Checking PTVC

[Kevin1989]

ok, i have a basic understanding of how to check it, using the clay method, and also using a a lightweight spring. My question its, when using the spring does it take a keen eye to catch it exactly during the over lap period? i figure it will be easier to not take the head off.

my next question is will my pushrod length need to be measured before or after this takes place? my pushrods are slightly different sizes and there is a 20 thousands of an inch shim on the exhuast side.

And then if there isnt enough room i understand degreeing the cam can help, is there major down falls to this?
also i plan on spinning this motor to about 6500 if that makes a difference.

[85_SS_302_Coupe]

You have to have the correct pushrod length already established in order to check clearance, otherwise you could be checking clearance with a pushrod that's too short and you may think you have clearance when you don't.

A light weight spring is one way...a solid lifter is another. You can make a junk lifter solid by either welding it or filling it with washers so it doesn't compress.

As for checking pushrod length, i needed help on that so i won't try to give what little i know about that in case i give you the wrong info.

[black90lx]

what cam are you running?

[Kevin1989]

what cam are you running?

fms f 303 with 1.7 rockers lift is 544 if I'm correct

[85_SS_302_Coupe]

Well someone correct me if i'm wrong, but rockers don't effect duration which is where PTVC becomes an issue, and an X303 is .544 lift which i have ran on a stock 302, and the F303's duration works on a 302 also. Soooo, my math says you should be fine. (of course, take that advice at your own risk lol).

[Kevin1989]

well I have read that that exact combo will destroy valves. So I'm skeered now lol

[JASON408]

Cam timing events and lift both affect piston to valve because its not that you dont have enough valve relief its that you dont have enough valve relief at certian spots in the piston travel as it relates to your cam . You can have 2 cams with 544 lift with a the same duration and have alot diffent piston to valve cam to cam . Becuase the durration is how long it the valve is open but the real numbers you need is when it starts and closes witch can be way differant this is where lobe sep and intake centerline come into play . The clay is the best way imo . because you can see where the valve is riding in the pocket. i have had more troble with valves not fitting in the pocket and having plenty of valve reilf still left so its good to check it with the clay

[Kevin1989]

Cam timing events and lift both affect piston to valve because its not that you dont have enough valve relief its that you dont have enough valve relief at certian spots in the piston travel as it relates to your cam . You can have 2 cams with 544 lift with a the same duration and have alot diffent piston to valve cam to cam . Becuase the durration is how long it the valve is open but the real numbers you need is when it starts and closes witch can be way differant this is where lobe sep and intake centerline come into play . The clay is the best way imo . because you can see where the valve is riding in the pocket. i have had more troble with valves not fitting in the pocket and having plenty of valve reilf still left so its good to check it with the clay

Okay, so i need to first measure pushrods? then get the correct pushrod? and put clay. How much clay am i putting on the piston. and what am i looking for after i turn the motor over a full turn?

[JASON408]

you also need a soild lifter or a old one welded / but dont need that much just enough clay to cover the valve reiefs , try to keep it away from the edges to keep as much clay out of the rings as possable . then rotate the motor around a few times, then cut the clay in half at the middle of the valve reilif and mesure the thinkness of the clay thats left . also look and the valve reilif and make sure the valve is riding good in the pocket

[Kevin1989]

Thanks for the advice Jason!, i wanna make sure i do this right, what kinda clearance am i looking for, i want it to be safe to spin this right up to 6500

[Steves LX]

Thanks for the advice Jason!, i wanna make sure i do this right, what kinda clearance am i looking for, i want it to be safe to spin this right up to 6500

Clearance you want at a minimum is .080 on the intake and .100 on the exhaust. Something else to keep in mind as well as far as the cam goes is just like Jason said on the cam and valve events. The exhaust valve is generally closet to the piston at 10 degrees BTDC and the intake valve is generally closer at 10 degrees ATDC. You also need to make sure your springs and seat pressures are all good if you plan on spinning it to 6500 so you dont get valve float.


Not to add to the confusion but if you decide to degree your cam in keep in mind that advancing and retarding it will change your P to V as well.

If you advance it you will decrease the intake P to V and increase the exhaust P to V
If you retard it you will decrease the exhaust P to V and increase the intake P to V

[Stangman]

Or just take it to "Steve's Barn-O-Mustangs" workshop! :lol::

[Steves LX]

Or just take it to "Steve's Barn-O-Mustangs" workshop! :lol::

I'm burned out and done working on stuff for awhile. I will give advise though if I have any!!!

[Kevin1989]

Or just take it to "Steve's Barn-O-Mustangs" workshop! :lol::

lol it might be hard to get it there with no cam haha. I'm learning to do this, I'm hoping after I get the clay in there everything will look okay so I won't have to degree the cam.
but all and all this is a big learning experience, all in serch of that 3 number:rolleyes:

[Steves LX]

lol it might be hard to get it there with no cam haha. I'm learning to do this, I'm hoping after I get the clay in there everything will look okay so I won't have to degree the cam.
but all and all this is a big learning experience, all in serch of that 3 number:rolleyes:

Well just remember or write down your #'s after you check it so you have something for reference later on if you decide to. Not sure what cam you are using, but as long as its not a anderson hi rev you should be alright to 6500 as long as your springs are 135lbs or more at the seat and there are no coil bind issues. Stock lifters should be o.k. as well.

[Kevin1989]

Well just remember or write down your #'s after you check it so you have something for reference later on if you decide to. Not sure what cam you are using, but as long as its not a anderson hi rev you should be alright to 6500 as long as your springs are 135lbs or more at the seat and there are no coil bind issues. Stock lifters should be o.k. as well.

its an F303, the only reason i have any worry is because i saw some people that said it has destroyed valves...

[black90lx]

that cam will not hit. there are so many people running it on a stock short block. put it in and dont worry.

[Kevin1989]

that cam will not hit. there are so many people running it on a stock short block. put it in and dont worry.

you gonna pay for it when it does? because about 50/50 people are saying dont do it... i want to just slap it in and go, i could have had it running over the weekend if i new for sure it wasnt going to hit. ive seen several cars with the combo that are fine. but its soooooo close.

[chris91]

My Vert had the F cam running 1.7 rockers.

[jad0087]

Put it in there and don't worry about it....I'm gonna say u might lose power shifting at 6500...

[Kevin1989]

its going in, with 1.6s, im not gonna take the chance, and we will see where it quits making power when i take it to Adam to dyno.

[jack90gt]

I have ran it with 1.7s and it cleared but with 1.6s you will be alot safer.....

[black90lx]

it will probably quit making power at 6k.

[Kevin1989]

6500 would be nice wont know untill Adam can mess with it again and see where it takes a dump.

[black90lx]

specs on f303
* Advertised duration: 288 intake/288 exhaust
* Duration at .050 in. lift: 226 intake/226 exhaust
* Gross valve lift: .512 in. intake/.512 in. exhaust
* Lobe separation: 112 degrees
* RPM range: 2,000 to 5,500

[jad0087]

6500 would be nice wont know untill Adam can mess with it again and see where it takes a dump.

why exactly do u want to spin it to 6500?

[Kevin1989]

why exactly do u want to spin it to 6500?

why the fuck not?

[jad0087]

chill the fuck out, maybe cuz it will more then likely lose power at 6500 and fall on its face

[Kevin1989]

chill the fuck out, maybe cuz it will more then likely lose power at 6500 and fall on its face

lol that wasnt mean to be shitty man, my bad. i was just saying. if it makes power there i would. if it doesnt, it doesnt. my bad Jared i dodnt mean it like that.

[jad0087]

lol that wasnt mean to be shitty man, my bad. i was just saying. if it makes power there i would. if it doesnt, it doesnt. my bad Jared i dodnt mean it like that.

alright, ya put it on the dyno and see what happens, im gonna guess it wont like it but u never kno, every cars different