Thread: I need some 383 stroker help, Please!!!

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Ok, here we go. I've got a 94 Z-71 350 that lost oil pressure. Instead of fixing it I decided to build a 383. I bought a crank kit (one piece rear main seal) rods, pistons, all balanced, bored the block .030. I got it in using the stock TBI with a 260 comp cam. It ran good for 15,000 miles and busted the number 5 piston from the top ring groove up about half way around the piston. I then bored it out to .040, built it again with more ring gap, in which it lasted 24 miles and it busted the number 7 piston in the same manner. I had the block cleaned again and went one more time. Now it has busted the number 6 piston. The first two set of pistons were from Power House and the last set was Silv-o-lite. I am running around 9.5 compression on just cheap pump gas. This truck is a daily driver.I have been told that the 350 TBI is not giving the engine enough gas and that is what is causing it. I'm ready to build it one more time if I can just figure out a way to keep it together.

Thanks for any imput,

Kodiak

Sure sounds like its too lean . LT1S10 should be able to help you. Do yourself a favor.Use forged pistons next time and correct the lean condition.

hey Kodiak, is the piston broke off or do it look like it was cut off. if its lean it should look like a cutting torch cut a hole in it or melted it. was you getting into it when it blowed or just riding?

lt1s10, it is broke. It don't look burned at all. Each time it has broke it has been at normal highway speeds. I have been really easy on it for the first 500 miles each time I have built it. The anti-knock sensor is off the block and my machinest told me that it wasn't needed so I never put another one back in it. Do you think that could have anything to do with it?

Kodiak

Originally posted by Kodiak
lt1s10, it is broke. It don't look burned at all. Each time it has broke it has been at normal highway speeds. I have been really easy on it for the first 500 miles each time I have built it. The anti-knock sensor is off the block and my machinest told me that it wasn't needed so I never put another one back in it. Do you think that could have anything to do with it?

Kodiak

i was hoping you would say burnt, i burnt a lot of pistons and all of them looked burnt so it i knew what it was. if the moter has a anti-knock sensor on it i would hook it up. if it is burning pistons then the knock sensor would retaird the time when it sparked knocked and you wouldnt be having ths conv. can you get a pic. of the piston?

Now, would he be raising the compression ratio or lowering it. I think by increasing the volume of the combustion chamber area he would be lowering compression RATIO, but increasing actual compression values by getting more air into that area due to increased bore and piston. It is harder to see the actual compression without testing it while the engine is running. By broken I would think too tight of ring gap or poor pistons, but by you saying that you are running down the highway normally and they break I would say detonation. The TBI is tuned for a stock 350 and it isn't a very smart fuel injection. By increasing the size and air flow at the same time I think it got too damn dumb. Sorry I really don't like TBI at all. The thing is, check your timing and use some premium or bump up the fuel because at that speed/load likely lower rpms, some throttle tip in possibly, it is quite prone to detonate. The timing is high because you aren't baggin on it and the stock TBI just ain't cutting it I guess. OR maybe it just doesn't like you and it wants to die and be laid to rest??

lt1s10, I can get a pic of each piston on tonight. The first time I built it, I went with the lowest ring gap I could,( the tighter, the longer it is going to last, My thinking). The second time I went with the upper end of the scale. But the third time, I added 30-40% to that and still the same problem.

I know this engine hates me, or loves to eat at my wallet. I've built a dozen engines with out a single problem, but all of them has had a good ol Holly on top.

Kodiak

I would use a Silv-O- lite in a stock 350 only. Not a 383 or a 400.I tried it one time in a boat. Little too much timing, detonation, cheap piston, same results you had .Piston exploded.Use a forged piston and get the TBI figured out before You go through another one. You're out of wiggle room.Buy the pistons first and then have the block bored to the pistons using manufactors piston to wall clearance specs.If that doesnt work can the block and start all over.In the end thats going to be a very expensive 383. Hope the next one works out for you.P.S. Make sure You or the machinist mike each piston and each cylinder wall all the way down.

Originally posted by Kodiak
lt1s10, I can get a pic of each piston on tonight. The first time I built it, I went with the lowest ring gap I could,( the tighter, the longer it is going to last, My thinking). The second time I went with the upper end of the scale. But the third time, I added 30-40% to that and still the same problem.

I know this engine hates me, or loves to eat at my wallet. I've built a dozen engines with out a single problem, but all of them has had a good ol Holly on top.

Kodiak

are you cutting your rings to fit? as far a the TBI go if its all hooked up you wouldnt have this problem. the knock senser should have reg. the time, and if it was out of range it should turned on the check engine light. if it was to lean then the o2 sensers skould have warned you. i dont belive it burnt a hole in the piston just ridding down the road. WOT in a 1/4 mile maybe. i hope you can get good pic. i dont know for sure but i think the computer would cut the motor off, if it got that lean.

I have pics of two pistons in my photo gallery, the third piston is still in the engine. Both pistons have broke in the same manner. I have been filing the rings for each hole and made sure that is the hole they go in. I went with Silv-O-Lite pistons this last time because my machenist said he would stand behind them. I haven't tore the engine down after this third time but I know this is what has happened to them ( spark plug smashed flat). I'm going to try it one more time later this month, and if it don't work this time, I may have a crank for sale.

Kodiak

Originally posted by Kodiak
I have pics of two pistons in my photo gallery, the third piston is still in the engine. Both pistons have broke in the same manner. I have been filing the rings for each hole and made sure that is the hole they go in. I went with Silv-O-Lite pistons this last time because my machenist said he would stand behind them. I haven't tore the engine down after this third time but I know this is what has happened to them ( spark plug smashed flat). I'm going to try it one more time later this month, and if it don't work this time, I may have a crank for sale.

Kodiak

i dont see anything that says those pistons ran lean. those pistons are broke. i belive you dont have enough gap in the ring. how much gap do you have in the ring when you check the gap in the block? it dont look like much gap in the ring thats on the piston in the pic. i belive i can make those rings butt each other just mashing them with my hand and that shouldnt be.
i belive the ring is to tight and when it get hot its pulling the top of the piston off. let me know what gap you had and let some others give their opinion. is the machenist gonna stand behind these pistons. i really dont see the heat.

i just went back and looked at the pistons again and you can see carbon still on the top of the piston, dont belive that would be if heat just eat a hole in you piston.

I'm not for real sure what ring gap I put this last time, but it seems like it was around .025 on the top ring. I was going by a truck repair manual the first time and went the lowest I could. That was the piston 5 pic. The second time, I went with the top end specs in the manuel and that is pic 7 with only 24 miles on the new pistons. When I got the Silv-O-Lites, it had a paper in the box that said add 30-40% more ring gap so I went with .025 with still the same results and that is what the machenist figured it up at. After this last time, I pulled the engine (almost a year ago, that is why I don't remember the specs), through it in the shop floor and went with a stock 350. Now I want my power back so it is time again. That 383 sure was a mud slinger.

Kodiak

Originally posted by Kodiak
I'm not for real sure what ring gap I put this last time, but it seems like it was around .025 on the top ring. I was going by a truck repair manual the first time and went the lowest I could. That was the piston 5 pic. The second time, I went with the top end specs in the manuel and that is pic 7 with only 24 miles on the new pistons. When I got the Silv-O-Lites, it had a paper in the box that said add 30-40% more ring gap so I went with .025 with still the same results and that is what the machenist figured it up at. After this last time, I pulled the engine (almost a year ago, that is why I don't remember the specs), through it in the shop floor and went with a stock 350. Now I want my power back so it is time again. That 383 sure was a mud slinger.

Kodiak

. 025 sounds like a lot. i dont know, let some other people look at them. i still dont belive its lean but i guess it could be.

From what I saw I'd say those rings killed your pistons. The spot right where the ring ends are is where the piston broke, if you didnt move the ring around then it sure does look suspicious. It seems to look like they butted and busted the top off. 0.025 is quite a bit even with those Silvo-lite. I used them once and ironically my engine was destroyed so I swapped to forged and I didn't look back. Problem with the engine was an exhaust valve seat (hardened because they were old '68 186 castings) came out and shattered on the no. 1 piston and then reverted through the bottom intake runner and dropped another 3 pistons. Ok, back to reality, I assume you are measuring them correctly so whats the deal I wonder. I don't see detonation being a problem from those pistons. Is there something you maybe overlooked, like the other rings, the proper piston fit, deck height. I doubt that you would have overlooked stuff like this on the 3rd time through but I can't really see why this would happen unless the rings were filed incorrectly or with a large variance which would hardly explain why only one piston goes at a time because that could be a time thing too among other things, different heats etc. Are you getting suitable cooling to all the cylinders? Proper cylinder oiling? What type of rings are these? I don't mean to insult I am just brainstorming possibilities.

EDIT: Also, Richard I was thinking of something 'else' the other day when I posted about the compression psi going up but the ratio down. With more air yes the psi would go up, but the ratio would also slightly raise because of the extra volume. However, if the chamber was to decrease by even 1 cc when the cylinder was bored another .010 this could create less ratio than if the bore was .010 less with a one cc smaller chamber. Whatever, its small numbers with small variables and variances, but on the general increasing the bore, while maintaining all other things that determine the ratio, would increase the comp. ratio slightly.

Yes good points indeed, the 350 picks up 5 ci, the 400 picks up 6 ci and so on. A 383 cannot be a 383 unless the 350 is bored 30 over as well. I checked the comp ratio calculator and that is a good rule of thumb for boring, its close but not so accurate as to actually know it without calculating but it works close enough. Thanks Denny, I'll remember that stuff.