A question for machinists
11-30-2001, 03:37 PM
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A question for machinists
Hello,
Was just wondering on a standard bore 350 with standard rod size standard stroke, whats the lowest possible quench height you can reach (with or without modifications to pistons) while keeping your compression at 9.5:1 to 10.5:1 range?
thanks!
[This message has been edited by tpi_roc (edited December 01, 2001).]
Was just wondering on a standard bore 350 with standard rod size standard stroke, whats the lowest possible quench height you can reach (with or without modifications to pistons) while keeping your compression at 9.5:1 to 10.5:1 range?
thanks!
[This message has been edited by tpi_roc (edited December 01, 2001).]
11-30-2001, 08:15 PM
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Your question is worded a little strange, I assume you are talking about the distance between the head and piston? You certainly wouldnt want to take away the quench area from the combustion chamber, that helps in preventing detonation (pre-ignition, whatever).
Compression ratio doesnt have anything to do with it, but piston-wall clearance, piston material, rod material, bearing clearance, and the tolerances of your rotating assembly have everything to do with it. Most people will tell you .040 is the safe number to go by. I have heard that you can run as little as .035 and still have clearance with factory type rods and no excessive piston-wall clearance. Less than that you are really playing with fire if you dont know what you are doing, and you have to remember that parts wear, so what works now may not work 50,000 miles from now. Add a couple thousandths of bearing wear, some cylinder bore wear, and next thing you know the piston is doing more than just kissing the head, its smacking itself to pieces on it. Trying to run as little clearance as possible should be left to a precisely machined race motor that sees teardowns often, not a typical street or street/strip type car.
More so than minimizing the quench distance (.040 will do fine for what needs to be done) is maximizing the quench area. The more the merrier.
Compression ratio doesnt have anything to do with it, but piston-wall clearance, piston material, rod material, bearing clearance, and the tolerances of your rotating assembly have everything to do with it. Most people will tell you .040 is the safe number to go by. I have heard that you can run as little as .035 and still have clearance with factory type rods and no excessive piston-wall clearance. Less than that you are really playing with fire if you dont know what you are doing, and you have to remember that parts wear, so what works now may not work 50,000 miles from now. Add a couple thousandths of bearing wear, some cylinder bore wear, and next thing you know the piston is doing more than just kissing the head, its smacking itself to pieces on it. Trying to run as little clearance as possible should be left to a precisely machined race motor that sees teardowns often, not a typical street or street/strip type car.
More so than minimizing the quench distance (.040 will do fine for what needs to be done) is maximizing the quench area. The more the merrier.
11-30-2001, 09:20 PM
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madmax: quench & compression are very related.
For the most part at least.
I talked to a machinist today and he said .035 woulld probably put me over 12:1 (without machining)
and i can machine my pistons obviously and change that.
But anywho... thanks
For the most part at least.
I talked to a machinist today and he said .035 woulld probably put me over 12:1 (without machining)
and i can machine my pistons obviously and change that.
But anywho... thanks
11-30-2001, 10:40 PM
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Sounds like you are confusing things, the quench area as it sits has nothing to do with compression ratio, the amount of space in the chamber before and after compression does. Quench area would basically be the amount of space (area) where the piston and combustion chamber are in close proximity to one another when the piston is at TDC. The quench distance or quench height seems to be what you are referring to.
Lets say you take one engine, use .040 clearance, and another you use zero clearance. Lets say the quench area is 1 square inch. So on one, you have .040 cubic inches, and the other is zero. Lets say the combustion chamber is 8 cubic inches on the one with .040 clearance, the piston has no dish, and the displaced volume is 60 cubic inches. The compression ratio of that example would be 60+8+.04/(8+.04)=8.463:1
Now take the one with zero quench, flat top pistons, 60 cubic inches of displacement, and instead of 8 cubic inches in the chamber, lets make it 8.04 cubic inches. Now the compression ratio of this engine is 60+8.04/8.04=8.463:1
So with a minimal increase in combustion chamber volume, the compression ratio doesnt change. So if I answer your original question, I can use a standard bore 350 block with standard rod size and standard stroke with a different combustion chamber volume and piston and run zero quench (well, not realistically but anyway) and have a compression ratio of anything I want to, 9.5:1, 10.5:1, 3:1, 12:1, whatever.
Now if you are trying to come up with a specific compression ratio, someone would need to know how far down in the hole the piston is at TDC, the cc of dish or dome on the piston, the intended head gasket thickness, and the combustion chamber volume. I'd also say that if he thinks you will be at 12:1 with .035 quench, you either have different/milled heads, or different pistons in your engine than a typical stock SBC. As an example, a typical SBC (this is very general mind you) with 9.5:1 compression runs around .042-.044 quench in stock form, and changing that from that figure to .035 would only raise the compression .15 with no other changes. Basically, you dont use quench distance to modify your compression ratio, it doesnt change much. Quench area is almost a fixed thing unless you start changing heads and pistons and matching them to one another.
[This message has been edited by madmax (edited November 30, 2001).]
Lets say you take one engine, use .040 clearance, and another you use zero clearance. Lets say the quench area is 1 square inch. So on one, you have .040 cubic inches, and the other is zero. Lets say the combustion chamber is 8 cubic inches on the one with .040 clearance, the piston has no dish, and the displaced volume is 60 cubic inches. The compression ratio of that example would be 60+8+.04/(8+.04)=8.463:1
Now take the one with zero quench, flat top pistons, 60 cubic inches of displacement, and instead of 8 cubic inches in the chamber, lets make it 8.04 cubic inches. Now the compression ratio of this engine is 60+8.04/8.04=8.463:1
So with a minimal increase in combustion chamber volume, the compression ratio doesnt change. So if I answer your original question, I can use a standard bore 350 block with standard rod size and standard stroke with a different combustion chamber volume and piston and run zero quench (well, not realistically but anyway) and have a compression ratio of anything I want to, 9.5:1, 10.5:1, 3:1, 12:1, whatever.
Now if you are trying to come up with a specific compression ratio, someone would need to know how far down in the hole the piston is at TDC, the cc of dish or dome on the piston, the intended head gasket thickness, and the combustion chamber volume. I'd also say that if he thinks you will be at 12:1 with .035 quench, you either have different/milled heads, or different pistons in your engine than a typical stock SBC. As an example, a typical SBC (this is very general mind you) with 9.5:1 compression runs around .042-.044 quench in stock form, and changing that from that figure to .035 would only raise the compression .15 with no other changes. Basically, you dont use quench distance to modify your compression ratio, it doesnt change much. Quench area is almost a fixed thing unless you start changing heads and pistons and matching them to one another.
[This message has been edited by madmax (edited November 30, 2001).]
11-30-2001, 11:44 PM
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I know exactly what quench is, and I know exactly what compression is.
If im building an engine and I go with 9:1 i'll have quench X, If i go with 10:1 i'll have quench Y, not X, because once you move the piston closer to the head you have a smaller quench area, and a larger compression ratio. I just want to get the smallest quench area i can without going over 10:1 compression.
If im building an engine and I go with 9:1 i'll have quench X, If i go with 10:1 i'll have quench Y, not X, because once you move the piston closer to the head you have a smaller quench area, and a larger compression ratio. I just want to get the smallest quench area i can without going over 10:1 compression.
12-01-2001, 12:31 AM
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"If im building an engine and I go with 9:1 i'll have quench X, If i go with 10:1 i'll have quench Y, not X"
This isnt at all true. I give up trying to define the terms, you arent getting it.
As for your question, I cant answer it without knowing the cc of the piston and the head. Knowing if the block is zero decked and the gasket thickness you want to use would be nice for a starting point. Without that information, the compression ratio cannot be determined no matter what quench distance you throw out. You shouldnt run less than .035 anyway because beyond that the chances of piston to head contact are much more likely.
This isnt at all true. I give up trying to define the terms, you arent getting it.
As for your question, I cant answer it without knowing the cc of the piston and the head. Knowing if the block is zero decked and the gasket thickness you want to use would be nice for a starting point. Without that information, the compression ratio cannot be determined no matter what quench distance you throw out. You shouldnt run less than .035 anyway because beyond that the chances of piston to head contact are much more likely.
12-01-2001, 01:32 AM
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Yea i know, I dont want to go extreme, but I want a really low quench height. Like .035. The thing is I've got to maintain a streetable compression. As far as heads/pistons you can consider them all veriable because I'm trying to design the engine BEFORE building it, instead of after 
I was thinking 64 heads, decking the block is deffinatly more than likely, head gaskets offer a little adjustability. Just seeing if there was any "common knowledge" that I didn't know
I was told the stock quench was about .05-.06 So i'm sure i could settle for .04, but I'm interested in hitting .035, I dont plan on high RPM's with this engine since Its going to be TPI, so that offers me the oppertunity to get just a LITTTTTTTTTLE closer to the heads than say a 7k rpm revver.
Thanks!
I was thinking 64 heads, decking the block is deffinatly more than likely, head gaskets offer a little adjustability. Just seeing if there was any "common knowledge" that I didn't know
I was told the stock quench was about .05-.06 So i'm sure i could settle for .04, but I'm interested in hitting .035, I dont plan on high RPM's with this engine since Its going to be TPI, so that offers me the oppertunity to get just a LITTTTTTTTTLE closer to the heads than say a 7k rpm revver.
Thanks!
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12-01-2001, 02:24 AM
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Stock quench might be that much with an aftermarket gasket, but those are alot thicker than what the factory was using on thirdgens.
With 64cc heads, zero deck, .035 gasket (and hence .035 quench) and a standard bore you'd be at 10:1 with pistons with an 8cc dish. Thats entirely doable on a cast iron head. Aluminum heads thats a cakewalk. With a 12cc dish you would be at 9.6:1, which is more than safe no matter what heads you use.
If youre dead set on running .035, just make sure you check the pistons that they are square in the bores and the clearances are good. I dont really like running clearances so tight, once you hit around .045 you have pretty much made the quench work like its supposed to. You may need to either have the pistons up out of the block just a little and use the common .039 gasket or use a thin gasket and deck the block just a little to get .035 quench. I'd say you are definitely looking at a dished piston with those heads though, which is not a bad thing at all. I'd get one that doesnt have a bunch of extra useless valve reliefs and has the dished area on the combustion chamber side.
With 64cc heads, zero deck, .035 gasket (and hence .035 quench) and a standard bore you'd be at 10:1 with pistons with an 8cc dish. Thats entirely doable on a cast iron head. Aluminum heads thats a cakewalk. With a 12cc dish you would be at 9.6:1, which is more than safe no matter what heads you use.
If youre dead set on running .035, just make sure you check the pistons that they are square in the bores and the clearances are good. I dont really like running clearances so tight, once you hit around .045 you have pretty much made the quench work like its supposed to. You may need to either have the pistons up out of the block just a little and use the common .039 gasket or use a thin gasket and deck the block just a little to get .035 quench. I'd say you are definitely looking at a dished piston with those heads though, which is not a bad thing at all. I'd get one that doesnt have a bunch of extra useless valve reliefs and has the dished area on the combustion chamber side.
12-01-2001, 03:01 AM
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Car: yy wife, crazy.
Engine: 350, Vortecs, 650DP
Transmission: TH-350
Axle/Gears: 8.5", 3.42
Sounds like you've been hit in the head a few times with a piston. 
Listen to this man. madmax is trying to tell you that there are better ways to increase compression than reducing the quench height. Reducing the quench height TOO much can have disastrous results.
If you understand what he's saying, as you claim you are, then you should realize that .035" is a 'c' hair to close.
As madmax has said, the engine has to be allowed to 'stretch' and clearances have to be large enough to compensate for wear.
The quench (as madmax said) has little to do with the comp. ratio. It has more to due with the clearance of the engine. Yes you can modify it, but it can be a thin line to walk on.
Worry more about the total combustion area within the cylinder. That is what will make all the difference. Increasing the comp. ratio does increase the VE of the engine, but you have to look at all the pros and cons and weigh the results of them.
AAAHHH HAAAAA!!! I think that's it. You are confusing combustion area with quench height!!! They are two totally different entities.
If you really want to risk it all, go with dome top slugs in a 58cc chamber, iron head. That'll decrease your clearance between the head and the piston!!!!! Oh, and run a cam with ~.620" lift, ~ 280* dur.@.050", an LSA of 106*, and an intake centerline of 108*. And don't forget to run a Fel-Pro copper head gasket that's .015" thick (compressed). Then advance the cam 4* so you have more low RPM torque. There aren't many engines that have more torque than the diesel engine in the flat bed truck that will be hauling your car for you!!!!!
J/K on that last paragraph. Don't really do that. OK?
AJ
BTW, I'm not assuming that you don't have any idea of what you are talking about. It's just that it's not that hard to get confused about the terms that are used when talking about engines. That's all.
Listen to this man. madmax is trying to tell you that there are better ways to increase compression than reducing the quench height. Reducing the quench height TOO much can have disastrous results.
If you understand what he's saying, as you claim you are, then you should realize that .035" is a 'c' hair to close.
As madmax has said, the engine has to be allowed to 'stretch' and clearances have to be large enough to compensate for wear.
The quench (as madmax said) has little to do with the comp. ratio. It has more to due with the clearance of the engine. Yes you can modify it, but it can be a thin line to walk on.
Worry more about the total combustion area within the cylinder. That is what will make all the difference. Increasing the comp. ratio does increase the VE of the engine, but you have to look at all the pros and cons and weigh the results of them.
AAAHHH HAAAAA!!! I think that's it. You are confusing combustion area with quench height!!! They are two totally different entities.
If you really want to risk it all, go with dome top slugs in a 58cc chamber, iron head. That'll decrease your clearance between the head and the piston!!!!! Oh, and run a cam with ~.620" lift, ~ 280* dur.@.050", an LSA of 106*, and an intake centerline of 108*. And don't forget to run a Fel-Pro copper head gasket that's .015" thick (compressed). Then advance the cam 4* so you have more low RPM torque. There aren't many engines that have more torque than the diesel engine in the flat bed truck that will be hauling your car for you!!!!!
J/K on that last paragraph. Don't really do that. OK?
AJ
BTW, I'm not assuming that you don't have any idea of what you are talking about. It's just that it's not that hard to get confused about the terms that are used when talking about engines. That's all.
12-01-2001, 01:58 PM
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I am talking about quench height, thus ".035"
I am wiling to go for less, but I still want as minimum of a quench height as I can get while staying at or around 10:1. .040 is fine, But i really dont want to go more than that. I can't believe im hearing TWO of you say that adjusting the quench height doesn't change compression....
But anyways I'll figure it out one way or another and I'll make my trade offs untill I've gotten the quench height i want or can live with, with the compression ratio i want or can live with.
I am wiling to go for less, but I still want as minimum of a quench height as I can get while staying at or around 10:1. .040 is fine, But i really dont want to go more than that. I can't believe im hearing TWO of you say that adjusting the quench height doesn't change compression....
But anyways I'll figure it out one way or another and I'll make my trade offs untill I've gotten the quench height i want or can live with, with the compression ratio i want or can live with.
12-01-2001, 03:03 PM
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Car: 88 Firebird WS6
Engine: 350 TPI
Transmission: T56
Axle/Gears: 3.42
From what I understand running normal to tight bearing clearances with forged rods and tight (cast or hyper) pistons at reasonable speeds (6500 rpm), you can do a quench height of .028" with no worries.
Thats usually decking the block so the pistons stick out .010" and using a .38 or .40 composition gasket. This method is 'more correct' on a street motor with Al heads than is using a thin gasket. The different expansion rates really need a composition gasket.
Tightening the quench is like free lunch. More compression, more power from the small bump in compression, but mostly from the better mixture properties, and LESS likely to detonate.
Don't get too close though, or it's no free lunch...
The .028" is safe for that combo. Toss any combination of sloppy bearing clearances, sloppy fitting forged pistons, aluminum rods and/or high rpm operation and this "safe" measurement is too close.
I went a little on the safe side with my 388. I had him deck the block a hair under to be safe. It ended up with the pistons sticking out .0077" with a fel pro 1010 gasket it comes in near .030" quench.
Thats usually decking the block so the pistons stick out .010" and using a .38 or .40 composition gasket. This method is 'more correct' on a street motor with Al heads than is using a thin gasket. The different expansion rates really need a composition gasket.
Tightening the quench is like free lunch. More compression, more power from the small bump in compression, but mostly from the better mixture properties, and LESS likely to detonate.
Don't get too close though, or it's no free lunch...
The .028" is safe for that combo. Toss any combination of sloppy bearing clearances, sloppy fitting forged pistons, aluminum rods and/or high rpm operation and this "safe" measurement is too close.
I went a little on the safe side with my 388. I had him deck the block a hair under to be safe. It ended up with the pistons sticking out .0077" with a fel pro 1010 gasket it comes in near .030" quench.
12-01-2001, 07:01 PM
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Ok, so this is what I'm looking at now.
1.)about zero deck height (give or take)
2.)flat top valve relieved pistons (maybe machined, or 'excessive' reliefs for slightly lower compression)
3.) 64cc heads with a nice amount of bowl work, granted I'll maybe only be able to trim 1 cc or so, maybe 2, who knows but the bowl works gunna happen anyways.
4.) whatever head gasket it takes, so like .035 compressed
And with this (aluminum heads btw) I should be at a streetable compression with good quench HEIGHT
side note: After coming off the nyquil I've been pounding for my cold I realized that I did say "area" in my first message when I MEANT to say "height", so my apologeese to madmax, and as for the other guy with the additude if your intent isn't to help, dont post.
Thanks guys.
[This message has been edited by tpi_roc (edited December 01, 2001).]
[This message has been edited by tpi_roc (edited December 01, 2001).]
1.)about zero deck height (give or take)
2.)flat top valve relieved pistons (maybe machined, or 'excessive' reliefs for slightly lower compression)
3.) 64cc heads with a nice amount of bowl work, granted I'll maybe only be able to trim 1 cc or so, maybe 2, who knows but the bowl works gunna happen anyways.
4.) whatever head gasket it takes, so like .035 compressed
And with this (aluminum heads btw) I should be at a streetable compression with good quench HEIGHT
side note: After coming off the nyquil I've been pounding for my cold I realized that I did say "area" in my first message when I MEANT to say "height", so my apologeese to madmax, and as for the other guy with the additude if your intent isn't to help, dont post.
Thanks guys.
[This message has been edited by tpi_roc (edited December 01, 2001).]
[This message has been edited by tpi_roc (edited December 01, 2001).]
12-02-2001, 01:12 AM
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Car: yy wife, crazy.
Engine: 350, Vortecs, 650DP
Transmission: TH-350
Axle/Gears: 8.5", 3.42
I'm "the other guy with the attitude".
I have no attitude. I was just joking with you on that last paragraph. I was tired and bored myself. Sorry.
As for all the other comments above that paragraph, if they didn't help you, then that's your loss. I was simply trying to help you and madmax 'understand' each other's comments better.
I do still stick with madmax about the fact that you are wandering into an area that should really only be handled by people who race for a living. Like in Pro-Stock when there looking for that last 5HP.
As far as having the block milled down to 'zero deck height' is another area that isn't needed. Actually when you have a block machined, you should really only remove as little as needed from the deck. Only enough to remove any warping or irregularities. That way the block can be used/rebuilt again later if it warps again, or more irregularities appear.
That's all I was trying to say. Sometimes we all get too "gung ho" (I know I have) about having our engines as perfect as the pros do, that we forget that our engine is also gonna be submitted to street duty. There are certain things that are done to race engines that shouldn't be done to our engines. One of those things is 'tight' clearances in certain areas of the engine.
AJ
I have no attitude. I was just joking with you on that last paragraph. I was tired and bored myself. Sorry.
As for all the other comments above that paragraph, if they didn't help you, then that's your loss. I was simply trying to help you and madmax 'understand' each other's comments better.
I do still stick with madmax about the fact that you are wandering into an area that should really only be handled by people who race for a living. Like in Pro-Stock when there looking for that last 5HP.
As far as having the block milled down to 'zero deck height' is another area that isn't needed. Actually when you have a block machined, you should really only remove as little as needed from the deck. Only enough to remove any warping or irregularities. That way the block can be used/rebuilt again later if it warps again, or more irregularities appear.
That's all I was trying to say. Sometimes we all get too "gung ho" (I know I have
) about having our engines as perfect as the pros do, that we forget that our engine is also gonna be submitted to street duty. There are certain things that are done to race engines that shouldn't be done to our engines. One of those things is 'tight' clearances in certain areas of the engine.AJ
12-03-2001, 11:29 AM
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AJ_92RS:
Since you seem to be firm in your stance on quench clearances. Are you suggesting that quench has no gains? or that clearance is more important? Most of us are here for reasons other than just a point A to point B daily driver. So if clearances are your issue, what do YOU feel is a good quench height number? .040? .045?
And since you're not a fan of decking, how would you acheive it?
Since you seem to be firm in your stance on quench clearances. Are you suggesting that quench has no gains? or that clearance is more important? Most of us are here for reasons other than just a point A to point B daily driver. So if clearances are your issue, what do YOU feel is a good quench height number? .040? .045?
And since you're not a fan of decking, how would you acheive it?
12-03-2001, 12:53 PM
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Car: 1989 C4
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Transmission: 700r4
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TPI, I agree with these guys as far as not needing to worry about certian things when it comes to an engine that see's street more than a circle track. I mean why bother? The Hp gain from this quest for qench area will be very minimal, although every bit helps.
To answer your question fully all the specs of your engine must be figured out first by measuring. Basicly you would need to get everything blueprinted individually to find the answer your looking for. It's quite clear that you want a real answer and I admire that. You need to have the block measured up, the pistons, rods, bearings, gaskets, crank and heads. All of these are factors in your quest and you cannot assume that flat top pistons are presicely flat top. The small tolerances you are looking for could be affected by even by a shisty bearing or imperfect head gasket.
I do hope you find the answer but without exact specs anything you hear here will be a guess.
Good Luck!
SSC
To answer your question fully all the specs of your engine must be figured out first by measuring. Basicly you would need to get everything blueprinted individually to find the answer your looking for. It's quite clear that you want a real answer and I admire that.
You need to have the block measured up, the pistons, rods, bearings, gaskets, crank and heads. All of these are factors in your quest and you cannot assume that flat top pistons are presicely flat top. The small tolerances you are looking for could be affected by even by a shisty bearing or imperfect head gasket. I do hope you find the answer but without exact specs anything you hear here will be a guess.
Good Luck!
SSC
12-03-2001, 01:16 PM
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Well I understand more than anybody the fact that the entire engine needs to be "designed" which is what im in the stage of doing right now. Nothing is set in stone, everyting is flexable, and I'm looking for the best solution. The rods are more than likely going to be 5.7, the crank will be stock stroke, the pistons maybe .030 over, the compression will be variable from 9.5 to 10.5 the bearings should all be standard thicknesses, I'm not asking for NASCAR tollerences, I'm just asking for a respectable quench and compression, why rebuild if you're not going to go 'better than stock'?? I understand the virtues of giving yourself clearances, but when it comes to forged parts you can run a little tighter. Granted the HP might not increase, but my chances of detonation because of the close quench will decrease offering me more timing flexability at the very least. If I'm going to do it im going to do it right, thats why I remain flexable. However, I'm convinced that while its an option, I'm going to improve the improvable, and quench is one of the many things that could use some work at very least. I heard racing engines can run as little as .025, another member said .028's fine before any problems, the lowest I asked for was .035, and I even mentioned .045 is feesable. I dont want a miracle, just tighter than stock tollerances and clearance
Maybe I'm wrong, but isn't this what modifications, performance, and the do it yourself attitude is about? "Professionals" and "racers" never would be where they are without chances and trial and error. I think numbers of .035 and .040 are MORE than reasonable.
Anywho im very open to input, and I'm not saying "NO" to anything. However if I'm going to blueprint or design an engine why bother if i'm not going to change anything?
Thanks for all the input!
------------------
1985 Iroc-z, 14 second 305, new engine in the works.
Maybe I'm wrong, but isn't this what modifications, performance, and the do it yourself attitude is about? "Professionals" and "racers" never would be where they are without chances and trial and error. I think numbers of .035 and .040 are MORE than reasonable.
Anywho im very open to input, and I'm not saying "NO" to anything. However if I'm going to blueprint or design an engine why bother if i'm not going to change anything?
Thanks for all the input!
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1985 Iroc-z, 14 second 305, new engine in the works.
12-03-2001, 08:07 PM
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Car: yy wife, crazy.
Engine: 350, Vortecs, 650DP
Transmission: TH-350
Axle/Gears: 8.5", 3.42
<font face="Verdana, Arial" size="2">Originally posted by tpi_roc:
AJ_92RS:
Since you seem to be firm in your stance on quench clearances. Are you suggesting that quench has no gains? or that clearance is more important? Most of us are here for reasons other than just a point A to point B daily driver. So if clearances are your issue, what do YOU feel is a good quench height number? .040? .045?
And since you're not a fan of decking, how would you acheive it?
</font>
AJ_92RS:
Since you seem to be firm in your stance on quench clearances. Are you suggesting that quench has no gains? or that clearance is more important? Most of us are here for reasons other than just a point A to point B daily driver. So if clearances are your issue, what do YOU feel is a good quench height number? .040? .045?
And since you're not a fan of decking, how would you acheive it?
</font>
I'm not at all saying that it has no gains. But you have to also look at reliability issues. If you run .0025" clearance on your rod main bearings, and .0025" on the crank main bearings then run a .025" quench height, then you are doing well for a race engine that is going to be torn down and all the bearings replaced, etc. after every race.
The average engine is going to wear the bearings .0005" for every 50K miles. Well 50K miles later, the 'play' in the bearings is going to increase. You only have to acount for half of the clearance growth due to the fact that the rod and main journals are round, and the decrease in distance of the pistons to the head will only take place on the 'up stroke'.
So. 50K miles later if you add the two increases of the clearances (the rod and crank mains), then halve them, the total clearance will allow the piston to become .0005" closer to the head. (And that's not figuring the amount the rod stretch, pin flex, crank flex, etc. that will take place at higher RPM.) Now the clearance is only going to be .0225" from the piston to the head. Then there's the carbon deposits that may be present after 50K miles. Whether they're on the valves, pistons, in the chambers, etc.
All of these things are going to happen on an engine that is used on the street. That's why GM allows production variables on their blocks. It's not uncommon to see a deck height on a stock block to be as much as .020" higher than spec.
If you are building a race engine, then go for it. Run the quench height at .025" or .028" or whatever. And I also have no negativity to your desire to know what is good for what. But for a practical (but yet high performance) engine, I'd say the bigger the better when it comes to quench height.
AJ
[This message has been edited by AJ_92RS (edited December 03, 2001).]
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