273 build questions

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Chi Town Runner

Chi Town Runner

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I'm a big block guy so am not that familiar with small blocks. I am helping a friend with his 66 4spd 273 HiPo Signet. After pulling the original engine apart the pistons were domed (I understand that was factory for HiPo 273s). I had mentioned that when I built my BB I used "Zero Deck" to get quench. My concern is, on his 273 , can you go zero deck with the factory castiron heads and the domed pistons (EGGE Part #L-2222)?

He's not building a screamer stroker just a healthy stock 273 HiPo.

Thanks for any guidance.

Frank :thumbup:
 
Seems to me if you zero deck the domed pistons, your compression will be pretty high.

Depending on the assumptions you make using the compression calculator, you wind up with a CR of between 10.0 and 11.5.

I used a cc kit to measure the dome volume of the TRW forged hipo pistons. I got a dome volume of about 10cc. All the sources I've found for head chamber volume either say 57 cc, or a range between 57 and 64.5 cc. I cc'ed two different pairs of heads. One came in at 63 cc and the other was 66. Here's the thread: http://www.forabodiesonly.com/mopar/showthread.php?t=199120&page=2

With zero deck height I get 10:1 assuming 64cc heads and the cheap fel-pro perma torq head gasket that works on all small blocks with a bore size of 4.18 and compressed thickness of .040. If you assume 57cc heads and you reduce the head gasket bore to 3.75 you get to 11.5:1.

My TRW domed pistons were .042 in the hole (measured on the flat part of the piston). That block was .040 over so it was rebuilt at least once. I don't know if it was ever decked.
 
I would love to know some numbers from the engine you tore down.

Is it standard bore, original pistons?
How far are the pistons down in the hole?
If you can cc the heads, what do they measure?

You will probably need to know this stuff in order to plan your build.
 
The block has been dissasembled already. It will be going in for machine work, parrallel decking, either .030 or .040 bore. The engine is not in my garage so i don't have immediate access to it. I'll get whatever #s I can off of it and get back to you.

I thought it was a pretty neat car, being a factory 4-speed, 8.75 rear end, bucket seats, etc. He has the fender tag and when we pull apart the interior we hope to find a build sheet, but I'm not too optimistic as the car was built in L.A.

We'll see.

Thanks for the info.

Frank :salute:
 
Just curious if you could mill .040 - .050 off the deck without causing problems. Would you need to also mill the intake?
 
I don't have many answers to your questions. I built my 273 a couple years ago.
I used .030 over Egge pistons and milled .030 off the heads and .020 off the intake. We milled the heads to make up for the valve grind and the dished head valves I used. My cc specs are buried somewhere in my office. I'll see if I can find them this weekend if you need em'. I checked compression with both the Fel Pro PT/blue gaskets and the silver Mopar Performance ones. I don't have the compressed thickness handy but the c/r with the Fel Pro's was 9.22/1 where the ratio with the Mopar Perf's was 9.67/1. I used the Mopar Perf. ones. I can burn 91 octane regular without ping but use 93 Shell. My take on the Egge pistons vs. originals as far as compression goes is mostly in the head gaskets. The original's were steel shim and slightly larger than the 273's bore size. The difference in the Fel Pro's vs the MP ones was about a half a point. Although I don't have the measurements, I'm sure the difference between the composite MP gaskets and the original steel shim gaskets would be another half point. If you factor in the difference in the bore size of the new gaskets (4.0+") vs. the original steel shim's I'll bet there's another half point of compression. Add all the compression lost due to overbore, valves and valve grinding and head gaskets and the 9.6/1 I got would be 10.5/1 just like original. If I had it to do over I would contact Cometic and get a set of head gaskets that were the proper bore size and as thin as they could make simply because no one makes the steel shim gaskets any longer.
I will say, the machine shop was impressed with the quality and consistency of the pistons. If you have some time check out my thread. Not a lot of technical but some good photos. tmm
 
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