I was thinking of getting the 670cfm tb unit from Holley. what other mods should i considered when bolting the tb on my LO3.

only other mod is a flowmaster.

 

you won't need that thing yet. the stock TBI is good up to 4500 RPM on a 305.

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-Tas
'89 Formula WS-6
[soon to be Torch Red with black hood and headlights =) ]

305, TBI, auto, 14x3 chrome flat based open element with K&N, Milodon 160* thermo, functional Formula hood, cross-flow Flowmaster, '99z28 rear pipes and tips....

Super GRK_Taz World
EFI & Intake Options
AOL IM: superGRtaz
ICQ 82881207

 

taz is correct, dont worry about using a bigger tbi until you have more mods. i am currently doing so, and would recomend against it. I noticed nothing but a lag off of idle because the rapid increase of air from idle doesnt have a large enough pump shot of fuel from the chip. and its an aftermarket chip. so you wont be too happy with that tbi till you do somethings like a manifold and headers or more.

 

o, and btw

just wait and buy the one im desiging.

 

Your lag is probably because the 305 doesn't pull enough vacuum for the larger bores so the speed of the air is too slow going through the fuel.

 

I'm pretty confident that the lag problem people get from the larger TBI is due to stock pump shot not supporting a larger quantity of air suddenly entering the intake when all else is equal. Were not talking carbs where vacuum signal to the venturi is critical. Since fuel is sprayed in under pressure, vacuum in a tbi motor is not as critical as with a carb.



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1988 T/A,
9" Ford, 3.50 gears, Auburn posi, 700r4 -w- 2100 converter
350 .060 over with forged 1 pc rms crank, and forged TRW pistons, 9.5:1 cr
Factory GM heads Pocket ported, 2.02/1.60 valves, back cut
Lunati roller 219/227, .479/.480, 112 LSA
Holley 700cfm 4bbl on TBI truck 7747 computer and chip by Howell-EFI
Edelbrock Performer EGR intake, Edelbrock TES and 3" cat

 

The engine still relizes on the vacuum for atomization.

 

my lag has disapeared now that i adjusted my fuel pressure. back when i adjusted it before a few months ago. i didnt read the article, and i analyzed the pod wrong, more spring pressure = higher flow. i thought it was the opposite. i also thought the fuel lines were swapped. i realized my mistake about a month ago, but just got around to changing it back. its still not as jumpy as it was with the little tbi. definatly better pull now all through, but not to much more than stock tbi with correct fuel pressure if any. i cant remember to well. but will be running a stock tbi soon, when i get time to swap back, cuz i dont need the 454 on yet.

btw: i was as lean as i could get.

 

I still say a TBI or CARB that is too big for a smaller engine can hurt the low end, but I didn't relize that you hadn't bumped up the pressure enough.