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| Realizations while breaking down an old RG engine... https://www.slantsix.org/forum/viewtopic.php?t=66582 |
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| Author: | Dart270 [ Thu May 12, 2022 11:37 am ] |
| Post subject: | Realizations while breaking down an old RG engine... |
Hello Slant Sixers, I bought a core Slant engine from the Drake's auction in October and finally got around to disassembling it. Rusty, greasy, stinky fun... Before pounding out a few seized pistons and pulling the crank, I decided to measure the piston-deck height at TDC. Hmm, 0.11" Never seen a 225 with that small a number before. Hmm, those rods have a different number than I'm used to seeing in an early 70s engine. Gee, that crankshaft appears to have a bit smaller stroke than a 225? Yep, this morning I put a ruler across the rods after pulling them and they are 7". It's a 198! This is the first time I've come across one and taken it apart. The small deck height was what got me thinking, and by the afternoon after the morning I measured it, I thought I might have a 198. Sure enough. Anyway, more parts for the pile o' spares... Happy motoring, Lou |
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| Author: | Greg Ondayko [ Thu May 12, 2022 11:39 am ] |
| Post subject: | Re: Realizations while breaking down an old RG engine... |
cool stuff. Is the Advertised Compression Ratio on a 198 Higher then the 1971-1975 225's? Greg |
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| Author: | volaredon [ Thu May 12, 2022 2:56 pm ] |
| Post subject: | Re: Realizations while breaking down an old RG engine... |
I wouldn't think so being with the shorter stroke and same head. So what's the plan? 225 crank and 2.2 pistons? Wonder how many more 198s were among that stash? Those rods make that engine worth more than a 225 huh? |
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| Author: | hyper_pak [ Thu May 12, 2022 5:28 pm ] |
| Post subject: | Re: Realizations while breaking down an old RG engine... |
Interesting. So if they have the same head cc's and the piston deck height is higher than a 225, how it it NOT have more compression? I am not saying 13 to 1 but more than 7 or 8 to 1. Because of the shorter stroke length. That's another 1/2" of volume (depth of piston at BDC) that a 225 has but a 198 doesn't. |
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| Author: | SlantSixDan [ Thu May 12, 2022 6:04 pm ] |
| Post subject: | Re: Realizations while breaking down an old RG engine... |
The pistons in a 225 stop lower in the bore at the top of their travel…and at the bottom of their travel. |
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| Author: | Dart270 [ Fri May 13, 2022 4:55 am ] |
| Post subject: | Re: Realizations while breaking down an old RG engine... |
Yes, to get similar compression, you would have to make compression height smaller to compensate for the decreased stroke of the 198 crank. Lou |
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| Author: | hyper_pak [ Fri May 13, 2022 5:20 pm ] |
| Post subject: | Re: Realizations while breaking down an old RG engine... |
Yea, I played with a compression calculator today. Shorter stroke by an inch reduces the CR. Duh |
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| Author: | Michael [ Fri May 13, 2022 7:46 pm ] |
| Post subject: | Re: Realizations while breaking down an old RG engine... |
A few years back, I put a 198 together as a "spare" engine (I didn't measure the piston depth.) I used a Comp Cams hydraulic cam that came in a trade and I updated the lifter/rocker set-up to match. I used a steel shim head gasket for laughs. The joke is on me now because that engine is in my 65 Dart Wagon - runs amazing!  (just needs 93 octane to control the pinging though.  )
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| Author: | Dart270 [ Sat May 14, 2022 8:15 am ] |
| Post subject: | Re: Realizations while breaking down an old RG engine... |
Hm, what head cc or amount of milling? That is the only way you should have ended up with higher compression, unless the cam was far advanced... Lou |
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