I am going to be puting a 350 out of a 77 truck in my car because my lg4 took a crap. I was wondering what my compression would be if I used the lg4 heads. Also would that help or hinder performance? It is pretty much stock except the rings and bearings have been replaced and it has a cam. I kow that the 305 heads are not supposed to have the best flow but would the compression or the flow do more. Thanks for your help.

Ben

 

That'll run awful. If you can, atleast try to get the heads off of the 350 in the truck. Since the heads would have a smaller piston face your compression should go up a little bit, but you're valves are so much smaller that it wouldn't work right.

Lata,
Mike

 

What is a smaller piston face? What exactly would be the differences that would cause it to run so bad. Does anyone know about what the compression of a 350 out of a 77 chevy truck would have and how much can be gained by different head gaskets?

Thanks for your help

Ben

 

No, it will work fine. You would just get more performance with a freer breathing 350 head. The compression would definitely go up and might make you have to run premium fuel all the time. More costly

 

I have access to both sets of heads, I was just told by someone that I might be able to get better performance because of the higher compression ratio. I was wondering, If I ported the 305 heads would they then be better or would you suggest just using the 350 heads?

Thanks

Ben

 

If you want to get the compression up you can run the 350 heads with a thinner head gasket. That'll compensate and you'll still have the (slightly) better valves. I forgot what the dimensions on the heads are, but its a pretty big difference between the two heads. One thing though that you will want to do is probably pocket port and then do a three angle valve job on the 350 valves just to help the air get in a little better...

Lata,
Mike

 

Compression will definitely go up. That is not necessarily a good thing due to fuel prices.

Porting the 305 heads will definitely make them flow better.

However, 305 heads have smaller valves than 350 heads. 305s are 1.84 and 1.5 at best. 350s will have a minimum intake valve size of 1.94.

What that means is 350 heads will perform better at higher rpms. The 305s might outperform the 350s at low rpms due to the higher compression.

That's the story in a nutshell

 

How much will the compression go up with the changing of head gaskets?

Thanks

 

Oh, and does anyone know where I could find the compression ratio for that engine?

Ben

 

This is just a guesstimate. I think with the 305's 58cc combustion chamber, versus the 350's 70ish-cc combustion chamber, a 350 that is normally 9 to 1 will go up to around 10 1/2 - 1.

 

Ok, I dont think I will do that, I dont want too much compression. Do you know what compression I could get with thinner head gaskets as I asked before, or rather what increase in compression because I guess the current compression is unknown.

Thanks

 

A good shop should be able to figure it out for you. That's their bread and butter. If they can't do it, go to the next shop--you definitely don't want those guys fiddling with your truck!

Without the specifics of the engine you have, it is not possible for anyone to figure it out.

If you are doing it yourself, you have some homework to do. At least you are asking intelligent questions

 

Ok, I run 58cc heads on two 355's and they flow great! One has 1.94 intakes shoved in.
If you were to put the 58's on a 77 350 stock pistons, you would be around 10:1 compression. This means you would have to use midgrade fuel instead of the lower octaine.
No big deal since midgrade is usually 7/10 cents more per gallon.
The mid and late 70's heads suck!!! BTW 78cc heads are what is common on most trucks.
The mids 70's heads are worse than LG4 heads. In the 70's is when they first came out with smog junk and it was what cut the HP down to 160 from 220. Ok the cam did its part cutting power also the CConverter but still.
Port the 58cc's and if possible $$$ wise get some 1.94 intake's put in and you wont be sorry. Of course if you were replacing the pistons my rating is in vein.
SSC

------------------
85 Camaro Z28, Cowl induction hood, Black-355/TB400,3:42 posi, Tons of goodies but if you ask, "Its stock"
82 Firebird, White, red in six months-355/TB350,3:42 Powertrax posi. Not an insane amount of goodies but it runs like a motha!
76 Chevy C10, Firemist blue, 355/Muncie HD 3speed,3:73 TorqLine posi. Show me another 12sec@4800ft SBC street truck??
91 GMC 1500 Sierra 4x4, Red, Was 4.3 now the proud recipient of the Firebirds LG4. 305/5 speed.
56 Buick Special, OG Blue&White, V8/auto. Maybee one day I'll get it going.

 

I'm also running 58cc, 305, heads on a 355, and they work fine. Sitting Bull is right with stock pistons it'll be around 10.5 : 1 but if you put in some dished pistons you can get it down. I think mine is about 9.5 : 1. I always put 92 octane in there anyway but I think it will run fine on mid-grade.

------------------
84 Camaro Z28
350 4 bolt main with 305 heads
Engle Cam 210/216 @ 0.050
K&N Filter
Weiand Action Plus intake
Accel Supercoil
Suspension Techniques lowering springs
Energy Suspension bushings

 

One thing to watch out for on the 350 heads. Sitting bull mentioned a minimum valve size of 1.94. Thats wrong. I've just looked at 4 sets of heads between the years 78 and 84. All came off 3/4 or 1 ton trucks. All 4 sets were 1.72 intakes and 76 cc chambers.If you can get some info on your buildup heres a link to a compression ratio calculator.
http://cochise.uia.net/pkelley/crc.htm

 

Wow! Those heads were even more horrible than I imagined. I never thought GM would be so cruel as to impose such small valves on a 350 ...

 

I am not doing a complete buildup with this motor, I have a roller 350 in the garage for that but I need someting affordable for now and would like to have decent performance and need to know my options. My cousin can port my heads for me, but I dont know what valves are in the 350 yet, All I know is that it had the rings and bearings replaced about 60,000 miles back and I am going to put a new gasket set on it and possibly do a little bit to the heads. How much does it cost for the machine work to put in bigger valves? I will have the stock pistons so I need to figure out whether the compression will be to high with the 305 heads. Will center valve cover bolt hole heads work with that motor because I have a set off of a 350 in the garage with 1.94 and 1.5 valves. I am not sure if they are good or not though.

Thanks

 

You can thank the Feds for that.

The mid 70s to early 80s heads all suck. They all pretty much had a very large 76cc chamber, norrow runners, and small valves. This was in an effort to make them better on fuel while still meeting the Feds regulations. (I once had an '81 GMC 1/2 ton with a 305 that was rated at 120HP, 230lb.ft. of TQ and only had 8.2:1 comp ratio.)

The engineers at that time didn't have the aid of these things that we all have in our homes called COMPUTERS!!! They didn't know that raising the comp ratio, increasing chamber swirl, and still keeping the runners small would actually help the VE% of the engine at low RPM. And that would (of course) raise it's fuel efficiency.

But then again, they had to also overcome the new CATALYTIC CONVERTOR!!!!! Back then that restricted the exhaust flow A LOT!!! The poor guys with the blue collars couldn't keep up with the government's white collar, tree hugging, 'Save the Earth' guys.

The narrow runners in the heads will help with low end torque, that's why they used them. Back then a Buick Regal weighed more than a '99 3/4 ton truck & a horse trailer does now.

So for good general advice, stay away from the asthma inflicted heads of the mid 70s-mid 80s. They work great though for a sub-4000 RPM redline. There are a few, select castings that are OK, but very few.

AJ

 

Well not to be pushy, but does anyone know if the newer style heads will work with it, I dont see why not. If so I might check into using those. The one thing I worry about is that the engine they came off of had one cylinder in which part of the edge of the piston appeared to be missing. I dont know if it melted, burnt, or broke off, but there were no metal fragments in it. I know that the engine overheated and blew a head gasket. Does anyone know what that would indicate happened or if those heads should be good or not? I guess that the pison could have been like that from the factory but that would have been some poor quality control.

Thanks for all of your help guys

 

Momar, the 350 CB heads will work if you elongate two of the back holes on the manifold the ones above 5&6 I beleive. If you were to get larger valves put in the 58's plus guides on all valves your looking $250+ I suggest you call some local machine shops to get a price. The 58's ported will give you that extra performance you looking for.
SSC

 

I just checked the casting number on the heads I have in the garage. It is 14102183. I know that some of you are going to think that it is 193, but I cleaned it off and it deffinately connects like an 8. I read that the 193s are tbi truck heads. I dont know what year they are or what they actually came out of. I was told that the motor came out of a police car, but it would not be hard for me to dismiss that idea being as he also told me it was an lt1 (the guy who had it before me). I knew it was not before I bought it. It was carbed and had a distributer hole. I read in another post while doing a search that 183 does not exist but if someone could try to find out I would really appreciate it. If they are 9s I dont know what the deal is because they are totaly connected and look like 8s. It is a 5.7 roller cam motor.

Thanks

Ben

 

Oh, and according to nastyz28.com the 193's are from a 86-88 efi 350 w/ 1.94 and 1.5 valves. If by some chance I am wrong about it being an 8 how is that possible. I thougth that the 86's were different from 87-88. Mine have the center bolt valve covers. Thanks for your patience, I just need to get stuff figured out. I am currently without a car but should have time over christmas break to take the motor out of that truck to get ready for my car and I want to get it done while I have the time.

Ben

 

You might want to get the L31 Vortec heads, if you are in the mood for something new. They are praised by virtually everyone for making real hp, right out of the box.

 

If you go to http://www.mortec.com/castnum.htm , they have a list of most every casting #.

Unfortunetly they aren't Vortec heads. At least they're not listed on Mortec as such.

One easy way to check is count the # of intake bolt holes. If there are only 8, then it's a Vortec. But if theere are more, then someone could have just drilled more in it. Actually, look for EGR passages. If there are none, then they're probably Vortec heads. Or maybe Fast Burns.

(PSSSST) Not likely

They're are some 'replacement' heads that aren't listed but in a few casting # books. Maybe that's what you have?

Did you check BOTH heads for the casting #? One may just appear to be an '8' instead of a 9 due to a casting flaw, or what not. Try that and see. I have the 14102191 heads and on one of them, if you look at the # at the wrong angle, it kinda looks like an '8'.

AJ

[This message has been edited by AJ_92RS (edited December 10, 2001).]

 

Well, are the numbers supposed to match the 3 digits on the bottom of the intake runners? I still think that they look like an 8, but it does appear that there might be a small gap or something which would make them a 9s. So they are probably the 193s. They do have the center bolt holes(wish they were vortecs) and the egr passages. Does anyone really know what compression I would be running on that 350 out of the 77 truck if I were to put the lg4 heads on them. I think that this might be the better way to go if possible because I dont even know if those others are any good. I dont mind running premium, I just need to be able to use pump gas.

 

The casting number for the block if that helps any is 14093638. I looked it up on mortec and found:

14093638...350...87-95...2 or 4...Roller or flat tappet cam
one-piece rear seal

That could be anything as long as it is a one piece rear main seal block. I noticed the 093 in that number. I dont know if it is coincidence or if you can tell what heads came on it by that or not though. All I know about that block is that it is a one piece rear main seal, roller cam, and it was carbed with the heads we have been talking about (probably 193). When I looked up those heads on nastyz28 it told me that they came from an efi car. Im puzzled.

Ben

 

Oh, and all mortec said about those heads were 87 and up 350.

Thanks

 

Reguardless of what casting they really are
it will be a nice budget performance improvement over those mid 70's truck heads (882,624 etc)U might consider giving them a quick pocket port under the valves, trim and streamline the valve guide boss and port matching the intake opening. You can fully polish the exhaust port too. Exessive hogging out is not nessessary. If they don't already have 1.94" intake valves, a machine shop can install them at reasonable cost. Probabily need a valve job anyways.

 

They have 194 and 1.5 valves, Its just that as I explained above that one piston seemed to have a problem and I didnt know if that could have been caused by something wrong with the heads.

Thanks

 

I'd bet the heads are fine. Sounds like the piston ring land gave up. Overheated and or detonation (ring butted). If you're really concerned pull the valves out of the one heads and look for bent ones. (piston contact). But again I'd bet they are fine. Good luck

 

Thanks for your help, thats cool. I will probably use those then. I will check the valves though. I will also be installing new valve seals. I would hate to put it in and start it up to find that they were shot and blow smoke all over when I started it. Plus they come with the gasket set I am getting. I am getting it because I also dont want to have to worry about oil leaks so I am replacing all of the gaskets and seals. Thanks for your help.

Ben