I was at the Keith Black piston site, tried to use their calculators for compression ratio for a hypereutectic domed piston and it asked for deck clearance. I couldn't find info so I left it blank. It said my CR would be apx 10.9:1 on an 060 overbore 392 with an .040 gasket.(I previously measured the chambers at 97cc, not saying that's totally accurate but pretty close, certainly not 110cc, I could be off maybe +/- 1cc? I used a medical grade syringe)
Probably the valve reliefs will have to be enlarged to clear the big valves(2.125 intake,1.945 exhaust), how much piston head volume might be a good guess that I'll lose in the process? Ummm....Hypereutectics CAN be notched, right?
What about the deck clearance?
I think I'm missing something here, what is it? An advertised 10:1 piston makes almost 11:1??? When the heads were milled and bigger valves installed, did it make that big a difference in chamber size or did I really botch the cc-ing??
I'm not saying I'm going with a hypereuctectic, just exploring options.
Thanks as always
Deck Clearance and other Qs?
Moderators: scottm, TrWaters, 392heminut
-
dan miller
- Posts: 86
- Joined: Wed Dec 27, 2006 5:05 am
Re: Deck Clearance and other Qs?
Hello NE57
392 heads? 97cc's sounds about right, depending upon how deeply the valves have been sunk. Sinking them doesn't hurt the flow.
What gasket? We use Best Gaskets, which compress to .049". They are very high quality and come in various bore diameters. We've had some water seepage issues, which have been cured by spraying a liberal coat of Copper Coat. The quality of Best gaskets is so good (coupled with the availability of many bore diameters), that we don't mind Copper Coating them. Another thing about Copper Coat is that the head and block clean up very easily.
The 1.945" exhaust valves are too large. Are the heads an old set of Mondello's? If you don't already have the heads, strongly consider leaving the valves the stock size. We're installing smaller (1.650") valves in out EMC engine, and will probably do the same in our JrFueler.
Although more costly, you'll be far happier with a set of Ross Pistons. You can get exactly what you want, and they will need zero modifications. Pat O'Neil @ Ross is as savvy as anyone on the planet, and he can get you zeroed right in. You'll have the ability to exactly dictate compression ratio, valve reliefs, and - most importantly - ring width. Thin is in. Some of the imports have scary thin rings - and are good for several hundred thousand miles.
Give yourself plenty of piston to head clearance. We set the piston/head on our EMC deal (steel rods) at low 30's and they hit. Replaced the small end rod bushings, reset piston/head at high 30's and they hit. Replaced the small end rod bushings, set the piston/valve at mid 40's and they hit. Replaced the small end rod bushings, reset them at almost 60 and are holding our breath. I'm pretty sure that they'll now clear. But, I was pretty sure that they would clear previously. lol Film @ 11. We're headed back to the dyno in several weeks, and I'll advise.
Danny
392 heads? 97cc's sounds about right, depending upon how deeply the valves have been sunk. Sinking them doesn't hurt the flow.
What gasket? We use Best Gaskets, which compress to .049". They are very high quality and come in various bore diameters. We've had some water seepage issues, which have been cured by spraying a liberal coat of Copper Coat. The quality of Best gaskets is so good (coupled with the availability of many bore diameters), that we don't mind Copper Coating them. Another thing about Copper Coat is that the head and block clean up very easily.
The 1.945" exhaust valves are too large. Are the heads an old set of Mondello's? If you don't already have the heads, strongly consider leaving the valves the stock size. We're installing smaller (1.650") valves in out EMC engine, and will probably do the same in our JrFueler.
Although more costly, you'll be far happier with a set of Ross Pistons. You can get exactly what you want, and they will need zero modifications. Pat O'Neil @ Ross is as savvy as anyone on the planet, and he can get you zeroed right in. You'll have the ability to exactly dictate compression ratio, valve reliefs, and - most importantly - ring width. Thin is in. Some of the imports have scary thin rings - and are good for several hundred thousand miles.
Give yourself plenty of piston to head clearance. We set the piston/head on our EMC deal (steel rods) at low 30's and they hit. Replaced the small end rod bushings, reset piston/head at high 30's and they hit. Replaced the small end rod bushings, set the piston/valve at mid 40's and they hit. Replaced the small end rod bushings, reset them at almost 60 and are holding our breath. I'm pretty sure that they'll now clear. But, I was pretty sure that they would clear previously. lol Film @ 11. We're headed back to the dyno in several weeks, and I'll advise.
Danny
Re: Deck Clearance and other Qs?
Unfortunately I didn't hear about the exhaust size thing until AFTER I bought these finished heads.
In a street application, what's going to happen with the oversizes valves? Will it make the motor run too lean? Will it scavenge raw fuel into the exhaust system?
Do you think there's some way to compensate for the big valves? I was wondering....if the big valves overscavenge the cylinder would a somewhat restrictive exhaust system mitigate that to some degree? Like using the cast iron manifolds maybe? Its not a racing motor so if the only effect of the big valves is loss of power, as long as its not a huge amount of loss, maybe I could live with it.
If its going to cause major problems, I have another pair of bare heads that came with a set of valves where its looks like the valves sizes are 2.020 and 1.769(? I need a better caliper) and the stems are smaller than stock. Supposedly the machine shop I got them from replaced the guides and did nothing else to them. This doesn't look 'regular'...I'll have to go over everything closely to see just what I've got. But if they check out as good maybe I'll get the spare heads finished and sell the big valve heads?
Ok, piston to head clearance. Isn't that the piston makers job? Doesn't sound like I have any way to control that other than getting a new set if its too close? You said you replaced the small end bushings..is that how you modify the clearance? Are the bushings offset in some way?
yeah yeah yeah...I'm full of questions
In a street application, what's going to happen with the oversizes valves? Will it make the motor run too lean? Will it scavenge raw fuel into the exhaust system?
Do you think there's some way to compensate for the big valves? I was wondering....if the big valves overscavenge the cylinder would a somewhat restrictive exhaust system mitigate that to some degree? Like using the cast iron manifolds maybe? Its not a racing motor so if the only effect of the big valves is loss of power, as long as its not a huge amount of loss, maybe I could live with it.
If its going to cause major problems, I have another pair of bare heads that came with a set of valves where its looks like the valves sizes are 2.020 and 1.769(? I need a better caliper) and the stems are smaller than stock. Supposedly the machine shop I got them from replaced the guides and did nothing else to them. This doesn't look 'regular'...I'll have to go over everything closely to see just what I've got. But if they check out as good maybe I'll get the spare heads finished and sell the big valve heads?
Ok, piston to head clearance. Isn't that the piston makers job? Doesn't sound like I have any way to control that other than getting a new set if its too close? You said you replaced the small end bushings..is that how you modify the clearance? Are the bushings offset in some way?
yeah yeah yeah...I'm full of questions
-
dan miller
- Posts: 86
- Joined: Wed Dec 27, 2006 5:05 am
Re: Deck Clearance and other Qs?
What's your name?
Zero problem with the questions. We're all learning, and everyone benefits from the questions and answers.
I don't believe the large exhaust valves will make any difference.
Do you know what heads you have? On 392 heads, the intakes are 2.00" and the exhausts are 1.750", so I suspect that's what you have.
Piston to head clearance is not the responsibility of the piston maker. The builder needs to specify the clearance, and if very close, the heads should be digitized. By the way, Ross Pistons digitized our Chrysler Industrial heads, so they have an exact dimensional reference to a mildly modified chamber. The reason we have issues is that we purposely hit both valves and the chambers. Not much, just a few tenths. Not enough to hurt anything, but enough to demonstrate that there's not much room left. The upside to running this tight, is that you can get maximum compression. The down side is that there is no room to move the cam forward or back. So, you have to get the cam exactly where you want it (over a period of time), and then get the piston (usually the second or third set by this time) pockets cut to the exact depth. This is a lot of fussing around for not much gain. With low compression (less than 14:1), I'd just leave plenty of room (both piston to head and piston to valve), and not worry about it.
On the EMC engine, we must have missed on something. We're OK on piston to valve, but piston to head was clanging pretty good. Hard enough to gall the wristpins and the bushings. Eagle rods are a little tight to start with, so they need to be opened up a couple tenths. They're probably OK for the street, but tight for racing. We use Eagle 7.100" long BBC rods on our EMC engine. The crank has to be ground to BBC size. Also, the Eagle rods are a touch wider than the Chrysler rods, so either they will have to be narrowed, or the crank journals widened to BBC width.
Danny
Zero problem with the questions. We're all learning, and everyone benefits from the questions and answers.
I don't believe the large exhaust valves will make any difference.
Do you know what heads you have? On 392 heads, the intakes are 2.00" and the exhausts are 1.750", so I suspect that's what you have.
Piston to head clearance is not the responsibility of the piston maker. The builder needs to specify the clearance, and if very close, the heads should be digitized. By the way, Ross Pistons digitized our Chrysler Industrial heads, so they have an exact dimensional reference to a mildly modified chamber. The reason we have issues is that we purposely hit both valves and the chambers. Not much, just a few tenths. Not enough to hurt anything, but enough to demonstrate that there's not much room left. The upside to running this tight, is that you can get maximum compression. The down side is that there is no room to move the cam forward or back. So, you have to get the cam exactly where you want it (over a period of time), and then get the piston (usually the second or third set by this time) pockets cut to the exact depth. This is a lot of fussing around for not much gain. With low compression (less than 14:1), I'd just leave plenty of room (both piston to head and piston to valve), and not worry about it.
On the EMC engine, we must have missed on something. We're OK on piston to valve, but piston to head was clanging pretty good. Hard enough to gall the wristpins and the bushings. Eagle rods are a little tight to start with, so they need to be opened up a couple tenths. They're probably OK for the street, but tight for racing. We use Eagle 7.100" long BBC rods on our EMC engine. The crank has to be ground to BBC size. Also, the Eagle rods are a touch wider than the Chrysler rods, so either they will have to be narrowed, or the crank journals widened to BBC width.
Danny
Re: Deck Clearance and other Qs?
My name is Neil.
So then, the big exhaust valves aren't detrimental? No power gain but also no serious problems? If that's the case there's no reason I shouldn't use them, since here they are, paid for and ready to bolt on? But if I was building a new set of heads smaller valves would be the ticket? I've read about overscavenging and I had visions of raw fuel burning thru the exhaust system. But that's not the case, right? Its for the street so practicality is an issue over max power.
Yes 392 heads, I checked the numbers b4 I bought them. When I bought the motor in March, I knew very little of this tech stuff, it was more like "I WANT those valve covers in my engine bay". Since then I've been learning so much more that I've come to the conclusion that this block may not be the best choice for all out power. I have a couple of issues with it now that I know a bit more about hemis. For now the stroker crank is out. When the car is finished(well, it'll never really BE finished) if I want more power I could build a stroker from a block with more integrity. But for a driver this block is OK i think, as long as I stay conservative. Really, if I can get into the low to mid 11's (doesn't seem unreasonable) it'll be the quickest car I've ever had so that alone would be a milestone.
What I have in mind for the car(66 dart) is somewhere between a ratrod and a restomod...ummm maybe a rat-stomod? I was in contact with somebody who apparently has experience with what I'm trying to do and he said it won't fit. My GF asked me what would I do if indeed I can't make it fit the Dart. I answered I'd have to change plans, put a smallblock in it and find another vehicle for the 392. "So you're going to clog the driveway up with MORE cars?"
"Yes, and your point?"
Oh, one more thing about overscavenging. If indeed some fuel/air gets sucked out the exhaust, would less overlap help?
Thanks,
Neil
So then, the big exhaust valves aren't detrimental? No power gain but also no serious problems? If that's the case there's no reason I shouldn't use them, since here they are, paid for and ready to bolt on? But if I was building a new set of heads smaller valves would be the ticket? I've read about overscavenging and I had visions of raw fuel burning thru the exhaust system. But that's not the case, right? Its for the street so practicality is an issue over max power.
Yes 392 heads, I checked the numbers b4 I bought them. When I bought the motor in March, I knew very little of this tech stuff, it was more like "I WANT those valve covers in my engine bay". Since then I've been learning so much more that I've come to the conclusion that this block may not be the best choice for all out power. I have a couple of issues with it now that I know a bit more about hemis. For now the stroker crank is out. When the car is finished(well, it'll never really BE finished) if I want more power I could build a stroker from a block with more integrity. But for a driver this block is OK i think, as long as I stay conservative. Really, if I can get into the low to mid 11's (doesn't seem unreasonable) it'll be the quickest car I've ever had so that alone would be a milestone.
What I have in mind for the car(66 dart) is somewhere between a ratrod and a restomod...ummm maybe a rat-stomod? I was in contact with somebody who apparently has experience with what I'm trying to do and he said it won't fit. My GF asked me what would I do if indeed I can't make it fit the Dart. I answered I'd have to change plans, put a smallblock in it and find another vehicle for the 392. "So you're going to clog the driveway up with MORE cars?"
"Yes, and your point?"
Oh, one more thing about overscavenging. If indeed some fuel/air gets sucked out the exhaust, would less overlap help?
Thanks,
Neil
-
Bored&Stroked
- Posts: 20
- Joined: Sat Dec 11, 2004 11:03 am
- Location: Columbus, OH
- Contact:
Re: Deck Clearance and other Qs?
If I was buying pistons, I'd either go with Ross (for unblown) or Venolia for blown - forged in either case. I'm using Venolia in mine (blown) - gave them the exact compression height, valve pockets, etc.. I'm running Oliver billet 6.86 rods (426), with the big pins - narrowed for the 92 . . . with standard rod journal sizes. I know a lot of guys are running BBC rods - which seems to be a cool way to go. I'm wondering how tough the rod journals are when you grind them down that far? Wondering if nitriding (sp?) would help with the BBC journal size?
57' 392 Hemi -- much to learn!