hot91t/a

whats the difference (if any) between a set of 350 heads and a set of 305 heads. im just woundering because my friend will be getting rid of his soon and i want his because mine have been around the block more times than his been. thanks.

DeWynter

The difference between the 305 and 350 are as follows
305
valve size: 1.845/1.505
Chamber size: 52.3cc

350
valve size: 1.945/1.505
Chamber size: 63.2cc

Intake and exhaust ports are the same.

92blue

iTrader: (1)

Combustion chamber size varies by casting #. In other words, not all 305 heads have a 52cc chamber, and not all 350 heads have a 64cc chamber. What are the casting numbers on the the 305 and 350 heads? You will find these on either head, under the valve cover. Also, what are your plans as far as your car? Are you changing heads only because you think his are in better shape than yours? Let us know, and we'll go from there.

DeWynter

I was surmising that he was talking about 305 and 350 heads from tpi motors which are all the same.

DuronClocker

iTrader: (1)

Stock 305s dont have 52cc heads. They are roughly 58cc (as above, not always exact), and stock L98 heads are 64cc.

You will lose compression going to the 350 heads, and the increase in valve size won't really offset this performance loss at all.

Stick with your 305 heads. If you want more performance, port and rebuild them.

DeWynter

These pages are strait from GM and Pontiac
Issued: 7 April 1989
Revised: 12 April 1990, 5-28-95, 7-1-99, 6-20-02
Bulletin #: CHEV-89 Page 1 of 1
Specifications for the 1989 Chevrolet engines.

R.R.
H.P. Disp. C.R. Ind. Make Model/Transmission Manifold Lifter Head cc
125/
130 173 9.14 PFI NA 10070150 1.5 H 27.3
140 307 9.24 1-4 Roch 1375x2250/1218/AV 22504068 1.6 H 59.85
170 305 11.18 TBI NA 14102183 1.5 H 53.0
195 305 10.49 PFI NA 10066015 1.5 H/R 52.3
220 305 10.49 PFI NA 10066015 1.5 H/R 52.3
230 350 10.22 PFI NA 10066015 1.5 H/R 63.2
240 350 11.53 PFI NA 14081005,10066013 1.5 H/R 53.6


Deck Piston
H.P. Disp. Cl Type Height Vol Valves Cam Lift Springs
125/
130 173 .005 Sumpted .280 20.54 cc 1710/1420 393/409 Outer w Damp
140 307 .002 Dish .072 5.42 cc 1750/1502 474/474 Outer Only
170 305 .013 Dish w/n 6.23 cc 1845/1505 350/385 Outer w Damp
195 305 .013 Dish w/n .058 8.24 cc 1845/1505 350/385 Outer w Damp
220 305 .013 Dish w/n .058 8.24 cc 1845/1505 415/430 Outer w Damp
230 350 .013 Dish w/n .060 8.87 cc 1945/1505 415/430 Outer w Damp
240 350 .013 Dish w/n .060 8.87 cc 1945/1505 415/430 Outer w Damp


H.P. Disp. Gasket Head Cast
125/
130 173 .061 10048696, 10048651
140 307 .030 22500142
170 305 .021 14102187
195 305 .016 14101081
220 305 .016 14101081
230 350 .016 14101083
240 350 .016 14101128

Issued: 28 March 1989
Revised: 6 April 1989, 9-5-95, 7-1-99, 6-20-02, 7-27-04
Bulletin #: PONT-89 Page 1 of 1

Specifications for the 1989 Pontiac engines.

HP Disp C.R. Ind. Make Model/Transmission Manifold R.R. Lifter Head cc Notes

110 151 8.50 EFI AC 25096867 10066657,10066656 1.75 H/R 50.30 A
125/
130 173 9.10 PFI Roch 10070150 1.50 H 27.30 B
138 307 9.24 1-4 Roch NA 22528212 1.60 H/R * 59.85 I
140 307 9.24 1-4 Roch NA 22504068 1.60 H 59.85 J
150 121 8.30 PFI AC/Bos 10042031 1.50 H 43.30 C
150 138 11.00 EFI Roch 17090054,17090130, 22532556,22538691 DIRECT H 47.00 G
17087259,17087260
170 305 11.18 TBI Roch 141102183 1.50 H 53.00 D
195 305 10.49 PFI Bos 10066015 1.50 H/R 52.30 E
220 305 10.49 PFI Bos 10066015 1.50 H/R 52.30 E
230 350 10.22 PFI Bos 10066015 1.50 H/R 63.20 F
250 231 9.00 SFI Bos Turbo 25505359 25525146 Upper 1.65 H 35.90 H
25507221,25525137 Lower

Cylinder Head Castings
A=10044485 B=10048696, 10048651 C=90209851 D=14102187 E=14101081 F=14101083 G=22530955,22539086 H=25533485,25539723, 25536702
I=22520142 J=22503317
* H/R Dia 0.698"


Deck Piston Dish/Dome
HP Disp Cl Type Height Vol Valves Cam Lift Gasket Springs

110 151 .036 Dish .160 15.80 cc 1720/1500 248/248 .044 Outer Only
125/
130 173 .005 Sumped .280 20.54 cc 1710/1420 393/409 .061 Outer Only
138 307 .002 Dish .072 5.42 cc 1750/1502 474/474 .030 Outer Only
140 307 .002 Dish .072 5.42 cc 1750/1502 474/474 .030 Outer Only
150 121 .010 Dish .020 18.70 cc 1690/1430 430/430 .050 Outer Only
150 138 .010ab Dish .118 4.50 cc Note a 424/424 .037 Outer Only
170 305 .013 Flat/notches 1842/1505 350/385 .021 Outer w Damper
195 305 .013 Dish .058 8.24 cc 1842/1505 350/385 .016 Outer w Damper
220 305 .013 Dish .058 8.24 cc 1840/1500 415/430 .016 Outer w Damper
230 350 .013 Dish .060 8.87 cc 1940/1500 415/430 .016 Outer w Damper
250 231 .020 Dish .190 25.23 cc 1750/1500 438/438 .060 Outer Only

Notes
a-This is a 4 valve head In 1.400 & 1.437 Ex 1.176 & 1.240

92blue

iTrader: (1)

I understand, but sometimes people don't have the original engines (rebuilt for example) in their cars. Just yesterday, I saw an 84 Camaro at the junkyard with an 87+ intake and center bolt valve covers. I lifter the intake up, and it was an unmachined roller block. Probably from a truck.

As far as the 305 tpi heads, my 305 H.O.s had a 58cc chamber.

DuronClocker

iTrader: (1)

Same casting used as in the TPI 305 cars. The 416 and 081 head castings are nearly identical and everywhere I've ever read said they are 58cc. My CR should go UP when I switch to 54cc heads (LT1), not down..

DeWynter

I belive one thing that happens is most sources count the 8.24cc dish of the pistons in with the cc of the head. Net cc of a 305 head is 60.24cc this can change with a non stock gasket. There is a difference between a NET cc mesument and the actual Head cc

92blue

iTrader: (1)

The combustion chamber size doesn't change with the gasket thickness, or the piston's dish. It is a separate measurement. The only things that will change the combustion chamber size is milling the heads, or even a port and polish job depending on what exactly is done. Compression will change with piston and gasket changes.

DeWynter

NET compression will change with gasket thickness, deck clearance and dish of piston "NET cc of the cylinder is calculated with all of these factors. The actual cc of the head does not change but some engines are listed with NET cc not Head cc

DuronClocker

iTrader: (1)

As far as I've ever said people use the phrase "head chamber size". Chamber size refers to the chamber of the head. The head gasket does not affect chamber size, nor do the piston dishes. We aren't talking about the compression ratio. Its obvious that gaskets and pistons will change the CR, but we are talking about a static value, the volume of the chambers in the heads. I've never heard anyone say the "net chamber size" when referring to head sizes and comparing them.

hot91t/a

well im building my 305 up and i just wanna know which one would give me better compression but still have valve clearence