I am currently saving to finish up my afr 180cc head, 10:1, tbi 355, with ebl, prominator, and wideband and I need to know where my holley 670 cfm tbi starts to choke. Desktop dyno with all the flow numbers put in and everything as accurate as I can get it made 430 hp and 457 ft lbs of tq with over 440 ft lbs from 2000 rpm to 4500 rpm and since this is a 5000 lb truck tq is very important. That is a completly smog legal setup. CA smog legal heads, manifold, tbi, and c.a.r.b. approved high energy cam.... my question is with the holley 670 cfm tbi handle all that power? I was hoping with the right fuel pressure and tune it wouldn't be a problem but I don't really know. I was reading an articly that said you could push 20 psi comfortably to the injectors. I beleive the injectors are 80 pph. I Don't really want to go tpi because I spent about 600 on the tbi stuff and I don't know if it would be smog legal not to mention the cost and hassle of a tpi swap.

What's the cam going into it? You should be fine with the Holley 670, but I can't really speak for the injectors. Personally, I would swap on a GM injector pod and use BBC GM injectors (which is what i'm running).

If those 80pph ratings are like GM injectors and rated at 9-13 psi then you'd need to run it around 23-24psi fuel pressure. At that you'd be able to support it. That'll effectively come out to be about 116pph injectors.

cam is this one

High Energy 252H Hydraulic Flat Tappet Camshaft Only
Lift: .425''
Duration: 252°
RPM Range: 800-4800
C.A.R.B. Approved*
More Details

I used ben@bigpond injector calculator and for some reason the less psi I put in the more hp it says it'll support.

Can you just bolt on a bb tbi?

would a bored 350 tbi with bb injectors have more potential? What kind of hp would it support?

Sorry for all the questions.

So does the bb tbi bolt onto an sbc? If it does that would be awesome.... 2.25 inch bores with some machining.

you are better off having a 350 tbi bored out, as it has the correct idle circuit for your relatively small cubic inches compared to a bbc.

Can you bore a holley 670 cfm tbi and 2" projection manifold? Also I don't think boring it would help any becuase the biggest injectors (that I know of ) holley makes for it are 85 or 80 pph which isn't close to bbc injectors.

Aren't there guys on here running a true bbc tbi on a sb? I just think it would have more power potential. How hard would it be to tune a bbc tbi to idle right on a sbc and is it possible?

The GM BBC injectors range from 75 to 81 #/hr. Not many people run a true BBC GM TBI unit as they are hard to come by. Then the '94 - '95 units have 46#/hr injectors at 30 psi stock for 75#/hr. No room for growth.

Best set up when used with the EBL is high fuel pressure (greater then 18 psi), and a vacuum referenced fuel pressure regulator. No issues with tuning, drivability, or power.

There are a bunch of people using larger then stock TBI units on SBC's. One crossfire setup is using TBI's bored to 2.1" or 2.2" (can't recall which) and BBC injectors at 20 psi. My 327 is running a 2bbl TBI unit bored to 2-1/16". With 81 #/hr injectors at 22 psi.

RBob.

A question on the VAFPR. The nipple for the vacuum routes the hose inside the throttle body, exiting at the front of the tB. Doesn't this pose a pretty significant airflow restriction?

This is a subjective statement "a pretty significant airflow restriction." It would depend upon what was used for vacuum line. If I ran it inside of the TB it would be the small plastic line and run along the outside edge. Very little restriction.

OTOH, by the time folks are at this level of modifications, many use an external regulator. Easier to swap springs for the proper fuel pressure range, and easier to adjust. And, has higher flow rate to allow for greater return fuel. Which is required when high flow fuel pumps are used.

RBob.

OTOH, here is a 30 PSI fuel pressure regulator.

eBay Motors: 454 TBI INJECTOR COVER ASSEMBLY W/REGULATOR NEW (GM) (item 320028150594 end time Sep-20-06 20:01:42 PDT)

OTOH, here is a 30 PSI fuel pressure regulator.

eBay Motors: 454 TBI INJECTOR COVER ASSEMBLY W/REGULATOR NEW (GM) (item 320028150594 end time Sep-20-06 20:01:42 PDT)

1 -BRAND NEW GM 454 TBI THROTTLE BODY INJECTOR COVER ASSEMBLY WITH 30 P.S.I. FUEL PRESSURE REGULATOR

THIS THROTTLE BODY INJECTOR COVER ASSEMBLY WITH 30 P.S.I. FUEL PRESSURE REGULATOR FITS 94 - 95 GM TRUCKS WITH 454 C.I.D.(7.4L) T.B.I. ENGINES

YOU COULD ALSO USE THIS REGULATOR COVER ASSEMBLY ON ALL GM 4.3L,5.0L,5.7L, AND 7.4L T.B.I. EQUIPPED ENGINES TO INCREASE THE FUEL PRESSURE TO THE INJECTORS

THIS ASSEMBLY COMES WITH COVER,PRESSURE REGULATOR,GASKETS,AND LOCTITE FOR COVER SCREWS

BRAND NEW - IN THE BOX - GM - PART # 17113079

WILL SHIP - USPS

I have no ties to this seller, just trying to help a fellow thirdgener out.

Quote:

you are better off having a 350 tbi bored out, as it has the correct idle circuit for your relatively small cubic inches compared to a bbc.

please explain "idle circuit" ?

The VAFPR I saw installed used a piece of regular, black vacuum hose, and it looked like a really significant airflow restriction to me. I can see where your idea of using a smaller hose would be less restrictive, but, if I'm going to spend the money to get a throttle body bored out to supply enough air for my 383, I don't want any restrictions in the airstream.

What external VAFPR do you recommend?

Also, what the heck does "OTOH" mean?

OTOH=On the other hand