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Author Topic:   piston to valve
ASTIKHOSSW
Journeyman

Posts: 90
From: UPLAND CA SAN BERNARDINO
Registered: Sep 2000

posted 11-02-2002 08:23 PM     Click Here to See the Profile for ASTIKHOSSW   Click Here to Email ASTIKHOSSW     Edit/Delete Message   Reply w/Quote
HELP,HELP,HELP i need your help.
Hi again fellas another question.
What is the closest piston to valve clearance
that can safely be run in our fords for drag racing only,and what are the benfits if you run closer then the norm or the wider than normal.The reason i'm asking, is i center lined my cam with 4 degrees of advance and my exhaust piston to valve is real close and the intake is over the normal.THANKS FOR YOUR HELP.

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kid vishus
Gearhead

Posts: 6590
From: middle of NC
Registered: Oct 2000

posted 11-02-2002 08:30 PM     Click Here to See the Profile for kid vishus   Click Here to Email kid vishus     Edit/Delete Message   Reply w/Quote
If it's too close for your comfort on the exhuast side, re-degree the cam, but put it in straight up. That should add some to the exhuast side, but take away a little from the intake clearance.

I have ran mine pretty close, too close actually and have they touched. Luckily, clevelands valves hit fairly flat on the piston, and unless they smack real hard, they dont get bent. Right now, I have about .070 on the exhuast side, and thats fairly tight, but as good as I could get it with my current camshaft.

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jsracingbbf
Gearhead

Posts: 2954
From: Batesville,MS. , U.S.A.
Registered: Mar 2002

posted 11-02-2002 08:33 PM     Click Here to See the Profile for jsracingbbf   Click Here to Email jsracingbbf     Edit/Delete Message   Reply w/Quote
As a rule of thumb, I run around .100 on the exhaust and .070 on the intake. You can probably get away with closer, but that's just my rule of thumb.

------------------
Jerry Smith
69 Mustang Pro ET Drag
70 Mustang retired former footbrake car
"Crawfish are Lucky! they get their Heads Sucked and their tails eaten!"

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V8 Thumper
Gearhead

Posts: 4681
From: Phoenix, Arizona
Registered: Dec 2001

posted 11-02-2002 08:39 PM     Click Here to See the Profile for V8 Thumper   Click Here to Email V8 Thumper     Edit/Delete Message   Reply w/Quote
I've got .120 on my exhausts and .080+ on my intakes, with flycut pistons

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ASTIKHOSSW
Journeyman

Posts: 90
From: UPLAND CA SAN BERNARDINO
Registered: Sep 2000

posted 11-03-2002 06:02 PM     Click Here to See the Profile for ASTIKHOSSW   Click Here to Email ASTIKHOSSW     Edit/Delete Message   Reply w/Quote
thanks guys that what thought,right now i'm at .055 on the exhaust and about .190 on the intake with the cam advanced, i guess i had better put it back straight up because i have had enough bad luck with this motor from hell.for those that want to know i am changing cams on the svo v-6 putting in one of those big ones [email protected] .740INT .714EXH.by the way does anyone remember the theory on degree of advance that will change piston to valve clearance.

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Rustang
Gearhead

Posts: 821
From: Clarion PA
Registered: Nov 2000

posted 11-03-2002 06:18 PM     Click Here to See the Profile for Rustang   Click Here to Email Rustang     Edit/Delete Message   Reply w/Quote
I wonder what kind of valve to piston clearance some of the Comp Eliminator and Super Stock guys run? (Alex?)
Last year when I was running in NMCA Factory Street I was talking to a Hot Street racer that claimed he was running .030-.040" clearance!
He didn't seem like the type to bullsh**, and the car was an all steel 3100# Duster with 400 cube small block running 9.40's naturally aspirated on slapper bars and 10" tires!

------------------
'68 mustang 351 clevor- [email protected]
'67 Stang, 351W [email protected]
'69 351C [email protected]
'78 Pickup [email protected]
'79 Pickup 460 ET=??

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Moneymaker
Administrator

Posts: 27499
From: Lyons, IL, USA
Registered: May 99

posted 11-03-2002 06:34 PM     Click Here to See the Profile for Moneymaker   Click Here to Email Moneymaker     Edit/Delete Message   Reply w/Quote
About .040 on the exhaust and .060 on the intake + the lash MAX.

------------------
Alex Denysenko
Co-Administrator and Moderator

NHRA/IHRA/SRA member and licensed Superstock driver
MCA member# 53321
NHRA and IHRA SS/LA National Record Holder '00, '01, & '02
Fleet of FoMoCo products including 88 ASC McLaren Mustang #28
Professional Manwhore
The Barry of BarrysGrrl

Quote #1: "I never met a magazine mechanic I liked."
Quote #2: "Make sure brain is in gear before engaging mouth!"
Quote #3: "If you can't run with the big dogs, stay on the porch!"

[This message has been edited by Moneymaker (edited 11-03-2002).]

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Mike_R
Gearhead

Posts: 178
From: Indianapolis, IN 46237
Registered: Feb 2001

posted 11-04-2002 12:32 PM     Click Here to See the Profile for Mike_R   Click Here to Email Mike_R     Edit/Delete Message   Reply w/Quote
The rule of thumb is, advancing the cam gives more exhaust valve to piston clearance and less clearance on the intake.

Retarding the cam gives more clearance on the intake side and less on the exhaust side.

So you would need to advance the cam more rather than retarding it.

For every 4 degrees advanced or retarded it will change the valve to piston clearance about .015" to .020". So if you advanced it 4 more degrees the exhaust valve would go from .055" to about .070-.075".

Whether it will run good with that much advance is another issue. It should work good if you have a very good flowing intake port and a very bad flowing exhaust port.

[This message has been edited by Mike_R (edited 11-04-2002).]

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kid vishus
Gearhead

Posts: 6590
From: middle of NC
Registered: Oct 2000

posted 11-04-2002 02:36 PM     Click Here to See the Profile for kid vishus   Click Here to Email kid vishus     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by Mike_R:
The rule of thumb is, advancing the cam gives more exhaust valve to piston clearance and less clearance on the intake.

Retarding the cam gives more clearance on the intake side and less on the exhaust side.


Oops, I must have had it backwards.

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kid vishus
Gearhead

Posts: 6590
From: middle of NC
Registered: Oct 2000

posted 11-04-2002 07:02 PM     Click Here to See the Profile for kid vishus   Click Here to Email kid vishus     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by kid vishus:
Right now, I have about .070 on the exhuast side, and thats fairly tight, but as good as I could get it with my current camshaft.


I also want to add, that is the total clearance with valve lash. And my lash is .028 hot.

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ASTIKHOSSW
Journeyman

Posts: 90
From: UPLAND CA SAN BERNARDINO
Registered: Sep 2000

posted 11-04-2002 07:12 PM     Click Here to See the Profile for ASTIKHOSSW   Click Here to Email ASTIKHOSSW     Edit/Delete Message   Reply w/Quote
i took the advance out of the cam this morning.
and checked the piston to valve clearance and i had .090 on the exhaust and .165 on the intake so when i took the 4 degrees of advance out of it raised the exhaust futher away from the piston and bought the intake closer to the piston.now with these numbers can i live with this.and by the way my heads flow 360 cfm intake
255 [email protected]" THANKS AGAIN

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