340 -> Run as-is or change parts?
#820867
10/03/10 03:39 PM
10/03/10 03:39 PM
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Joined: Jan 2003
Posts: 1,482 Lake Orion, MI
goldduster318
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I recently picked up a 1970 340 from cudaboy. It is as follows: 0.030" over Stock replacement pistons (shown below, please identify)...look to be at zero deck MP 280/280 .474/.474 cam Strip Dominator Intake 2.02 "J" heads...appear to not be ported Homemade deep pan (this is going). This will be going into a 1970 Duster, street car, all steel, TTI's, 4-speed, 3.23's and 26" tall tires. Now with that being said, what would you change? I have magnum heads on my 360, and those could go on there...air gap intake? different cam? I'd like to use what I have other than oil pan, intake, & cam if possible. Suggestions please! Thanks!
Last edited by goldduster318; 10/03/10 04:27 PM.
'70 Duster 470hp 340/T56 Magnum/8 3/4 3.23 Sure-Grip
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Re: 340 -> Run as-is or change parts?
[Re: ademon]
#820869
10/03/10 04:15 PM
10/03/10 04:15 PM
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Joined: Aug 2003
Posts: 12,291 Kent, Wa
340SHORTY
Truck Nut
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Truck Nut
Joined: Aug 2003
Posts: 12,291
Kent, Wa
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3.91 gears and drive it like you stole it.
I am truckless..
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Re: 340 -> Run as-is or change parts?
[Re: 340SHORTY]
#820870
10/03/10 04:21 PM
10/03/10 04:21 PM
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Joined: Jan 2003
Posts: 1,482 Lake Orion, MI
goldduster318
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Not interested in any more gear. its 3000rpm at 70mph with 3.23's with such short tires. Its a street car/cruiser...and I do take it on the freeway.
Also, please suggest a carb. I already have a 600 vac secondary holley but that may be a bit small.
'70 Duster 470hp 340/T56 Magnum/8 3/4 3.23 Sure-Grip
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Re: 340 -> Run as-is or change parts?
[Re: crlush]
#820877
10/06/10 11:04 PM
10/06/10 11:04 PM
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Joined: Jul 2003
Posts: 6,167 Maryland
GO_Fish
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master
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Maryland
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That one pic looks like the valve tips have different installed heights??? I'd be checking that out if I didn't upgrade to magnum heads.
Scott B.
"I'm a self-made man... I started with nothing, and I still have most of it!"
68 360 rusty B'cuda 'vert (GO Fish)13.59@ 98.72 mph
69 340 GTS stock 14.18@ 95.60 mph
01 5.9L Ram 1500 Quad Cab 4x4
01 3.5L 300M 16.23@ 86.97 mph
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Re: 340 -> Run as-is or change parts?
[Re: GO_Fish]
#820878
10/07/10 09:36 AM
10/07/10 09:36 AM
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Joined: Jan 2003
Posts: 16,123 Grand Haven, MI
patrick
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I Live Here
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Grand Haven, MI
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if it were me, if the pistons are .014" above deck or lower, I'd go magnum heads with hughes #1110 springs and choose the head gasket accordingly.
cam for your gear, I'd go comp XE262 or voodoo 60402.
headers, and a dual plane (LD340, air gap, or perf RPM)
I'd stick with the 600. you probably won't loose much below 5000 RPM...
1976 Spinnaker White Plymouth Duster, /6 A833OD 1986 Silver/Twilight Blue Chrysler 5th Ave HotRod **SOLD!*** 2011 Toxic Orange Dodge Charger R/T 2017 Grand Cherokee Overland 2014 Jeep Cherokee Latitude (holy crap, my daughter is driving)
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Re: 340 -> Run as-is or change parts?
[Re: patrick]
#820879
10/07/10 07:13 PM
10/07/10 07:13 PM
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Joined: Jan 2003
Posts: 1,482 Lake Orion, MI
goldduster318
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The pistons appear to be .005 below the deck. They also have valve reliefs but i cannot be too sure how many cc's they are. I have no idea what the CC is on "J" heads vs my stock magnums anyway. My magnum heads already have the "R/T" springs and titanium retainers.
Anyway, I think the XE262 is too mild for this application. I'm running rather short tires of less than 26" with the 3.23 ring. I currently have a hotter cam (summit k6901) in my very low compression 360 and that has good enough street manners.
I'm thinking the XE268 would be as low as I would go. I might stick with the purpleshaft even. Its not really a daily driver car anyway.
'70 Duster 470hp 340/T56 Magnum/8 3/4 3.23 Sure-Grip
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Re: 340 -> Run as-is or change parts?
[Re: goldduster318]
#820880
10/07/10 09:38 PM
10/07/10 09:38 PM
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Joined: Feb 2005
Posts: 28,312 Cincinnati, Ohio
Challenger 1
Too Many Posts
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Too Many Posts
Joined: Feb 2005
Posts: 28,312
Cincinnati, Ohio
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Those are the low compression pistons, like what was said the smaller cambered magnums would bump the compression up from where it is now. I'm betting around 8.8 to 1. Makes for a doggy motor if you ask me. The last 340 I built and have driven now a lot was the KB243 pistons which stick out .029 above the deck and I went with edlebrock open chamber heads which gives me 10.1 to 1. The motor makes way more power than with stock heads and stock 2 valve relief hi compression pistons. I run a 600 which performs great for me. The timing chain slop looks about normal to me?
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Re: 340 -> Run as-is or change parts?
[Re: GO_Fish]
#820882
10/07/10 11:37 PM
10/07/10 11:37 PM
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Joined: Jan 2003
Posts: 1,482 Lake Orion, MI
goldduster318
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the 360 is .040 over already, cylinder walls aren't perfect although it doesn't burn oil. It only has "8:1" pistons with the magnum heads, and well the bearings are really worn too...been running 14psi hot oil pressure and not climbing quickly when revved for the last two years.
I did get a good deal on this 340...forged crank, good cylinder walls, etc...heads/intake/block/& crank are worth more than I paid for it anyway. Not a risk. I'd like to run it more than the 360 as its going to be higher compression and much more servicable.
The pistons are down the hole in that 360 (they are flat) about .1"
This 340 with them being .005 down the hole (they are supposed to be .007 above based on the quoted compression height) is worth about 1cc compared to zero deck. and J-heads have been between 64 and 68cc depending on who worked on them. Really it depends on the cc of the valve reliefs.
with 10cc worth of valve reliefs: 9.97:1 with 15cc worth of valve reliefs: 9.43:1 with 20cc worth of valve reliefs: 8.95:1
I used the 4.070 bore for all the calcs other than the head gasket which is 4.1", 68cc chambers, .039 compressed gasket thickness, and .005 below deck.
Anyway, my point is that the 340 with the magnums or even with the "J" heads will have more compression than my current 360.
'70 Duster 470hp 340/T56 Magnum/8 3/4 3.23 Sure-Grip
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Re: 340 -> Run as-is or change parts?
[Re: goldduster318]
#820883
10/08/10 08:58 AM
10/08/10 08:58 AM
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Joined: Jan 2003
Posts: 16,123 Grand Haven, MI
patrick
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 16,123
Grand Haven, MI
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Quote:
Anyway, I think the XE262 is too mild for this application. I'm running rather short tires of less than 26" with the 3.23 ring. I currently have a hotter cam (summit k6901) in my very low compression 360 and that has good enough street manners.
I'm thinking the XE268 would be as low as I would go. I might stick with the purpleshaft even. Its not really a daily driver car anyway.
actually, advertised, your cam is a lot bigger, but .050 numbers are about the same as an XE262 (218/224 for t, 218/228 for yours). .2" lift will probably be much higher for the XE262 or the voodoo, making the total area under the curve much higher for more power, while the shorter advertised duration and corresponding earlier intake valve close point will help with cylinder pressure and torque.
personally, I think most people tend to over cam their motors. big car, tall gears, I would stick with my recommendations, or at the very most go with an XE268. my old XE262 equipped 360 made great power from ~1800 RPM to ~5500, and pulled my 3950 lb 5th ave with authority.
1976 Spinnaker White Plymouth Duster, /6 A833OD 1986 Silver/Twilight Blue Chrysler 5th Ave HotRod **SOLD!*** 2011 Toxic Orange Dodge Charger R/T 2017 Grand Cherokee Overland 2014 Jeep Cherokee Latitude (holy crap, my daughter is driving)
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Re: 340 -> Run as-is or change parts?
[Re: patrick]
#820884
10/08/10 07:53 PM
10/08/10 07:53 PM
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Joined: Jan 2003
Posts: 1,482 Lake Orion, MI
goldduster318
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I do have a lighter car by about 700lbs and a 4-speed which helps a lot. That 360 burns the tires off anyway, I can't go full throttle in 1st gear as it is...and that thing has AT BEST 8.4:1 compression. Anyway, the pistons are the Sil-vo-lite 1267's. ( http://www.summitracing.com/parts/UEM-1267-030/ ) They're claiming 10.2:1 which i have a hard time believing but the compression height of 1.824 makes sense. That should put them out of the bore .007 but my measurements (maybe not proper) with a dial indicator on a magnetic base put them below .005. .012 difference is still less than the thickness of the head gasket. I also saw that the valve reliefs are 10cc's. This engine did run 13.30's in a 2950lb demon race car with a 4-speed and 4:10's and the purpleshaft and street dominator. It can't be a total turd.
'70 Duster 470hp 340/T56 Magnum/8 3/4 3.23 Sure-Grip
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