273 piston options

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I would consider using a 360 head, or a big valve 340/360 head. However, for that to work, you will need to use a custom type piston to make up for the compression loss due to the larger combustion chamber. Also will require notching the top of the block/bore, to clear the big valves.
Been there done that, back in the day.
 
360DartGT66 said:
I’d like to say 7k but as high as the stock stuff that’s going in it will allow - for now.
If I buys pistons that fit the stock rods then that’s what’s going in it now.
I’ll be using the stock rockers and flat tappet lifters for now.
I’ve got a set of solid roller lifters but I’m thinking solid flat tappet for starters. I dount think that will be the limiting factor just yet.
I’ll be doing oiling mods and Adding a stiffer spring to the Melling 72HV pump I found in the engine when I took it apart.
This is going to be a fun project for me, not a race engine. If the parts I choose limit me to 6k then that’s what the limit will be. Until I decide to buy a better crank and rods. Or springs and rockers if that’s what’s limiting me.
Short version: I’m aiming for 7k.
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At 7k, if you keep your tune up in check you shouldn’t have any issues. The stock crank and rods will take 7k all day long. Just make sure you have good rod bolts.
 
360DartGT66 said:
I’d like to say 7k but as high as the stock stuff that’s going in it will allow - for now.
If I buys pistons that fit the stock rods then that’s what’s going in it now.
I’ll be using the stock rockers and flat tappet lifters for now.
I’ve got a set of solid roller lifters but I’m thinking solid flat tappet for starters. I dount think that will be the limiting factor just yet.
I’ll be doing oiling mods and Adding a stiffer spring to the Melling 72HV pump I found in the engine when I took it apart.
This is going to be a fun project for me, not a race engine. If the parts I choose limit me to 6k then that’s what the limit will be. Until I decide to buy a better crank and rods. Or springs and rockers if that’s what’s limiting me.
Short version: I’m aiming for 7k.
Click to expand...
I have a 1965 273 short block in the garage with the domed 10:1 Commando style pistons that are 0.030" over. I haven't had it apart so don't know the history of the motor other than the man I got it from had it as a backup block for this custom race car. The Silver Bullet Dragster Comes Full Circle
My plans have changed and I don't need a 273 anymore so if you are interested in the used pistons, I could see about pulling the motor apart to see how the pistons look. I am not sure yet if I'm going to let the rods and crank go, but I definitely won't be using the pistons.
 
Charrlie_S said:
I would consider using a 360 head, or a big valve 340/360 head. However, for that to work, you will need to use a custom type piston to make up for the compression loss due to the larger combustion chamber. Also will require notching the top of the block/bore, to clear the big valves.
Been there done that, back in the day.
Click to expand...
I have a set of 360 heads and I’ve considered using those. I’m aware of the notching/shrouding issue but I think perhaps the increased flow capability compensates for that. The chambers are much bigger though so domed pistons and perhaps some cutting on the heads to get to a reasonable static compression.
We have E10 gasoline at 95 octane as well as E85 over here in Sweden and some stations sell 98 octane.
 
gzig5 said:
I have a 1965 273 short block in the garage with the domed 10:1 Commando style pistons that are 0.030" over. I haven't had it apart so don't know the history of the motor other than the man I got it from had it as a backup block for this custom race car. The Silver Bullet Dragster Comes Full Circle
My plans have changed and I don't need a 273 anymore so if you are interested in the used pistons, I could see about pulling the motor apart to see how the pistons look. I am not sure yet if I'm going to let the rods and crank go, but I definitely won't be using the pistons.
Click to expand...
Wow, that sounds like a great idea!
How about I see if I work anything out with the other guy who was having custom pistons made first?
 
360DartGT66 said:
I have a set of 360 heads and I’ve considered using those. I’m aware of the notching/shrouding issue but I think perhaps the increased flow capability compensates for that. The chambers are much bigger though so domes pistons and perhaps some cutting on the heads to get to a reasonable static compression.
We have E10 gasoline at 95 octane as well as E85 over here in Sweden and some stations sell 98 octane.
Click to expand...

If you mill 360 heads .040 and .038 on the intake side of the head you can get the chambers down to 64.7 cc. I've run them on a + .040 bore 273 and it was amazing, pulled to 7K no problem. No bore notches, but I did make sure the chambers were centered on the bores with offset dowels. But in reality, I think early 273 heads flow almost as much as 360 heads with a little clean up. I second your idea of a solid flat tappet cam. The limiting factor will be the valve train, take the time to set it up as well as you can.
 
gzig5 said:
I have a 1965 273 short block in the garage with the domed 10:1 Commando style pistons that are 0.030" over. I haven't had it apart so don't know the history of the motor other than the man I got it from had it as a backup block for this custom race car. The Silver Bullet Dragster Comes Full Circle
My plans have changed and I don't need a 273 anymore so if you are interested in the used pistons, I could see about pulling the motor apart to see how the pistons look. I am not sure yet if I'm going to let the rods and crank go, but I definitely won't be using the pistons.
Click to expand...
I checked out that link. Wow.
 
Keep in mind one full point of added compression only equals about a 3% increase in power. I'll be damned if I'd go over about 10.5. Beyond that, you get diminished returns since you have to have race gas or E85 involved. I'd keep it simple.
 
RustyRatRod said:
Keep in mind one full point of added compression only equals about a 3% increase in power. I'll be damned if I'd go over about 10.5. Beyond that, you get diminished returns since you have to have race gas or E85 involved. I'd keep it simple.
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I hear you.
 
Rat Bastid said:
At 7k, if you keep your tune up in check you shouldn’t have any issues. The stock crank and rods will take 7k all day long. Just make sure you have good rod bolts.
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Where would you suggest I aim for bearing clearances and oil pressure, aiming for 7k?
And do you think cast - not even hypereutectic - pistons are safe, too?
 
360DartGT66 said:
Where would you suggest I aim for bearing clearances and oil pressure, aiming for 7k?
And do you think cast - not even hypereutectic - pistons are safe, too?
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.0020-.0022 on the rods and .0023-.0025 on the mains. Full groove mains and a HV pump. Pressure should top out at 80-85.

As long as you don’t run into detonation the cast piston will take quite a bit. To be safe, I’d follow RRR’s advice of 10.5:1 or even 10:1. That will help keep you out of trouble.

7k on solid lifters doesn’t require a whole bunch of spring. And the 273 rockers will take all of that and then some.
 
RustyRatRod said:
Keep in mind one full point of added compression only equals about a 3% increase in power. I'll be damned if I'd go over about 10.5. Beyond that, you get diminished returns since you have to have race gas or E85 involved. I'd keep it simple.
Click to expand...


Interesting that you mention E85. There isn’t much close to me, but I’ve been looking into it. What’s really strange is how viscous it is. It’s almost oily. I have no idea what’s in it (yet) that makes it so oily and viscous, but I do know it changes the tune up. By a quite a bit.
 
360DartGT66 said:
This is very interesting.
Is there any way we could work together here? Are you getting 0.030” over pistons then? What will be the specs?
I’ll gladly cover some of the cost if I can piggyback off the work you’ve put in.
Mind if I give you a call later?
Send me a PM with your number in that case.
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We haven't settled on final piston specs yet, and yep.....030's. We have to make one more cut on the 302 heads, and then he can do all the math and tell the dude at Race Tech what we need. I have a set of Cometic head gaskets that have a bore size of 4.040 and a compressed thickness of .027 . We're shooting for around 9.0 to no more than 9.5 compression. I just want something with enough power to get out of its own way without zinging it out of its mind, and still get good gas mileage for what it is. I'll shoot you a PM when we get the specs set. They will be flat tops with 2 valve reliefs. If the same specs work out for you, then you can call them and ask for the same things.

:thumbsup:
 
So, BID they shifted D-Darts at 7000+ and were turning 8000+ in the traps, but that's drag racing only, and not high mileage hoonage, the stock rods and heavy-ish 10.5:1 pop-ups were the limiting factor; the the forged 273 crank is reputed to be good for regular use spinning to 8300 max, but the rest of the package would need significant upgrades to last going there.

I'm actually eyeing a 300.5Cid 273 build myself as I have a small bearing 3.58" stroke SCAT 4340 crank for my '66 Formula S' OEM 273 Commando. Pistons will be custom and I'll be using K1 rods and a Hughes Engines main stud girdle. In my case I'm aiming for a streetable peak HP RPM of 5500-6000, and a safe(ish) rev-out (for autocross) to 7000 (valve float not before 7500). I'm aiming for 10.5:1 compression, which may require dished pistons with that stroke. Heads will be ported 273 or "...302" head castings with 1.88" and 1.6" valves. I'll be running an LD4B intake with 1/2" partially open spacer, a 650-750 QFT Circle Track carb, and Doug's headers. I have a set of ported 273 heads already, not sure if one is good or not (stuck valve); their flow was nothing to write home about but they did support 317 WHp @ 5809/314 FtLb @ 4785 on a 0.030" over 318 at about 9.75:1 with a fairly hot Hughes cam (Max Velocity mechanical cam, part number: HEV4550AS.).

I have not gotten to the point of configuring pistons yet, but they will be custom ordered from one of my builder's sources (Diamond, Wiseco, JP, a couple of others...) The cam will likely be a custom mech roller from Comp.
 
Rat Bastid said:
Interesting that you mention E85. There isn’t much close to me, but I’ve been looking into it. What’s really strange is how viscous it is. It’s almost oily. I have no idea what’s in it (yet) that makes it so oily and viscous, but I do know it changes the tune up. By a quite a bit.
Click to expand...
It sure shouldn't be oily. My guess is, it's additives to somehow help it not evaporate so easily. As you know, alcohol is here one second and gone the next. I don't like any of it. Never have. We had it made with good old gas and wrong headed people screwed it all up.
 
Kanter offers the 4 bbl pistons. A friend of mine used them a few years ago, and they were really nice. They have coated skirts and are a little taller than the Egge's. The part number is 12631K PST 2222TXXX and are 50.74 each. The phone number is 973-863-3685. You'll have to call for size availability. I would recommend them over Egge's.
 
JDMopar said:
We haven't settled on final piston specs yet, and yep.....030's. We have to make one more cut on the 302 heads, and then he can do all the math and tell the dude at Race Tech what we need. I have a set of Cometic head gaskets that have a bore size of 4.040 and a compressed thickness of .027 . We're shooting for around 9.0 to no more than 9.5 compression. I just want something with enough power to get out of its own way without zinging it out of its mind, and still get good gas mileage for what it is. I'll shoot you a PM when we get the specs set. They will be flat tops with 2 valve reliefs. If the same specs work out for you, then you can call them and ask for the same things.

:thumbsup:
Click to expand...
Please do! I've been looking at those head gaskets myself but nothing seems to be in stock right now.
 
CPDave said:
So, BID they shifted D-Darts at 7000+ and were turning 8000+ in the traps, but that's drag racing only, and not high mileage hoonage, the stock rods and heavy-ish 10.5:1 pop-ups were the limiting factor; the the forged 273 crank is reputed to be good for regular use spinning to 8300 max, but the rest of the package would need significant upgrades to last going there.

I'm actually eyeing a 300.5Cid 273 build myself as I have a small bearing 3.58" stroke SCAT 4340 crank for my '66 Formula S' OEM 273 Commando. Pistons will be custom and I'll be using K1 rods and a Hughes Engines main stud girdle. In my case I'm aiming for a streetable peak HP RPM of 5500-6000, and a safe(ish) rev-out (for autocross) to 7000 (valve float not before 7500). I'm aiming for 10.5:1 compression, which may require dished pistons with that stroke. Heads will be ported 273 or "...302" head castings with 1.88" and 1.6" valves. I'll be running an LD4B intake with 1/2" partially open spacer, a 650-750 QFT Circle Track carb, and Doug's headers. I have a set of ported 273 heads already, not sure if one is good or not (stuck valve); their flow was nothing to write home about but they did support 317 WHp @ 5809/314 FtLb @ 4785 on a 0.030" over 318 at about 9.75:1 with a fairly hot Hughes cam (Max Velocity mechanical cam, part number: HEV4550AS.).

I have not gotten to the point of configuring pistons yet, but they will be custom ordered from one of my builder's sources (Diamond, Wiseco, JP, a couple of others...) The cam will likely be a custom mech roller from Comp.
Click to expand...
Wow, this site sure does deliver!
The 360 that was in my car when I bought it had an LD4B but I sold it in favor of an LD340. The larger ports made more sense. It was in great shape and the LD340 was not...
 
Rat Bastid said:
.0020-.0022 on the rods and .0023-.0025 on the mains. Full groove mains and a HV pump. Pressure should top out at 80-85.

As long as you don’t run into detonation the cast piston will take quite a bit. To be safe, I’d follow RRR’s advice of 10.5:1 or even 10:1. That will help keep you out of trouble.

7k on solid lifters doesn’t require a whole bunch of spring. And the 273 rockers will take all of that and then some.
Click to expand...
Thank you very much!
 
Rat Bastid said:
Interesting that you mention E85. There isn’t much close to me, but I’ve been looking into it. What’s really strange is how viscous it is. It’s almost oily. I have no idea what’s in it (yet) that makes it so oily and viscous, but I do know it changes the tune up. By a quite a bit.
Click to expand...
If you elect to run e85 on a carbureted application, you’re better off ordering a drum of e98 ethanol and blending your own fuel from there with non ethanol premium pump. e85 at the pump varies from 50% to 83% depending on the seasonal blend.
Calculate Ethanol % of Mixture
 
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