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Re: Quench
[Re: WannaRunner]
#512219
11/01/09 03:20 PM
11/01/09 03:20 PM
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Joined: Jan 2006
Posts: 8,162
USA
360view
Moparts resident spammer
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USA
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I am interested in the question of whether flat top pistons are superior ... either for most effective quench, or faster flame speed, or fewest hot spots, or conducting the least heat toward the ring lands, etc This article about the GM LS7 engine http://www.popularhotrodding.com/tech/0504phr_chevy_ls7_engine_review/index.htmlhas the quote Special cast pistons were developed for the LS7, which feature an anti-friction skirt coating, anodized ring lands, improving hardness and wear resistance. Larger-bore pistons are by nature heavier than their smaller-bore counterparts, and here the LS7 design team countered this tendency by moving the pin bosses inward and employing a shorter high-strength full-floating piston pin. This approach yields a piston assembly that is lighter, while the shorter pin represents a mechanically stiffer arrangement. With a flat-top design, the pistons deliver a compression ratio of 11:1. the picture has the caption: Topping the rod is a flat-top piston helping the LS7 achieve a compression ratio of 11:1. The piston features a skirt coating to reduce bore friction, and hard-anodized ring lands, which enhance durability and temperature resistance. Note the short compression height and the lightweight reactive ring pack; pins are full-floating.
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Re: Quench
[Re: WannaRunner]
#512220
11/02/09 11:45 AM
11/02/09 11:45 AM
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JohnRR
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Quote:
Quote:
The performance pistons I have seen are D shaped dish and that's what you need unless you need a HUGE dish ...
I'm having Diamond make me a piston with a pop up quench dome AND a D shaped dish
John, is the pic. above considered a pop up quench dome and a D shaped dish??
Thanks.
it could be used as one but a step dome usually would not go to the edge of the piston like that , if it were used in an open chamber head you would to have to be absolutely postive the chamber did not overhang the bore , most will ... unless you are building something around a 4.280 or under bore size.
to me that looks like a piston designed to the zero decked .
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Re: Quench
[Re: JohnRR]
#512221
11/02/09 01:03 PM
11/02/09 01:03 PM
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Joined: Feb 2003
Posts: 12,675
Columbia, CT
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I run those pictured dishes at .010 above deck unless the bore is larger than 4.355. I also tend to have the chamber sizes reduced by milling. You want the distance tight as you can. Closer to .030 the better. You will also want to choose the cam carefully as too small will give you more grief than too large will when building for quench.
Well, art is art, isn't it? Still, on the other hand, water is water! And east is east and west is west and if you take cranberries and stew them like applesauce they taste much more like prunes than rhubarb does. Now, uh... Now you tell me what you know.
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Re: Quench
[Re: WannaRunner]
#512222
11/02/09 05:01 PM
11/02/09 05:01 PM
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JohnRR
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Quote:
Yes, all things being equal, would it be better running a flatop verses the piston pictured above??
~thanks
That all depends on what compression ratio you need to be able to run the octane fuel you want.
If you choose a flat top and end up with 12.5 compression but want to run 89 octane fuel then yes you would need a piston that looks like the one above to get an octane friendly compression ratio and still have quench.
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Re: Quench
[Re: moper]
#512223
11/02/09 05:05 PM
11/02/09 05:05 PM
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JohnRR
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Quote:
I run those pictured dishes at .010 above deck unless the bore is larger than 4.355. I also tend to have the chamber sizes reduced by milling. You want the distance tight as you can. Closer to .030 the better. You will also want to choose the cam carefully as too small will give you more grief than too large will when building for quench.
why unless the bore is larger than 4.355 , and what would you do then ?
The only thing I have to go by for a quench pad is the KB piston and they don't run it out to the edge of the piston , at least the pictures I have seen of them they do not ?? but this of course is ASSuMEing that the KB pad is correct ... but now that I think of it their piston specs for big block mopar engine is less than optimum 
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Re: Quench
[Re: RapidRobert]
#512225
11/02/09 05:44 PM
11/02/09 05:44 PM
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Joined: Feb 2005
Posts: 3,957
SW Fla.
CYACOP
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Quote:
Quote:
The only thing I have to go by for a quench pad is the KB piston and they don't run it out to the edge of the piston , at least the pictures I have seen of them they do not ?? but this of course is ASSuMEing that the KB pad is correct
(1) correct, not out to the edge (2) I think KB expects (rightly so) a person to measure their (quench) clearance & mill the quench pad down to where it's right for each eng. that's what I'm doing on my 451.
And what happens if you dont?
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Re: Quench
[Re: CYACOP]
#512227
11/02/09 06:03 PM
11/02/09 06:03 PM
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JohnRR
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Quote:
Quote:
Quote:
The only thing I have to go by for a quench pad is the KB piston and they don't run it out to the edge of the piston , at least the pictures I have seen of them they do not ?? but this of course is ASSuMEing that the KB pad is correct
(1) correct, not out to the edge (2) I think KB expects (rightly so) a person to measure their (quench) clearance & mill the quench pad down to where it's right for each eng. that's what I'm doing on my 451.
And what happens if you dont?
Depends , if they are too tall they hit the head, if you have too much distance between the head and the piston you negate the quench effect and get no benefit from it .
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Re: Quench
[Re: RapidRobert]
#512228
11/02/09 06:05 PM
11/02/09 06:05 PM
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JohnRR
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Quote:
Quote:
The only thing I have to go by for a quench pad is the KB piston and they don't run it out to the edge of the piston , at least the pictures I have seen of them they do not ?? but this of course is ASSuMEing that the KB pad is correct
(1) correct, not out to the edge (2) I think KB expects (rightly so) a person to measure their (quench) clearance & mill the quench pad down to where it's right for each eng. that's what I'm doing on my 451.
I did the opposite , machined the chambers so they were all the same depth considering the last set of heads I did the middle of the head was about .020 DEEPER than the ends of the head .
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Re: Quench
[Re: WannaRunner]
#512230
11/02/09 07:33 PM
11/02/09 07:33 PM
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Joined: Feb 2005
Posts: 4,310
Prospect, PA
BSB67
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Quote:
Quote:
It would be helpful if you would tell us what cylinder head you are planning to use with that piston, or post a picture.
CNC'd Stealths
Maybe it is in the post somewhere and I missed it, is this a 500" motor?
If it is, an option is to have the combustion chamber opened to what you need and run a flat top.
When Jeff is done with the CNC work, presuming he still cleans up the combustion chambers/unshroud the valves, they will be at about 88cc. The valve reliefs on most flat top pistons are 4 to 6 depending on the piston. Depending on your cam, you are already pretty close to pump friendly combo with 0.040 quench. Just an option.
Get the CR you want and good quench, that is what is most important. After that, piston shape is splitting hairs.
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Re: Quench
[Re: JohnRR]
#512231
11/02/09 08:37 PM
11/02/09 08:37 PM
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Joined: Jan 2008
Posts: 299
Fitchbug, Mass.
WannaRunner
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Fitchbug, Mass.
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Quote:
Quote:
Quote:
The performance pistons I have seen are D shaped dish and that's what you need unless you need a HUGE dish ...
I'm having Diamond make me a piston with a pop up quench dome AND a D shaped dish
John, is the pic. above considered a pop up quench dome and a D shaped dish??
Thanks.
it could be used as one but a step dome usually would not go to the edge of the piston like that , if it were used in an open chamber head you would to have to be absolutely postive the chamber did not overhang the bore , most will ... unless you are building something around a 4.280 or under bore size.
to me that looks like a piston designed to the zero decked .
This one I believe is to be used .015 in the hole....
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Re: Quench
[Re: JohnRR]
#512232
11/02/09 08:40 PM
11/02/09 08:40 PM
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Joined: Jan 2008
Posts: 299
Fitchbug, Mass.
WannaRunner
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Fitchbug, Mass.
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Quote:
Quote:
Yes, all things being equal, would it be better running a flatop verses the piston pictured above??
~thanks
That all depends on what compression ratio you need to be able to run the octane fuel you want.
If you choose a flat top and end up with 12.5 compression but want to run 89 octane fuel then yes you would need a piston that looks like the one above to get an octane friendly compression ratio and still have quench.
I'm running 91-93 octane E85 in my runner now. (jetted up my carb) I would like to run around 11.0cr in the new motor.
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Re: Quench
[Re: BSB67]
#512233
11/02/09 08:51 PM
11/02/09 08:51 PM
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Joined: Jan 2008
Posts: 299
Fitchbug, Mass.
WannaRunner
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Quote:
Quote:
Quote:
It would be helpful if you would tell us what cylinder head you are planning to use with that piston, or post a picture.
CNC'd Stealths
Maybe it is in the post somewhere and I missed it, is this a 500" motor?
If it is, an option is to have the combustion chamber opened to what you need and run a flat top.
When Jeff is done with the CNC work, presuming he still cleans up the combustion chambers/unshroud the valves, they will be at about 88cc. The valve reliefs on most flat top pistons are 4 to 6 depending on the piston. Depending on your cam, you are already pretty close to pump friendly combo with 0.040 quench. Just an option.
Get the CR you want and good quench, that is what is most important. After that, piston shape is splitting hairs.
512 stroker, around 11.0cr
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Re: Quench
[Re: WannaRunner]
#512234
11/02/09 11:22 PM
11/02/09 11:22 PM
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Joined: Feb 2005
Posts: 4,310
Prospect, PA
BSB67
master
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master
Joined: Feb 2005
Posts: 4,310
Prospect, PA
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Quote:
Quote:
Quote:
Quote:
It would be helpful if you would tell us what cylinder head you are planning to use with that piston, or post a picture.
CNC'd Stealths
Maybe it is in the post somewhere and I missed it, is this a 500" motor?
If it is, an option is to have the combustion chamber opened to what you need and run a flat top.
When Jeff is done with the CNC work, presuming he still cleans up the combustion chambers/unshroud the valves, they will be at about 88cc. The valve reliefs on most flat top pistons are 4 to 6 depending on the piston. Depending on your cam, you are already pretty close to pump friendly combo with 0.040 quench. Just an option.
Get the CR you want and good quench, that is what is most important. After that, piston shape is splitting hairs.
512 stroker, around 11.0cr
Then the flat top will get you very close to this.
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Re: Quench
[Re: RapidRobert]
#512235
11/03/09 10:32 AM
11/03/09 10:32 AM
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Joined: Jan 2003
Posts: 74,948
U.S.S.A.
JohnRR
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Quote:
Quote:
I did the opposite , machined the chambers so they were all the same depth considering the last set of heads I did the middle of the head was about .020 DEEPER than the ends of the head .
open chambers?. that's what I was going to have to do to a set of 906's if I hadn't found some 915's for a decent price.
Yes , 452's , they are a pair of Paul Rossi street fighter heads I bought in 1989, the worst of the 2 heads was an NOS casting.
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Re: Quench
[Re: WannaRunner]
#512236
11/03/09 10:34 AM
11/03/09 10:34 AM
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Joined: Jan 2003
Posts: 74,948
U.S.S.A.
JohnRR
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Quote:
Quote:
Quote:
Yes, all things being equal, would it be better running a flatop verses the piston pictured above??
~thanks
That all depends on what compression ratio you need to be able to run the octane fuel you want.
If you choose a flat top and end up with 12.5 compression but want to run 89 octane fuel then yes you would need a piston that looks like the one above to get an octane friendly compression ratio and still have quench.
I'm running 91-93 octane E85 in my runner now. (jetted up my carb) I would like to run around 11.0cr in the new motor.
91-93 octane E85 ??? are you mixing it ??? I thought E85 was 105 octane ??
12.5 would be fine with E85 , where are you getting it near Fitchburg ? I want to run it in the engine I'm building but it looks like I'll have to run into Chelsea from Southern NH to get it .
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Re: Quench
[Re: JohnRR]
#512237
11/03/09 12:58 PM
11/03/09 12:58 PM
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Joined: Feb 2003
Posts: 12,675
Columbia, CT
moper
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John, I run them tighter until the bore gets large enough and the piston short enough that after a few thousand miles of use the piston rock takes up a bit of the quench. From what I've seen, which is limited I admit... Once you're past the 440 +.030 bore the pistons can rock a bit. Add to that the loss in skirt and stability from the stroked crank and the extra sideways pushing.... I want to make sure nothing hits after a bunch of miles. No other reason than that. But remember I'm starting at .030. Guys starting at .040 dont have to worry. As things wear, that distance gets tighter as the piston changes direction.
Well, art is art, isn't it? Still, on the other hand, water is water! And east is east and west is west and if you take cranberries and stew them like applesauce they taste much more like prunes than rhubarb does. Now, uh... Now you tell me what you know.
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