hi im new here! i got a 85 t/a with lg4 305 and auto.was wondering what to expect if i swapp a 350/290 crate and use stock carb and intake and upgrade exhaust. thanks

 

Welcome aboard thirdgen.org.

Compared to the 150 horse net rating of your original engine, you can expect about 210-220 net horses out of that crate with headers and good flowing exhaust all the way back, and air cleaner upgrade (the single snorkel is a big restriction).

Not a bad swap for a fresh engine with a little more power. If you want to go beyond there, the heads and cam will be your first restrictions. Your '85 305 heads would work better on that engine than the ones that come on it.

 

hey thanks for answer!!! the 85 would be better? smaller chambers right? would this effect drivibility? is it poss to use one of the 330 or thezz3 zz4"s in this car or stock intake wouldnt work? thanks a lot......jef

 

The '85 heads have smaller chambers and intake valves but better ports. Putting those 305 heads on a crate engine like that is pretty common, actually. The heads are typically treated to 1.94" intake valves, basic port clean-up work, and good valve springs. Works pretty nicely.

The 330 horse 350 HO is also pretty popular, but needs a different intake manifold and doesn't have the exhaust cross-over passages that the stock EGR valve uses as an exhaust source. You can either plumb exhaust up to the intake manifold using the hot air choke boss on the GMPP Vortec spreadbore Performer intake, or just leave the EGR non-functional (might have slight pinging problems under light acceleration). Slightly higher stall torque converter helps it work better.

The ZZ4 is a great engine, also doesn't have the exhaust cross-over passages, but your stock carb and all will mount on the intake manifold that comes with it (basically an Edelbrock Performer EGR). The cam is a little more aggressive, and higher stall torque converter is a good idea. The factory came out with a swap kit (no longer available) that used this engine as the base - basically what I cloned when I built my 350 (but with cast iron heads).

 

cool thanks for the info!! i think i will try and get a short block and reuse my heads and intake.im not looking for a real screamer but a substantial power increase.the car is a daily driver.what kind of power do you think is will have if i use the lg4 heads and good free flow exhaust? very noticable i hope!!......jeff

 

what size chambers are 85 LG4 heads??? 58??
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if i got a 330 hp short block or a zz4 short block can i still use my lg4 heads??

 

Best of luck with your swap I'm in the process of doing the same thing, more or less!

 

N/A

 

Your 305 heads (416 castings) have 58cc chambers. The 290 crate has 76cc chambers plus dished pistons, for low-8:1 compression ratio. Putting your 58cc chamber heads on the crate shortblock will bring you into the high-8/low-9 CR range - quite safe for street pump gas use.

The ZZ4 has 58cc chambers, but the heads are aluminum which transfer heat more readily, which reduces power and effective compression, so a higher static compression ratio is typically used with aluminum heads. Putting 58cc iron heads on a 350 would require more piston dish than the ZZ4 engine has.

The L31 shortblock has 12cc dish pistons, which will bring your CR with 58cc heads to the mid-9's. That's basically what I have with my 350. The 290 horse crate has more dish in the pistons (not sure what that number is off the top of my head).

A good cam would be a Comp XE-series in the 258-262 duration range.

 

yea i think ill try that cam in the the 290 short block and reuse my heads. its kind of a budget wise project.if i put a good exhaust..hi flow cat and exhaust with y pipe..etc do think performance would be a big improvant over stock?.i really appreciate you guys help!!!!....jeff

 

thanks!

 

For the $ the Vortec crate replacement at $2279.95 (free shipping advertised thru Pace Performance) looks to be the value of the day, IMO. Roller cam/vortec heads/one piece seal. Beehive springs and a cam later....you'd have a stout performer.

The 350 HO is missing the roller cam, although it does have the provisions in the block.

The LO5 roller cam replacement is listed at $1800, I wouldn't pay more (or much less) for a non-roller motor. That engine would have potential with the LG4 heads-stock heads are, what, 67-68cc?

Let us know which way you go. I've priced some of these recently but decided to stick it out with a re-build of an existing motor.

 

im kinda up in the air right now cause if i go with vortec heads,i dont believe i can use my stock intake. i gonna try to stick with stock intake and carb to save money. this is a daily driver gets about 100 a day.thats why i was thinking of the short block 290 with the 58cc heads and a nice cam.

 

Stock LO5 are 64cc. The 290 horse heads are 76cc.

 

An '85 will have the two piece seal. Going to a one piece will also require a new flexplate, an additional expense (although they're pretty cheap).

I saw a new GM two-piece shortblock assembly for around $1100 not including shipping somewhere. Everything you have would bolt right up. New cam/lifters for around $200, gasket set, shipping and misc stuff will have you real close to $1500 easy. Maybe more if your heads need work.

Make sure you add up all the little things before you jump. You could be real close to the cost of a long block that will bolt in the day you get it, with a warranty AND let you drive the car while waiting to have your existing heads worked on-if that's an issue.

 

hopefully my heads are ok car been babied for 70 k miles.if i get a longblock 290 it will have the 76cc heads vs the 58 for the 305.so i was thinking i culd get more power for the money and if i get a 350/330 my intake wont fit.so im kinda stuck!just curious what power difference to expect from either combo?? any ideas??