Valve spring pressures on a pump gas Blown 440 motor
#2920821
05/10/21 04:24 PM
05/10/21 04:24 PM
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Posts: 43,292 Bend,OR USA
Cab_Burge
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I'm going to test some higher valve spring seat pressure on a pump gas blown 440 motor for a customer, I bought some Manley roller springs that have between 315 lbs. to 325 lbs. on the seats and between 640 to 675 lbs. opened at max lift. I haven't verified the actual lift at the retainers yet with these springs as I am waiting on the new Manton Series 5 pushrods to get here, I'm relying on the cam card and advertised ratio on the Comp Cams stainless steel shaft rockers
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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Re: Valve spring pressures on a pump gas Blown 440 motor
[Re: Cab_Burge]
#2920875
05/10/21 06:34 PM
05/10/21 06:34 PM
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Posts: 10,016 Frostbitefalls MN (Rocky&Bullw...
gregsdart
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Cab, i read today about this. If you have three inchs of intake valve face exposed to boost, a 10 psi boost reduces spring pressure by 30 lbs! So calling a couple of blower experts would seem like a great idea.
8..603 156 mph best, 2905 lbs 549, indy 572-13, alky
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Re: Valve spring pressures on a pump gas Blown 440 motor
[Re: Cab_Burge]
#2921247
05/11/21 03:54 PM
05/11/21 03:54 PM
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Al_Alguire
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Depending on how crazy you get the exhaust side is where you might want to pay some attention to. Valve material and spring pressures. Doubt you are doing anything very crazy boost wise but just in case
"I am not ashamed to confess I am ignorant of what I do not know."
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Re: Valve spring pressures on a pump gas Blown 440 motor
[Re: Al_Alguire]
#2921416
05/11/21 10:11 PM
05/11/21 10:11 PM
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Cab_Burge
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Al, the owner doesn't know what the boost pressure was before, I'm going to advice for 3.0 Lbs. or less on Oregon pump swill at this altitude, 3500 Ft above sea level The local 1/8 mile track, Madras, is around 2500 Ft above sea level, I don't know if he will ever run it there on a Friday street car night or not He has another Roots blown street car also so maybe between the two we can swap pulleys to make more or less boost in this car if not I have Littlefields phone number
Last edited by Cab_Burge; 05/11/21 10:12 PM.
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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Re: Valve spring pressures on a pump gas Blown 440 motor
[Re: kwikblownhemi]
#2921484
05/12/21 01:51 AM
05/12/21 01:51 AM
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Cab_Burge
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I have no idea of what your asking on the intake valve pressure differences I've dyno tested around 8 Roots blown gas motors, 3 hemi and several BB and SB Chevy. The last pump gas Hemi (4.250 borex4.375 stroke and 9.3 to 1 mechanical compression ratio) made 924 HP at 7300 RPM with 130 F manifold intake temps. with 7.5 lbs. of boost with 12% under driven and 33 degrees BTDC ignition timing, we swap the pulleys and got 13% overdrive and put race gas in it and retarded the timing to 25 degree BTDC. with those changes it made 1027 at 6500 RPM with 12.0 lbs. of boost with 190 F intake temps and then went into detonation 30 minutes later after the best pull at 7.5 lbs. of boost The dyno operator thought we took out to much timing so I bumped it up to 27 BTDC and it went into detonation at 6300 RPM 25 minutes later than the first pull with 12.0 lbs. of boost with more overdrive Stupid me Looking back later I should have set the timing at 20 BTDC to start with on those changes with the increase boost I didn't know how big the intakes temp would make compressing the air that much more Hot air expands, correct The last N/A Hemi I built and dyno tested was a 572 C.I. with Holley dual dry 1150 CFM throttle bodies on a single plane Stage V inline intake and FHO CNC ported Stage V street heads, it made 799 HP at 6500 RPM on Oregon non ethanol pump swill. My message is Roots super charger consume a lot of HP when compressing the air
Last edited by Cab_Burge; 05/12/21 03:08 AM.
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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Re: Valve spring pressures on a pump gas Blown 440 motor
[Re: Cab_Burge]
#2921493
05/12/21 07:51 AM
05/12/21 07:51 AM
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kwikblownhemi
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My message is Roots super charger consume a lot of HP when compressing the air True, and they add a lot of heat to the air while doing it. I've been running a Jimmy on a street/strip car since '78. They look impressive, but they are a terribly inefficient way to generate boost. In order to calculate the effect of boost on spring load, the pressure in the cylinder (the other variable in the pressure differential) has to be known . Obviously, the pressure in the cylinder varies dramatically during the engine's 720 degree cycle. A simple boost x valve area calculation is only going to be correct when the cylinder is at atmospheric pressure, which is what the manifold pressure measurement is referenced to. For a professional answer on the springs, Mike Jones at Jones Cams would be a good person to ask.
Last edited by kwikblownhemi; 05/12/21 07:57 AM.
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Re: Valve spring pressures on a pump gas Blown 440 motor
[Re: gregsdart]
#2921526
05/12/21 09:38 AM
05/12/21 09:38 AM
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Joined: May 2019
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INTMD8
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Cab, i read today about this. If you have three inchs of intake valve face exposed to boost, a 10 psi boost reduces spring pressure by 30 lbs! I've seen many mention this but I don't really follow. So 10psi through the intake cycle is also filling the cylinder, so there will be a pressure differential across the valve but not by the entire 10psi. As the piston is coming up and intake valve is closing, there is pressure in the cylinder and as soon as the intake valve touches the seat you begin compression cycle and cylinder pressure instantly far exceeds manifold pressure. Just not understanding the theory behind that I suppose. (boost subtracting seat pressure). I'm no expert on diesels but from what I've read it doesn't seem like they use much valve spring but some with compound turbos are at 150+psi boost. More of a problem on the exhaust side of a turbo motor IMO (valve trying to close against turbine drive pressure as intake valve is opening)
69 Charger. 438ci Gen2 hemi. Flex fuel. Holley HP efi. 650rwhp @7250 510rwtq @5700
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Re: Valve spring pressures on a pump gas Blown 440 motor
[Re: INTMD8]
#2921643
05/12/21 12:59 PM
05/12/21 12:59 PM
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dizuster
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More of a problem on the exhaust side of a turbo motor IMO (valve trying to close against turbine drive pressure as intake valve is opening)
But worse yet the exhaust valve is OPENING against a HUGE amount of cylinder pressure on a turbo motor. So that would indicate you'd want less valve spring, not more. In the end, it's nothing to worry about. Put the spring in it that the cam calls for and be done with it.
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Re: Valve spring pressures on a pump gas Blown 440 motor
[Re: dizuster]
#2921684
05/12/21 02:06 PM
05/12/21 02:06 PM
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Joined: May 2019
Posts: 713 Lake Villa Il
INTMD8
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[
More of a problem on the exhaust side of a turbo motor IMO (valve trying to close against turbine drive pressure as intake valve is opening)
But worse yet the exhaust valve is OPENING against a HUGE amount of cylinder pressure on a turbo motor. So that would indicate you'd want less valve spring, not more. In the end, it's nothing to worry about. Put the spring in it that the cam calls for and be done with it. I wouldn't say that indicates you'd want less spring pressure as much as the stiffest pushrods you can find (and maybe delay EVO)
Last edited by INTMD8; 05/12/21 02:06 PM.
69 Charger. 438ci Gen2 hemi. Flex fuel. Holley HP efi. 650rwhp @7250 510rwtq @5700
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