I need some numbers, 350 and 305 head volume, dish and relief volume...
09-27-2002, 10:58 AM
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I need some numbers, 350 and 305 head volume, dish and relief volume...
on a stock low compression 350, how big in Cc's are the valve reliefs and the dish?
What is the stock headgasket compressed highed,
What are the combustion chamber sizes for both a 350 and 305 head
deck hight should be -0 on a stock unrebuilt block, and I assume it's customary to trim this -.015 for truing purposes....
on a stock low compression 350, the top ring is .250 from the top of the piston correct?
In case you havn't noticed, I've got some calculators here and I'm trying to plan out on paper my build up, I just want to make sure I don't go over my mark on compression here... please respond with anything you can... right now with 305 heads I'm looking at anywhere from 9-12 to 1...
What is the stock headgasket compressed highed,
What are the combustion chamber sizes for both a 350 and 305 head
deck hight should be -0 on a stock unrebuilt block, and I assume it's customary to trim this -.015 for truing purposes....
on a stock low compression 350, the top ring is .250 from the top of the piston correct?
In case you havn't noticed, I've got some calculators here and I'm trying to plan out on paper my build up, I just want to make sure I don't go over my mark on compression here... please respond with anything you can... right now with 305 heads I'm looking at anywhere from 9-12 to 1...
Last edited by Xenodrgn; 09-27-2002 at 11:02 AM.
09-27-2002, 01:00 PM
#2
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I'll give you my observations over the years on this, not saying that they will absolutely hold true for all years, models, etc.
305 heads are ALL spec'ed at 58cc although they vary in reality- usually larger, not smaller. Early on they came with 1.74/1.50 valves but with the advent of the L-69 HO 305 in the early 80s they started improving on them with 1.84/1.50 valves and other improvements.
3rd gen-era f-body 350 heads with centerbolt valve covers are spec'ed at 64cc (cast iron, the aluminum vette heads are 58cc). Valves were 1.94/1.50. There were no 350s available in 3rd gens before the centerbolt heads came along that I'm aware of (except maybe a few freak production cars that slipped through). Before the centerbolt 350 heads, low compression 350 motors of the 70s and early 80s, like used in 2nd gen Camaro were 76cc heads and yielded VERY low compression- below 8.5:1. Valves were almost always 1.94/1.50.
Stock pistons in a 350 were almost always the dished-and-eyebrowed -12cc units. This is a VERY common 350 piston. The same basic design has been used in the late-70s 350s through the 80s and right up into todays ZZ-series long and short blocks.
Stock 305 pistons could be either flattop or 12cc dished with eyebrows, depending on year and application.
Deck height for either piston is usually spec'ed to be around .025" "in the hole" although some are even further in. You have to deck the block to get it UP TO zero deck.
Head gaskets for years were steel shim head gaskets with a compressed thickness of about .016-.018" This is much thinner than most rebuilder gaskets like the common fel-pro .039" compressed thickness composite gasket. In the 80s I'm pretty sure they ran the same basic one but with a special coating on it, although I haven't torn apart a truly stock one of that vintage in recent memory.
305 heads are ALL spec'ed at 58cc although they vary in reality- usually larger, not smaller. Early on they came with 1.74/1.50 valves but with the advent of the L-69 HO 305 in the early 80s they started improving on them with 1.84/1.50 valves and other improvements.
3rd gen-era f-body 350 heads with centerbolt valve covers are spec'ed at 64cc (cast iron, the aluminum vette heads are 58cc). Valves were 1.94/1.50. There were no 350s available in 3rd gens before the centerbolt heads came along that I'm aware of (except maybe a few freak production cars that slipped through). Before the centerbolt 350 heads, low compression 350 motors of the 70s and early 80s, like used in 2nd gen Camaro were 76cc heads and yielded VERY low compression- below 8.5:1. Valves were almost always 1.94/1.50.
Stock pistons in a 350 were almost always the dished-and-eyebrowed -12cc units. This is a VERY common 350 piston. The same basic design has been used in the late-70s 350s through the 80s and right up into todays ZZ-series long and short blocks.
Stock 305 pistons could be either flattop or 12cc dished with eyebrows, depending on year and application.
Deck height for either piston is usually spec'ed to be around .025" "in the hole" although some are even further in. You have to deck the block to get it UP TO zero deck.
Head gaskets for years were steel shim head gaskets with a compressed thickness of about .016-.018" This is much thinner than most rebuilder gaskets like the common fel-pro .039" compressed thickness composite gasket. In the 80s I'm pretty sure they ran the same basic one but with a special coating on it, although I haven't torn apart a truly stock one of that vintage in recent memory.
Last edited by Damon; 09-27-2002 at 01:07 PM.
09-27-2002, 01:11 PM
#3
Supreme Member
Depends on exactly which "stock 350" you have.
The dished piston volume varies.
There is a good listing of "stock replacement" type cast pistons
on the Keith Black piston internet site. (Silv-o-lite) These are designed to replace the stock GM piston on a rebuild.
http://www.kb-silvolite.com/
But it's around 11 to 13 cc's.
The stock 350 block is 9.025" from crank centerline to top of the deck. They do vary a little. 9.30+ is not unusual.
A "0decked" block is 9.00"... And not stock.
Most pistons are .025" to .045" or more below the deck on a stock motor that hasen't been decked.
So a stock 350 with typical 13.0cc dished pistons
that only come to .045" from the top of the block
with a stock 76cc head is 8.07:1 if it has the stock .015" shim head gasket. Changing to a 305 head (58cc) would increase the cr to 9.60:1 with that same .015" shim gasket.
If the stock piston happens to come to .025" from the top of the block then cr would be 8.37 and 10.05 respectively.
A .039" felpro replacement gasket (common) would lower this to
7.97 and 9.44 respectively.
You can download a good compression ratio calc for windows
from Performance Trends
www.performancetrends.com
The stock shim gasket is .018" new and .015" compressed
with a vol of 3.5cc's.
Felpro .038" to.041" composite replacement gasket vary from
8.8cc to 9.3cc. 9.1 is common.
There is a .051" "corvette" gasket also.
So by tearing down your dished piston motor and measureing the piston to deck height you can juggle the final cr to your liking
with the different available head gaskets, when swapping on a set of 305 heads.
The old "416", and "081" centerbolts are the ones to look for.
Be sure to upgrade the valves to 1.94 x1.5 or 1.6 at least
and give them some porting and you'll have a good budget
street motor.
The dished piston volume varies.
There is a good listing of "stock replacement" type cast pistons
on the Keith Black piston internet site. (Silv-o-lite) These are designed to replace the stock GM piston on a rebuild.
http://www.kb-silvolite.com/
But it's around 11 to 13 cc's.
The stock 350 block is 9.025" from crank centerline to top of the deck. They do vary a little. 9.30+ is not unusual.
A "0decked" block is 9.00"... And not stock.
Most pistons are .025" to .045" or more below the deck on a stock motor that hasen't been decked.
So a stock 350 with typical 13.0cc dished pistons
that only come to .045" from the top of the block
with a stock 76cc head is 8.07:1 if it has the stock .015" shim head gasket. Changing to a 305 head (58cc) would increase the cr to 9.60:1 with that same .015" shim gasket.
If the stock piston happens to come to .025" from the top of the block then cr would be 8.37 and 10.05 respectively.
A .039" felpro replacement gasket (common) would lower this to
7.97 and 9.44 respectively.
You can download a good compression ratio calc for windows
from Performance Trends
www.performancetrends.com
The stock shim gasket is .018" new and .015" compressed
with a vol of 3.5cc's.
Felpro .038" to.041" composite replacement gasket vary from
8.8cc to 9.3cc. 9.1 is common.
There is a .051" "corvette" gasket also.
So by tearing down your dished piston motor and measureing the piston to deck height you can juggle the final cr to your liking
with the different available head gaskets, when swapping on a set of 305 heads.
The old "416", and "081" centerbolts are the ones to look for.
Be sure to upgrade the valves to 1.94 x1.5 or 1.6 at least
and give them some porting and you'll have a good budget
street motor.
Last edited by F-BIRD'88; 09-27-2002 at 01:22 PM.
09-28-2002, 07:08 AM
#4
Not to complicate the issue, butt I've cc'ed some TRW stock replacement dished pistons (350) that had 16cc of dish including the reliefs and rim. Get a syringe and some transmission fluid, and a small piece of Lexan, then check yours out.
09-12-2019, 10:07 PM
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Re: I need some numbers, 350 and 305 head volume, dish and relief volume...
I found this thread looking for some dish 4 valve relief piston volume numbers, which I found - sort of.
I'm trying to figure out if I should...
1/ put some ported 58cc 305 heads with 1.94/1.6 valves and a stock gasket or
2/ get some 64cc promaxx 183's (maybe cut to 62) with thinner head gaskets to help keep the compression at 9.5:1 approximately regardless of the heads.
The engine it's going on is a 350 at 040 over with stock replacement pistons (cast dish 4 valve relief), recently rebuilt.
The 305 heads are a little cheaper, which helps me maintain my budget street engine goal, but the promaxx aluminum heads flow really well.
I really have no idea how well the 305 heads will perform compared to those new aluminum heads, which is what i hope I can get a feel for.
The cam it most likely going to be a comp magnum 270H, since it's part of the budget program i'm on and it's available. I als have an edelbrock 7501 ready to go on it and still deciding on a carb.
Does anyone have any experience on how well those ported 305 heads will work in comparison to those aluminum ones?
I'm trying to figure out if I should...
1/ put some ported 58cc 305 heads with 1.94/1.6 valves and a stock gasket or
2/ get some 64cc promaxx 183's (maybe cut to 62) with thinner head gaskets to help keep the compression at 9.5:1 approximately regardless of the heads.
The engine it's going on is a 350 at 040 over with stock replacement pistons (cast dish 4 valve relief), recently rebuilt.
The 305 heads are a little cheaper, which helps me maintain my budget street engine goal, but the promaxx aluminum heads flow really well.
I really have no idea how well the 305 heads will perform compared to those new aluminum heads, which is what i hope I can get a feel for.
The cam it most likely going to be a comp magnum 270H, since it's part of the budget program i'm on and it's available. I als have an edelbrock 7501 ready to go on it and still deciding on a carb.
Does anyone have any experience on how well those ported 305 heads will work in comparison to those aluminum ones?
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