350 or 305? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

fenderbluesman63 · 06-12-2002, 12:50 AM

i am having trouble identifying a motor i have in one of my parts trucks..the motor was represented to me as a 350, but i looked up the casting #on the heads and they are 305 heads..i cant see or find the casting #'s on the block (engine is on the 6-cyl mount position and pressed against the firewall) i wont be able to remove the engine for a while, so i was wondering if there is a way i can id the engine without the #'s..also the engine has a computer control distributor on it, but of course no computer...how badly is this affecting performance? the engine has a WILD cam, headers, edelbrock intake,carb, side pipes etc...it seems like it isnt perfoming like it should and i suspect the distributor isnt helping perfomance as it is sluggish...any help greatly appreciated...are there any external differences that would id this block like #of freeze plugs or anything? i am familiar with pontiac mostly and this is my first chevy, so please help the newbie!

**COBALT** · 06-12-2002, 01:01 AM

No way to know unless you get behind the driver's side head and clean off the pad back there. You could try crawling underneath and getting it from below, then stick a shaving mirror up there...

Any other identifying numbers may be variances between the 305 and 350. My stamped number was on a pad on the deck just in front of the passenger's side head (right in front next to the timing chain cover.

O'l Buck · 06-12-2002, 01:29 AM

if the number is accurately stamped on the pad in front of the rh cylinder head, you can run the suffix code from it at nastyz28.com, but sometimes the numbers get stamped wrong at the factory and if it was ever a dealer installed crate engine, there won't be any number there......as far as the dizzy goes, My sister had one of those comp controlled dizzys in a 82 c-10 with a 305, it never seemed to affect the performance, but i can't remember how the wiring was to bypass the computer part, it's just 2 of the wires tied to gether in a loop if i remeber right, maybe someone else knows how it should be.

70c10 · 06-12-2002, 12:37 PM

After you clean the rear of the block with degreaser, use some childrens Play-Dough and make an impression. Peel it off slowly and you will have a mirror immage of the block numbers. Good luck!

Blue68 · 06-12-2002, 03:33 PM

Believe it or not, 305 heads have been used on 350 blocks. It was done to raise compression on the engine. This was useful on engines that had the deep dish pistons. Of course, larger valves and porting were part of the procedure.

You should be able to get the casting number off the back of the engine in front of the bell housing.

Longhorn Man · 06-12-2002, 08:19 PM

But putting normal 305 heads on a normal 350 will just choke it.

fenderbluesman63 · 06-13-2002, 12:25 AM

ok guys i found the #350 on the pass side block(i hope it wasnt the tranny, but i dont think so,i will recheck in the morning) you will never guess how i got the #s ...pressing hard with my thumb and index finger...who woulda thunk it...so i guess its a 350 block with 305 heads...WAY too much cam and compression...no wonder it ran like crap..i did notice the heads have screw in studs and everything looked brand new...clean as a whistle...the guy i bought it from said his son built the motor and he didnt know exactly what he did, but it was fast...yeah right..dog city...guess i need to find some good double humps and measure the piston reliefs...and get a good ignition going and ditch the electronic dist.thanks for the help guys..

fenderbluesman63 · 06-13-2002, 12:30 AM

i forgot to explain...the block was grreasy, and it left a perfect impression of 350 backwards on my fingers..i was feeling around trying to read it like braille, when it the idea struck to press really hard. the numbers showed up as clean spots on my fingers...

mikep · 06-13-2002, 01:01 AM

my dads got a 3/4 ton 78 with a 305 headed 350. Its got dished pistons , 9.5:1 compression , 1.94/1.50 valves and some bowl cleanup work, edelbrock performer cam and manifold with a 600 cfm edelbrock carb and headers with 2 1/2 inch duals . It runs very well, gets good gas mileage ( 18 unloaded hwy and 15 city , pulls 21 inches vacuum , probably never hits the high side of 5000 rpm and idles smooth. He loads a 5000 lb cabover camper up on it most of the summer and drives up hills just fine. Its not a powerfull monster but I'd say 350lbs of torque or so suits him just fine.

06-12-2002, 12:50 AM	#1
fenderbluesman63 Registered User Join Date: Apr 2002 Location: lr,ar Posts: 11	350 or 305? i am having trouble identifying a motor i have in one of my parts trucks..the motor was represented to me as a 350, but i looked up the casting #on the heads and they are 305 heads..i cant see or find the casting #'s on the block (engine is on the 6-cyl mount position and pressed against the firewall) i wont be able to remove the engine for a while, so i was wondering if there is a way i can id the engine without the #'s..also the engine has a computer control distributor on it, but of course no computer...how badly is this affecting performance? the engine has a WILD cam, headers, edelbrock intake,carb, side pipes etc...it seems like it isnt perfoming like it should and i suspect the distributor isnt helping perfomance as it is sluggish...any help greatly appreciated...are there any external differences that would id this block like #of freeze plugs or anything? i am familiar with pontiac mostly and this is my first chevy, so please help the newbie!

06-12-2002, 01:01 AM	#2
COBALT Senior Member Join Date: Sep 2001 Location: Seattle, WA, USA Posts: 5,817	No way to know unless you get behind the driver's side head and clean off the pad back there. You could try crawling underneath and getting it from below, then stick a shaving mirror up there... Any other identifying numbers may be variances between the 305 and 350. My stamped number was on a pad on the deck just in front of the passenger's side head (right in front next to the timing chain cover. __________________ '69 3/4 ton C20 2wd-350ci/TH400 '69 3/4 ton Custom 20 2wd-350ci/4sp Manual '99 2wd 5.7 Chevy Tahoe Seattle, WA.

06-12-2002, 12:37 PM	#4
70c10 67-72 Addict! Join Date: Feb 2002 Location: The TAX State! Posts: 7,856	After you clean the rear of the block with degreaser, use some childrens Play-Dough and make an impression. Peel it off slowly and you will have a mirror immage of the block numbers. Good luck! __________________ Jim 1970 C/10 Fleetside w/Ghost Flames Lowered 4.5" front and 4" rear (Raked) 355/350 Turbo w/shift kit 10" Redneck Performance Verter w/2500 stall Hooker Super Comps part#2808-1 Performer RPM Air-Gap 12 Bolt w/3:73 gears- Eaton Posi Comp Cams XE262 with 1.6 Crane Energizers, Road Demon 625 and Brodix IK 180 heads

06-12-2002, 03:33 PM	#5
Blue68 Registered User Join Date: Apr 2000 Location: Frisco, Tx, USA Posts: 606	Believe it or not, 305 heads have been used on 350 blocks. It was done to raise compression on the engine. This was useful on engines that had the deep dish pistons. Of course, larger valves and porting were part of the procedure. You should be able to get the casting number off the back of the engine in front of the bell housing. __________________ http://home.comcast.net/~r.landrum/w...tos.html-.html '68 C-10 LWB, '98 Z-71 350 w/accessories (Serpentine), Edelbrock Performer, Edelbrock 1405 (600cfm) carb, GM HEI, CompCam Extreme 4x4 roller cam, Thorley Headers, Carter Electric Fuel Pump, Vintage Air, 700r4, 3.73, disc brakes and power steering upgrades.

06-13-2002, 01:01 AM	#9
mikep Used to have a truck Join Date: May 2002 Location: port orchard WA Posts: 1,552	my dads got a 3/4 ton 78 with a 305 headed 350. Its got dished pistons , 9.5:1 compression , 1.94/1.50 valves and some bowl cleanup work, edelbrock performer cam and manifold with a 600 cfm edelbrock carb and headers with 2 1/2 inch duals . It runs very well, gets good gas mileage ( 18 unloaded hwy and 15 city , pulls 21 inches vacuum , probably never hits the high side of 5000 rpm and idles smooth. He loads a 5000 lb cabover camper up on it most of the summer and drives up hills just fine. Its not a powerfull monster but I'd say 350lbs of torque or so suits him just fine. __________________ No truck :-(

06-12-2002, 01:29 AM	#3
O'l Buck Recovering Truck Driver Join Date: Mar 2002 Location: Orleans, NE USA Posts: 1,883	if the number is accurately stamped on the pad in front of the rh cylinder head, you can run the suffix code from it at nastyz28.com, but sometimes the numbers get stamped wrong at the factory and if it was ever a dealer installed crate engine, there won't be any number there......as far as the dizzy goes, My sister had one of those comp controlled dizzys in a 82 c-10 with a 305, it never seemed to affect the performance, but i can't remember how the wiring was to bypass the computer part, it's just 2 of the wires tied to gether in a loop if i remeber right, maybe someone else knows how it should be. __________________ 67 K-20 350, SM465, Eaton rear, 4.56 no spin option 00 Dodge 2500 4x4, 24V cummins, 5 speed Chad South Central Nebraska

06-12-2002, 08:19 PM	#6
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	But putting normal 305 heads on a normal 350 will just choke it.

06-13-2002, 12:25 AM	#7
fenderbluesman63 Registered User Join Date: Apr 2002 Location: lr,ar Posts: 11	ok guys i found the #350 on the pass side block(i hope it wasnt the tranny, but i dont think so,i will recheck in the morning) you will never guess how i got the #s ...pressing hard with my thumb and index finger...who woulda thunk it...so i guess its a 350 block with 305 heads...WAY too much cam and compression...no wonder it ran like crap..i did notice the heads have screw in studs and everything looked brand new...clean as a whistle...the guy i bought it from said his son built the motor and he didnt know exactly what he did, but it was fast...yeah right..dog city...guess i need to find some good double humps and measure the piston reliefs...and get a good ignition going and ditch the electronic dist.thanks for the help guys..

06-13-2002, 12:30 AM	#8
fenderbluesman63 Registered User Join Date: Apr 2002 Location: lr,ar Posts: 11	i forgot to explain...the block was grreasy, and it left a perfect impression of 350 backwards on my fingers..i was feeling around trying to read it like braille, when it the idea struck to press really hard. the numbers showed up as clean spots on my fingers...



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