Does anyone know if the MP P4120249 and the 340 valve spring are the same item?

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

List under 'A' engine valve spring chart (standard length valves) in

Mopar Engines 9th edition

Installed Height 1.67/1.70
Single/damper
OD 1.50
wire diameter .206
cam lift .440/.510


(A engines are 273-318 & 340-360)

P4120249 is considered a MP (mopar performance) spring

There's a 340 HP spring # 2863439 that has identical specs to the P4120249

Which are (for both):

color code red
length 1.92
solid length 1.09 (I assume this is collapsed length)
wire diameter .206
OD 1.502
load 1.700" 69lb
load 1.200" 260lb
calculated rate 386

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Yes, they interchange.

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Joshua

Thanks, I never thought to look in the "LA" motor section, of the performance book. I have a Crane cam in my engine, and found several bad valve springs. These were the matching Crane springs for the cam. The cam specs are very similar to the >460 lift MP cam, which calls for the P4120249, which I do have, but I also have the 340 springs, and that is what I installed (cheaper). These springs are not near as stiff, as the spring specs on the cam card. But unless the Crane cam has a crazy ramp I think they should work. I know there are quite a few people running the 340 spring with a bigger cam then this.

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

Charlie, the stock 340 springs should be good to at least .500" lift.

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Official Cookie and Mater Tormentor.

Charlie,

I ran P4120249 springs with the Mopar Performance 276° dur, .490" lift cam and it was fine. I don't think you'll have any problems. How fast do you spin this particular engine?

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Joshua

I used the P4120249 springs, but re-used the /6 keys and retainers. Then I read on this forum that you should use new hardware. I don't know how much danger there is of retainer failure. Not a lot, I hope. The springs are nice and snappy, seems like.

I posted about pictures of 340 springs and retainers to illustrate why larger diameter retainers are used with the larger diameter 340 springs. http://slantsix.org/forum/viewtopic.php ... ers#218421

You might also read this short thread: http://slantsix.org/forum/viewtopic.php?p=223388

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Joshua

I just installed the 340 springs (found 6 bad dampers in the Crane springs on the engine). The cam is a Crane 720791, Lift .460, adv dur 290, .050 dur 228. The cam card calls out spring pressure of 110 lbs at 1.688 and 285 lbs at 1.275. The 340 springs are a fair amount less then that. Not sure what RPM I will be turning. I have had a misfire, and hopefully these valve springs will cure it. Probably about 5,000 rpm, but not over 6,000.
Before the misfire showed up the car ran 13.5's at 96 mph, with 3.91 (7 1/4 rear) gear, 26 inch tire. I have gone up to a 28 inch tire. This is the thread with the car/engine build.
http://www.slantsix.org/forum/viewtopic ... sc&start=0

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

That's a fairly mild cam. I wonder why they specified such high valve spring loads? Running under 6000 RPM I think you'll be just fine.

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Joshua

I agree. I was thinking the lobes migth be fairly agressive, to get a lot of "area under the curve", but that is not the case. Whenever I get a cam, and degree it in, I also plot the profile, every 5 degrees, while I have the dial indactor and degree wheel on the engine. I just list the numbers as X degrees @ Y lift. Then in the future I can plot it on a graph.

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

Cool Idea Charrlie.
Frank

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Scrapple: Because a mind is a terrible thing to waste.
73 Duster - Race Car
66 Dart Wagon - DD
178" FED
82 D150
All Slant powered

Tried to post earlier, guess it did not post.

I ran just this cam with a few different motor combos. Ran 340 springs and at one point stock springs. Never had any valve float problems. Crane made a good cam in this one, but their install and behavior specs are all wrong (RPM range, spring pressures, centerline...).

I sold mine cheap to a racer who then dropped off the face of the earth...

Lou

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