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Old 06-09-2014, 06:45 PM
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Piston to valve clearance

I have already degreed the cam, and getting .11 -.13 intake and .123 -.126 on exhaust. Add the thickness of head gasket of .020 puts them at .13 -.14 intake and .143 -.146 exhaust. Don't thouse numbers seem pretty wide?

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Old 06-09-2014, 07:55 PM
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Post the cam specs and what the build is
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Old 06-09-2014, 08:08 PM
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Build sheet?

Dart Shp 400 block
Scat forged crank 3.75 stroke
Scat forged rods 5.7
Probe forged dish pistons 12.5 cc dish
CC magnum 280 eom roller on billeted core
.525 lift with 1.6 rockers = .560 lift
adv dur 280 @ 050 224
LSA 110, 106 ICL retarded 4 deg
CC Ultra Pro Magnum Rockers
RHS 200cc/64cc pro action heads
Edelebrock RPM Air Gap intake
Built TH 350 w/Coan 2700 stall
Eaton 3.73 rear gear
Car is 76 Nova approx 3350 wt
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Old 06-09-2014, 08:25 PM
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Quote:
Originally Posted by busterrm View Post
I have already degreed the cam, and getting .11 -.13 intake and .123 -.126 on exhaust. Add the thickness of head gasket of .020 puts them at .13 -.14 intake and .143 -.146 exhaust. Don't thouse numbers seem pretty wide?
Plenty of clearance and that's a problem for you why??

Most advice will tell you .100" minimum to avoid problems with lifter pump on hydraulic valvetrains, I've run solid's as tight as .045" or so on intake side, .070" on exhaust side.....but wouldn't advise a rookie to do that.

You are golden right now, what are you worried about?? Cam is not real big at 224 duration @.050"....and piston is far away from valve at peak lift point on cam lobe, it is at TDC during overlap from exhaust stroke to intake stroke where valve-to-piston is closest, so peak lift of .560" with 1.6 rocker has nothing to do with it.

Why are you retarding cam 4??

Probe pistons generally have deeper valve relief than Speed-Pro/TRW/Sealed Power.

Nice street combination for a 400, by the way.
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Old 06-09-2014, 11:14 PM
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should be a solid 12 second car if drag raced,,,I keep my P-V at least .090,,,Im sure you are fine,but its a good idea to check P-V at -4,0,+4
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Old 06-10-2014, 08:00 AM
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Originally Posted by ericnova72 View Post
Plenty of clearance and that's a problem for you why??

Most advice will tell you .100" minimum to avoid problems with lifter pump on hydraulic valvetrains, I've run solid's as tight as .045" or so on intake side, .070" on exhaust side.....but wouldn't advise a rookie to do that.

You are golden right now, what are you worried about?? Cam is not real big at 224 duration @.050"....and piston is far away from valve at peak lift point on cam lobe, it is at TDC during overlap from exhaust stroke to intake stroke where valve-to-piston is closest, so peak lift of .560" with 1.6 rocker has nothing to do with it.

Why are you retarding cam 4??

Probe pistons generally have deeper valve relief than Speed-Pro/TRW/Sealed Power.

Nice street combination for a 400, by the way.
I have built many flat tappet engines with max 475 lift, and this is my first with greater than 500 lift. Just curious if there is a rule about too much PTVC. Retarding it to get into the area for a safe DCR. Deck is 23 with gasket 20, quench is okay, DCR will be about 8.2 with intake closing at the retarded 70 degrees(69 after degreeing cam).
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Old 06-10-2014, 09:44 AM
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Whoops. Mod please delete this post.

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Old 06-10-2014, 10:50 AM
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Quote:
Originally Posted by busterrm View Post
I have built many flat tappet engines with max 475 lift, and this is my first with greater than 500 lift. Just curious if there is a rule about too much PTVC. Retarding it to get into the area for a safe DCR. Deck is 23 with gasket 20, quench is okay, DCR will be about 8.2 with intake closing at the retarded 70 degrees(69 after degreeing cam).
Nope, no rule about too much piston-to-valve clearance, as there is really no such thing...too little however, can be a problem if valvetrain is over-revved and floated,.... or if none exists - is a BIG problem...BANG.

You're fine

Hope you have the 8.5" rear, last '76 Nova I did began life as a straight 6 car and had the 7.5", I had to swap that out.

It was also closer to 3650 lbs with the 383 w/ported smogger iron heads/TH-350 trans, manual disc brakes but power steering, No AC and no lightening at all. Those HEAVY reinforcement bars behind the bumpers were going to be the first thing on the list to remove, along with the bumper shocks. Car ran 12.50's easily though, 4.11 gear. Sold before it got lightened.

Last edited by ericnova72; 06-10-2014 at 10:57 AM.
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Old 06-10-2014, 04:25 PM
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Originally Posted by ericnova72 View Post
Nope, no rule about too much piston-to-valve clearance, as there is really no such thing...too little however, can be a problem if valvetrain is over-revved and floated,.... or if none exists - is a BIG problem...BANG.

You're fine

Hope you have the 8.5" rear, last '76 Nova I did began life as a straight 6 car and had the 7.5", I had to swap that out.

It was also closer to 3650 lbs with the 383 w/ported smogger iron heads/TH-350 trans, manual disc brakes but power steering, No AC and no lightening at all. Those HEAVY reinforcement bars behind the bumpers were going to be the first thing on the list to remove, along with the bumper shocks. Car ran 12.50's easily though, 4.11 gear. Sold before it got lightened.
Yeah, I was thinkiing of taking out the reinforcement bars and bumper shocks, out with back seat too. It has a 8.2 10 bolt year end that I put in it. It did have the 7.5 in it, its got a eaton posi in the 8.2.
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Old 06-10-2014, 05:44 PM
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Quote:
Originally Posted by busterrm View Post
I have built many flat tappet engines with max 475 lift, and this is my first with greater than 500 lift. Just curious if there is a rule about too much PTVC. Retarding it to get into the area for a safe DCR. Deck is 23 with gasket 20, quench is okay, DCR will be about 8.2 with intake closing at the retarded 70 degrees(69 after degreeing cam).
No rule about too much piston to valve clearance, the problems are with too little this is a measure to insure that piston and valves don't meet. Generally .080 for the intake and .100 for the exhaust are considered the minimum safe dimension.

The clearance to worry over in a combustion sense is the squish/quench step to piston crown. For a street engine with steel rods in a range of .035 to .045 inch is highly desirable because it develops a huge amount of turbulence and jambs most of the mixture in front of the spark plug while offering the late burn a detonation avoiding heat sink because of the ratio of low mixture volume between a lot of surface area. At the same time this distance is mechanically safe sufficient to keep piston from colliding with the head.

Bogie
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