2 cylinders destroyed

[Paul_G]

I had the procharger on the 383 for a while. Got it all dialed in. AFR's at WOT in the high 11's. It was running great, till it died. Cylinders 4 and 6 are destroyed. The others show just a little detonation, could pull a bit more timing but nothing destructive like 2 and 4.

It is a 452 headed stock 383, flat top L2315 pistons, mild cam, with an Eddy Performer 383 dual plane. It ran fine on 87 octane fuel prior to the super charger. Had 91 octane in it with the super charger. I am trying to figure out why it destoyed 2 cylinders like this.

Could it have been from the dual plane intake? Cylinders 2 and 4 both feed from under the plenum.

 

[RemCharger]

The only problem with running boost..
Nevermind i see you found it!


But seriously, it will start torching the weakest link. Just happened to be side by side.
Too much timing
Too shitty gas
Too lean

 

[Don Frelier]

But those look to be the richest of the bunch.
Perhaps before the ProCharger?

 

[Curiousyellow71]

Bummer, It sounds like the dual plane could have caused it. Could also be a issue with your carb hat or a combination of things. Would have had to monitor afr on those holes to know for sure. How small of cam?

 

[pnora]

What were the plugs looking like. To me it was to rich. Rich is just as bad as lean. You get a flame kernal glowing in the ring lands which then helps with detonation.

 

[Master Gunner]

One of the big rules of thumb I remember from the 70's was that when you put a blower on, you had to drop the compression. The old roots type blowers liked 8-9:1, or alot of octane. Probably even more imprtant now with the crap we have for fuel.

Mark

 

[lewtot184]

head gasket let go between 4&6. chunk of piston gone on #4; not enough end gap on the top ring? i'd say the short block wasn't set-up for boost. no quench with poor chambers and maybe too much compression or timing for the boost?

 

[Paul_G]

Bummer, It sounds like the dual plane could have caused it. Could also be a issue with your carb hat or a combination of things. Would have had to monitor afr on those holes to know for sure. How small of cam?

The hat is in question. For hood clearance they cut the top of the hat maybe 1/2" and welded a flat plate on it. They had it mounted at an angle going on to the carb. I repiped it to go on the carb straight from the front.
The cam is a

SUM-6401

1-bolt

222/234 @50

466/488 lift

114 LSA​

What were the plugs looking like. To me it was to rich. Rich is just as bad as lean. You get a flame kernal glowing in the ring lands which then helps with detonation.

2 and 4 had the straps burnt off. The rest were not bad, just a little rich like the cylinders.

head gasket let go between 4&6. chunk of piston gone on #4; not enough end gap on the top ring? i'd say the short block wasn't set-up for boost. no quench with poor chambers and maybe too much compression or timing for the boost?

The boost was under 7 psi, under 5 most of the time. I had the blow off valve removed letting boost blow to atmosphere through the mounting pipe.

 

[Paul_G]

I am going to get a running 440 motor home engine tomorrow and try this again. My plan for the MH engine is to pull the pistons, replace the rings and open the gaps. Probably going to use 440 source heads with ARP bolts and cometic head gaskets. And a single plane intake. There's an M1 on FABO, and a Street Dominator locally.

 

[RemCharger]

Sounds like a good plan, my buddy has had that exact combo running/racing for years. He used stock heads.
The source heads I'd be worried about quality of the valves. The heads can break off.

Oh and he did torch one piston once on the first shortblock, attributed it to some cloggage in the carb.

 

[Curiousyellow71]

I would hazzard a guess the performer killed it. Shorter is usually bad for the carb hat though. Cometics use a very smooth finish on the block and head surfaces or they will seap antifreeze(supposedly). All the engines we have run were surfaced so I haven't got any idea what the limit is. I suspect coating the cometics would possibly work.
Street dominator should be shorter then a m1. Might help with the hat? I like the M1 but I would sacrifice intake manifold height for a taller carb hat.

 

[diesel_lv]

For your application, under boost, the intake won't make much difference, dual plane/single plane. Air is being "forced" through. I've only run boost on 2 types of engines, iron head 2 valve V8, and aluminum 4 valve DOHC V8. The iron head w 8.5:1 and pulled 1° timing for every pound of boost. 4 valve is at 8.5:1, 23° total timing and none taken out all the way to 14psi on 91 octane. Both were run at 10.5:1 AFR at WOT. But both are completely different animals.

Ring gap n timing would be my concerns.

As said above, if you use Cometic MLS head gaskets, sealing surface on both heads n block need to be prepped for them.

 

[Master Gunner]

The boost was under 7 psi, under 5 most of the time. I had the blow off valve removed letting boost blow to atmosphere through the mounting pipe.

Right, but what was the comprssion ratio before you installed the blower, assuming you didn't change pistons.

Mark

 

[Doorkicker]

I love superchargers, and run them on everything, but they turn small problems into, well...

There's a lot of great comments here. Personally I don't think it's the intake. My guess is your head gasket let go. But, it seems clear you had some detonation. Flat tops with stock(?) heads isn't going to be crazy static compression, but that cam, while not big, will create added cylinder pressure.

If I was a betting man I'd say you had high cylinder pressure cause of a cam/supercharger missmatch, you detonated hard, popped the head gasket and crap from one cylinder trashed the other.

 

[HEMI-ITIS]

https://theblowershop.com/wp-content/uploads/2015/08/Effective_Compression.pdf

 

[lewtot184]

some kind of boost-retard may be in order here.

 

[69L48Z27]

I’m in the ring gap camp. Looks like the cylinder walls are destroyed and chunks of piston are missing from ring lands being tore up.

 

[furious70]

Fwiw I've been boosted efi with a dual plane on a 383 since 2012 and have always had very even distribution.
On a stock parts house reman.
With OEM .020 head gasket.
Fuel and timing management matters.

Edit: at a height of 12psi

 

[Paul_G]

Right, but what was the comprssion ratio before you installed the blower, assuming you didn't change pistons.

Mark

The 383 was about 9.12 static compression when using the calculator from Summit racing. .

 

[GrabberOrange69]

I’m definitely in the ring gap camp. I’ve never had a supercharged B/RB, but it was common on late model fords I was running and hanging with. The extra heat butts the top ring and it destroys the ring land and piston top. Same with nitrous.

Theres a Total Seal chart in the article on this link: Ring gaps

Sorry to hear your plight because that sounds like a cool combo. Look on the bright side: now you can stroke it, forged pistons, and turn up the boost! ;)