1986 iron head motor pistons ???
11-11-2007, 06:42 PM
#1
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Thread Starter
1986 iron head motor pistons ???
What type of pistons does an iron head 86 motor have ?
What compression would a 64cc chamber make on one of these motors ?
What compression would a 64cc chamber make on one of these motors ?
11-11-2007, 07:07 PM
#2
Burning Brakes
According to Mike Antonick's "Cor-Vette Specs," the 86 has "impacted cast aluminum" pistons weighing 21.1 oz each. And I thought the heads iron heads were 64cc stock. Could be wrong though.
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11-11-2007, 07:30 PM
#3
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Thread Starter
76cc ??
for some reason i was thinking they where 76cc 624 casting heads.
I think I had read that somewhere. I could very well be wrong though.
I think I had read that somewhere. I could very well be wrong though.
11-11-2007, 09:32 PM
#4
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The 1984 - 1986E, 624 heads ARE 76 cc. You can figure your stock clearance volume from the CR. Then subtract the the difference in head volume (76 - 64 =) 12 cc and re figure the CR with the new, smaller, clearance volume.
The 1986E pistons carry a different part number than the 1984 - '85 forged pistons. Because of the different part number, I had always guessed that they were cast.
RACE ON!!!
The 1986E pistons carry a different part number than the 1984 - '85 forged pistons. Because of the different part number, I had always guessed that they were cast.
RACE ON!!!
11-11-2007, 09:58 PM
#5
Cor-vette specs also states:
Your stock compression ratio is 9.5/1
Your head gasket thickness is .021 (which you could increase in size to slightly decrease your c/r)
I just built a vortec engine with 64cc heads. I used flattop pistons and, I believe, a .045" thick head gasket. That combo yielded a 10/1 or maybe 10.1/1 ratio which is a bit high, but with the right distributor you can control your advance curve to keep from having detonation problems.
If you do have a slight dish piston, you will likely have a ratio in the high nines.
BTW, with a comp 262H cam with .469 lift, my dyno sheet shows 372hp @5100 and 422# tq @4200 with a poorly jetted 725 holley (just for the dyno, plan on L98 intake). With the L98 intake and a good tune you should be able to surpass these #s.
I honestly had no idea that the 86 had such large chamber heads.
Your stock compression ratio is 9.5/1
Your head gasket thickness is .021 (which you could increase in size to slightly decrease your c/r)
I just built a vortec engine with 64cc heads. I used flattop pistons and, I believe, a .045" thick head gasket. That combo yielded a 10/1 or maybe 10.1/1 ratio which is a bit high, but with the right distributor you can control your advance curve to keep from having detonation problems.
If you do have a slight dish piston, you will likely have a ratio in the high nines.
BTW, with a comp 262H cam with .469 lift, my dyno sheet shows 372hp @5100 and 422# tq @4200 with a poorly jetted 725 holley (just for the dyno, plan on L98 intake). With the L98 intake and a good tune you should be able to surpass these #s.
I honestly had no idea that the 86 had such large chamber heads.
11-11-2007, 10:16 PM
#6
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They are cast pistons.
11-11-2007, 10:17 PM
#7
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Originally Posted by motorholmes
but with the right distributor you can control your advance curve to keep from having detonation problems.
RACE ON!!!
11-12-2007, 06:30 AM
#8
Pro
Thread Starter
flat tops...
9.5/1 with 76cc chamber would almost have to be flat top.
Seems like it would even be less than 9.5/1. More like 9/1.
Chevrolet must have been a little optimistic on this one.
Seems like it would even be less than 9.5/1. More like 9/1.
Chevrolet must have been a little optimistic on this one.
11-12-2007, 08:29 PM
#11
Le Mans Master
pinging
I have an 86, and even with the stock heads, it always pinged.
I got 88 aluminum heads, cleaned up the chambers a little, and put a thicker head gasket(.040 squished), with multec injectors, and it pings slightly. mods include throttle body bypass, and mat relocation.
I did a rebuild on my 350 in my 57 Chevy truck, and it's a 4 bolt 2 piece seal 350, hypereutectic pistons, '88 corvette 128 heads, and with the 1.5 roller rockers, no pinging. With the1.6 roller rockers, it pings all the time. I went back to the 1.5's.
The cam is a crane cam with 266 duration, .487 intake,.492 exhaust, and timing is initial at 8 degrees, with a total of 34 degrees at 2900 RPM with a msd billet distributor run off an MSD-6-al box, adjustable vacuum advance, and a light spring with a medium spring, and modified advance weights.
With a 160 thermostat, aluminum radiator, oil cooler, edelbrock alum. water pump, it runs at about 170 all the time, sooooo
with a 3:38 rear, traction bars, sway bars, 4 speed, it is pretty quick for a 50 year old............now if I could only stop and turn fast.....
anyway
The rockers make a big difference in the SOP dyno. I seem to feel the acceleration difference and at the same time, hear the ping, especially like in an alley with block walls on either side. Or in traffic with a semi on each side. So watch the cam plus rocker equation when you decide to upgrade.
I got 88 aluminum heads, cleaned up the chambers a little, and put a thicker head gasket(.040 squished), with multec injectors, and it pings slightly. mods include throttle body bypass, and mat relocation.
I did a rebuild on my 350 in my 57 Chevy truck, and it's a 4 bolt 2 piece seal 350, hypereutectic pistons, '88 corvette 128 heads, and with the 1.5 roller rockers, no pinging. With the1.6 roller rockers, it pings all the time. I went back to the 1.5's.
The cam is a crane cam with 266 duration, .487 intake,.492 exhaust, and timing is initial at 8 degrees, with a total of 34 degrees at 2900 RPM with a msd billet distributor run off an MSD-6-al box, adjustable vacuum advance, and a light spring with a medium spring, and modified advance weights.
With a 160 thermostat, aluminum radiator, oil cooler, edelbrock alum. water pump, it runs at about 170 all the time, sooooo
with a 3:38 rear, traction bars, sway bars, 4 speed, it is pretty quick for a 50 year old............now if I could only stop and turn fast.....
anyway
The rockers make a big difference in the SOP dyno. I seem to feel the acceleration difference and at the same time, hear the ping, especially like in an alley with block walls on either side. Or in traffic with a semi on each side. So watch the cam plus rocker equation when you decide to upgrade.
11-12-2007, 08:34 PM
#12
Ooops
I forgot to mention that my block is .010 decked and .030 bored, which gives me a little higher compression than a stock block.
Is it vortec heads you're looking at? I think it's a great choice for buget performance. Especially since you can get RHS vortecs (assembled) with .500 springs for under $650! And the flow numbers are huge and the design should really complement the high-torque L98 intake.
I have a SBC chart on my desktop that shows flow #s for many stock and aftermarket heads. You'd be suprised how well they measure up. They blow the doors off of World SR Torquers, for example.
Is it vortec heads you're looking at? I think it's a great choice for buget performance. Especially since you can get RHS vortecs (assembled) with .500 springs for under $650! And the flow numbers are huge and the design should really complement the high-torque L98 intake.
I have a SBC chart on my desktop that shows flow #s for many stock and aftermarket heads. You'd be suprised how well they measure up. They blow the doors off of World SR Torquers, for example.
