Which Junkyard Throttle Body to choose

[RobertISaar]

it also looks infinitely more awesome. :)

[EagleMark]

This may give the idea, it was a post by Six Shooter and would cover our DIY Dyno as well...



Injectors on top of velocity stacks?

[RobertISaar]

1. that is ridiculous, and i want SO BAD!!!

2. i bet the injectors above the throttles is due to a couple of reasons, #1 being it won't mess with an optimal intake tract. #2 i would assume it would allow better use of the engine's fuel as a coolant for the air charge. possibly better atomization?

[EagleMark]

If you noticed later in video it is all enclosed, well bottom half of air cleaner is there to cover it all.

[Six_Shooter]

The only reason injectors are placed close to the valves is for driveability and emissions. For high power and high RPM applications placing the injector higher in the runner (without a lot of bends) will get the fuel suspended more evenly in the intake charge.

I still love that video of the guy "driving" the engine, in the test cell.

Now they have computers that run the engines to simulate being on a track:

[1project2many]

The only reason injectors are placed close to the valves is for driveability and emissions.

Yep. Low rpm operation allows more time for fuel to be heated and subsequently to vaporize. When fuel vaporizes it expands and as it expands the gas tends to displace oxygen needed for combustion. The complications of wet flow manifolds haven't really disappeared. Placing injectors in the plenum of a large intake, away from the runners can cause the manifold to become fuel saturated at idle and low speed and can cause it to behave like an old carby engine with the float level too high. Additionally vapor handling is a big deal for OEM applications and a plenum with unburned fuel hot soaking in the summer sun is going to require a well thought out strategy to prevent excess evaporative emissions unlike a race car used offroad only. At 6k plus rpm fuel delivered by an injector is drawn into the cylinder in very short time, vapor handling isn't as important, and race manifolds can usually have injectors placed wherever they choose. But for us street guys it's usually safer to select a location closer to the valves.

I've always liked listening to this one:
http://www.youtube.com/watch?v=aRMpi1esjoQ

[EagleMark]

I could only take 50 seconds of that and was laughing so hard I woke the wife up... WOT was great!

So it's the low RPM, that's why the F1 cars idle in pits at like 6000 RPM... guess there's no issue with manifold getting wet at 12,000 or so RPM. One video said piston was traveling 300 times per second!

[daleulan]

My dyno lab isn't quite as nice looking but that's basically how I have my lab set up - the computer drives the engine. For steady-state calibration I can do it manually. For emissions testing on the three cycles I test on (HDDT, WHTC, ETC) the setpoint data is at 1 Hz; it looks like about 20Hz setpoint data on this dyno to get the time resolution down for those fast gear shifts. That's quite an impressive fuel cloud above the injectors.

For transient fuel control, injecting right by the intake valve is nice. Not only for emissions but to make transient calibration easier. For starting, though, I liked throttle body injection. It was much more forgiving. I recall being frustrated when I first needed to do gasoline start calibration at -40 with multipoint - lots of wet plugs during the calibration. I resorted to firing the plugs a dozen times per TDC to keep them dry 'till I got the calibration close. Much more spark than that and the engine runs on electricity... I could only do three cold starts in a day because it was just in a cold room. Probably should have rented a glycol chiller and forced the issue. For natural gas (the fuel I mostly tune to) multipoint is only an emissions and backfire advantage - basically the feedback from the O2 sensor is faster because of reduced transit delay and there's less fuel to ignite in the intake for when it decides it wants to spit back. That last point is especially important if you have a plastic intake manifold. I punched a pretty big hole through one of those plastic GM Vortec truck manifolds one time. If you have fuel film issues with natural gas then you have other difficulties in getting the engine to start - like oil viscosity.

[1project2many]

I could only take 50 seconds of that and was laughing so hard I woke the wife up... WOT was great!

lol. Hope you weren't drinking the morning coffee when it started.

there's less fuel to ignite in the intake for when it decides it wants to spit back. That last point is especially important if you have a plastic intake manifold. I punched a pretty big hole through one of those plastic GM Vortec truck manifolds one time.

The aftermarket supercharger kits that have a supplemental injector at the TB can do the same thing, and for the same reason. I once worked on a truck which had been modified for more airflow and the aftermarket injector controller was no longer supplying enough fuel. Snapping the throttle at low boost resulted in a pop which was small enough, luckily, to blow the plastic plug out of the back of the intake without additional damage. I never found the original plug though.

I once spent a month trying to work out a cold start issue on TBI with a customer's car back in my beginning days. The engine had to sit for almost 6 hrs before it would occur, and it never happened above 10 degrees. I had only the weather for cooling so I got one start in the morning and one in the evening. No WB display back then, NB wasn't warmed up, 160 baud ecm, and much less understanding of the code than these days. What a long and frustrating job that was. I would have given up my toolbox for a cold room. :)

[gregs78cam]

So to run this thing I am thinking I want a '94 or '95 PCM, as that will be able to do both sequential fire and control the 4L80E. Would it also be possible to do DIS? I guess I need to re-read the DIS thread. I think it would be sweet to have a cam sensor mounted where the distributor "used to be", and have the DIS coils mounted above that at the back of the manifold. A crank trigger would be easy to work in.

EDIT:

I don't know why it didn't occur to me earlier, but I already have the perfect setup for doing DIS???? Electric water pump that I can space off the block however far I need to. A nice 1" thick chunk of aluminum that is my alternator belt tensioner mount sitting right next to the crank, and a JESEL belt drive with my camshaft spinning right there in plain sight.

[JeepsAndGuns]

Witch PCM specificly are you talking about? The 7427?
It will do batch fire, but wont do sequencial. It can also do DIS from what I read. Thats my next project after my mpfi.

[Six_Shooter]

DIS is just a few offset settings away.

Technically any of the common Delco ECM/PCM could control a DIS set-up.

[gregs78cam]

It will do batch fire, but wont do sequencial. It can also do DIS from what I read.

This I know...

It can also do DIS from what I read.

This I didn't. Thank you both for the clarification.

I was discussing using a '7727 I think, or whatever came in the '94-95 F, B, bodies.

[EagleMark]

I was discussing using a '7727 I think, or whatever came in the '94-95 F, B, bodies.

16188051 and 16181333 $EE is what came in them. No chip, Flash through ALDL port PCM, SFI, Optispark Distributor. like my wrecked LT1 woody Wagon...

[RobertISaar]

hmm.... you could probably run DIS on it, but it might possibly be unnecessarily complicated.

i'm not too up to date on the PCM end of the 94-95 LT1 stuff, but if the high-res portion of the optispark can be tuned out, you could use a northstar-style crank trigger and ICM, that would generate the 4X signal the PCM uses for the main calculations.

not sure how well the LT1 PCM would like the lack of the 180X signal though...

otherwise, could used the optispark unit to grab reference signals (4X and 180X), then use the ignition control circuit of the PCM to trigger a northstar ICM that has a northstar style crank trigger to read(since it needs at least that to know which cylinders to fire).



but like i said, potentially complex.