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

[fast_n_low86]

Hello everyone.

The time has come for me to upgrade from a small block 350 to a BIG block 454. This is my first big block and swap and I think I'm kinda jumping into the deep end with this. What are some things I need to know for the swap. I am putting this into my '86 Sierra Classic 1500 and currently have a TH350 transmission, dual exhaust set-up (header back & 2.25" pipes), I'm running an electric fuel pump and regulator, electric fans x2 on a 3 core radiator.
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.

 

[RustyPile]

For starters (no pun intended), flex plate, accessory mounting brackets, four core (or equivalent) radiator... An adjustment to your fuel budget is also required.

 

[Vbb199]

Bigger carb, bigger air filter, bigger exhaust piping maybe.

 

[Rickf]

Depending on the brand of headers, don't be surprised if the a/c box starts to melt. Ask me how I know.

 

[fast_n_low86]

Bigger carb, bigger air filter, bigger exhaust piping maybe.

I'm already running a 600cfm edlebrock performer. Bigger yet?

 

[fast_n_low86]

Depending on the brand of headers, don't be surprised if the a/c box starts to melt. Ask me how I know.

That's all good. It's empty anyways. Took the a/c out as soon as I bought the truck

 

[Vbb199]

I'm already running a 600cfm edlebrock performer. Bigger yet?

For a 454 depending on chamber size, and head flow, i feel like 700-750 is gonna be more in the area you want to be, 4bbl

But i suppose if youre trying to get the best possible MPG, the 600 will suffice with appropriate jetting.

 

[85K304SPD]

New fan shroud, brackets... other than that, its a big jump in CID, so all the stuff that GM did differently (radiator, exhaust, carb, transmission, suspension, etc..) on a 454 to make them perform better. The small block stuff will work, but big block stuff is bigger for a reason.
Go for it, and see what happens, but a pretty straight forward swap. I just did it on my K30.

 

[Bextreme04]

That's a 454 from a 79 Pickup. Unless you swapped the heads and/or the cam out... its going to be a low compression dog and won't be spinning up past about 4500rpm anyways. 600CFM will be plenty.

The only thing you should need is to modify the exhaust to connect to the headers on the big block. Other than that, everything should transfer right over. You'll need the big block alternator and PS brackets, but those should have been on the motor already?

 

[Bextreme04]

The only difference on a big block truck for you suspension wise would be a bit heavier front spring. If you have a Big 10 or the F44 front spring option, you would have that heavier spring in there already. The big block weighs about 200lbs more than the small block... so you'll feel the difference in the front end but not much. It's basically the difference between having a big dude in the passenger seat or riding empty.

 

[GTX63]

A swap to a big block can be an upgrade or a downgrade depending on what you are planning to use it for. If it is one stock motor going out and another stock motor going in, the Qjet has more than enough flow to feed the 454. Most of the SB small blocks I have run average about 12mpg. The 454 should be around 10 mpg. For some people that can get old, especially when the difference in a small block and a smogger big block isn't much unless towing or hauling.
Yes, BB coil springs will help ride and reduce the front end sag.
The swap isn't so bad. We used to throw BBs into Chevelles, Novas, Camaros, etc without much more than used parts from the donor Impalas.

 

[fast_n_low86]

For a 454 depending on chamber size, and head flow, i feel like 700-750 is gonna be more in the area you want to be, 4bbl

But i suppose if youre trying to get the best possible MPG, the 600 will suffice with appropriate jetting.

750 it is

 

[Vbb199]

Eric made a good point up there though. Unlikely it'll run much over 4500, you may not need any larger than 600-650cfm

 

[fast 99]

For comparison most Q jets flow about 750 CFM. If the 454 is low compression net HP will be in the area of 220 with cast manifolds. However, torque will be substantially more than a small block. If you already have a good operating Carter 600 use it. Then down the road if you want to change to something else it isn't a big deal. What some fail to understand is these trucks aren't 3500# Camaros. They primarily need torque to move not HP. If you overbuild the engine all that will happen is lots of trips to gas stations and poor drivability.

 

[Bextreme04]

For comparison most Q jets flow about 750 CFM. If the 454 is low compression net HP will be in the area of 220 with cast manifolds. However, torque will be substantially more than a small block. If you already have a good operating Carter 600 use it. Then down the road if you want to change to something else it isn't a big deal. What some fail to understand is these trucks aren't 3500# Camaros. They primarily need torque to move not HP. If you overbuild the engine all that will happen is lots of trips to gas stations and poor drivability.

No, they CAN flow UP TO 750cfm. The good thing about a quadrajet is that the primaries are tiny and give good drivability and efficiency at the low rpm, low throttle, conditions that you will be in 99% of the time. The design of the secondary lets it flow as much as it needs on the top end. On a stock smogger era truck 454... there is no way it is using more than 600cfm