quench height

[Catholic Damage]

ok, so ive been doin a lil bit of research on the 4.5 stroker im gonna be building(simply because the stock rods bent, and i got a good bonus check, and why the hell not?)
4.2 stock crank and rods, oe bore aftermarket 4.0 pistons (year 97), head has been milled(head gasket blew 20k miles ago), dont know how much.
going to be running higher compression pistons(were bought before found the rods to be bent), havent ordered head gasket yet, so i can get whatever thickness needed.
whats all this talk about quench height, how can i figure out about what mine is, how do i fix it, does it need to be fixed? and what the hell is it EXACTLY? i got a pretty good idea, but going this far into a motor rebuild is new to me, and im learning along the way, and want to do it right, the first time.
school me, boys!

thanks in advance, so far this forum has been great.

 

[Talyn]

whats all this talk about quench height, how can i figure out about what mine is,

Best way to do it is to install a piston or two with the crank in place and measure TDC. With a 4.2L rod, 4.2L crank, and a 4.0L piston you will most likely be below deck a lot.

how do i fix it,

Custom pistons or deck the block to reduce deck clearance and quench.

does it need to be fixed?

With a tight quench (.050" or so) you will get better resistance to detonation and a better burn

and what the hell is it EXACTLY?

Quench is the distance between the flat top of the piston and the flat part on the head. You figure by taking the deck clearance figure and adding it to the head gasket thickness.

 

[gradon]

Go over to www.jeepstrokers.com and use the calculator to get an idea what your quench will be. There are variances in deck heights, so as Chris said, it's best to install the crank and a piston on each end and measure the distance the flat top is below the deck when it's at TDC.

 

[Talyn]

One other thing. When you measure deck clearance you will need to use the pistons you are planning to use in your build, installed on the rods you are going to use. And of course if you are boring the block it will be measured after the bore job.

 

[Catholic Damage]

kk... so, install the crank and rods when i get them with the pistons i have. measure he height of the piston to top of block..
havent ordered a head gasket yet, so im assuming i can order a certain thickness based on what number i come up with with my setup?
is there a particular spec i should be looking for, with head gasket?

thanks, you guys did a good job of helping me. im trying to track down a crank and rod set now.

 

[Talyn]

Thats the basic idea, but there is more to it. You need to install the bearings and have the pistons installed on the rods. You measure the deck height using a dial indicator and a bridge or a magnetic base. Find TDC on the piston with the indicator, then 0 it on the deck, 90* to the deck. With out disturbing the angle or moving the indicator a whole lot, slide it on to the very top of the piston. You may need to rock the piston a bit to get a accurate measurement. Really, the machine shop should do this so they can determine how much to deck based on the clearance you want.

 

[seanyb505]

Really, the machine shop should do this so they can determine how much to deck based on the clearance you want.

My machine shop said they could do this, but it would take longer and was going to add cost to the total bill. Just something to think about. As far as getting a general idea for quench, I found the original stroker calc from madxj to be very easy to use. It also allowed you to look at different variations side by side. If you play around with it long enough you'll learn how a few different measurements are derived.