TBI injector selection

bronx · Post by **bronx** » Thu Dec 06, 2007 8:35 am

I am new to the megasquirt world and have a couple questions on how to implement TB fuel injection. I've searched the forums and the megamanual, but have not found the exact information I'm looking for.

My project consists of a 71 Bronco with a 351w crate engine with a 4bbl carb intake. I've decided to run a TB fuel injection setup due to the limited and costly multiport injection intakes for a 351w. I'm looking at the auto-nomics TB for my project, but I'm unsure of what type of injectors are needed for my application.

My question is: Do I need to run 4 big injectors, or can I run smaller injectors and double the pulses?

I'm not sure if I'm using the right logic here since I believe injectors are measuered in lbs/hour, but any advice/clarification would be appreciated.

Thanks

bleoh · Post by **bleoh** » Thu Dec 06, 2007 9:27 am

It is in the manual in the Injectors and Fuel Supply section.

Hope this link works.
http://www.megamanual.com/v22manual/minj.htm#size

bronx · Post by **bronx** » Thu Dec 06, 2007 4:45 pm

So it looks like I need 48lb injectors for my setup. I found some through summit racing for $50 each. I thought about going with a factory setup, but the only widely available 351w fuel injection setup is for f-150, 250, and 350 trucks. The problem with setup is the intake manifold is too tall for the bronco. I know TBI is not the best way to run FI, but I figure it's better than a carb.

73Eldo · Post by **73Eldo** » Fri Dec 07, 2007 5:33 pm

How about starting out with one of the GM TBI's off of a 350/5.7 those were and still are very common and easy to come by in junkyards since they were on most of the V8 trucks built between 87 and 95. There are people that make the square bore to GM TBI adaptor plates so it shouldnt make your hood issue any worse that a typical 4bbl carb. That will let you get going cheap and get the hang of things then you may get other ideas on what you want to do. Other cheap option is watch ebay for one of the older Holley systems. The early ones were 670cfm with 2 85hr injectors. I have seen them go complete for under $200. I have one running on a 500 cid cadillac so it should easily run a 351 unless its a real high performance (and $$) motor that you plan to spin real fast for extended periods.

What are the specs on the motor?
What is your primary use for the truck going to be?
What do you hope to gain with EFI?

bronx · Post by **bronx** » Sat Dec 08, 2007 5:39 pm

I think I'll start out with a Stock/Holley 2bbl TBI. I want to get my project on the road, then I'll work on a more extravagant setup.

Thank you all for your help!
(I'm sure I'll have more questions though as my project progresses)

73Eldo · Post by **73Eldo** » Sat Dec 08, 2007 7:24 pm

I started out with a complete analog holley 2bbl system (with the 5 dials) then switched to the MS. It was nice to have all the mechanical bits installed and working without all the extra programing and setup of the MS. After working all the bugs out of my setup in megatune and getting the hang tuning the MS is way better than the analog holley setup.

bronx · Post by **bronx** » Sun Dec 09, 2007 7:29 pm

So can I use and 2bbl unit off a chevy? I see that Holley has different part numbers for a 4.3L, 5.0L, and 5.7L.

Chevydave · Post by **Chevydave** » Mon Dec 10, 2007 3:02 pm

You could go to a junk yard, pick your part, and get a TBI with injectors off a 350 real cheap. I get'em here for less than $50.

73Eldo · Post by **73Eldo** » Mon Dec 10, 2007 5:34 pm

I think the 4.3,5.0,& 5.7 are more or less the same throttle bodies only the injectors are different. Only the 7.4 has the larger body and they never turn up in the yards around here, even on ebay they are not that common. I guess that is why Holley offered a 670 cfm TBI upgrade for the chevs which I think is the same as the projection one just has different sensors to be a direct fit to the OE truck vs the holley controler. Around here the 4.3 and 5.7 are very common. I dont see many 5.0's. The OE stuff all has IAC motors. THe Holley stuff IAC is an option on the newer stuff but most of the analog systems used a fast idle solenoid which works alright but not as cool as having the IAC.

ibuiltmine-o1oo · Post by **ibuiltmine-o1oo** » Mon Dec 10, 2007 8:20 pm

Ive been looking into TBI info lately, and this is a site with a couple good points of info....

http://home.earthlink.net/~jcgebhart/msindex.html

enyawix · Post by **enyawix** » Sun Dec 23, 2007 9:37 am

I am in the same boat with bronx. 351w and GM TBI. what sensors will work? Can I buy the OEM sensors for a GM 1500 truck? What about fuel pump?

73Eldo · Post by **73Eldo** » Sun Dec 23, 2007 11:47 am

There is a list with part numbers in the manual under the 'Wiring & Sensors', all you need to know is the thread size for the CLT. The IAT you are usually adding anyway so you might as well just get the one in the manual. Many of the MS vendors offer sensors with connectors to save you the trouble of getting them separate.

The GM TBI's dont need much fuel pressure so most pumps will work fine.
I have used a few Holley Universal Inline ones and have not had any problem with them plus they are quieter than the OE ones I have in other cars. In tank is the best bet for longterm life but the biggest pain to install and repair. If you can get a tank for your vehicle that was made for an intank pump I would go that route, if they never made one start with the basic inline one then make changes like sumps and baffles later if needed.