Super 200 ate pistons, reccomendations?

[George66Falcon]

Good evening, gents!

I've been working on and off on a supercharged 200 for awhile now. I made the mistake of using vacuum caps to cover the vacuum ports instead of the carb box instead of mechanically sealing them (I'll be tapping the ports and running a screw with sealant into each of them) and went lean under throttle. I broke a bunch of rings, bent a few connecting rods, and broke a piston skirt -- thankfully the block/cam/head are OK. I've picked up a set of forged connecting rods, but now I'm thinking it's time to consider some forged pistons as well.

My concern is spending a lot of money for something that won't be right. I fed my engine's specs into Grok and it came back with a reccomendation of a 20cc dished piston to lower the CR to 8:1. I'm running the 250 2v head with an m122 blower, water-to-air intercooling, meth/water injection, and 20lbs of boost.

Do you think the recommended pistons are appropriate? I appreciate your feedback!

 

[aussie7mains]

I recommend you back the boost off, 20psi is going to break something, especially with the fuels you can buy. What you could do is go to a 250ci six, this will drop the boost pressure but have a stronger bottom end power, that long stroke really gives a LOT or torque. I would also drop the CR to around 8:1, there are pistons for our unleaded crossflows down here in Australia that would do it, however they are NOT forged. I run up to about 18psi with stock pistons, but Im on LPG which has much better anti knock. Err on the side of caution. Are you injecting the water methanol upstream of the blower? Also IMO your better off with a draw through system, that way you get the benefit of latent heat as fuel is vaporised, this also helps with rootes blower sealing. Are your 200 rods NOT forged? We never had anything other than forged in Australia, and always nodular iron cranks, which are bullet proof.

 

[pmuller9]

Yes, 8 to 1 pistons are appropriate.

What is the camshaft profile?

Is the supercharger running wide open?
If so how are you controlling the pressure at the supercharger before the carburetor at part throttle?

What does the ignition timing curve/map look like?

 

[George66Falcon]

I recommend you back the boost off, 20psi is going to break something, especially with the fuels you can buy. What you could do is go to a 250ci six, this will drop the boost pressure but have a stronger bottom end power, that long stroke really gives a LOT or torque. I would also drop the CR to around 8:1, there are pistons for our unleaded crossflows down here in Australia that would do it, however they are NOT forged. I run up to about 18psi with stock pistons, but Im on LPG which has much better anti knock. Err on the side of caution. Are you injecting the water methanol upstream of the blower? Also IMO your better off with a draw through system, that way you get the benefit of latent heat as fuel is vaporised, this also helps with rootes blower sealing. Are your 200 rods NOT forged? We never had anything other than forged in Australia, and always nodular iron cranks, which are bullet proof.

Thanks for the feedback! I'd love to switch to a 250, but I just can't find one for any reasonable price. Our early 200 rods are forged, and later ones are cast.

As far as the supercharger, it is using its built in bypass valve, and methanol is injected with nozzles in the lid of the carburetor box after the blower. The water to air into your cooler is integral to the blower, so I wasn't keen on running any kind of fluid through it. My concern would be that it would simply drop out of suspension.

 

[George66Falcon]

Yes, 8 to 1 pistons are appropriate.

What is the camshaft profile?

Is the supercharger running wide open?
If so how are you controlling the pressure at the supercharger before the carburetor at part throttle?

What does the ignition timing curve/map look like?

The supercharger has its stock bypass valve. I'm using a slotted link on the supercharger's throttle body that connects it to the carburetors throttle so that they open/close in tandem. I'm using the stock 200 camshaft.

The HEI I'm using has had it's centrifugal advance locked out. I'm embarrassed to say that I don't recall the exact timing I am running, I adjusted it for highest vacuum and left it there.

 

[pmuller9]

The HEI I'm using has had it's centrifugal advance locked out. I'm embarrassed to say that I don't recall the exact timing I am running, I adjusted it for highest vacuum and left it there.

Your Holley Sniper is controlling the ignition timing?

If so, you should be retarding the timing 1 degree for each pound of boost.
The initial timing should be around 10 degrees and go to about 32 degree around 2800 rpm with the boost retard reducing the timing from that timing curve.

 

[George66Falcon]

Your Holley Sniper is controlling the ignition timing?

If so, you should be retarding the timing 1 degree for each pound of boost.
The initial timing should be around 10 degrees and go to about 32 degree around 2800 rpm with the boost retard reducing the timing from that timing curve.

I'm not actually using the sniper anymore. After a fuel pressure regulator, 3 O2 sensors, and an IAC motor I decided it wasn't worth the trouble and sold it. I'm now using an mad650bt blow thru carb.

 

[pmuller9]

I'm not actually using the sniper anymore. After a fuel pressure regulator, 3 O2 sensors, and an IAC motor I decided it wasn't worth the trouble and sold it. I'm now using an mad650bt blow thru carb.

You need to boost retard the ignition timing or you will continue to do engine damage.

 

[George66Falcon]

You need to boost retard the ignition timing or you will continue to do engine damage.

That I will certainly do.

 

[pmuller9]

Here is my suggestion.

MSD Ignition 6523 MSD Ultra 6AL Plus Ignition Boxes | Summit Racing

Free Shipping - MSD Ultra 6AL Plus Ignition Boxes with qualifying orders of $109. Shop Ignition Boxes at Summit Racing.

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[George66Falcon]

Here is my suggestion.

MSD Ignition 6523 MSD Ultra 6AL Plus Ignition Boxes | Summit Racing

Free Shipping - MSD Ultra 6AL Plus Ignition Boxes with qualifying orders of $109. Shop Ignition Boxes at Summit Racing.

www.summitracing.com

I've heard that one's really good, thank you for the recommendation.

 

[powerband]

... interesting fabbed forced induction system , more pics would be nice.
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20lbs boost and minimal Fuel and Ignition controls is more than enough on mostly OEM internals to lead to early failure.
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my initial attempt with Buick V6 derived Draw-Thru on 250 worked great - for about a week :.
above @1 bar:
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... for high boost levels and RPM's, likely stronger Pistons/ Rods and cam would keep it together longer.
Toyota Rods are reportedly best option and custom Forged Pistons with optimal compression height .
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anvil strong 200 and stroked version 250 offer the 200's higher and lighter RPM spinning capability and the 250's low RPM grunt - torque to be optimized with forced induction.
200 - 250 rod lengths

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3 years reliable now with centrifugal SC / modd' Holley 2Bbl , stock internals , @ 8:1 CR with built- but not milled head and close attention to AFR's, ign. has vac/adv until boost then centif' locked out @ 26 degrees advance, Rpm limit @ 5K. Boost comes on @ 2200 , just above cruise and blow-off limits to @ 1/2 bar.
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have fun

 

[George66Falcon]

Unfortunately, the juice isn't worth the squeeze for me, at this point. I've picked up a good big block ford motor for less than the cost of a set of connecting rods (I can find them all day for less than a good inline six), so I'll be installing that and building a manifold to suit my supercharger. I've been tinkering with my boosted inline six for a long time now, and people want way too much money for the parts these days.

 

[Frank]

Unfortunately, the juice isn't worth the squeeze for me, at this point. I've picked up a good big block ford motor for less than the cost of a set of connecting rods (I can find them all day for less than a good inline six), so I'll be installing that and building a manifold to suit my supercharger. I've been tinkering with my boosted inline six for a long time now, and people want way too much money for the parts these days.

Once you have your new engine all fabricated and in place, post us some pics here! Your creative setup on the 6 is sweet. Would like to see how the 8 turns out.