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Valvesprings/Valvetrain for extreme duty NA road course use:

captdistraction

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there's a shocking lack of information out there about the coyote valvetrain and its requirements to work in a road course environment. To the point where people either are willing to guess and try random parts (usually at their own peril with mixed results), or stick with the factory or factory "racing" parts (usually at their own peril with mixed results)

Doing my own research, I believe the PAC-1234x spring may have been used by Roush Yates Engines to build out their IMSA/PWC 302R upgrade engines. That information is unconfirmed but I've reached out.

What I wanted to find out is have people successfully used aftermarket springs/retainers/valvetrain components for a length of time with excellent reliability? I can count a dozen broken motors on here that had aftermarket parts there, (though as many if not more stock ones as well).

The concerns with the PAC spring I've seen are:

Its 240lbs/in,
Seat Pressure 92 @ 1.575" (100 @1.500)
Open Pressure 200 @ 1.000" (though I've seen 218, 230 as well for different specs)
(though numbers vary depending on install height, cam lift and other factors)

The boss 302 oem spring (which can vary significantly) 67lbs (300N) to 157lbs (700N)

its a bit of a jump and presents the following concerns:

Will it bend or break the hollow valvestems of the boss 302 valves? (PAC says no, internet says maybe, 1 case of a turbo car doing such)

Will VCT work with it? (some say yes, some say yes with less accuracy, my tuner says absolutely not)

Are they a true drop in? (pac says yes, but recommends Ti retainers)


I'm looking down this rabbit hole as one of my failures may have been related to a boss 302 valvespring failure (or float near redline). Obviously I can lower the redline and try to avoid the limiter, but sometimes in racing all bets are off and I want to engineer the strongest most reliable setup I can.
 

Mad Hatter

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Not terribly relevant but when we built my engine (stretching the word "we")... We measured all the new Boss OEM springs and found them very very close to each other. So we just used those instead of aftermarket.
 

Grant 302

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Its 240lbs/in,
Seat Pressure 92 @ 1.575" (100 @1.500)
Open Pressure 200 @ 1.000" (though I've seen 218, 230 as well for different specs)
(though numbers vary depending on install height, cam lift and other factors)
One of those 3 specs is wrong. I suspect the 200 should be 230 open and that the rate is 240. If the 92/200 seat pressures are correct, the rate would be 187 lbs./in. and that doesn't jive with the 100 @ 1.5" which would be a 200 rate to the 200 open pressure.

240 rate sounds like overkill compared to OEM ~175. Especially considering an N/A application.

Which failure and why do you suspect float?

I don't see the spring rate causing issues with tuning or breaking the sodium filled stems.

What RPM are you planning on running? Which cams?

There are a couple of options with lower rates than 240. If you really feel the need to go aftermarket.

I want to engineer the strongest most reliable setup I can.
Those two characteristics don't usually go together. Focus on the reliable part.
 

BigTaco

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I did some research on the Roush/Yates valve springs years ago but never did find a definitive answer as to who made the springs for them. Good luck with the new valve springs.
Rick,
I’m 99.99% sure they are these exact springs(1234X).
 

captdistraction

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We think the crank failure was driven by a valve event, a reversal of force when I lifted was the result of a bent valve and the kickback sheared the crank at the timing sprocket. All conjecture of course.

That and concerns about others who have broken the boss springs made me want to research this.

4500-8000 is the intended usable range with a limiter hopefully set at 7800 depending on how the dynograph curves and the horsepower amounts (to massage the car into the ruleset)




Sent from my iPhone using Tapatalk
 

Grant 302

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We think the crank failure was driven by a valve event, a reversal of force when I lifted was the result of a bent valve and the kickback sheared the crank at the timing sprocket. All conjecture of course.
The crank snout didn't shear. The break would be cleaner and spiral in nature or the key would give. And something else would have broken first if the valve train event was the primary failure. There are so many weaker parts between that valve to the snout and from the snout back to the affected piston.

When you're looking at other valve spring failures...you gotta find the primary reason. And ignore what's irrelevant...like a turbo or drag application.
 

captdistraction

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bringing back up a thread that went nowhere: Just want to see if there's any other examples of cars running this PAC1234x spring with full VCT without modifications. I'll defer ultimately to the tuner but looking for information. My understanding is its on the high side of rates that the VCT can work with.


Not in the least bit interested in anything outside the scope (that I pray is clearly defined) above.
 

captdistraction

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Well, at this point I'm going to just roll with them and see. I have a tune, my tuner said good 50weight oil should keep them held in place and I should have logs in the coming weeks.

I did buy some pac/tfs 208lb-in springs, but they're still in the box until I see how this goes. They're probably a better choice for someone with VCT looking for a beefier and more consistent spring than the boss/gen2 spring
 

JAJ

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What about the fully-wallet-emptying titanium valve setup from FP? Is it an option? Or is there a risk that the Ti valves will tulip on a road course? Just curious...
 

captdistraction

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What about the fully-wallet-emptying titanium valve setup from FP? Is it an option? Or is there a risk that the Ti valves will tulip on a road course? Just curious...
Not for these heads. They offer that titanium kit for the 350 head, and also a GT4 kit (Which is another pac spring, lightweight valves and titanium retainers).

My engine builder wasn't comfortable running the PAC 1234X with VCT and locked my cams out.

They're more drag racing oriented but he told me that they see VCT issues in the log from time to time.
Interesting
 

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