Small block to big block swap. What do i need to know?

[fast 99]

Just for fun I used this calculator on a 454 at 4500 rpm 85% efficiency. Came up with 306CFM.

Another example,
Have a 302 Ford I routinely wind up over 7,000 RPM. Took a 600 off and installed a 450 Holley it runs much better. It's not the same animal but only flows 320 CFM at that RPM.

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[82sbshortbed]

I had a 305 with a crappy edelbrock in mine. I hate edelbrock so I called national carburetor and told him I was planning on adding a cam, intake and hedders and what kinda quadrajet would he put on it. He told me a stage 2 would work fine. So I got it fir about 300 bucks. I put it on with an edelbrock performer intake. If fired right up with no adjustments. They do all that for you before they ship it.

Well, looking on Facebook market I for a GenV four bolt main 454 with intake, rv cam and hedders. Also bought a th350 from him too with a shift kit in it. Put them in no problem except you'll need a shorter fan shroud for sure. Also added bb springs in front.

It had another crappy edelbrock 1407 on it. Well, that got pitched and the quadrajet was pulled of the 305 and put on the 454. Again no adjustments. That carb is great on the 454. Great throttle response and I've run it up over 5,000 rpm no problem. Never starved for gas. And the th350 help up under the extra hp too.

I've got 275/60/r15's on it with a Trutrac 8.5 10 bolt 3.73 posi rear end in it too. It ran great but I wanted od. So I sold the th350 and put in a 700r4. Now I can run 65 at 2,200 rpm and it's perfect for me.

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Oh it don't have none of that smog bs on it either! Not the prettiest but she's a runner. Lol

 

[Turbo4whl]

What are parts off the 350 I can swap over to the 454 to save some time and money in the swap. The 454 is a Gen IV, with the casting number 361595.

Some tips and insight is appreciated.

Parts you can use from the small block: The distributor, the alternator, and the metal engine mounts.

The rubber engine mounts are different and they mount in different holes on the cross member.

As stated, the accessory mounts are different, you may need to re-clock the alternator. Hopefully you got all the accessory mounts with the mark 4.

Did you get the power steering pump and brackets with the mark 4? You can use that also, but if it is an early model the relief valve has an SAE inverted seat for the pressure hose. Just use the relief valve from you original P/S pump. That will fit your "O" ring hose.

 

[bucket]

A big block will literally bolt into place and fit fine using small block mounts. You will need big block accessory brackets, the ones you get will determine whether or not you can reuse your alternator and power steering pump. As long as nobody has put the wrong flywheel/flexplate on your small block, you can use your original starter. You can use your original distributor, as long as it's not the electronic spark control version. Your current exhaust can be adapted to your big block headers/manifolds. You have electric fans already, so no need to worry about the fan shroud.

 

[Craig Nedrow]

Here is my big block swap in my K20 writeup. Upgrades are in there, but briefly, 750 holly, as my 600 Ebrock was way small. Ebrock air gap, small cam, used all the small block stuff EXCEPT mach fuel pump...BBC has a different pump, sb pump works, but bairly. I know you are using a electric pump, just for info.

https://www.gmsquarebody.com/threads/1973-k20-350-to-454-swap.29840/

It toasted my 350, so I rebuilt it. Basically 4l60e center section, new bushings, and went to needle bearings, 34e sprage, Sunnex race. In my trans build. And will it smoke the tires? Hope you got some maypops, as I went through every pair in the back, habit forming.

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12.5 x33 BFgoodrich smokin there life away.

 

[potent rodent]

dont forget the flex plate the sb 350 is internally balanced and the bb is externally balanced u cant use the 350 small block flex plate

 

[idahovette]

Depends on the BBC^^^^^^^^

 

[idahovette]

Just the 454 is externally balanced.

 

[potent rodent]

yes 454 ext bal 427 internally

 

[potent rodent]

along with the 366 and 396

 

[pduffyd]

Fastnlow86.
I have an 88 454 mkiv in my 76 C20 square chassis. I was going to put an 4l80 behind it but the cost to do that didnt make sense to me. So I rebuilt my SM465 manual trans, and changed the diff gears from 4.11 to 3.42 in my 14 bff.
Also im running the stock 800cfm qjet
You can tell what it is by looking down the primaries, on the left side there is a bump, see this photo.

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I dont know how long an unbuilt 4l60/ TH700 will last behind a bbc. I distroyed 2 behind a mild build 350sbc (320hp) in my 84 Monti Carlo SS.
I know the 454 normally came with a TH400 behind them in trucks the TH350 just wasnt rated for the torque loads, hense the reason I was looking at the 4l80 for that extra gear, so I didnt need to mess with the axel gearing. Its a beast of an auto trans.
Its the only problem when going bigger you got to think of everything behind it too. Good luck

 

[Grumpy Grizzly]

Im planning a 454 out of a '79 RV swap from my 350 in a '89 'burban. I have an Edi Q-jet 750 Ill be throwing on there as well. One thing to keep in mind (from what I have been gawkin at on the interwebs) is that you will most likely want to change out the 700R4 to a TH400 and a corp. 14 bolt or Dana 60 (full floating rules!!) so you dont tear the 10 bolt axle apart in high torque situations. Then (as someone said) you will want a 4 core or better rad-i-a-tor to keep the beast cool. I did read that the transfer case should be ok(?) but I will most likely put a dana300 or something beefier just for peace of mind (I wish I could afford and Atlas II oof). Again, that is for me anyhow.

 

[Bextreme04]

Im planning a 454 out of a '79 RV swap from my 350 in a '89 'burban. I have an Edi Q-jet 750 Ill be throwing on there as well. One thing to keep in mind (from what I have been gawkin at on the interwebs) is that you will most likely want to change out the 700R4 to a TH400 and a corp. 14 bolt or Dana 60 (full floating rules!!) so you dont tear the 10 bolt axle apart in high torque situations. Then (as someone said) you will want a 4 core or better rad-i-a-tor to keep the beast cool. I did read that the transfer case should be ok(?) but I will most likely put a dana300 or something beefier just for peace of mind. Again, that is for me anyhow.

Why would you possibly want to swap a passenger drop NP241C for a D300? You'll have less low range gearing and it isn't really any stronger. If you do, and get rid of that passenger drop 241C.. i'll be happy to take it off your hands for you

 

[Grumpy Grizzly]

Why would you possibly want to swap a passenger drop NP241C for a D300? You'll have less low range gearing and it isn't really any stronger. If you do, and get rid of that passenger drop 241C.. i'll be happy to take it off your hands for you

Well, you got a point. I will keep what I got then.