273 build idea......

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Hipo65

Hipo65

Yeah I'm "That Guy"
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hey guys when i got my dart the dude threw in another 65 904 & 65 rebuilt 273 long block he claimed to have hi-po pistons in it (i broght my bore scope & knew otherwise) none the less its is a .030 over 273 that has never been fired! Upon dissambly of it to check er out i noticed the low comp pistons seem alot higher @ TDC than i remember them to be stock, Is that rite for stock low comp piston's? check out pic...(its apx.035-.036 down the hole @ TDC) Qustion is would it be a better idea to build a zero deck flatop 273 or get the domed hi-comp pistons? I need to cc the heads too they look like they have been shaved aswell. stock charger 273 runs like a champ just somkes a little when ya drop the hammer its gonna get a re freash this winter, just wondering what way to go thanks for the input.
 

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Sure, why not. I always wanted to try a zero deck flat top 273. The closed chamber 273 heads are very efficient and would work well with a little porting on the small bore 273. I would recommend a thin Cometic head gasket also. Just a guess but you should end up with a 9.5:1 motor. tmm
 
I think .080" in the hole is typical, plus the commonly available perma-torque head gasket doesn't help matters. That block may have been decked a good bit. Not sure how much is too much but problems with intake manifold fitment and valve geometry can occur if too much is removed.

I couldn't find much in the way of piston options for the 273. Of course you can have any piston you want custom made but that will run you nearly a grand. Otherwise choices are low compression stock pistons or Egge's reproduction of the domed hipo pistons.

I also have a used set of TRW forged pistons, also domed but no longer made. I found the TRW domed pistons have a higher compression height than the Egges. Using the Egges gets you a CR in the low 9's. Of course there are lots of variables at play.

There is quite a bit of detail in my thread. I haven't made the final decision yet because I haven't pulled the heads off my other motor to get them cc'ed, but I will probably end up with the Egge's.

http://www.forabodiesonly.com/mopar/showthread.php?t=199120&page=2
 
I say run what you got. Domed pistons are too high for todays gas anyway unless you run big heads or a big cam. Most 273 2 barrel pistons are up high like that.
 
I would run it as is, but that being said, a engine with small bores is harder to get compression in. The factory commandos had dome pistons to reach a advertised 10.5 to one, as a comparison, a 340 can be 10.5 with a flattop. A zero deck 273 will have a lower compression ratio than say a 408 with zero deck. So the thing to do with the 273, is try to find (or have made) $$$$ a true flattop, thin gasket, and run small chamber heads.. But like I said, I would run it as it is... 2 cnts
 
RustyRatRod said:
Ummmm......what?!?!
Click to expand...

Sorry, that didn't make much sense did it. Deck the block to zero deck height. If the pistons have valve reliefs you may loose a little compression because of the reliefs. You may need valve reliefs depending on the cam you run. Dumb statement I know. Tmm
 
Eather way i end up going i did order comitic .036 head gaskets in 3.700 bore. FYI there not cheap! apx 200 bucks for a set! Upon tearing it down im not so sure id trust whoevers work eather,the front oil seal in the timing cover was installed backwords & they had a small hydrolic cam of un kwon mfg. (.405 lift @ valve ish by doen the math) with the stock rockers & push rods from the old solid cam! the adjusters were dam neer maxed out cup contacting rocker allmost & looked to be way to much preload on the lifter on its base. My plan is hope i can reuse the stock pistons in the o.e. motor in the car now but wont know till winter when its pulled for sure. I had it apart to put the E-4 cam in it & the timing chain was looooooose but the rest looked normal for its age. Just kicken around some ideas. I to thought the pistons on the 2bbl motors were down .080 ish for some reason. hmmmmm?
 
The bore does have a bearing on compression, but nothing as much as stroke. A short stroke engine is more difficult to get compression up. You can build a domed piston 383 with closed chamber heads and only end up with 10.5, yet the 383 is a relatively large bore engine. Since its stroke is almost the same as a 340, even though it has a large bore, it makes it more difficult to get high compression figures because of the short stroke.
 
Figure out how much CR you got now then dicide where to go from there
 
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