TBI, Fuel Per Hour, and Turbochargers

crash-harris

crash-harris

Famous Member
Just happened to be watching Stacy David at work one day and they plugged a new product from MSD on the parts bin section of the show.

This -> http://www.summitracing.com/parts/msd-2900/overview/

It has 4 injectors and built in fuel rails in place of the float bolts and bolts in place of a 4 bbl carb. They specify that the injectors are 80 lb./hr. but I'm not 100% sure if they mean 80 lbs. each, or total across all 4 injectors.

These built-like-a-carb fuel injection throttle bodies with all the sensors (except O2) and the computer on them seem like great candidates for a simple blow-thru setup that would not in involve pressurizing a carb and blowing gas all over the place. And the MSD and Edelbrock systems come within-cab tuners (Edelbrock one comes with a wireless tablet :shock: )

But my question is this. Would these be good candidates for the big sixer and a turbo in a blow-thru configuration? I know that the factory N/A multi-port EFI use six 14 lb./hr. injectors (84 lb./hr. total), so the replace-a-carb systems would have to supply more than 80 lb./hr. total, or is there something I'm missing on TBI theory? Don't really know much about throttle body injection other than the Dodge TBI system was a PITA to have on nearly anything.

Here's a list of similar available systems from Summit Racing (should be priced in order low-to-high) -> http://www.summitracing.com/search/depa ... ottle-body
 
From what I remember, TBI systems use huge injectors, so I would expect 80lb/hr is per single injector.
 
I just re-read the description on one of the MSD systems and it stated that each injector is 80lb./hr.

That's 320 lb./hr. of fuel :shock:
 
You're getting hung up on those numbers and forgetting the basics of calculating fuel supply/pressure required.

For 320lb injectors:
You'll support X HP at about 50% BFSC
80% duty cycle for the injectors

320*.8 = 256
256/.5 =512 HP supported

The difference comes in when you figure out how many injectors you need. 320/8 = 40lb injectors.

Fuel pressure also plays a role in that as well, you can bump up the pressure to eke some out.
 
I also realize that numbers are relative from any manufacturer and at any given point in any day (values change with variables such as temp, etc.).
 
Was looking @ that MSD Atomic FI when it came out. Didnt see any info on if it would work on a blow through. (assume it would?) Thinking they had 2 sizes? the smaller one for a turbo 300 six ? :unsure:
 
Looks like the Edelbrock E-Street TBI setups can be had from 500 to 800 CFM, but I can't find anything in reference to power adders...
 
I have been eyeballing that Powerjection kit for about a year for my Cadillac. Thing is, at $1500 you could buy three junkyard GM TBI setups or a Megasquirt kit and many hours of dyno tuning time. Given that most of the things you need to run fuel injection exist for the sixes, there should be very little fabrication involved, making the kit approach even more cost prohibitive.
 
You could also get a Cummins 6BT for that price, but if I'm going to turbo a 300, I don't want to worry about gas being blown all over the place or having to tear into a carb multiple times to rejet or worrying about floats getting crushed (or finding solid ones). And my driving takes me over various elevations (it's not flat here at all. My shop is about 1300+ feet above sea level and my current home is only about 500 feet above sea level). Also haven't had great experiences with factory TBI setups, so shelling out for the easy plug n' play (one of these days) is all worth it to me. As for the stock EFI setup, adjustable regulator/larger injectors and the Megasquirt (regulator and injectors raise cost at least another $300 assuming you have all the necessary factory EFI components), you have more wiring, less underhood room to work with, and if you want/need to get to the valve cover, you're looking at a whole afternoon and more gaskets just to get the job done.

Now, if I ever get to retrofit a 9N with a turbo 300, a carb should be ok since it won't ever travel too far :mrgreen:
 
Based on my research with other kitted fuel injection setups, I wouldn't expect anything approaching the reliability or flexibility of factory TBI setups. GM and Ford leveraged countless millions of dollars over nearly two decades designing their TBI setups to be reliable and durable enough for countless millions of vehicles. MSD, Edelbrock, and PPI don't have nearly the resources of Ford or GM, and I find it really tough to swallow they would be able to produce anything that's head & shoulders better.

I've emailed a few people selling these kits on ebay and CL, asking about why they're selling and universally the answer is "it didn't work as well as I thought it would." I'm sure some of that is poorly set expectation, and some of it is people who just aren't good at wrenches, but I gotta believe some portion of these people were genuinely and legitimately disappointed. If I really believed a $1500 PPI PJ3 kit would be a painless bolt-on for my Cadillac, I've have forked over the $1500 two years ago. But from what I've read (on the internet, admittedly!) a few hours at a junkyard and parts from a '95 Tahoe is going to yield better results. Maybe not easier up front, but definitely easier in the long run. I have honestly yet to talk to a single person with a kit like this on a single car that a couple years later would do it all over again. Everyone I've encountered thus far goes back to a carb or on to Megasquirt. So, I'm still arm chair engineering... :D

But, having Megasquirted an XR4Ti and Megajolted a Falcon, there just isn't that much cost involved. Certainly not $1500. My entire XR4Ti build was only $800. Most everything can be readily sourced from the junkyard, and the amount of wiring necessary to make either work isn't much. Three sensors, injectors, and a vacuum line? Child's play! Most car stereos have more wiring than that! :)

When something goes wrong, there are dozens of MS & MJ people I can turn to. But I don't know a single person running any of these kits. There is some piece of mind in knowing what your support structure looks like... :)
 
I've always read and found that the MSII kits are closer to a grand and utilize all of the same factory sensors, including the knock sensor and VSS in addition to the MAP, 02, TPS, Intake temp, all the tons of wiring. I just really like the idea of the PPIII setup. Seems that most of the similar kits, like the MSD one, flow 1000 CFM. But the numbers I've run, a turbo'd six should be running 600-750 CFM.

One day I'll get to try it both ways though :mrgreen:
 
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