Yav8

Master Mechanic
Aug 19, 2014
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I will agree the running 350 vortec 880 casting will have a roller cam. No flat tappet cam problems and it only takes a cam and valve springs intake and carb and a HEI and your their. Have the th350 rebuild and a mild converter and now for the rearend. I have done a few 12.50 bracket cars and only used the stock 7.5 with upgrades.. Always on a builders budget because half the fun is in the hunt for parts. 3.73 gears from most any S10 4 cylinder truck and a posi for a late model camaro or firebird. These are 28 spline so a after market 28 spline axels from Summet Jegs or Rock Auto. The last piece is the rear cover with the axels brace studs. This will keep the axel caps from moving around. If your realy on a budget most any s10 after 91 or 92 with a posi rearend will be a 28 spline with a guvloc posi. Look for a 4 wheeler as most will have the posi rear. If your good at scrounging part you should have this done for $1200 to $1500. Half the fun is in the hunt for parts.
 
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Nov 2, 2023
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If you want a 400hp small block, you know what I'm going say next: Ditch the small bore block.
Could you make 400hp out of a 307? In my opinion: maybe. But I have a feeling it’ll involve a radical setup and a lot of RPM to do so.
Grabbing a 350 from a newer C/K1500 should net you a decent block, but the Vortec cylinder heads are a toss up with cracking issues.

But before I continue, is your budget of $5K just for the engine, or is it everything you mentioned?
5k on the motor
 

UC645

Royal Smart Person
Apr 20, 2020
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5k on the motor
Perfect, that’s a damn good starting point for an engine nowadays.

Were I starting from scratch again, I’d go with a plan like this:
94-up 350 roller block- for ease of cam instillation and less likely to be fubar with its use of more modern oils. Vortec heads are a 50/50 though.
Grab a ready made rotating assembly from the likes of Eagle or Scat, balanced. You can swap out the flexplate and balancer for SFI-spec units without any changes.
Get a set of bare AFR Enforcers so you spend less (or the same) amount of money setting them up how you need them for your cam, you will need to buy valves from AFR though.
Since those are set up for guide plates, you’ll need to get plates, rocker studs, and rockers. Don’t waste your money on the roller tip ones, they net little improvement over a stock steel rocker. Go with the bigger rocker stud size, the smaller ones tend to flex under high rpm. Same rule for your push rods.
Do NOT skimp on lifters, get them from somewhere like Howard’s, Johnson, or direct from Morel. I wouldn’t trust Comp lifters with all the quality issues that have been going around the last few years. Go with tie-bar lifters if the engine is going to see high lift or if it’ll see over 5,500 RPM. The stock dog bone lifters can come out from under the bones and lift them up with a high-lift cam, causing them to spin in the bores, high RPM will do the same thing.
If you go with the Enforcer heads, you’ll need an older, pre-TPI intake, they have the bolt holes for Vortec style intakes, but AFR claims that the ports don’t line up. I can’t confirm this though.
And for oiling, just get a high volume pump of your choice, and buy the spring kit if you feel you need the higher pressure, the pumps are the same.
If you haven’t decided on what you’re going to do with the car primarily, go with a Road Race style oil pan. They’ve got baffles that will provide oil control for any situation, but Canton and Kevko are your only options for a pan that won’t hang below the crossmember.

If you’re serious about power, talk to your engine builder about converting a 2 bolt main block to a splayed 4 bolt with aftermarket caps.
This will require honing and drilling the block for the extra bolts. The stock 4 bolt engines have issues with cracking between the bolt holes because they’re so close together.

All in all, depending on cam, intake, CR, and headers, that’s a combo that should be good for 450hp reliably. But talk to a builder first, even if you’re chucking it together yourself.
 
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64nailhead

Goat Herder
Dec 1, 2014
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Tall order to get 400hp out of a small bore and short stroke SBC. It will take rpm that will require a balanced rotating assembly, either a great set of heads or a good set that are reworked by a knowledgeable porter, and a cam that will be considered anything other than daily driver friendly. And the last piece to get it done easily, will be a compression increase to the edge of pump gas use - again, not ideal for a daily cruiser.

Or forced induction that will blow your $5 budget.

A stock 350 short block with a cam and $1500 worth of heads would be inside the budget imo.
 
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SS_Malibu

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Sep 27, 2021
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There are a few good options here and none of them include the weak 307. All of which are around your $5k budget.
 
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L05edSS

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Nov 29, 2022
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I just picked up a 307 Chevy not Olds thinking it was a 350 the guy told me it was a 350 and I looked up the casting Numbers (3970024) comes back to a 69-73 Chevy 307, either way, I want to Put it into my 81 Monte Carlo 229 v6 I know I need to replace everything but my goal on the 307 is 400hp I'm not sure if this is possible on this motor but if it is how can I achieve it while on a budget of 5k, I picked up a th350 that I'm gonna bolt to still don't know what rear end most likely an SS rear end or GN maybe ford 9 IN still not sure But my goal is to get it all going by August 2024
i'm gonna be the odd ball here. i love the idea of a hot 307. i dont know much about them in fact just went to see what the bore size is a little bigger than the 305 not quite 4" though so might have to be careful on valve sizes & heads. theres tons of info out there many doing builds of them for free info & ideas. rearends, the 9" i come to understand the pinion location on those makes them very inefficient might want to get your own understanding of it, goin with a SS 7.5 rear only difference from those to any other gbody 7.5 is they have 3.73s. there are AGAIN builds of them out there where upgraded from 26 to 28 splines and s10s pull front wheels off ground with em. then theres the 8.5 that are tougher.

now theres a 318 build going on with a colab of david vizard, unity motor sports and some other guy. they drifted away from the orig point which was to take what was there that came from factory and mod only what it came with to get 318 hp called mission imposible, maybe theres some ideas there to save some $ and i forgot to ment it was supposed to be done with the stock 2 barrel carb.
 
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bracketchev1221

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Here was one that was done for cheap and junk. You can make 1 hp/cu in kinda easily if thats ok.
 
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78Delta88

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May 23, 2022
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I was thinking about that one. There's another couple good ones out there. I think the one done in Canada, don't remember name of builder at moment.

A friend of mine in high school had the 307 in his Nova and it did ok on the street. I did the carb work for him. It wasn't a land rocket but it wasn't a total slug either.
 
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78Delta88

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Yep so 325 torque 290 horses, not bad. Under square, so maybe better head flow and you could square it at 325 horses. That would be an issue of cost/benefit analysis.

Side note though and unrelated..., I always see builders putting the cam in while on the stand. When you get the block back from machine shop and new cam bearings are in, set the block standing up. Let gravity be your friend. Cam drops straight down. Cam goes in easier doesn't bang around the bearings. Once the cam is in, then put it on the stand.
 
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Here was one that was done for cheap and junk. You can make 1 hp/cu in kinda easily if thats ok.
Derek's builds like this is realistically what anyone will some skill can do. It is a sbc, so many options and sbc cores out there, especially since the LS craze. Give it a checkover, if everything is sound, new gaskets, timing chain and maybe a mild cam. Then add maybe Vortec heads, still available new and the matching intake. Those will both swap to a 350. Just curious, how bad a stock Vortec heads for cracking? They aren't Dodge 5.9 magnum bad are they? I know Engine Quest started with Vortec sbc heads supposedly for that reason and then did the Magnum heads which flow very well, on my 2000 Dakota with 5.9 swap. My stock Magnum heads cracked badly into the coolant.
 
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