Piston to head clearance
03-24-2017, 07:24 PM
#1
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Piston to head clearance
I've got a 350 I'm puting together with scat rods, hyper Pistons stock crank. The piston is .013 in the hole (closest to top deck). Was goin to use .015 shim gasket. But now thinking :018 after measuring with dual indicator . This engine would never see over 5,000-5500 rpm. With 75 cc head compression is right at 9.3. Think it would hit head or be alright? Caint find a gasket at .020. This will be driven on street wth a little play at track. I have read guys running tight on circle track but this engine will be driven everyday.
03-24-2017, 08:39 PM
#2
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Car: 84 TA orig. 305 LG4 "H" E4ME
Engine: 334 SBC - stroked 305 M4ME Q-Jet
Transmission: upgraded 700R4 3200 stall
Axle/Gears: 10bolt 4.10 Posi w Lakewood TA Bars
Re: Piston to head clearance
You are .013 in the hole. Recommended quench is .040. You should be looking for a .027 head gasket. There is a nice .028 Victor Reinz available.
Did you account for piston rock in your .013 measurement?
Did you account for piston rock in your .013 measurement?
03-25-2017, 07:00 AM
#3
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Re: Piston to head clearance
I was shooting for 35 quench for a bit more compression. With no rings and rocking piston and holding down hard on opposite side, I get .005 in hole.
I didn't finish typing when I said closet to top deck, 2 measure at .013 and up to .015.
I have heard guys running tighter around .028 and kissing head at 7500 in circle track.
But this will be drove daily.
I didn't finish typing when I said closet to top deck, 2 measure at .013 and up to .015.
I have heard guys running tighter around .028 and kissing head at 7500 in circle track.
But this will be drove daily.
03-25-2017, 07:10 AM
#4
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Re: Piston to head clearance
I hit reply by mistake.
Can I run at .031 with .018 head gasket till I can afford beter heads?
Also wondering if the piston was pounding carbon from being to tight would the knock sensor pick it up? I'll be running ebl and I've almost always have wud show in seat.
Can I run at .031 with .018 head gasket till I can afford beter heads?
Also wondering if the piston was pounding carbon from being to tight would the knock sensor pick it up? I'll be running ebl and I've almost always have wud show in seat.
03-25-2017, 05:49 PM
#5
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Car: 84 TA orig. 305 LG4 "H" E4ME
Engine: 334 SBC - stroked 305 M4ME Q-Jet
Transmission: upgraded 700R4 3200 stall
Axle/Gears: 10bolt 4.10 Posi w Lakewood TA Bars
Re: Piston to head clearance
NO. You are asking for trouble.
Without any other changes, if 1 point in compression is 4% in HP,
then if you have a 400 HP engine, you are talking about 16 HP.
But the difference you are talking about in the quench distance
is probably a difference of only about .1 point, or 1.6 HP.
Do you really want to trash your engine over 1.6 HP?
If your piston is is kissing the head, you don't need to worry about
the knock sensor. You are already screwed.
Without any other changes, if 1 point in compression is 4% in HP,
then if you have a 400 HP engine, you are talking about 16 HP.
But the difference you are talking about in the quench distance
is probably a difference of only about .1 point, or 1.6 HP.
Do you really want to trash your engine over 1.6 HP?
If your piston is is kissing the head, you don't need to worry about
the knock sensor. You are already screwed.
03-27-2017, 12:25 PM
#6
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Re: Piston to head clearance
The reason I was goin with tighter quench is I thought it made the engine more efficient, requiring less timing with cleaner burn.
The little bit of compression bump was just a bonus.
The heads I'm using for now are 1971 "336" heads at 76cc and have been milled to 75cc, with about 5,000 miles on them. There just a spare set I have till I get some better heads.
So quench at .033 using .020 head gasket to dangerous turning less than 5-5500 rpm then I will use .028.
What's the diference between .035 and .045 quench? I'm curious as when tight is tight enough to the point of no gain?
The little bit of compression bump was just a bonus.
The heads I'm using for now are 1971 "336" heads at 76cc and have been milled to 75cc, with about 5,000 miles on them. There just a spare set I have till I get some better heads.
So quench at .033 using .020 head gasket to dangerous turning less than 5-5500 rpm then I will use .028.
What's the diference between .035 and .045 quench? I'm curious as when tight is tight enough to the point of no gain?
03-27-2017, 06:52 PM
#7
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Car: 84 TA orig. 305 LG4 "H" E4ME
Engine: 334 SBC - stroked 305 M4ME Q-Jet
Transmission: upgraded 700R4 3200 stall
Axle/Gears: 10bolt 4.10 Posi w Lakewood TA Bars
Re: Piston to head clearance
I'm curious as when tight is tight enough to the point of no gain?
Every engine combo is different.I don't there is a magic number you can put on this.
1 thing for certain, if you go too close, you will have trash.
You are getting lost in chasing numbers instead of building a good, reliable engine.
You said, just a spare set I have till I get some better heads.
Every engine combo is different.I don't there is a magic number you can put on this.
1 thing for certain, if you go too close, you will have trash.
You are getting lost in chasing numbers instead of building a good, reliable engine.
You said, just a spare set I have till I get some better heads.