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Discussion Starter · #1 ·
Since I have a FAST 102 lying around I see no reason to not put it on Big Red (LS1). To do the upgrade I'd be putting on a 92mm throttle body of some sort which I suppose would lead to some kind of OTRCAI to round it out. Those things all seem pretty straightforward.

My question, however, is about the FAST and injectors. I removed the FAST complete with stock LS2 injectors and stock LS2 fuel rail since I didn't need them on the Punkin as it was getting a blower. Would it make sense to just put on the FAST with the LS2 rail and injectors instead of getting adapters/spacers and o-rings to fit the LS1 injectors onto the FAST? With a new throttle body and probably headers at the same time I'll be having it tuned anyway so surely that could accommodate the new TB and LS2 injectors?

If that wouldn't cause any problems, pretty much all I'd further need to do the swap is a MAF extension harness and a MAP extension harness.

Is the LS1 MAF overly restrictive? Can an LS2 MAF be used on an LS1 without a lot of complexities involved in order to gain a good bit of air flow capacity?
 

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ls1 MAF is :poop:

i am running an LS2 MAF on my 04. werks gud. just needs t00ning.

TB will need t00ning, too.

running ls2 injectors should be ok, just need the adapters for the injector plugs. you can also run ls1 injectors with the LS2 rail with some spacers.

if you do the FAST on an 04, use the forward MAP location just behind the TB if you can.
 

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I rather by rails and run ls1 length injectors. But you just need adapters to plug the harness in if you want to use all the ls2 stuff.
You'd need more adapters to run the other maf, depends if you'd like to keep the iat separate or not. Can put the map in the back but I ended up moving mine forward but that was for the 3bar.
 

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Discussion Starter · #4 ·
My FAST is already drilled for the MAP up front so I'd plan to run an extension harness to make it work.

I didn't realize the injector plugs would need adapters, probably need one for the MAF as well. So, either way I go I'll have to get a few supporting parts. Perhaps the LS2 fuel rail with the LS1 injectors using fuel rail spacers and new orings would be the most simple plan.
 

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Discussion Starter · #5 ·
I didn't realize that the injector adapters were so inexpensive, perhaps the LS2 injectors already on the FAST would be the way to go using those plug adapters. Then I'd just need an LS2 MAF and adapter for that. Since the LS1 already has the IAT separate from the MAF I assume I just need an adapter plug from LS1 harness to LS2 MAF. Not sure if anyone makes one, will look around.
 

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I didn't realize that the injector adapters were so inexpensive, perhaps the LS2 injectors already on the FAST would be the way to go using those plug adapters. Then I'd just need an LS2 MAF and adapter for that. Since the LS1 already has the IAT separate from the MAF I assume I just need an adapter plug from LS1 harness to LS2 MAF. Not sure if anyone makes one, will look around.
a few places do. i forgot where i got mine, maybe hawks motor sports? if not, caspers electronics probably makes it.
 

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If you're doing all of that, then absolutely get an LS2 MAF (especially if you'll do an OTR intake). The LS2 MAF is larger, and looks a lot better than the squared-off LS1 MAF. I ran one on my 04 for many years after my LS1 MAF took a crap. You just need an inexpensive adapter harness since the connections on an LS1 MAF (3-wire) are different than the LS2 (5-wire).

**Word of caution though. Swapping from an LS1 to LS2 MAF could cause your car to run like complete crap since the MAF scaling will be off. I had to drive to my tuner with my LS1 MAF on the car, then swap the LS2 on on once I got to the dyno. YMMV though, so try it out and see what happens.
 
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If you are going with the FAST 102, why would you only run a 92mm TB on it? Kind of defeats the purpose of that intake
 

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Discussion Starter · #15 ·
^^^Exactly. When I had the 102 on my LS2/6.0L It was never held back by the throttle body. In fact, I used the same 90mm OEM throttle body when I put a blower on it. Again, never held back by the size of the TB. Same concept as carb sizing, bigger isn't necessarily better. To be clear, the TVS2300 on the LS2 is only running at 6-7 psi.

On the LS1/5.7L I want to keep the off-idle throttle response crisp, the 92mm is the way to do that without choking it at the top end. The engine is completely stock except it will eventually have the FAST and shorty headers and a tune of course.
 

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^^^Exactly. When I had the 102 on my LS2/6.0L It was never held back by the throttle body. In fact, I used the same 90mm OEM throttle body when I put a blower on it. Again, never held back by the size of the TB. Same concept as carb sizing, bigger isn't necessarily better.

On the LS1/5.7L I want to keep the off-idle throttle response crisp, the 92mm is the way to do that without choking it at the top end. The engine is completely stock except it will eventually have the FAST and shorty headers and a tune of course.
Holdener did a video about TB size on PD blowers. The bigger the better (until it isnt the smallest restriction)
 

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Discussion Starter · #19 ·
Holdener did a video about TB size on PD blowers. The bigger the better (until it isnt the smallest restriction)
My tuner was watching things through the whole RPM range and said my LS3 throttle body wasn't holding it back by his estimation. I'm only running 6-7 psi.

bruh.

i think we are talking naturally aspirated here.
In general yes, but I did mention above that I'm running a OEM LS3 90mm throttle body on my blown LS2 and it doesn't appear to be a restriction. Given that, point being I can't see a 92mm TB being a restriction on a NA 5.7L.
 
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