budget 273 build

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JJR

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Hello, my name is Jedidiah Rumbolz. I have a 1966 dodge dart gt with a 273 that is in need of a rebuild. I was wondering if any of you know a couple tricks to get a couple easy horses out of this engine. I am aware of a package called the D- Dart that dodge did in 1966 for racing in D/Stock. I believe it had a 273 with a .500 lift cam, 4speed, and a 8 3/4 with 4.88 gears. Will the heads on my engine flow at that lift? I only planned on taking this engine to 6000rpm. How much spring pressure can a stock valve train take?
 
Welcome to FABO!

...dunno how much "budget" of a build this was, but the OP in this thread is trying to build a smooth 273 using some old school parts

http://www.forabodiesonly.com/mopar/showthread.php?t=199120&highlight=273+build

...also, look up member "273" I think he's working on building up a 273 as well. Try to familiarize yourself with the search function-it works well as long as you vary your verbiage.

Also, consider making a thread on the welcome wagon forum-introduce yourself and your Mopar so we can all get a gander--maybe create a rebuild thread if that's the direction you're headed?
 
Welcome to FABO. There have been many 273's built around here in the last many years. As Tx mentioned, get practiced up at using the search function. You will find days worth of reading on the subject. I rebuilt mine a few years ago and you can get to my thread by clicking on the link just below. Also please post some photos on the 66 Dart thread I started. Lot's of us here. toolmanmike
 
Welcome to FABO Jedidiah!

Sounds like it's going to be a fun project. The "D" Dart, while fairly mild by today's standards, was really designed to be a race car. We really need to know what your intended use is?

1) Daily driver/ decent mileage?
2) Locally run "hot rod"...meaning cruising to shows & hang outs?
3) Serious power & maybe some racing?

The 273 can easily do all of the above, it's just that component choice is spread a little wider because of the small cubes.....Meaning compression, cam, and gearing choices.

Any extra info you can give will be helpful to us, so we can help you. :thumleft:
 
It's rather unfortunate that there are few piston choices for a 273 off the shelf...but there are so few people who actually want to build one up for performance...most will just opt for a 360.
 
Egge makes the original style 10.5:1 pistons. Last set I ordered from them arrived at the house less than 36 hours later.

There are a number of good cams for the 273. Racer Brown, Sneider, Isky still have their 60s performance grinds that work well. For the D dart cams no one reproduces them. The 273 in my dart, I put a racer brown ST-1. Peppy little cam (450/450) with a little bit of lope to it. I picked up a sneider 468-F (468/468). The racer brown has a bit more duration, but my tells me this is a hot little cam.

I'm starting a new budget build on a new project this month, will be posting progress. ToolManMike has an old build thread as do I. Will look for the links in a bit
 
Welcome to FABO.


What is a 273? Just kidding.


You cannot increase the valve size without having to notch the bore for clearance. However, with a little porting, you can get a 273 head to run.
 
JJR said:
Hello, my name is Jedidiah Rumbolz. I have a 1966 dodge dart gt with a 273 that is in need of a rebuild. I was wondering if any of you know a couple tricks to get a couple easy horses out of this engine. I am aware of a package called the D- Dart that dodge did in 1966 for racing in D/Stock. I believe it had a 273 with a .500 lift cam, 4speed, and a 8 3/4 with 4.88 gears. Will the heads on my engine flow at that lift? I only planned on taking this engine to 6000rpm. How much spring pressure can a stock valve train take?
Click to expand...

I wouldn't build it to D Dart spec's.
Building a 273 is like any other engine CR/Cam/Headers/Porting/Intake&Carb

273/318 heads flow a little low for a 318 but are plenty for a 273 size engine though
probably not much in the .500 range. With reasonable cam and CR they flow enough for 300-325 HP. pocket porting and port matching is always helpful plus it help you make good power with a smaller cam which is one of the two things you dont want to over do on a 273 Carb being the other. Something like 9:1CR, comp xe262h, 1 5/8 headers and a dual plane with a 600 cfm carb.

Plus a ???HP 273 is gonna have less bottom end power than an equal hp 360 and gonna make it at an higher rpm so your gonna need to run a lot more gear for similar performance. minimum i'd go is 3:91 but 3:55 and up is good. and the so called 10.5:1 pistons are more likely gonna give you low 9 CR.

Also read the sticky on porting 318 heads
 
273 said:
When I calculated out the dome, drop in the hole, head gasket and the cc on the head and the numbers we closer to 10.25:1 on the egge .030 over. Not sure wher you got the info that the dome tops got such low compression...
Click to expand...
 
I already had a 273 Commando to begin with. This is how I did mine, it's a fun car to drive with this:

1970 duster
1965 - 273 commando
Cam: Comp Cams Magnum 282S - 282/282 Lift 495/495 (solid) Beehive Springs
Edelbrock D4B intake / Holley 670 Street Avenger
Pertronix Ignitor & Flame Thrower coil
Hooker Headers
2.5" Dual Exhaust / Super 44 Flowmaster
8 3/4 - 3.55 - SureGrip
727 auto / Shift Kit
10" 3000 stall converter
B&M Quicksilver Shifter

I would not go under 3.55 on the rear, but I guess it's up to how you plan to drive the car. My car likes a bit of converter since it does not put out a lot of tourqe from a stop.

Here's a video

[ame]http://youtu.be/HxSr8bkjC1s[/ame]
 
I did up a 273 for a friend maybe 15 years ago. The car was a 65 Dart GT, original 235 hp 273, 4spd car, he'd already swapped in an 8 3/4 with 3.23 gears. I bolted down a set of 302 castings, stock size valves with a good basic valve job, cut the heads .030 and brought the chambers down to 57cc if foggy memory serves me right (I measured and calculated compression to be 10.4), installed a Crane Power max H-260-2 cam and lifters, swapped the iron intake for a Holly Street Dominator, and put a set of Spitfire headers on, made for a nice little wake up, drive it any where, any time car.
 
chewy said:
When I calculated out the dome, drop in the hole, head gasket and the cc on the head and the numbers we closer to 10.25:1 on the egge .030 over. Not sure wher you got the info that the dome tops got such low compression...
Click to expand...


How did you guys calculate the compression on your engines?

Here is a thread to explain how to do it accurately with reasonably priced readily available equipment.

http://www.forabodiesonly.com/mopar/showthread.php?t=278215
 
krazykuda said:
How did you guys calculate the compression on your engines?

Here is a thread to explain how to do it accurately with reasonably priced readily available equipment.

http://www.forabodiesonly.com/mopar/showthread.php?t=278215
Click to expand...

There are more than one method for taking the measurements. If the pistons are out of the engine for example, you can use liquid displacement, and measure how much volume is displaced... anyways

I did it by simply adding ot subtracting the volumes of all spaces in the combustion chamber.

A. Bore x stroke cylindrical volume
B. Piston side clearance tube top groove volume to low spot on valve releaf side of piston.
C. Dome volume (measured liquid rise mehod)
D. In the hole volume, Cylindrical from deck to low side of piston.
E. Gasket cylindrical volume
F. Head combustion chamber volume

Compressed volume after unit conversion.
Cv = B - C + D + E + F

Full volume
Fv = A + Cv

Then take the ratio between the two Fv and Cv solving for x; x/Cv=1/Fv


Kinda makes me wonder if the 9.0 reported above they forgot to subtract dome volume...
 
krazykuda said:
How did you guys calculate the compression on your engines?

Here is a thread to explain how to do it accurately with reasonably priced readily available equipment.

http://www.forabodiesonly.com/mopar/showthread.php?t=278215
Click to expand...

Here's how I checked the compression on my 273:

I checked my actual compression today with a 100 cc graduated cylinder. I wanted to know whether I should use the fat "perma-torque blue" head gaskets or the thin
Mopar gaskets. The thin ones are what I want. I used the full fill method as per the Isky cc kit. Put the piston at tdc, install the head and torque it with the gasket of choice and tip the block up so that the spark plug hole is straight up. Use the graduated cylinder and fill the chamber to the bottom of the plug threads. Then spin the crank till the piston is at bottom dead center. Fill the cylinder to the bottom of the plug hole threads keeping track of the fluid amount both times. Divide the full cylinder number by the combustion chamber number and you have your true compression ratio. The thicker perma-torque gasket produced a 9.22 comp. ratio and the thinner Mopar gasket had a 9.67 ratio. That's the one I'll use. I'm glad the machine shop shaved .030 off the heads! LOL I used ATF for fluid and light grease to seal the edge of the piston to the bore. I guess I was a bit disappointed the the ratio wasn't closer to 10.5:1 but grinding seats and the dish of the new valves and the thickness and cylinder diameter of the head gaskets all loose compression. Who knows what the factory 10.5 ratio really was. It will be pump gas friendly for sure. Mike
 
JJR said:
Hello, my name is Jedidiah Rumbolz. I have a 1966 dodge dart gt with a 273 that is in need of a rebuild. I was wondering if any of you know a couple tricks to get a couple easy horses out of this engine. I am aware of a package called the D- Dart that dodge did in 1966 for racing in D/Stock. I believe it had a 273 with a .500 lift cam, 4speed, and a 8 3/4 with 4.88 gears. Will the heads on my engine flow at that lift? I only planned on taking this engine to 6000rpm. How much spring pressure can a stock valve train take?
Click to expand...

A basic re-ring,GOOD valve job,& pocket porting in the 88-90% zone,would make life righteous. (stock valve size's work....)
 
Wow, you had the same pistons as I had. Mine slugs weren't very far in the hole ( like .047) , but I wouldnta thought there was that much difference between our ratios with your heads 6cc smaller than mine.
 
JJR said:
Hello, my name is Jedidiah Rumbolz. I have a 1966 dodge dart gt with a 273 that is in need of a rebuild. I was wondering if any of you know a couple tricks to get a couple easy horses out of this engine. I am aware of a package called the D- Dart that dodge did in 1966 for racing in D/Stock. I believe it had a 273 with a .500 lift cam, 4speed, and a 8 3/4 with 4.88 gears. Will the heads on my engine flow at that lift? I only planned on taking this engine to 6000rpm. How much spring pressure can a stock valve train take?
Click to expand...

What transmission do you have? What do you intend to do with your Dart? Valve spring pressure should be matched to the cam you choose. 6,000 rpm is easy for a 273. If this is a street motor I would stay under .500 in lift to use single valve springs and the good Viton positive valve seals like Mopar Performance sells. The "64" to "67" 273 valve train is very stable since it is solid lifter with adjustable rocker arms from the factory.
 
One factor explaining why it's hard to duplicate the factory 10.5:1 compression may be that all the head gaskets available today have the large bore holes (340 size). That has to knock it down a notch.
 
The whole reason I bought the car was to get good at power shifting a 4 speed and because the car is slick looking. I have cut a couple good shifts, I am just not good enough at it to appreciate a higher horsepower engine. I believe the 4 barrel version in my GT had the high compression piston(10.5to1) and CP sells forged pistons to that spec for a 273. Cam lift for my GT stock is .425 inch lift and 248 degrees advertised duration for intake and exhaust. The only thing I plan on doing to the heads is gaskets matching and a three angle valve job while also retaining stock valve size. I realize shaving some metal off around the throat and bowl will definitely improve flow but I'm not going to get that crazy this go around. I also would like to put an aluminum single plane on it(edelbrock torker)for the weight loss and because it does not have the bends like the stock cast iron. I don't think the runner size is too big for this engine, it shouldn't hurt low end performance to bad. I was also definitely thinking about swapping the old AFB for a holley no bigger than 700 to 750cfm. I like the the idea of dougs headers with 1-5/8 inch primaries but for this build I think the tubes are a little big so I think I stick with the manifolds. Any ideas on what cam I should use for this combo. I don't know if a .500 plus lift cam would be worth it without massaging the ports. I don't mind a rough idle so a longer duration an tighter lobe separation wouldn't bother me especially if it pulls like a freight train on the upper rpms
 
Also I planned on swapping the 7 1/4 for an 8 3/4 with something in the range of the 3.90s to 3.55s.
 
mvh said:
One factor explaining why it's hard to duplicate the factory 10.5:1 compression may be that all the head gaskets available today have the large bore holes (340 size). That has to knock it down a notch.
Click to expand...

...just for grins...I ran a few numbers and combos on this calculator:

http://torinocobra.com/Randys_tools.htm

first I found a combo with a .030" over 273, zero decked pistons with a 6cc dome, 57cc combustion chambers, and an .040"x3.70" gasket...and a few other details...yielded 10.7:1 static CR. When I changed the gasket diameter from 3.70" to 4.14", it dropped the static CR (drum roll please)....

0.2:1 from 10.7:1 to 10.5:1...

While there may be a benefit from more appropriately sized head gaskets, I don't think in this case it would produce anything more than a negligible effect.

The reason it's tough to get an actual 10.5:1 CR with a 273 is because there aren't that many pistons to choose from, and the ones which are available off the shelf would require some balancing to get correct and consistent volumes. Another is Mopar left a little to be desired with deck height and shift consistency. Yet another is consistent combustion chamber volumes. Compounding those factors is that every cc added or removed has a greater impact on the outcome compared to if you were dealing with a 340 or 360. Basically, if you want an honest 10.5:1 273, you're going to sink a good bit of money and time into thorough blueprinting and parts selection.

JMO...
 
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