bspencer18

before I shelled out money for a 350, I want to mod my 305 as much as possible (86 Camaro Z28, 4 barrel holley carb 650cfm). Would adding a carb'd intake manifold, shorty headers, and possibly new heads be all? Suggestions Please.

Also if I just did the intake and headers should the heads be done as well?

Night rider327

iTrader: (13)

I don't think it's money well spent going into a 305 too deep, but if you use parts that can wk on both a 305 and a 350 then when it comes time to do a 350 swap you will be ahead of the game as you will already have some good parts to work with.

I would go with 1996-00 chevy truck L31 350 vortec heads. The vortec heads will drop your compression alittle now (from 9.5 to 9.0) , but they flow great and will make power on the 305 and 350.

Fel pro 1094 head gaskets.

Vortec intake like the edelbrock performer or performer rpm or summit stage I or stage III.

Hedman long tube headers, or hooker shorty headers. 1-5/8" tubes, 3" coll.
Aftermarket Y pipe, etc.

Drive it like that for awhile while you build your suspension up and get a 350 to rebuild.

Don't waste money on a cam swap, pistons, etc for the 305.. All of the above parts will swap over and work well with a 350 later on

sofakingdom

iTrader: (1)

Headers, yes definitely. Along with every other piece all the way to the street. But NOT for 86 Z28 LG4; get the headers, cat, & cat-back for something like 89 Z28 350.

Wouldn't bother with heads or intake on a 305.

fireburdluvr85

Instead of just the heads why not get the whole engine? 96-01 vortec 350's are a good base to work with.

86LG4Bird

iTrader: (1)

^THIS^

ex-x-fire

Yep, a roller cam is a nice upgrade.

sofakingdom

iTrader: (1)

All else is null and void while that exhaust is on there.

That's GOTTA GO, first.

Leave the 305 alone. Abandon it. No heads, no cam, no intake, no ... nothing. Straight into the trash.

I agree with the 96-up 350 suggestion; AFTER exhaust.

bspencer18

Ok so for now this is what Im going to upgrade:

Dynomax Super Exhaust System
Cyclone Intake Manifold
Flowtech Headers
Flowtech Catalytic Converter Y-Pipe
Get 373 gears put into current Rear End
New front end, replace all shocks & springs
New stock heads

Not all at once, few things here and there, this is my daily driver for now and just want it to be fun to drive daily driver

dmccain

iTrader: (2)

New stock heads? And what heads do you have in mind?

bspencer18

Should I rebuild the ones I have?

86LG4Bird

iTrader: (1)

What's wrong with them?
The most I would do to a set of stock heads is replace the valvestem seals if it's smoking on startup and decel.
Don't even think about "rebuilding" them.
Good advice in this thread. Read it.

bspencer18

Vortec, off of 96-01 gmc/chevy

bspencer18

No smoking, was thinking maybe vortec heads eventually, and like you mentioned replace valve stems, clean injectors, and new gaskets.

Night rider327

iTrader: (13)

Yes to the vortec heads.

The way you worded the "new stock heads" sounded like you was going to buy rebuilt 305 heads.

Nobody really calls the vortec heads "stock".

Be sure it's the L31 5700, 5.7L 350 vortec heads from 1996-00 chevy/gmc full size truck, van, suv. The last 3 digits of casting numbers will be 062 or 906.

A lot of people don't know what they have or try to coan people. I seen MANY listings for 1980's TBI 350 truck heads (swirl port heads) listed as "vortec" heads.
Also GM did have a 305 "vortec" head out for awhile.. You do not want that one.

fireburdluvr85

Won't vortec heads have have valve clearance issues on a 305 and drop compression?

86LG4Bird

iTrader: (1)

There will be no valve clearance issue with stock Vortec valve sizes.
The drop in compression will be more than compensated by the better flow and consequently better cylinder filling, as long as you stay with a smallish cam.

MoJoe

iTrader: (5)

Lots of good advice so far. And I'll add my $.02...

Looks for upgrades that will work on whichever engine is in the car... headers, y-pipe, cat back, rear axle/gears.

A mild cam upgrade is fairly cheap and will provide a mild increase over factory. I did a Crane CompuCam on my 84 LG4 almost 20 years ago, and was pleased with the result. As a Daily Driver, along with the 3.73 rear gear, this little bit of power increase may be enough for your needs.

If you want to go bigger, a Vortec 350 take-out long block will likely be your most economical upgrade. The added bonus is this will upgrade you to a roller cam. While it is on the stand, add an LT1-ish cam (LT4 cam needs head work), dual plane carb intake for Vortec heads, flexplate for 1-piece RMS crank (if the engine doesn't come with one, or wrong one...168vs152 tooth).

MoJoe

iTrader: (5)

BTW, If you are shopping for Vortec parts, this would go nicely on a Vortec 350...

https://www.thirdgen.org/forums/engi...2464340-a.html

sofakingdom

iTrader: (1)

I think the key to this is contained in this comment...

While I completely agree with Joe, and in fact did certain things myself 20 years ago (and 30 and 40 and...), that's different from TODAY.

Times have changed. The competition has changed. Parts availability has changed. The relative value of various things (i.e. relationship of price to benefit derived from them) has changed. In short, there's ALOT of things I did "back in the day", that I would NOT do today.

In fact, for all the small block and big block Chevy motors I have built over the years, I doubt that I will ever again build either, with rare exceptions.

The other options that are out there now, are just WAY TOO MUCH better.

Don't waste time, money, or mental effort on a 305. Doesn't matter what you do; you'll get your a$$ kicked. Not a way to enjoy this hobby. It's bad enough with a 350. ANY 350. But a 305... {sofa just shakes his head} My last rent-a-mule was a Kia Optima. I'll be that pitiful thing would drill 95% or more of the cars on this forum so hard it wouldn't even look like a race.

Times have changed.

I'm sure all the people with flathead Frods woulda posted a lot of the same stuff you see here, if only Algore had invented the Intewebz at the time the SBC was knocking all their d***s in the dirt back in the late 50s / early 60s. I missed that though; I got into the hobby about the time the 327 was doing that to all the 283s. Then I got my a$$ handed to me repeatedly by 350s doing it to all my 350s.

I like to think I learned the lesson early on: which is, don't let your sentimental fondness for what you're familiar with, get in the way of common sense.

MoJoe

iTrader: (5)

Sofa, you make good points, if all-out-performance is the (leading) goal. In my case, if I wanted to enter the arms race, I would have gone down the LS swap path instead of the L31 I got. An LS swap is appealing, but too much $$ and hassle. A 383, while nicer (bigger) than a 350, does inflate the budget.
There are still people building flat-heads, 283s and dare I say 305s, and enjoying the hell out of them.

With this is mind, an 11:1 383 that idles at 1200rpm, winds to 8000 to post 500hp, but gets 8mpg is probably not Spencer's idea of a fun daily driver. But, that is where these arguments lead: ditch the 305 for a 350. If you're going to build a 350, then a 383 isn't much more$$. You need to get the best heads. Etc. At what point short of a ProStock engine is it OK to stop?

OP is doing a lot of smart things: freshening the steering and suspension, and replacing the exhaust... all beneficial regardless of the engine.
Maybe an engine swap is too daunting. Maybe he wants a bit of DIY. Maybe he wants to open the engine. Maybe after all of the above $$$, his budget only has enough for a cam and intake on the engine. Maybe that IS good enough for Spencer.

big hammer

vortecs are good heads and flow decent. but there is an issue with putting them on a 305. compression ratio. yes, they lower the static compression ratio some. but when you add a mild performance cam your dynamic compression ratio slips even further. and that's the number that really counts. you can run 8.4-8.6 dynamic compression on pump gas.

now say vortec heads lower your static compression ratio to 9:1.

then you add a mild performance cam, say 210\218 @ .050 with an intake closing point of 59*. not a large cam by any means.

now your static compression ratio is 7.2:1. this is really low and will affect performance.

then say you have a +.020 deck height, (which is likely) 10? cc stock pistons, 3.9", .030 compressed headgaskets, and the vortecs 64 cc chambers, you're now at 8.4:1 compression.

if your actual static compression is down to 8.4, now your dynamic compression is 6.7:1. and she will be lazy.


a 8:1 DCR should be a nice, safe place to be for you with cast heads and 91 octane.

Night rider327

iTrader: (13)

Vortec heads (stock 062 and 906) are reported as 64cc chambers, But I have measured at least a dozen now and all came in at 62 to 63cc.

I thought they was 64cc as well about 6-7 years ago and someone on another board told me pretty much what I just said, so I grabbed a pair and CCed them. Then over the last 5 years, ever set I have had for mine or my customer builds I CC just to see.

If the 62-63cc is still too much for your 305, then have the machine shop mill .028" to .032" off them and that will put you in the 58/59cc range. Machine shop don't charge that much. The shop I use for machining charges $56 per head

Orr89RocZ

iTrader: (20)

Yup just mill them

big hammer

You'll have to mill them a lot to get your DCR back up after adding any kind of a cam to it.

Night rider327

iTrader: (13)

Big Hammer.... I don't see why.. How is under .035" milling A LOT?
DCR is based on SCR and cam size.

Use what you said above but put the right 4.100 x .015" head gaskets, .025" in the hole, 64cc vortec heads, 10cc dish pistons.

I get 8.648 SCR
Now like I said every set I CC'ed as been 62/63cc, so spit the diff, 62.5 cc

8.791 SCR

Using your 210/218@.050 spec cam.. I get
7.580 DCR

Flat mill .006" to .007" = 1cc.. So using the 62.5cc figure from above.. Mill .024" to .028" and you end up with a 58.5cc chamber

This brings the DCR with that 210/218* cam up to 7.926

Go ahead and take .006" more from the head and you got your magic 8.018 DCR and a 9.309 SCR

So to sum it up Mill heads down to 57.5cc which is around .030" to .035" cut and you are where you need to be based on the info you gave above.

big hammer

You are right, you were getting what I meant. You shouldn't just be slapping vortecs on a 305 without addressing the compression issue properly. This is how we end up with lazy 305's everywhere.

And that cam is still a small choice. You can see how a larger one would be detrimental to the DCR on a 305.

I'm not sure you could go to a moderate cam like a 218/228 without taking additional steps to keep your DCR up. But if you did it right that would be a nice performing 305 instead of another lazy one.

DynoDave43

iTrader: (11)

big hammer, and others...all this talk about SCR and DCR loss with Vortec heads on a 305....does this all assume 350 (L31) Vortec heads on a 305, and not 305 (L30) Vortec heads on a 305?

Bigfoottpi11

this: http://www.hioutput.com/tech/400hp/400hp.html

big hammer

That's correct. Most guys use the 1.94 valve, 64cc Vortec head.

Night rider327

iTrader: (13)

Yes, that is correct. The L31 350 vortec heads are 62-64cc.
The L31 vortec heads are much easier to find than the L30 305 vortec heads and also flows better..

The issues is the small bore size of the 305 needs small cc chamber heads to make compression.

The 9:1 and 9.5:1 305s uses 58cc heads to get that compression, L31 vortec heads are 62-64cc. That works good on a 350 but drops the compression on a 305

Most 350's stock from the 70's and 80's uses 72-78cc heads, so the swap to a 62-64cc head bumps up compression on those stock engines

Night rider327

iTrader: (13)

Right.. I know people do it, but i do tend to forget at times that a lot of people just slap what ever parts together with out knowing the specs and figuring how how to make X work best.

DynoDave43

iTrader: (11)

Thanks for the replies, guys.

My last question...don't want to take the OP too far off topic. From what I can find, the valve sizes are the same between L30/31. Is it the combustion chamber shape, or port configurations that account for the flow differences?

big hammer

Vortec 305 heads have smaller valves.

Night rider327

iTrader: (13)

Quite a few differences in the two really. Valve size is not the be all end all when it comes to vortec heads, but the L30 heads do have smaller valves.

1.84" intake valve vs. 1.94" for the L31
The L30 heads are 160cc intake port, where the L31 is 170cc port

The chamber is where a lot of difference is. The L31 heads are a true fast burn style thats kidney shaped.

The L30 heads are more like an older bowl chamber with a "bump in" in the center. Sort of like the swirl port head chamber. The spark plug was moved more to the center and toward the exhaust though.

Here's the L31 chamber
http://www.crankshaftcoalition.com/w...at_vortec1.jpg

Here's the L30 305 vortec head chamber
http://www.crankshaftcoalition.com/w...BER_CN_059.jpg

DynoDave43

iTrader: (11)

Thanks Night rider327. I had heard the combustion chamber shapes were different, but had not seen them.

I've seen enough cataloging errors over the years not to be surprised by this, but I was assuming the L30/31 valve sizes were the same based on these:

http://www.jegs.com/p/Chevrolet-Perf...32025/10002/-1

http://www.jegs.com/p/Chevrolet-Perf...14064/10002/-1

Forgetting the relative merits of building a 305/L03, if a fellow had an opportunity to buy some L30 heads Vs. L31s....

L30: Proper alignment of chamber and bore. Smaller chamber maintains good compression. Improved flow over stock 305 swirl port heads.

L31: Bigger valves, better chamber shape, larger intake port = better flow. Larger chamber lowers compression. Chamber slightly bigger than bore.

On an L03 base, say with shorty headers or TPI manifolds, and a GMPP TBI intake and proper tune....which head would be better? Or would there likely be little difference in this application?

big hammer

depends. what cam are you thinking about going with?

DynoDave43

iTrader: (11)

Good question. Still formulating a plan in my head for what I'd like to do.

I know the next time I go to the strip, I'd like NOT to run 16.5s again!

Actually, it ran just what I expected, so no great surprise. And it's my third L03, so I'm not disappointed. I knew what I was buying. But I would like to improve.

It will say TBI, so anywhere from L98 levels of power, or a little more? 220 - 250ish? A stock L30 makes 220, so I think it's doable.

So I'm kind of guesstimating somewhere between stock "peanut" cam, to LT1 - LT4 type.

dmccain

iTrader: (2)

It would be easy with said head swap, mild cam,headers and 3in exhaust to push 230-250hp. A set of 342 or 373 gears and that 16.5 time would drop into mid or upper 14 sec times easily. Every 305 ive ever owned ran in the 14s without much work and my 91 z28 done it completely stock. DynoDave your car is awesome even if it does run 16s. Clean Clean!

DynoDave43

iTrader: (11)

Somewhere in the 14s would be a lot of fun. I guess I've got some parts collecting to do in the coming years. Big winter swap meet coming up in January!

And thank you for the compliment. It's been a lot of fun to own so far. Turns the most mundane of errands into a fun trip.