400+ hp 273

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I know it's not a budget build but i think 400 HP is resonable, I'm thinking the key ingredients is 10:1 compression, .5oo"+ lift cam and 200+cfms and peak power 6500-7000rpms. which could be accomplished with decking the block and gasket size combo to get .40" quench with factory flat tops, stock rods with arp, ported and milled factory heads and solid flat tapped high lift cam which would be budget but I want a little more since I'm gonna be running it on Mosport road course track here in Canada.

The main problem I'm having is deciding is on valve size combos 1.78-1.50, 1.88-1.60 1.94-1.65 or something else and which heads to go with ported factory or 302 or magnums or rhs and I was wondering could you down size from a 2.02 in a eddy head to 1.94 or less with new valve seats I know at one time they did come with 1.94 valves.
 
308 heads, 1.88-1.60, and have them gone through, not sure the 302 head can be opened up enough to make power at 7500rpm.
 
Yea, 302 heads can be opened up to 340 size windows. A lot of work, but, possible so I was told.
The 308 has a large open chamber that might be a problem with the wanting ratio. Milling it down maybe a way to get what you want. Maybe.

I would use the largest valve possible. Which I am not sure if a 1.94 is doable.I think so, since someone said the RHS head fit with that valve size. Just to be sure, I never known a Edel. head with anything but a 2.02/1.60 set.

If you plan on a 6500+ RPM run, read this!!!!

http://www.forabodiesonly.com/mopar/showthread.php?t=103623
 
To get the best balance between flow and shrouding the intake valve should not exceed 51% of bore... so 3.628 bore means nothing larger than 1.8ish... I think if I were building it I'd use EQ Magnums milled down to 52ccs and the 1.92 valve. A custom forged piston to get me zero deck and have decent valve reliefs that gives 10:1 static with a .028 Cometic gasket. That leaves .028" quench, and with a solid lifter cam around 240-250° @ .050 it's around 8.25 dynamic so it's good for pump fuel. That's what I'd do.
No pistons on the shelf will work with the cam you need to run. No head gaskets on the shelf will give decent static compression because they're thick and the bore's almost 1/2" larger than a 273s. No open chamber head will work for the same reason as the gasket (way too much volume). Porting a set of 302s to work will be cost prohibitive when the EQ heads are 1/2 the money and will feed it well enough in as-cast form. Unfortunately 273s are the small block 383... It's afflicted with not much solid support by the aftermarket.
 
I want run RHS I forgot about EQ's it's I just the valve size 1.92-1.65, how much airflow would I lose. In the end I think they would flow less than ported out stockers with 1.78-1.50.
 
OldmanRick said:
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.
Click to expand...

Hello!
 
Wow Scrappy, that cam is music to my ears because i love the revs. In a 273ish engine it would have to scream.

Probably not too good on a autocross track though:smile:
 
WHOAAAAAA Sracppy, nice place there. Hell of a intake. WHew!

273, I like your cam style.
 
Looks like the Howards Cam I tried on my Dyno Program. 229/237 @ .050
.555 lift. I used my stock 273 specs and just changed the cam from a Isky E4 to this cam. I got 357 hp. @ 6000 and 340 tq @ 4500. I know the dyno programs aren't accurate but it's a place to start. I tried the same set up with a 4" stroke crank and got about the same hp but more torque and at 1000 rpm less. tmm
 
273 said:
I want run RHS I forgot about EQ's it's I just the valve size 1.92-1.65, how much airflow would I lose. In the end I think they would flow less than ported out stockers with 1.78-1.50.
Click to expand...


The EQs are cheaper and lighter. You did say road racing... In as cast form the EQs flow enough to make 480hp at 5500 on a 358" with a hydraulic roller and Nascar spec 2bbl. I think Hughes advertises them around 220ish at .500 and that's pretty close. You will spend twice the EQs cost to have a set of used factory cores completely done and the base porting. At least I know what it costs me. You will lose somewhere around 20-25cfm at .500 by using the smaller valve, but you have to keep in mind the bore size is TINY. The cylinder wall is more than 1/8" tighter to the valve and as little as .050" can make a big difference in terms of unshrouding. The bigger valve can only make use of the port if the air can pass around the entire circumference easilly. Once shrouding happens, the additional curtain area of the larger valve is useless and the valve itself is heavier.
 
OldmanRick said:
Wow Scrappy, that cam is music to my ears because i love the revs. In a 273ish engine it would have to scream.

Probably not too good on a autocross track though:smile:
Click to expand...

Are we talking about proper race car or something that sees a little track work and mostly used on the street?

That cam would be a bit of a pig under 2000-2500 remember it has 12:1 comps, but if your racing you should have your revs over that anyway, so I think it would be an ideal circuit cam.
Also having the IR manifold helps with driveability.

We have 289 Fords in historic touring car racing spinning to 8000+rpm and they would be using a cam similar to that.

If you want your 400+hp and want it streetable then turbo or supercharging is what you will be needing.

We are dreaming at the end of the day aren't we?:thumleft:
 
June 1991 issue of Mopar Action has a 67 dart 273, 11.5 compression trw's, x heads [which require a bore notch] MP 508 hydraulic cam,what looks to be a holley strip dominator,cyclone headers, 4500 converter, 5.50 geared 8.75. It ran 10.86 ET. You can
make power with small cubes.It takes a little RPM , or boost, but not always a lot of money. Notch your cylinders and you can use a good set of heads.
 
Scrappy, i didn't think anybody would cam that big on a circuit, but i guess it's go big or go home.....:smile:.
 
I will be driving around town and towed to the track with racing set up for Time Attack (Solo 1). I been doing some calculation I/E valve centers is 1.87, (1.92+1.625)/2+1.87=3.6425, .060 273 is 3.685-3.6425=0.0425 doesn't leave much room but with notching I think it should be ok so I'll be deciding on RHS or EQ's does anyone have experience with these heads?
 
I'm not sure why you're worrying about the valve centerlines - They are not affected by valve sizing and the shrouding issue is only on the intake valve. As I underatnd it, you want to size the intake specifically, then fit whatever exh valve you can in there. I believe you do not need to notch with 1.92 or smaller intake valves as I understand it. You do for larger than that tho.
 
I was talking to a very knowledgeable certain someone and if i remember right, the 1.92 wont fit the 273 bore, rhs heads were the heads in question as well.fwiw
 
The reason for the valve centers is to include the gap between the valves so the distance across the valve including the gap is 3.6425, .0175 bigger than stock bore and Wild I think they can be made to fit with notching because I've read a lot post where poeple use 2.02 with notches but to me that's way too much valve or I'd use eddy heads.
 
Get the eddy heads, and get the inlet valve size reduced.
You'll save about 15kg over the front wheels.
 
Moper, the main question I have with this build is which valve size combo I should go with once I figure that out that will narrow my head choice since I need close chambers heads.
 
Scrappydoo, want to run eddy heads for the weight savings and better handling. To put in smaller valves, would I need to just install new valve seats or is there more involed.
 
If you want to pay to play go for what ever you think will work. At the point of considering installing smaller where larger resided... might as well stick with factory 273 or "302" casting heads and spend on porting. IMO the 1.92s are the largest to even consider, and slightly larger than it really should have. But reducing valve size is a pain in the *** and isnt cheap (new seats required). The EQs get my vote again for potential ootb, weight (compared to RHS), and price. With a streetable and strong midrange cam they wil still move enough to clear 400hp.
 
273, i'm curious what some of the cyl. head experts are gonna say about the smaller seats. If the throat cut is already 85-90% of the valve, which most performance heads have, going to a smaller seat would probably create a big step and would require welding or epoxy work that would probably get pretty pricey. At that point a better alternative may be a unfinished bare head, if one is available, a let a porter create exactly what you need.

I'm a really slow typer......Hello Moper.
 
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