Flip66

iTrader: (1)

I have a create motor that is suppose to be 300 HP at the crank would a 350 TBI with the police injectors 206 or a 454 TBI I have both just trying to figure out which will work best.

Ronny

iTrader: (1)

I will suggest the smaller of the two will be easier to tune. If you find the smaller unit is restrictive you could always swap in the 454 unit at a later date. There is a tutorial on Ultimate TBI mods to make the smaller unit flow better. I found it with a search.

Flip66

iTrader: (1)

Yeh I have read a bunch threads it looked everyone said the smaller was good to about 250 275 HP if you had the 61lb injectors and the 454 was harder to tune.

kdrolt

The 4.3/5.7 TBI using 42.6mm bores can flow enough air to make 310-330 fwhp based on flow data. Stock fuel pressure + copcar injectors can provide enough fuel to make ~280 fwhp. Using larger injectors and/or raising the fuel pressure can provide enough power that you won't be fuel limited, so the 4.3/5.7 TB air flow will eventually limit the output (in the low 300s at the flywheel). Porting the TBI inlet (part of the so-called Ultimate TBI mods) should raise the air flow by approx 5%, so you might get into the 350 fwhp range.

That's really the point where you want to use either a bored TBI (46+ mm), or the bbc TBI (50.8mm). Regardless of either sbc or bbc TBI, the ECM EPROM will need custom tuning to work properly and make optimum power.

Many older posts at TGO talked about the limits of TBI: only two bores, wet flow, only two fuel injectors --- and how these eventually limit the power output. But the L98 and LT1 engines used 48mm diam dual-bore throttle bodies and they make adequate power, so airflow doesn't have to be a big problem with a dual-bore TBI; wet flow induction systems like carbs and TBI also have evaporative intake cooling that the port injection engines lacks and the mixture distribution really isn't that much of a problem; and finally GM used 28-32 psi as the stock fuel pressure on the 94-95 454 SS pickup, so the fuel delivery can be increased in a stock TBI by either larger injectors, raised fuel pressure, or both.

So many of the older TBI posts at TGO are misleading, especially when it comes to power limits on TBI engines. The one point that isn't misleading is the need for ECM retuning on a modofied TBI engine. HTH.

Flip66

iTrader: (1)

that is a big help thanks do you thing the 61lb injectors will work fine maybe use the 454SS regulator?

kdrolt

You need to either mod your FPR so that you can adjust it (see the Tech Articles), or buy an aftermarket unit. IIRC the 94-95 454 FPR has it's pressure set point fixed ay 28 to 32 psi by the coil spring within it. The v6 and sbc v8 uses a less stiff spring to get 9 to 13 psi. Read the Tech Article on making the TBI FPR adjustable so you'll understand how they work, and then you can decide on whether to do it or buy an aftermarket unit.

The 61 lb/hr should achieve ~330 fwhp using 30 psi fuel pressure, and that's right about where the v6/sbc (unported) TBI throttle body starts to become a flow restriction. Remember though that the simple math just tells you what you could make if everything worked properly --- and that means ECM tuning. Stock speed-density EFI, as used on GM TBI, on a modified engine isn't just plug-and-play. HTH.

Flip66

iTrader: (1)

Thanks for the great info do you have any place you recommend getting a chip from or is there some one here will do it.

Flip66

iTrader: (1)

taking your advice started doing the work on the TBI unit for more air today.