273, or 318?
- Thread starter DartGuy67
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Dale Davies
Well-Known Member
OK, main bearing diameter I had forgotten about.
As I mentioned a 1940 Chev project in post #94, I do not row the boat the same direction as everyone else. I like something different. The guy I bought the Chev coupe from has one with a pretty good body. 8 to 10 years and he still can not decide on the engine to use.
-301 turbo from the Firebird
-A 350 vortec that he is not sure of the condition.
-454 Chev from his 72 GTO that he now has a 455 Pontiac engine for.
-an LS from salvage.
His thought for me was just get a LS as everyone else is doing. Not my river to paddle.
Dan the man
Well-Known Member
What are the size of the valve's in inches? Is the length the same?
Dale Davies
Well-Known Member
Definately yes. Keep the original parts for when time comes to sell the car. The new owner may want a concours queen. In the mean time you can be on a stealth mission that checking casting numbers will not reveal the difference. Just passing filling stations in OD.
You can get a 3.58" crank that has 340/273 main bearing diameter. Eagle, Molnar, and Scat all offer them. Heck, if you're feeling froggy, Molnar has a 3.79" stroke crank. It has SBC sized rod journals though. As @toolmanmike mentioned, pistons for a stroked 273 might be "fun" trying to find. Heck, 273 pistons for the stock crank are kind of an issue unless you're happy running Egges.
Dale Davies
Well-Known Member
The 5.3 LS intake valves are either 1.9" or 2.0" head diameter. The Mopar and Ford valves are a slight bit longer. Ford guys have been installing the slightly shorter 327 Chev valves for years. Those are very close to the same length as the LS valves. Now I understand the 5.9 Magnum uses 8mm valve stems that are the same length as the LA valves. Swapping comes down to the cost of all the parts, valves just a portion. There is springs, retainers and locks. Also you may need screw in rocker studs and guide plates. If you swap out the 3/8" valves for the Magnum valves you will save weight. The Magnum valves have 2 keeper grooves like the LA but the smaller diameter requires keepers and possibly retainers. Depending on what springs you have and the cam, you MAY get away with reusing those. Compatability with the keepers has to be verified before trying that.
Because the LS are still in production by the millions, parts are inexpensive and readily available. Parts through the dealers are normally pricey as compared to as good or better quality parts from say Summit or Jegs. That depends on manufacture. Most stuff is cast or forged in China these days. Some rebox into their boxes and ship. Others perform QC checks and finish machining in the US. Probably a better quality product. The Japanese products we got in the late 50's and 60's was of poor quality. But the Japanese did customer satisfaction surveys and took what was stated to heart. The Chinese are where Japan was 50 years ago, but getting better. I do have a concern on Chinese stuff. First is that purchasing Chinese manufactured supports the CCP and PLA as any major business is tied to the communist party. Second is they come here, western countries, and buy up resource companies including farm land. Generally they employ Chinese citizens that supposedly are immigrants. Now if you want to set up a company manufacturing a product, you must first form a partnership with a Chinese entity who holds 51% ownership in the company, while you pay most or all setup costs. This entity whether a corporation or individual will be closely affiliated to the communist party. Once they see the product and processes involved, they will set up another company and produce tbe same product or very close copy for less money. Intlectual property theft, and you have no leg to stand on. Patent law means nothing to them.
Dale Davies
Well-Known Member
I would go with Molnar or Scat myself. Pistons would befinately need to be ordered, large number of manufacturers to chose from there. Cost will be an issue. Molnar or Scat would probably finish the rod journals to the Mopar 2.123" diameter for you. Otherwise Chev 6.125" or 6.2" rods would need to be sourced. Of course stroke and rod length need to be nailed down before ordering the pistons. The 273 bore is an odd one in that it is larger than most in the 3.5" area but smaller than the 3.7" bunch. The thin wall casting will not allow boring that much out. A few of the V6 engines have pistons that would be close but are all 4 valve head designs. Their compression height is also pretty short with small diameter gudgeon pins.
Dale Davies
Well-Known Member
One advantage to building and possibly stroking a 273 is the small bore diameter is going to aid detonation resistance due to the reduced flame travel. Enhancing swirl will also benefit detonation resistance. Widen the intake port on the cylinder wall side. Use a sonic thickness measurement tool to make sure you do not find a water well. The top of the port should be raised mainly on the cylinder wall side. This will aid swirl which relates to quicker burn before detonation threshold is reached.
A 3.79" stroke would give 318 CID so if someone grilled you on displacement, you could respond with a completely straight face. 11:1 CR on pump gas and it would be torquey and snappy. Still look like a 273. Stealth mission.
Dan the man
Well-Known Member
Buy the kit comes with pistons, rings, bearings, why buy everything individually?
318 , 340 shares the same oil pan and external dimensions as 273. Without looking at casting numbers no way to tell the difference. Is a 340 in place of a 273 stealthy?
So if you want to stroke a 273 and keep it looking stock that is great. But the interesting aspect is the modifications done to give the underdog the edge. So then the stealth side of things is not as interesting.
That's the way my simple mind looks at it. If ya like the 273 small bore use it. If you can make the smaller bore with high compression work that's a bonus. If everyone thought the same things would get old quick.
So if you want to stroke a 273 and keep it looking stock that is great. But the interesting aspect is the modifications done to give the underdog the edge. So then the stealth side of things is not as interesting.
That's the way my simple mind looks at it. If ya like the 273 small bore use it. If you can make the smaller bore with high compression work that's a bonus. If everyone thought the same things would get old quick.
Dan the man
Well-Known Member
Just me, but I wouldn't have a 273
Dale Davies
Well-Known Member
I was thinking CS separately. In a kit, request 273 bore pistons. Should be doable.
You guys build it, tune it and dyno it, and post the results.
cudamark
Well-Known Member
Well, there are differences if you just look a bit. 340 is cast and stamped into the block, so, no need to look up casting numbers unless you want to. Also, the engine mount ears on the block are different. Sure, it's subtle, but, easy to spot if you know what you're looking for.
Dale Davies
Well-Known Member
To each their own. Your car, your dime. Do what makes you happy. No worries.
I could stroke the 289 in my 1940 Ford Fordor, but it was running well until the electric fan stopped and it got hot sitting in the drivethru of an A & W. That is how I got into doing the heads and cam. The cam was out of a 351 with low miles. A race car it is not. I am looking for snappy ppepperformance on the street and where I can pass on the highway.
mygasser
Well-Known Member
he's still not got a car yet, too much procrastinating
A 273 is like a 289 Ford, why bother?
A 318 is a fine starting point for any build.
If your 273 has a steel crank then, stock 318 with trick pistons, if NOT.
I have several versions, a 110 overbore with turned down 340 pistons is one, (small bore 340@333cubes)
A 90 thou overbore with 360 turned down crank, with 360 flat top 1971 pistons is another, (360)
Or just get a 360 block for $50 and have a 408 stroker...
The choices are endless lol
A 318 is a fine starting point for any build.
If your 273 has a steel crank then, stock 318 with trick pistons, if NOT.
I have several versions, a 110 overbore with turned down 340 pistons is one, (small bore 340@333cubes)
A 90 thou overbore with 360 turned down crank, with 360 flat top 1971 pistons is another, (360)
Or just get a 360 block for $50 and have a 408 stroker...
The choices are endless lol
Dale Davies
Well-Known Member
My 40 Ford came with the 289 2V. I put an Edelbrock RPM Airgap and Performer 600 carb on it. Ran great until the electric fan quit. Mopar 273 and Chev 283 are similar and the 307 and 305 Chevs get the same dirty looks, toss 'em and grab a larger sibling to build or just throw in and go.A 273 is like a 289 Ford, why bother?
A 318 is a fine starting point for any build.
If your 273 has a steel crank then, stock 318 with trick pistons, if NOT.
I have several versions, a 110 overbore with turned down 340 pistons is one, (small bore 340@333cubes)
A 90 thou overbore with 360 turned down crank, with 360 flat top 1971 pistons is another, (360)
Or just get a 360 block for $50 and have a 408 stroker...
The choices are endless lol
Granted the small bores of the 273 SBM and the 305 Chev can restrict valve size and head choice. But the small bore has an advantage, flame propagation. Distace is less so the combustion is completed before conditions for detonation develop in the cylinder. Thus a bit more compression can be built in to compensate.
I hate todays world where it is all throw away and we wonder where the "enviornmental crisis" came from.
It is like lawn mower heads that the valves get to sticking. Ask at most small engines about replacing the valve guides and touching up the valves and seats, they most likely will tell you it is cheaper to put a new head on. Made in China, of course. So it is less expensive to send the old heads to China, melt them down and cast new ones and ship them back?
I like those little engines and they did run well.
Dan the man
Well-Known Member
A 360 block for $50? That's funny. 289 is a good engine for a cruiserA 273 is like a 289 Ford, why bother?
A 318 is a fine starting point for any build.
If your 273 has a steel crank then, stock 318 with trick pistons, if NOT.
I have several versions, a 110 overbore with turned down 340 pistons is one, (small bore 340@333cubes)
A 90 thou overbore with 360 turned down crank, with 360 flat top 1971 pistons is another, (360)
Or just get a 360 block for $50 and have a 408 stroker...
The choices are endless lol
There's a pistons for a Holden engine that might work.
A 273 is like a 289 Ford, why bother?...
The choices are endless lol
Both are great engines as they are. Especially 289 K motors, I would take one of those over any 302. Why bother with the bores and strokes and extra parts, no extra expense is required to make either run great. All you need is a cam and good induction to make a strong, reliable, efficient engine.
mygasser
Well-Known Member
agreed and the 289 ford isn't a good comparison anyway as it has the same 4" bore as the 302 and 351 so....
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