Jinmajay, 490 cfm is got to be pretty close to the correct number for a stock TBI as you can get around 290 HP or so out of them in stock form, which means they must be flowing somewhere around 490.

So it may be that 2 units is too much flow for your engine, but I'd try it first to see. One nice thing about tuning EFI systems is you'll be able to back out how much pressure drop you have across your intake system at various RPM's and this helps in figuring out if you have too much or not enough intake flow.

Its not the end of the world if 2x490 is too much for your engine, I think as I mentioned in an earlier post in this thread there are some 2.8L engine sized TBI units that use the same base plate and injector pods. I estimate they flow around 325cfm in stock trim, so if the 490's are too much you could use these instead.

I'm curious to see how well a system like this can work, so when you get to the tuning phase I'll help you as much as I can.

I'm assuming your stock 350 injectors are the ones that typically flow 61 lbs/hr @ 12psi.

Each HP requires about .5 lbs/hr of fuel, so to make 550 HP you need 550 x 0.5 = 275 lbs/hr of fuel delivery.

At the stock 12 psi assuming an 80% injector duty cycle your flow with 4 injectors would be-

4 x 61 x .8 = 195 lbs/hr

So you need to bump your fuel pressure up to make 275. The flow increases as the square root of the pressure increase, so the pressure is calculated as:

New pressure = 12psi x (275 * 275)/(195 * 195) = 24 psi

The stock injectors fortunately work fine at that higher pressure (some guys have successfully run them as high as 30psi), so you should be fine on that.

Your fuel pump needs to be able to supply at least about 170 liters/hour at that 24 psi.

Paul T.

 

Thanks for all that calculating. I did a similar run through on the Mega Squirt site and from what I remember, came out basically where you did. I did by an adjustable (ext) fuel regulator to put on the outlet side of the TBI's and it has the vacuum port adjust. I believe this will help out a lot at idle.
Poo, poo on the smaller throttle bodies! Got to make the big ones work. I did not increase the diameter of bore any. I have the original 4.3 CPI fuel pump I plan to use as I just replaced it and it doesn't have that many miles on it. I believe they put out 60 psi and I’m not sure of the GMP flow. I figured I would hook it up and watch the fuel pressure gauge to see if it drops off at near WOT.

Yes, they are the 61 lb injectors. I got a flow matched set that have been serviced from the injector man.

Thanks and we'll be talking.

 

Consider placing the vac line for VAFPR to a manifold vac source. I placed a threaded nipple where the brake booster attaches on starboard side rear of manifold.

I believe the logic is that changes in vac may be less abrupt. However when a GM VAFPR was used many ran line to the TBI unit for vac. Do not T it into map vac source for sure. That must be dedicated.

 

I know this is about tbi but I wanted to show my custom oil pan I made to fit the stroker crank.

I would like to start a post of my own but I'm not sure hw it woudl be received being the engine is going into a Safari van.

 

nice I want to see this finished already

 

i'm still waiting to

 

I'm waiting on my transmission tools from Pro build automatics. Not to worry, I will need some help with filling in the tables. You all will be the first to know.

 

What ever happened to this project?

 

well?, I bought a H3 Hummer (my fault) and I have a 17 yo boy (also my fault). Go to my website to see both. The boy is driving my wife and i crazy! Things will be better in 10 months. I also bought a Hornet race car (website yes my fault). I am going to built a detached shop (plans on website) and this shoul help me to get back at it. I have done other work to teh project since you last heard from me. Take a look.

 

Cool, I'm glad to hear it didn't just die. I know life gets in the way of projects... I'm only JUST NOW getting around to installing TBI in my boat (a project I bought parts for 2 years ago).

I just remembered seeing this project a while back, thought it was really cool, and since I signed up to ask some questions, I checked back on it...

Glad to hear you haven't dumped the project.

 

Alright it's been a little more than 10 months what happened??

 

 

in for future updates

 

This is a work of art. Not a 4 barrell but similar. If you saarch this threads you will see others.

https://www.thirdgen.org/forums/tbi/...tbis-dual.html

I wish I had his talent...

https://www.thirdgen.org/forums/tbi/...le-bodies.html

 

I had read through those a long time ago. Definitely look nice.

 

I think you have done an awesome job! I would love to know how this works out. Pictures of the fuel linkage was very smart. I would say swift but I know that took a lot of thinking. I admire people that takes the time to think things out of their mind instead of their pocket. If you got time look me up on Google and give me a call, I think we have a lot of the same interest.

Carroll's Motorcycle & ATV Repair

Asheville N.C.