273 Supercharged...ITS HAPPENING PEOPLE!!

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Should run 400 horse easy. I ran a 273 in my 1968 4 door for yrs. Street/strip car. 10.5:1 compression, 557" solid purple cam, rpm intake, 700 holley dp, 1.6 rockers, 904 trans., 4800 stall turbo action converter, 4.88 gears. All added up to 12.60 1/4 mile at 104 mph and 1.60 60 ft. Good luck. I loved the under dog quality of yhe 273.
 
sireland67 said:
$950 for good forged pistons is insurance, cheaper than a broken pile of cast iron.
The cast pistons "might take 10 psi a couple of times" I would not take them over 5.
Also throw in about $250 more for a good balance job.
Do not cheap out on the short block, it is the foundation of your build.
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Man I get it. And I would tend to agree. The simple answer is I have to draw a line financially somewhere. Not to give you my life story but I'm in a bit of a time crunch as well. I was told Pistons would be a few months. I just don't have that kind of time right now. We are selling our house in March so to have this car in pieces when trying to pack up is not what I want. If anything I won't push it until I can get the Pistons and change them out. But it's just not in the cards right now.
 
WEBBY said:
You mentioned a cast crank, I thought all 273's had forged cranks. The ports are much bigger on the cast iron 34o intake than the 273 heads. Thanks Webby.
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I figured the intake would have to be port matched. From what I found the early 65-67 273's were forged crank. The later 68-69 were cast. Mine is a 68 so I got the cast version.
 
sireland67 said:
$950 for good forged pistons is insurance, cheaper than a broken pile of cast iron.
The cast pistons "might take 10 psi a couple of times" I would not take them over 5.
Also throw in about $250 more for a good balance job.
Do not cheap out on the short block, it is the foundation of your build.
Click to expand...

I hear you. When you say balance do you mean a dynamic balance on the crank? Or do you mean getting all the rods and Pistons as close as possible? I am planning to do the rods and Pistons. Down to at least a thenth of a gram like I do all my VW stuff.
 
The bob weight needs to be added or removed from the crank throws to be properly balanced. The bob weight is the weight of the piston assembly including the rings, wrist pin and attaching hardware and the rod , cap, bolts and bearings.
 
chrissock said:
I've spent most of the morning looking at head gaskets for this thing. I'm going to put ARP studs in it but I really don't need a thin gasket. Just want something that's going to hold the extra cylinder pressure. Also most gaskets say they will work for 318 to 360 but I'm assuming that's only because the bore hole is larger than my little 4" hole. Any thoughts on a good gasket before I pull the trigger?
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They may be pricy, but as far as I know the only head gaskets that fit "PROPERLY" are the Cometics. Their gaskets come in a 273 bore with different available thicknesses.
 
IfItsGotWheels said:
They may be pricy, but as far as I know the only head gaskets that fit "PROPERLY" are the Cometics. Their gaskets come in a 273 bore with different available thicknesses.
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Just make sure the block and head surfaces are finished properly. If they are too rough the Cometics won't seal properly.
 
toolmanmike said:
The bob weight needs to be added or removed from the crank throws to be properly balanced. The bob weight is the weight of the piston assembly including the rings, wrist pin and attaching hardware and the rod , cap, bolts and bearings.
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Yea ok. Thats what I was thinking. Yea my plan is to do those myself. I have a scale that will get that done.
 
You can balance the pistons to the same weight but it takes a special fixture to do the rods. Then it takes a balancing machine to do the crank. They also spin the balancer and the flywheel adding or removing weight as necessary. If you have lightweight rods and pistons they can take weight off the crank throws by drilling. If they have to add weight, they use special metal called Mallory metal that is heavier than the iron in the crank. Quite expensive!
Balancing an engine properly is a machine shop job and cannot be done in the home shop.

Here's a pretty good article about engine balancing: http://www.hotrod.com/how-to/engine/ccrp-0803-engine-balancing/
 
toolmanmike said:
You can balance the pistons to the same weight but it takes a special fixture to do the rods. Then it takes a balancing machine to do the crank. They also spin the balancer and the flywheel adding or removing weight as necessary. If you have lightweight rods and pistons they can take weight off the crank throws by drilling. If they have to add weight, they use special metal called Mallory metal that is heavier than the iron in the crank. Quite expensive!
Balancing an engine properly is a machine shop job and cannot be done in the home shop.

Here's a pretty good article about engine balancing: http://www.hotrod.com/how-to/engine/ccrp-0803-engine-balancing/
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Ok.....So maybe its a terminology thing we are fighting lol. What you are referring to I call a Dynamic balance. Meaning that the rotating assembly is done as a unit and not individually. The rods and pistons like I am referring to I call a static balance just because its not done in conjunction with the crank. The goal being just to get all the rods and pistons to weigh as close to the same as possible.

I get that that is always a good idea but in an application where the engine is not turning over 5500-6000 is it just a piece of mind thing or more of a longevity thing?
 
Is longevity on harmonics in the engine.

Heavier than stock pistons you will need to add Mallory to the crank.
Lighter than stock pistons you will need to remove weight from the crank.
Does this make sense?
 
sireland67 said:
Is longevity on harmonics in the engine.

Heavier than stock pistons you will need to add Mallory to the crank.
Lighter than stock pistons you will need to remove weight from the crank.
Does this make sense?
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Yes. I get the concept of the balancing process. As far as I can tell There is not a machine shop around me that can do the balance work for anywhere close to $250. So Its a big expense that I am trying to make sure its a must not a should kind of thing. Most guys local seem to think its important once you start to spin a motor over 6000rpm. Other than that not necessary.
 
Sounds like the OP understands how it works just whether or not it's necessary. My machinist who did my 360 said if I was planning on not going much over 4500 rpm the dynamic balancing isn't needed, but since my long-term plan is to get it redlining around 6000 rpm I got it done. Helps it run smoother too, and if I remember correctly it wasn't more than $300 or so for both staticand dynamic balancing service.

I'm not familiar with VW boxer-style engines but I know on cross-plane crank V8s (all old American engines) the counterweights are very important and need to be as close to the measured bob-weights as possible or else it puts a lot of strain on the crank. This is unique to this configuration of engine, other types with flat-plane cranks, inline 6's, etc. that dynamic balancing isn't as crucial. At least that's my understanding...
 
replacement pistons are made to replace stock pistons without need to rebalance. weigh stock pistons + pins, weigh new pistons + pins. if within 10% good to go, done that
 
My machinist told me if the new piston weight was within 10 grams of the old ones no balance is needed.
 
MOPEkidD-3 said:
Sounds like the OP understands how it works just whether or not it's necessary. My machinist who did my 360 said if I was planning on not going much over 4500 rpm the dynamic balancing isn't needed, but since my long-term plan is to get it redlining around 6000 rpm I got it done. Helps it run smoother too, and if I remember correctly it wasn't more than $300 or so for both staticand dynamic balancing service.

I'm not familiar with VW boxer-style engines but I know on cross-plane crank V8s (all old American engines) the counterweights are very important and need to be as close to the measured bob-weights as possible or else it puts a lot of strain on the crank. This is unique to this configuration of engine, other types with flat-plane cranks, inline 6's, etc. that dynamic balancing isn't as crucial. At least that's my understanding...
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Exactly.... VW engines are the same concept but unless your going to spin over 6000 it's just overkill. I was just trying to decide if it's something I HAVE to do or just a would be nice kind of thing.
 
Marcohotrod said:
replacement pistons are made to replace stock pistons without need to rebalance. weigh stock pistons + pins, weigh new pistons + pins. if within 10% good to go, done that
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This is along the same lines as what my machinist said. He has been reasonable on most things but balancing was almost $400. So it's not a cut and dry decision.
 
Cast pistons will take 7-8psi no problem,bump on 10psi and you're pushin
it,won't take too much of that for long.
Bob weight is rod big end + rod brgs.+(rod small end+piston/pin/rings/
divided by 2). If you keep it under 6K you should be OK unless you're particularly unlucky
and have a poor OE balance job,(it happens),I wouldn't sweat that TOO much.I would
say do it in a second if money were not tight tho' just the same.
Oh just remember,the cast pistons may take that running the rite A/F &
spark curve,but they'll melt faster than Paris Hilton in the arms of a chance to get noticed
again if they're not !!!
 
Killer6 said:
Cast pistons will take 7-8psi no problem,bump on 10psi and you're pushin
it,won't take too much of that for long.
Bob weight is rod big end + rod brgs.+(rod small end+piston/pin/rings/
divided by 2). If you keep it under 6K you should be OK unless you're particularly unlucky
and have a poor OE balance job,(it happens),I wouldn't sweat that TOO much.I would
say do it in a second if money were not tight tho' just the same.
Oh just remember,the cast pistons may take that running the rite A/F &
spark curve,but they'll melt faster than Paris Hilton in the arms of a chance to get noticed
again if they're not !!!
Click to expand...

Love the Paris Hilton reference!!! I will have a Fuel Injection set up and I plan to sneak up on a good 8 psi tune. Not planning on trying to perfect this thing day one on a dyno.
 
Buying new rods, but not changing the pistons?? Then not balancing an assembly that has different rods and will need to make decent RPMs to make any boost/power???
Your making a bunch of poor decisions here...
 
Bakerlite said:
Buying new rods, but not changing the pistons?? Then not balancing an assembly that has different rods and will need to make decent RPMs to make any boost/power???
Your making a bunch of poor decisions here...
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see what the old rods weigh, see what the new rods weigh, then decide, etc.
 
chrissock said:
Love the Paris Hilton reference!!! I will have a Fuel Injection set up and I plan to sneak up on a good 8 psi tune. Not planning on trying to perfect this thing day one on a dyno.
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Sub'd
Sheit is finally gettin real now :)
 
Marcohotrod said:
see what the old rods weigh, see what the new rods weigh, then decide, etc.
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When's the last time you found an Eagle forged rod to fit a 273 that were the same weight as a factory rod?, not to mention he's talking about swapping out cranks...The rods are overkill...
 
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