Valve spings vs. Boost - 2003-04 Mach 1 Registry Owners Club

Botis05 · 02-23-2011, 11:33 PM

I'm running 17psi from a Kenne Bell 2.1L....ported heads but stock cams and springs. Is 17psi pushing the springs to the limit or should it be good to go? Someone recently told me that I was probably floating some valves with that much boost and stock springs. I asked how I would know this was happening and he didn't know.

tvanlant · 02-24-2011, 08:33 AM

Stock springs have a seat pressure of around 65 lbs. That means at 17 psi, you will only have 48 lbs of seat pressure. That is pretty low.

Depending on what RPM you are going to turn, this may cause some valve floating issues. When you get valve float, the engine will act like it is "stumbling" or misfiring at high rpms. It will usually start at a specific RPM (the RPM at which the springs can control the valves anymore) and will most likely float every time at that same RPM.

Scott McClure · 02-24-2011, 04:51 PM

Plenty of 03-04 Cobra's with stock springs running boost in the mid to high 20's. It's more about what rpm your spinning the motor too.

311-420 · 02-24-2011, 05:54 PM

It's an rpm thing

Botis05 · 02-24-2011, 06:03 PM

My shift like come on at 6200 so I usually hit around 6400 on a shift. I've never noticed any high rpms misfires that weren't due to something else.

Do springs wear over time?

Scott McClure · 02-24-2011, 06:09 PM

Quote:

Originally Posted by Botis05

My shift like come on at 6200 so I usually hit around 6400 on a shift. I've never noticed any high rpms misfires that weren't due to something else.

Do springs wear over time?

6400 is fine and yes valve springs wear out over time.

Botis05 · 02-24-2011, 06:52 PM

Quote:

Originally Posted by Scott McClure

6400 is fine and yes valve springs wear out over time.

As in ...these are the springs that came with the car in 2004, might be time for something else?

Scott McClure · 02-24-2011, 07:00 PM

Quote:

Originally Posted by Botis05

As in ...these are the springs that came with the car in 2004, might be time for something else?

How many miles on them? If your worried you could get the Livernois springs that work with your stock retainers. They're pretty reasonable.

Botis05 · 02-24-2011, 08:34 PM

Quote:

Originally Posted by Scott McClure

How many miles on them? If your worried you could get the Livernois springs that work with your stock retainers. They're pretty reasonable.

It will be awhile before I go into it. If I'm going to take the blower off etc then I'm going to powder coat the valve covers while I'm at it etc.

They have 55k miles on them I believe. If I go that route I might as well get some custom cams made as well. I'll see what happens when we get it off the dyno in a few weeks. Make future plans from there.

icutice2 · 03-04-2011, 11:24 PM

Quote:

Originally Posted by Botis05

I'm running 17psi from a Kenne Bell 2.1L....ported heads but stock cams and springs. Is 17psi pushing the springs to the limit or should it be good to go? Someone recently told me that I was probably floating some valves with that much boost and stock springs. I asked how I would know this was happening and he didn't know.

Something that I just found out a few motors later, with the stock cams they dont release the heat and motor gets real hot, can melt pistons ect, just heads up

Botis05 · 03-05-2011, 02:56 AM

Quote:

Originally Posted by icutice2

Something that I just found out a few motors later, with the stock cams they dont release the heat and motor gets real hot, can melt pistons ect, just heads up

I've never actually heard that before. Any specifics on why/how?

02-23-2011, 11:33 PM	#1
Botis05 Registered User Join Date: May 2008 Location: Raeford, NC Posts: 178	Valve spings vs. Boost I'm running 17psi from a Kenne Bell 2.1L....ported heads but stock cams and springs. Is 17psi pushing the springs to the limit or should it be good to go? Someone recently told me that I was probably floating some valves with that much boost and stock springs. I asked how I would know this was happening and he didn't know. __________________ White 04 Mach 1, 6spd w/KB2.1L at 17psi, and 100 shot. Custom built by Fastlane Motorsports

02-24-2011, 08:33 AM	#2
tvanlant Registered User Join Date: Sep 2009 Location: Olathe, KS Posts: 81	Re: Valve spings vs. Boost Stock springs have a seat pressure of around 65 lbs. That means at 17 psi, you will only have 48 lbs of seat pressure. That is pretty low. Depending on what RPM you are going to turn, this may cause some valve floating issues. When you get valve float, the engine will act like it is "stumbling" or misfiring at high rpms. It will usually start at a specific RPM (the RPM at which the springs can control the valves anymore) and will most likely float every time at that same RPM. __________________ '99 Cobra

02-24-2011, 04:51 PM	#3
Scott McClure Mach1 member Join Date: Aug 2003 Location: East Haven, CT Posts: 3,349	Re: Valve spings vs. Boost Plenty of 03-04 Cobra's with stock springs running boost in the mid to high 20's. It's more about what rpm your spinning the motor too. __________________ 2011 Mustang GT Grabber Blue Automatic 2003 Mach 1 Whipple 2.3 718 rwhp 735 rwtq @25 psi SOLD

02-24-2011, 05:54 PM	#4
311-420 Can't be bridled Join Date: Sep 2007 Location: Texas Posts: 7,006	Re: Valve spings vs. Boost It's an rpm thing __________________ 2004 Mach 1 #6956 5spd w/IUP Eaton swap, longtubes, built 3.73 SRA 452hp/409tq dynojet🏁

02-24-2011, 06:03 PM	#5
Botis05 Registered User Join Date: May 2008 Location: Raeford, NC Posts: 178	Re: Valve spings vs. Boost My shift like come on at 6200 so I usually hit around 6400 on a shift. I've never noticed any high rpms misfires that weren't due to something else. Do springs wear over time? __________________ White 04 Mach 1, 6spd w/KB2.1L at 17psi, and 100 shot. Custom built by Fastlane Motorsports

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