974 heads... flow numbers

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The reason why I ask is , I have. Sets of 974s ,051s even 302s and the 920s
I am trying to get the most "bang for buck" with my 273. I know the chambers are
larger on all of these heads compared to the 920s I can cheat some of the cc's with
A thinner head gasket using one of the other heads. I have been told that between flow and compression ,flow will give more power Over compression.
And I can belive that to a point.

my engine has a overbore of .060 ,not liking that at all but its is what it
Is. Thinking of sleeving the block back down to a STD. Bore size.and us the 4bbl piston
Want to run the .284, .528 mopar purple shaft with a 800 TQ. And
The torquer340 manifold . 904 trans with a "loose"converter.
4:30 gears and 26in tires.... down the line put my 4speed in "missing a few parts
For the manual right now".
Can anyone give me any ideas?
Or if I am way off base here point me in a betterDirection .:prayer:
 
A curveball.Check out 69 Cuda 440's 273, cam test thread. Absolutly sweet. E.T.'s,Dyno H.P.,and an explanation why.Check it out,you will learn something.
 
There are a couple issues with building a 273 - piston choice and head gasket choice. Both are critical because it's a small, short stroke engine and needs all the compression it can get. If it were me I wouldn;t sweat the .060 over. You could have it sonic tested to be sure for a lot less than sleeving all 8 but IMO it's probably fine. they were cast back when making them way thick wasn't a budget issue. I'd get a set of custom pistons with a flat top and good valve reliefs and plan to runa set of Cometic custom head gakets. Then you can design a tight small chambered engine that will make some decent power on pump gas. Otherwise you're spending more to cobble something together with what I'd call old and sub-standard parts. Use the 302 heads - upgrade the valves to 1.88/160, do a little basic clean up, and reduce the chamber to give you a true 10:1 with a tight (.030) quench distance. he .528 is a decent cam but much better can be had. I'd look for a modern solid profile with 225° or so @ .050" and lift around .500. Run a 318/360 Performer (easy to get at swaps - nobody likes them on 340/360s) and port match that to the heads. That Torker's not worth any time on this combo. I'd also recommend a new Thunder AVS 650 or Holley 570 Avenger. That would be my starting point. Even witht he gearing the trick is torque for a 273. It will rev just fine - but you need it to get the car moving and accelerate it. Not just make high rpm horsepower.
 
moper said:
There are a couple issues with building a 273 - piston choice and head gasket choice. Both are critical because it's a small, short stroke engine and needs all the compression it can get. If it were me I wouldn;t sweat the .060 over. You could have it sonic tested to be sure for a lot less than sleeving all 8 but IMO it's probably fine. they were cast back when making them way thick wasn't a budget issue. I'd get a set of custom pistons with a flat top and good valve reliefs and plan to runa set of Cometic custom head gakets. Then you can design a tight small chambered engine that will make some decent power on pump gas. Otherwise you're spending more to cobble something together with what I'd call old and sub-standard parts. Use the 302 heads - upgrade the valves to 1.88/160, do a little basic clean up, and reduce the chamber to give you a true 10:1 with a tight (.030) quench distance. he .528 is a decent cam but much better can be had. I'd look for a modern solid profile with 225° or so @ .050" and lift around .500. Run a 318/360 Performer (easy to get at swaps - nobody likes them on 340/360s) and port match that to the heads. That Torker's not worth any time on this combo. I'd also recommend a new Thunder AVS 650 or Holley 570 Avenger. That would be my starting point. Even witht he gearing the trick is torque for a 273. It will rev just fine - but you need it to get the car moving and accelerate it. Not just make high rpm horsepower.
Click to expand...

couldn't agree more :thumblef:
 
Many thanks for your opinion and input.
I got those heads and that manifold on the shelf"didn't think they were
Worth a **** really."
I'm not sure how many miles are on this engine and I need to see
How much taper is in the bores .hence the not liking the .060. Overbore
This engine is my work in progress
 
I have several 273 blocks of lesser bore if needed and if date matters what month and year are you looking for or around?
 
From what I'm reading, when it gets right down to it the 273 performers
The "best"running the basics............. 3 C's
Cam carb and compression
As long as I got the 4bbl pistons a a small chamber head(with a littlie work done)
And a mech cam under .530 all shound good?
 
Sounds good. I'd 2nd the 302 heads. I'm accumulating parts for a torque 318 right now and using those for the swirl port in them.

I don't know if I would run 360 valves in the heads, though. The best thing I think anybody can do is run the smallest valve that will not restrict on the induction that an engine will draw into it. The reason being is that it keeps velocity up and reduces shrouding. If you think about how air moves through a runner from the carb, eventually, it will run into the valve. Shrouding is a condition that happens when the air flow is restricted by the edge of the valve against the cylinder head and wall of the piston chamber.

The valves/ stems are at a steeper angle than the cylinder, so as the valve progresses downward, the head of the valve comes closer to the upper portion of the cylinder wall on the intake side, which causes the flow to disrupt.

This can be corrected by deshrouding the engine block and head, but if you run larger valves with the small bore, it will duplicate the standard shrouding of a 318 that those heads came out of, due to the smaller bore and larger 360 valve combo.

Another theory is that if you can use a cam to move the valve for the flow you want, it's best to do that, than to move up in valve size, because there is less of a valve head for the air to flow past.

The limitations have a lot more to do with the entire volume of the cylinder head and intake combined runner, along with it's geometry, than the size of the valve at the end. If you've gone through and ported the cylinder head and are utilizing a larger runner intake, you may benefit from going with a larger valve, if the rest of the engine will use it (forced induction, larger displacement, anything else that will aid in moving more CFM, etc.)

I think quench with a good piston and the 302 heads with stock valves, a 3 angle cut, the cam suggested above and a 273/318 runner intake will do you well. For what it's worth, a 1.88 barely clears an .060" 273 cylinder wall, which means there will essentially be zero flow on that side of the valve.

I would suggest using a Weiand 8007 if you use a spread bore or a Weiand 8022. They have a true 273/318 port size. The Edelbrock Performer will work too, but it requires gasket matching, because if it's intermediate port size that is neither 273/318 or 340/360. I'm not a fan of that, because widening the ports slows the air down at that spot in the runner. The Weiand is a cheap manifold that can be found easily, too.

The Street Demon 625 is choice for street use. Bench tested and tuned. That Edelbrock Thunder AVS 650 is a good unit, too. Easier to change jets in than the Demon, but the Demon will whup it's *** in atomization and torque. Both are awesome street carbs with the tunable secondary air doors. I'd run a Holley 4776 600cfm Double Pumper if you are going racing.
 
chuck perry said:
From what I'm reading, when it gets right down to it the 273 performers
The "best"running the basics............. 3 C's
Cam carb and compression
As long as I got the 4bbl pistons a a small chamber head(with a littlie work done)
And a mech cam under .530 all shound good?
Click to expand...

Nope. The 4bbl pistons will not generate the static compression especially given any available head gasket nor is it tall enough or of the right configuration to generate an effective quench.
While I agree with some of what Dave notes in terms of head theory - most of it IMO is overly concerned with relatively small details that don't add up to more power. You will get more power from the larger valve, especially given the rpm range you're contemplating. If you're really concerned about the shrouding then you can notch the bore but I'd rather not bother. Just my opinon of course.
 
moper said:
Nope. The 4bbl pistons will not generate the static compression especially given any available head gasket nor is it tall enough or of the right configuration to generate an effective quench.
While I agree with some of what Dave notes in terms of head theory - most of it IMO is overly concerned with relatively small details that don't add up to more power. You will get more power from the larger valve, especially given the rpm range you're contemplating. If you're really concerned about the shrouding then you can notch the bore but I'd rather not bother. Just my opinon of course.
Click to expand...

Yep, put the biggest valve you can fit in there without hitting the cylinderwall before maximum lift.
 
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