Notching pistons, how far can you go? - Ford Mustang Forum
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post #1 of 10 (permalink) Old 03-14-2017 Thread Starter
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Notching pistons, how far can you go?

So my Teksid 2v is in the final stages of machining. The shop mocked up the 2v heads on the Mark VIII short block today, to check PTV clearance. With my Comp 270s, the valves just barely kissed the piston. The guy told me I needed .080" notched into the piston. But the problem is, the pistol crown thickness is only .25", so it'd leave me with .17". He is uncomfortable with how little material would be left, but of course it's up to me in the end. The pistons are stock Mark VIII hyper pistons.

After researching all day, I've read many things. .15" is minimum, it'd be fine with no boost, or you shouldn't notch hyper pistons at all. What say you?

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post #2 of 10 (permalink) Old 03-14-2017
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Hypers need .200 material thickness because they are cast. You need to be careful when cutting to make sure the valve relief to back side of the ring groove is thick enough.

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post #3 of 10 (permalink) Old 03-15-2017
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What valves are you using?

You can get a set of modified valves from CMS that has the margin cut down and that clears up A LOT of ptv room.

As far as reliefs go, my machinist buddy typically goes .050" on the reliefs in mark 8 pistons.

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Rebuild in the works. New crank, 2013 Boss rods, srp .020 over flat top pistons with valve reliefs, 12:1 compression, ported pi heads, comp xe278ah cams.
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post #4 of 10 (permalink) Old 03-15-2017 Thread Starter
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I'm using stock valves. I ended up getting a set of -5.2cc diamond pistons with valve reliefs. A little more dish than the MK8s, but should be alright I think. A tiny bit less compression will let me run more timing in the tune I'd think.
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post #5 of 10 (permalink) Old 03-15-2017
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Are the Mark VIII pistons flat top?
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post #6 of 10 (permalink) Old 03-15-2017
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Quote:
Originally Posted by Screaming04Gt View Post
I'm using stock valves. I ended up getting a set of -5.2cc diamond pistons with valve reliefs. A little more dish than the MK8s, but should be alright I think. A tiny bit less compression will let me run more timing in the tune I'd think.
Yeah you should be ok. Dont forget though, more timing doesnt mean more power. There is a point where timing makes mbt and you could advance more without problems but it serves no purpose. A lot of people think that compression requires less timing due to detonation but thats only part of it. The compression makes the engine more efficient and it requires less timing to make mbt. Mine just made 368 rwhp with 25 degrees of total timing. Mind you, I didnt get to lean on it any more and try more timing because things went boom. However, I dont know how much more it would have made.


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Originally Posted by 40th GT View Post
Are the Mark VIII pistons flat top?
Mark 8's are almost flat top. They have 3cc of volume.

1998 GT
Rebuild in the works. New crank, 2013 Boss rods, srp .020 over flat top pistons with valve reliefs, 12:1 compression, ported pi heads, comp xe278ah cams.
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post #7 of 10 (permalink) Old 03-15-2017
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I have a set of those Valves that are shaved sitting in my basement. I didn't use them because the machine shop didn't like them; they were worried about that warping due to leff material around the contact area and them not being stainless steel. Take this for what it's worth.

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1987 Mustang GT Hatchback - 2V Mod Swap In The Works

1997 Lincoln Town Car, PI Intake/Cams, Sofa-On-Wheels, "Fat Tony" we call it

2001 GT Convertible - D1SC / Geared / Cammed / 440wh 400wt - TOTALED 2/2019
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post #8 of 10 (permalink) Old 03-15-2017 Thread Starter
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Any idea what kind of power I'll be putting down with those pistons? I also have a trick flow track heat intake, Comp 270 cams, slightly ported/polished heads, 28lb injectors, BBK long tubes, full off-road exhaust. I'll be tuned for 93. I'm shooting for 325rwhp at least.

Any other ways to squeeze a little more compression out of it? My heads are being shaved just a few thousandths to smooth them up, but not enough to change compression. Don't want to deck them or the block since it'll mess with the front cover.
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post #9 of 10 (permalink) Old 03-15-2017
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325wheel sounds like a good goal. Cams with a lower lobe separation angle can bump up the dynamic compression at lower RPM. You'll need a different rotating assembly or heads to change static compression.

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325rw sounds like a lot, but I'm a pessimist. With slightly worked PI heads and those cams, along with that intake I'm thinking maybe 310. Don't worry about dyno numbers though, only thing that matters is how it actually runs. I've seen lots of guys here over the years get a little heartbroken over their dyno numbers but ended up with a car that runs like it made 50 more hp than the dyno measured. With even minimal supporting mods - gears, chassis/suspension and tires, your car should have no problem getting into the upper half of 12's when you get that stuff under the hood done.


2001 GT Convertible
/1967 Coupe
All the usual bolt-on's /200 I6, C4

And a few Explorers too... 2008 4.0 XLT 4x2, 1996 XLT 5.0 4x2, 2003 Sport Trac XLT 4.0 4x4
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