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What should piston to wall clearance be
I am rebuildiing my 502 and have new JE forged blower pistons. The instructions say 004-005 piston to wall and plus up to 002 -003 extra for marine use. I dont think a too loose is good either is it? Any experience here? Thanks Greg
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Re: What should piston to wall clearance be
Do exactly what JE says. My machinist had it set up and bored for regular use and I called JE and told them what I was running( cold block no t-stat for a procharger) We had to go back and open it up. People want to build these tight like car engines and that's why they blow 'em up.
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Re: What should piston to wall clearance be
Marine engines need more clearance between the piston and cylinder wall because of two things.
1. The pistons are under a greater heat load and run hotter, hence, they are expanded more. Remember, aluminum expands a lot with heat. 2. Marine blocks run cold and therefore don't expand as much as automotive blocks. So you need .002 more clearance so the the piston doesn't scuff in the bores. |
Re: What should piston to wall clearance be
I run Mahle pistons in my NA 540's. The piston to wall clearance is .0065. I run a crossover with no thermostat.
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Re: What should piston to wall clearance be
with all due respect Reed, i think you are wrong on both counts. in an apples to apples comparison, the internal thermodynamics of a marine engine and an automotive engine are precisely the same. and if you are running your block cold you wouldn't need larger clearences... you would need tighter clearences... not to mention that overcooling the block is a dumb thing to do from a metallurgical stand point anyway. piston to wall clearences are simply a function of the material the piston is made out of , its total mass and how much cam grind the manufacturer puts in it. running big clearences is no magic speed secret... its just a way to guarantee that you get bad ring life and average sealing. if you want the motor to make power and live, you run it at normal operating temeratures with as tight a piston to wall that the specific piston you are using will tolerate.
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Re: What should piston to wall clearance be
It has nothing to do with speed, it is survival of the engine. Pistons are hotter and will expand more so you need more space when building at room temp.
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Re: What should piston to wall clearance be
Originally Posted by kennyo
Do exactly what JE says. My machinist had it set up and bored for regular use and I called JE and told them what I was running( cold block no t-stat for a procharger) We had to go back and open it up. People want to build these tight like car engines and that's why they blow 'em up.
Solid Advice given here! Make sure your machinist also follows the ring manufactures honning procedure as well. Torque plates, ring gap, and RA finish. |
Re: What should piston to wall clearance be
Originally Posted by stevesxm
with all due respect Reed, i think you are wrong on both counts. in an apples to apples comparison, the internal thermodynamics of a marine engine and an automotive engine are precisely the same. and if you are running your block cold you wouldn't need larger clearences... you would need tighter clearences... not to mention that overcooling the block is a dumb thing to do from a metallurgical stand point anyway. piston to wall clearences are simply a function of the material the piston is made out of , its total mass and how much cam grind the manufacturer puts in it. running big clearences is no magic speed secret... its just a way to guarantee that you get bad ring life and average sealing. if you want the motor to make power and live, you run it at normal operating temeratures with as tight a piston to wall that the specific piston you are using will tolerate.
Different manufacturers require differnt clearances for their alloys and shape of piston. Depending on application, the rule of thumb is to add .001+ for differances in expansion. |
Re: What should piston to wall clearance be
Piston to wall is a function of bore size, stevesxm is on another planet, h2o temp in high hp is low because of the volume of h2o required in block and difficulty of regulating temp.Piston to wall should also consider use, big diff if your are going to run wot for extended periods or cruise at part throttle.
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Re: What should piston to wall clearance be
HP,
I am running the srp (JE) 4032. (Std 4.466 wtih .064 =4.530) The SRP chart calls for .0030/.0035 @ .500 up from btm skirt. (cold water pickup marine app may require an additional .002-.004) We went with from skirt up .003.5, then .004 then .005 close to bottom ring; kinda a taper in towards rings to minimize piston slap cold. I'll let ya know how it works on my very heavy deep v twins. p.s.did above on last 502 and still running after 200+ hrs on single deep v. |
Re: What should piston to wall clearance be
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Re: What should piston to wall clearance be
Originally Posted by stevesxm
with all due respect Reed, i think you are wrong on both counts.
Originally Posted by stevesxm
in an apples to apples comparison, the internal thermodynamics of a marine engine and an automotive engine are precisely the same.
The thermodynamic snapshot of a combustion event is pretty much apples to apples when observing a spark triggered cycle using a similar fuel in a similarly tuned motor, but differences such as one being carbureted and roots supercharged, versus another being normally aspirated with port fuel injection will alter the thermodynmic profile of the event significantly. But an automobile motor runs in an environment where it gets its coolant up to stable design temp quickly and holds it there. It runs under very light consistent loading, and only short bursts of moderate loading. It is designed, and is successful, to eliminate thermal hotspots internally during normal operation, and also runs a temperature profile that encourages complete, emissions free combustion events. Additionally, consumer NVH (noise, vibration, harshness) characteristics MUST maintain a very high priority to minimize people griping about cold start piton slap, etc. This is why most auto motors run cast (or hyper EU) pistons - they have a lower thermal expansion than forged. Boats depend on raw water cooling, and HIGH volumes of it. A boat's cooling system MUST maintain stable temps at extended WOT operation, so the end result is that it passes a LOT of water at lower speeds as well. Thermostats (when they are used) are lower temps that favor power production over emissions optimization. Higher output motors can't even make do with high flow thermostats, and usually run without any. This is a drawback due to running a motor designed around passenger car specs and put in an application where it puts out twice the max design HP for extended periods of time. A far as combustion heat, each event at WOT produces basically the same thermo snapshot, but piston temps are not the byproduct of ONE combustion event. After each event, a cooling process takes place until the next combustion event. A piston cools by conduction, convection, and radiation. Heat is transferred off of a piston through oil, through ring contact to the liner, into incoming intake charge air, down the connecting rod, and into crankcase air. Each heat transfer medium must eventually release it heat load into the environment. The eventual environment is the "planet" in that all of the internal heat has to get out through oil coolers (into cooling water), through block radiation into the engine compartment, and out into the atmosphere, through crankcase venting blowby (usually back into the intake, but partially into the atmosphere as well), through the exhaust into the atmosphere, and out through the cooling water, also into the atmosphere and into the seawater. Since there is no creation or destruction of energy, our motors are all "planet cooled". But as you can visualize, ANY motor running under a heavier load than another similar one will have components intimately involved in the combustion process that are running at higher temps due to the inability to cool completely between combustion events. A marine motor WILL run its pistons hotter than an auto application. This makes the pistons expand more, and close up the cleaances. A marine motor WILL have cooler water in the block than an auto application. This will (minimally) make the bores stay snugger (near the bottom of the stroke) than those in a car application, closing up clearances.
Originally Posted by stevesxm
and if you are running your block cold you wouldn't need larger clearences... you would need tighter clearences...
Originally Posted by stevesxm
not to mention that overcooling the block is a dumb thing to do from a metallurgical stand point anyway.
Originally Posted by stevesxm
piston to wall clearences are simply a function of the material the piston is made out of , its total mass and how much cam grind the manufacturer puts in it.
Originally Posted by stevesxm
running big clearences is no magic speed secret... its just a way to guarantee that you get bad ring life and average sealing.
Originally Posted by stevesxm
if you want the motor to make power and live, you run it at normal operating temeratures with as tight a piston to wall that the specific piston you are using will tolerate.
Please call me when you prepare to run your 600 horse motor for the first time in your boat at passenger car piston clearances. I will fly down with gas money and suntan lotion to ride with you in support. I'll even bring money for the guy who has to tow you back to the ramp. mc |
Re: What should piston to wall clearance be
well... youll notice i was careful to say apples to apples... and having built an awful lot of engines over the 25 years i was doing it... including a fair number of marine, my experience doesn't suggest any material difference. your notion of combination and circumstance is, of course correct... but i made no "one size fits all " suggestion...
and if you can;t find a way to keep your thermal balance correct so that your motors operate at essentially nominal temps... well then build them as you see fit to compensate.. that a decision and a compromise you make when you start. one that i was unwilling to make. i have used the je pistons in the cars we ran at daytona... for 24 hrs straight... at 600 hp... all day... and all night. and never stuck a one... or blew one up for that matter... an environment that makes the marine seem tame by comparison. and the mass makes all the difference in the world as far as the total growth per delta t. the total volume of the material determines the total growth. pistons w/ more mass grow more than ones with less. that is the simple physics of it. i ran 4" je at .007 because they were thick and soft and 4 " cosworths at .004 because they were thin and WONDERFUL material... the cosworths were able to use 1 mm rings because the stability was so much better... and made significantly more power because of that... on motors that ran in conditions where the operating temps were, in fact less than we wanted, i ran them tighter... and they were better because the block isn't the only element in the equation. and they were ALWAYS better than the loose motors. and lasted much longer. now.. if you want to perpertuate the myth that marine service is somehow more mystical than " dry service... in the SAME load conditions... well, simply... it makes no difference to me... but in the real world, the marine environment is EXACTLY the same dyno as the the dry environment... SAME loads , and , if done properly, the same cooling. the motor doesn't care if its in a boat, on a dyno or in somebodies camaro. it will make the egts as per the load demands over time. in an apples to apples there is zero difference... except in what people do to them. but hey you want to run them cold and combine to compensate... thats up to you. you want to run them loose enough to rattle and lose ring seal, knock yourself out. ill still be running while you are on your third set. |
Re: What should piston to wall clearance be
you still want to apply an apples to apples for a marine versus an auto. Or even an auto race situation.
Then you want to try to tell me that a 24 hour race engine is the same application as a marine performance motor? ANY motor that runs under a 24 hour load situation can be optimized - temps, cooling system, oiling system, you NAME it. And exactly how many start up and reheat cycles did that motor have to deal with? Maybe 1? And in the infield, if you were able to somehow tell me that you didn't have reasonable periods of throttle off time and cycling rpm thru the gears for heat refresh, then I'm all ears. And when did EGT's become the only thing that contributed to piston expansion over extended loaded runs? Thick piston with more mass expanding more than the SAME ALLOY in a similarly designed thinner, less mass, piston? Only because you are able to pull more heat out of the thin one on the dead stroke. YOU take a piece of 3" tall 3" diameter aluminum round bar and a piece of 3" tall 3" OD x 2.75" ID aluminum hollow bar of the same identical alloy, throw em in your oven at 500 degrees for 2 hours and measure em. THEN you tell me that more mass equals more expansion. Material differences in the Cosworth piston versus the JE don't count. Auto racing make marine environment tame? Depends on what characteristic you are talking about. If you are talking about mechanical fatigue, maybe maybe not. A marine setup typically runs a particular rpm for long periods where an auto race motor cycles up and down. Maine engines are more susceptible to harmonic frequency issues due to this. Valvesprings are a particular concern here. We can get into a buncha diffrent areas where one is "worse" than the other, but a marine application IS AN EXTENDED DYNO RUN. And a car race has periods of thermal recovery due to throttle lifting for braking and modulation in the corners. As far as running them hot or cold? I'd love to run a 900 horse BBC at 160 degrees stable with rapid warmup and the ability to hold it there at WOT as well as not overcool it at slow cruise. I'm happy that you've built 25 years worth of marine motors that are better than most in many ways. Ever thought about becoming a consultant for JE? You can tell them to put a new note in their catalog tech section under "recommended clearances". You can tell them to put "Go buy Cosworth Pistons". And then send them your consulting bill. I like rattly pistons on startup that fit real nice at WOT in my cold, clearance compensated underengineered (and certainly underfunded) motors. Maybe when you get finished with set of pistons you can donate em to me. Your trash should work just fine in my motors. Heck, in mine, they'll never touch the bores anyway... :) |
Re: What should piston to wall clearance be
Originally Posted by mcollinstn
I think he's right. So does JE.
The internal thermodynamics of NO TWO engines are precisely the same... Much less the internal thermodynamics of two different applications, loading profiles, and cooling profiles. The thermodynamic snapshot of a combustion event is pretty much apples to apples when observing a spark triggered cycle using a similar fuel in a similarly tuned motor, but differences such as one being carbureted and roots supercharged, versus another being normally aspirated with port fuel injection will alter the thermodynmic profile of the event significantly. But an automobile motor runs in an environment where it gets its coolant up to stable design temp quickly and holds it there. It runs under very light consistent loading, and only short bursts of moderate loading. It is designed, and is successful, to eliminate thermal hotspots internally during normal operation, and also runs a temperature profile that encourages complete, emissions free combustion events. Additionally, consumer NVH (noise, vibration, harshness) characteristics MUST maintain a very high priority to minimize people griping about cold start piton slap, etc. This is why most auto motors run cast (or hyper EU) pistons - they have a lower thermal expansion than forged. Boats depend on raw water cooling, and HIGH volumes of it. A boat's cooling system MUST maintain stable temps at extended WOT operation, so the end result is that it passes a LOT of water at lower speeds as well. Thermostats (when they are used) are lower temps that favor power production over emissions optimization. Higher output motors can't even make do with high flow thermostats, and usually run without any. This is a drawback due to running a motor designed around passenger car specs and put in an application where it puts out twice the max design HP for extended periods of time. A far as combustion heat, each event at WOT produces basically the same thermo snapshot, but piston temps are not the byproduct of ONE combustion event. After each event, a cooling process takes place until the next combustion event. A piston cools by conduction, convection, and radiation. Heat is transferred off of a piston through oil, through ring contact to the liner, into incoming intake charge air, down the connecting rod, and into crankcase air. Each heat transfer medium must eventually release it heat load into the environment. The eventual environment is the "planet" in that all of the internal heat has to get out through oil coolers (into cooling water), through block radiation into the engine compartment, and out into the atmosphere, through crankcase venting blowby (usually back into the intake, but partially into the atmosphere as well), through the exhaust into the atmosphere, and out through the cooling water, also into the atmosphere and into the seawater. Since there is no creation or destruction of energy, our motors are all "planet cooled". But as you can visualize, ANY motor running under a heavier load than another similar one will have components intimately involved in the combustion process that are running at higher temps due to the inability to cool completely between combustion events. A marine motor WILL run its pistons hotter than an auto application. This makes the pistons expand more, and close up the cleaances. A marine motor WILL have cooler water in the block than an auto application. This will (minimally) make the bores stay snugger (near the bottom of the stroke) than those in a car application, closing up clearances. Only if you planned to pin the block on the end of a great big connecting rod and make a piston out of it. On this planet, a cold block equals smaller bores. Yes, it is certainly a dumb thing to do. But given the parameters of what we start with (a passenger car motor designed for 300horsepower), it is a necessary concession that has to be made in order for it to not eat itself at WOT. If we started with 600hp continuous duty industrial diesels, we could run them exactly as their designers intended. But then all our 35' performance boats would run 20mph WOT due to the weight, we would have no room for passengers (or adult beverages) since the motors would be 10' long, and we would have to learn how to dock quickly and leap out as the boats rapidly sink tail first when stopped.. there's nothing "simple" about piston to wall clearances. It also has nothing to do with a piston's MASS except for a partial relationship between THICK HEAVY pistons being tougher, stronger, and a lot harder on rod bolts. You also left out the cylinder liner expansion characteristics, the loading and cooling curves of the application, the duty cycle, and the thermal window in which it will be required to operate. There's nothing SIMPLE about the complex math that goes into determining these things, and nothing simple about the trial and error and R&D that goes into fine tuning the theoretical numbers. The only SIMPLE part of it is that the piston Mfrs have done all this for us and all we have to do is SIMPLY follow their hard-earned recommendations. There are NO MAGIC SPEED SECRETS. The ways to make big block marine horsepower have been established a long time ago and everybody has access to them. The ways to make these motor dependable and lon lasting are also well established and everybody has access to them. No secrets here. Bad ring life? Do you expect that you will get GOOD ring life with your pistons scuffing the cylinder walls, smearing them with surface aluminum? Rings don't seal very well with aluminum scrapings on their faces and in the grooves. Why do you say that running PROPER cold clearances will hurt your ring life. RUNNING clearances will end up being CORRECT for piston stability and ring geometry. Hello. Hello. Can you hear me now? Normal High performance MARINE temperatures are, exactly as stated in the above text. As tight a piston to wall clearance that will be tolerated in a high performance MARINE application is exactly the marine clearance numbers that JE recommends. Please call me when you prepare to run your 600 horse motor for the first time in your boat at passenger car piston clearances. I will fly down with gas money and suntan lotion to ride with you in support. I'll even bring money for the guy who has to tow you back to the ramp. mc Dam I forgot how good you were at this stuff. Welcome back! :drink: HPJUNKIE stick to what JE tells ya. If you think thats aggresive take a look at what Ross pistons recommends. |
Re: What should piston to wall clearance be
Go ahead and build it with normal car clearances, you'll figure it out when your running a 100lbs of oil pressure and pumping oil out the dipstick, breathers, mains and anywhere else it can find it's way out of the motor.
Been there done that. You need the extra clearance to run high rpms for extended periods of time. You don't run a car motor at 5k for 30 minutes under a full load. Cross over, oil cooler, what ever, you still create too much heat in the cylinders to make it last. It's one of the reasons you don't just buy GM crate motors and stuff them in a boat with brass freeze plugs. |
Re: What should piston to wall clearance be
.0055 ?
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Re: What should piston to wall clearance be
Wow.
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Re: What should piston to wall clearance be
How about ring end gap? :D
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Re: What should piston to wall clearance be
Actually my motor has a crossover ,runs about 110 degrees. I run it mostly 28-3500 rpm with an occassional burst to 6200 under 7psi boost. Very seldom do I cruise at 45-5000 or so rpms. Seldom not never. So.0065 on the pistons and 050 per inch on the top ring and 055 per inch on the second ring per JE . I will look at the ross piston page for comparision. Greg
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Re: What should piston to wall clearance be
GPM thats 0055? How big of boat?
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Re: What should piston to wall clearance be
The ring gap was fine, no sign of butting. The manufacturer originally said to run .0055 clearance. after seeing the pistons they said I should run .0075.
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Re: What should piston to wall clearance be
Originally Posted by HPJunkie
GPM thats 0055? How big of boat?
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Re: What should piston to wall clearance be
GPM is that what your running now? (0075). Do you run at high rpms for extended periods of time? (Lots of heat) Are you supercharged? Thanks Greg
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Re: What should piston to wall clearance be
Originally Posted by HPJunkie
GPM is that what your running now? (0075). Do you run at high rpms for extended periods of time? (Lots of heat) Are you supercharged? Thanks Greg
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Re: What should piston to wall clearance be
I would like a cat. I was thinking about an Eliminator 28 single. Whose do you have? Are you running an m-1 m-3 m-4? I have an M-4 and only ran it 1 time. Then boom. I used to have an M1 for 4 seasons. I think I had junk stuck in the oil cooler impeding flow to the motor. Maybe bad gas. Oh well gonna play! Greg
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Re: What should piston to wall clearance be
Originally Posted by HPJunkie
I would like a cat. I was thinking about an Eliminator 28 single. Whose do you have? Are you running an m-1 m-3 m-4? I have an M-4 and only ran it 1 time. Then boom. I used to have an M1 for 4 seasons. I think I had junk stuck in the oil cooler impeding flow to the motor. Maybe bad gas. Oh well gonna play! Greg
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Re: What should piston to wall clearance be
yes I agree. I am thinking I will put this setup on the dyno before installing in the boat and watching the fuel pressure and egts etc. What kind of boost are you running? can you get 115 out of it? Greg
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Re: What should piston to wall clearance be
Originally Posted by HPJunkie
yes I agree. I am thinking I will put this setup on the dyno before installing in the boat and watching the fuel pressure and egts etc. What kind of boost are you running? can you get 115 out of it? Greg
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Re: What should piston to wall clearance be
Really, your outta control! Thats really cool. White knuckle baby! What compression ,Race gas? :D
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Re: What should piston to wall clearance be
Originally Posted by HPJunkie
Really, your outta control! Thats really cool. White knuckle baby! What compression ,Race gas? :D
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Re: What should piston to wall clearance be
Originally Posted by stevesxm
with all due respect Reed, i think you are wrong on both counts. in an apples to apples comparison, the internal thermodynamics of a marine engine and an automotive engine are precisely the same. and if you are running your block cold you wouldn't need larger clearences... you would need tighter clearences... not to mention that overcooling the block is a dumb thing to do from a metallurgical stand point anyway. piston to wall clearences are simply a function of the material the piston is made out of , its total mass and how much cam grind the manufacturer puts in it. running big clearences is no magic speed secret... its just a way to guarantee that you get bad ring life and average sealing. if you want the motor to make power and live, you run it at normal operating temeratures with as tight a piston to wall that the specific piston you are using will tolerate.
Piston expansion, size, and design are a product of several factors. 1. Ultimate compression ratio.Blown motors are higher. 2. Duty cycle. I know race engines are stressed highly... but there are periods of deceleration where cylinder vacuum draws oil up onto the upper cylinder and piston. This helps with the transfer of heat and lubrication. 3. Lubrication. Oil helps keep the pistons from scuffing along the cylinder walls... but it also acts as a medium to transfer heat out of the piston top (from the underside) and also into the cylinder wall. A lot of high performance rods have a port that squirts oil onto the underside of the piston crown and down the major thrust side of the cylinder wall. This is great for cooling a piston... but it makes oil control a problem. 4.Pistons aren't just "cam ground", they also have a taper.That taper is there to compensate for the expansion of the crown from heat . Ideally the piston when running at operating temps will be almost straight up and down. That is one reason engines are noisy when cold. There is also another aspect about forged pistons that most people don't know or understand why. That is an offset wrist pin. Most hiperf pistons don't have an offset because people don't care about the noise. JE will offset the pin of you ask them. 5.Automotive racing engines are designed to run at higher temps because of thermal efficiency. You can't run raw sea water at high temps through an engine block and heads unless you want to see your engine dissolve from the inside. So... if you want to cool your engine with superheated corrosive salt water, go right ahead. The other option is a huge intercooler, and it's going to suffer also from the corrosive effects of the salt water. That is the reason the Viper motors that have been marinized by Ilmor have heat exchangers and are naturally aspirated. They can't stand having salt water flowing through an aluminum block. Ilmor runs bigger piston clearances when they marinize the engines... Do you want to tell me you more know about racing engines than Ilmor? 6. Most people are trying to run supercharged engines using pump gas.. not racing fuel. Everything is a compromise. |
Re: What should piston to wall clearance be
Originally Posted by BADKACHINA
Go ahead and build it with normal car clearances, you'll figure it out when your running a 100lbs of oil pressure and pumping oil out the dipstick, breathers, mains and anywhere else it can find it's way out of the motor.
Been there done that. You need the extra clearance to run high rpms for extended periods of time. You don't run a car motor at 5k for 30 minutes under a full load. Cross over, oil cooler, what ever, you still create too much heat in the cylinders to make it last. It's one of the reasons you don't just buy GM crate motors and stuff them in a boat with brass freeze plugs. BADKACHINA - Actually, I stuffed a ZZ502/502 crate in my boat and have run it for 4 seasons now. Brass freeze plugs and all :D Lots of WOT. Including a hand full of +25 mile just about WOT romps during local poker runs. Hey, maybe I've just been lucky. But the ZZ has held up well. Still runs as well as the day it was dropped in the boat. Maybe the 20 hr. oil changes helped :) Great thread, and information. I'm about to deliver my engine to a machinist/assembler for some upgrades. And because of the anticipated increase in hp, I was wondering about piston/wall clearance. I plan to have that checked. Like I said, maybe I've just been lucky. |
Re: What should piston to wall clearance be
I think lucky also.
Originally Posted by Kidnova
"It's one of the reasons you don't just buy GM crate motors and stuff them in a boat with brass freeze plugs."
BADKACHINA - Actually, I stuffed a ZZ502/502 crate in my boat and have run it for 4 seasons now. Brass freeze plugs and all :D Lots of WOT. Including a hand full of +25 mile just about WOT romps during local poker runs. Hey, maybe I've just been lucky. But the ZZ has held up well. Still runs as well as the day it was dropped in the boat. Maybe the 20 hr. oil changes helped :) Great thread, and information. I'm about to deliver my engine to a machinist/assembler for some upgrades. And because of the anticipated increase in hp, I was wondering about piston/wall clearance. I plan to have that checked. Like I said, maybe I've just been lucky. |
Re: What should piston to wall clearance be
Would the tolerance change with coated pistons (ceramic dome and Teflon skirts ),piston sprayers,closed dry sump with 10# suction ?
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Re: What should piston to wall clearance be
Originally Posted by CcanDo
Would the tolerance change with coated pistons (ceramic dome and Teflon skirts ),piston sprayers,closed dry sump with 10# suction ?
The rest of it is two fold. One: what block/coolant temp you planning to run? Cold blocks = smaller bores (with a touch of taper) |
Re: What should piston to wall clearance be
mcollinstn,the first set is finished.Sheet metal intake is the second set.
The blocks are new cnc bowtie gen IV.The first set is: bore 4.535,6.635 rods and 4.75 crank.Pulled 1,000 hp @ 6,000,non inter cooled,6.2 # boost,10#suction,+40*intake manifold air temp,110* water temp, 32 *timing,.065 clearance w/coated pistons w/dlc pins and sprayers. The next short blocks will be 4.375 crank w/a little heavier flywheel,same rods and pins below the support rails.The heavier flywheel is first, for idle torque. |
Re: What should piston to wall clearance be
Would ceramic coated piston tops add or subtract from the clearance? My builder said run 006 and another said run 0065. JE max is 0075. Out of 2 meltdowns none were from skuffing of the pistons to the cylinder. Both were detonation. This time I ceramic coated the pistons, chambers and Exhaust ports. I wonder if that was a mistake. Keeping the heat in the chamber might increase the detonation possibility. No teflon on the skirts though.
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Re: What should piston to wall clearance be
Originally Posted by Kidnova
"It's one of the reasons you don't just buy GM crate motors and stuff them in a boat with brass freeze plugs."
BADKACHINA - Actually, I stuffed a ZZ502/502 crate in my boat and have run it for 4 seasons now. Brass freeze plugs and all :D Lots of WOT. Including a hand full of +25 mile just about WOT romps during local poker runs. Hey, maybe I've just been lucky. But the ZZ has held up well. Still runs as well as the day it was dropped in the boat. Maybe the 20 hr. oil changes helped :) Great thread, and information. I'm about to deliver my engine to a machinist/assembler for some upgrades. And because of the anticipated increase in hp, I was wondering about piston/wall clearance. I plan to have that checked. Like I said, maybe I've just been lucky. I don't think you've been lucky Kidnova. You always had a good tune, good cooling and good maintenance. That is why you never needed the insurance of extra clearances. BT :cool: |
Re: What should piston to wall clearance be
HPjunkie,4.56 bore will unshruod the valves.However,cylinder wall is that much thinner and effected by boost pressure,crank diameter,RPM and crank to rod ratio.
Your ceramic coating should be fine and not trap heat subject to a good set of adequate tube size headers and propped so the motor is not lugging. |
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