FireInMe17

What is the 305 piston dish for a 1987 305 TPI engine? I'm trying to figure out my compression for a 305 with 64cc 906 Vortec heads and I can't find the piston dish specs anywhere and its driving me crazy because until I do I can't calculate it. So does any one know? I found stock OEM replacement pistons online with a 10cc dish but I don't know if its the same for my pistons.

Sonix

iTrader: (1)

I want to say they are 12cc's, but i'm not 100% sure.
Factory CR was 9.3:1 for 1987
https://www.thirdgen.org/1987-chevy-camaro
knowing the heads are 58cc, you could work backwards to determine the piston dish. Your end result CR would be ~8.8 or something right?

If you don't have the heads yet, what about looking for 305 Vortec heads? I believe the main (only?) difference is that the chambers are smaller. They are likely to be in less demand, and therefore cheaper.

Guest

Old 416s were 58 cc, but not 081s. The number I keep seeing for them is 55 cc.
Unless you're going to change pistons, the heads need to be milled.

FireInMe17

Well I already have the 906 vortec heads and the reason I went with the 906 heads is because I got a brand new set off a never fired crate motor for $200. Plus the 350 vortec heads flow better and have better combustion properties than the 305 vortec heads do, at least from what I hear. I guess I'll just have to find one flat top pistons with smaller valve relievesin them to up my compression. What do you guys think I should go with?

Guest

You're at the point where it's better to get a used 350. Putting new flat-tops will cost about the same as my local salvage yards ask for the typical 350.
Putting your Vortecs on one of those will put you around 9.1:1, if it has the common dished pistons.
But why not just get your Vortecs milled? At this point, it's your cheapest and easiest option, assuming you've already bought a matching intake manifold. So you drop to 8.9:1, not a big deal. You can then run regular unleaded.

FireInMe17

Originally I was going to just get a 350, but I couldn't find any around here with anything less than 200K miles or needing a complete rebuild. Then I found a 305 with 120K that ran good that was a complete engine and I just bought that.

And now I kinda like the idea of having a 5.0 instead of a 5.7 so I can put Vortecs on a 305, make it look mostly stock, and still whoop *** against a 350 car. From what I've read(And I've read a lot....) the problem with the 305 not being a powerhouse is pretty much the valvetrain. Almost every one that I've talked to said that you can really wake up a 305 with a better cam and an actually decent valvetrain in it. The heads are just the start of this. Vortecs are good for around 30% more hp and tq from what I've seen. On a 305 that puts out 200hp stock, thats 260hp right off the bat, IF I can keep similar compression. Then there comes 1.6 roller rockers to complete the roller block and roller cam in the engine. Then I add a 191 intake 196 exhaust cam to wake it up even more. Add 24 ilb injectors that I have for it, do a little bit of tuning to make them work with the larger cam and Vortecs and that will boost the power even from there. Then, you add my 3" headers and full 3" Flowmaster American thunder exhaust to free up even more power by allowing it to exhale in the same way that the Vortecs let it breath. Speaking of breathing, I'm going to port and polish the entire intake and heads to make it breath even better.

This is pretty simple stuff, I just have to keep good compression to make it all work correctly. I'm hoping for 300hp and 400 ft/ilbs out of it, and I think that I can do it considering that it makes 200hp and 300 ft/ilbs stock.

If I get 6cc dished pistons, that will give me 9.2:1 compression which wont be noticable at all. OR, If I mill the block down to 0.016" deck height, I will get the same. If I zero deck it, I get 9.7:1. But I don't know how thats going to affect my valve clearances.

Curious_George

I just tore apart my '87 305. I have not taken out the pistons yet, but they "look" to be about 10cc dish pistons. this particular motor had the metal shim head gasket... so if you plug my numbers into a compression calculator, I get @ 9.3:1 compression. If I change my numbers to include 64cc heads, the compression drops to @ 8.7:1

CG

FireInMe17

What head gaskets are you using in your calculation?

Curious_George

In this case 0.015, which is what I took off of it (steel shim head gasket from the factory). A lot of people use them for rebuilds and have had good luck with them.

CG

FireInMe17

Ok those are the same ones I'm going to use, the fel pro 1094 0.015" 4.100" head gaskets

Curious_George

A few words of caution when building a motor... I just rebuilt a 350 for my '87 IROC to replace the tired 305, there are a lot of combination's of parts that will yield good result. There are also an equal combination of parts that will yield horrible results. Do your home work and don't regret your motor build by making bad decisions.

If you are intent on using those 64cc Vortec heads on the 305, then I would buy flat-top 4 ~ 6cc pistons. Do not deck the block, just have them hit it to make it perfectly flat and to clean it up. Make sure the pistons you buy have the same compression height as the OE pistons (1.560). A lot of replacement pistons are 1.540 (-0.020).

Also, if the heads have been shaved or milled, this will alter your valve train geometry and you may need different length pushrods, especially going with 1.6 rockers. You may or may not need anything different, but you do not know until you check all these things as you are putting the motor together. You cannot take anything for granted. You must check and measure as you go along.

CG

Guest

I'm not sure where you found 30%, but on an LB9 that's optimistic. Think more like 30 HP.
The cam you propose is smaller than the stock cam for an 87 LB9 / T5 combo, so no gain in HP from that, though it should help off-idle torque.
If you're dead set on rebuilding the engine, which is what you're doing if you decide on new pistons and a decking, then skip the cast pistons and at least go hypereutectic, like the Speed-Pro H534. KB has some, too.
Even still, have the heads milled. 0.030" is safe. And if the cam you choose doesn't close the intake valves any earlier than the '87 LB9 / T5 cam, then 9.7:1 would be fine. Vortecs with flattops and 0.035-0.040" quench makes for a very efficient chamber.
Vortecs have relatively poor exhaust ports, so choose a cam that has quire a bit of extra duration for the exhaust. If I was doing your build, I'd do the ZZ4 cam, no question. I wouldn't consider any other for what you're proposing.

FireInMe17

Then what's stock lift for what I have? I was told that anything near 200 lift would be too big for a 305 and I can't imagine anything bigger in it. Besides, I'm not making my 305 a screamer, I'm making it good for low to mid range torque. I should make max torque around 3000rpm and that's good.

Guest

Look, 191 / 196 is the duration. That sounds like the stock L31 cam, so the lift is around 0.415 / 0.430". The stock '87 LB9 / T5 cam is about a 202 / 207 duration, with similar lift.
My own LB9 experience was when I first got my '86 IROC-Z, but mine was automatic. I used a Comp 212/218-110, 0.440 / 0.454 cam in it, with a custom chip. And headers. That build was great from 2000-5000, though that cam with a carbureted 305 should pull 5500. TPI changes things.
I'm no expert in TPI cam selection, but there are people here who are very good.
You can run up to 0.480" lift with little hassle. Let the TPI guys here help you pick a cam, instead of whoever you've been listening to.

FireInMe17

Can I even use a ZZ4 cam without modding my heads? And if I'm going to do a ZZ4 and do the mods to make it work I might as well just do an LT4 hotcam.

Guest

Uh huh. I thought you wanted good lower-rpm torque?
I like the ZZ4, but it does have 0.510" exhaust lift. If that bothers you, then there's this : http://www.compcams.com/Company/CC/c...?csid=212&sb=2
But since you need to buy new springs anyway, you may as well just use the ZZ4, since it is 30% cheaper to start with. That'll cover the cost of the springs.

FireInMe17

Well the problem with the vortec heads is that they only accept up to .500 lift max from the research I've done. So while I would love to go .500"+ lift the vortecs won't take it unless I mod them.

Guest

I have a pair of Vortecs, mine only have 0.485" clearance between the seals and the retainers. But thats what the +0.050" locks are for. So you can gain clearance cheap, with no need to cut the guides. But with the offset locks, you then have to check a few other things. Do your rockers clear your springs and retainers? Do your rocker slots hit the studs?
The locks are about $15 for a new set. Even with these, the ZZ4 approach is still cheaper than the Comp 0.480" cam.

FireInMe17

Ok so the ZZ4 would be a pretty good cam for what I want with more lift than stock, and more power. What kind of compression should I be looking at for using it? If I get 6 cc pistons I will almost get my stock CR back of 9.3:1, if I get flat tops, I get 9.8:1. The higher the better, but I want to be able to use 87 octane gas and not worry about ping or detonation.

Plus, I don't know about valve clearances with using flat tops. I assume the valves won't open much into the cylinder, and I still have the deck height on top of the distance from the valves to the bottom of the heads to consider. I'm really in the dark with this kind of stuff, this is my first engine build so bear with me learning all this....

Curious_George

4 ~ 6cc ARE flat-top pistons. The valve cut-outs in the pistons are where the 4 ~ 6cc come into play. Depending on what brand piston you get, they will be in the 4 ~ 6cc range.

CG

FireInMe17

Yeah I know, the 10cc pistons I have right now are flat tops. When I say flat top 0cc, I mean completely flat, no valve relieves. But will that work? I dont mind spending another $250 or so to get good pistons that will give me back my compression to make this thing fly.

Guest

The more you type, the more you contradict yourself. We all want to have our cake and eat it too, but there are practical limits.
True flat-tops, forget it.
'87 octane?
Just get the Vortecs milled, and keep your dished pistons.
You're willing to spend an extra $250 on 305 pistons, but won't do a 350, and won't go for 93 octane? Contradictory.
If you want daily driveable fun, then put your money in a 350 to go under those Vortec heads.