SpriceyStuff
Well-Known Member
Hey guys. I was curious if anyone knows about any 198 size rods for a cast crank with the narrower journals? I’m looking to boost compression in my late model slant.
Long rods for cast crank 225?
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SpriceyStuff
Well-Known Member
So the journals are narrower, but is the crank pin the same diameter? If that's the case, then that's certainly a viable option. Is that something a body could do at home, or is that something I'd have to go to a machine shop for to make sure it's precision balanced. Glenn Everitt built a wicked slant, but he used Molnar H-Beam rods, which have long been discontinued for cast cranks. But his pistons were all balanced to within 0.03 grams, IIRC. I'd imagine that once you start messing with rods you have to start rechecking precision balances to make sure you don't end up with vibration issues. Definitely something I would strongly consider though. That machine shop bill can't be too high.
my68barracuda
Well-Known Member
The pin end is the same width on both the cast and steel crank rods.
Narrowing the big end of the connecting rods is not difficult, but it is machine shop work. Maintaining the specified rod side play on the big end is important. One would also need to re cut in the lock slots.
To keep the rod properly centered, the same amount would need to be cut from each side.
I have K1 long rods on the cast crank in the slant in my 68 Barracuda. I got them while they were still available from K1.
Narrowing the big end of the connecting rods is not difficult, but it is machine shop work. Maintaining the specified rod side play on the big end is important. One would also need to re cut in the lock slots.
To keep the rod properly centered, the same amount would need to be cut from each side.
I have K1 long rods on the cast crank in the slant in my 68 Barracuda. I got them while they were still available from K1.
Molnar (bought out K1) was making them. Call them. They will probably whoop you up set.
SpriceyStuff
Well-Known Member
That's kinda what I figured. Thanks! I know some guys at machine shops around town, so I'll look into some 198 rods at some point before I go to throw my motor together and see how much they'll charge me to grind on em a bit
my68barracuda
Well-Known Member
As Colombo would say,
‘Just one more thing’
ARP has different part numbers for the slant six cast and steel crank rod big end bolts.
How they are different and how that would play into narrowing a set of steel crank rods, if at all, I don’t know.
‘Just one more thing’
ARP has different part numbers for the slant six cast and steel crank rod big end bolts.
How they are different and how that would play into narrowing a set of steel crank rods, if at all, I don’t know.
No, he barely or sometimes not at all pronounced the "h" so it's "Just one more ting" lol
kesteb
Well-Known Member
The 198 rods are not just laying around waiting to be picked up. So you may have a problem finding some.
I would place a call to Molar/K1 first, the cost to acquire, machine, notch, add ARPs, & re-size is going to rival a new set of rods easily.
CNC-Dude
Well-Known Member
Yes, you quickly will be approaching the cost of aftermarket rods. Plus, don't forget after narrowing them, they'll have to be re-chamfered on both sides in the big end. So all those things almost make it cost prohibitive because you still end up with an inferior rod for the same cost or more than an H-beam rod.
Best of luck locating some 198 rods, they are very hard to find. If you are just looking to increase compression, why not just shave the deck or head or both?
I thought I had a set of 198 rods located so I started looking into what all that would get me in a long-rod motor. Others with more experience may weigh in to correct me, but IIRC it boiled down to yes, raising the compression but also lightening the rotating assembly to make for a quick and high-revving engine. As in more of a race motor than a street motor. It turned out the rods were for a 225 not a 198 so that's as far as I got down that path.
Just some food for thought...
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my68barracuda
Well-Known Member
That makes the assumption that K1/Molinar will do a run of cast crank long rods, as that is what this post was about initially
CNC-Dude
Well-Known Member
He has made short runs of long rods for the Ford and Chevy 6 cylinder guys before when approached about a "group buy", so its possible he would do the same again for the Slant since he's made them before, and he already has drawings and tooling to do it with....
Rug_Trucker
Love my 3.8 Buicks
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IIRC stock pistons have the pins at the wrong height to use 198 rods. So pistons go on the shopping list. Used to be 2.2 turbo ones?
I thought about swapping a 225 crank into my 198 at one time. Bad idea with the existing pistons.
I thought about swapping a 225 crank into my 198 at one time. Bad idea with the existing pistons.
Depending on how the supply of used engines is where you live, it might be easier and cheaper to find a core engine with a steel crank. Guess it depends on whether or not Molnar is willing to do a set of rods for you and what they'd charge for the extra work.
Supposedly the KB268 pistons work, and they have pin lock grooves. Only problem is they're sold in sets of 4 so you need to buy 2 sets to get 6 pistons, and they're about $285/set. Campbell Enterprises sells a set of Wiseco pistons with rings for about $500, but they're flat tops so you end up with a little over 10:1 compression ratio. The KB's give a little over 9:1 iirc.
I spoke with Tom Molnar last week and he seemed open for another run of rods. He just needs enough interest. I THINK he said five sets would do it. My memory is terrible. He seemed particularly interested in my long rod closed chamber head build though. Said he really likes the slant 6.
Rug_Trucker
Love my 3.8 Buicks
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I may end up buying the van next door. My buddy sold it to the neighbor. 1980 I believe. Solid lifter, peanut head, cast crank(?) 8.25 double tag rear end. 3:55's with a sure grip. I did what I call an RV port job on it. Rebuilt a super 6 BBD and pulled the 1bbl off and did the electro crap intake. It has the 833OD!
Sounds very cool!
CNC-Dude
Well-Known Member
They are made from the same blanks as the forged rod Slants, so it wouldn't be any trouble for him to make them....
Right, but the big end is pretty different. And it's not just a case of grinding the big end down to the .940 width, because the rod bearing tang is in a different location, so they have to make ah whole new rod. dangit all.
Now keep this in mind. A lot of people don't know this. There are TWO distinctly different slant 6 cast crankshafts. There's a light one and a heavy one. Pretty easy to tell apart, because the counterweights are a good bit smaller on the light cranks.
my68barracuda
Well-Known Member
Post this over at .org it is likely that a couple of folks over there would be interested in a set of cast crank long rods. That would help get the order numbers up.
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