swapping from a NBS 4.3 to a V8

Jan 13, 2002
18,105
0
0
46
San Antonio, TX
#1
I see this question come up alot on this board and others, so I thought that my real world experiences would help out anyone considering swapping a NBS 4.3 to a NBS v8. I will update this again when the actual swap happens.

Truck:
2001 Silverado base model reg cab

Stock Engine/tranny:
2001 4.3 V6 / 4L60E

New Engine / tranny:
2001 LS1 5.7 V8 / 4L60E

I bought the LS1 minus a couple of key items: Wiring Harness, Alternator, A/C compressor, and Electric fans. Know from the start that all this info, unless otherwise noted, works for swaps from the 4.3 to 4.8/5.3/5.7.

Now some comments always seem to come up when people ask about doing this swap:

Question:
I'm swapping to a 4.8/5.3...Do I need a new wiring harness?
Answer:
Yes.

Question:
I'm swapping to a 5.7 LS1...Do I need a new wiring harness?
Answer:
Yes.


Question:
I'm swapping to a 4.8/5.3...Does the wiring harness have to be custom made?
Answer:
No. any stock wiring harness from a 4.8/5.3 will work fine and is fairly priced at about 400. the 5.7 wiring harness will not work, though. will not plug into the truck.

Question:
I'm swapping to a 5.7 LS1 and using LS1 accessories...Does the wiring harness have to be custom made?
Answer:
Yes. due to the location of the alt and the injector plug, a 4.8/5.3 wiring harness will have to be modified to fit. A custom made wiring harness would be easier to use here.

Question:
I'm swapping to a 5.7 LS1 and using 4.8/5.3 accessories...Does the wiring harness have to be custom made?
Answer:
No. any stock wiring harness from a 4.8/5.3 will work fine and is fairly priced at about 400. the 5.7 wiring harness will not work, though. will not plug into the truck.

Question:
Do I need to change out my radiator?
Answer:
No. the 4.3 has 28" radiator like the 5.3. but it's not a terrible idea to upgrade.

Question:
Do I need a new PCM?
Answer:
No, the 4.3 PCM can be reflashed. but if you search for it, you can find package deals of used PCMs and wiring harnesses for around 300.

Question:
I'm swapping to a 4.8/5.3...Do I need all new belt accessories?
Answer:
Only have a partial answer here...but NO, not all of them.

Question:
I'm swapping to a 5.7 LS1 and using 5.7 bracketry and intake...Do I need all new belt accessories?
Answer:
YES. you need all 5.7 accessories.

Question:
I'm swapping to a 5.7 LS1 and using 4.8/5.3 bracketry and intake...Do I need all new belt accessories?
Answer:
Only have a partial answer here...but NO, not all of them.

Question:
Do i need to replace the Fuel Pump?
Answer:
No. it is the same part.

Question:
Will the driveshaft have to be modified?
Answer:
No.

Question:
Will the stock intake system work?
Answer:
No. I'm having to buy an aftermarket intake system to get this done.

Question:
Will the stock tranny work?
Answer:
This is a big question. the stock tranny WILL work. :read: the bell housing is slightly different, but will mate up to the 5.7

Question:
Will the stock engine mounting locations work?
Answer:
no, you'll have to secure some 4.8/5.3L mounts and registers.

Question:
Will the stock exhaust system work?
Answer:
No. you'll either have to remake the entire system or get a 4.8/5.3/6.0 system.

so...if you are considering a swap to a V8, here's what you need:

swap to a 4.8/5.3:
complete engine
belt accessories brackets
4.8/5.3 engine mounts
4.8/5.3 wiring harness
new exhaust system
4.8/5.3 intake system
new PCM or reflash 4.3

swap to a 5.7 LS1 and keeping 5.7 intake and acessories:
complete engine
belt accessories and brackets
4.8/5.3 engine mounts
custom built wiring harness
new exhaust system
new PCM or reflash 4.3

swap to a 5.7 LS1 and using 4.8/5.3 accessories:
complete engine
belt accessories brackets
4.8/5.3 engine mounts
4.8/5.3 wiring harness
new exhaust system
4.8/5.3 intake system
new PCM or reflash 4.3

So as you can see, the swap from a 4.3 to a 4.8/5.3/6.0 is not the nightmare everyone seems to make it out to be. with everything that swaps over...I see nothing wrong with dropping in a 4.8 or 5.3 even....you can get them cheap if you look. swapping to a 5.7 requires a bit more seeing that the belt accessories don't swap.
 
#4
Re: swapping from a NBS 4.3 to a V8

DemoN said:
Question1:
Do I need a new wiring harness?
Question2:
Does the wiring harness have to be custom made?
Question3:
Do I need to change out my radiator?
Question4:
Do I need a new PCM?
Question5:
Do I need all new belt accessories?
Question6:
Do i need to replace the Fuel Pump?
Question7:
Will the driveshaft have to be modified?
Question8:
Will the stock intake system work?
Question9:
Will the stock tranny work?
Question10:
Will the stock engine mounting locations work?
Question11:
Will the stock exhaust system work?
1. yes... some of the sensor locations are very different
2. not really, but to save time and if you are not electrically inclined
save burned up wires and parts.
3. no, but the larger displacement does require more capacity in
the cooling department.
4. no, but the programming will need to be changed.
5. yes, if you use the OE LS1 manifold.. brackets and accessories, if you
use a 4.8/5.3/6.0L intake some can be used.
6. no.. the OE will handle the output, but a fuel return line should be
configured on the LS1 fuel rail. the fuel pump does not like to deadhead
pressure.
7. no, the trans will stay in the OE location.
8. either the LS1 or GENIII truck intake will work, but the injectors are
different...
9. yes.... proper setup and programming will determine trans life. a shift kit
is usually in order.
10. no, youll have to secure some 4.8/5.3L mounts and registers.
11. youll ahve to either go a custom route or use the 4.8/5.3/6.0 exhaust.
airdeano
 
Jan 13, 2002
18,105
0
0
46
San Antonio, TX
#5
Re: swapping from a NBS 4.3 to a V8

airdeano said:
5. yes, if you use the OE LS1 manifold.. brackets and accessories, if you
use a 4.8/5.3/6.0L intake some can be used.

airdeano
Can you please explain the reasons for this a bit? my understanding is, if you have the mounting brackets for the componants, then some of the 4.3/4.8/5.3 accessories will still swap. is it incorrect?
 
Aug 14, 2001
54,150
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0
45
New Jersey
www.picturetrail.com
#6
Re: swapping from a NBS 4.3 to a V8

airdeano said:
5. yes, if you use the OE LS1 manifold.. brackets and accessories, if you
use a 4.8/5.3/6.0L intake some can be used.

let me step in here just to clairify something and try to fix the confusion (and i could be totally wrong at the same time so bear w/ me)

Demon has a COMPLETE LS1 w/ acc. brackets. He wants to take just the acc's off the 4.3 (not the brackets) and bolt just the acc's up to the original LS1 brackets. If he does that he should be fine correct? :dunno:
 
Jan 13, 2002
18,105
0
0
46
San Antonio, TX
#7
Re: swapping from a NBS 4.3 to a V8

CKTA said:
let me step in here just to clairify something and try to fix the confusion (and i could be totally wrong at the same time so bear w/ me)

Demon has a COMPLETE LS1 w/ acc. brackets. He wants to take just the acc's off the 4.3 (not the brackets) and bolt just the acc's up to the original LS1 brackets. If he does that he should be fine correct? :dunno:
that's exactly what i mean doug, thanks :D
 
Mar 15, 2002
898
0
0
Austin
#8
Re: swapping from a NBS 4.3 to a V8

The trannies might work, but the bellhousings are definately different.

Also the fuel lines on the 4.3 are hard lines, while the ones on the genIII v8's are not, that shouldn't be a big issue at all though
 
Mar 15, 2002
898
0
0
Austin
#10
Re: swapping from a NBS 4.3 to a V8

all you need is new motor mounts? what are registers? the part the mount goes into on the crossmember where the engine sits?
 
Jan 13, 2002
18,105
0
0
46
San Antonio, TX
#11
Re: swapping from a NBS 4.3 to a V8

just cuz i thought i should keep it updated too....just bought my wiring harness, new 200 amp alternator, and ls1 fans. :D


but i'm still getting conflicting info on the a/c compressor. :think: i'm still hearing the 4.3 one will fit in the ls1 brackets.
 

chevydad

New member
Nov 12, 2004
310
0
0
latrobe, pa
#12
Re: swapping from a NBS 4.3 to a V8

click the link in my sig and call them. they will know and have the parts you need. ask for brian he just did the swap you are talking of on his personal truck as well as many others.
 
Jan 13, 2002
18,105
0
0
46
San Antonio, TX
#13
Re: swapping from a NBS 4.3 to a V8

I'll tell ya...Brian was VERY helpful. told me some things I didn't know, clarified alot that i was wondering, and saved me from making a costly mistake. I'll update the first post with the information he passed to me.
 

chevydad

New member
Nov 12, 2004
310
0
0
latrobe, pa
#14
Re: swapping from a NBS 4.3 to a V8

DemoN said:
I'll tell ya...Brian was VERY helpful. told me some things I didn't know, clarified alot that i was wondering, and saved me from making a costly mistake. I'll update the first post with the information he passed to me.
he knows his ****. we have been talking about putting a 5.3 or ls1 in my 83. if i had the money it would be done.
 
Jan 13, 2002
18,105
0
0
46
San Antonio, TX
#17
Re: swapping from a NBS 4.3 to a V8

lct812000 said:
relating to an LS1 swap....what's the base HP and torque on an 2001 LS1?


Off subject, do you have another vehicle to drive while you are doing the change?
Base RWHP: 290-330. the average seems to be about 314.
Base RWTQ: 300-345. The average seems to be about 325.

Yeah...my cuz is loaning me his honda for the week. :D
 
Oct 6, 2004
4,041
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39
Lake Conroe Texas
#18
Re: swapping from a NBS 4.3 to a V8

DemoN said:
Base RWHP: 290-330. the average seems to be about 314.
Base RWTQ: 300-345. The average seems to be about 325.

Yeah...my cuz is loaning me his honda for the week. :D
EDIT: what gear ratio was used to get those numbers? You've got 3.42's right? Do the f-body's have the same ratio?(I'm not up on my f-body knowledge like I should be) If not, do you plan on changing gear ratios?

Will you have this swap completed in time for the Houston meet?? I'd like to see your ride in all its glory.
 
Last edited:
Jan 13, 2002
18,105
0
0
46
San Antonio, TX
#19
Re: swapping from a NBS 4.3 to a V8

lct812000 said:
EDIT: what gear ratio was used to get those numbers? You've got 3.42's right? Do the f-body's have the same ratio?(I'm not up on my f-body knowledge like I should be) If not, do you plan on changing gear ratios?

Will you have this swap completed in time for the Houston meet?? I'd like to see your ride in all its glory.
most of the dynos were taken on 3.42 gears in a 10 bolt i believe. i'll be changing to 3.73 LSD

no...wont be done for the houston meet :(
 
Jan 13, 2002
18,105
0
0
46
San Antonio, TX
#20
Re: swapping from a NBS 4.3 to a V8

first post has been update with information concerning the wiring harness. Note that a custom wiring harness would be preferred if swapping in a 5.7 LS1 and using 5.7 accessories, brackets, and intake (as i'm doing).