273 for early A

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JDMopar

JDMopar

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I made a post in the Small block section, but wanted to put it here also for early A folks who might not go there much. Any help and ideas appreciated.

I'm planning to build a 273 to put in a 65 Barracuda that I bought last summer. I'll add my thoughts on the plan in my head after reading dozens of 273 build threads I searched here. RRR, ToolmanMike and others, please tell me if I'm on the way to screwing it up! Here goes. 273 block, .020 or .030 over with the Egge 10.5 compression pistons, 340 steel crank, just because I have one laying around, 302 heads with better springs to match the cam. Howards cam Howards Cams Hydraulic Flat Tappet Camshaft and Lifter Kits CL711381-10 , stock rockers from a later LA, D4B intake with no more than a 600 Holley. Stock exhaust manifolds that came on the Barracuda, with dual 2 1/4 inch exhaust to the back bumper. Probably will use a 998 or 999 automatic...whichever one is the lockup version. The car is intended to be a driver/cruiser that I'm not afraid to get in and head to Myrtle Beach or Winslow, Arizona to go stand on a corner....lol. Probably 2.76 or 3.23 gears. I just want it to get out of it's own way, sound good at idle, and get decent gas mileage. Thanks in advance for your thoughts and suggestions. :)
 
Looks good. That cam looks close to a 340 cam. We used to run the 340 cam in 273's and 318's all the time. Use a windage tray. I'd run flat top 2 barrel pistons if it were me, you may only find 91 octane here and there. 3.23's will get you around 20 mpg cruising to Arizona. 2.76's are the go to highway gears and you should get over 20mpg, but the fun factor goes down unless you are into highway flying. What other parts do you have for the 273 on hand?
 
The only thing I have is a 273 Bare block with main caps. I'm not opposed to using the 675 heads from a 318 with the higher compression pistons if my 302's are all cracked. I have 2 sets of 302's, and who knows how many 675's...lol. I have a D4B intake also, and it already fits later heads.
 
Sounds like you should be good. I'd run flat top pistons with the 302, but have them magnefluxed before spending any money on them. Use the pop ups with the 675 heads. Make sure you have clearance between the valve springs and rocker arms. The D4B intake is great, but it is for 64-65 heads. I have an extra set of 64-65 heads if you want to run those. Assuming you have plenty cranks, rods and misc parts.
 
I’ve got pretty much everything I need, as far as crank, rods, windage tray and oil pans. I’m hoping to get lucky and get 2 good heads out of the four 302’s I have laying around. My D4B will fit the later heads. I had it on a 318 in my 71 Challenger a few years ago. If I have to do any major grinding on the bolt holes to get it to work on this particular motor, I will just use one of the Edelbrock Performers that I have laying around. I’m wondering if the cam I listed will be too big for an 8.? compression motor? If it is, I have a few smaller cams stashed back that aren’t as big. I’d have to look up the specs, but I have a Lunati cam and a Mopar Performance 761 cam. I have a 761 cam in the 360 in my Challenger, and it works great.... but I know it will be much different in a 273.
 
Early 340 cranks are balanced for heavy forged slugs. and heavy rods.

That's a good cam for torque and fuel mileage, but with only 38* of overlap, she won't have hardly any idle-lope to her, which you seem to have alluded to. And log manifolds will kill any that mighta tried to sneak thru.

That cam will probably not want any more than 9.5 compression ratio, which with a ten over 273, makes a minimum total chamber size of 66.5cc. That will be tough I think, with those pistons.
At 8/1 it's gonna be real soft on the bottom and pretty abysmal performance with your listed gears.
As will be said;
Good luck
 
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That 340 crank is going to be overkill, sell and aquire a 273 crank as the EGGE pistons will already be balanced for it IIRC. Your 340 crank will support the 998/999 convertor but the balance charge will be more than the cost to machine a 273 crank for a 998 convertor. 302 heads are semi closed chamber, and your egge pistons are pop ups: Run the correct head gasket for that interference combo!
 
273's are close to 9:1 with flat tops. The pistons are about .02 from the deck. We had to run 675 heads on my brothers 67 to run regular gas. I'd run a 318 crank if you have one in your stash, same balance as a 273 and even a cast 318 crank is pretty stout. The cam is not too big for a 273 in an early Barracuda. If you don't have 64-65 heads you can sell the D4B and get whatever you want, since it is the best intake for those heads. What the specs on the cams that you have in your stash?
 
2511AE0C-0158-4F2E-8240-2CC05DAC9F18.jpeg
Here’s the Crane.
 
I do have plenty of 318 cranks, and have been discussing that with the guy who is doing the balance work for me. We had pretty much decided to use a 318 crank since the bob weight will be closer. I’ll just keep the 340 crank around in case I need it later. I need to take my 302 heads and get them checked before going much further, I suppose.
 
Another member put late model heads ( I think 302 ) in his early A build. Cracked a OEM early A exhaust manifold too ( manifold hits late model head casting ).
Your OEM exhaust manifolds flow very poorly anyway. Some have compared the crock in that left manifold as "pooping through a straw". Larger pipes from those manifolds isn't going to help much.
 
Yeah, I know. I’ve been thinking about a set of Dougs headers, or at least using one pair of 340 HP manifolds that I have in my stash.
 
The cam you linked in post #1, does not match the card in post #11, which also does not match the P4452761Kit
Oh, I sorta see what you did there,sorry;

Product Line: Howards Cams Hydraulic Flat Tappet Camshaft and Lifter Kits
Summit Racing Part Number: HRS-CL711381-10
Duration at 050 inch Lift: 208 int./214 exh.
Advertised Duration: 255 int./261 exh.
Lobe Separation (degrees): 110

This P4452761 cam-kit will run well,at 9.6Scr, and the 54* of overlap will have a nice lil lope.The paper says 50* overlap ;which would be right for a 110cam, while the math says at 108 it's 54*
To make best use of it, those 54* of overlap demand long-tubes. The compression plus power durations at 108LSA, total 234* compared to 242* with the Howards. When both are installed at 108, the compression distance is nearly the same so the only thing the 761 gives up is smooth idle and fuel-economy; which, IMO, is a good trade. The 220@.050 compared to the 208@.050 is ~2 cam sizes bigger, moving the power peak from ~4700 to ~5100, and that is where the power comes from; I get a potential of about 20hp on that difference; with at 9.6 Scr(compared to 9.5 on the Howards) almost no loss of low-rpm torque, except what the typical Mopar long ramp cam brings to the game. Depending on your altitude, both 9.5 and 9.6 Scr might require premium fuel at full-load.The 761 may not like the factory TC, so in your case, you can solve the TC to crank issue with a custom 2500 to 2800 TC, depending on your final Scr, and how close you can cheaply/affordably get.
>I like that 761; it's a heck of a cam in a bigger engine with a manual trans (closer ratios) but in your application, I fear it might be too much. Getting the Scr just right will be very tricky, and how often are you gonna need the extra ~20hp at 5100? Ima thinking an extra 20 ftlbs at stall would be waaay more useful to you

The 272H10 is measured at .004 Tappet lift, so cannot be directly compared to a Mopar at .008, or the unspecified Howards. But that's ok, cuz IMO it's a lil wrong for your combo anyway.If I estimate the .008 events, I get a kindof in-between cam to the other two, but with really long acceleration ramps. And it's a single pattern cam with no compensation for the Mopar exhaust ports. It may be a good cam in a certain combo, but I think not the best in yours.

However, if you already own it........... it might not be so bad as a starter cam. Plus you get to degree it and find out what it measures at .008, so then you can compare it to other .008s. And then if you don't like it, at least you will have a pretty good idea of what next cam to get. Plus it will have a lil idle-lope, about like a stock 340.
And that's my opinion.

Actually, my opinion
is to target a 9.5 Scr with a tight-Q, see how close you can affordably get, then order the cam that takes best advantage of that. The Intake closing event will be around 58* so you can build a combo around that, as big or as little as you want, or can stand, just by manipulating the intake/exhaust durations and overlap period. You can go from mild to almost wild, with just a lil lope to quite a bit. Maybe there's an off-the-shelf cam, and maybe not. But the 58* will get you a cam that is in the ballpark, especially if a fast-rate. As said; the 2bbl flat-tops might get you what you need. At .020(3.4cc) in the hole, 9.4Scr@.048Q, is easy(cheap), with 57cc heads.
 
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I'd say both "stash" cams are a bit large for your intended usage. If you look at 302 head flow numbers, not much advantage of going past .450 -.500 lift. One of my friends 273 dyno'd 260+ HP with 2 barrel pistons and an E-4, .425 lift and 216 duration, cam, Commando intake and distributor, 67 heads, and a 600cfm Edelbrock carb.

Shady Dell Speed Shop
 
Thanks guys. That gives me some good things to consider. Are the 67 heads open or closed chamber? AJ.... some people complain about your detailed explanations, but I really appreciate you taking the time to make things make sense!
 
JD, I hope you can keep your two threads in 2 different forums straight. It's not a good idea to do that. 273 threads could effect both early A's and 67-69 cars as well.
 
If your not married to that 273 block, 318 blocks are given away and considering you may not be using the "10.5:1" Egge pistons (debatable CR) and may go with a flat top, youll find many more flat top 318 pistons available. Changing cams, intake and exhaust just makes keeping the 273 size the head scratcher. you can dress up the 318 all you want with 273 badges and no one will know. The thing with the 273 was its high revving 4bbl option (and the small V8 it was designed to fit in) neither are in play now so a 318 is already now a big bored 273. No one builds a 260 Ford, they all build 289/302's. Unless your building a 4bbl 273, Id go with a 318 to start. JMHO.
 
Mike....I have been checking both threads. I copied and pasted it to this forum because a lot of people with 273 knowlege post here, but not there.

Pishta, I have given a 318 a lot of thought, and may go that way if I can restrain myself from letting it snowball too much....lol. Lots more choices with a 318 that don’t cost out the ying yang.
 
JDMopar said:
Mike....I have been checking both threads. I copied and pasted it to this forum because a lot of people with 273 knowlege post here, but not there.

Pishta, I have given a 318 a lot of thought, and may go that way if I can restrain myself from letting it snowball too much....lol. Lots more choices with a 318 that don’t cost out the ying yang.
Click to expand...

If you go with a 318, then you can put larger valves in the heads...
 
I'd build the 318 in a heartbeat over the 273....could actually do the 318 with better pistons for less money me think....
 
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