How to reduce flow rate

[trades707]

I have three GM throttle bodies from S-10 2.8L mounted on my 48 Lincoln Flathead V-12. (Looks sharp.) However, the part no. 5235130-ACR TBI injectors flow about 33 lb/hr. Figuring the 60 deg V-6 was about 125 HP with two injectors, my 180 HP V-12 with 6 injectors will need a flow rate of about 1/2 the 33 lb/hr rating. Is there some way to slow the injectors down? Might there be an injector with a lower flow rate? How low can I reduce the pressure and still get a good spray? Other ideas?
Thanks
Abe

[Xnke]

Get injectors from a single-injector 4-cylinder car, OR see if the computer can run a slow enough pulsewidth with the injectors you've got.

Don't lower the fuel pressure if you can avoid it, as it's already pretty low and while atomization might be fine at a lower pressure, it might not and that could cause other problems when you first go to get it started.

For now, set it up and see if you can get it to run. Once it's running, see if you have issues with running too rich at idle speed, and if you don't have issues running at idle, don't worry about it-you're fine!

[trades707]

Thanks for the encouragement. I gave some thought to having the Fuel Tech controller use only the center throttle body until an off idle RPM to be determined, but then I'd need a progressive linkage for the throttle plates to avoid lean condition.
Abe

[Loyd]

sounds like a neat install, picture?

[1project2many]

X2 for pictures!

You're likely to run into trouble with that application and the stock injectors. At some point the ecm will be commanding pulsewidths smaller than the injector can reliably and consistently deliver. Installing six injectors from single four cylinder applications will make the issue worse. The fours were only slightly less hp than the 2.8 but the injector provided more fuel since only one was used. There may be an option, though but I don't know if it can be done solely with junkyard parts.

GM used two different styles of injectors in their TBI. Most of the V6 and V8 vehicles received injectors physically the same as your 2.8 TBs. But the big block medium duty trucks and some G vans used physically smaller injectors. Holley makes a pod that will attach to your TB which uses the smaller bottom feer injectors Once you move to that style injector you can source new injectors from 92-94 2.2 PFI engines which can be found in Cavalier and S10 among others. Flow for these injectors ranges from 16-17 psi @ 43.5 psi. Obviously you could drop pressure slightly if needed.

The TB on the medium duty trucks has a governor and looks different. They don't show up on Ebay very often and they usually go cheap. You could try your luck by buing one and trying to switch the pod to a "regular" TB .

http://yabe.chudov.com/TBI-ROCHESTER-PRODUCTS-CARBURETOR-CARB-for-1994-CHEVY-KODIAK-GMC-TOPKICK-1823/1823-0002.jpg

http://yabe.chudov.com/TBI-ROCHESTER-PRODUCTS-CARBURETOR-CARB-for-1994-CHEVY-KODIAK-GMC-TOPKICK-1823/ebayhist.html

Multec Bottom Feed injector data:
http://www.gearhead-efi.com/Fuel-Injection/attachment.php?attachmentid=2866&d=1344522961

A little discussion about Holley TBI and Holley injector part nos:
http://www.gearhead-efi.com/Fuel-Injection/showthread.php?1102-Delphi-bottom-feed-injectors


A picture of a Holley injector pod.
http://i.ebayimg.com/00/s/NDAwWDYwMA==/z/~qUAAOSwe-FVABnc/$_1.JPG

http://www.ebay.com/itm/Holley-TBI-Injector-Pod-Commander-950-Throttle-Body-Injector-Pod-2-Barrel-/390973118422?hash=item5b07d057d6&vxp=mtr

[trades707]

OK, I'm interested. But how does a multitek injector designed for 70 psi fuel pressure work at 13 psi? Would be good for a 60% reduction in flow rate. Or do we need a new high pressure pump. Looks like Holly eliminates the internal regulator.
Thanks
Abe

[1project2many]

18 lbs/hr at 43.5 (stock pressure) is more than enough for 180 hp. Most TPI systems run at 43.5 psi or higher. Holley does put a regulator on the injector pod.
http://i.ebayimg.com/00/s/NTAwWDUwMA==/z/AkAAAOSw3ydVit97/$_1.JPG

But I don't know if the replacement pod I linked to has one. There are more complete kits, I believe. Or possibly the four bolt pattern for the Holley regulator matches the GM regulator dimensions. There's one of the Holley parts on Ebay for $50 right now... Seems cheap enough for a test fit. If the GM regulator fits you can replace the spring with one for a 30 psi base and make the regulator adjustable to make up the difference in pressure.

[fastacton]

I'd be tempted to try it as-is and see how it works before buying new pods and injectors. If you go down just a couple of psi on the fuel pressure, you can still get a good spray pattern. I've seen TBI systems running as low as 9psi with a bad pump or regulator and the injectors still spraying well. It's not hard to make the factory regulators adjustable, they've just brazed over the adjustment screw. If you can't get the fuel flow low enough after that, then I'd look at injectors/pods. I'm no expert on flatheads, but I would think they'd need a little more fuel than a modern head design for the same amount of power anyway. I think I might try putting TBI on the Continental flathead 6 in my Clark Planeloader soon. How far away are you from firing it up?

[edfiero1]

Get injectors from a single-injector 4-cylinder car,


I dont think this is the solution to a lower flow rate. The 4 cylinder cars used only a Single Injector but it was good for around 60 lbs/hr

[1project2many]

Exactly... the four cylinders were only slightly less hp than a 2.8 but they provided that power with one injector.

[Xnke]

Another solution is alternating injection, then you're only firing three injectors at once. Doubles your pulsewidth for the same flow rate.

[RobertISaar]

depending on the ECM used, that certainly is a possibility.