273 Performance build possibilities.

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Rev6868

Rev6868

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I am curious about the possibility of a performance 273 build. If this idea is just downright stupid let me know.
I like unique things and I was wondering if it is possible to build a solid built 273 with high RPM and decent power.
I have a 1968 Dart (originally slant 6) currently with a 318. I'm not 100% sure on the future of the vehicle but I'm thinking its going to be a driver. Jump in and go. It currently serves that purpose but I'd like some more pep.
If this is possible what could I expect? HP/TQ, drivability, Maximum power capability, RPM. etc...
Thanks
 
Chrysler didn't think it was stupid. They built the Commando and the D Dart.
 
There is no replacement for displacement. You are limited to heads on a 273 , The valves with some heads hit the bore at the top and may need to be notched depending what head you use with a 273. Also 318 will work better on pump gas.
 
We are building a 273 for Todd and had to get the Domed High compression pistons from Egge engine parts to make it a High output engine. 12-1 compression. 273 has close chambered heads with small valves. 318 will be more bang for the buck.
 
I’ve got a 273 with high hp for the street. All custom built- custom pistons, custom ground cam and balanced and lightened lower end. 66’273 closed chambered heads, 5/16” stems on the valves. Machine shop built. The fully squared the block before anything was done. After the price tag I’d do a 318 if I was to do it again. Especially since it is in front of a 904 and 8-3/4 with 3:23 rear gears and 24.5” tires. The life expectancy of the engine is less than 40k
318 all day long. Magnum actually 318.
So many parts and off the shelf.
 
Love my 273. I did a basic rebuild with an Isky E4 cam and some ported heads. It runs good and it is fun to drive. I have a roller cam 318 and I had a stroker and sold it to a friend but I wanted to keep the original engine. No regrets. It's your choice.
 
Higher compression on the SBM is detrimental to head gaskets. Ask me how I know, I was running 12.0 to 1 compression pistons in a street car with a 273 in the early 70's. I ended up contacting Ed Hamburger and he spec'd out putting SS o-rings in my block and running his copper sandwich gaskets. This indeed stopped me from blowing out head gaskets.
 
What do you have now. A 273 is a great little engine, no special parts needed. Zero deck, closed chamber heads, heads that flow about 190 cfm with a little clean up. Forged crank, solid cam and valve gear from 1964 to 1967. 265 hp with Isky E-4 cam and 2 barrel pistons. Torque from 275-300 ft lb. They are a quick revving engine and easily rev to 6,000+. They can get good mpg if you try.
 
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Demonracer said:
Higher compression on the SBM is detrimental to head gaskets. Ask me how I know, I was running 12.0 to 1 compression pistons in a street car with a 273 in the early 70's. I ended up contacting Ed Hamburger and he spec'd out putting SS o-rings in my block and running his copper sandwich gaskets. This indeed stopped me from blowing out head gaskets.
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I had a 340 block o-ringed with inconel wire and copper gaskets in the 80's . The new way is copper o-rings in the head and multi layer steel gaskets. They will withstand 60# of boost. He still does some blocks but now copper rings and steel gaskets. Aluminum blocks he leaves the sleeves protrude the block .002 -.003 due to block growth.


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Rev6868 said:
I am curious about the possibility of a performance 273 build. If this idea is just downright stupid let me know.
I like unique things and I was wondering if it is possible to build a solid built 273 with high RPM and decent power.
I have a 1968 Dart (originally slant 6) currently with a 318. I'm not 100% sure on the future of the vehicle but I'm thinking its going to be a driver. Jump in and go. It currently serves that purpose but I'd like some more pep.
If this is possible what could I expect? HP/TQ, drivability, Maximum power capability, RPM. etc...
Thanks
Click to expand...
All it takes is money. "stupid" is a matter of opinion. If it makes you happy, it's not stupid.....just do it.
 
One thing to keep in mind is, for street type builds, for the most part, a given level of “rowdiness” will get you to certain hp/ci level.
This won’t change very much with different displacements.
So, if you built an engine that’s 1.15hp/ci……. That’s roughly 315hp out of a 273, 365hp from a 318, or 410hp from a 360.

The 400hp+ 360 will be easier(and likely cheaper) to build than the 315hp 273.

It just depends on what you’re looking for.
 
Yup, you just have to decide what makes you happy. Raw horsepower, you may want to rethink. Beating a 350 Chubby with a 273.....yeah, that does if for me. :lol:
 
Wow thanks for the replies! Very cool to see the compression ratios and peoples experience. Certainly a lot to read and think about here.

@4spdragtop I suppose 300-400 hp/tq range. Much easier if I just get a blueprint 408 build. A friend of mine (who builds cars, but not the engines themselves) thought it could be interesting to build a high RPM 273. That got me thinking about it.
But I think if it comes out a penny less than 300 if not 350 it really wouldn't be worth it.
My google searches have not really resulted in much examples to reference.

There is also the idea of being able to alter the power output using a turbo or supercharger or nos. Idea being a quiet driver vehicle most of the time, but it can (somewhat) easily open its exhaust plus increase the power. How much? Honestly, enough to at least surprise a modern middle of the road v8 muscle car I.E. 2020 Mustang. 2016 Challenger. Enough to feel the car move in to a nice level of snappy power.

@66fs Thanks! The car has a mild 318 and a 4spd a833. Keeping it like this for a while and driving the car, but am considering ideas for a drivetrain overhaul including TKX 5-speed and new rear. But i'm debating on the purpose of the car. There is an idea of keeping the car a driver, but wanting some power, or ability to get more power. Drivable enough I could start it right up and go get groceries, but enough power to have a bit of fun.

@cudamark
"Beating a 350 Chubby with a 273.....yeah, that does if for me." Hah! Exactly!!! Also btw to clarify when I say "stupid" I'm mostly meaning my lack of knowledge of whats possible or how viable. I don't really know much about this in particular.
 
Rev6868 said:
Wow thanks for the replies! Very cool to see the compression ratios and peoples experience. Certainly a lot to read and think about here.

...@66fs Thanks! The car has a mild 318 and a 4spd a833. Keeping it like this for a while and driving the car, but am considering ideas for a drivetrain overhaul including TKX 5-speed and new rear. But i'm debating on the purpose of the car. There is an idea of keeping the car a driver, but wanting some power, or ability to get more power. Drivable enough I could start it right up and go get groceries, but enough power to have a bit of fun...
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Purpose of the car is the first thing to decide. I always liked the 273 as you can drive like a normal engine and if you want to go faster, just let it wind out. You already have a 4 speed. To be honest if you don't have a 273, any Mopar small block will work. You don't have to run a large cam to get a 273 to rev high. What rear and and gear ratio is in the car now?
 
Rev6868 said:
Wow thanks for the replies! Very cool to see the compression ratios and peoples experience. Certainly a lot to read and think about here.

@4spdragtop I suppose 300-400 hp/tq range. Much easier if I just get a blueprint 408 build. A friend of mine (who builds cars, but not the engines themselves) thought it could be interesting to build a high RPM 273. That got me thinking about it.
But I think if it comes out a penny less than 300 if not 350 it really wouldn't be worth it.
My google searches have not really resulted in much examples to reference.

There is also the idea of being able to alter the power output using a turbo or supercharger or nos. Idea being a quiet driver vehicle most of the time, but it can (somewhat) easily open its exhaust plus increase the power. How much? Honestly, enough to at least surprise a modern middle of the road v8 muscle car I.E. 2020 Mustang. 2016 Challenger. Enough to feel the car move in to a nice level of snappy power.

@66fs Thanks! The car has a mild 318 and a 4spd a833. Keeping it like this for a while and driving the car, but am considering ideas for a drivetrain overhaul including TKX 5-speed and new rear. But i'm debating on the purpose of the car. There is an idea of keeping the car a driver, but wanting some power, or ability to get more power. Drivable enough I could start it right up and go get groceries, but enough power to have a bit of fun.

@cudamark
"Beating a 350 Chubby with a 273.....yeah, that does if for me." Hah! Exactly!!! Also btw to clarify when I say "stupid" I'm mostly meaning my lack of knowledge of whats possible or how viable. I don't really know much about this in particular.
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BIG difference between 300 HP 273 and a 400 HP 273!
 
This is easy. Get the Blueprint 408 and dress it up like a 273 Commando.
 
Rpm is gonna be your enemy, 300 hp is gonna be about 5500 rpm 400 hp will be around 7000 rpm other then that should similar parts to do the job, probably don't want to go much bigger than a 1.88 valve.

If your gonna build a 273 or even a 318 you can't be shy about using deep gears, high rpm small engines need a lot of gearing if that is a problem you'd be better off with a bigger engine. Plus you need higher stall speed.

7000 rpm x 28" tires / 110 mph x 336 = 5.30 rear gear
5000 rpm x 28" tires / 110 mph x 336 = 3.79 rear gear

The usual set of 3.55's (4686 rpm @ 110 mph) is generally closer to ideal for a larger engine than a smaller one.
 
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273 said:
Rpm is gonna be your enemy, 300 hp is gonna be about 5500 rpm 400 hp will be around 7000 rpm other then that should similar parts to do the job, probably don't want to go much bigger than a 1.88 valve.

If your gonna build a 273 or even a 318 you can't be shy about using deep gears, high rpm small engines need a lot of gearing if that is a problem you'd be better off with a bigger engine. Plus you need higher stall speed.

7000 rpm x 28" tires / 110 mph x 336 = 5.30 rear gear
5000 rpm x 28" tires / 110 mph x 336 = 3.79 rear gear

The usual set of 3.55's (4686 rpm @ 110 mph) is generally closer to ideal for a larger engine than a smaller one.
Click to expand...
Alright AJ Jr.
 
Well if i can have fun with a 265 6 with a 4 speed behind it, a 273 v8 should be just as good

the smaller and less well supported the motor is. the more custom work is necessary and the higher the cost....

but thats paid back by the open track day when you spank the *** of something much bigger and well specified ...

what you got in there...... they ask

erm a 4.3 litre six cylinder that looks like it started out as a back-up generator for a small computer centre :) look..... and they do......

it makes your day...... makes it all worthwhile,
especially as you drove it to the track and back, at modern highway speeds with no overheating and on half a tank of fuel

i'd say that is a WIN any day of the year

Dave
 
Lol

New guy shows up and drops a match into a barrel of dynamite.

Hilarity ensues

New guy wonders what just happened and mistakes it for us trying to be "helpful"

Lol
 
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