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 Post subject: 225 vs 198 rod strength
PostPosted: Fri Jan 01, 2021 9:07 am 
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Supercharged
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I was looking at the caps of my 225 and 198 rods side-by-side and noticed that next to the rod nut the 198 rod cap is quite a bit thinner. Has anyone ever have an issue with a 198 rod in the cap area? I'm going to be swinging somewhat heavy TRW L2502F pistons and would like it all to stay together. This is my first long-rod build so I'm just seeking a little reassurance. Also, I'm narrowing the rods to fit a cast crank like Doug did with his Buster build.

A Google Drive picture link is below. Sorry for the shadow in the picture. Upgrading my garage lighting is in the near future.

https://drive.google.com/file/d/1D4frpB ... sp=sharing

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PostPosted: Fri Jan 01, 2021 8:12 pm 
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I wonder if the 198 which I assume is based on the old 170 is a light build design. Smaller cars etc. 225 was used in a lot of different vehicles, some quite hefty. just a thought.


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PostPosted: Fri Jan 01, 2021 8:31 pm 
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plymouthcranbrook wrote:
I wonder if the 198 which I assume is based on the old 170 is a light build design. Smaller cars etc. 225 was used in a lot of different vehicles, some quite hefty. just a thought.

but the 198 and the 225 used exactly the same block. same bore size. Only difference between a 198 and 225, was the crank (for the longer stroke of the 225) and those rods.
You can put a 225 crank and rods (same pistons even, that the 198 used) into a 198, and you have a 225.
but the "hot setup" is to use 198 rods on the 225 crank, with custom pistons (basically Mopar FWD turbo engine ones) in a 225 block.... because the stroke is "built in" to the crank, the 198 rods being longer, puts the pistons closer to even with the top of the block instead of (roughly) 3/16" down, as a 225 comes "stock" from the factory, gets more compression ratio and because the 2.2 pistons are "shorter" than /6 pistons, an engine built that way, will rev quicker due to less weight in motion.
the only problem is that 198 rods are the needle in a haystack...... and the sticking point that is keeping more of us, from building such an engine.


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PostPosted: Fri Jan 01, 2021 9:01 pm 
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I've turned my long rod motor over 6700 and sprayed it. Never hurt a rod yet. 2.2 turbo pistons.

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PostPosted: Fri Jan 01, 2021 9:06 pm 
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slantzilla wrote:
I've turned my long rod motor over 6700 and sprayed it. Never hurt a rod yet. 2.2 turbo pistons.


Yours are OE 198 rods then?

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PostPosted: Sat Jan 02, 2021 7:15 am 
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Turbo EFI
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[quote="Joshie225"]I was looking at the caps of my 225 and 198 rods side-by-side and noticed that next to the rod nut the 198 rod cap is quite a bit thinner. Has anyone ever have an issue with a 198 rod in the cap area? I'm going to be swinging somewhat heavy TRW L2502F pistons and would like it all to stay together. This is my first long-rod build so I'm just seeking a little reassurance. Also, I'm narrowing the rods to fit a cast crank like Doug did with his Buster build.

Have you weighed both rods?
Also there were many different vendors for the rod, could be a certain vendors shape.

I have been watching uncle tony and some of his ideas.
He doesn't like the long rod.
Subject for debate for sure.

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PostPosted: Sat Jan 02, 2021 9:36 am 
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Joshie225 wrote:

Yours are OE 198 rods then?


Stock rods, resized with ARP bolts.

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PostPosted: Sat Jan 02, 2021 9:39 am 
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Rick Covalt broke a 198 rod on one of his race motors a few years ago. The problem from what I remember was the rod bolts were replaced but the rods didn't get resized afterward from what I remember. You can find the thread in his Valiant Race car thread I'm sure. However, a thinner cap area can allow the B/E to get egg shaped with higher RPM, leading to spun bearings and breaking through the cap area. You may have to sort thru several sets to find a set with the thickest caps and beams.

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PostPosted: Sat Jan 02, 2021 10:32 am 
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hyper_pak wrote:
Have you weighed both rods? Also there were many different vendors for the rod, could be a certain vendors shape.


I've only weighed the 198 rods, 735 g. I haven't yet separated the aluminum block's rods and pistons and I have no other 225 rods at the moment. If you look at the 2 cap forgings they are very similar in shape, but next to the rod nut the 198 rod is much thinner.

hyper_pak wrote:
I have been watching uncle tony and some of his ideas. He doesn't like the long rod. Subject for debate for sure.


Original slant six rods and pistons are 1950's tech. I want to do better. A shorter deck block and correspondingly shorter pistons would make for the best overall package, but longer rods are what's practical. The 198 rod looks a little spindly, but it's $570, minus what I'd put into the 198 rods, to do better.

I've watched enough of 'Uncle' Tony. I think he leads a lot of people astray. Including himself.

I have some 6.800" aftermarket big Chevy rods I could narrow to fit the cast crank, but I'd also have to make a bushing for the small end and do .060" each of block and head milling to get my target 9:1 CR with my forged 2.2 pistons.

CNC-Dude wrote:
Rick Covalt broke a 198 rod on one of his race motors a few years ago. The problem from what I remember was the rod bolts were replaced but the rods didn't get resized afterward from what I remember. You can find the thread in his Valiant Race car thread I'm sure. However, a thinner cap area can allow the B/E to get egg shaped with higher RPM, leading to spun bearings and breaking through the cap area. You may have to sort thru several sets to find a set with the thickest caps and beams.


Anything high RPM needs more bearing clearance unless everything is especially rigid. Crankcase, crank and rods. There's no sorting through multiple sets of OE 198 rods at this late date. I think I'll play with one of my 6.800" Chinese big block Chevy rods ($144! for 8!) and see what kind of weight loss I can achieve.

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PostPosted: Sat Jan 02, 2021 11:57 am 
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The Hooptie mill runs OEM 198 rods, with the small end lightened up, a lot. They had a resize and a diet of flash/tubbiness removal. Drag raced it from 2007 to 2018 with no Rod or Crank related issues. I can't remember the weight, but it was considerably lighter assembled than even the OEM 225 rods and pistons. Recall that I've got those Metric .045" over 3.445" Toyota Hypereutectic's dangling out there. Lite. The metric rings are challenged by the long stroke, so I experience ring flutter.
I don't think the rods are going to be your limiting factor. The biggest issue I have with the Hooptie is the soft launch. I've rarely drop below a 2.1x second 60'. It makes plenty of beans, but it won't leave the line. That's all on the converter. When I transfer Hooptie bits into the '63 GT, I'm going to spring for a converter, 'cause the one I've got isn't doing me any favors.

I've got a set of bottom loading 7.005" Aluminum rods someplace in my stuff, along with a set of Molnar 7.005's/Forged. The bottom loading R&R's need creative machine work of the block/bores to install. If your set on your path to the cast crank, when I have my girdle off, I'll get some measurements for you. It's pretty simple, so you can likely make one up yourself pretty easily. It spans the 2nd and 3rd caps, as the forward and aft sections on Mains 1 & 4 didn't allow for an oil pan. Someday I'll build a full girdle that fits all four.

If I were to do it again, based on the Unobtainium properties of 198 rods these days, I'd go Molnar or R&R top loaders in Aluminum. My next build may use the Titanium 7.400's I commissioned. Those are Forged thickness, and I wouldn't want to tear up the tooling to cut them down to fit a cast crank. The guy that built them for me said, "Never again."

The only failure potential I saw after the original build was the Machine shop that assembled the long block didn't take into account where the throws put the big ends in proximity to the pan rail. When I tore it down to repair the head, I checked to find out why the engine was detonating on pump Premium. I had ~0.010" to the lip of the block clearing one of the rod nuts. (4.475" Stroke.) That was with the ARP rod fasteners, which had smaller 12 point nuts.You bet I gave it some more room! The stroke was supposed to be 4.440", which is why my fuel calc's were off. A pretty big error. There were more errors made, but I moved my machine work to another shop, and have been with them ever since.

I have another set of 198 rods upon which I started the "Lightening" work, If you ever do suffer a failure, let me know, and perhaps we can work something out. I also still have the 210 build stuff I purchased from you some time back. After a long chat about extracting power from low deck engines with Mike Jeffery, I cooled off on that build. Mike was helping Wayne with "Waynes World." Still might do it, just because a 170 or 210 wielded in anger sounds so wicked! :lol:

CJ

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PostPosted: Sat Jan 02, 2021 1:26 pm 
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Aren't the Molnar rods still out there???


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PostPosted: Sat Jan 02, 2021 2:12 pm 
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Killer6 wrote:
Aren't the Molnar rods still out there???


Not for the cast cranks.

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PostPosted: Sat Jan 02, 2021 2:54 pm 
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Joshie225 wrote:
hyper_pak wrote:

I have some 6.800" aftermarket big Chevy rods I could narrow to fit the cast crank, but I'd also have to make a bushing for the small end and do .060" each of block and head milling to get my target 9:1 CR with my forged 2.2 pistons.

As cheap as those are, that's likely going to become the next "go to" source for better rods....

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PostPosted: Sat Jan 02, 2021 3:08 pm 
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Wow! Lots of stuff above!! :D

Yes I had a catastrophic failure, probably my own fault.

Seymour's Valiant (And many others) had 198 rods and went 11.40's for a long time, no problem.

Larry Bird was working with Molnar on some new cast rods just a little while ago. Not sure if they did another run or not.

He also found a Ford rod ( I think) that was almost drop in. You may do a little search on here.
I know he asked on here if anyone was interested in getting some cast rods.

As a weird aside. The guy that does some of my engine work is a 460 Ford specialist. He told me that many years ago they used to take 198 rods and put them into 460 engines. So they must not be too weak. :D :D

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PostPosted: Sat Jan 02, 2021 8:05 pm 
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Rick,

Thanks for chiming in!

I took my 6.800" Speedmaster (speed disaster?) BBC rods and gave them a whirl on a friend's lathe to get them down to the proper big end width for a cast crank 225. Out of the box these rods are about .050" too wide and the the big end is offset so all .050" was taken off one side of the rod. There is still a little offset, but that's the breaks. This was an easy operation once we chucked up inside the big end of the rod with a sacrificial aluminum bearing and took advantage of the gapin the gap-bed lathe. I don't know what you call that bridge piece near the head-stock, but it took some coaxing to remove.

The rod material is pretty tough so many small cuts were needed to remove the needed .050"

Next I need to make a simple tool to press out the very thin-wall small end bushings and find material to make steel bushings to accept the press-fit .901" pin.

These rods 95 grams heavier than the 198 rods and I'm not sure how I'll get that much weight off of them. I'll keep y'all posted.

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