IC 392 Stroker Motor Advice UT Results

C

cbmind

Member
So I've had this idea in my head about wanting to do an IC392 stroker motor. Max cubes. 450 plus? Is 500 attainable?

Here's where I'm at-

1. Have a complete motor.
2. Disassembled and hot tanked.
3. Magnaflux/ mag particle on the block. No concerns.
4. Ultrasound of cylinder walls for wall thickness and deflection


This guy achieved a 4" stroke. Look at info in #14.

75' IH 436SV

I am in the process of building up a 75' 392. It has been bored 0.040 over and offset ground to a 4.00" stroke. With it now being a 436, gaining 44 cu.in. It would also need longer rods to gain the full stroke. I have a custom set of groden nitrous/blower rods(which took forever to get) and...
forums.ihpartsamerica.com

I've been advised by others that it may be possible to remove .250" from the wall, based on previous experience in doing so with 304 and 345 blocks.

Am I looking at a faulty sonic test here?

Can I use stock replacement head gaskets or need custom? I talked to Cometic, they can produce them, as long as the overbore works out.

What's the feasibility of stroking the crank to, and even beyond, 4"? I'm okay with welding and offset regrinding, if it' even possible.

Is there any benefit to sleeving the block to attain a larger overbore, or longer skirt to prevent the piston falling out the bottom?

All I'm after is a max cubic inch ic392 that will run on pump gas. Fuel injection will be used.

1980 Scout Traveler- d60 front, 14b rear, th4l60, np241c, 38s. Wet weight is roughly 7500lbs.

Advice is appreciated.

Hoping Robert Kenney will chime in.

Thank you.
 
Last edited:
odSteve said:
It would have been interesting to see the answers posted here - kind of one of the purposes of the forum.
Click to expand...

I spoke to Jim this morning. Legend!

He suggested stay away from dreams of a large displacement motor, and focus on moving more air through it. I.e., supercharger.

He suggested a minimum wall thickness of .110". More than that, and you'll get into overheating issues.

He gave a few key details of one 392 build he did, which I believe is Robert Searles' motor.

1. IC392
2. SB400 stock bore pistons @4.125"
3. Dodge slant six rods.
4. Remove as much rotating mass as you can. They realized 20lbs removed! Much of it from going to a forged aluminum piston and removing the bob weights from the connecting rods.
5. Bush the small end of the rods for a BBC wrist pin.
6. Offset grind the crank. The realized a displacement of 427ci.

As for heads, he mentioned MPG Head Service and their CNC porting program for IH heads.

He did say years ago he had the chance to talk to the IH factory engine designer, and that the designer agreed they were raspy motors. The designer said the best numbers they ever saw, wee from putting 304SV head bowls in 392 heads, among other things. These were the heads used on the factory backed Baja racers. That's pretty extreme and sweet at the same time.

I'll call him again soon, and pick his brain.

Thank you Zaed!
 
Here's some more info from Jim-

1. Not certain if it's possible to take it beyond 4" stroke. Have to mock it up and see.
2. Not certain if the block can be sleeved because the walls are so thin anyway. May be interference at the bottom also.
3. Ford 460 V8 heads have bore spacing close enough to entertain their use. In his words, they only have 3 bolts that won't make up. Bore spacing is very, very close. More to gain from an aftermarket aluminum head than any overbore.
4. The dodge slant six rods were an off the shelf item, and had the big end narrowed. 7.0" center to center.

Good stuff.
 
Don't forget to knife edge those bob weights and a good windage tray. On the heads, perhaps an intermediate option is to use 345 heads for the smaller chamber and put the bigger valves in them. Fundamental problem is the exhaust ports are dinky.
 
Windage tray or crank scraper?

I considered a crank scraper.

Unfortunately, I'm limited to the improved cooling 392 head.

I thought the 460 head comment was pretty cool.
 
So with some more info in hand, the crankshaft has been sent to Ohio Crank to see what they can do with it. I asked for-

1. Maximum stroke increase with offset grind only.
2. Maximum stroke increase possible to reach 500CID.
3. Cost of the two options above.

See what they come back with.
 
Fun, lots and lots of fun.

Something different.

The rest of the truck is somewhat unique, so why not the motor?

Result= big smile when on the gas pedal.

Like to be able to pull down 500ft/lb of torque, 400HP.

Seems the simplest way is displacement. May not be the cheapest, but seems to be the simplest.

The heads have me worried honestly.

This will be an occasional offroader, mostly cruiser, family fun wagon. It won't see many miles.
 
Following with interest! I did a bit of work on the 345 in my scout, but nothing like what you're up to. Any plans to dyno test it???
 
Man, I want to bad.

Everyone talks about it, but few have done it.

Dyno testing is on the list to do, once complete.
 
None of the following suggestions are anything new, all recip. engines must be thoughtfully developed and managed taking all variables into consideration. Throughing parts at a stock engine will only do so much before finding the weak link in the chain. Many have been found.

Stroking is a simple process that can be applied to any engine. Usually a lower pin location (larger compression height), will yield a more durable build. That means balancing rod length with the cylinder length and stroke. The big block Chevrolet offers many rod designs and length option to allow you to optimize rod ratio, rod angle, piston velocity, piston pin location ETC. The reduction and offset grind in main bearing diameter will hand you a small increase in stroke

There is really one significant limitation when considering an IH SV and any performance upgrades, the heads. Significant improvements can be made as I'm sure you've seen and read but there will always be a limit. Without flow non forced induction, the SV will hit a brick wall for horsepower. Regardless if you increase the displacement or other go fast methodology.

Head gasket failure under pressure.
Even though the SV has only 4 head bolts per cylinder, so long as you avoid detonation, over temping parts and yes spark plugs to, and maximize block and head deck thickness, you can lean on them fairly hard. Induction charge cooling and careful oil temp control will do well for either turbocharging or super charging.

For forced induction, consider underside piston oil jets, either from the big end of the rod or custom plumbed from the main oil gallery. Piston temp is critical. Run high quality forged pistons and the correct clearance. Never lean on a cold engine, always let the coolant reach full running temperature before making a pass, so you avoid scoring a piston. the block must expand as the piston does under high loads or you'll possibly run out of oil clearance.

Anyhow, whatever you decide to take on, chose your path carefully and thoughtfully. Don't just settle for off the shelf parts that seem to fit together. Many companies will custom machine forged piston and ring packs for $100/hole. Weisco is one I have used many times.
 
Don’t bother turbo charging a 10 to 1 engine. Unless you like purchasing racing fuel stay somewhere in the 7 1/2 to 8 to 1 range.
 
Also keep quench spot on at .04 to .045”
Cometic will make custom head gaskets. Much better than composite gaskets. I use them on all of my performance build’s including supercharged engines.
 
Robert Kenney said:
Also keep quench spot on at .04 to .045”
Cometic will make custom head gaskets. Much better than composite gaskets. I use them on all of my performance build’s including supercharged engines.
Click to expand...


I talked to Cometic.

They offered copper head gaskets, and another, possibly MLS, I don't remember.

I also talked to Lubbock Gasket.

They offered a copper material, too, but didn't suggest for a vehicle other than race conditions.

Robert, what material are you requesting when you get Cometic head gaskets, and at what rough cost?

Lubbock will do their "standard" material, whatever that is, for around $250.

I need to talk to them both further.

I sent a rubbing of the block head surface, and cylinder head surface, along with the head gasket that was removed during tear down, to Lubbock Gasket to see what they can do for me.

Regarding CR- I know this no modern engine, but can it not be tuned as such to prevent detonation, and run premium gas, at something better than 8:1? Am I rolling the dice at say, 9:1CR with forced induction? I had planned on running an engine management system with FI, (probably MPFI, if I can sort it out), that controls fuel, timing, etc. On the low end, a Holley Terminator ECM with their harness, whether or not forced induction of any kind is used. E85 fuel is also plentiful here. FWIW.

Thank you!
 
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