is it a direct bolt on, plug and play, or what has to be done to adapt it, i know its the same CFM as the holly TBI unit, sure it would be cheaper to pull a 454 TBI off of a truck or motorhome......what years would work on an 89 305 TBI??? Thanks

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www.rvmorsemachine.com

very impressive site and not bad $$$ thanks

 

Keep in mind that the 305's and 350's both used the same TBI, which flows between 490 to 520 cfm depending on whose numbers you believe. That's plenty of air flow for a 305 unless you are talking about a pretty hot set of heads and a cam to let you make peak HP well over 6000 rpm.

Here's useful calculator that tells you how much flow you should have for an engine:

http://www.4secondsflat.com/Carb_CFM_Calculator.html

It shows that your current TBI is good up to around 6000 RPM on your engine.

However if you are planning to build a 305 to spin to the moon and you really need the airflow, the only issues I'm aware of on using a 454 are the throttle linkage and the IAC unit. People typically cut off the original 454 linkage plate and weld on the correct SBC linkage plate for their car.

The IAC connector is different but you can either hand wire on a SBC connector or use an adapter cable from www.turbocity.com . I believe your current TPS sensor will mount right on the 454 units.

Another popular way to go is to have your current TBI unit bored oversize, this can be done by www.rvmorsemachine.com or search on ebay for a seller who uses the name xtremefi .

However keep in mind that if you put a larger unit on your engine than it really needs you'll go slower, not faster. This is because there is an optimal range for the velocity of the air as it goes through the unit, and by going too big the airflow velocity drops down too low, which hurts the cylinder filling (and VE) and you make less power.

One way to see if your TBI unit is hurting your performance is to scan and log the ECM on a full out run. Then take a look at the MAP values when the engine is at full RPM and load, and compare that value to the MAP value displayed when you turned the ignition on before you started the engine. The difference in these values is showing you how much pressure drop you have across your TBI unit at full throttle. If the pressure drop values are very low then the TBI unit is not restricting the air flow, but if they are too high then either your TBI unit is too small or your throttle isn't opening up all the way. I'll let someone else chime in on what the optimal pressure drop value should be at full throttle as I'm still experimenting with this.

Good luck-

Paul T.

 

i agree with the having to much TBI wont do good, but i plan o building a built 305 stroker and will need the more CFM, wish i could ball park between the stocker and the 454 unit, maybe that boring of my TBI may work out, anyone have any experence on that, was it worth it or not (we are talking a lightly modded 305 not my planed motor)...... im the one that rather fabercate something than buy it out of a box so this is the main reason im asking about this over buying a Holley TBI