I had a chance to take apart my stroker 170 (210) engine.
What's wrong with this picture??



This has alway been a good running engine, it ran mid 14's on the motor and 12.90s with a shot of N2O but sticking a turbo on it seems to have uncovered the weak link... light weight cast pistons.



All but one piston now has broken skirts and the broken pistons fit loose in the bores to point of poor oil control.

The good news, the cylinders are not scuffed or damaged and the engine's bearings look like new.
I'm now hunting around for some stronger pistons at 3.500 bore size.
We may end-up going another .004 oversize to get to 89mm (3.504)

After 10 years, since building this engine... I had forgotton how much grinding and drilling we had done to the 198 crank in order to fit it into the 170 block. This crank has a bunch of big, deep drilled, balancing holes in it.
DD

That's the same thing I ran into, on my first turbo motor (1979). TRW forged pistons helped.

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

Excuse the "beginner" question... I haven't had this problem occur (thankfully): Why does the piston shatter below the rings? I would think that the stresses would be above the rings, on the top of the pistons.

-Mac

On this engine, we have a 1.56 "rod ratio" (5.7 con rod on a 3.64 stroke) and that tends to slap the piston "side to side" pretty hard.
DD

I wander if it was a bit loose on the bore clearances to begin with. Which rods did you use in this build, 170 or 225 rods ?


The skirts on those poor pistons is of a weak design anyhow, new slugs you shoudl be in good shape. I would go for the 3.504 just for the good ring choices. Or if you are wanting to push a turbo hard get CP to custom some pistons and let them and the guys at Total Seal pick the ring set
( I know CP = $XXX.00).


I really like that stroker setup, Mopar should have made that one there self. That engine should love the RPM and make the best use of the poor slants head over any other setup. If there was room for the 225 rods
( which I doute) that would really be a sweet setup. Even with the short rod it should rev quite nice with good torque to boot once it got in the rpms a bit.


What camshaft where you running in this engine? Funny thing about the camshafts for the slant, you meantioned more duration on the intake side had shown good results. I seen two different cam programs come up with that same setup . About 6 more degree on the intake than exhaust depending on valve size, flow, and compression.


Jess


Opps, you posted while I was typing

I just put my oil pan back on after a season of 21psi on an 80k mile motor and everything was fine. I checked the rod bearings and they were fine as well. I put new ones in since they were cheap off of ebay. I know you said you built the motot a while ago but do you remember the piston to wall clearance and what piston was used?

How fast did you go with the turbo? What kind of boost level did you run at?

See guys.... this is why I am so interested in Tom's stuff. I am going to push my stuff to make the corn gas go.

So may I ask Doc, what would you have done different if you built it today? (I know, I know... trade secrets)

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Chris'
Autobody
Restoration
Service

Actually, I've been trying to piece together stuff for my turbo build. So far I've been back and forth on how many cubes to use and such. One question though cause this idea ran past me. The 170 is a lower deck motor correct? So would putting a 170 crank into a 225 block allow you to use the 225 rods? I would guess there would be enough height difference, but just something that I would like to try since I need custom pistons anyway.
Have you found that less cubes will make up the difference in the rpm's Doc?

You'd need some really long custom made rods for a 170 crank in a 225 block. The 170 has a much lower deck height, and you're taking about an inch of stroke out of the motor. So you'd need a half inch longer rod to bring the pistons up to the 225 deck height, and even more rod length if you're using modern import pistons or want to bring them to the top of the deck like a normal 170.

_________________
"Mad Scientist" Matt Cramer
'66 Dart - turbocharged 225
My blog - Mad Scientist Matt's Lair

I don't "keep secrets" when it comes to SL6 info... I am always willing to help anyone crazy enough to want to build a Slant!

I now have a chance to do the "low block 198" engine build again so stronger pistons are at the top of the "do different" list. The good news is the piston selection has improved since I designed this combo.
At the time, I was focused on getting a "near square" bore to stroke relationship so I took the bore right out to 3.5 and used 140 CID Cosworth Vega pistons... we had to machine out the rod's small end to the Chebby .927 piston pin size to make those pistons work. In hind sight, now I have a block and a set of nice 170 rods at the end of their "service range" so it may-be time to detune this engine for it's last "go" as a street performance mill.

Today, I feel it is more important to keep the cylinder walls and con rod "eyes" as thick as possible so I would (will) downsize on the overbore and use pistons with the pins in the .900 to .905 size range. (that leaves me with some nice 170 con rods with .927 pin holes that will need bushings or special pistons)
I have already pull-out all my 170 con rods, already thinking that we may just prep a different set. Fact is, we will most likely set aside the 3.5 bore block and rods... and move the 210 parts into a new block, combined with 2.2 pistons at a 3.445 - 3.465 size. That gives us a 206 CID engine.

The 210 block sure got a lot of "fussing-over", all the edges are rounded, all the extra weight cut-off, the oil passages reamed-out, even the lifter galley is opened-up for the roller cam and lifters this engine started with. The next block will not get that level of "fuss".
DD

Doug,

You said the crank ended up with lots of big holes in it. What could be done differently to minimize the drilling? I'm on the fence as to whether I should use the 198 crank with the 170 rods I have for a stroker or just build a 170 with extra light rods and pistons. I have some trick 535 gram 6.200" rods if I do the 170.

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Joshua

Most of the crank drilling was caused by the Vega pistons, the bottoms of those pistons did not clear the first and last counter weights on the 198 crank. We wacked a 1/4 inch off the ends of those counter weights, then had to drill material off the opposit side of the crank to get it back in balance.

Looking at the KB268 2.2 piston and also at GM 2.8 V6 slugs, I see more room in this area so the amount of counter weight trimming for piston clearance should be less, if any.
DD

You engine was just "rejecting" the parts.

Chevy 2.8? there was a POS engine! 4.3's were much better.

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'72 Duster 198 stock cam, 3:23's Hookers on jack stands for 8 years in the driveway
'79 Maxivan 360 Offy Qjet Comp RV cam/rusting in the driveway.
93 D350 160HP Cummins Auto Dually Clubcab needs a injector pump
2005 Golden Couch Buick