360 Magnum vs 340 mild street build - my experience

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I am finally installing my fresh Magnum 360 this week. My only wish during the build was that someone made a Magnum piston with more squeeze and roughly the same weight as the stockers like the 340 has with the KB107's. I wound up using factory replacement Speed Pro H655CP's.
 
What was your calculated comp ratio if I may ask?
 
JoePole1 said:
I am finally installing my fresh Magnum 360 this week. My only wish during the build was that someone made a Magnum piston with more squeeze and roughly the same weight as the stockers like the 340 has with the KB107's. I wound up using factory replacement Speed Pro H655CP's.
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I asked this very question to Brian (OU812) IIRC & he had an answer to that. Search for he threads of what I started and OU812 replies on this.
 
Good thing for me I wasn't on the internet then, and the only car shows I like to enter my car in are the ones where the cars are moving down the track. I didn't say the cam moved the power band down 2000 rpm's. What I said was, the 340 really came to life from 3k - 6k. The way the car was set up favored bottom end torque and the 360 seem to move straight out of the box without any issue. To further this I used the two engines for a comparison of the 340/360 with the same components, I removed the heads, intake, carb, and cam from that 340 and put them on the 360. At the strip, the 360 went 3 tenths faster in the same car, same gear, same tranny and TC. I did replace the dished pistons in the 360 with 4 valve relief speed pro cheapies so the compression would be just about the same.
 
Sold my 340 to build a magnum 408 stroker , Torquestorm supercharger with snow water methanol.
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318willrun said:
Interesting points.
  • First, I bet some will argue that point about the magnum head being superior to the "X" head in stock form or if they both were even "home ported". I will say I think if the magnum head has an advantage in performance (which I think it does), it's not much.
  • To your second point, the LA 360 is almost always going to have factory dished pistons (eww) and in most cases the piston being in the hole a tad more than the magnums. This will give the magnums a better compression ratio, and that's not including the closed chamber heads boosting compression as well if the LA 360 had X heads.
  • Though I haven't weighed the components, there are enough folks out there stating the magnums have a lighter rotating assembly and better ring placement on the pistons.
  • My opinion is the magnum would outperform the LA 360 with X heads if the same size cam, intake, and carb was used on both stock short blocks.
  • Oh, I have a LA 360 with the cheap speedmaster heads in one of my Dusters.
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The Duster with the cheap Speedmaster heads , I'm assuming they are PCE281.1773. First what kind of power do you think that car is putting out? secondly do you think these heads could support 450hp? thirdly do you think that stock magnum heads with a full porting including bowls would flow like the speed master heads?
 
65TTCuda said:
The Duster with the cheap Speedmaster heads , I'm assuming they are PCE281.1773. First what kind of power do you think that car is putting out? secondly do you think these heads could support 450hp? thirdly do you think that stock magnum heads with a full porting including bowls would flow like the speed master heads?
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  • They are the "unported" SM heads. 730 to my front door on Black Friday Sale is what I paid.
  • I don't know the power of the engine, there are "ball park calculators" online that can try an guess. It runs 12.9's with 3.23's, stock converter, and about 3400 lbs at the start line. My cam is very small (less than a factory 340), so I am NOT taking advantage of the heads.
  • Fully ported Magnum heads would outflow my "untouched" SM heads is what I'd guess.
  • Keep in mind, the car only went about 2 tenths faster with the SM heads vs untouched stock 360 heads. Again, that would be due to the small cam in my opinion.
 
318willrun said:
  • They are the "unported" SM heads. 730 to my front door on Black Friday Sale is what I paid.
  • I don't know the power of the engine, there are "ball park calculators" online that can try an guess. It runs 12.9's with 3.23's, stock converter, and about 3400 lbs at the start line. My cam is very small (less than a factory 340), so I am NOT taking advantage of the heads.
  • Fully ported Magnum heads would outflow my "untouched" SM heads is what I'd guess.
  • Keep in mind, the car only went about 2 tenths faster with the SM heads vs untouched stock 360 heads. Again, that would be due to the small cam in my opinion.
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How do u like the converter you have in your truck? The Hughes I think it’s a 24-30. I know everyone says get a custom converter etc….. but for off the shelf what is your opinion of it? Thanks
 
Your post is mild street builds 340 vs 360 but your comparisons are quarter mile.
What is the point of these 340 vs 360 threads?
 
85D150 said:
How do u like the converter you have in your truck? The Hughes I think it’s a 24-30. I know everyone says get a custom converter etc….. but for off the shelf what is your opinion of it? Thanks
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I like it for what I paid.
 
Well 'kinda'. Read your last few posts (#56 )
A stock tire 68-70 340's strength was the quick revving short stroke street light to street light.
No need to bolt on or add anything for street performance.
 
318willrun said:
  • They are the "unported" SM heads. 730 to my front door on Black Friday Sale is what I paid.
  • I don't know the power of the engine, there are "ball park calculators" online that can try an guess. It runs 12.9's with 3.23's, stock converter, and about 3400 lbs at the start line. My cam is very small (less than a factory 340), so I am NOT taking advantage of the heads.
  • Fully ported Magnum heads would outflow my "untouched" SM heads is what I'd guess.
  • Keep in mind, the car only went about 2 tenths faster with the SM heads vs untouched stock 360 heads. Again, that would be due to the small cam in my opinion.
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Forget ET, tell us how much MPH you picked up at the stripe, that's a far more accurate indication of horsepower
 
ir3333 said:
Well 'kinda'. Read your last few posts (#56 )
A stock tire 68-70 340's strength was the quick revving short stroke street light to street light.
No need to bolt on or add anything for street performance.
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Yes, post 56 was just saying that the drag strip "proved" the outcome. Not just me saying I went out of town and I think by the seat of my pants...... to most, that's worth nothing.
 
replicaracer43 said:
Forget ET, tell us how much MPH you picked up at the stripe, that's a far more accurate indication of horsepower
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Well, ET does mean something if the car doesn't spin. Sometimes changes can add bottom end torque and move the car in the first 150 ft quicker. In the 1/8 mile I gained 2 mph. The side by side comparison to the cast heads was done with 2.94's. I had to go back and watch the video of result to get the results LOL
 
318willrun said:
Well, ET does mean something if the car doesn't spin. Sometimes changes can add bottom end torque and move the car in the first 150 ft quicker. In the 1/8 mile I gained 2 mph. The side by side comparison to the cast heads was done with 2.94's. I had to go back and watch the video of result to get the results LOL
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^^^ By the way, the car gained about 2 mph the last time out when I added timing. Soon after a couple other things are wrapped up, I'll be getting back to this car. It's been to long.... ha! Because of more compression and a better cam, I'm confident the 360 in our '80 truck is making more power and the Duster would go faster if we swapped.
 
318willrun said:
36 years of owning many small block Mopars. Yes, 340's were among the many LA's that included 273-360's.
My first hand experience of 340's vs 360 magnum is just this: 360 magnum hands down wins in the typical "add camkit and headers, " mild street build using the long block.
This is NOT a bash 340 thread. I love 340's. << Re-read that, I LOVE 340's. I'm also a realist. I'm not comparing the low cost of the 360 mag vs the collector value of the 340. I'm talk'n the performing of the two in the typical "Add your cam and headers" to the mild street guy out there. I'm very impressed with the 360 magnum, and I've built both in mild street builds.
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depends on what you consider mild . i/m close to driving what i consider a mild build 340 30 over zero decked crap speedpro forged heavy pistons comp cam 20-227-4 and TF heads .That is mild a granny could drive the car, think it will top the mild 360 ?
 
318willrun said:
What did the '70 Duster "all original" run in the 1/4 ? ever try it ? I know people that bought them brand new and tried to get into the 13's with 3.91's and couldn't with the only thing changed from show room was slicks.
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13.9 @101 was best for my 70 340 cheater slicks 3.23 gears
 
Nat said:
depends on what you consider mild . i/m close to driving what i consider a mild build 340 30 over zero decked crap speedpro forged heavy pistons comp cam 20-227-4 and TF heads .That is mild a granny could drive the car, think it will top the mild 360 ?
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360 magnum built the same would beat it...... my opinion of course :)
 
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Nat said:
13.9 @101 was best for my 70 340 cheater slicks 3.23 gears
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and my stock 360 (stock 360 heads, less than stock 340 cam), without headers, and 2.45's and stock converter on a normal radial tire went 13.9's all day. It had eddy intake and 750 holley. 1976 Duster
  • again, I love 340's. But in mild form I just found the extra 20 cubes pays dividends.
 
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I could be wrong but i don't think the 360 would out perform the stock 340 4 speed with 14 inch tires street light to street light? Many big inch big HP cars found that out the hard way.
Quite often the big inchers would pass the 340 at the big end...but the quarter mile is not street performance.
 
318willrun said:
and my stock 360 (stock 360 heads, less than stock 340 cam), without headers, and 2.45's and stock converter on a normal radial tire went 13.9's all day. It had eddy intake and 750 holley. 1976 Duster
  • again, I love 340's. But in mild form I just found the extra 20 cubes pays dividends.
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Are you happy with your choice of cam? I just bought a 360 magnum long block and want to drop it in my Duster at some point. (Once I am done messing with the 318!) Just trying to decide on a cam.

Cley
 
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