AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
- Joined
- Jan 19, 2014
- Messages
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If you absolutely crave a high-powered 273, then just turbocharge it.
The 273 is a great engine for an early-A, or a grocery-getter; or in a Second gen, a touring engine .
There is a rule of thumb that almost everyone acknowledges, and it goes like this;
For street performance, you need one cubic inch for every 10 pounds of ready-to run car, with you in it. So
a 273 is good for 2730 pounds including driver
a 340 is good for 3400 with driver, and
a 360 is good for 3600 with driver
And the reason for this is because of the 1 hp per cubic inch guideline. This level is easy to build to, and is low-maintenance, and it makes a durable engine.
So if you have a 3600# car(with driver);
and you build a 273 to 360 hp,(to do what a 360 scoffs at, at 1.0 hp/cube) , yur 273 will be at ~1.32 hp per cube, and has really become waaay more race than street.(see note 1).
It will be a "beast" alrightee. It will require a hi-stall TC and 4series gears and the best gas you can find, and will probably require some form of anti-knock additives.
Without the stall/gears, she will be a beast in every sense, just not the kind of beast you want; rather a cow, and a pig, and a lazy dog.
And with the Stall/gears, she will finally wake up, but she'll be a city car, and still just 1.5 gears (see note 2) to 60mph. And you will have to know all the places to find premium-grade fuel.
So, when it comes to a 3600-loaded street car, the 273 is waaaay out of it's element. If you make a "beast" out of it, it will have beastly manners, and it will drink fuel, like a beast. The beastliness will soon make it a weekends only bomber, and eventually, it will spend maybe very few hours a year actually driving.
For a performance street application, I just cannot understand the infatuation with a 273. It's a two-seventy-three.
note 1
What you may not realize, is that to make power with a small engine, requires rpm; cuz that's how the formula works;
torque times rpm/5250= horsepower.
And when you increase the engine's operating rpm, by up-camming it, you always trade away some low rpm torque to get that hi-rpm power. So, you end up with an engine that is soft in the sub-3500rpm zone where 95% of your driving is likely to be.
Note 2
To hit 60mph with say 27" tires,requires a gear ratio of 7.38 to hit it at ~5500 .
With a standard TF, with gears of 2.45-1.45-1.00, and say 10% slip in the TC, this will require second gear and ~4.56s, for 60=5420.
Are you gonna run 4.56s?
For peak power at or near 5400, that 273 will be a dog below 3000,maybe even closer to 3500, so you are gonna need a stall in that zone.
Are you gonna run a 3500TC?
Highly unlikely that you will run 4.56s cuz 65=3680@zero-slip, maybe up to 200 more with that 3500TC. So really, your cruise speed is down to 50= about 3000, and now the 3500 is cooking the trans oil.
So better to get a 3000TC.
But on the 1-2 shift, the Rs will fall from 5400 to 3200, and your engine is in the dog-zone; She really wants that 3500.
This is what yur up against with a 273.
But more likely is that you will run 3.91s (or less).
First gear will get you about 46mph@5800. At the 1-2 shift, the Rs will drop to ~3400
Then, second gear will get you,60=4230@zero-slip, perhaps 4650@10%slip,on your tach, and so for RapidTransit, your engine is gonna need to making some power there.
If you have built your 273 to be a "beast", then 4650 is barely above peak torque. And the power won't peak until say 5400@73mph.......
So like I said, she's a 1.5 gears to 60mph, car.
I interpret that as slow, because the engine is only going thru the power-peak once, then dropping into the soft zone, before struggling back up the power curve..... half way, and then your zero to sixty time-trial is done.
If that's what you want, then have at it.
And we haven't even talked about the engine-build required, to powerpeak at 5400.
So for this application; it doesn't matter what engine you install, they are all governed by the same 60mph@5500, requires a 7.38 gear ratio.
So lets flip it around;
If 3.91s is all you want to run, then with 27s and a regular TF trans then
60=4650@10% slip. And so, for RapidTransit to 60mph, you want to pass thru the power peak twice and end at say 4900. So, still for RapidTransit, the engine has to be build to that spec, and sooooo the 273 cannot possibly be Rapid, unless supercharged. Whereas a 360 might still be spinning the tires.
And if 3.23s is all you want to run, well you see how this is going, right?
The 273 is a great engine for an early-A, or a grocery-getter; or in a Second gen, a touring engine .
There is a rule of thumb that almost everyone acknowledges, and it goes like this;
For street performance, you need one cubic inch for every 10 pounds of ready-to run car, with you in it. So
a 273 is good for 2730 pounds including driver
a 340 is good for 3400 with driver, and
a 360 is good for 3600 with driver
And the reason for this is because of the 1 hp per cubic inch guideline. This level is easy to build to, and is low-maintenance, and it makes a durable engine.
So if you have a 3600# car(with driver);
and you build a 273 to 360 hp,(to do what a 360 scoffs at, at 1.0 hp/cube) , yur 273 will be at ~1.32 hp per cube, and has really become waaay more race than street.(see note 1).
It will be a "beast" alrightee. It will require a hi-stall TC and 4series gears and the best gas you can find, and will probably require some form of anti-knock additives.
Without the stall/gears, she will be a beast in every sense, just not the kind of beast you want; rather a cow, and a pig, and a lazy dog.
And with the Stall/gears, she will finally wake up, but she'll be a city car, and still just 1.5 gears (see note 2) to 60mph. And you will have to know all the places to find premium-grade fuel.
So, when it comes to a 3600-loaded street car, the 273 is waaaay out of it's element. If you make a "beast" out of it, it will have beastly manners, and it will drink fuel, like a beast. The beastliness will soon make it a weekends only bomber, and eventually, it will spend maybe very few hours a year actually driving.
For a performance street application, I just cannot understand the infatuation with a 273. It's a two-seventy-three.
note 1
What you may not realize, is that to make power with a small engine, requires rpm; cuz that's how the formula works;
torque times rpm/5250= horsepower.
And when you increase the engine's operating rpm, by up-camming it, you always trade away some low rpm torque to get that hi-rpm power. So, you end up with an engine that is soft in the sub-3500rpm zone where 95% of your driving is likely to be.
Note 2
To hit 60mph with say 27" tires,requires a gear ratio of 7.38 to hit it at ~5500 .
With a standard TF, with gears of 2.45-1.45-1.00, and say 10% slip in the TC, this will require second gear and ~4.56s, for 60=5420.
Are you gonna run 4.56s?
For peak power at or near 5400, that 273 will be a dog below 3000,maybe even closer to 3500, so you are gonna need a stall in that zone.
Are you gonna run a 3500TC?
Highly unlikely that you will run 4.56s cuz 65=3680@zero-slip, maybe up to 200 more with that 3500TC. So really, your cruise speed is down to 50= about 3000, and now the 3500 is cooking the trans oil.
So better to get a 3000TC.
But on the 1-2 shift, the Rs will fall from 5400 to 3200, and your engine is in the dog-zone; She really wants that 3500.
This is what yur up against with a 273.
But more likely is that you will run 3.91s (or less).
First gear will get you about 46mph@5800. At the 1-2 shift, the Rs will drop to ~3400
Then, second gear will get you,60=4230@zero-slip, perhaps 4650@10%slip,on your tach, and so for RapidTransit, your engine is gonna need to making some power there.
If you have built your 273 to be a "beast", then 4650 is barely above peak torque. And the power won't peak until say 5400@73mph.......
So like I said, she's a 1.5 gears to 60mph, car.
I interpret that as slow, because the engine is only going thru the power-peak once, then dropping into the soft zone, before struggling back up the power curve..... half way, and then your zero to sixty time-trial is done.
If that's what you want, then have at it.
And we haven't even talked about the engine-build required, to powerpeak at 5400.
So for this application; it doesn't matter what engine you install, they are all governed by the same 60mph@5500, requires a 7.38 gear ratio.
So lets flip it around;
If 3.91s is all you want to run, then with 27s and a regular TF trans then
60=4650@10% slip. And so, for RapidTransit to 60mph, you want to pass thru the power peak twice and end at say 4900. So, still for RapidTransit, the engine has to be build to that spec, and sooooo the 273 cannot possibly be Rapid, unless supercharged. Whereas a 360 might still be spinning the tires.
And if 3.23s is all you want to run, well you see how this is going, right?
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