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305 sbc questions

General engine tech -- Drag Racing to Circle Track

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rfoll
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305 sbc questions

Post by rfoll » Wed Oct 30, 2019 9:07 pm

I pulled the 305 out of my 84 El Camino because something funny and as yet un-determined was going on. The engine has only 100K and the bores appear to be perfect. As is usual for engines of this vintage, it has the quenchless dished pistons. I'm thinking of upgrading to these..https://www.summitracing.com/parts/slp- ... /chevrolet Flat top pistons.They weigh 616 grams with the pin. In theory the compression would come out to something like 8.8:1 with the 416 heads. I have 2 questions. Will a set of the powdered metal rods form a Vortec 350 work ok with the new pistons? the 305 rods look rather spindly. Also, will I have problems with sealing the heads with a .015" steel shim head gasket without surfacing the block and heads. I usually clean them with 80 grit on my long board. The deck is currently .030" on one side, and .035" on the other.
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F-BIRD'88
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Re: 305 sbc questions

Post by F-BIRD'88 » Thu Oct 31, 2019 2:04 am

I'm getting 9.6-9.7 cr. 58cc heads.
Plan on balancing the crank with both those changes.

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Re: 305 sbc questions

Post by rfoll » Thu Oct 31, 2019 9:35 am

The federal mogul website says 8.84:1 for a standard bore piston and a 58 cc head. Their calculations tend to be high. I plan to cc the current deck to see where I am currently. If the flat top ratio comes out too high, I can always use a 64 cc chamber.
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Re: 305 sbc questions

Post by F-BIRD'88 » Thu Oct 31, 2019 10:35 am

Learn how to calculate cr yourself or use a app.

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Re: 305 sbc questions

Post by BillK » Thu Oct 31, 2019 10:46 am

The PM rods will work fine, they went to them in the later 305's anyway. If you really want to wake it up put a 400 crank in it and it becomes a 330 or so. I did one of those in an 85 or 85 Trans Am. That thing really ran good.
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rfoll
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Re: 305 sbc questions

Post by rfoll » Thu Oct 31, 2019 11:25 am

F-BIRD'88 wrote:
Thu Oct 31, 2019 10:35 am
Learn how to calculate cr yourself or use a app.
I've had a 50 cc burette for about 40 years. It's going to get those pistons, and I'll manipulate the volumes to get my desired CR. A 64 cc chamber will drop the cr by 1/2 point if necessary.
PICT0006.JPG
When your piston looks like this, a change is in order.
You do not have the required permissions to view the files attached to this post.
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Re: 305 sbc questions

Post by F-BIRD'88 » Thu Oct 31, 2019 12:04 pm

You need to verify the pin height on those.
Some say 1.56" but are 1.54".

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Re: 305 sbc questions

Post by rfoll » Thu Oct 31, 2019 5:04 pm

Here's a real shocker, I measured the deck at tdc with the stock dished piston and got 20 CCs. With a 3 CC steel shim gasket volume and a 58 CC chamber the static comes out to 8.8:1. This is the first time I have ever measured a factory engine and got more than the advertised ratio. A quick estimate for a flat top does indeed come up to about 9.7.
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Re: 305 sbc questions

Post by Schurkey » Fri Nov 01, 2019 12:58 am

rfoll wrote:
Wed Oct 30, 2019 9:07 pm
will I have problems with sealing the heads with a .015" steel shim head gasket without surfacing the block and heads. I usually clean them with 80 grit on my long board. The deck is currently .030" on one side, and .035" on the other.
"80 grit" and "steel shim gasket" are not things that I'd expect to play well together.

Steel shim gaskets are typically recommended with "Flat" and "Smooth" gasket surfaces. The Fel-Pros have a rubberized coating, though, and I don't know how that affects their sealing on a rough surface.

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Re: 305 sbc questions

Post by F-BIRD'88 » Fri Nov 01, 2019 8:44 am

Get the heads shaved .005" ....If the heads are flat then the block decks are not as critical.
It will seal. Install gasket on clean dry surfaces.
Re torque head bolts after fire up.
The GMPP head bolts are good for this.
Smaller hex

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Re: 305 sbc questions

Post by rfoll » Fri Nov 01, 2019 9:12 am

Schurkey wrote:
Fri Nov 01, 2019 12:58 am
rfoll wrote:
Wed Oct 30, 2019 9:07 pm
will I have problems with sealing the heads with a .015" steel shim head gasket without surfacing the block and heads. I usually clean them with 80 grit on my long board. The deck is currently .030" on one side, and .035" on the other.
"80 grit" and "steel shim gasket" are not things that I'd expect to play well together.

Steel shim gaskets are typically recommended with "Flat" and "Smooth" gasket surfaces. The Fel-Pros have a rubberized coating, though, and I don't know how that affects their sealing on a rough surface.
I like the 80 grit to remove the old gasket material and rust from the water jacket holes. It will be easy enough to go over it with a 180 or something finer once the surface debris is gone. This is a very low mile engine and all surfaces are in very good shape. This isn't going to be a racer, I'm going to squeeze a little more torque and fuel economy out of it. I got as much as 19.7 mpg with a 3.08 rear gear, and I know I can get more. All of the engines I have rebuilt for fuel economy have seen significant improvements in power.
So much to do, so little time...

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Re: 305 sbc questions

Post by rfoll » Fri Nov 01, 2019 9:24 am

F-BIRD'88 wrote:
Fri Nov 01, 2019 8:44 am
Get the heads shaved .005" ....If the heads are flat then the block decks are not as critical.
It will seal. Install gasket on clean dry surfaces.
Re torque head bolts after fire up.
The GMPP head bolts are good for this.
Smaller hex
I actually have a set of these. What is so special about them? I usually use Permatex High-Temperature Thread Sealant 59235. on my head bolts, and I have noticed it hardens up some after it sees heat. That would make any re-torque readings inconsistent.
So much to do, so little time...

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Re: 305 sbc questions

Post by F-BIRD'88 » Fri Nov 01, 2019 9:33 am

Smaller hex head allow socket to go between rockers to retire without removing rockers.

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Re: 305 sbc questions

Post by Orr89rocz » Fri Nov 01, 2019 1:24 pm

I believe gm performance makes a .028” composite gasket with a 4” bore that might work instead of a shim. I’ve used it on a stock 350 deck with afr heads

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Re: 305 sbc questions

Post by turbo camino » Fri Nov 01, 2019 1:33 pm

DON'T PANIC

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