400+ hp 273

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I'm liking the EQ heads, Looked up the flow numbers for both EQ and RHS heads, EQ was better at low lift and RHS was better up high a more over all flow, put both in my Dyno program and the EQ's have a slightly better curve and peak power 426HP @ 6600.
 
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.
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Big open chamber to help with unshrouded valves with custon piston.....

At least my thinking.
 
If I'm playing this game I'm finding a 273 block and I'm finding old heads with different size valves and I'm setting them up with checking springs and pushing the valves down into the bore until they hit the cylinder walls. You can't measure the valves in the head from outside to outside and say, "Oh that is smaller than the bore, I'm okay." The valve does not open parallel to the bore but at an angle and as it opens it gets closer to the cylinder walls as the wall curves in around the bore.

The more you mill the heads to get compression, the more you lower the valve into the bore and the greater interference you get. Bigger valves, greater lift, milled heads, smaller bore, zero deck and pretty soon you are notching the bore down into where the top ring seals.

I'm just sayin', this is gonna be expensive when you stretch the limits. Take the time to check carefully.
 
I guess it time to take it out of theroretical and start to see what's practical I'm gonna dig up another standard bore block have a machine shop bore a 0.060 0.040 0.030 and see how different heads fit and I read how to build a cheap flow bench using the bore of the block it doesn't give cfm numbers but can see if one heads flows more than others.
 
273 said:
I guess it time to take it out of theroretical and start to see what's practical I'm gonna dig up another standard bore block have a machine shop bore a 0.060 0.040 0.030 and see how different heads fit and I read how to build a cheap flow bench using the bore of the block it doesn't give cfm numbers but can see if one heads flows more than others.
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Because you're looking to maximize the effort - I'd have them bore, hone, and chamfer the bores but not install the head dowels. Then put the block on a stand and turn it over with a head loosely bolted. By looking down through the bottom of the bore you'll be able to see where the valves are in relation to the bore walls, and by tracing the bore on the head gasket surface you're able to use offset dowels to center the chambers over the bores better. This is another one of those things that can be wayyyy off from the factory.
 
moper said:
Because you're looking to maximize the effort - I'd have them bore, hone, and chamfer the bores but not install the head dowels. Then put the block on a stand and turn it over with a head loosely bolted. By looking down through the bottom of the bore you'll be able to see where the valves are in relation to the bore walls, and by tracing the bore on the head gasket surface you're able to use offset dowels to center the chambers over the bores better. This is another one of those things that can be wayyyy off from the factory.
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X2, Blueprinting trick that completely slipped my mind. Good advice.
 
scrappydoo said:
Get the eddy heads, and get the inlet valve size reduced.
You'll save about 15kg over the front wheels.
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Sorry buddy, but that is *** backwards.

IQ has a good post!
Moper's on top of things. He's a smart guy
 
IQ52 said:
If I'm playing this game I'm finding a 273 block and I'm finding old heads with different size valves and I'm setting them up with checking springs and pushing the valves down into the bore until they hit the cylinder walls. You can't measure the valves in the head from outside to outside and say, "Oh that is smaller than the bore, I'm okay." The valve does not open parallel to the bore but at an angle and as it opens it gets closer to the cylinder walls as the wall curves in around the bore.

The more you mill the heads to get compression, the more you lower the valve into the bore and the greater interference you get. Bigger valves, greater lift, milled heads, smaller bore, zero deck and pretty soon you are notching the bore down into where the top ring seals.

I'm just sayin', this is gonna be expensive when you stretch the limits. Take the time to check carefully.
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People forget the valves 18* angle.lol
 
Moper I like the dowel trick, Thanks everyone for your input so far. I'm in the middle of a move right now when I get settled in I'll get back to this build and post what I find and anymore tech and tips will be appreciated.
 
After reading 1wild&crazyguy's sticky on 318 head porting I'm gonna stick with the stock heads and do em up cause even with the small 1.78-1.50 there still pretty tight in that little bore. Now I want to stay with the small valves but I was thinking of maybe going with 1.88-1.60 so the valve job is on fresh meat or maybe and inbetween size. How much bigger does the valve got to be to be on fresh meat and is it really worth it?
 
The 1.88 will bring the seat up a bit. You may want to look at an 11/32, nail head, performance valve too. There are gains to be had there as well.
 
I'm thinking of running a thin stem nail head valve, but does the valve have to be a certain % larger so the valve isn't sinking in the seat to be on fresh meat something like 1.82-1.55?
 
Good advice IMO from Moper. And yes, it is worth it.

The 1.88-1.60 is a lot and would be good for this IMO. It'll be a little tight with .15 space left in the stock bore. (.075 on each side of the valves as installed.IDK if you can go to a 1.94 size. With the 1.60 exhaust valve, you'll have 3.54 width just in valve size in a 3.63 bore to give you .09 clearance, for .045 on each side of the valve installed. (YIKES!)

The MoPar Performance "Engines" book suggests a notch in the cylinder bore for the intake valve @ 1/4 deep / 1-1/4 wide by .070 deep into the cylinder wall for valve clearance and air flow. Do not go into the rings travel area.
 
The next valve size up for MoPars is the 1.88/1.60, use them and worry not.
 
Thanks Rumblefish360 that's what I'm gonna do but I'm gonna look similar size valve in the 11/32 stem, it's too easy to get stuck on these little details :)

So the build spec's so far is
Block 0.060" bore honed and torque plated, squared zero decked with custom pistons, scat rods and indexed crank. I'm gonna port the heads 1.88-1.60 valves with 5 angle valve job with beehive springs, 1.6 roller rockers, custom 268ish solid roller cam, RPM airgap, 650 Holley, me built headers, 4 gear and around 4.56 out back.
 
Back in 1978 I bought a 273 that was laying in the back of a jobsite trailer for $200. It was used in a circle track car. It ran like a scalded dog 7,500-8k no problem and pulled hard all the way. I installed it in my 1970 T/A Challenger and mounted the six-pak setup while having motor work done on the 340. I swear it was faster than the 340, never ran it thru the traps with the 273 so just seat of the pants deal.

I ended up turning a rod bearing (go figure). So I took it apart. It came with a thermoquad, LD4B manifold, Racer Brown STX-21 solid flat tappet cam, bored out .120 and had 12.5 domed pistons, heads were X heads 2.02 valves and yes there were notch's in the block. Don't know if it was ported out. It had an aluminum flywheel and instant throttle response and what I remember the most was the sound it made at 7k+ I loved that sound, nothing like it.

400hp? I would bet on it.
 
Rbob, i know what you mean. Short stroke and a light flywheel. I was there also in the 70's. It was brand "C" but those engines will make the hair on you neck stand up:D.
 
Six pack 273 that's awesome, my uncle pick up stock 69 340 with six pack for $1200.
 
Might check out the S/S 273 racers.Not many out there,might have the "flow cone" you are looking for.
 
rumblefish360 said:
Sorry buddy, but that is *** backwards.

IQ has a good post!
Moper's on top of things. He's a smart guy
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It's been a while since this post but I just read it so I feel I should give a reply for what its worth (which isn't much).

This thread started with someone who wanted to race his 273 on a circuit, now I have some experience with this (but with historic open wheelers from the 1960's) and if I was to build an outright track car that had to use a 273 but was allowed free reign on what you could modify then getting as much weight out of the car would be a priority and I don't see why you can't reduce the valve size in the eddys. Not easy to do but doable.
And I would make it rev as hard as I could within what the budget allowed.

But the reality is the op's car is going to be street driven and not purely a race car so what I suggested is a waste of time.
 
Scrappydoo I would like to use Eddy heads mainly for the weight savings and i think they can be done also but they would eat up huge portion of my engine budget, I'm gonna stick with the stockers after reading 1wild&crazyguys sticky on porting 318 heads, I always read that 273/318 flowed 135 cfm but never seen a flow test until his and Shady Dells and they flow enough stock 175 cfm for 350hp and with a little work 420+hp with stock valves which is prefect since there the only size that really fit the 273 bore I'm still thinking of notching the bore for them cause there even tight in there.
 

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I just hope you run the car at Mont Tremblant one day , would love to hear it scream around the track , a great track with a few good straights and good turns changes in elevation . 273 @8,000 would sound great echoing through the mountains
 
This thread makes me want to get my 273 running and put in something.. I don't know what to put it in, though! Maybe my dad will part with one of his Baracuda's (Or just for ***** and giggles I could put it in my '82 Porsche 928 that needs an engine, and make all the Porsche purists want me dead.. It originally came with a 4.5, and a 273 is 4.5 LOL).

I'm curious to see how this build comes out. If the price isn't completely insane, I might just build my 273 like yours someday..
 
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