Critique my 340 build .......

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orangecrush

orangecrush

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The only machine shop in my vicinity aren't the most talkative bunch. I need some insight before we button this thing up. Any thoughts or concerns would be appreciated :
Bottom end:

68 340 .030 over
TRW L-2316 forged flat top w/ 8cc valve relief, .030 above deck (shouldn't be an issue from what I'm being told)
Stock rods w ARP's
Stock forged crank
Lunati 60403 @ .050 IN/EX: 226/234;Lift IN/EX: .494"/.513"
Worked X heads flow around 240 @ .050, 75 cc
With current head gasket I calculated 9.2:1 compression (not sure how to get more if needed)
Airgap and 670 Street Avenger
TTI headers
3500 stall
3:91 gear

Look okay ? I do have an objective eventually which would be mid-low 12's.

Thanks all.
 
.030 above deck! WOW! And open chambered X heads, with how thick of a gasket to get 9.2-1.

FYI, factory hi comp 340's were I think, .018 out of the hole?

Someone correct me here! Somethin in the head aint jiven.

OH crap, welcome aboard!
 
Adam, the pistons sound realllllllly outta the hole. It's gotta be a thick gasket on top there.
 
They're .030 above - if all clears after checking (shop said I should be okay, my only concern is compression. Did the calculation with one of the on-line calculators. Gasket I plugged in was 4.18 diameter and .038 thick - came up with the 9.2:1 or so. If I need more and have the clearance - what's a good thinner gasket ? How might this car perform (Dart). Thanks.

Looks like thinner gasket may be out of the question, eh ?
 
If you are .030 out of the hole, a .038 gasket ain't going to cut it, unless there is about .035 relief in the head for the pistons.

Your piston to head clearance will be .008 with a .038 gasket = BOOM!!!
 
rumblefish360 said:
Adam, the pistons sound realllllllly outta the hole. It's gotta be a thick gasket on top there.
Click to expand...


Rob
The factory 340 pistons sat .018" out of the hole like you said and even though they were rated at 10.25:1 the were more like 9.5:1.
 

I'm sure you know better than most, but many have said I should be fine (including the shop), done alot of research. IF all clears well - my question is regarding compression - should I shoot for more and how .... As far as something ain't right - what are your guesses if so ? Engine mocked up nice, previously had the old forged, domed, high comp TRW replacements from back in the day..
 
Are you sure those pistons are sitting that far out ? I just looked them up and they are stock 68-71 340 compression height. If they are that far out it sounds like the block was milled big time.
 
Is this what you measured? Or off a spec sheet? Something doesn't sound right . Double check everything once more.

And welcome to FABO
 
I installed 3-4 myself, took it by the shop for them to measure. They'll shave 'em all for 40-50 bucks, but it'll mean even more compression drop and mo' money still. Again, there opinion (they did the head work as well) is I should be okay for clearance. We'll see ... still don't know where I'd have room to bump compression if I should ?
 
Theres something wrong some were. Either the pistons arent .030 out of the hole or the block has been decked. Those pistons have a 1.84" compression height and should only be .018 out. That far out of the hole and you will have more then 9.2:1 compression and a unsafe quench distance. The pistons are going to hit the heads with that tight of a clearance.

Did the shop CC the heads ?
 
Keep in mind NASCAR truck series engines are limited to 365 cubes and make over 700 hp with a governed 9.0-1 ratio.
 
Good catch. The compression ratio still sounds real low to me though.
 
I guess we'll assume the block was decked. I used one of the on-line compression calculators to get the 9.2:1 with all figures plugged in. the 8cc valve relief, etc. So let's say I get them shaved 10-15 thousandths. I will lose compression but gain back some due to reduction in valve relief, or do I shave heads as well? This is the kind of conversation I can't get into with the shop - they're so figgin' tight lipped - afraid I might learn something I guess, the "holier than thou" attitude. They measured the deck height, they did the head work, they're saying I should be okay with the .030 above. All I can do is check it this weekend, just don't have either a valve spring compressor to install light springs (or coiled coathanger trick) nor do I have any solid lifters laying around so ..... story of my life with this car! I'm going to post a picture of the two different pistons if I can figure that out.
 
I get the same figure, It just didnt sound right to me. Sounds way low.
 
That's a little weird, so I'm not the only one with the exact same issue ? I'll try to watch that thread's progression as well - maybe let him be my "guinea pig"?

Never mind - just made a phone call to member (and friend) "rebeldart" - we're talking about the same motor/car here, didn't know about this site till earlier today, he's a member and I've been trying to help him out ! Anyway, we'll be working on it this weekend. I'll let him post updates. Thanks and sorry for the "repeat". Great site and I'll be hanging out as well!
 
Thanks - I can rent a compressor for free at a local parts shop and I've made "test" springs out of a piece of coathanger wire coiled around a dowel back in the day (wayyyyy back!) One of us we'll update later.
 
Wait, a zero deck piston with 5 cc valve reliefs in a 72 cc head and a .039 gasket eqaul 9.8-1 so sez the KB site and with thought to the KB107 piston in my 360.

Is it that much different in a 340?

Holy crap, I just went to that thread, I guess it is what it is! My bad, but error on the side of caution. I'm thinking piston to head contact ..........BAMMMMMMM!
 
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