Over a month ago, I bought a complete kit to overhaul my 350 in my 89RS which was supposed to be swapped out from an 89 4x4. I just now got around to tearing it down. I took off the drivers side head before removing the engine and discovered that it was a 5.0L.

I can get an older 350 block with the 2 piece rear seal, but will everything else work?

Is there a place for the knock sensor?

What about putting the newer 305 heads on the 350 block?

I'm po'd about the whole situation because all these years it was thought the engine was a 350 and it's not. I got a cam for an 89350, will it work in the older block? Is the ecm going to have a nervous breakdown? I have a chip for an 89 caprice classic with a 350, will that work?

I'm disgusted and don't have money to buy another kit, but can get an older (not real sure what year, 77-80?) 350 for almost nothing. If I use the heads from the 350 will my old manifold bolt up so I can use the new Y pipe I bought for it?


Any suggestions will be appreciated.

Rodger

P.S. I'm not really new, but haven't been on in so long I had to re-register.

 

Your asking about what you would have to buy to put in an older 350, right? If your trying to save a few $ it would be cheaper to just buy a set of pistons for your 305. A decent set of cast pistons could be aquired for around $200. To buy the new flywheel/flexplate (whatever you have), rear main, headers (your stock manifolds won't clear the dipstick), and other little things your out more than $200. Then you can still sell those 350 pistons and get back most of the money you spent on the 305 set. I'd be more concerned about the cams being different. If you have a flat tappet cam now and a roller in the kit your in even worse shape. There again you can get new pieces and make back some of the cost in selling the kit pieces.

 

damnit, i should right a friggin tech article about this, its asked so often.
i just finnished doing this, so i speak from experience.
you need: 350 motor, the flexplate, starter, and dustcover from the 350 motor. you CAN make the dipstick clear your stock manifolds. it IS a PITA though. i did it first try, despite what people say about it no being able to b done. you gotta pu some crazy bends in it. as for using the 305 heads, not recomended. they are small valves and small chambers. so it'll be like 12:1 comp and no flow. use 350 heads. there is a place for the knock sensor, it just screws in the water jacket plugs.
intake bolt angles will be diff on the old heads and your new intake, but you can elongate them with a drill, or just get a 86 or older intake. other than that i think your ok. i dont know about that computer **** though, im runnning a 305 TPI system and chip slapped on a 350 40 over and it does alright.

 

Thanks, I was able to find a 1990 block for $50 with no heads. I must use my 305 heads for this because I can't find any 350 heads for it.

Seems like it's hard to find anything around here for a 350, either nobody wants to get rid of them or they are bulding them.

RR

 

Watch your compression ratio. With 350 pistons and 305 heads your going to be very close to the 10:1 range. 350 heads are 64cc chambers and 305's are 58cc. With a 90 block everything else should interchange.

 

10:1 my *** . with flat tops it'll be over 12:1
if you absolutely MUST use those heads, use the thickest head gasket you can find, and get big dished pistons. port the hell out of em too. im tellin you though, it aint that hard to find a set of old 350 heads. they're gonna be 76 cc chambers, but its better to have 9:1 with good flow than 12:1 with no flow. hell, i got two of em, one needs a seat put in its cracked and the other is just rusty you can have em if you come to md to pick em up. those heads are one every damn 350 built from like 70something-86, just need to change the intake bolt angles if the intake is newer than 86. no biggie. even after that theres a whole lot of 350's in junkyards. a set of juckyard heads are cheap and a valve job is around 100. its not worth building a good motor and putting ****ty heads on it, believe me i know. go on and spend the little extra and oyu wont be dissapointed

 

You're not going to get over 12:1 compression in a 350 with a flat top, no matter how tight the quench is or how small the chambers are. And a flat-top with 76cc heads is under 9:1 and pretty lame. Shoot for 64cc, you prolly could use the 59cc with flat-tops running premium, or you could 'shape' the chambers to lower the compression some and improve the flow.

 

The jump from 76cc chambers to 64cc chambers only yeilds a 1-1/2 change in the ratio, example; 10:1 with 76cc is 11.5:1 with 64cc. So how is going from 64cc heads to 58 cc heads (half the change of the example) going to cause a full 2.0 change in the ratio?

 

I looked up the the casing numbers on the heads and this is what I came up with.

14102187...87-91...305..........1.84"/1.5" valves

Looks as though the exhaust is the same as a regular 350? The intake is 1.84" instead of 1.94", so hopefully that won't cause much trouble.

The block casting is 14093638. It just said it was a 87-94 350 with or without roller cam.

RR

 

A "regular" 350 has a 1.60 exhaust valve, IIRC.

 

Will the .10" make a big difference? I Guess I can drive it around for awhile until I find the 350 heads for it.

RR

 

305 heads have smaller runners, combustion chambers and valves. When you put them on a 350 you have an engine with great low end power. Too bad the heads choke the engine above 3500 rpm or so. That's why they don't do good on a 350. It's not that 1/10" makes alot of difference, everything adds up and creates the difference.

 

Please show the specs on this statement. I have never seen 'stock' 350 heads (with exception to late 60's/early 70's) that have 1.6" ex valves. News to me.

And yes, that .10" on the ex. valve will make a difference. Especially since GM makes weird ex. runners. That's why dual pattern cams were invented. To try to help SBC ex. designs.

 

IIRC, If I Recall Correctly. So I didn't, I can't be right all the time. What do you want from a big block guy.

 

most 350's are 1.94 1.50's or older ones are 1.94 1.60 or 2.02 1.60's
64cc is the ideal chamber for a perf 350.
58cc is ok, but hose small valves will not flow very good on a 350. i am not sure but a friend of mine who used to be a mechanic told me i couldnt use them because the compression would be too high(he said high 11's low 12's) now he has been wrong in the past, but that is what i was going by in my previous statement. if im wrong about that im sorry, but that dont change the flow of them heads. the only reason i say 76 cc heads is cause they are easy to find. 64 cc is definetly the way to go, but i couldnt find a set around here.

 

It's done and it runs like it's never run before! I can't believe the added power this thing has compared to what it used to be like! It's damn amazing!!! The only problem I seem to be having is the thing won't stop pinging at slower speeds. I guess I'll have to run a higher octane now that the compression ratio is way up there.

RR

 

Being very simple with the math, assuming 717 cc displacement volume, 11 cc I get the following static compression ratios:

76 = 9.2:1
64 = 10.5:1
58 - 11.4:1

Since these don't include valve reliefs or the volume between the piston & wall above the top ring, your actual is probably less. But, anything above 10:1 will probably require higher octane, anyway.

Bigger intake valves and freer flowing ports would probably help it run even better.

------------------
82 Berlinetta, orig V-6 car, now w/86 LG4/TH700R4. 2.93 limited slip. Cat-back from '91 GTA, ZZ3 intake, Accel HEI SuperCoil. AMSOIL syn lubes bumper-to-bumper. Daily driver, work-in-progress (LG4 w/'87 LB9 block, ZZ3 cam, ported World 305 heads, Hooker headers & y-pipe, 3" Catco cat & 3" cat-back, Spohn SFCs).
57 Bel Air, my 1st car. '66 396, 9.7 CR forged TRWs, Weiand Action+, Edelbrock 1901 Q-Jet (Holley 3310 on the way), GK 270 cam, Magnum rockers, Jacobs Omnipack, 1-3/4" Hedders & 3" Warlocks, TH400 w/TCI Sat Night Special conv & Trans-Scat shift kit, MegaShifter, 3.08 8.2" 10-bolt w/Powertrax, AMSOIL syn lubes bumper-to-bumper. Idles smooth @ 600 RPM in D. Best 15.02/95.06 @ 5800' Bandimere (corrected 13.93/102.4 @ sea level).

 

I found this formula:

Compression Ratio = (Cylinder Volume + Chamber Volume) / Chamber Volume
Cylinder Volume = PI/4 * Bore^2 * Stroke

There's also an automatic compression ratio calculator at this Address:
http://www.musclecars.net/KnowledgeB...mpression.html

If I did the math right, I came out with over a 14-1 compression ratio. That don't sound right, but It's still pinging a little even after adding premium.

RR