" is to cause an eversion of the fuel/air charge as the piston approaches top dead centre, which helps to minimise local hot spots (which contribute heavily to preignition.) This also has a slight beneficial cooling effect on the metal parts - but the eversion and turbulence of the fuel/air charge is a greater effect, and far more important.

"Ideal quench" is usually taken to be .045-.060" calculated. Calculate thusly:
- Add together the block deck height (distance from the centreline of the crankshaft to the ground top surface of the block) and the compressed thickness of the cylinder head gasket. This will tell you where the cylinder head ground deck surface will be.
- Add together the crank throw (half of stroke,) the centre-to-centre length of the connecting rod, and the piston compression height (centre of wrist pin bore to flat upper surface of piston, irrespective of dome or dish.) Subtract from first number.

Final quench may be tuned by:
- "Decking" the block (grinding material off of the surface)
- Selecting a different head gasket (bear in mind, you're working with compressed thickness here! Two head gaskets by different makers may have the same thickness on the shelf, but be .010-.015" different once the screws are torqued!)
- Selecting pistons with a different compression height
- Selecting connecting rods with a different centre-to-centre length
- Offset grinding of the crankshaft (modifies stroke length and alters quench)

Typically, the easiest adjustment is to have the block "decked," since quench on a production engine is typically a bit more open than desired (.050-.200", in some cases, as I recall.) There are a couple of performance head gasket outfits that will stamp you a custom gasket from dead soft copper stock, and give you several more options than typically found in production. Everything else is custom work, and usually requires one-off parts or a hefty shop bill.

As I mentioned, quench is planned and built for in order to create an "inside out" shift in the fuel/air charge as the piston approaches TDC - which moves the (relatively) hot outside of the charge toward the centre of the bore, which displaces the (relatively) cool inside of the charge outwards. This works to create an overall cooling effect, and to reduce tendency to preignition. Reducing the tendency toward preignition means you can run a lower-octane fuel (higher octane numbers/AKI indicates a resistance to ignition and combustion,) which saves you a few bucks at the pump over the life of the engine. Just try buying 120LL AVGAS anymore...

Make sense now? Proper quench planning is how you can run a high-CR stroker on 89AKI - or even 87AKI - fuel without pinging!

 

OWWWWW!
My brain hurts.

And I thought keeping my VCR from flashing 12:00 was a pain.
HAHAHA

 

Out of all the things that I lost in life I think I miss my "Mind" the most...lol...Tj

 

LOL I dont miss that one bit.........

 

hoooolly macaroni. my head hurts. so check this out...
can i just bring the piston to TDC and measure with a depth mike to the flat part of the piston and add the compressed gasket thickness to it?

 

Yep - just make sure you're not measuring at the dish or dome of the piston top (it's pretty obvious.)

(Hey - you did ask the question! What's the point in everything I've learned if I don't teach?

(Oddly, I've been rereading Taylor and Ricardo lately, and I've not seen any mention of "quench height" - by name or by description. Seems to be a fairly recent development then - Ricardo did his work in the late 1930's, Taylor in the late 1960's, I'll have to check Blair again - he did his in the 1990's, and may have covered it - especially since he was focussed on motorcycles first, and it was a motorcycle performance trick before it went to automotive. I don't know if it's directly applicable to Diesels, tho.)

 

ok, i'll set an indicator on top to make sure that the piston is at nominal tdc