switch 1987 TBI 350 to 4bbl carb and intake from 1979 400ci?

[MuddiGGEr25]

I know what most will say about switching to an older less effencient system, however that is not my question. i understand it will not be as good as running the TBI but if i cant find my culprit before engine swap in about a week then i want to go th easiest and least expensive route to install the 350 into my 1981 RV. 

The RV has a seized 400CI 1979 4bbl cali engine. rebuilt everything less than 4000 miles ago but she ran it dry for 50-200 miles, but everything is in immaculate shape.




I do not have the time/effort/money to work the 400 back to life because we will most likely be closing/moving into a house in the next 6 weeks.  therefore i have a 454 im putting in a mild RV cam and replacing the 1987 TBI 350 with.

I have done several searches and changed my wording up but most threads ended in an argument with no results or answers, because most time when people talk of switching a TBI to carb for whatever the reason its usually the post 1987 block that has the serpentine belt and accesories moved.


I just want to know does anyone know if i can simply pull the intake off the 1979 400 6.6l carb and all and install it onto the 350 TBI block? The RV isnt going to get great MPG no matter what i do, and the 454 isnt either lol.  I am fairly positive that the 350 was modified when it was rebuilt because i dont know a single 350TBI stock that can pull 18,000+ lbs 13FT tall at 55mph in a crosswind, let alone a pre 1988. regardless of gearing. and still get 6-7.5 mpg steady


I know i will need a electric fuel pump no matter what since the TBi block does not have a mech pump and the RV does not have a intank pump.

I think the carb should be sufficient if anything just a tad rich being jetted for a slightly larger displacement but not expecting to spin to 6000.

[MuddiGGEr25]

Sorry forgot to add, I looked up these 2 basic cheapie intake manifolds on summitracing.com 

The first one is obviously TBI and says 1987-1995 Gen 1 SBC 305 and 350

The second one is the one listed for 6.6L and 5.7L up to 1986 and is the carb manifold.

just by looking at these pictures it looks like it should be a straight forward swap unless im missing something which is why i made this thread.

[Stewart G Griffin]

Which engine are you working with?   the 350 or the bigblock?

[MuddiGGEr25]

Today I am working with the 350 that will be going into the RV to replace the 400 but later this week I will be replacing the 350 with a 454 I just need the 350 running properly to put in the RV so we can go camping

[Stewart G Griffin]

So why not just stay with the 350 or switch to the 454 now?

AS far as the intake, the 400's "should" work on the 350 because i don't think the trucks switched to vortec heads until 98 (but i'm not totally sure).  If the middle intake bolts on the 350 are angled you're good.  If they point straight up, you'll need a new intake or could modify the 400's.

 

[MuddiGGEr25]

Because the 400 is siezed up in the motorhome and we need to get it running and my 454 wont fit without modifications and the 350 is more than capable of moving the rv and trailer.  And the 454 would be going in the burb for towing and mudding since thats what i have just uaing the carb temporarily to make it run would be easier and less headaches for this summer until i have time to pull the harness and ecm and wire it all into the 1979 chassis. Im working with what i have b3cause i am in the middle of a layoff and dont have alot of cash right now for parts or wiring conponents lol

[VileZambonie]

Your post is confusing and hard to follow so let me see if I understand what you are asking.

You have an engine that is from an 87 TBI truck 5.7L that you want to put in an 81 RV that has a seized 79 400 sbc. You want to put the TBI 350 in the RV but swap over the intake, carb, distributor etc and omit the TBI and all of that good stuff? You want to know what you have to do to accomplish this correct? Where does the 454 play into this? Are you sure the 5.7L does not have a fuel pump block off plate?

[csdineley]

You might have to modified the bolt holes on the intake. On Tbi heads the intake bolts are at a slightly different angle. But other wise it will work just fine. When I switched mine, I actually got a little better mileage. Also might want to check for a mech. pump provision some blocks in 87 still had it, Mine did.

 And the Vortec heads started in 96.

[MuddiGGEr25]

Your post is confusing and hard to follow so let me see if I understand what you are asking.

You have an engine that is from an 87 TBI truck 5.7L that you want to put in an 81 RV that has a seized 79 400 sbc. You want to put the TBI 350 in the RV but swap over the intake, carb, distributor etc and omit the TBI and all of that good stuff? You want to know what you have to do to accomplish this correct? Where does the 454 play into this? Are you sure the 5.7L does not have a fuel pump block off plate?

Sorry about that, but yes everything you said is accurate. I only intend to omit the TBI temporarily until this fall once the RV is parked for the season so I have time to rip the dash apart, and run all the wiring, fuses, ECM, o2 etc, etc.

I do not see a blockoff plate were the mech fuel pump should be, the indentation and what looks to be the bolt holes are there but i am not sure if they are threaded. However I would be much more comfortable with a 12V frame mount fuel pump and a regulator that could bring it down to 5-7psi for the carb, then just back the regulator off to 12-14PSI for the TBI once installed. of course i would need to change the TBI internal spring as well. and I was thinking by having a variable regulator, i could do 3 things: 1. turn the PSI up for a little more power for towing or windy days 2. turn the PSI down when not towing the rig, and also when idling to just run the 150A alternator. 3. be able to run the carb all summer then swap to the TBI without having to switch pumps. i know some are designed for carb swaps and some are designed for TBI swaps into older chassis's


The 454 comes into play like this: we bought the motorhome for $750 total knowing the engine needed work, I traded the 4kW generator on board for a 454 longblock with waterpump and carb installed from a 86 mudder. the RV has 400W of solar and 500Ah of battery reserve so generator is largely unnecessary and it was disconnected from fuel 12 and 110V lines for the last 5 years anyway so it was useless in anycase.


 The 454 is currently resting in the back of the suburban waiting for flywheel, cam & lifters,starter, and exhaust manifolds.

 the TBI 350 that we are speaking about is currently in a 1988 suburban that i drive daily. and the engine was transplanted into that body 41K miles ago so I will need to take my time and mark everything for the TBI when ready because some of the wires are no longer original,. i.e. extensions, splices, relays, etc.

The said 454 will go into the 1988 suburban the same day once the 350TBI is pulled, it will also need a regulator to reduce the TBI FP down a little bit, although i have run a motorcraft 2150 (i know i know ford product) off this exact pump i installed for over 500 miles until I could get a mechanical pump ordered. that was on a 302 pushing about 450ft-lbs not sure how picky the q-jets are




I hope that makes it easier to understand, and yes I know I will need to get a HEI dizzy for one of them since i only have 1 spare around right now.

[MuddiGGEr25]

You might have to modified the bolt holes on the intake. On Tbi heads the intake bolts are at a slightly different angle. But other wise it will work just fine. When I switched mine, I actually got a little better mileage. Also might want to check for a mech. pump provision some blocks in 87 still had it, Mine did.

 And the Vortec heads started in 96.

This is exactly what im trying to figure out before I pull it apart, the dizzy i know will need to be changed like i said above, but mainly I am wondering if the 87 350 small block was tapped the same as the 400 small block in 1979.  Thats why I showed the pictures because they both appear to have the same angle for the heads and one is for the 400 and one is for a 87tbi. 


only other question would be is there such a thing as a TBI to quadrajet adapter?  i figure it would be largely inefffencient and expensive, thats why i was thinking just swap the intake/carb with dizzy and call it good for April-Nov lol