AutoX86Z28

can i port some 305 heads and put them on my chevy 350?



i wanted to do this because i heard if u put them on then it raises your compression ratio to like 10:5 or 11....is this true also?

Sitting Bull

It will raise your compression maybe 3/4 of a point. What that works out to is dependent upon where you're starting. I'd increase the intake valve out to 1.94", too. Follow the instructions linked at the end of my sig.

AutoX86Z28

did u feel a good power increase on that upgrade? is it worth it?

Air_Adam

What heads do you have now? There is a casting number under your valve covers... what is it?

Some heads are better then others, and thats especially true of the 350.

Sitting Bull

Did I ever!

Well worth the effort

Plus the heads will work really well on almost any streetable small block you will have in the future. Does that turn your crank? I know it turns mine

AutoX86Z28

i have the stock 350 heads....idk the casting number because i have aftermarket valve covers.....anywhere else i can look?

ME Leigh

No the casting number is onl under the valve cover.

Gumby

Id find a set of the big valve 305 heads. Not sure on the specs but there are some with bigger valves that everyone throws on the 350. Id run atleast a 1in open hole spacer if not 2in. [hood room]

Air_Adam

Yes, they are only under the valve cover to the best of my knowledge.

When you get the valve cover off, look between the pairs of valves for a number. It is a long number.

All we need are the last three digits of that number to know what you have, so no need to try to remember all the numbers, just the last three.

AutoX86Z28

the heads came with the motor but not the valve covers. all i can tell is that its a sbc 350 out of a '76 1/2 ton van.

F-BIRD'88

If your motor is a stock motor from a 76 chevy van then the compression ratio will be quite low (8.5:1 or less)
These motors had junk low perf , low compression 76cc heads on them combined with dished pistons.
Changing the head to a ported, small (58cc) chamber 305 based casting will raise the compression ratio nicely (but not to 11:1). You'd want to install new 350 sized valves (1.94in 1.60 ex) in your home ported 305 heads for best results.

You're new compression ratio will still be under 10:1.
A nice, low $$$ up grade.

1983Fbody

I'm also running 305 heads on a 350, ported them pretty much the same as the tech article up there. Very good work, If you want to get more specific there are a couple good books out there on the subject. I sat down in the book store for a couple hours and wrote down notes ;-) Sitting Bull has taken all the fun out of it, now you'll never have to know how it feels to have the book store employees give you dirty looks!

Gumby

Great job for a camera phone and a few buddies to stand around to block the view. No different than going to the library. But the library will charge you 10 cents a copy to copy copyrighted stuff.

AutoX86Z28

is this motor not going to give me the torque i want or power im expecting out of it? jw because in 76 didnt they use the same motor in the camaros as the vans? i may be stupid and wrong so correct me if im wrong

AutoX86Z28

anybody ??????

Air_Adam

Ok, you likely have either 624 or 882 heads. Thats a bad thing.

305 heads would be an excellent upgrade from those heads, especially since you already have the dished pistons. Because you have dished pistons, your CR will be around 9.5-10 with the 305 heads, which is perfect for a high performance engine on pump gas.

If you do switch to 305 heads though, I'd suggest having larger valves installed first. Your 350 heads should have either 1.94/1.5 valves or 1.94/1.6 valves. The 305 will have 1.84/1.5 valves. IMO, you should have 1.94/1.6 valves installed in the 305 heads if they are going onto a 350.

YenkoZL1

Who in there right mind wants a 305 head on a prebuilt 350? The vavles are waaay small(1.84 150) and they dont flow. The only thing you'll get out of them is extremely high compression. 58cc heads that are cast iron cannot be used with a flat top piston b/c the compression wont be streetable. They dont sell 100 plus octane fuel like they use too(70s). Your better off buying an aftermarket head bro. SR Torquer is a good head to build or use right out of the box, and everyone knows about the vortec. If your looking for high compression mill the head until your satisfied. A 305 head isnt worth putting on a built 350. By the time you get done paying for port jobs and polishes and stuff like that you could buy a new set of heads with beefier valves that perform better.

F-BIRD'88

Yenko:
If you'd ever actually rework a 305 head with HOME PORTING AND LARGER VALVES and test them on a flow bench
and try them on a motor, you'd have a whole other opinion.

I have modified many set of these heads for 350's
with great results.

When you sweep out the chamber for the larger valves
in these heads you end up around 60-62cc's

Most flat top pistons don;t come all the way to the top.
the cr won't be near as high as you think.
Won't result in exessive compression on most 350 flat top motors. The small combustion chamber is actually more detonation resistant.

Cost is far less than aftermarket heads.

400+hp is well within reach.

ljnowell

Dont listen to that stupid sh**. Take your heads you have, ado your port and polish and go for it. It'll make a big difference. Ive seen a lot of bad *** engines running cast heads. Also. 305, 350 it dont matter, if you are gonna reqork em its all good, that little 305 head wil lbe better than a large chamber **** head.

AutoX86Z28

ok thanks for the help and opinions guys.....and girls if there was any. :hail: :hail: if i find a cheap pair of 305 heads i think ill give it a try....otehrwise ill just port and polish my 350 heads

F-BIRD'88

?????????????

AutoX86Z28

does that mean that u dont know? lol

F-BIRD'88

No, it means you're not making any sense.

Can't figure out what you're trying to say.

AutoX86Z28

what i meant was, is this motor whether or not it has modifacations going to be slow? does that make any better sensE?

F-BIRD'88

1. No.... raising the compression ratio and improving the breathing by replacing the cylinder heads is essential thou. The stock heads that came on those motors will really limit (low compression ratio, poor breathing) any other gains from other upgrades. A modified ported 305 head is a good way to achieve this, among other choices.

How much power are you trying to get?
Is the motor healthy otherwise? (Compression test, oil pressure, etc)

Why don't you remove one of the valve covers and see what head you actually have (casting number) and go from there.

You have lots of choices available.

AutoX86Z28

i am trying to get as much hp as i can out of this motor, but i want it reliable also be cause i need it as a daily driver.

as far as i know the motor was a great motor. very reliable. i didnt do the tests that you mentioned.

will the aftermarket valve covers have the casting number on them?

again im sorry for the confusion.....im not good at communication arts

ME Leigh

Valve covers just sit on top of the head. Take the four bolts holding them down and pull them off. Under that on top of the head (1) is the casting #, that is what you want. What valve covers on there means nothing.

F-BIRD'88

WOW!!! Didn't know the weed was that good in Wisconsin....



HELLO!!!! The cylinder head casting number is underneath the valve cover. Ya have to remove the valve cover to see it. There are 4 bolts holding the valve cover on. Put down the hash pipe and Remove these 4 bolts and the valve cover will come off real easy. Look between the valve springs, on the top of the cylinder head.

Then look at the head casting number listings to see what you've got.Here

AutoX86Z28

yea its pretty good here.......straight from jamaica...........JK



yea ive put my motor together i just didnt notice the little numbers under the valve cover.

FirstGen

ahahahahaha

Air_Adam

Pull off the valve cover (only need to take off one) and look between the valve springs. There is a number cast onto the head there. I dunno which springs they are between, but they are there.

Stekman

on the driver side the casting number is like between #1 intake and #3 intake. Ok i suck at explaining...DIAGRAM TIME, with the I and E standing for valves (intake and exhaust)

EI *casting num* IE EI IE

If its the pass side your on:

EI IE EI *casting num* IE


Thats where i THINK they are, its been a while since ive looked at my heads.

jmd88iroc-z

I thought I'd slip in a question on your thread, man. Hpoe you don't mind. Are the 305 heads put on '88 tpi Iroc 305s already set up for a 350?, or would they need "adjustments"?

Sitting Bull

The intake valve is smaller on the 305 heads, 1.84" versus the 1.94" on the 350. Other than that they will just bolt right on.

YenkoZL1

Did I hear home porting kit in your last post? How many people have the ***** to rework a set of heads that are on tight budget knowing that just the smallest misshap could ruin the head? Second who has the right tools to make the right measurements? 305 heads are nasty when they come off a block. They need a lot of work. You can rework any head and get way better flow numbers but if your paying for it, 305 heads are not the way to go. But hey Im not doggin the Eastwood home porting kit at all. If you know your **** and can drill anything and everything then your one step ahead of most. Im just saying its not worth paying a machine shop to cure a set of heads from asthma.

FirstGen

good point, however it takes quite a bit to "ruin" a set of heads unless you do something stupid like grind on the valve seat or something...lol

Jeffsblown305

I have a set of 305 chevy heads with 175 intake and 1.55 exhuast valves that are 58cc on a 91 gm 305 replacement engine I dont know all the specs on the engine but it is .040 overbore and I am going to put on a B&M 144 super charger and I am going to install 76cc 195in 160 ex valve heads as this is what the blower rebuilder told me to do was wondering if anyone can tell me what the preblower compression ratio might be with these heads and also want to know if any one wants my tbi heads off this motor I also have bothe a 4bbl and tbi intake to fit these heads if anyone is interested. thanks for anyhelp you might be able to give.

ME Leigh

No way to know without measuring. But i'd guess 8.0-8.5:1

Don't put 76cc chamber heads on it. 64cc heads would work better. This of course is assuming you have dished pistons in there.

AutoX86Z28

LOL wow this thread is old, ive already built 2 more motors since then, reminds me of how dumb i was when i was starting out

TWICEtheRICE

I don't think its worth it. The time you spend porting them out and unshrouding isn't worth it. You can't even port them out that much before grind into the pushrod guides. Its a lot of effort for smaller valves.

Now saving up for some real heads would be the ideal choice. I know how it feels wanting stuff asap, but if you wait and save you can get some 2.08/1.60 high compression heads and woop. Or just get vortec.

Jeffsblown305

ok the blower shop said the compression needs to be in the 7:1 or lower range thats why Iam going with 76cc you can run 8:1 with the blower but it will require race fuel and I dont race this thing I only take it to shows its a work in progress lol any way he said if I had flat tops to have the valves unshrouded and have the head opened up to 82cc so I can run more boost without detnation.

F-BIRD'88

Jeff: the blower shop is right. A compression ratio of 7/7.5:1 on a motor with a street supercharger, will allow the most (practical) boost with the least amount of ignition retard for the fuel octane used. ( less compression ratio+ less retard allows more boost on a specific fuel octane. = best practical street performance.

Adding a water injection system to the mix allows you to run more compression (8.5-9:1) with the same high boost a minimal ignition retard and make ven mor power.

The water inhibits detonation by absorbing excessiive heat and moderating the fuel burn rate. It also cools the temp of the air entering the motor when it vapourizes into steam.
the steam created also steam cleans the inside of your motor preventing and removing carbon buildup.

I'd be careful on how much and where I onshrouded the valves to open up the chambers size on those heads.
You do not want the head to be larger than the bore edge.
305's have small bores.

You'll have to remove the heads from the 305 and measure piston dish volume and piston to deck clearance at TDC to be able to calculate the compression ratio with a specific head volume. Anything else is just guessing.

When it comes to a supercharged motor , guessing will get you a busted motor every time.

In my opinion if I was going to run as much boost as a 7:1 compression ratio will allow, I would trear down the motor and increase the piston ring gaps some, especially the top ring gap. The extra ring gap is nessessary because of the extra heat created by the supercharged power.
Without the extra big ring gaps the rings will butt at WOT with high boost. ( resulting in a busted ring land) Most remanufactered motors are built with minimun ring gaps and piston to wall clearance, usually not enough for a hi- output hi boost supercharged motor.

How much boost are you planning on running?

Jeffsblown305

I was advised to run no more then 4-6psi I plan on running 2-4 this is mostly for show not go but I will lay out the specs for you since you sound like you got a good idea of what Iam trying to do

i decided to use my stock block instead of the 91 gm 305 truck block

87 305 stock bore stock rods stock pistons stock crank have not removed heads yet so dont know about them .
gm cam roller part # 14097395
duration 288/308
duration @ .50 196/206
max lift with 1.5 rockers 431/451
109 centerlobe
76cc chamber heads with only a three angle valve grind and swirl polished 195in 160 exh valves heads were already done.
was considering haveing a machine shop open them up to 82cc
am useing a rol extra thick hightemp head gasket for a 350
useinga mallery distributer and coil the big coil
rs45tc spark plugs and 1-5/8 tube headers 2-1/4 from headers to mufflers and 2-1/2 from mufflers out the back
like I said this is not a race car I only drive it to car shows

F-BIRD'88

At 4psi boost you'll be fine with a 8.5:1 +/- compression ratio. A 7:1 cr is required for 10psi or more.

don't bother opening up the heads. I would use a differnt cam. I would use a Lt4 hot cam for power. Or a factory corvette LT1 or LT4 cam for a good power/ smooth idle compromise. They both have moderate duration and blower friendly wide LSA. The cam you picked is a litle mild with the wrong LSA for a blower motor.

A blower motor likes 112+ LSA and some more duration the LT1 or LT4 cams are just the ticket. A LT4 hot cam would be best for power. ( roller)

if you limit the boost to 4-6 PSi the stock ring gaps will be fine.

I would run cooler champion RV8C spark plugs with the blower. They are the right plug for you. ( been there done that)

If you want to run a flat tappet hyd cam, a Crane #113801 is just right for a street blown 305. (again been there done that)

Blown motors like lots of initial ignition advance but limited total advance. Depending on the boost you want about 26-30 degrees total advance at high RPM WOT. this requires limiting the advance travel. A blower motor like vacuum advance too but requires the vacuum advance to be custon tailered to the blown engins needs. lots of vac advance when there is no manifold boost pressure ( intake manifold vacuum), quickly falling off to no vacuum advance once the boost comes in. ( Crane adjustable vacuum can)

F-BIRD'88

This is a very rough ball park gestimate of your compression ratio.

stock bore stock stroke 305
stock deck height .025"
flat top pistons -5cc valve reliefs (4)
350 felpro .039" gasket
76cc heads
the cr would be 7.63:1 good for 8-10+ psi boost (92 octane)

64 cc head your cr would be 8.60:1 good for 4 to 8 psi (92 octane)

58cc head your cr would be 9.2:1 good for up to 4 PSI (92 octane)

ME Leigh

I'm betting it has 10cc dishes.

Jeffsblown305

Thank you firebird 88

I found after reading the book on the 91 305 that it is a 9:1 comp with the 58cc heads 190hp that are on it now and that contray to what I was told it is not a roller cam motor it is a flat tappet I tore the motor down this afternoon and found it to be in really good shape rods are tight cylinders show very little wear but the valves in the 58cc heads are really small I am going to get the block # to verify what the book said as this came out of an 87 chevy van but is a gm new 305 in 91 and the heads on it casting # says they are 91 305 tbi heads it had a tbi intake but one thing I noticed was the harmonic balancer is the smaller 350 version makes me wonder if someone didnt put 305 heads on a 350 block I will know once I run the block codes and will let you know
as far as my stock 87 enginge goes the book says it is a 305 8.6:1 comp with 58cc heads 150 hp and I have tore it down and put in new rings and bearings and did a valve job but otherwise is stock but it has been 6years since the teardown and about 30K miles or less as I said before it doesnt get driven much. I just dont remeber what pistons it had so will have to remove the heads and find out . thank you

Jeffsblown305

well I got this cam cheap only paid $80.00 for it and since I already have it well you know

F-BIRD'88

Ya know what they say "Cheap, good pick one"

You could always sell it to someone else ( cheap) and get a better one (cheap).

Jeffsblown305

yes true I could I found a zz4 cam on ebay for 139 I think thats a good price will it work for me ? I am considering for now any ways just puting on the new heads and runing the car and rebuilding the other engine the one with the 91 heads witch after runing the block # I found out is an 1985 year still dont know if is 350 or 305 will find out tomarrow when gm's tech gets back with me