New 401 TBI Project

1980_Cj7

Well, now that we got all our 401 nightmares worked out and the engine is in and running well...I'm bored! Need a new project.

Soooo, just got most of the pieces we need to do a junkyard GM TBI on our 401. Got all the components from the same vehicle, a 1990 Suburban with a 350. Then, got the bigger 2 barrel throttle body from a 1989 Chevy Duallie with a 454.

My first question is concerning our dual plane Edelbrock Performer intake manifold. I got the 350 throttle body still bolted to the intake manifold. Looks like the intake was made just for the throttle body. The 454 throttle body is a different matter though. It came with an aluminum adaptor bolted up to it that mates up to a Quadrajet spread bore intake manifold. I guess Chevy used that setup until they depleted their inventory of carburetor style intakes.

It's kinda nice in a way as it sits the throttle body up higher, and it is very smoothly ported from the throttle plates to the intake manifold opening. I would still need to get an additional adaptor to transition from the spread bore adaptor to my square bore Performer intake though. I'm thinking this extra height with the adaptors might be good and act like a high rise intake almost. My question is, the Chevy adaptor isn't completey partioned off. It's kind of, but there is still a connection from one throttle plate to the other. Didn't get the spread to square adaptor yet, so I don't know if that will be "partitioned" or not.

I'm wondering if not having a complete separation between the two banks of the engine is going to be a problem. My understanding is the dual plane separation prevents pistons on the intake stroke on one bank from sucking exhaust, thru an open exhaust valve on the opposite bank, via the intake manifold.

I think I could pretty easily weld some partitions in the adaptors to complete the separation. What do you guys think?

PS-sorting out that wire harness last night reminded me of my old fishing days and line tangles, ha, ha.

401 Pacer

FYI, there have been Perfomer manifolds made expressly for TBI, perhaps yours is that style.

That adapter on your 454 TBI is also a heater of sorts, note the heater hose connections. If you're building a hot engine this may not be what you want (hot air = less dense = lower performance)

On a similar tack, no need to worry about that little opening in the division between the left and right throttle plates. If you add another adapter/spacer under this, make sure there are smooth transitions from each adapter and then to the intake itself, otherwise you'll induce unwanted turbulence.

I would run a matching Performer, and leave the water hoses disconnected.

1980_Cj7

Just checked out Edelbrock's web page. Far as I can tell, all the intakes they offer for AMC's are set up for square bore carbs. Couldn't find anything for a quadrajet or throttle body. Guess we'll have to adapt. Besides, our Performer intake doesn't even have 1,000 miles on it yet. Hate to go out and buy another one.

401 Pacer

For some reason Edelbrock's site doesn't list all the manifolds available....perhaps they've discontinued some. On the other hand, now that I've engaged the brain, they probably only made a TBI manifold Performer for Chevy and not for AMC.

milnersXcoupe

Would the 454 TBi be a good choice for lo_buking a Draw Thru Turbo set up on a 360 ? :-|

runnamuck

the coolant passages under the t.b. are there for smoother idle. they don't really effect once off idle. the slight draw in power was a trade off gm gladly made for smoother idle. anyway, if it were me i would hook it up, considering every manufacturer today uses something similar and still making impressive numbers.

1980_Cj7

I think I'm going to just get or make an adapter to go from the TB to the Performer intake. First problem is the out to out, side to side dimension on the TB bores is wider that the widest part of the opening on the Performer square bore intake. Now I know why most people are using the smaller GM TB.

So, I'll have to get or make an adapter with some thickness to it so it can funnel down to the intake opening. Makes me wonder what's the sense of have the bigger TB if it's going to get necked down. Although, if I make the opening the full size of the intake opening, I won't be losing any effective area.

On a side note, I just noticed the sticker, or what's left of it, on the hose coming off the GM adapter. It says "401". And that's the way I got it, no lie. I didn't doctor it. What a coincidence! Maybe that's an omen.

Soylent_Green

You'll have to keep that piece of hose intact.

Patf10

how much bigger are the butterflies on the 454 TB than those of a 350 TB, im considering building amegasquirt TBI for my 360 and im not sure that a 2bbl 350 TBI will flow enough

runnamuck

as far as i know the throttle body itself is the same, gm made up differences with the injectors until they started using a 4 venturi t.b. on big block applications. the q-jet "adapter" (engine coolant warmed plate) is just wider than the square bore. the t.b. can be unbolted from the plate and bolted to an adapter like one of these (either 1/2" or 3/4"):

http://www.howellefi.com/shop/customer/home.php?cat=256

(note: i'm not indorsing howell, they were just the easiest to find.)

or you can keep the factory plate and just get a q-jet to square-bore adapter about anywhere.

but heck i could be way off but i don't think so.

zero cool

The throttle body off the 350 (as well as the 305 and 4.3 V6) are all rated to flow 670cfm. The bores of the throttle body off a 454 are bigger and the unit is rated to flow 750cfm. They both have the same bolt pattern.

Holley makes a TBI to squarebore adapter plate that you can get at Summit or Jegs. The openings are made big enough to fit the 454 throttle body. The 350/305/4.3 throttle body sits on it just fine as well.

Here you can see the adapter plate bolted to the Edelbrock performer manifold on my 401.

Here's a picture of a 454 throttle body bolted up.

milnersXcoupe

Dial Zero for 'Cool' :t: ...........Great Pix - :shock:

Patf10

i think this is what i am going to end up doing, then i may also do a EDIS8 for timing, my brother built a EDIS for his 6 and its smoooooth

1980_Cj7

How do you delete a duplicate/double post?

1980_Cj7

Patf10 wrote
how much bigger are the butterflies on the 454 TB than those of a 350 TB, im considering building amegasquirt TBI for my 360 and im not sure that a 2bbl 350 TBI will flow enough

The 454 has 2" butterflies and flows 670 CFM. The 350 has 1 11/16" butterflies and flows 520 CFM.

Read more here. Other than finding a used one, this is the only place I could find where you can buy a big block TB. Holley told me about the place when I called their tech department. Chevy discontinued the big TB, and Holley only makes a replacement for the small TB.

http://www.strokerengine.com/TBIkit.html

ironman_gq

sounds like a great project. Just how difficult is it to wire in a TBI

zero cool

ironman_gq wrote
sounds like a great project. Just how difficult is it to wire in a TBI

If you get a fully intact harness from a donor vehicle, it's not hard. Very tedious but not especially hard.

Patf10

i need to start getting my system together. Injectors from a 350 should supply a 360 i think.

zero cool

Patf10 wrote
i need to start getting my system together. Injectors from a 350 should supply a 360 i think.

I'm running a throttle body from a 350 on my 360 and it runs fine. You'll have to reprogram it to run well but a 350 is a good starting point.

ironman_gq

you may want bigger injectors if this motor is going to breathe really well. I think that even on the 350's they can start to run lean with performance mods.