im debating on two motors. a stock 350 or a 305 bored over at 30+. i have a 86 z28. with the factory 305 in it now. i want more power. i have the stock rear end, but a new high geared t-5 trany. which would be the best cost effective motor with a lot of power. also if i bore a motor out what else should i do to the motor? any suggestions are appreciated.

 

There are two very passionate sides out there, those who say the 305 will work fine, and others who say the 350 will make more power so just do it.

I'll start by saying your weak link is the T5 tranny. If you want to protect it, you need to keep torque down but also avoid needing to pop the clutch at high rpm's.

Second, you said "cost effective" - very subjective. How do you measure that, HP per dollar spent, HP increase per dollar spent, what? The machining costs of a 305 are the same as a 350, but the parts (pistons and rings) are more expensive for the 305. So, if you had both a 305 and 350 block in hand needing the same amount of rebuild, the 305 would be more expensive. Having the block tanked, crank turned, rods resized, cam bearing replaced, are typical rebuild items (rods optional).

The three performance-limiting parts of the 305 are cam, heads and exhaust. Exhaust should be done even with a 350, and a performance cam costs the same for either engine. It could be argued that stock 350 heads, depending upon what you get with the engine, are okay for performance, but World S/R Torquer 305's are about the same cost as S/R Torquers for a 350, so that really depends upon what you start off with. Most 350 smog heads are terrible, so I'd call that part a wash from a cost perspective (although a smog-headed 350 may still make more power than your beefed up 305). A big advantage of the World heads is that they come with screw-in studs, while stock iron heads have pressed-in (not as durable or able to take higher valve lifts).

The other performance limiter of the 305 is the small bore, which tends to shroud the valves and limit flow. The World 305's help that situation, but you're less limited with the 350's 4" bore.

But, the big point: 305's are pretty tough, and a stock lower end can stand up to a lot of upgraded power. So, decide first if you really need to rebuild the lower end. If not, you're looking at $650 for heads, $120 for cam, $700 for exhaust, $75 for gaskets. It would cost you somewhere around $1500 to buy and rebuild a 350 with the above mentioned work and parts, more if you want better than stock heads or get a performance crate engine, and you haven't addressed exhaust yet.

So, in my mind, if the 305 lower end doesn't really need to be rebuilt, it's more cost effective to go with the 305, to say nothing about the savings from not tearing up your T5. But, you're settling for less power than a 350 would make, and if you need to rebuild the bottom end of the 305, you're probably better off going with a 350 (and take it easy on your tranny once it's in).

------------------
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 September 11, 2001).]

[This message has been edited by five7kid (edited September 11, 2001).]