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340 -> Run as-is or change parts?

Posted By: goldduster318

340 -> Run as-is or change parts? - 10/03/10 07:39 PM

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!
Posted By: ademon

Re: 340 -> Run as-is or change parts? - 10/03/10 07:45 PM

sounds good i would switch out the strip dom for the air gap with your set-up.
Posted By: 340SHORTY

Re: 340 -> Run as-is or change parts? - 10/03/10 08:15 PM

3.91 gears and drive it like you stole it.
Posted By: goldduster318

Re: 340 -> Run as-is or change parts? - 10/03/10 08:21 PM

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.
Posted By: ScottSmith_Harms

Re: 340 -> Run as-is or change parts? - 10/03/10 08:23 PM

Carb = Thermoquad
Posted By: Tom Fox

Re: 340 -> Run as-is or change parts? - 10/03/10 08:51 PM

you will want to verify those pistons don't actually stick out above the deck before decideing what heads to use.
Posted By: DaytonaTurbo

Re: 340 -> Run as-is or change parts? - 10/03/10 09:24 PM

Edelbrock intake, - an air gap, rpm or even a ld340 would all be good choices. Your holley 600 wouldn't be an overly bad choice, although it may restrict power around 6000rpm and up. Depends on how high you plan to rev it. Actually one interesting combo I would like to try in an applcation like yours would be a ld340 intake with a holley 650cfm spreadbore double pumper. LD340 intake is squarebore but was cast with extra meat in that area so it could be hogged out to spreadbore. And that holley should flow well and the small primaries should give good mileage/throttle response. Don't know about how well that cam would do for you though.
Posted By: goldduster318

Re: 340 -> Run as-is or change parts? - 10/06/10 02:01 AM

I definitely want to keep a squarebore carb. I guess I could run the 600 in the time being as I know it works since its on my current 360.

I'll put the dial indicator on the pistons later to see their relation to the deck soon.

Anyway, I found some other interesting stuff when I pulled it apart:










Anybody want that oil pump pickup and pan???
Posted By: Baxter61

Re: 340 -> Run as-is or change parts? - 10/06/10 06:11 AM

Id put an airgap on it, get double pumper carb, and clean it up and run it.
Posted By: crlush

Re: 340 -> Run as-is or change parts? - 10/06/10 12:21 PM

Love that oil pickup, if those pistons are zero deck or in the hole a bit the magnumn heads with your setup would wake it up a bit, definetly go with the air gap, holley 750 vac sec. Ask cuda boy if its been line bored, you might need a under size timing chain, or a tentioner.
Posted By: GO_Fish

Re: 340 -> Run as-is or change parts? - 10/07/10 03:04 AM

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.
Posted By: patrick

Re: 340 -> Run as-is or change parts? - 10/07/10 01:36 PM

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...
Posted By: goldduster318

Re: 340 -> Run as-is or change parts? - 10/07/10 11:13 PM

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.
Posted By: Challenger 1

Re: 340 -> Run as-is or change parts? - 10/08/10 01:38 AM

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?
Posted By: GO_Fish

Re: 340 -> Run as-is or change parts? - 10/08/10 02:43 AM

Quote:

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.



Why are you looking to build the 340 instead of your 360? With everything else being equal, I'd think the 360 with Mag heads would be all over the 340 with J heads.
Posted By: goldduster318

Re: 340 -> Run as-is or change parts? - 10/08/10 03:37 AM

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.
Posted By: patrick

Re: 340 -> Run as-is or change parts? - 10/08/10 12:58 PM

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.
Posted By: goldduster318

Re: 340 -> Run as-is or change parts? - 10/08/10 11:53 PM

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.
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