I hope somebody can answer this question before I go to the trouble of swapping the heads. Right now I have a 350 engine with 305 heads (casting #14101081). These heads have 1.84 intake, 1.5001 exhaust and 58cc. I bought the car with this setup and have checked the block casting number to verify that it is a 350. The mods I have done to this car include headers, accel distributor, and an Edelbrock 600cfm carb. I have a set of 350 heads (casting #333882). These heads have 1.94 intake, 1.5 exhaust and 76 cc. From reading all the other posts, I know these aren't the best heads I could get, but wanted to know if they are worth swapping for the 305's? I have not pulled the heads to see what kind of pistons are in it, but I assume they are stock pistons. So I am not certain what my current compression ratio is. I do run 87 octane gas with no detonation. Thanks for any help!

well, if your 305 heads were machined out for 1.94 intakes, unshrouded, and pocket ported i think you would be good to go. with the set up you have now, i would put the 350 heads on and save yourself some money for the machine work.
the runners on 305 heads don't flow as good as 350 ones would, though.

now on the other hand, you might be killing your compression. my setup has a total of 74cc's INCLUDING the 12cc dished pistons with a deck height of .035 which brings me around 9.8:1 CR. basically, you need to find out what your compression is. remember, a bigger bore means LESS compression.

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87 iroc-z 355 TPI 5 spd. 51006 SLP cam adv. 4* (106.5* centerline)
hypertech stage II chip/ 160* stat./ Airfoil, accel AFPR
19# injectors, ported plenum and runners. 9.8:1 compression
stock heads, pocket ported, 1.94 int., unshrouded.
stock exhaust manifolds and y pipe! hopefully soon to change
3.45 rear (stock)
Flowmaster, K&N w/ hacked airbox/removed MAF screens
14.38@100mph 2.2 60'

The 882 heads use perimiter-bolt valve covers and all 6 intake bolts at the same angle. They may or may not fit your car without dealing with those things.

They have 76cc chambers, which will make your CR take a major nosedive. Also, they are one of the main reasons why 350s in the 70s had 185 HP. You don't want those on your car.

My advice would be to keep driving what you've got now if it works, and keep looking for something else. Doing all that work to swap the parts you've got is a whole lot of maze with very little cheese at the end.

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"So many Mustangs, so little time..."
ICON Motorsports

305 heads (casting #14101081).
Im not sure that those heads are 58cc.
last 3 numbers on my 58cc "601"
i think that they are 64cc.
But unless you have trouble with spark knock keep the heads that you are running now. these 58 or 64cc heads can take 194 vales but most machine shops dont recomend cutting in that deep.

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85 Camaro RS T tops 350/350, stealth intake. holley street avenger 670. ported 58cc heads. comp magnum 270H cam,Crane 1.6 roller rockers,edelbrock accu-drive, MSD 6 series ignition on HEI, K&N extream air cleaner, true dual exhaust with 18 inch glasspacks.
82 Firebird 305/250 action plus intake, accel distributer with ccs 8mm wires foam air filter.
The only "cat" i have uses the litter box

355 IROC Z-
I'm not sure what you were referring to by "a bigger bore means less compression". Did you mean a bigger chamber in the head? Just changing to a larger cylinder bore with the chamber size being constant will always yield more compression, not less.

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'93 2wd truck
408 sb, vortecs, 454 TBI, Comp Cam, dual exhaust

I've done a lot of research on 305's because that is what I have. The biggest problem with the heads is what 355 Iroc said. they don't flow very well. In fact, if you look at a dyno sheet for a stock 305, even if the engine can rev higher, the HP takes a nose dive past 4500 rpm's. Basicly, the engine is starved because it can't fill the chambers fast enough and the loss of power. It may even be worse on a 350 but i've never seen a dyno sheet for one so i don't know. Granted the 76cc 350 heads won't help any and i would stick to the 305's for now also. But they would flow better above 5 grand. Porting the 305's would help some but you can't go to far with them because you will hit a water jacket. If you were dead set for the 305 heads(and it doesn't sound like you are) i would get the world SR heads(thats in the future for my 305) Anyways thats my .02 cents. Laters

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89 RS Conv 305 700R4
85HO heads
Edelbrock intake
Holley 600
Hedman Hedders and Y pipe
Flowmaster
B&M MegaShifter

[This message has been edited by Chvywolf (edited March 25, 2001).]

stick with 305 heads.

ODB

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*I do custom performance mods on Edlebrock Performer carburetors (dualplane intake mods in the works),
White 1986 Irocz, 305 with iron #416 heads,
383 with aluminum TFS heads,
Edlebrock Performer-RPM intake and Performer #1407 carburetor, +110hp shot of crack, 700R-4 tranny, Vigilante 2400 lockup converter, 3.25:1 Ford 9" rear, Mcreary Road-Stars, SLP-stainless 1.75" shortie headers & Y-pipe, single 3" Borla exhaust, Linginfelter-TPI camshaft part number 74216 pulls 17" vacuum solid. Cam specs 213/219 @.050 114-LSA, sometimes advertised at 216/219 @.050 112-LSA .462/.470 lift @1.5:1 ratio. Using Harland Sharp 1.65:1 roller rockers. MSD-6AL, billet distributor, multi-retard, blaster-3 coil, and RPM switch. SouthSide machine subframe connectors, SSM lift-bars, Moroso 4" underdrive crank pulley.

N/A runs 10.9 @124,
Crack-runs 10.3 @135
haven't run at track since Oct-99
* vizit miy homepayge * http://www.geocities.com/trailerparkpage/

Thanks to everyone for the replies to this question! I think for the time being I will stick with the 305 heads, and keep looking for another set of 350's.

Thanks again!

SCRA, get out the calculator and tell me what you come up with

i run 305 heads myself and have done everything that i mentioned in my previous post. they work for me.

I know it's been awhile since this post was current, but I ran across it and will show that a bigger bore does mean more compression when chamber volume is constant. I will simplify a few things for math sake, but the principle is the same.

Some assumptions:
1. Zero deck height.
2. Chamber volume=64 cc
3. Flat top pistons with no valve reliefs.
4. Head gasket thickness=.040 in, also same size as cylinder bore.
5. Stroke constant for both engines.
6. CC's=cubic inches x 16.387

Compression ratio=(swept volume + deck height(0) + head gasket volume + chamber cc(64) + piston domes or dishes(none)) / (deck height(0) + head gasket volume + chamber cc(64) + piston domes or dishes(none))

FIRST ENGINE=4" bore, 3.5" stroke:
1. Swept volume=4.00 X 4.00 X 3.5 X .7854=43.98 c.i.=720.70 cc's.
2. Deck height=0 cc's
3. Head gasket volume=4.00 X 4.00 X .040 X .7854=.50 c.i.=8.19 cc's.
4. Chamber volume=64 cc's.
5. Top of piston volume=0 cc's
COMPRESSION RATIO #1=(1+2+3+4+5)/(2+3+4+5)=10.98:1

SECOND ENGINE=4.125" bore, 3.5" stroke
1. Swept volume=4.125 X 4.125 X 3.5 X .7854=46.77 c.i.=766.42 cc's.
2. Deck height=0 cc's.
3. Head gasket volume=4.125 X 4.125 X .040 X .7854=.53 c.i.=8.69 cc's.
4. Chamber volume=64 cc's.
5. Top of piston volume=0 cc's.
COMPRESSION RATIO #2=(1+2+3+4+5)/ (2+3+4+5)=11.54:1

Obviously, a bigger bore with everything else constant does indeed yield a higher compression ratio.


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'93 2wd truck
408 sb, vortecs, 454 TBI, Comp Cam, dual exhaust

Yep. That fact could spank some 383, 400 peoples.

Compression, hard to come by on a 305, hard to get rid of on a 400.