Ok, I'm going to be swapping out my Holley 300-66 intake manifold for an Edelbrock Performer RPM Air-gap carb manifold with a TBI adapter plate. The question is this... What type of nitrous kit do I get? A TBI kit, or a Carb kit? Or with both work?

nobody knows?

You would definitly need to get one for a tbi unit, because a carbed nitrous system isnt going to give you the right nitrous/ fuel mix that you need to run nitrous on you tbi car correctly. A TBI nitrous kit will inject nitrous and more fuel into the system at the same time, hence a wet nitrous setup. And you cars computer has no idea that your shooting nitrous. So even though you have a carb intake on, you need a tbi nitrous system. your tbi adapter plate will mount to your intake, than the nitrous plate will mount to your tbi adapter plate, then the TBI unit will mount to the nitrous plate. Make sure before you do all of this that it will fit under your hood. I just put a air gap intake manifold on a carbed car and the open element air cleaner barely fits, and then once you add the thickness of the adapter plate, plus the thickness of the nitrous plate, you might be too tall, or might have to modify the air cleaner, or use a different air cleaner to clear the hood.

You can use either. I am using a carb setup for mine as it was cheaper. You just need to get the correct jets for the fuel pressure you are running. As xj mentioned, you may have clearance issues. I had to remove the spacer ring, and run a drop base filter, and modify the stud for the air cleaner, to get it all to fit under the hood. That is with a Wieand 7525 intake, which likely is shorter than the air-gap. You will want to find a very thin TBI adaptor, I am using the holley peice, so it is rather thick. IIRC the turbo-city one is thinner.

HTH
--john

Do the carb nitrous kits inject nitrous plus extra fuel, like the tbi kits? (I dont do anything with carbs very much, thats why i asked)

Any wet kit injects both fuel and nitrous. You just have to make sure it is an adjustable kit. I would be certain, that all carb kits are wet kits, as the carb has no way of knowing it needs to add fuel.

Here is my setup, you can see both the nitrous and fuel lines.

This is a nitrous bases question, not a carb based one. I'd buy the carb kit for sure...

Dewey, I just picked up a 7525 and am planning on putting a nitrous plate on it too. I am running a 454 TBI and a regular 4150 nitrous plate blocks the sides of the bores. Is that a dominator size plate you are using? Just curious. I actually plan on gettin the Edelbrock RPM spreadbore kit.

Brian

Using a square flange carb style nitrous kit on a TBI system works very well. I used a fuel pressure regulator to limit the pressure down to 7 psi, like a carb system would have. I was running 30 psi at the TBI and 7 psi at the nitrous kit. I went up another 150 HP on a 305 that was already making about 370FWHP. The best 1/8 mile pass on nitrous was 8.90s at Kennedale.

Picture Deweys setup with an Edelbrock Performer RPM, center mounted TBI adapter, 454 TBI, square flange nitrous plate. The adapter and nitrous plate combined were 1" thick.

The plate is the a normal NOS Super PowerShot for the squar flange. Part #12530NOS

Here is a shot of down the bores. As you can see, not blockage at all.


One other note, I had to use studs for the intake, as I could no longer find bolts that fit. I also had to do some grinding on the throttle body to get it to clear one of the bolts (you can see that in my earlier shots). The throttle body on mine, hits the front/drivers side nute in mine, since I am no longer using the recesed bolts that came with the holley adaptor.

I never said there was.

The TBI interference that you found is why I ditched the Projection adapter. That and the fact it was creating un-even air/fuel distribution. I bought a thin adapter off of Ebay from an unknown source that had 2" holes in it and bolted in place of a square flange carb. I then ground on the outer sides of the nitrous plate to clear the throttle blades on the 454 TBI unit.

Thanks for the view Dewey. I will definately be getting a spreadbore plate now. You may not think you are getting any blockage but I sure do. I can see the top of the nitrous plate under the throttle bores. You ought to grind the nitrous plate similar to what Fast355 is saying to clear the bores. Right now it looks like yout TBI is dumping fuel on to the top of the plate.

Brian

Its not the nitrous plate you are seeing, rather the Projection adapter.

Yup.

Fast, I wasn't aguing with you, I was responding BHall71, you snuck a post in there, while I was replying.

BHall71, I can promise you, that the nitrous plate is not causing a blockage at all. in fact, with the square bore on the 7525 intake, it fits very well, very smooth transition.

Ah ha I see now! That adapter plate you have has angled sides routing the A/F towards the center. duhh The adapter plate I have is 5/8" thick with no room for this taper. I lined up a friend of mines square bore nitrous plate and it blocked off the 2" TBI bores. I will still get a spreadbore nitrous plate to use with my adapter plate. Sorry about the confusion and thanks for the info! I am very anxious to get this single plane on.



Brian

man, i forgot all about this thread. I went ahead and got the carb nitrous kit anyway, also purchased a performer RPM air-gap manifold. As for the worries about clearing the hood, well, the car is hoodless right now. I will be purchasing a cowl induction hood once everything is together and I can measure out how big of a scoop i'll need.

The kit i bought has jets that go from 50 to 175

I would start out with some lower jets and work your way up if you need to, you dont want to feed your car too much if it cant handle it, and you dont want to push the envelope right off the bat.

exactly how i planned on doing it. start out with the smallest, but probably won't go past 100

what do you think about using a throttle body spacer with this whole setup? rpm air-gap, nitrous plate, tbi adapter plate, spacer, then the throttle body?

There's no need for the TB spacer IMO...

i didn't think so, but I bought it and am using it on the current setup (Holley 300-66 + 502-6) and my father went thru the trouble boring it out to 2" I'd hate to just toss it to the side, especially if it can still be put to use.

With the adaptor plate, nitrous plate and an air gap, you don't need the spacer, you already raised the injectors from the manifold floor, and you have a MUCH bigger plenum volume. TBI loves big plenums. I would get rid of the spacer.