Quench deck....
Thread Starter
11 Second Club
iTrader: (9)
Joined: Nov 2004
Posts: 1,360
Likes: 0
From: Thornton, CO
Quench deck.... I was reading through a couple others threads and I was touchy on some things.
Mahle -12cc pistons. They are a full dish piston. Probably not the best piston to run N/A with I would assume. They come .008" out of the hole and I am running .045" Cometics. Quench should be good for my application I would think.
Compression to be right around 11:1.
How will these pistons affect power output?? Or will they?
I went with these pistons planning on boosting later on, but some things have changed recently and that might be WAY down the road.
Discuss please. The motor isn't in the car yet, so if it is going to be a mistake to run the Mahle's N/A for a while I might change them.
Thanks!
Mahle -12cc pistons. They are a full dish piston. Probably not the best piston to run N/A with I would assume. They come .008" out of the hole and I am running .045" Cometics. Quench should be good for my application I would think.
Compression to be right around 11:1.
How will these pistons affect power output?? Or will they?
I went with these pistons planning on boosting later on, but some things have changed recently and that might be WAY down the road.
Discuss please. The motor isn't in the car yet, so if it is going to be a mistake to run the Mahle's N/A for a while I might change them.
Thanks!
Thread Starter
11 Second Club
iTrader: (9)
Joined: Nov 2004
Posts: 1,360
Likes: 0
From: Thornton, CO
Seems some of you have an opinion on this until I ask. 
Just trying to figure out if the full dish affects the quench and how much it will affect the performance of a N/A motor.
Just trying to figure out if the full dish affects the quench and how much it will affect the performance of a N/A motor.
What is the bore and stroke of the engine?
What is the bore diameter of the .045" head gaskets?
What is the cc volume of the combustion chambers in the heads?
Answer these questions and we can verify the 11.1:1 CR question.
A piston is dished for two reasons:
1. to reduce the compression ratio
2. to allow additional piston to valve clearance which can be a problem with high lift, long duration cams.
Typically, a dish that is over 10 cc's will yield a CR in the range of 9.0 to 10.0 depending on the stroke and combustion chamber volume. What CR do you want to run?
Regarding quench, you want to have a quench of about .040" to minimize detonation and the resulting knock retard and power loss it causes. Your numbers indicate that your quench would be about .037", so that should be fine regarding KR. I think that your biggest problem may be lower than expected CR.
All my best,
Steve
What is the bore diameter of the .045" head gaskets?
What is the cc volume of the combustion chambers in the heads?
Answer these questions and we can verify the 11.1:1 CR question.
A piston is dished for two reasons:
1. to reduce the compression ratio
2. to allow additional piston to valve clearance which can be a problem with high lift, long duration cams.
Typically, a dish that is over 10 cc's will yield a CR in the range of 9.0 to 10.0 depending on the stroke and combustion chamber volume. What CR do you want to run?
Regarding quench, you want to have a quench of about .040" to minimize detonation and the resulting knock retard and power loss it causes. Your numbers indicate that your quench would be about .037", so that should be fine regarding KR. I think that your biggest problem may be lower than expected CR.
All my best,
Steve
I ran the calculation for you on DynoSim Pro and the result is 10.68:1. I think that that is a pretty good CR for a daily driver, occasional drag strip car. How do you plan to use the car?
Steve
Steve
Trending Topics
Originally Posted by Steve Bryant
I ran the calculation for you on DynoSim Pro and the result is 10.68:1. I think that that is a pretty good CR for a daily driver, occasional drag strip car. How do you plan to use the car?
Steve
Steve
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
Topdon ONE vs. Artidiag 800 BT2: Which is the Diagnostic Tablet For You?
Pouria Savadkouei
Gas Monkey Built a 6-Wheel Ferrari Testarossa With a Corvette LT4 Engine
Verdad Gallardo
7 Most Reliable High-Performance Engines GM Has Ever Built
Verdad Gallardo
Amazing '71 Camaro Restomod Is Modern Muscle Car Under the Skin
Verdad Gallardo
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
I have a -19cc dish and 56cc heads at 11.17 static ratio and it work great. I run 91 octane with 28.5 degrees advance with no knock. I even sprayed a 100 shot on top of that without pulling timing and still had no knock. Most of the engine building competitions use a small chamber head with a dished piston. The dish also gives you some extra room for a bigger cam.
Most piston companies will put some flat area on the piston to make a "quench pad". If you find a company with a good desighn, it's deffinatlly better to run the dish and a smaller chamber. If the piston is just somewhat of a "bowl" desighn, I wouldn't be looking to run it in my N/A car. There are diffrences between N/A and F/I pistons. One is designed to draw air in and force it out while with the other, all the air is forced in and out.
TECH Enthusiast
Joined: Dec 2001
Posts: 548
Likes: 0
From: Dublin, CA
One question I haven't seen answered, is why some think that higher horsepower F/I motors would not need a quench area. The higher dynamic compression a motor has, the higher the odds of detonation are. You can richen and retard an F/I motor to reduce cylinder pressure and power, but you begin undermining the whole reason to go F/I. Which is power.
It is usually because you rely more on the chamber design of the head rather than the piston. The boost will in effect help remove the exhaust gasses. I think some of the boost guys have the most advanced setups out there for ls1's. I think keeping quench tight with a thinner gasket and dishing the pistons is a better idea than trying to use thick ones to bring the static ratio down.
TECH Enthusiast
Joined: Dec 2001
Posts: 548
Likes: 0
From: Dublin, CA
Yes, boost will help push exhaust out.
Quench surface creates a cool area furthest from the spark plug, which is the most likely heat spot that can cause detonation. The quench area also creates a tight squish between piston and head to clap mixture towards the plug which also reduces detonation.
Both quench and squish are important to reduce detonation, and F/I motors are prone to detonation due to higher cylinder pressure. So why would someone say quench not required for F/I, but is required for N/A?
Quench surface creates a cool area furthest from the spark plug, which is the most likely heat spot that can cause detonation. The quench area also creates a tight squish between piston and head to clap mixture towards the plug which also reduces detonation.
Both quench and squish are important to reduce detonation, and F/I motors are prone to detonation due to higher cylinder pressure. So why would someone say quench not required for F/I, but is required for N/A?
Originally Posted by blu00rdstr
Yes, boost will help push exhaust out.
Quench surface creates a cool area furthest from the spark plug, which is the most likely heat spot that can cause detonation. The quench area also creates a tight squish between piston and head to clap mixture towards the plug which also reduces detonation.
Both quench and squish are important to reduce detonation, and F/I motors are prone to detonation due to higher cylinder pressure. So why would someone say quench not required for F/I, but is required for N/A?
Quench surface creates a cool area furthest from the spark plug, which is the most likely heat spot that can cause detonation. The quench area also creates a tight squish between piston and head to clap mixture towards the plug which also reduces detonation.
Both quench and squish are important to reduce detonation, and F/I motors are prone to detonation due to higher cylinder pressure. So why would someone say quench not required for F/I, but is required for N/A?
I have no idea. Maybe experiece with a thicker gasket. I personally would run the same quench on either application. We build nitrous motors, but other than static compression it is very similar to how I would do a boosted engine. The only difference is I would just swap to a bigger cc head to reduce compression ratio. My je pistons on my current motor are a full dish with a flat bottom and have worked out great. The tune is just as important as the mechanical setup. If the tune is off (ie not enough fuel, too much spark) then problems will occur.
Thread Starter
11 Second Club
iTrader: (9)
Joined: Nov 2004
Posts: 1,360
Likes: 0
From: Thornton, CO
Originally Posted by strokedls1
The only difference is I would just swap to a bigger cc head to reduce compression ratio.
Thanks again for the help.
TECH Apprentice
Joined: Apr 2002
Posts: 308
Likes: 0
From: Austin, TX
I think most people here are confused about what the original poster is asking.
I'll use some different terminology in an attempt to clarify things. There are two types of piston designs to lower compression (basically anything that has more than just valve reliefs).
1. Full dish (most of the bore area is dished out) and there is very little quench pad left intact. Picture a piston where the only flat part is a small edge around the entire bore.
2. Reverse Dome pistons (the chamber area is the only part of the piston that is dished out. This keeps all the quench pad intact. Picture a piston where the only part that is not flat is the part that matches up with the chamber on the head.
Up until recently I had only heard of reverse dome used in ls1 applications (Diamond and JE are all I've ever seen ). And just assumed they were all done that way.
Based on few things I’ve recently read, it seems that some people are getting away with a full dished piston, but if you ask anyone who has been doing ls1 fi stuff for a while, they will say that they would never personally use anything but a reverse dome and that reverse dome is better.
Now for a NA pump gas car, I think you would be crazy running a fully dished piston. This has nothing to do with compression ratio. It is just the fact that you then have no quench. and are going to be way more prone to detonation.
I'm not a professional engine builder or engineer, so get other opinions before making a decision.
I'll use some different terminology in an attempt to clarify things. There are two types of piston designs to lower compression (basically anything that has more than just valve reliefs).
1. Full dish (most of the bore area is dished out) and there is very little quench pad left intact. Picture a piston where the only flat part is a small edge around the entire bore.
2. Reverse Dome pistons (the chamber area is the only part of the piston that is dished out. This keeps all the quench pad intact. Picture a piston where the only part that is not flat is the part that matches up with the chamber on the head.
Up until recently I had only heard of reverse dome used in ls1 applications (Diamond and JE are all I've ever seen ). And just assumed they were all done that way.
Based on few things I’ve recently read, it seems that some people are getting away with a full dished piston, but if you ask anyone who has been doing ls1 fi stuff for a while, they will say that they would never personally use anything but a reverse dome and that reverse dome is better.
Now for a NA pump gas car, I think you would be crazy running a fully dished piston. This has nothing to do with compression ratio. It is just the fact that you then have no quench. and are going to be way more prone to detonation.
I'm not a professional engine builder or engineer, so get other opinions before making a decision.
Thread Starter
11 Second Club
iTrader: (9)
Joined: Nov 2004
Posts: 1,360
Likes: 0
From: Thornton, CO
That is exactly what I am worried about.
I have done the research, and now I am starting to think these pistons aren't going to work too well with this set-up.
Which sucks, because I have a decent amount of money and work into it so far.
Any other opinions??
The only thing I am thinking is this....
-12cc full dish or a -12cc reversed dish will have the same amount of quench area total anyways right?? Or is it just the quench pad that matters??
Why would shops sell the full dish if they basicly sucked? Even further than that...why would a company continue to manufacture pistons that don't work well??
I have done the research, and now I am starting to think these pistons aren't going to work too well with this set-up.
Which sucks, because I have a decent amount of money and work into it so far.
Any other opinions??
The only thing I am thinking is this....
-12cc full dish or a -12cc reversed dish will have the same amount of quench area total anyways right?? Or is it just the quench pad that matters??
Why would shops sell the full dish if they basicly sucked? Even further than that...why would a company continue to manufacture pistons that don't work well??
