Quench??

[Backwoods Rambler]

A little background: I'm a young-ish (almost 30) shadetree guy, my experience has been with Small Block Chevy's and Big Block Caddy engines (I love those things) and the term quench NEVER came up in any of those builds.

So, simply stated; what is it? What makes the I-6 so special that I now need to give so much consideration?

I live in front range of Colorado and spend a decent amount of time at elevations exceeding 9k ft. I've been told that at our elevation, there's more flexability regarding octane (I currently run 85 always) and quench as they relate to pinging. How do those factors come into play??

Before anyone tells me to search, I spent a bit of time looking around the site and and the internet. From this site I got an idea of where it should be .075 ~ .088?? But why, and how do you adjust the quench without changing the CR? But, I also played around with the calculator and my quench #'s never changed from .0725 From the internet I got very technical descriptions of what it is.

Remember, this is me -> <- Notice I'm still under the shadetree

Please keep it simple or my head might go


Oh and thanks in advance for the insight.


BTW: If you want to get an idea of my skillset check the link in my sig. You'll see that I like to learn on the fly (even mid project) and take advice of those with more experience very seriously. Specifically this thread was a great learning experience for me.

[amcinstaller]

i wouldnt mind hearing an explanation as well. it gets argued so much it would be nice to know exactly what the commotion is about.

[Mgardiner1]

I think Flash did i great job of explaining it in the "compression ratio" faq located in the faq section. I've quoted it below

QUENCH

Quench is the distance of the Flat surface of the piston, at TDC( Top Dead Center) and, the same flat surface of the head.

So quench, is Part of the combustion at TDC but not all.
As the piston enters the top of it's travel, the air in this area is much closer to the head then the bowl of the piston or the head.
as the piston hits TDC the air is Squish out of the thin area of the piston to the bowl..............This will do two things.

1st the better the fuel and air is mixed, the less chance of a knock do the uneven burn

2nt the Squeezing of the air from the tight side of the combustion chamber to the bowl actually causes a cooling affect of the air as the piston is causing heat by the compressing of the air. The cooler the air is, the less chance of a hot spot in the combustion chamber, will fire the fuel be for the spark plug does
If you have .100 at TDC there is no affect or quench...........the closer you bring the piston to the head the better quench affect you will get.
but will also raise you compression ratio, Defeating you hole purpose of quenching or cooling the intake charge or air.

The answer??????????

If you enlarge the head bowl chamber you will not affect the quench height but will lower you static compression ratio!
By the same note you could have you piston dished deeper and you would lower you compression ratio with out affecting Quench.
If you shave you head you will raise you compression ratio but Quench will be unchanged......
If you deck your block, you piston is now higher up in the combustion chamber causing compression ratio to go up(bad idea) but will also make a smaller quench area(good idea)
If you have .100" of quench (piston to head clearance) there is little to no affect
If you had .000 head to piston clearance you would have the best quench Possible........However with piston expansion and rod stretch(AT HIGH RPM) the minimum clearance is .045"(absolute minimum is .040")
The strokers Quench above^^ is .063.......If i would have installed the stock .051"(stock) head gasket, my SCR would have been less but my quench would have been .071 Also i thing the piston to deck height is more in the .030 then the .020 that i choose for our example. Which would change that .071 to .081............

Now you have the facts, all you have to do is decide how much compression you can live with, and how much more Cash you are willing to spend, to get closer to or get that .045 Quench

Just one more thing to consider if you live at sea level you will not be happy with a simple stroker as it will not run on anything but premium fuel.........and maybe not even then.

Were as, someone that live at a elevation of say 7.000 feet, might, MIGHT be able to run on the cheap stuff with out pinging or Knocking...............

[seanyb505]

I just spent 15 minutes writing a reply and then you go and post a link Serves me right. Good info though

[Backwoods Rambler]

Nice, obviously I didn't see that post. He even covered the elevation issue. Thanks for that quick and simplified reply.

[amcinstaller]

yea i think that about sums it up. thanks

[hmd100100]

Just one more thing to consider if you live at sea level you will not be happy with a simple stroker as it will not run on anything but premium fuel.........and maybe not even then.

This sentence made me nervous now as I live at sea level and considering a simple stroker. I don't understand why it needs premium fuel and why it may not even work. I read the whole reply and sort of understand the basice concept of why Quench is important, but still can not understand the relationship between that and the sentence in the quote above !!!!!

P.S. I have a 2000 4x4 4.0 xj sport

[oletshot]

With a simple stroker, quench gets worse than it already is in a stock 4.0 (which isn't great to begin with). The simple stroker uses rods from the 4.2 and pistons from a 4.0. The pistons are designed to rebuild a 4.0, not stroke it, so the pin height isn't right for the stroker. The parts all fit together, but not quite the way they would/could if you used custom pistons.

[Alex22]

Altitude plays an important role in determining compression ratios. If the altitude in the area where the vehicle is driven is significantly higher than sea level then the compression ratios will vary. To determine the effects of the altitude on a calculated compression ratio use the following formula:

Correct Compression Ratio = FCR minus [(altitude/1000) x 0.2]

To get your stroker to run properly at sea level you might need to buy an offset CPS or an aftermarket piggyback unit to control the timing. The elevation issue had to do with its effect on the A/F ratio but I'm not sure exactly how.

~Alex

[Mgardiner1]

Either that, or if you had an aftermarket cam with the right specs, it would bring your dynamic compression ratio down enough to run on pump gas, you would just be taking a slight hit in the performance department.

If you read enough on here you'll see everybody is concerned and discuss' how many more cc's they can get from the piston dish, or the combustion chamber. Reason being, is when you shave the top of the engine block to improve your quench numbers, you are also raising your compression ratio as there is not as much room in the combustion chamber with the piston traveling closer to the head. One way to improve quench and keep compression ratio under control, is to shave the block (for example) .035, that decreases the combustion chamber by 7 cc's. Therefor, one way to keep the compression ratio the same is to remove 7 cc's of material from the piston, or split the difference between the head combustion chamber and piston. You will have the same volume of compressed air at TDC, but the piston will be physically closer to the head, creating a more ideal quench/efficiency.

[Cheromaniac]

Just one more thing to consider if you live at sea level you will not be happy with a simple stroker as it will not run on anything but premium fuel.........and maybe not even then.

I don't know who made that statement but it's a load of old bollocks! My stroker runs happily on 91 octane at sea level in 110*F Dubai mid-summer heat, and it has a stock cam with a 9.25:1 CR and a quench of 0.088". I'm even running the hottest plugs available (Champion RC12LYC).

[Mgardiner1]

Not to hijack your thread...... but.....

Do you guys think that an engine with 9.6 SCR, 8.25 DCR, and .051 quench, would ping on low grade fuel?

[seanyb505]

I would start high and work your way down. Fill it up with 93, next tank 89, and if you can go lower go for the 87. Im not sure if it wouldnt ping on low grade, The CR is higher than what I would shoot for, even with the good quench.

[gradon]

I have a tank of 91 in there now (been using 93 since build) and no problems. I'll try 89 on next fill-up. This is a .061-62"(.051"HG and .010-.011" deck clearance) quench 10:1 scr, 8.56 dcr engine.

[Mgardiner1]

I have a tank of 91 in there now (been using 93 since build) and no problems. I'll try 89 on next fill-up. This is a .061-62"(.051"HG and .010-.011" deck clearance) quench 10:1 scr, 8.56 dcr engine.

What altitude are you at?