[Simon]

I'm looking to replace the Holley vacuum secondary carb on my GTO with a FiTech throttle body EFI system. Current intake manifold is a performer RPM.

I understand that a single-plane manifold will work better with a throttle body EFI (don't need vacuum to suck the fuel out of with EFI, more stable vacuum reading for MAP sensor + more even fuel mixture balance), so am looking to replace the manifold too.

Any recommendations?

[steve25]

No so!
The much finner fuel atomizing that a throttle body type injection system makes is 100% usable on a duel plane intake also !
just as many of the factory's did when throttle body injectors first came out they used them duel plane manifolds.

You did not provide any of the needed info to make the choise you are asking about .

The pick of the manifold should still be based on the driving needs of your car, I.E. The weight of your car and its gearing come first .

For instance the Performer rpm and the Torker II both have pretty much the same stated power band, but if your motor is a 400 CID with 3.23 gears or less then the manifold you have now will give far better street driving performance then a single plane will!
Throttle body or carb wise a 400 CID motor that needs to make 100% VE at 6000 rpm needs a 700 cfm rating on its carb, or throttle body, a 455 with the same needs will call for a 788 cfm unit.

[74Grandville]

I think this topic is maybe due to this video. (Start at 6:00)

https://youtu.be/2sQJPZYSoUI

seems the EFI had a lot of trouble on a dual plane intake due to fuel distribution.

[455TA]

No problem running the performer rpm with the fitech efi system. I am doing it with my 462 Trans Am with e-heads. Runs mid 11's with limited tuning to it. You have to use the thin adapter plate to convert the 4 barrel quadrajet flange on the rpm intake to a 4150 flange.

[JLMounce]

I've run the FiTech on a P4B as well as a torker II.

Choose the manifold based on your needs, not because a single plane could work better. With that said, the couple people at FiTech I've talked to about the issue did mention that single plane manifolds tend to work slightly better with the system.

[Simon]

Thanks folks. 74Grandville - yes, that video & forum threads along the same lines are why I am asking.

Car details;

'69 GTO
Carb Holley 3310-3 (750cfm vac secondaries)
Performer RPM inlet (coolant crossover separated)
#13 heads (exhaust crossover blocked with aluminum)
0.060" (possibly 0.065"?) over 400 block
RAIV pattern cam + Rhoads lifters
TH400
Unknown brand small/high-stall converter
3.55 safety-track
295/50R15 rear (drums), 195/65R15 front (discs)

I'm in the UK, so need to plan a bit when ordering new parts.

[grivera]

Originally Posted by 455TA

No problem running the performer rpm with the fitech efi system. I am doing it with my 462 Trans Am with e-heads. Runs mid 11's with limited tuning to it. You have to use the thin adapter plate to convert the 4 barrel quadrajet flange on the rpm intake to a 4150 flange.

What is the part number on the adapter plate?

[Mace1971]

Summit SUM-G1420. Only $7 with two gaskets and it's only .124" so doesn't create any clearance problems. It's not really an adapter but a sealing plate to make sure there are no leaks when mating a square bore to a spread bore intake.

[grivera]

Originally Posted by Mace1971

Summit SUM-G1420. Only $7 with two gaskets and it's only .124" so doesn't create any clearance problems. It's not really an adapter but a sealing plate to make sure there are no leaks when mating a square bore to a spread bore intake.

shipping is as much as the plate! Any idea if this one will work?

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

More expensive but free shipping. The Amazon description says spread-bore carb to Edelbrock manifold. But, the summit description for the same part says: "Carburetor Sealing Plate, Open Center, Square Bore Carburetor to Spread Bore Manifold..."

[Mace1971]

I think the sealing problem is caused by the exterior shape of the carb pad on the intake. The one you post mirrors the same spread-bore carb pad and may not completely seal.

You should probably use this one: https://www.amazon.com/Edelbrock-273...YFT1HD2NJ5SRE5

The description is all hosed up and obviously for a different product but the plate shown matches the Summit model and isn't tapered like the other one.

[grivera]

great, thanks

[JLMounce]

I had my FiTech on an Edelbrock P4B and now on a Torker II as well. The FiTech didn't care which manifold it was on, it ran great on both.

So my advise is to pick the best manifold for your combination and not worry what style it is. FWIW however, the TBI setup semi-cures some of the single plane issues that arise with carburetors, because it doesn't need that vacuum signal. On my Torker II I have excellent throttle response even off idle.