which FI system?

[jekbrown]

I don't really want to invest $5k to get a new crate Ramjet V8 (though it would be cool!)... what are the best options with respect to doing an FI conversion on a 350?

I have a stock TBI system I bought from a ck5 member... but everything I have heard about those older TBI systems makes me wonder if it wouldn't just be better to get a different system.

So... which one? Holley Projection? Colley Comander TBI or MPI? Edelbrock Performer ProFlo? Holley Stealth Ram? Accell Pro Ram? There are a ton of options... some even use factory TBI stuff (which, like I said, I have!). I want to be able to plug a laptop into it and make adjustments.... paying someone to burn chips etc is kinda lame.

if you've done a FI conversion, please post up your thoughts!

j

 

[ryan22re]

In my opinion TBI sucks on most anything but a stock or close to stock engine. The positives though, are the parts availability. Stock or modified stock systems I think are the best bet. I would hate to get stuck in the middle of nowhere with a burnt up aftermarket ECU (probably really rare though).

But then again, would be great to buy a complete conversion, bolt it on, do some tuning and go. I don't think you can say the same thing for most modded stock stuff. Seems like the stock style stuff requires more tuning and homework than aftermarket stuff.

Have you considered a L31 vortec swap or TPI swap? I have been throwing around an LT1 with a TP1 L98 wiring/computer. But in the end, I will probably stick to stock TBI.

Have you checked out MegaSquirt? The prices are dirt cheap, and is primarily a do it youself thing. Buy unassembled ECU's in kit form and solder away. You can also purchase partially assembled kits and fully assembled kits too. Check them out at www.msefi.com Read that website for a couple of days, and see if you think it is for you. A TBI converted to MegaSquirt could be alot cheaper than a chip burning setup for stock computers. Plus if you decided to upgrade to multiport or some other kind of injection, you would just have to change the configuration of your ECU.

 

[85mudblazin]

Propane!!!!!

 

[k20]

Im a powerhungry SOB, so Im planning a cam swap, from the gentle one in it now, to one thats a little more hairy. Unfortunately, my current FI wont be able to handle the size cam I am planning, so I am going to change FI's. To one of these bad boys http://www.mass-floefi.com/

 

[Russell]

Not quite sure I believe their claims of perfect air fuel ratios without tuning, lol

A MAF TPI can only account for about a 15 - 20% change in the engine's pumping efficiency, I don't see why their system wouldn't be much the same...

 

[k20]

The way the MAF system works is you have a baseline chip, and then using the MAF and the O2, it tunes itself more or less.

Speed density, which is what most of the aftermarket FI's is, just plain sucks. Wish I had known more when I bought mine.

http://www.carcraft.com/techarticles/24549/ theres an article describing the 2 systems

 

[dyeager535]

I'm just going to have to say that the article indicated isn't even close to accurate in regards to MAF. Go read the stickies over in thirdgen.org's diy-prom forum and decide for yourself. There are threads talking about which is better. MAF has some major limitations, and if you are tuning your own engine, a MAF sensor is an expensive piece of junk when it fails, which complicates intake tract routing compared to MAP.

When my MAF sensor fails, I'm going MAP, no question about it.

 

[k20]

The one I posted doesnt complicate routing because the MAF goes right on top of the throttle body, or I believe I read on that site, that they can even put it under the throttle body if that is what you require.

Now, onto the MAF vs speed density. I did my reading on third gen. What I gather from it all, is that the speed density will make slightly more power if its tuned perfectly. The MAF will get it pretty close all the time. With speed density, its basically like a carb when it comes to temperature differences and altitude differences. You are stuck in one set of parameters.

Thats said the MAF will adjust all the time for the thinner air of altitude, changes in air density based on temperature, etc etc.

Also, the speed density will rely on a vacuum signal, and if you are running a cam with a little bit of a bump (ok, a lot of a bump) then its gonna screw with that signal.

What alllllllllll this boils down to, is my opinion, and what I gather from everything that I have read. I want something that is 98.5% of perfect all the time, I can give up those 10hp from the restriction of the MAF sensor and the being slightly off the correct tune.

Ive dealt with the speed density, and tuning of chips. It still aint right.

 

[Russell]

The biggest thing with Speed Density, is that you need to realize that it is going to take some work to get the tune perfect.

However, I think that site definitely has some false advertising going on. The MAF may be able to detect differences in the mass of air entering the engine, but ECMs only have so much wiggle room with adjusting their injectors etc.

With the stock GM ECMs, that is 0xFF (255 decimal). Really not that much room at all, hense the 15 - 20% ability to account for an engine with a larger cam etc.

Maybe they run an aftermarket ECM with a huge amount of RAM, and the ability to account for far more significant differences in the engine as far as pumping the air goes, but they still would have issues with rich idle mixtures.

With a big bumpy cam, you're going to get valve overlap, which allows some of the fresh air charge to quickly zip through the combustion camber, and out the exhaust valve while both are open. The 02 sensor then picks that up, and reports a very lean condition to the ECM. So it pours tons of fuel in to account for as much, and makes things insanely rich.

So, prehaps maybe this company is able to make such claims if you've got an engine that is built to accomodate their EFI system, but while I hate to rain on the parade, if you plan to build a wild engine and slap that EFI on top, expect to be doing lots of tuning to get your A/F ratio right at an idle, and get your spark / timing curves perfect.

Besides, tuning really isn't as hard as people crack it up to be, just takes time. You go for a drive, log the datastream, then when you're done driving, you park, and take 10 minutes to look at the log, and back off timing where you had pinging that caused engine retarding, increase it where it didn't, and adjust your VE tables to account for any lean or rich spots on the blm table. It then takes 5 seconds to burn the chip, and pop it back into the ECM.

The only reason why it takes years to get the chip right, is becuase every time you drive, you find something you can tweak just a touch to get just that much more power and economy out of the engine. After the first 10 tunes or so, you are typically good enough that you could just call it quits, but once you realize how easy it is to do the tuning, you usually just keep going.

 

[ryan22re]

I think MAF's are overrated. Plus for one to work "properly" it has to have a straight section of tubing before and after the sensor. Not the case in either position you mentioned. Plus, there is always an airflow restriction limited by the size of the sensor itself. And, the sensors don't like to get wet, dirty or oiled by a washable filter element, all of which are very possible in an off road truck.

Speed density is the way to go. Just my .02. I would go with an edlebrock/holley/accel speed density system anyday over MAF. Just another $300 part to fail if you ask me.

 

[k20]

O yeh I figure they do have some false advertising. I think just about every company does to sell their products, always have to take advertising with a grain of salt.

 

[Burt4x4]

I have nothing to compare it too but I run Edlebrock MPFI on my 454 and the throttle responce is amazing, I did have to get a Dyno tune as I was having troubles tuning it my self...shear lack of knowledge on my part...

Side note: The EFI tech that tuned my setup said he likes the Holley Comander 950's softwere way better than Edelbrock's. The Holley uses a laptop and is more 'user friendly' according to this guy. As you may know the Edle. setup uses a hand held control modual that basically is a buch of modifiers that you scroll thru and change percentages and such..

I am having lots of fun driving my K5 with MPFI & a 454

 

[dyeager535]

The numbers I've heard between speed density and MAF are about +5HP to MAP.

But even then, again stock for stock, MAP has a lot more tuning that can be done than MAF. For the most part, I throw any claims of "most power" out the window. A top fuel dragster engine makes a bazillion more HP than my motor, but at idle and cruise, that power means nothing. This goes along with "power under the curve".

In a vehicle not used for racing or where high engine RPM isn't the only place you need power, peak numbers are almost worthless, and thus "flow restrictions" and the like are less and less meaningful as they usually apply to higher engine speeds. Driveability is about fine tuning, MAP can do this better than MAF, at least as we are talking about OBD! stock systems.

My question is, whats wrong with the stock TBI systems? Used (trucks) 1987-1995, I would think GM to have changed quicker if there was a real issue with them. I think plenty of people here will attest to the stock TBI's dependability and driveability. Of course at this age and in a forum that pretty much deals ONLY with these systems, you are going to see failures. But there is nothing really mechanically wrong with the system as stock.

 

[Russell]

Again, we arn't trying to rain on your parade, K20, or make you look uninformed, but we've got first hand experience with these systems, and are trying to prevent the headache that we've been though, lol

I've also heard good things about the Holley systems as well, but for cost conern issues, I'll be sticking to the stock stuff I don't need to be revving past 5000 rpm on any of my rigs anyways!

 

[k20]

O yeh, I know y'all aint out to lead me astray, just stating my experiences with speed density, and being less than thrilled with what I have on mine, even after a dozen or so chips.

One of the main things that makes me think that MAF would offer superior driveability is the fact that is what alot of new cars come with, and you know that is what they are after, mileage and driveability. Just seems to me that the speed density stuff is older tech, by the time the TBI stuff on our trucks came about, the seed density style injection had been out, in chevy's since 80 or 81 (correct me if Im wrong), and say the ford style MAF (I think they were first manufacturer to go to it en-masse), didnt come out till 87 or 88, so the TBI in the comparable years had its bugs worked out, making it appear superior. Do any manufacturers still use the speed-density style of injection? I dont deal with enough new stuff to say one way or the other, just seems that the new ones I have dealt with, have a MAF setup.

Just seems to me that the MAF can make its curves up on the fly, suited to the conditions at that exact moment, wherease MAP, has to rely on its tables of data, and its only gonna be as good as that data, and whoever the programmer was.

 

[Cricket]

Just started running stock TBI. It's a nice simple system and cheap to buy. Add a painless harness with ALDL and it really is a pleasure. Course I am happy with a purely stock set-up.

 

[jekbrown]

yeah, i dunno if I wanna run the stock stuff... I mean, if I wanted to get a bling cam and heads later... the stock TBI really isn't good for much beyond stock hp/tq is it? Seems like the aftermarket bling is more upgrade friendly...

j

 

[stallion85]

I recently installed a Holley Pro Jection kit on my 350. I bought it used from a friend for $400. I installed in an afternoon and have been pretty happy with it so far. It took me a while to tune it in, it really woke up my 350! Throttle response is great and having the engine running while you are sideways helps out a lot too.

Mine is the older 2D version IIRC, it has a stand alone computer and cannot be hooked up to a laptop like some of the newer ones. They can be found on ebay for around the same price I paid if you are looking for a budget bolt on system.

 

[Cricket]

yeah, i dunno if I wanna run the stock stuff... I mean, if I wanted to get a bling cam and heads later... the stock TBI really isn't good for much beyond stock hp/tq is it? Seems like the aftermarket bling is more upgrade friendly...

j

Your right about TBI having limitations unless your willing to put in a custom chip with head changes, et. Most of the performance guys seem to be going with MPFI. Ryan B or Burt 4x4 should be able to give you some good advice on advanced injection.

 

[Ryan B.]

I've done several EFI swaps.
I did a tpi swap a few years ago on my 350 with a 300 horse cam in it. The tpi really woke up the engine. It was one of the best modifications i did to my truck.
I converted from a MAF setup over to speed density. I found a 730 ECM and MAP sensor for $50 on ebay, and got a chip from street and performance, spending 20 minutes on the phone to the owner telling him all of my specs for the vehicle this was going in.
For a mailorder eprom chip, all in all i was way happy with it. Adding a VSS took care of any stumbling when i'd do some hard braking with an auto trans.

Last year i swapped in a 2004 6.0L in my k5 and i've been VERY happy with this engine. All i really did was a K&N, a performance tune, and flowmaster exhaust.. It Flat out spanks my old TPI 350 across the board.

Any newer Vortec/GenIII engine, 5.3, 5.7LS1, 6.0L or even an 8.1L is a great choice.
Slightly better mileage i'd say, along with more power across the whole powerband.. especially the top end it'll scream till the 6200 rev limiter. The party would be over with the tuned port at about 5K-5200.
The driveability is freakin awsome with this GenIII engine, it doesn't want to stall out like the old tpi setup would like to, the 6.0L seems to want to stay running even when i bog it almost stalling it on the trail.

Knowing what i know now... I would do the 6.0L swap all over again.
In fact i swapped one in my tow rig after it proved itself in my k5.

PS. if you guys have any EFI questions TPI or GenIII/LS1, you can shoot me a pm.