Would putting 305 HO heads on a 350 be a good idea. The 350 has I believe 76cc heads and has about 8.5-9.0:1 compression. They are late 70's smog heads off a pickup truck. What if any performance gains would there be and what will this do to my compression ratio? Would the valve springs be up to the task of a cam with .465" lift? overall would this be a good idea or not? Thanks guys.

 

You would gain compression, that's for sure - close to 10:1. Whether you'd gain anything else depends upon exactly what 350 heads you have. Some truck 350s had 1.72" intake valves, while the 305 has 1.84".

There isn't any difference between 305 and 305HO heads, by the way. But, your best bet would be to just get some better 350 heads. With the 305 small ports and small valves, press-in rocker studs, limited lift springs (.465 is pushing it), you could easily do much better.

If you go with the 305 heads anyway, do some port work on them, get bigger valves installed, replace the studs with screw-in, and get better springs.

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82 Berlinetta, orig V-6 car, now w/86 LG4/TH700R4. 2.93 limited slip. Cat-back from '91 GTA, Accel HEI SuperCoil. AMSOIL syn lubes bumper-to-bumper. Daily driver, work-in-progress (LG4 w/'87 LB9 block, ZZ3 cam and intake, World 305 heads, Hooker headers & y-pipe, 3" Catco cat & 3" cat-back).
57 Bel Air, my 1st car. 0.030 over 396, 9.7 CR forged TRWs, Weiand Action+, Edelbrock 1901 Q-Jet, GK 270 cam, Magnum rockers, Jacobs Omnipack, 1-3/4" Hedders & 3" Warlock header mufflers, TH400 w/TCI Sat Night Special conv & Trans-Scat shift kit, LT MegaShifter, 3.08 8.2" 10-bolt w/Powertrax, AMSOIL syn lubes bumper-to-bumper. Best 15.1/95.5 @ 5800' Bandimere.

 

I use the 58cc heads on all my cars, because they came stock on the 305's and its chaper than A/M heads and less piston has to be used to create higher compression when one goes to 350. Well they do increase compression dramaticly and the 1.84 intakes are perfect for street/strip use. I talked to sevral machine shops "4" to see what it would run me to get lager valves droped in and they all told me the same thing. If you are using these for street performace dont go for 1.94 valves! I asked why? They said "4 shops mind you and 1 was out of town 40 miles" They do nothing! The larger valves will flow more air only at higher rpm! The they went on to say "all 4 mind you" with a street vehical 350cu these will hurt you until the 6500+rpm area where more flow is needed Ie circle track situation. Basicly the moral of the story is is you have em use em, port them and if they have 1.84 intakes dont go for 1.94's.
SSC

 

3-angle-valve job! Porting and Polishing! Valvesprings/Retainers! 1.84" intake valve is great for street/strip...but for a 350, I would still spring for the standard 1.94 valves. I would even try to put 2.02 valves into that head. 10:1 compression is good enough for street use. Definitely go for the 305 heads, scrounge thru a scrapyard. Build them up! Save about 800 bucks.

-ws6formula-

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1989 Pontiac Formula WS6
69,000 miles.
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305 TBI, 4.10 gears, SLP Zexel/Torsen Limited Slip Differential, 700r4 B&M TransPak, LT4 Hot Cam/Valvesprings, GM Aluminum Driveshaft, 2700 RPM Stall, Edelbrock Performer RPM intake manifold, Turbocity TB. Ran on 6-19-2001 again: UPDATED: 14.1 @ 97.68 mph. Dyno'd Bone Stock @ 172.6 rwhp, 266 ft-lbs. of rw-torque.

 

i think that 1.84 to 1.94 would be worth it.

i think that you would be able to pick up a lot of flow from that. now 1.84 to 2.02 would be overkill but for street use and something that would see 6500 occasionally 1.94's would be fine. 2.02's are supposed to be valves for 6500+ RPM's and not the 1.94's

 

true about the 2.02's being more higher rpm oriented than the 1.94's but one must remember that the combustion chamber size is being reduced with these heads. Where's the extra flow going to go? were droping from 76cc heads to 58cc thats 18cc. Some one thats good with math "not me " could figure out the differences between the combustion chamber size and the valve needed to flow the correct amount of air, not too much or too little.
Kinda see what I mean?
SSC

 

Combustion chamber size has nothing whatsoever to do with flow requirements. Flow occurs when the piston isnowhere near the top of the cylinder. CID determines flow. Think about it... you could have a piston with a suitable dish in it, and a head with an absolutely flat surface and therefore a CC volume of 0... would this mean that no flow at all would occur?

The reason the 1.94 valves don't help a 305 head is beacuse the passages are so small. To use my favorite analogy of a string of pieces of hose to represent the various parts of an engine's induction and exhaust system, imagine you have a series of 25' pieces of ½" hose all strung together, and you measure the flow when you turn on the faucet; and then you replace one of the pieces in the middle with a section of 1" hose and measure the flow again. Do you think it will have changed? I doubt it. Putting larger valves in 305 heads is exactly the same situation.

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

 

Rb said it perfectly (as is the usual). Once you Change the Cam On the 305's, The LImiting Factor Is the Heads. ( exhuast aside )

The heads In stock Form wont even support 300 Hp out of a 305. Your Not going to be able to Do it with a 350 either, because it only wants to pull MORE air. Slap a Set of A/M heads on a Lg4 with a Good Cam, and You get a Huge Jump In Power, whats this tell you ? The stock heads are Not sufficent. Add 50 More CI and the problem only compounds itself.

Completely Hogged out, Maybe the 416's might be "okay" for a Hipo Street App, But Unless you are doing the Work Yourself, the Money Could be MUCH better spent on a Set of Vortec's.

Hell, Even getting a 3 angle valvejobber and having the larger valves installed On the 416's will Run You Up over the price of a Pair of new Assembled Vortec's, and Never Flow nearly as Much.




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