Would it be possible to install 350 heads on a 1985 305 to increase HP?

 

Someone correct me if I am wrong, but 350 heads are too big for a 305. The combustion chambers are way too large, they will kill your compression and kill your power. The larger valves may increase flow, but that would only be a good idea if the compression ratio stays the same or higher.

 

350 heads on a 305 is how you make more power .... just get Vette Aluminum heads as they are 58cc like the 305 heads. But they have I believe (correct me if Im wrong) 1.94/1.55. Or if you can only get iron with 64cc or larger, just get different pistons to up your compression again.

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1989 Trans Am GTA, L98 5.7L TPI, TH700-R4, T-Tops, dual cats, 9-bolt rear, 3.27,
- K&N Air Filter
- Dynomax muffler

1992 Camaro RS, LO3 5.0L TBI, T-5, T-Tops, 3.08, L69 Dual Snorkel - Sold
- K&N Air Filter

Honda engines ROCK, I have one on my lawn mower but I still have to push it.

 

What 350 heads are you talking about?

305's use 58cc chamber heads and have a very small 3.736" bore. 350's use either 64cc or 76cc chamber heads (although the above-mentioned aluminum are 58cc). However, some also have 2.02 intake valves, which are a problem with the small 305 bore.

Even if the 350 heads have 64cc chambers and 1.94" intake valves, you are taking a big hit in compression ratio - especially on an '85 305 which has dished pistons. You can shave the heads to decrease the chamber size and increase compression, but unless the 350 heads are something other than the typical stock factory heads, the increased flow will hardly be worth it.

Even the 58cc chamber aluminum 350 heads have problems, because in order to produce the same power with aluminum as with iron, you need to have higher static compression with aluminum. So, even though you'd maintain the static compression you had with the 305 heads, you'll still lose out in net power gain.

Your best bet for 305 replacement heads is World Products S/R Torquer 305's. They're made for our 305's, and are better than any 350 head for a 305. They can be improved by pocket porting (bowl cleanup), but otherwise are the closest to bolt-on that you'll find. They also have screw-in rocker studs, that most factory 350 heads don't have, and the casting quality is superior to production 350 heads.

Don't EVEN get me started on trying to make Vortec heads work on a 305...

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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 02, 2001).]

 

I thought they made 305 vortec heads, guess not huh?

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1987 Black 305 TPI 5spd IROC, seems to be fully loaded, but can't find RPO codes.

AIM: IROC 5spd

 

Um I think Vortec heads work really well on a 305. Seem to produce real good power on my Brothers 305 TBI. How many TBIs do you see running 13's Naturally Aspirated? So what are you saying if we had used the Torquer heads we would have better results?

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89 Trans Am Turbo 3.8L All stock 43,000 miles #1053 of 1555

Past Thirdgen:
86 Trans Am w/ built 355TPI with SLP goodies and too much other stuff to List. One sweet *** car, wish I would have had a good enough Job to pay insurance on three cars so I could keep it, but for a 89 Turbo Trans Am w/ Low miles, I think I made the right choice!