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‘65 GMC 1000 305ci V6 Sm420, ‘66 C10 LS/480, ‘58 Biscayne 348ci/powerglide
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Discussion Starter · #1 ·
I have heard of guys doing 265, 283, 292’s but any one ever try a 305ci V6? I daily drive one now and will be picking up another spare in about a week or so. Low revving, high torque, but also bulletproof. Wondering if I find someone to balance the crank if it would be worth an eBay efi and turbo.
 

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Rod...from a Chrysler?
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Had to google this engine. And I call my self a GM fan.
I'm all for something different. Will a stock crank and rods hold up for this application?
 

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‘65 GMC 1000 305ci V6 Sm420, ‘66 C10 LS/480, ‘58 Biscayne 348ci/powerglide
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5 Posts
Discussion Starter · #3 ·
Had to google this engine. And I call my self a GM fan.
I'm all for something different. Will a stock crank and rods hold up for this application?


See not entirely sure, these engines we're discontinued due to the fact they were ”too reliable”. I would guess so. Like I said a beat the hell out of one daily, never been rebuilt. Just looking for a little more fun and something different out of it.
 

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Rod...from a Chrysler?
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My search revealed that parts would be expensive and hard to find.
I'd pass on that engine.
 

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I love a 305 V6. This is a simple low horsepower high torque engine. One of those engines I should have kept around and made a generator out of.

It is better to think of and treat it like a NA diesel then a gas engine.

I am not going to discourage you to not run the 305. The thing is a cool engine. But it was never designed to be a high horsepower engine. That is not saying you can not build it onto one with enough cash. But if that is your goal then maybe you should start with a different v6 like a 4.3, 3.8(or several aluminum options) that will offer more hp/dollar then a 305 will.

I have seen lots of people throw around the idea of a turbocharged 305 or 351 and they all seem to end without the turbo.

If you leave the 305 mostly stock or make some mild (reliability) upgrades it can be a great engine. Run it and be happy.
 

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‘65 GMC 1000 305ci V6 Sm420, ‘66 C10 LS/480, ‘58 Biscayne 348ci/powerglide
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5 Posts
Discussion Starter · #7 ·
I love a 305 V6. This is a simple low horsepower high torque engine. One of those engines I should have kept around and made a generator out of.

It is better to think of and treat it like a NA diesel then a gas engine.

I am not going to discourage you to not run the 305. The thing is a cool engine. But it was never designed to be a high horsepower engine. That is not saying you can not build it onto one with enough cash. But if that is your goal then maybe you should start with a different v6 like a 4.3, 3.8(or several aluminum options) that will offer more hp/dollar then a 305 will.

I have seen lots of people throw around the idea of a turbocharged 305 or 351 and they all seem to end without the turbo.

If you leave the 305 mostly stock or make some mild (reliability) upgrades it can be a great engine. Run it and be happy.
Not looking fo high horsepower out of her but like I said this is my daily. If I got 50-100 horse I would be stoked. What I’m after is just a little more pep in her step. I have access to a 351, and picking up a spare 305 and 4 speed in a week or so. What I was planning to do is go through the spare block prob balance the crank just to get it to rev a bit higher. Slap efi and eBay turbo on it. Then yank my original block and give it some love. If I blow up the spare then so be it... wasn’t my original engine.

If your talking about reliability stuff though. Just basics or stuff for these particular 60 degree blocks?
 

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‘65 GMC 1000 305ci V6 Sm420, ‘66 C10 LS/480, ‘58 Biscayne 348ci/powerglide
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Discussion Starter · #8 ·
whats the 305 in? Can they be converted to v-12s?
how much hp does it have now
It’s in a 1965 GMC 1000 (c10) though in this generation Chevy and GMC were not the same trucks. Mine is an e code I think they claimed 165hp 275ftlbs at like 1800 rpm. Mine is prob a healthy 150hp and definitely still has the torque. It will chirp tires in second and third gear. We were pulling out a big block 1974 the other day and my buddies brand new 4.3l couldn’t do the job. Pulled mine over and had not a single issue...


As far as the v12 thing they made them and prob could be converted but what the hell would you put something that massive in...?
 

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Not looking fo high horsepower out of her but like I said this is my daily. If I got 50-100 horse I would be stoked. What I’m after is just a little more pep in her step. I have access to a 351, and picking up a spare 305 and 4 speed in a week or so. What I was planning to do is go through the spare block prob balance the crank just to get it to rev a bit higher. Slap efi and eBay turbo on it. Then yank my original block and give it some love. If I blow up the spare then so be it... wasn’t my original engine.

If your talking about reliability stuff though. Just basics or stuff for these particular 60 degree blocks?
Well.
Upgrading the rods(custom), the oiling system, the bearings(custom), the pistons(custom) (unless you can find some 4 ring forklift ones), the lifters/pushrods/rockers, intake and fuel system, cam(custom), and a good amount of head, crank, and block work.

Now if you dont care about the engine just do what I have done with half a dozen smog bbc's and run rich then blow 4 to 6psi through the stock restricted (peanut) heads. Your going to make some power(if you don't wash the walls). But only want to do it in brief periods because it does not take much to destroy factory stuff and turning up the psi higher then you know you should will happen. Followed by busted rods or pistons.


The "safer" and frankly cleaner way as it leaves the block looking stock is to increase the NA compression. You really should still upgrade a few things here. But you will have a tune for one rpm curve letting you have a proper ratio at all times instead of a compromised one with a blow through setup.


Now I dont like to make custom parts. I will however take a existing factory part and machine it slightly. Rods come to mind. There are several sets of factory forged rods out. You may be able to measure your rods and find a modern forged set that is close. Change the pin then install a "better" piston that matches your bore.

The 305 may have parts from a dozen diffrent brands. But you will be able to get parts even if you need to machine those parts slightly to make them work.

One of those things once you lay out the disassembled parts, take measurments, and then spend weeks searching and a few more weeks machining(you may destroy a few) then you will have a "custom" say Toyota rods and forklift(4 ring) pistons, with sbc lifters, Ford valves, and a oil pump out of a cummins.
You know. Old school hotrodding stuff making power by making things work(and a ton of math/machining).
 

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Not looking fo high horsepower out of her but like I said this is my daily. If I got 50-100 horse I would be stoked. What I’m after is just a little more pep in her step. I have access to a 351, and picking up a spare 305 and 4 speed in a week or so. What I was planning to do is go through the spare block prob balance the crank just to get it to rev a bit higher. Slap efi and eBay turbo on it. Then yank my original block and give it some love. If I blow up the spare then so be it... wasn’t my original engine.

If your talking about reliability stuff though. Just basics or stuff for these particular 60 degree blocks?
Stock bottom end should have no trouble handling 4-6 psi, the parts are massively overkill for their power level.

Balancing the crank is going to do nothing for getting it to rev higher, because crank balance isn't the issue...it won't rev because heads are tiny valve, intake is tiny 2 barrel, and cam is tiny stock low rpm oriented.
You want more RPM, than add a mild cam, turbo it with EFI, do some port clean-up on the heads if you can....and live with what you get.
There are no aftermarket 4 barrel intakes made for this engine, and you will have to build you own headers to turbo it.

I have not a clue what adapter you will have to make or buy to get the EFI bolted to the stock 2barrel intake.
 

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Draw through turbocharger.

4 barrel carb with a electric fuel pump and a boost referenced regulatior that will maintain level float levels in conjuction with boost so your not running super rich or lean.

Your building the exhaust, intake, and running a diffrent carb so draw through keeps things simple. No need to intercool something like this. The intake and exhaust do not even need to be pretty. A exhaust log and intake log feeding the heads. Not efficient but easy enough to build on a shop floor with a MIG and a square edge.

Your heads become a bottleneck so cam, valves, lifters, rockers, etc all need to be played with at a minimum.

You really should start with seeing what you can do with the heads. That will give you the amount they can flow. Then you can size the turbo and start playing with the math on flow to come up with a design for the intake.
 

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‘65 GMC 1000 305ci V6 Sm420, ‘66 C10 LS/480, ‘58 Biscayne 348ci/powerglide
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Discussion Starter · #14 ·
Stock bottom end should have no trouble handling 4-6 psi, the parts are massively overkill for their power level.

Balancing the crank is going to do nothing for getting it to rev higher, because crank balance isn't the issue...it won't rev because heads are tiny valve, intake is tiny 2 barrel, and cam is tiny stock low rpm oriented.
You want more RPM, than add a mild cam, turbo it with EFI, do some port clean-up on the heads if you can....and live with what you get.
There are no aftermarket 4 barrel intakes made for this engine, and you will have to build you own headers to turbo it.

I have not a clue what adapter you will have to make or buy to get the EFI bolted to the stock 2barrel intake.

Awesome this was kind of want I was wondering. I did talk to only one other guy “that knew” these engines which is where I got the crank thing. Was planning on doing hg’s in both blocks any way. So now I’ll just see what I can do to open up these heads first. Bigger valves, polish and cam. Hell that might just do the trick there. Still want to do it just to say I did though too. And was planning on building headers, piping and adapter myself. Looking to get started on this in the next week or so. I’ll post to keep you updated and any technical questions I come up with. I’m a master tech... but I don’t build engines. Thanks guys!
 

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Your biggest Natrurally Aspirated problem is intake manifold....unless you can build your own, you are stuck with the stock piece.

You can port the heads, cam it up, add headers and TBI and it won't help much because it is still sucking through that tiny intake.

The turbo idea would really help....building your own Sequential E.F.I. intake manifold would really open things up.
 
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