Looking to see if anyone has experience using this specific kit. Saw it pop up while browsing and have to admit it intrigues me, especially since the price seems to have come down.

https://speedmaster79.com/Chevy-GM-L...Complete-Satin

This would be going on a 2000 C5, LS3/L92 6.2L, SBE and stock heads (no porting) with a BTR LS3 Stage 2 cam (Specs: 225/238 .612"/.585" 113+3). T56 and 4.10s. Intended use is a weekend warrior with a bunch of casual road racing use in the warm months. I am not too concerned with overall power gains, more so interested in the increased driveability and mostly the sound! I’m thinking about adapting an LS1 or LS2 throttle body to act as a servo with custom linkage to actuate the 8x throttle bodies mechanically, so DBW vs DBC is not really a concern.


Concerns:

-Need to figure out motion ratio of DBW TB vs ITB linkage to make sure they’re 1:1

-Need to fab up a vacuum manifold to supply vacuum to MAP, brake booster, HVAC system, and maybe a port for IAT. I'd need to tap a fitting into each runner between the throttle blade and the head, then join them at a common log mounted to the valley...

-PCV – can add a port on this vacuum manifold to plumb similar to an OEM setup – or just run lines from the valve covers to a vented catch can.

-Filtration – I only drive my car on nice weather days, so elements aren’t a concern but there is still the issue of general dust/debris/leaves/etc. Filters/screens look goofy and rob power

-Tuning – obviously MAF is going bye bye and I will have to convert to Speed Density, anyone know of any other special considerations when using HPTuners to calibrate an ITB setup?

Any other first hand input/experiences are welcome.

 

I'm not an expert but I can't think of anyone I've heard of using speed density (IAT and MAP, correct?) to run ITBs. Usually its just RPM, IAT and throttle position makes for a good guess at airflow. And I think you're majorly glossing over the DBW to cable throttle linkage. I can't tell exactly what you're thinking you can do, but if you're thinking you can fool the PCM into thinking the DBW is working when you're actually pulling on a cable, that is not going to work. The map between pedal position and throttle blade angle are nothing like a cable.

 

This is meant to be a thread that encourages constructive conversation, so thanks for your input.

In terms of the DBW aspect, I think you may have misunderstood. I'm not trying to fool the PCM, since a throttle body will still be plugged in, fully controlled and communicating with the PCM. This is no different than unbolting the TB from your intake manifold and hanging it up anywhere in the engine bay - it will still electrically function and rotate the blade/shaft.

I'm well aware that the pedal position percentage (TPS%) is not equal to throttle blade position. What I am getting at is using the stock TB (modified) to work as a slave in controlling the mechanical linkage for the ITBs. So for example, say you input 20% pedal input (TPS) and that equals 5% throttle body (servo) opening, or whatever the curve is. The idea would be to set up the mechanical linkage such that 5% throttle body opening equals 5% ITB opening, which is certainly doable.

Looks like I'm not the only one to have this idea....


The tuning is more what I'm interested in - I wonder if HPTuners has Alpha N capability for the Gen 3 PCM...

 

Ahhh yes I see what you're saying. That's a very interesting setup there for sure. Pretty impressive. From what I understand (and again I'm not an expert) from talking with a successful LS tuner that used to be near me, the C5 PCM knows what the throttle body diameter is. I SUSPECT that is needed to command a blade angle based on a desired airflow number. Just because something sounds hard doesn't mean it's impossible of course but it sounds hard to adapt to whatever the PCM does with the TB diameter. The flow characteristics of a TB like stock with a known area will be completely different to the flow characteristics of 8 ITBs with (for example) 1/8th the area each. Why I think Alpha N would be the go to. Hopefully someone with more experience than me will join the fun. I'd love to have ITBs myself so if there's a solution out there I'll definitely be filing it away for the future.

 

Word of advice, for the vacuum source that you will tap into each runner... Make it and the vacuum log of considerable size. I just went through this with a buddy and his GT40 and Borlas ITB kit. Originally we drilled and tapped for around an 1/8" line I believe and a smaller manifold, very basic log.. It was not enough for the iac and all to keep up and we could not for the life of us keep the iac in a proper range without everything else swinging hard one way or the other.. I would go closer to 1/4" and a decent sized log.

 

Get in contact with forum member robz. He's run IRTBs on his C5 with great success.

 

Not sure about hptuners but EFILive Cos5 has an alpha N TPS VE table.

 

Never done it myself but what you're planning sounds practical. Probably a lot of work, but that thing looks pretty cool, so it's probably worth it.

Connecting the runners to get a vacuum signal that mimics an intake manifold's vacuum signal sounds like a great way to fool the PCM into thinking nothing has changed. Keep us posted on the results.

 

In for results.

My initial thought about that video is the force it takes to move all those ITB's compared to the stock blade. The OEM TB servo motor was built/designed to only tilt a single blade. The longer the lever arm used to get the correct motion ratio of OEM TB shaft rotation to ITB rotation will increase the torque required of the OEM TB. That may get into durability.

That being said, IF you did that it would be wise to make this where you can easily replace said servo.

In HPT, I suspect you could read TPS voltage 0-5V and then correlate it to TB blade angle using a digital protractor somehow. If I had to guess for simplicity sake, 0V is off, maybe .5V is idle and 5V is 90* rotation or WOT You would need to fab linkage that maintains that. Adjustable threaded rod with heim joints will allow you to fine tune the adjustment.

 

Do you have any more information on running Alpha N in HP Tuners? Or mimicking it with the appropriate tables/scalars?

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Luckily it’s not a lot of addition work to add vacuum ports to each runner. Just drill and tap for 1/8” NPT, then run a ¼” flexible line to a common vacuum block mounted to the valley plate that has provisions machined in it for MAP and IAT. Realistically the IAT could even just be hung close to a rear trumpet since the engine is just sucking engine bay air anyways.

How much internal volume on the vacuum log do you suggest? I’m thinking a 1”x1” square aluminum block, maybe 6” long, something physically large enough to be able to plumb 4x fittings on each side, with a MAP port at the front and IAT at the rear.

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Thanks – will do.

Hmmmm, I was hoping I could solve this problem in HPT since I already have it.



For some reason I am sensing some sarcasm in your post…hopefully that’s not the case?

The physical part of the work is not a big deal as I enjoy this kind of tinkering and fabrication – helps the winter go by faster. Just the tuning that concerns me.​​​​

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I’m not sure what kind of return spring is installed on the ITBs, but if there is one I’d be removing it. With no spring on the ITBs they should rotate very freely with almost no resistance at all. Go take the spring off your screen door on your house and see how easy it is to move, same principle. The return spring inside the DBW TB should be sufficient to control/close the ITBs, and with there being negligible resistance on the opening stroke (linkage included), the servo should be able to open them.

Solid linkage with heims is the way to go, no cables.

 

100% sincere. I love this kind of stuff.

 

I would definitely vet Speedmaster for quality control before making a purchase from them.....many reputable speed shops will not carry their goods because of quality issues. As it was explained to me, think "everything copied in China" type of situation. I would ask around to make sure their products are the quality you expect.

Good luck with your project.

 

Totally agree, and yes, speed density is the way to go on this, Alpha n is too crude.

 

What do you mean by too crude?

Can you elaborate on the tuning strategy for HPTuners? I'm fine with forcing speed density (disable MAF), begin to tune VE table, but I'm interested in WOT strategy since I've read that the MAP signal jumps to 100kpa at around 30% throttle.

 

100kpa MAP signal at 30% throttle sounds like a side effect of bad plumbing for the MAP sensor. Unless of course they were also seeing full power at 30% throttle.

I wonder if it would be helpful to use a long log, and locate the MAP sensor a long ways from the lines that go to the ITBs, so the sensor sees a good average of the ITB pressures.

 

Hm, perhaps remotely mount the MAP....

So, 8 individual lines feeding a relatively large volume log/manifold, and then a separate line running to an external location of the MAP.

Maybe even tee the individual lines from each runner together before they join into the vacuum manifold so that it's already an "averaged" signal.

 

Interesting I had this on the brain once! One question can I hook up my normal air plenum (vararam) to this pushing the AA?

 

Both good ideas, I think. Join the opposing pairs with tees, run those four lines into a manifold, and put the MAP sensor a few inches away...

Or use 8 MAP sensors and average them electrically. They're cheap, right? (This time it really was sarcasm!)

 

Alpha N ( TPS vs. RPM) is fine for the track but not as good as speed density (SD) for every day street driving can be on port fuel injection. I understand what you are saying when using an IR setup but x to 20% or 25% throttle of SD (MAP vs. RPM ) tuning is better than none and that's idle to part throttle cruise tuning. I haven't used Alpha n in HP tuners, only SD or MAF. In HP Tuners there are tables that can be used to change the TB rate of opening that will also improve the cruise and low end on a FBW IR setup. I would say that when using an IR setup, SD is marginally better but still better than Alpha N.
I haven't tried this but if I had to tune a C5 or C6 in Alpha N I would tap into the pedal position sensor (PPS) and make a device with either op amps or A to D then D to A converter to change the PPS signal to go 0 to 5 volts from 0% PPS to 100% PPS, feed that into the MAP signal to the ECM using a SD tune.

HTH, Julio

 

Looking forward to watching this progress. I have always thought ITBs looked super cool!