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TBI Swap

toomany

toomany

1/2 ton status
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Thinking of doing a swap to fuel injection on my 400. Ideally I'd like to like to go with a Fast system. But that is a little out of budget right now. A Speedway motors standalone TBI harness (http://www.speedwaymotors.com/Speedway-1985-1992-TBI-Engine-Harness,46375.html) popped up on my local craigslist for $100. I've seen it posted a few times before, so I'm guessing not much interest in the local market.

I've got a few questions regarding TBI in general. I'm 100% confident that I can do the swap with no problems...so let's take that out of the equation. I know how the system functions, what each sensor is/does and what happens when they aren't in the correct range. My questions are mainly with the tune-ability and the limits of the system.

Some background on the motor. It's a 1976 400 with some aluminum Bowtie heads. 2.02/1.60 valves. Cam is a Lunati Voodoo. .489/.504 lift, 268/276 duration (227/233 @ 050), 110 lobe separation. Compression comes in at 9.55 scr and 8.68 dcr. Currently running a Q-jet on a Performer RPM Q-jet manifold. Headman 69230's with 2 1/2" dual exhaust. (motor stuff starts at post 38 in my build, http://coloradok5.com/forums/showthread.php?t=306311)

The motor run really strong overall. I've got some problems down low with the carb. It's driveable, but I know it can be better. I've got another carb I'm going to mess with on there tomorrow. I"ve also got no choke hooked up and with the subzero temps cold starts are a bitch. If I can get it better with the carb route I may stay with it (probably just need a power piston spring change or rod/jet change). Up top it runs awesome. Mash the throttle and all hell breaks loose. It'll break the tires free in 1st, 2nd and 3rd. Revs to 6000+ like nothing.

Now my questions. Can a TBI be setup to run well on my motor? I'm mainly looking for drive ability over max power, but would not like to leave a whole lot on the table if I can avoid it. How about my cam, is it too big? I get a solid 12" of vacuum once it warms up.

I've already got an electric fuel pump mounted (and still using, the one on the motor hasn't been hooked up yet). So I'm covered there. I think I've got a TBI distributor and throttle body around here somewhere. That just leaves the sensors and an adapter for the carb manifold.

I'm also considering TPI. Have the manifold and wiring and associated parts for that already, just no computer. But again don't know the limits of the system. I've even got a CrossFire setup too, but I don't want to use that (if you know the system you probably know why). I even have an LT1 intake/computer/wiring/sensors I could use. But that would require drilling/milling/welding a hole for a distributor and I believe a Vortec dizzy.

I realize any of these systems won't be plug and play...I know that some tuning will need to be done. Just looking for some guidance
 
Not much help but I'm interested in the reply. I'm going to say it will work, but will obviously be a good bit of trial and error if doing mail order tuning.
 
Megasquirt just seems so complicated. I can't even figure out what I would need and what it would cost!
 
y5mgisi said:
Megasquirt just seems so complicated. I can't even figure out what I would need and what it would cost!
Click to expand...


This. I've looking into MS, read a ton on it and still don't really understand it to the point I feel comfortable doing it. I suppose if I jumped into it and forced myself to learn I'd get it. Maybe I'll look into it again.
 
If you go through the three articles where they ad a basic tbi to a 77 nova and tune it, it doesn't seem that bad. you do have to wade through a lot of info. but it seems much more affordable.

The self leaning kits start around $2k:eek1:
 
The software gives you a base map to get your car started. Then you start from there. If you mess up you can always go back to the base map.

On a side note, the sloppy mechanics guy does crazy turbo LS swaps Check out his turbo chevy 2500 vids. :eek1:
 
y5mgisi said:
Megasquirt just seems so complicated. I can't even figure out what I would need and what it would cost!
Click to expand...

For a simple tbi, it looks like the just need the MS1, their wire harness MS to motor), and the harness to the laptop.
 
Im no TBI genius but from the various reading Ive done I don't think the GM computer will be to happy with that cam. I think they like LSA in the 112-114 range.

You can make a GM throttle flow pretty good with some machining but it takes playing with fuel pressure and I think 454 injectors.

I have a holley TBI in my 82 it flows great, runs pretty good but tuning it to be perfect is proving to be a bit of a headache.
 
The computer on the TBI requires a even steady smooth flow of vacuum more than anything really. If that does indeed idle at 12'' then the TBI can be made to handle it. You first will need a plate to adapt that intake to the tbi body. Then it probably would need the TBI body ported, plus either 454 injectors or they also use cop car (I believe out of the Caprices) that flowed more than the standard 350 ones, but less than the BB ones. Instal an O2 sensor in it, find some way to get the speed sensor hooked up, raise the FP up to 15psi or so and then have to do the chip burns or have someone knowledgable on that process make you one for that engine. Then viola, a good running always starting hardly ever failing simple to find parts for FI system.

Im a huge fan of the TBI over any of the LS, TPI, ect systems for one large reason. Really, even with all the sensors unplugged and nothing hardly hooked up it will start and run in a limp mode. No matter what, no matter how bad it actually runs and how slow you actually go, a TBI will almost always fire up and move unless it has no spark or the fuel pump is dead. That solid reliability just makes it worth its weight in gold and its so simple its stupid.
 
and with long tubes I suggest you spend the few extra bucks and little extra wiring for a heated O2 sensor
 
I admit, I don't know much about megasquirt. If it works, great.

As to stout motors on TBI, check out thirdgen.org. People have done it, I don't think it's impossible. Don't know where you start running into problems with MAP, but it's not like it just quits working or something, the ECM just needs to know what needs to be going on at a specific vacuum.

I would say a 454 throttle body would be required (with the 454 injectors of course) but I'd also look into what sort of restriction that might impose on a ~400CID motor running at ~6000RPM. The 454 TBI may not flow enough to support the motor in stock trim regardless. My suspicion is that it won't. They were never made for high RPM applications.

I would throw any thought of TPI out. You run that thing too high and the motor is too large for TPI. You could probably do an LT1 intake setup or something, but as you know, once you start getting one-off from stock, it starts getting expensive and complicated. Even then I think the stock TPI throttle body is far too small for your setup. Form what summits (limited) CFM calculator shows, you'd need a minimum of 590CFM for that application, but 765CFM would be the "race" figure, and what I'd go with if the intake tract supports it.

Crossfire has been done successfully on thirdgen as well. Two 350 TBI's would flow somewhere around 1000CFM, so plenty, IF they will work with crossfire and it's not a huge hassle.

The good thing about the TBI is that it's a straight harness swap. Everything else is a bunch of cutting, splicing, adding, subtracting, etc.
 
I believe with porting and the pod spacers people have gotten upwards of 900cfm out of a 454 TBI body.

There is a formula to figure out CFM's needed based on displacement and rpms plus something else. That 400 shouldnt need more than 750 cfms to get it close to what the carb will give you, plus the added benefits of FI.

thirdgen.org is a great site to look at for that, also www.454ss.com is another good one as well, they deal with the BB, but the concept and tuning of a hot 400 SB will be very close to a stock or mild BB as far as air fuel is concerned.
 
Thanks for all the replies/help so far.

COCHEV said:
The software gives you a base map to get your car started. Then you start from there. If you mess up you can always go back to the base map.

On a side note, the sloppy mechanics guy does crazy turbo LS swaps Check out his turbo chevy 2500 vids. :eek1:
Click to expand...

I've been following his builds over on YellowBullet. Stupid amounts of power out of throwing parts together.


COCHEV said:
For a simple tbi, it looks like the just need the MS1, their wire harness MS to motor), and the harness to the laptop.
Click to expand...

I'm going to look into MS more. I think it'd be a system that can grow with me and whatever changes come down the road.



skyhigh4by said:
Im no TBI genius but from the various reading Ive done I don't think the GM computer will be to happy with that cam. I think they like LSA in the 112-114 range.

You can make a GM throttle flow pretty good with some machining but it takes playing with fuel pressure and I think 454 injectors.

I have a holley TBI in my 82 it flows great, runs pretty good but tuning it to be perfect is proving to be a bit of a headache.
Click to expand...

That was one of my concerns, the cam being too big. I don't think it's that large, but may be out of the range of adjustment.


454Sub said:
The computer on the TBI requires a even steady smooth flow of vacuum more than anything really. If that does indeed idle at 12'' then the TBI can be made to handle it. You first will need a plate to adapt that intake to the tbi body. Then it probably would need the TBI body ported, plus either 454 injectors or they also use cop car (I believe out of the Caprices) that flowed more than the standard 350 ones, but less than the BB ones. Instal an O2 sensor in it, find some way to get the speed sensor hooked up, raise the FP up to 15psi or so and then have to do the chip burns or have someone knowledgable on that process make you one for that engine. Then viola, a good running always starting hardly ever failing simple to find parts for FI system.

Im a huge fan of the TBI over any of the LS, TPI, ect systems for one large reason. Really, even with all the sensors unplugged and nothing hardly hooked up it will start and run in a limp mode. No matter what, no matter how bad it actually runs and how slow you actually go, a TBI will almost always fire up and move unless it has no spark or the fuel pump is dead. That solid reliability just makes it worth its weight in gold and its so simple its stupid.
Click to expand...

That was the main draw of TBI, it's simplicity.


dyeager535 said:
I admit, I don't know much about megasquirt. If it works, great.

As to stout motors on TBI, check out thirdgen.org. People have done it, I don't think it's impossible. Don't know where you start running into problems with MAP, but it's not like it just quits working or something, the ECM just needs to know what needs to be going on at a specific vacuum.

I would say a 454 throttle body would be required (with the 454 injectors of course) but I'd also look into what sort of restriction that might impose on a ~400CID motor running at ~6000RPM. The 454 TBI may not flow enough to support the motor in stock trim regardless. My suspicion is that it won't. They were never made for high RPM applications.

I would throw any thought of TPI out. You run that thing too high and the motor is too large for TPI. You could probably do an LT1 intake setup or something, but as you know, once you start getting one-off from stock, it starts getting expensive and complicated. Even then I think the stock TPI throttle body is far too small for your setup. Form what summits (limited) CFM calculator shows, you'd need a minimum of 590CFM for that application, but 765CFM would be the "race" figure, and what I'd go with if the intake tract supports it.

Crossfire has been done successfully on thirdgen as well. Two 350 TBI's would flow somewhere around 1000CFM, so plenty, IF they will work with crossfire and it's not a huge hassle.

The good thing about the TBI is that it's a straight harness swap. Everything else is a bunch of cutting, splicing, adding, subtracting, etc.
Click to expand...


I've been a member on Thirdgen.org for 10+ years. I don't venture into the injection boards though. My other auto hobby is F-bodys (too many to list). I know TPI runs out of breath early. A stealth ram would be more suited probably. The crossfire would be more problems than it's worth I think. I've read a few Vette builds that use it, but haven't been too impressed with the results.



454Sub said:
I believe with porting and the pod spacers people have gotten upwards of 900cfm out of a 454 TBI body.

There is a formula to figure out CFM's needed based on displacement and rpms plus something else. That 400 shouldnt need more than 750 cfms to get it close to what the carb will give you, plus the added benefits of FI.

thirdgen.org is a great site to look at for that, also www.454ss.com is another good one as well, they deal with the BB, but the concept and tuning of a hot 400 SB will be very close to a stock or mild BB as far as air fuel is concerned.
Click to expand...


I'll check out the 454ss site.



After thinking about it, I'm going to look into MegaSquirt some more. I like the idea of self tuning. Not having to wait for a tune to come in the mail and not having to pay to have it done each time I might need a change. Once I get over the initial learning curve it shouldn't be too bad.
 
Cool! Please do a write up on it. I'm a ways out from doing that. I'd like to try it out simple on a 350 and junk yard tbi parts like diyefi did in that 77 nova.
 
You might consider EBL from DynamicEFI: http://www.dynamicefi.com/

It's based on GM TBI hardware with updated software, easier to tune, and sort of self learning (you drive it in a learning mode, then make the changes in a semi automatic way). RBob is the guys user name over at thirdgen who does it and he's a real helpful guy, so you'd have someone to ask for help if something weird happened. You could ask him if he thinks TBI will do your job.
 
my cam specs are -- Adv. Dur. for the Intakes- .260 Exhaust- .264. Duration @.050 Intakes- .204 exhaust- .214. cam lift for the intakes- .284 exhaust- .300. Valve lift for the intakes- .426 exhaust- .450. Lobe separation is 113'

It pulls a solid 21" vacuum @ 800rpm. A very reputable tuner told me this cam is about as far as TBI can go but was very surprised that it pulls that much vacuum.
 
I went Megasquirt in 2006 and have had to do almost nothing to it since then (but sometimes I can't leave well enough alone: http://coloradok5.com/forums/showthread.php?t=181264). If you don't want to dig in and understand spark and fuel tables, warm-up enrichment, transient enrichment methods, injector characteristics, etc., then it's not for you. If you want low cost and maximum flexibility for future changes then it's great!

I started mine using the HEI distributor and internal ignition control. Later I changed to a crank trigger and a Ford EDIS distributorless setup. Then a year or two ago I got rid of the wideband O2 and went with dual NB O2's. All I had to do was change a few setting in the software in each case.

Doing it with TBI would be pretty easy. You can even get (or build) an adapter harness to plug in the MS ECU instead of the TBI one with no wire splicing. Then you browse the MSEFI forums for an engine setup sort of similar to yours and borrow their tables as a starting point. You can even buy a pre-assembled controller that comes pre-tested. Later if you wanted to do transmission control, you just add in the GPIO unit and you can control a 4L60-E, 4L80-E or whatever and set all your own shift points, lockup points, pressure, etc.

You can do all setup and tuning with free Megatune software, but it's worth the $60 or so to get TunerStudio, which has automatic tuning capability. Basically you get the basic tables in and injector specs set right so the engine can start and run. Then you start using it at very low rpm and load until it's getting the right AFRs. Then slowly work up into higher ranges. If the changes are massive, you can stop and manually tweak your fuel tables into a smoother curve and then start auto-tuning again.

As for cams, you can tune ANYTHING with Megasquirt. For the most extreme cases, Alpha-N is used, which is basically pure open loop. But I'm sure you're still in the range where MAF or speed density would work.
 
skyhigh4by said:
Im no TBI genius but from the various reading Ive done I don't think the GM computer will be to happy with that cam. I think they like LSA in the 112-114 range.

You can make a GM throttle flow pretty good with some machining but it takes playing with fuel pressure and I think 454 injectors.

I have a holley TBI in my 82 it flows great, runs pretty good but tuning it to be perfect is proving to be a bit of a headache.
Click to expand...

In my reading when I was gonna hop up my tbi system a lot of people mentioned that the holley injectors are know to not flow consistently. you would think theyd be better being holley but quite a few people mentioned the issue with them. that may have something to do with your tuning issues
 
Is there a for-profit entity behind megasquirt, or is it an open source community driven thing, or what?

I personally find tuning GM TBI to be annoying. I'm an engineer by trade and am fully capable of understanding all the details, but you end up with many screens full of parameters and none of it is documented. Some people understand some of the stuff and a few people understand most of it, but nobody seems to understand it all, or at least they haven't written it down in a coherent way in one place. Bottom line is you end up on Thirdgen or someplace begging for help.

Once I got the Dynamic EFI and did the self-learn a few times, I pretty much stopped. I just want it to run reliably. I may self-learn it again now that I have the 1-tons and new exhaust...
 
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