melted pistons again need help

[vairy8]

This is my second post, and second rebuild on my 502, that I have had less than 1 year. Sorry if this gets to long, but I want to include as much as possible. The first time motor melted 2 pistons, dropped a valve seat and locked up. I did basic rebuild-
new stock pistons, stock bore, heads rebuilt, crank and rods touched up.
I put on new intake, edelbrock performer RPM, revolution marine manifolds, and comp cams 1.44 , 1.47 lift
I ran the motor on dyno with every thing except the manifolds, basically to make sure everything was OK. 485 HP At 5500 rmp 535 ft lbs at 3200 rpm.
The motor ran great for 40 hours and did same thing, but this time dropped a valve, bent a rod and my crank.
now here is what I have
540 ci eagle crank and H beam rods JE 8.4to1 pistons and m-1 procharger @7psi figure go all out this time,but I have a few qusions.
I am looking at edelbrock aluminum heads, but would like to hear what anyone else would recomend, and as far as my cam goes to reuse or not?
I am also going to run msd ignition, aeromotive fuel pump and regulator, but my boat has 2 fuel tanks that have selector valve to switch tanks. I want to eleminate that and run both 3/8 lines to one 1/2 line to my seperator, pump, regulator, then to carb will this work and draw off each tank evenly? again sorry this is so long, but any feed back would be a huge help -Thanks Aaron

[Daytona100]

WOW that is some crappy luck. Kinda went thru the same thing last season. Blew a motor first time after several years of boating. I hope im good for another 5+ years. Hope all works out see you at the lake. :)

[Infomaniac]

That is a carb Procharger???
You are gonna melt pistons until you get the proper carb for it.
I can get you a carb that works with it but they are not cheap.
Best thing to do is sell it and get another source of boost.

[Jerrys59]

This is my second post, and second rebuild on my 502, that I have had less than 1 year. Sorry if this gets to long, but I want to include as much as possible. The first time motor melted 2 pistons, dropped a valve seat and locked up. I did basic rebuild-
new stock pistons, stock bore, heads rebuilt, crank and rods touched up.
I put on new intake, edelbrock performer RPM, revolution marine manifolds, and comp cams 1.44 , 1.47 lift
I ran the motor on dyno with every thing except the manifolds, basically to make sure everything was OK. 485 HP At 5500 rmp 535 ft lbs at 3200 rpm.
The motor ran great for 40 hours and did same thing, but this time dropped a valve, bent a rod and my crank.
now here is what I have
540 ci eagle crank and H beam rods JE 8.4to1 pistons and m-1 procharger @7psi figure go all out this time,but I have a few qusions.
I am looking at edelbrock aluminum heads, but would like to hear what anyone else would recomend, and as far as my cam goes to reuse or not?
I am also going to run msd ignition, aeromotive fuel pump and regulator, but my boat has 2 fuel tanks that have selector valve to switch tanks. I want to eleminate that and run both 3/8 lines to one 1/2 line to my seperator, pump, regulator, then to carb will this work and draw off each tank evenly? again sorry this is so long, but any feed back would be a huge help -Thanks Aaron
Better try to sort out your problems before you do anything.

[paradigm shift]

When you say dropped a valve can you describe in more detail. What did the valve stem look like if there was much left? Do you have signs of detonation? Signs of running lean? Fuel pressure readings and do you run a fuel pressure cut out? Any weakness in your fuel system will haunt you. Boost and lean or detonation will melt one down in a hurry. What brand valve and model do you run. I am assuming it was an exhaust that failed? Sorry for your trouble man that sucks. Hang in there.
You will get some good info here just do your research. I am not much help with procharger carb set up and from what I have read they can be tricky to get set up. There are some guys on OSO running prochargers for a while so they do work.
Lots of questions but you said that is was run on a dyno first but your numbers can't be right with 7 psi boost.

[ECeptor]

Lots of questions but you said that is was run on a dyno first but your numbers can't be right with 7 psi boost.
If you are happy with 450-500hp there is no reason to have a supercharger on your 502. If you have the right heads and cam you can get 500hp easy and have a much more reliable (and cheaper) set up than you do right now.
What is your power goal?

[SmokinLowriderSS]

When you say dropped a valve can you describe in more detail. What did the valve stem look like if there was much left? Do you have signs of detonation? Signs of running lean? Fuel pressure readings and do you run a fuel pressure cut out? Any weakness in your fuel system will haunt you. Boost and lean or detonation will melt one down in a hurry. What brand valve and model do you run. I am assuming it was an exhaust that failed? Sorry for your trouble man that sucks. Hang in there.
You will get some good info here just do your research. I am not much help with procharger carb set up and from what I have read they can be tricky to get set up. There are some guys on OSO running prochargers for a while so they do work.
Lots of questions but you said that is was run on a dyno first but your numbers can't be right with 7 psi boost.
Please, clarification is in order. In my mind, a dropped valve is a lot different from a melted piston. My old diesel truck "dropped" a valve a few months ago. It broke of at 4,000 RPM on the freeway, not pretty inside. Melted pistons are usually caused from Detonation (or "pre-ignition") and is an entirely different animal. If you broke a valve, stuff-happens (especially if they were not fairly new), broke 2, THAT'S weird, and flags a problem to me. Maybe floated them and interference happened? Seems unusual to me on a low-comp motor tho.
If you have detonation from lean conditions, that MUST be sorted out or you will spend more money breaking more parts untill it is. Someone here will have this one but I THINK I recall hearing that dyno best HP mixture setups are usually too lean to actually run on a driving basis. Someone will correct me if I am off here (and it never made much sense to me) but I am sure I've heard it from a variety of sources.
Also, ECeptor is right. If you want about 1HP per CID, that's easy to do unblown with the right parts mixture. My MkIV 454 should be just shy of 500 HP after a head porting and headers on an 8.5:1 single 4-barrrel setup. Also cheaper and MAY be more reliable over the long run.

[TurboNova]

A couple of things here, If you are running a procharger with a carb, What carb? How much boost? How are you taking out timing when in boost? When you guys ran it on the dyno how did you check the tune? With an O2 sensor or EGTs? Just from your post, I'd say it was way too lean if you are melting pistons. I've never seen a piston melt from too rich. Detonation is also something to look at but usually takes out the head gasket first. Also stock pistons and boosted isn't a really good idea unless you are really on your game.
If you are shopping heads I would recommend Dart Pro 1s they are just about the best thing out there right out of the box. If you are going with a 540 engine then you will also need a new cam for your combo.
My suggestion would be to ditch the Carb and go EFI with your procharger and make it run like a new car does. You will then have total control of timing and fuel. There are several good systems out there FAST, Big Stuff 3 and Accel DFI then there are even more if you want to spend the big bucks Motec, EFI technology, Autronic.

[vairy8]

thank for all the replys so far. I am changing carburator to holly super charger tuned carb 850 mechanical dual feed. as for the second time the motor failed when we took it apart it had 2 pistons that were melted down to the top ring grove and one valve head was completely missing, broke or melted I could not tell. head and piston was pretty ugly. and when I say I was happy with 480 hp I mean for cheap almost stock rebuild, still was not enough for my boat. It is 30' conquest enforcer. the only thing I am reusing is the block fuel is getting upgraded and ignition. I know it sounds stupid to put all the money into motor until I find out the problem, but hope replacing everything and monotoring it alot better will solve problem. I am still not sure about pulling fuel from 2 gas tanks.

[TurboNova]

thank for all the replys so far. I am changing carburator to holly super charger tuned carb 850 mechanical dual feed. as for the second time the motor failed when we took it apart it had 2 pistons that were melted down to the top ring grove and one valve head was completely missing, broke or melted I could not tell. head and piston was pretty ugly. and when I say I was happy with 480 hp I mean for cheap almost stock rebuild, still was not enough for my boat. It is 30' conquest enforcer. the only thing I am reusing is the block fuel is getting upgraded and ignition. I know it sounds stupid to put all the money into motor until I find out the problem, but hope replacing everything and monotoring it alot better will solve problem. I am still not sure about pulling fuel from 2 gas tanks.
Is this carb set up for blow thru? If it isn't you may have to change the floats. It should also have annular boosters. This time around I would tune it with a wideband O2 meter on the dyno or in the water. I would suspect the you had a lean condition. Is this procharger intercooled? Make sure you have a rising rate fuel pressure regulator also, you should have 14-16psi of fuel pressure at 7psi of boost.

[vairy8]

I read thru some of your replys and I might not have been clear about the engine falure. It was stock pistons, no boost! stock carb, stock fuel pump, stock ignition the only things I replaced was cam, intake, and manifolds. Then ran on dyno, they had all kinds of stuff checking air to fuel ratio. We did not set it up lean to get more hp. I wanted it ran with all my parts so I could just drop in and go, no oil leaks, valves set and carb tuned. like I said it worked great for 40 hours, I also checked plugs twice they looked good.
I was just coming on plane around 4500 rpm and motor started missing, went straight back to beach and pulled plugs, found 1 all beat up. the only thing I can think of is fuel from tank to pump. It has 2 tanks that go to a valve up high on transom that lets switch from either side. would A blockage somewhere in there cause the problem?

[vairy8]

Is this carb set up for blow thru? If it isn't you may have to change the floats. It should also have annular boosters. This time around I would tune it with a wideband O2 meter on the dyno or in the water. I would suspect the you had a lean condition. Is this procharger intercooled? Make sure you have a rising rate fuel pressure regulator also, you should have 14-16psi of fuel pressure at 7psi of boost.
Yes carb is set up for blow thru, but I am not sure about annular boosters.
yes procharger is intercooledl, and I have not purchased fuel pump or regulator yet I plan on getting aeromotive a1000 pump and boost reference bypass regulator.

[TurboNova]

Yes carb is set up for blow thru, but I am not sure about annular boosters.
yes procharger is intercooledl, and I have not purchased fuel pump or regulator yet I plan on getting aeromotive a1000 pump and boost reference bypass regulator.
I have used this pump on a blow through boat but if you want to run much more than 10psi I would look into a magnafuel pump and regulator. The A1000 and their carb regualtor is only good to fuel pressure of about 20psi. Make sure you don't go too small on the fuel line either. The fuel system is no place to go cheaper.
For you to really get a carb dialed in on a blow thru you will need solid floats, annular boosters and screw in air bleeds.

[vairy8]

I have used this pump on a blow through boat but if you want to run much more than 10psi I would look into a magnafuel pump and regulator. The A1000 and their carb regualtor is only good to fuel pressure of about 20psi. Make sure you don't go too small on the fuel line either. The fuel system is no place to go cheaper.
For you to really get a carb dialed in on a blow thru you will need solid floats, annular boosters and screw in air bleeds.
Thank for info I only plan on 7psi boost I will have someone with more knowhow than myself to dial carb in.

[cstraub]

The canfield 310s or the AFR 315's hard anodized would be good choices and make good power. Either on a 540 and 7lbs should be capable of making 800 to 900HP depending on how conservative you get with final tune.

[ECeptor]

thank for all the replys so far. I am changing carburator to holly super charger tuned carb 850 mechanical dual feed. as for the second time the motor failed when we took it apart it had 2 pistons that were melted down to the top ring grove and one valve head was completely missing, broke or melted I could not tell. head and piston was pretty ugly. and when I say I was happy with 480 hp I mean for cheap almost stock rebuild, still was not enough for my boat. It is 30' conquest enforcer. the only thing I am reusing is the block fuel is getting upgraded and ignition. I know it sounds stupid to put all the money into motor until I find out the problem, but hope replacing everything and monotoring it alot better will solve problem. I am still not sure about pulling fuel from 2 gas tanks.
If you are satisfied with 500hp, sell the blower and run naturally aspirated. Will be much more reliable.

[SmokinLowriderSS]

thank for all the replys so far. I am changing carburator to holly super charger tuned carb 850 mechanical dual feed. as for the second time the motor failed when we took it apart it had 2 pistons that were melted down to the top ring grove and one valve head was completely missing, broke or melted I could not tell. head and piston was pretty ugly.
Looks like a lean-out, detonation trouble. Tops of pistons actually melted. Valve likely broke (only takes about 1,500 more degrees to melt steel than aluminum) but possibly from detonation pounding as it melted pistons. A lot of the guys here with high-HP engines are running ignitions with knock-sensors, that might well save you more than cost. Sounds like full throttle leanout maybe, insufficient feed volume to keep the carb(s) filled. Be sure to find out what your sustained WOT fuel pressure is. Should hold 7 to 9 psi above your boost pressure (like posted earlier). You probably better be thinking of 1/2" lines feeding the gasoline everywhere, and plenty of pump.
If 480 HP wasn't enough, 500 won't even be noticable. Smells like you want 700HP land, get ready to pay. Up front lets you play a long while reliably, you've already met the back door pay method.

[Gearhead]

If I understand correctly you mentioned running the engine on the dyno. What did the fuel curve look like?
Melted pistons as well as a dropped valve can be indications of an extreme lean condition under load.
What do the spark plugs look like?
If the engine is indeed running lean, a proper fuel curve and fuel delivery system can cure the situation.
I had one full size customer with an all steel Camaro 355" SBC that was running mid 11's with a factory Holley carb. He purchased one of the aftermarket carbs (i'll leave the builder unnamed), bolted it on without dyno testing and instantly picked up three tenths. The only thing was... three passes down the track and a valve head melted off and the rest is history.
Upon rebuild we put the engine on the dyno and found the carb had an extremely lean fuel curve, thus the performance increase and damage. We reworked the fuel curve to a good safe level and maintained good performance without additional engine problems.
Hope this helps a little.