305 Performance Rebuild

Locus2298

Not-quite-so-new-guy
May 20, 2021
16
0
1
Hey guys, I have an 86 MC, LS, with the original 305. Heads have 14014416 casting numbers, which if I have my info right, are 1.84int/1.50exh, with 58cc heads. I was planning to install the next parts on it, all from summit:

- Comp Cams K12-600-4 kit
Cam specs:
279int/297exh
At 0.50 227int/241exh lift
.479int/.465exh valve lift
- Holley 0-4777SAE 650CFM double pumper carb
- A forged rods kit, tbd
- KB KB144.030 piston kit - advertised to have 10.5:1 CR with the heads I have
- Weiand 7547-1 Single Plane Intake

My question is, does anybody has a similar setup? What HP and TQ numbers are you pulling with a similar setup? Will this even work? I would like a nice low-end torque with hard mid-torque. I have a TH350, 300HP kit on it, stock converter and stock rear end.

Any opinion will be greatly appreciated.

I already know that a 350 will be better, however, I'm from Costa Rica and getting hands on a good junkyard block here is close to impossible, even more impossible to get a full 350 or any other SBC, so I want to squeeze all power from the 305 I have. Thanks.
 
Last edited:

Clone TIE Pilot

Comic Book Super Hero
Aug 14, 2011
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Galaxy far far away
You don't need the Holley, the stock computer Qjet is more than enough for a 305. Just get a 87 ECM and a ZZ4 PROM chip.

Stock heads are ok but 059 Vortec heads would be a big improvement. Though Vortecs need a different intake and valve covers.

An 86 MC should have a 2004r, I rather have an OD trans. A sub 4 speed is a big handicap these days.

You need to match the cam's rpm band with the TC's stall speed. Very likely you will need more stall.
 
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Locus2298

Not-quite-so-new-guy
May 20, 2021
16
0
1
You don't need the Holley, the stock computer Qjet is more than enough for a 305. Just get a 87 ECM and a ZZ4 PROM chip.

Stock heads are ok but 059 Vortec heads would be a big improvement. Though Vortecs need a different intake and valve covers.

An 86 MC should have a 2004r, I rather have an OD trans. A sub 4 speed is a big handicap these days.

You need to match the cam's rpm band with the TC's stall speed. Very likely you will need more stall.
Yes, the stock Qjet was removed before I got the car. It had a very bad Edelbrock, which I replaced with a regular rebuilt Qjet. TH350 also came with the car when I got it. Vortec L30 heads are very difficult to get where I live.
 

DRIVEN

Geezer
Apr 25, 2009
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You said you want to build for torque but your parts list says otherwise.

Since you're stuck with the 305 block, why not build a 336? Aim for 9.5:1. Keep the 416 heads, dual plane, and Q-jet. Pick a cam that focuses on mid-range. Is your '86 block a 1 piece main that's prepped for roller cam?

You have a stock converter and lame highway gears. The combo you spec'd in your first post wants more converter and deeper gears.

Build for torque.
 
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Locus2298

Not-quite-so-new-guy
May 20, 2021
16
0
1
You said you want to build for torque but your parts list says otherwise.

Since you're stuck with the 305 block, why not build a 336? Aim for 9.5:1. Keep the 416 heads, dual plane, and Q-jet. Pick a cam that focuses on mid-range. Is your '86 block a 1 piece main that's prepped for roller cam?

You have a stock converter and lame highway gears. The combo you spec'd in your first post wants more converter and deeper gears.

Build for torque.
The block is 1 piece main, but not prepped for roller. And I know, that cam likes a 2000rpm stall converter minimum. What cam you would recommend?
 

DRIVEN

Geezer
Apr 25, 2009
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Probably something more like a Comp XE256H. I think it would give you better power where you want it.
 
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Locus2298

Not-quite-so-new-guy
May 20, 2021
16
0
1
Probably something more like a Comp XE256H. I think it would give you better power where you want it.
Great, thanks for the advice. I want to take advantage of the heads I have, as it seems those were the ones that came with the HO305 and a bit difficult to find it seems
 

pagrunt

Geezer
Sep 14, 2014
9,339
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Elderton, Pa
Another power add on would be (depending on emmision regulations doen there) would be putting on a Monte SS type exhaust system which is cat back. The stock SS system adds some horse power over the stock standard system, about 10 to 15 but any where you can squeeze power from take it.
 
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