400+ hp 273

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273

273

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I'm looking to build a 400+ HP 273 all the info I've read so far says it can't be done or cost to much or not streetable.

But a lot of these naysayers like to Quote "There is not replacement for displacement" which is true for torque. Torque is the function of how much fuel and oxygen you can get in every intake stroke and how much it's compressed. Horsepower is how much fuel and oxygen you can pass through the engine in any given amount of time (RPM).

The problem with 273 is the bore size of 3.625" it will limit the displacement (torque) and valve size (horsepower) so the question becomes what's the limit of cfms that the head can produce within a 273 bore. 273/318 heads ported can flow 200-250 cfms at 28" of water which should be good for 400-500 HP. Now what about 340/360 heads? I think you would run out of rpms before you run out of cfms.

So I started to look at other engine builds with similar specs and the best one I found was the 2v 4.6L Ford with a 3.552" bore which is way smaller than (4.5L) 273 3.625" bore. 400 HP 4.6L seem to make it at 6500 rpm the high end of streetable.

As for the lower torque output most people leave out is the effect of gearing has on torque to the ground. 400 lb-ft X (2.50:1 X 3:1) = 3000 lb-ft split between the tires 300 lb-ft X (2.50:1 X 4:1) = 3000 lb-ft same output to the ground.

So any constructive 273 builds or tech especially concerning heads and valves would be welcome. Please and Thanks
 
Welcome 273, i can't wait to see the responses to this thread. I always love a screamin' small block and this sure would have to be one.

There is a member here..Rob, don't remember his site name off the top of my head. I'll try to search for you and let you know. He is from Canada also and just recently did a 273 for another member. He knows his stuff along with 1,000s of other members here.

This thread will be popular in my opinion. I'll post when i locate his Name here.
 
To get the ball rolling here this is a link to a post on page 2 of a video of a 450 hp. 273 on a dyno. Now, there is no specs on this engine and no dyno sheets for proof about what it is, how it was built or how much power it produces so use your own judgement there. It can be done it just takes more money to make it happen. But, if you figure hp to cubic inches it might not cost that much more.
(1.6480 for 450 hp.) If you use the same factor for a 318 you would need 524 hp. A 500 hp 318 would be a spendy proposition too. It takes a solid bottom end, some good heads and a sizable roller cam. The whole package must be capable of 7000+ rpm and stay together. Not for the faint of heart or for the street. tmm
http://www.forabodiesonly.com/mopar/showthread.php?t=189011
 
OldmanRick said:
Welcome 273, i can't wait to see the responses to this thread. I always love a screamin' small block and this sure would have to be one.

There is a member here..Rob, don't remember his site name off the top of my head. I'll try to search for you and let you know. He is from Canada also and just recently did a 273 for another member. He knows his stuff along with 1,000s of other members here.

This thread will be popular in my opinion. I'll post when i locate his Name here.
Click to expand...

Did we ever see the dyno sheet after that one was built? tmm
 
273, Wild knows his stuff about heads and could give you some good info.
By the way.....Hello Wild.

"RobR" was the member i refered to earlier. He has a thread " 273 Freshen...pics ". I don't know how to post a link yet, still new here myself. Maybe someone else can or you can search his name.
 
No mike we didn't.....dont think it made anywhere near 400 to 450hp and he never claimed that, but it was a nice build with lots of pics and this member is even newer here then i am so just trying to get him started:smile:.
 
First problem to this is build is not displacement.

1. Your Ford engines are not the old engines were working with are they?

2, Head flow is where the power is made in a major way. Valve size has a issue with it all. There is a limit to the valve size for the small bore. If you want to exceed the size, a notch in the cylinder is needed.

3. While correct on air in and air out coupled with fuel of course, who much can the 273 breath in is the combo of head flow and cam duration. You'll need larger duration lobes to get more air and fuel in. Unless a pressure system is introduced.
Considering the size of the engine, it will take more duration to feed the engine what you'll need for this adventure than it would for a larger engine. This is why it is so often recommended to go larger.

6th, Stroke is torque over bore size. Bore size is closer to HP. A longer stroke makes more low end torque.
The longer the stroke the shorter the RPM band, all else otherwise being equal in the build between engines. Even if the displacement was the same.

Cost is what ever your pocket can spend. Some have more to spend.

Streetability is a idea in one's head that doesn't always match what the next gut thinks. On a laymans term, a general high powered engine's power abilty can be made by cfm X's 2, and this would not be the limit.

If you already have the 273, are the heads ported? With what valve sizes? What is there flow rates and stall point?
Is there a fuel limit (Octane) to look out for in this build.
Is there a limit on cam style/cost.

The Fords come with roller cams? The ones you mention. To add a roller to a MoPar (Old style) is pricey.

Personally, if you want to do it, I say go for it and I'll be here awaiting each step of this build. You'll need 1.465 HP per cube to get there. This is not hard. But many do not want to build a engine this small at this power level. For a 360 to do this, it is a 1.1 HP per cubic inch.

The cam for such a 360 can be a good bit smaller than 230* @ 050 so long as the rest of the parts are good.
 
Hey Rumble, how about a billet 340+.60, 13.1 comp. W2s or W5s, Serious roller and valvetrain with a 2.60/2.70 stroke to 273, haven't done the exact math. That should make 400+ @ about 9500 and sound like nothing most people here have ever heard. Bring back the old Modified production/Gas days...hehe.
 
rumblefish360 said:
First problem to this is build is not displacement.

1. Your Ford engines are not the old engines were working with are they?

2, Head flow is where the power is made in a major way. Valve size has a issue with it all. There is a limit to the valve size for the small bore. If you want to exceed the size, a notch in the cylinder is needed.

3. While correct on air in and air out coupled with fuel of course, who much can the 273 breath in is the combo of head flow and cam duration. You'll need larger duration lobes to get more air and fuel in. Unless a pressure system is introduced.
Considering the size of the engine, it will take more duration to feed the engine what you'll need for this adventure than it would for a larger engine. This is why it is so often recommended to go larger.

6th, Stroke is torque over bore size. Bore size is closer to HP. A longer stroke makes more low end torque.
The longer the stroke the shorter the RPM band, all else otherwise being equal in the build between engines. Even if the displacement was the same.

Cost is what ever your pocket can spend. Some have more to spend.

Streetability is a idea in one's head that doesn't always match what the next gut thinks. On a laymans term, a general high powered engine's power abilty can be made by cfm X's 2, and this would not be the limit.

If you already have the 273, are the heads ported? With what valve sizes? What is there flow rates and stall point?
Is there a fuel limit (Octane) to look out for in this build.
Is there a limit on cam style/cost.

The Fords come with roller cams? The ones you mention. To add a roller to a MoPar (Old style) is pricey.

Personally, if you want to do it, I say go for it and I'll be here awaiting each step of this build. You'll need 1.465 HP per cube to get there. This is not hard. But many do not want to build a engine this small at this power level. For a 360 to do this, it is a 1.1 HP per cubic inch.

The cam for such a 360 can be a good bit smaller than 230* @ 050 so long as the rest of the parts are good.
Click to expand...

100% correct! Just to add info about valve size limits on small bore engines, look at the combustion chambers of any late model dual over head cam engines. With 4 or 5 small valves, the whole combustion chamber is valves. That cannot be done with 2 valves and a small chamber.
 
I'm in the planing stage of this build, I'm building a autocross 65 cuda factory automatic 2 barrel car. Already bought all the suspension parts think of installing T5 trans and around 4.88:1 rear gears still deciding on wheel and tires, haven't decided if going with flares, rear wheel lips need repair any ways.

As for the engine has 50,000 miles on it runs like a dream as for the engine build I was thinking custom pistons 0.060 over if sonic check proves it can, a chevy 6.3" rod with early 2" bearing and have the crank turned offset to 3.41" stroke which would make it a 292 cid mainly for lighter pistons and extra cubes can't hurt lowering peak power a few 100 rpms. l'm Looking for 10:1 compression 268ish solid roller maybe eddy airgap rpm intake to keep as much bottom end as I can, heads maybe ported stockers or 302's or magnums or rhs. As for valve size I guess it would depend on the choice of heads, know bigger the valves the more it shrouded, I've seen flow comparisons with a chevy head with 1.94 between 350 bore and 305 bore and head lost 5 cfms across the board, anyone flow any mopar heads with a 273 bore.
 
This is gonna be a build way out off my knowledge. There are members here that autocross, probably not with a 273" engine, but they can be a lot of help to you. All i could add would be you need a lot of torque or a lot of gear.
Good luck with your build and i hope it's sucessful :thumleft:.
 
Thanks Mike.
Rick, the old school days you mention were the ones I watched and learned from those who built them. While the builds were basic and wild ones, the crafty ones offset the stroke as 273 mentions of doing. A bit expensive to do, but do-able it is. IDK how far he can offset the MoPar crank. Nor do I know of any off the shelf pistons for such a stroke anymore. MoPar used to have a good selection of stroker cranks for the roundy boy's to suite the track they were at or class with displacement limiting factors.

A great example of the old days and crazy builds came right from Ford with the almost laffable Cleveland 4v engine. In S/S racing, the heads were still to big for the displacement. A little off set crank work.... now the heads were a working !!!

I remember my Grand Father-in-law talking some crazy *** things he did back in the day. A Ford man that raced HEMI's. It is a shame we never really got to talk much. He was a real nice guy easy to speak with.
http://charliedodge.com/
 
273, if you don't mind paying the piper of such work as in off set crank grinding which will probably lead to custom slugs... well, have at it. Keep in mind, some where around here I do think someone knows the part number and maker of the small block Chrysler con rod with the proper width bottom ends but Chevy journal size. (AKA, A wider Chevy rod for the extra space in a MoPar rod)

For me, going through all this effort of doing a 273 and then stroking it with trick work would be cool IF you did the work for fun. How ever, it is now NOT a 273 anymore now is it. What is the point?

You could do all this work on a much more common 318 or a spendy 340 block with it 4.07 bore to start with. Or maybe something simple like a 4 inch arm in a 318? .030 overbore equals 390 cubes IIRC.
 
IIRC, LOL, set up the 273 with a bunch of squeeze, give it loads and loads of cam, carb, converter and gear, let her rip. Gas mileage be damned! Full steam ahead!
 
Rumble, back in the days when most of the rules were weight to cubic inch, there were crazy combinations. I feel the same as you about our elders before us, very smart men and i still miss them. Thanks for the link, very cool man.

I envy the area you live, i still believe that was the greatest street action in the 60s/70s any time in this country, woodward ave, Detroit included.
Nothing personal against Michigan....Just my opinion:smile:.
 
Rumblefish360 "For me, going through all this effort of doing a 273 and then stroking it with trick work would be cool IF you did the work for fun. How ever, it is now NOT a 273 anymore now is it. What is the point?"

Technically it's a stroker but only adds 9 cid, the reasoning is, I'm buying custom pistons and new rods anyways I want to get the pistons light as possible. Since I'm getting rods anyways get longer and the crank needs turned down for chevy rods I might as well get 2" bearings and offset the crank for an even shorter pistons.
 
If you go to a 3.75" bore with the stock stroke on the 273 you can fit a RHS head with 1.94/1.625 valves on what is now a 292 ci engine. I have on the shelf the heads we used to make 463 HP with that combination. They are the RHS LAX heads flowing 264 cfm @ .500", 280 cfm @ .600" and 283 cfm @ .700". They have Chevy 7/16" stud mounted Scorpion rockers and use a stud girdle that also mounts to the cylinderhead bolts. These heads go over .700" lift and rev to 8000 RPM.

Before anyone starts to argue about the LAX being a shaft mounted rocker arm system, you are correct, but these LA heads ARE USING the stud mounted rockers. The LA head comes with unmachined and untapped pedestal bosses that you can machine for correct rocker arm geometry with taller valve spring installed heights, longer valves and high lift cams.
 
Congrats IQ, that a serious build:thumleft:. Just curious what type of car it went into.....street, track?

The more i thought about the head flow and the valvetrain i'm sure this was destined for a track somewhere. The OP should be thrilled to see this, should be just what he's looking for.
 
IQ52 that's .125 overbore can it be done?
 
I will quote myself,

"I have on the shelf the heads we used to make 463 HP with that combination."

It should have made a lot more than that, but the dyno time was not available before it had to be torn down and the stock heads and a flat tappet cam went in for a 65 Dart (I think).
 
IMO, it's not a question of if it can be made. But rather if there's a reasonable return for the cost. I know of several 302 Fords and 302 and 283 Chevies that went 9500rpm and made 500+hp. The key to small displacement power is rpm. Because horsepower is figured over time, and the more pops per cylinder in a given time, the more power gets to the tires. The trick with the older technology is getting the induction and exhaust systems good enough to take advantage of the physics that comes along with those rpms. The oldschool road race guys would destroke the engines to have a better horsepower curve and less torque using the heads of the day. IQs got a great package there and honestly I never considered using the pedestals on the LAX heads. Never even occured to me...lol. In any event, get enough air in and out to rev them and you've got your power level. Whatever that costs is what you have to spend. If that's worth it to you, you're golden.
 
Dead bang on Moper. If money on such builds were an issue, then in the game we would not be. Use of a Chevy would be the starting point since it is a cheaper engine. to start with.
I did notice the RHS head in pictures looking like it could take the pedestal mount on the "LA" head. 1 head cast, 2 machined from one casting.
Nice post IQ.

273, before you start any machine work, we'll go right to the step one of it all. The block. Once it is all torn down and cleaned up and ready for machine work, have the shop sonic check it. They will find out the cylinder wall thickness. From there, a judgement call can be made to just how far it is you can bore the block out.

The shop should have a torque plate for the engine. If not, they should get one or you need to find a shop that has one.
 
High comps 12:1, big roller cam and 8000rpm. and obviously heads that will flow enough for the bore size.
273
Is this for historic racing by any chance?

you say you are using a 2 barrel? or this is what it has now?
 
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