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Old 08-11-2013, 06:44 PM
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Is this motor being built,or,is it off the shelf & you're just turnin yours in as a core?If already built,can you verify pistons & compression hgt,head gasket thickness?If it's an off the shelf rebuild,I would definitely verify these as these are things that will make or break your engine.Not to mention make you choose the wrong cam.

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Old 08-11-2013, 06:50 PM
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I was unaware of that, rear is out of a 95 6 speed z, guy I got it from told me 355s so I'm guessing they're 342s? I was thinking of going xe262 with 1.6 rockers but I know the stock heads don't flow well, I've never done any port work..
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Old 08-11-2013, 06:53 PM
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I just know silvolite flat tops, .28 gaskets...I'm guessing 9:5:1 cr...
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Old 08-11-2013, 06:59 PM
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L-31 Vortec heads on a 305.

The GM L-31 heads (062 or 906) work real good on a 305 w flat top pistons.
But you need to shave them down to 58-59cc and install with a thin .015" head gasket to get the cr right
on a 305.
Use a Vortec intake manifold. There are may cams with .460" or less valve lift that work on stock vortec heads.
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Old 08-11-2013, 07:22 PM
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Quote:
Originally Posted by deadbird101 View Post
I just know silvolite flat tops, .28 gaskets...I'm guessing 9:5:1 cr...
I would definitely ask the builder,becuz,IIRC,& sometimes I don't,the Silv-o-Lite's only come in a 1.54 compression hgt.If the block hasn't been decked any & they use a .028 gasket,your piston could be .073 in the hole.Even @ 0 deck,you'll be .048.
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Old 08-11-2013, 07:27 PM
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Quote:
Originally Posted by F-BIRD'88 View Post
Best check the axle ratio as a 3.55:1 ratio does not exist for the 7.5" rear.
factory for that car is 3.23. Optional is 3.73. Most are 3.23:1 (5 speed)

.

rear gears for most 80's 3rd gen f bodys are 3.23 and 3.42
don't remember 3.73 ever being offered until you got into the firehawk
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Old 08-11-2013, 07:30 PM
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Quote:
Originally Posted by deadbird101 View Post
I just know silvolite flat tops, .28 gaskets...I'm guessing 9:5:1 cr...
this exactly what I am getting at. "rebuilder" non stock 1.54" pin height results in a cr drop unless the block was decked .020"++ to correct that.

I get 9.28:1 (58cc head) they are usually bigger than that ( less compression ratio)

The XE262 cams need 10:1/10.50:1 cr compression and heads that flow. and gears
Full port 4416 1.94" valve or sweetened up vortecs

This is why people are disappointed when building a 305. They don't pay attention to the details and build a lame off spec motor.

The details matter. The smaller the CID the more critical the specs are.
Like piston deck height @ TDC

The 4416 heads can be flat milled to 52cc if nessessary.

The .015" shim head gasket for 350's works fine on 305's.
This will help.

it is cheaper to just buy the right 1.56" pin height flat top hyper 305 piston in the first place. +$ 30 upgrade

Don't expect much from a motor built off spec.

Last edited by F-BIRD'88; 08-11-2013 at 07:39 PM.
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Old 08-11-2013, 08:03 PM
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If keeping the 1.54" DH SL pistons:

You can fix this motor by measuing the assembled result and then tearing it down and remachining the block decks and the heads to new spec and using a felrpo #1094 .015" shim head gasket.
You would want a finished assembled piston deck clearance @ TDC of .025"
and a finished cylinder head chamber volume of 54cc .
The only way to know how much further correction machining is required to bring it to spec is to measure the assembled short block and CC and the heads
This will give you a 10.50:1cr with your SL pistons
The 305HO heads need full effort porting to get the intake and exhaust port flow up.
Fully hand port the 4416 heads to a felpro 1205 gasket and be generous streamlining and contouring deep in the ports around the guide bosses. raise the whole roof of the port and open up the pushrod pinch.
1205 gasket
just like my pictures show. add a 1.94" intake valve. A 1.55" exhaust valve is a option.

Heads will need guide boss height machining and pushrod slot lengthening in the head for 1.6 rockers.
Valve Springs must be up to the task. and need correct shim to installed height spec . as the valve lift will be over .500" w 1.6 rockers. crap $2 springs won't cut it.

A 750cfm carb makes more power than a 600cfm carb on this motor.

I recomend using Molyslip Canada Inc. :: Molybdenum Lubricants, Performance Lubricants, Copaslip Anti-Seize, EP2 Grease, Wear Reducing Lubricants, Oil Additive in the oil for this cam.

Champion RV8C plugs 34-36deg timing @ max advance.

Now it is XE262H-10 cam w/1.60 rocker ready and runs on 92+ octane gas.

now you will have a decent highPerf 305 HO 4.10 gears and the 5 speed manual trans is just right.
Needs good exhaust system long tube headers ans some sticky tires.

On every thing that you guess at and don't bother checking for your self, deduct 10 horsepower.
Lighten the car weight: It is free horsepower. If it don't make it go , stop or steer, consider removing it.

Last edited by F-BIRD'88; 08-11-2013 at 08:24 PM.
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Old 08-11-2013, 08:48 PM
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Use premimum genuine GM hyd lifters with the hard steel alloy foot.
They are the best there is .
Reduce spring pressure and rocker ratio for engine cam run in. Then install high perf springs and shim to spec.
The exhaust spring seats are deeper than the intakes on these heads.
Then add the 1.6 rockers.
Don;t forget the Moly di sulfide paste on the cam lobes and the Molyslip E in your oil.

The Molyslip E has both Moly and Zinc in it. (Read the MSDS pdf) It has been saving high perf cams/lifters and reducing engine wear for 40+years. In the USA it is refered to as MR. Moly.
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Old 08-11-2013, 09:07 PM
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here is your cr math to end up wiht a 10.50:1 cr using those SL pistons
87 octane gas will not work.
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  #26 (permalink)  
Old 08-12-2013, 07:06 AM
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O/P
is your 305 roller compatible block?
not sure if the 86 was or not.. maybe someone (F-BIRD88) CAN TELL YOU ,if so I'd run a roller as it's cheaper to save now than to loose a lobe..

the 85/86 305ho with carb has a blower motor and duct work to blow on the carb to keep vapor lock/boiling the fuel at bay.. make sure you have this.. as the cars engine bay is cramped and even the hood with 4 vents(two at nose and two at back sides) don't help enough when parked..
my 86 when the relay went would take forever to start because the fuel boiled out..
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Old 08-12-2013, 07:12 AM
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I have a 4 inch cowl hood for it, and the a/c is all gone, will I still need it? Would I have to do the same ammpunt of head work for the xe256? How much would the vortec heads have to be milled?
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Old 08-12-2013, 07:48 AM
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Quote:
Originally Posted by deadbird101 View Post
I have a 4 inch cowl hood for it, and the a/c is all gone, will I still need it?
no,
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