The Best Tricks for 273 Cylinder Heads

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69 Cuda 440

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Much has been mentioned about what works best for the 273/235 HP Commando Engine
Casting #2658920 Cylinder Heads.

Going with a 273 Block, and bored .040 to a finished bore of 3.665"

I'm asking for input from the Technical Thread.

The car will used for the Drag Strip, as we are entering with a group of match racers who
will be entering this 'Special Pony Car Class' for cars that had a weight break of 12.50 to 13.49,
based upon manufacturers advertised horsepower and shipping weight.

We're going with 10.5 - 1 Pistons, a Lunati blueprinted stock camshaft, and 4.89 Gears in a 4-Speed car.

Cars must use the stock-type camshaft, and maximum 4.89 rear-end gears. Obviously headers, and 9" wide-slicks
are permitted.

Stock intakes must be used, but Carburetors up to 600 CFM are permitted.

The stock cylinder heads can have matched ports (intake and exhaust), no deeper than 1/4", and no runner porting.
But, any size valve can be used, and the combustion chamber can be polished

Experts,,,,,,,,,,What do you suggest.
 
69 Cuda 440 said:
Much has been mentioned about what works best for the 273/235 HP Commando Engine
Casting #2658920 Cylinder Heads.

Going with a 273 Block, and bored .040,

I'm asking for input from the Technical Thread.

The car will used for the Drag Strip, as we are entering with a group of match racers who
will be entering this 'Special Pony Car Class' for cars that had a weight break of 12.50 to 13.49,
based upon manufacturers advertised horsepower and shipping weight.

We're going with 10.5 - 1 Pistons, a Lunati blueprinted stock camshaft, and 4.89 Gears in a 4-Speed car.

Cars must use the stock-type camshaft, and maximum 4.89 rear-end gears. Obviously headers, and 9" wide-slicks
are permitted.

Stock intakes must be used, but Carburetors up to 600 CFM are permitted.

The stock cylinder heads can have matched ports (intake and exhaust), no deeper than 1/4", and no runner porting.
But, any size valve can be used, and the combustion chamber can be polished

Experts,,,,,,,,,,What do you suggest.
Click to expand...

my quess is that the rules state the cam must have stock lift #'s but there is alot of room to play with ramp speed and duration/overlap.
 
younggun2.0 said:
my quess is that the rules state the cam must have stock lift #'s but there is alot of room to play with ramp speed and duration/overlap.
Click to expand...

Correct Mr. Young Gun,,,,

Though the stocks specs were .425 lift with a 248* duration, we can use any camshaft, just as long as the lift is within .010 lift of stock specs.
 
Neat stuff. I would look at a 1.88/1.60 install ,with good cutters. Might want to round up a few stock mistakes,air flow bench test for the best. Essentially,I would look at the N.H.R.A stock class 273 combos.The trick is completely read the rule book,take advantage of loopholes.Don't just analyze the heads,look at the whole project.
 
69 Cuda 440 said:
Correct Mr. Young Gun,,,,

Though the stocks specs were .425 lift with a 248* duration, we can use any camshaft, just as long as the lift is within .010 lift of stock specs.
Click to expand...

i am good friends with a guy that holds several stock eliminator records. there is alot in the camshaft lobes....... some might even float the valves on purpose with a very aggressive lobe ramp..............
 
If can't do any porting I don't see how bigger valves will help, Need to find someone that knows a lot about valve jobs that helps Mid and Low lift to work with stock cam, knock away any casting flash you find and clean up parting lines if you keep it looking stock.
 
Why I posted good cutters.Head porting,in a tool,done correctly.
 
A-Body Bomber,

I'm not sure bigger valve's will produce anymore performance, as valve shrouding
will hamper any gain.

Though we can't port the heads, we can have the bowl area's opened up with
a concentric cutter-tool.

'Pony Car Class'
65' thru 67' Mopars..........273/235 HP
65' thru 67' Mustangs...... 289/225 HP
68' Mustangs..................302/230 HP
58' thru 61' Corvette's......283/230 HP
65' and 66' Chevy II's.......283/220 HP
68' AMX.........................290/225 HP
67' thru 69' Javelin's.........290/225 HP
 
If lift is measured at the valve?, 16 rockers as close to each other on ratio as possible and then cheat the lobe lift to make up for the poor 59* geometry.
 
69 ,that tool you listed is a "cutter".Sorry, for any misinform on my part. Actual concrete info,have that bowl at 87/88 % ,of the intake valve size.That is best recovering size,on shift recovery.Just a generalization,gives you a starting point.
 
69 Cuda 440 said:
'Pony Car Class'
65' thru 67' Mopars..........273/235 HP
65' thru 67' Mustangs...... 289/225 HP
68' Mustangs..................302/230 HP
58' thru 61' Corvette's......283/230 HP
65' and 66' Chevy II's.......283/220 HP
68' AMX.........................290/225 HP
67' and 68' Javelin's.........290/225 HP
Click to expand...

This is so cool.....i could fill this thread with advantages & disadvantages on these available engines....lol......The 273 with the 3.31 and long rod looks great as far as the Mopar is concerned. Are there posted rules you could link us too? How about tire diameter? Man you really set my mind in motion. If i only had the time and the green, i'd be all over this :D.
 
Old Man Rick,,,,,,

9" wide slicks are permitted.

Some wanted to go back to the original 7" wide maximum, and some wanted to go back to
the 'Cheater Slick' but the majority overuled, and the conventional 9" width is fine for this
Pony Car Class, as long as it fits under the wheel-well.

And the 9" slick costs less than vintage 'Cheater Slicks'.

28" diameter, is the standard.

There may be a few more cars added,
 
This sounds like a lot of fun. I would check out a pro stock eliminator head guy and have him do the valve job and pick a cam for you. I know of one 273 Dart running in stock that ran in the 10's.
 
Interesting,Vettes in a pony car class. I.I.R.C, extra engine setback,behind the front spindle.Also near 50/50 stock weight bias.Might wanna check it out......
 
69 Cuda 440 said:
Old Man Rick,,,,,,

9" wide slicks are permitted.

Some wanted to go back to the original 7" wide maximum, but the majority overuled,
and 9" is fine for this Pony Car Class, as long as it fits under the wheel-well.

There may be a few more cars added,
Click to expand...

That's good that it's a 9'' imo. Reason i asked about diameter was that i'm sure some guys will try 24/25/26" tires to add to the mandatory rear gear.

Just wondering how competitive this class will be? There's always guys that will throw big wallet's at stuff when there are rules to be pushed. This kind of racing is what i love....like the old days when the builders had some leeway to experiment with combo's.

I see your in NC. Is this a local thing or is IHRA/NHRA sanctioning this class? Reason i ask is, who are the police?
 
Sorry to step on your thread here about cylinder heads. It's a very intriguing concept for a class. If you decide to move forward with your build, please start a thread in the Racer's forum as i would like to follow it and comment when i can.

Thanks, Rick
 
Old Man Rick,

Actually it's a Racing Group that we started in New York. We added the 58' thru 61'
Corvette's, because there are 5 cars in the group.

No 'shorty slicks' permitted. We are trying to keep everything on an even 'keel'. Mandated Size 28" x 9.0" x 15"

And 'No Camaro's, just Mopar 273's, Chevy 283's, Ford 289's, 68' Ford 302's, and AMC 290's.
-----------------------------------------------------------------------------

Getting back to the valves, one shop has suggested using the 1.88" Intake, but
cutting them down to 1.84".

They have used this combination before, and they have flowed well on the 'Air-Flow
Bench'.

But they still use the stock size exhaust valve.
 
Where is the maximum lift measured? What about piston choice limitations? Oil pan or oil control limits? Connecting rod limits?
 
moper said:
Where is the maximum lift measured? What about piston choice limitations? Oil pan or oil control limits? Connecting rod limits?
Click to expand...

The lift is measured at the camshaft, not the valve.

The factory states that the camshaft has a .283 lift, and with a 1.5 ratio rocker-arm, equals .425 lift.

But we are permitted to utilize an after-market camshaft that is no more than .010 lift over stock. (ie; error-zone for the camshaft).

Any duration and overlap is permitted. As well as a 1.6 ratio roller rocker-arm.

So the camshaft can have a true lift of .293, and with 1.6 ratio rocker
arms, the total valve lift can be no more .469" for the 273 Mopar.
 
A little acid porting to help with the runner volume...old stocker trick.
 
The port's minimum cross sectional area dictates the maximum valve you should use. I think I'd use the factory valve but us a cut down 1.88. That will allow the step at the top of the intake valve seat angle to be minimized without back cutting, and allow the seat to be right at the top without making the shrouding worse. I'd also mill the head a bit to reduce the shrouding. Use a thicker head gasket to get you back to 10.5:1. Good on the 4sp - because you'll want a cam that has very fast rate of lift and those mean rpm. Find heads and an intake with the least core shift you can find and you may not want to acid "port", but you might want to cc all the intake ports and use the acid to make them all the size of the largest as cast... Yes, technically it's cheating...lol.
 
Thanks Moper,,,,,,,,,,

Great information. It looks like we will be using a 1.88" Intake, cut down to 1.84".

Since the cylinder head chamber can be smoothed out, we may take a
'little off the sides' to help prevent shrouding of the Intake Valve.

Camshaft (lift at the valve) will be .469
 
69 Cuda 440 said:
The lift is measured at the camshaft, not the valve.

The factory states that the camshaft has a .283 lift, and with a 1.5 ratio rocker-arm, equals .425 lift.

But we are permitted to utilize an after-market camshaft that is no more than .010 lift over stock. (ie; error-zone for the camshaft).

Any duration and overlap is permitted. As well as a 1.6 ratio roller rocker-arm.

So the camshaft can have a true lift of .293, and with 1.6 ratio rocker
arms, the total valve lift can be no more .469" for the 273 Mopar.
Click to expand...

Good
 

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