On3 302 Valve Spring Upgrade Necessary? - Ford Mustang Forums : Corral.net Mustang Forum
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post #1 of 8 Old 02-12-2017, 03:23 PM Thread Starter
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Question On3 302 Valve Spring Upgrade Necessary?

I did a couple hours of research before posting this, so forgive me if I missed it somewhere. I tried!

Im gathering parts to upgrade my 93 lx (currently bone stock). I've got the On3 76mm Turbo Kit, and picked up an explorer intake manifold and the GT40p heads to make the most out of the boost. I know I need to have the heads resurfaced, get ARP head studs and FelPro 9333 gaskets. Based off what Im reading online, 8-10 lbs of boost will get me to my power goal of ~450hp with this setup.

I'm planning on running the stock cam. My question is: Is there any need to upgrade the rockers, or the valve springs?

Thanks for any help.

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post #2 of 8 Old 02-12-2017, 09:07 PM
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If those heads are salvage picks, it can't hurt.

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post #3 of 8 Old 02-12-2017, 09:29 PM
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If you have it apart that far you might consider slapping in an F cam. It won't hurt the street manners and it is a lot better for boost.


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post #4 of 8 Old 02-12-2017, 11:00 PM Thread Starter
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If you have it apart that far you might consider slapping in an F cam. It won't hurt the street manners and it is a lot better for boost.
Well, I do like the idea of using the F cam and having to run less boost to make my power goal. And as I understand it, I can keep the rockers that came on the GT40p heads with that cam.

If I run the F cam, I will definitely need the upgraded valve springs though.

Bottom line: Why bother spending an extra 200 on a cam and 150 on springs when I can simply run more boost to hit my goal?

^I don't mean that in a sassy way. I'm genuinely trying to figure out the best way to do this on a budget.

Thanks for the feedback.
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post #5 of 8 Old 02-13-2017, 05:38 PM
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the 70mm would have been a better choice for a bone stock 302. The 70mm comes on early & strong. Remember it's the total area under the curve, not peak numbers. With your current plan, you will whiteness what is called turbo lag.
Money used to upgrade to the 76mm would have been put to better use on a new set of springs. You have successfully pushed the efficiency sweet spot without supporting modifications needed to realize increased benefits. In short you've already shot yourselve in the foot.

If the $200 dollar cost of an alphabet cam &/or $150 cost to upgrade to new springs are a cause for budget issues? You might not like the path you're heading down.

Not that it's never happened before, but I have not personally seen a bone stock 302 & an On3 kit make 450whp on 8#'s. Regardless of added bolt on's.

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post #6 of 8 Old 02-15-2017, 06:28 PM Thread Starter
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the 70mm would have been a better choice for a bone stock 302. The 70mm comes on early & strong. Remember it's the total area under the curve, not peak numbers. With your current plan, you will whiteness what is called turbo lag.
Money used to upgrade to the 76mm would have been put to better use on a new set of springs. You have successfully pushed the efficiency sweet spot without supporting modifications needed to realize increased benefits. In short you've already shot yourselve in the foot.

If the $200 dollar cost of an alphabet cam &/or $150 cost to upgrade to new springs are a cause for budget issues? You might not like the path you're heading down.

Not that it's never happened before, but I have not personally seen a bone stock 302 & an On3 kit make 450whp on 8#'s. Regardless of added bolt on's.
Funny you should say that....my foot is safe because I did in fact get the 70mm kit. Sorry for the typo/brain fart.

It's not that they're out of my budget by any means. It's more of a case of not wanting to go hog-wild spending money that I didn't need to spend. Since a kit of upgraded valve springs and new seals for the GT40p heads is only $120 shipped, I suppose there's no reason not to grab those. Would the majority here agree that I should grab the F cam while I'm at it?

Thanks again for the advice!
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post #7 of 8 Old 02-15-2017, 07:40 PM Thread Starter
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I'm doing a little reading on the cam swap...

Looks like I'm gonna need to choose springs that will compensate the .512 lift of the F cam. Bear in mind I'm new to this, but I should be safe picking any springs that compensate up to .550 lift, correct?

Also, are the stock rockers on the GT40p's fine to run with an F cam and upgraded springs?
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post #8 of 8 Old 02-15-2017, 09:07 PM
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Just as a point of reference, the motor (factory 302) in my 89 LX has 190k km's on it and I was getting valve float above 5000 rpm at 5.5 psi with a Hellion kit and 62mm turbo. That's with the stock springs on stock heads. Admittedly my valve train is tired and has seen a lot of mileage but if the springs are tired more boost may not equate to more power.

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