Low comp. + no quench vs. high comp. + quench???
#2122658
08/01/16 02:56 PM
08/01/16 02:56 PM
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Joined: Jan 2003
Posts: 13,382 Marion, South Carolina [><]
an8sec70cuda
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Have somewhat of a dilemma w/ the 440 in my dad's road runner. Basic specs...440 + .040", Ross flattops .005" down from 0 deck. 509/292 purpleshaft, 1 7/8" headers, 6 pack induction, 906 heads w/ mild porting, .040" head gasket. It pings under load in hot weather w/ pump 93 gas in it. In cool weather the thing runs GREAT. You have to lug it to get it to ping...it is a 4 speed. Obviously the hotter it gets, the worse it is.
I have a set of ready to bolt on, mildly ported, big valve set of closed chamber 915 iron heads sitting on the shelf. I'd love to throw them on this car and gain some grunt, but I know it will raise the compression a decent amount. I have not CC'd them, but they are close to factory specs...minimal clean up cut on the decks.
So will the gain in compression be offset by the gain in quench as far as it tolerating pump gas? I'd hate to put them on and find out I need to mix some race fuel in it to drive it hard. What do yall think?
CHIP '70 hemicuda, 575" Hemi, 727, Dana 60 '69 road runner, 440-6, 18 spline 4 speed, Dana 60 '71 Demon, 340, low gear 904, 8.75 '73 Chrysler New Yorker, 440, 727, 8.75 '90 Chevy 454SS Silverado, 476" BBC, TH400, 14 bolt '06 GMC 2500HD LBZ Duramax
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Re: Low comp. + no quench vs. high comp. + quench???
[Re: an8sec70cuda]
#2122691
08/01/16 03:44 PM
08/01/16 03:44 PM
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Joined: Jan 2003
Posts: 13,382 Marion, South Carolina [><]
an8sec70cuda
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I've pulled the timing back to 35° and that helped. The car is driveable like it is, just can't lug it in hot weather.
I want to put the closed chamber heads on to gain power, but not sure if it'll be a spark rattling nightmare if I do.
CHIP '70 hemicuda, 575" Hemi, 727, Dana 60 '69 road runner, 440-6, 18 spline 4 speed, Dana 60 '71 Demon, 340, low gear 904, 8.75 '73 Chrysler New Yorker, 440, 727, 8.75 '90 Chevy 454SS Silverado, 476" BBC, TH400, 14 bolt '06 GMC 2500HD LBZ Duramax
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Re: Low comp. + no quench vs. high comp. + quench???
[Re: an8sec70cuda]
#2122697
08/01/16 03:57 PM
08/01/16 03:57 PM
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Joined: Jan 2003
Posts: 13,382 Marion, South Carolina [><]
an8sec70cuda
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It's about 9.9:1 right now. Should be 10.8:1 or better w/ the closed chamber heads, but it'll have good quench.
CHIP '70 hemicuda, 575" Hemi, 727, Dana 60 '69 road runner, 440-6, 18 spline 4 speed, Dana 60 '71 Demon, 340, low gear 904, 8.75 '73 Chrysler New Yorker, 440, 727, 8.75 '90 Chevy 454SS Silverado, 476" BBC, TH400, 14 bolt '06 GMC 2500HD LBZ Duramax
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Re: Low comp. + no quench vs. high comp. + quench???
[Re: an8sec70cuda]
#2122713
08/01/16 04:10 PM
08/01/16 04:10 PM
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Joined: Feb 2011
Posts: 4,302 Nebraska
72Swinger
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Nebraska
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That is a good question. Best bet is aluminum 75cc heads but probably not in the cards. Colder plugs will make a difference.
Mopar to the bone!!!
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Re: Low comp. + no quench vs. high comp. + quench???
[Re: an8sec70cuda]
#2122720
08/01/16 04:21 PM
08/01/16 04:21 PM
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Joined: Jan 2003
Posts: 14,513 So. Burlington, Vt.
fast68plymouth
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I'd just run some octane boost in the hot weather, maybe pull another degree or two out of it, maybe try slowing the advance down a bit.
It has no quench now, so you could lower the cr a little with a thicker gasket(and not lose any quench benefit cuz you don't have any now) which should help some.
I would not be confident that combo with 10.8cr and quench would be ping free.
68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123 Dealer for Comp Cams/Indy Heads
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Re: Low comp. + no quench vs. high comp. + quench???
[Re: an8sec70cuda]
#2122728
08/01/16 04:25 PM
08/01/16 04:25 PM
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Joined: Jan 2003
Posts: 13,382 Marion, South Carolina [><]
an8sec70cuda
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I am not interested in working w/ the 906 heads anymore. A little less timing and/or colder plugs and it'll be fine like that. I'm wondering if the better quench of the closed chamber heads will be offset by the higher compression making it even less pump gas friendly?
Different heads aren't in the equation. This motor will be replaced by a 540" hemi whenever I get around to assembling it.
CHIP '70 hemicuda, 575" Hemi, 727, Dana 60 '69 road runner, 440-6, 18 spline 4 speed, Dana 60 '71 Demon, 340, low gear 904, 8.75 '73 Chrysler New Yorker, 440, 727, 8.75 '90 Chevy 454SS Silverado, 476" BBC, TH400, 14 bolt '06 GMC 2500HD LBZ Duramax
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Re: Low comp. + no quench vs. high comp. + quench???
[Re: fast68plymouth]
#2122733
08/01/16 04:28 PM
08/01/16 04:28 PM
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Joined: Jan 2003
Posts: 13,382 Marion, South Carolina [><]
an8sec70cuda
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I would not be confident that combo with 10.8cr and quench would be ping free. OK, so I'd gain power but you think I'd probably be worse off than I am now as far as pinging.
CHIP '70 hemicuda, 575" Hemi, 727, Dana 60 '69 road runner, 440-6, 18 spline 4 speed, Dana 60 '71 Demon, 340, low gear 904, 8.75 '73 Chrysler New Yorker, 440, 727, 8.75 '90 Chevy 454SS Silverado, 476" BBC, TH400, 14 bolt '06 GMC 2500HD LBZ Duramax
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Re: Low comp. + no quench vs. high comp. + quench???
[Re: an8sec70cuda]
#2122758
08/01/16 04:59 PM
08/01/16 04:59 PM
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Joined: Jan 2003
Posts: 8,032 Tulsa OK
Bad340fish
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I saw this in two real similar 360 motors. One was a 9:1 with no quench and one was a 10:1 motor with quench, both motors had X heads.
The 9:1 motor had trouble on hot days like you speak of. The 10:1 quench motor was fine and was able to run a few more degrees of timing.
The biggest difference was on the track, the quench motor performed much better. I don't recall the difference but it was almost one second and several MPH faster than the non quench motor was.
This was a long time ago but both motors were pretty close. Both guys worked at the same machine shop so there was lots of consistencies between the builds, the biggest difference being the piston choice and attention to quench.
I built a quench 340 around the same time with iron heads that was a little over 10:1 and ran fine on pump gas.
Last edited by Bad340fish; 08/01/16 04:59 PM.
68 Barracuda Formula S 340
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Re: Low comp. + no quench vs. high comp. + quench???
[Re: an8sec70cuda]
#2122784
08/01/16 05:54 PM
08/01/16 05:54 PM
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Joined: Aug 2003
Posts: 43,277 Bend,OR USA
Cab_Burge
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Being a street car do you have the vacume advance hook up? If not do you know what the timing is doing at the RPM it is pinging at when lugging it? The ignition timing, spark plug heat range and manifold inlet temps. will determine when it pings, cool things down on any of those three and it probally won't ping anymore I had a 21 ft inborad/outdrive plesure boat with a 8.5 to 1 compression ratio SB Chey 356 C.I. with irn heads, it would ping a little at the lower elevations we used it at, not up higher on the same gas. I change the spark plugs from RJ12YC to J11Y and that stop the pinging I wouldn't, and don't, run more then 9.5 to 1 compression on pump gas on the street with a iron headed motor, quench or no quench
Last edited by Cab_Burge; 08/01/16 05:56 PM.
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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Re: Low comp. + no quench vs. high comp. + quench???
[Re: Cab_Burge]
#2122787
08/01/16 06:10 PM
08/01/16 06:10 PM
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Joined: Jan 2003
Posts: 13,382 Marion, South Carolina [><]
an8sec70cuda
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I think I may try these heads anyway...just to see. The timing is locked out. The car has a vintage air AC system...the lines are real close to the distributor and wouldn't clear the vacuum pod on the first distributor I had in it. So I put one in that's locked out w/ no pod on it. One of those things that became temporarily permanent. Been that way ever since we put it together back in 2007 or so.
CHIP '70 hemicuda, 575" Hemi, 727, Dana 60 '69 road runner, 440-6, 18 spline 4 speed, Dana 60 '71 Demon, 340, low gear 904, 8.75 '73 Chrysler New Yorker, 440, 727, 8.75 '90 Chevy 454SS Silverado, 476" BBC, TH400, 14 bolt '06 GMC 2500HD LBZ Duramax
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Re: Low comp. + no quench vs. high comp. + quench???
[Re: an8sec70cuda]
#2122857
08/01/16 07:47 PM
08/01/16 07:47 PM
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Joined: Jan 2005
Posts: 2,540 Milwaukee WI
TRENDZ
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Milwaukee WI
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Yeah, get some dynamic timing going in this thing and swap the heads.
"use it 'till it breaks, replace as needed"
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Re: Low comp. + no quench vs. high comp. + quench???
[Re: TRENDZ]
#2122862
08/01/16 07:55 PM
08/01/16 07:55 PM
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Joined: Mar 2007
Posts: 3,287 West Coast, USA
jbc426
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Chip, what's the cranking compression on the thing now? Where is you initial timing set at, and which advance springs are you running? Or, when does you mechanical timing come in?
It may be as easy as running stronger advance springs to delay the timing until the engine builds some higher rpm.
1970 Plymouth 'Cuda #'s 440-6(block in storage)currently 493" 6 pack, Shaker, 5 speed Passon, 4.10's 1968 Plymouth Barracuda Convertible 408 Magnum EFI with 4 speed automatic overdrive, 3800 stall lock-up converter and 4.30's (closest thing to an automatic 5 speed going)
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Re: Low comp. + no quench vs. high comp. + quench???
[Re: an8sec70cuda]
#2122899
08/01/16 08:57 PM
08/01/16 08:57 PM
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Joined: Jun 2003
Posts: 9,225 Charleston
sixpackgut
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Charleston
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I think the white head gaskets that 440 source sells are .050 gaskets. Not sure about that but they were really nice head gaskets that I always ran on my BB. I would swap heads
Last edited by sixpackgut; 08/01/16 08:58 PM.
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