I am changing the entire top end of my 305 motor. Torquer heads, camshaft, 670 holley carb, full roller rockers, rpm manifold, double roller timing chain. I've heard that i should use 350 head gaskets. What about the manifold gaskets? I want to get a kit that will come with all the gaskets I need from Summit, but i don't know if i should get the ones for 305 or 350? And which gasket kit would you guys prefer? Thanks a lot.

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Pat Hirsz
www.iit.edu/~hirspat/MyPage2.htm
88 305TBI
Mods:Hooker Aerochamber 3" exhaust, no cat,SLP 1 5/8" headers and y-pipe March pullies, no smog, 180 thermo,
14x4 K&N, 3.42 gears(open), Ultimate TBI Mods,AFPR,MSD(ignition,coil&wires),Edelbrock TBI Manifold, 190ltr/hr fuel pump,
Eibach springs with KYB's all around,
Centerforce dual friction clutch
Harwood cowl hood, Z-28 wing, fresh paint(black)
120,000 miles, 5spd, T-tops
0-60mph-7.0s-Gteched

92 RS, 305TBI, auto, 3.08 gears, 180 thermo, glasspack (no muffler)

 

Why would you use 350 head gaskets on a 305? The 350 has a 4.00" bore and the 305 bore is onle 3.74". You'd have a big gap to fill up with junk from the combustion process. Call Summit and order 305 FelPro head gaskets and a cam change kit.

 

well according to world products u have to use the 350 head gasket if u put the 1 on for the 305 it shrouds the valve.... so call summit and ask.

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305, TPI,compucam 2030 cam, air foil, 8.8 wires, accel super coil, dynomax headers, custom y-pipe, cut out, 80 series flowmaster, 2.73's and an open diff(3.42-3.73 on the way). and a stage 4 chip :0). hittin a sad 15.2 before the chip.

 

The gasket is larger than the cylinder bore... so if the gasket is shrouding the valve, the cylinder is shrouding it even worse.

Use a 305 gasket. FYI manifold gaskets are same between 305 and 350.

 

I guess I stand corrected. Everyone I've spoken to has told me the 350 head gaskets must be used with 350 heads on a 305 or there will be overheating. I would think that would leave a rather large area for carbon & junk to build up though. As for the valve shrouding or other clearance issues, I've spoke to people on this site running L98 aluminum and other 350 heads on 305s and nobody has experienced this before with up to .525 lifts. I'll be putting my L98 aluminums on shortly. I'll post any problems I have, if any.

 

Well I dunno but most people who put Aluminium L98 heads on 305s 'round here use 350 gaskets with no problems.

 

Negative. World says to use 350 head gaskets, so do it. Not because the 305 gaskets shroud the valves, but because they've reshaped the combution chamber so the 305 gaskets aren't right for their heads.

Use the 350 gaskets like the head manufacturer recommends.

(The intakes are the same for 305 and 350, though, so a 350 set will work fine.)

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82 Berlinetta, orig V-6 car, now w/86 LG4/TH700R4. 2.93 limited slip. 2-1/2" cat-back, ZZ3 intake, Accel HEI SuperCoil. AMSOIL syn lubes bumper-to-bumper. Daily driver, work-in-progress (LG4 CC system w/'87 LB9 block, ZZ3 cam, ported World 305 heads, Hooker 2055 headers, 3" Catco cat & 3" catback, restalled TC, Spohn SFCs).
57 Bel Air, my 1st car. '66 396, 9.7 CR forged TRWs, Weiand Action+, Holley 750VS w/4150 conversion, GK 270 cam, Magnum rockers, Jacobs Omnipack, 1-3/4" Hedders & 3" Warlocks, TH400 w/TCI Sat Night Special conv & Trans-Scat shift kit, MegaShifter, 3.08 8.2" 10-bolt w/Powertrax, AMSOIL syn lubes bumper-to-bumper. Idles smooth @ 600 RPM in D. Best 15.02/95.06 @ 5800' Bandimere (corrected 13.93/102.4 @ sea level).

[This message has been edited by five7kid (edited October 16, 2001).]

 

Absolutely, even the guys at Chevy High Performance mentioned this specific detail when assembling their 305 in this month's issue. Use the 350 head gasket on that 305!

 

Thanks a lot guys. Every other gasket in a 305 is the same as in a 350 right? So i can get the full gasket set for a 350 which would include the timing chain, oil pan and all other misc. gaskets needed to complete the cam and head swap and they would work fine on my 305?

 

Yes, all the other gaskets will work fine.

 

Well, I'd have to see it but I cant see how a gasket that is larger than the cylinder bore would create a problem thats not there with a 350 gasket. IMO if thats really the case, then how is the bore of the cylinder not a problem for the shape/design/size of the combustion chamber on the head? Sounds like they designed the head for a 350 and the combustion chamber is a fair amount larger than the bore somewheres. I guess they really arent 305 heads then.

I know Willie said he is using 350 gaskets with his L98 aluminum heads, but there may be a problem since those were designed for a 350. I know that the iron heads wont work with a 305 gasket, its slightly into the chamber in some areas.

 

From what I understand, the gasket needed depends on the head you're using. For example, WP 305 S/R Torquer heads can not be used with a 305 gasket, but some other 350 heads can. Some heads have larger combustion chamber designs and need the extra room of the 350 gasket to keep from shrouding the combustion chamber. Over a period of time, the extra .260 gap will fill up with combustion waste (carbon, etc), so the compression will change slowly with mileage but not as fast as using the 305 gasket and starting with a smaller chamber size. I wonder what the effect of taking the edge from the top of the 305 cylinder to smooth the transition to the 350 gasket would be?

 

Unfortunately, I tossed the 305 gaskets before I got the new heads or gaskets. But, comparing the factory chamber shape to the World 305 shape, I can see what they're talking about. The chambers are the same volume, but the shapes are quite different, so the 305 gasket would hang slightly into the World chamber (near the plug, I believe - I'm not at home so I can't go out and look).

I didn't bother getting new 305 gaskets, so I can't lay one on top of a 350 gasket to tell you what the difference is. If somebody has access to both a 305 head gasket and a loose World 305 head, perhaps they can explain exactly what the problem is.

 

Well if the gasket protrudes into the chamber, yea... that would be bad.
I have a 305 and 350 gasket, and a 350 block here too. No 305 block or WP heads tho, so I cant help a whole lot. The gaskets are pretty much the same except smaller holes where the cylinder is.