Throttle Body Talk

[futurevr4man]

I considered posting this in the intake manifold thread but its slightly different.

I want to start by saying that my car is a toy and a hobby, I am just experimenting with stuff. So whether its necessary or not, is not what I'm looking for. Just a good discussion regarding our engines and throttle body choices along with potential gains and losses associated.

With that being said, I have got a new intake manifold and true 90mm throttle body on order and should be here in the next few weeks. My hot side piping is 2X 2.5" off the turbos going through a dual core inter cooler and then merging into a single 3.5" pipe up to the throttle body. Currently, it is necking down to the stock 62(?) mm throttle body.

My question to everyone is, do you think I will see any significant gains from my new 90mm and intake manifold (assume the runner length is the same as stock)? I have always heard that you lose resolution in the throttle, but every example I have read of that is because the individual is running smaller cold side piping than the size of the throttle body (2" piping with 2.5" throttle body for instance). With mine being built to match, I have a feeling I won't lose too much (if any) resolution in my pedal.

One other thought I had, the evos run the same size throttle body as we do stock, but we have 50% more cylinders than they do. And they see nice gains from increasing to a 65 or 75mm throttle body/intake manifold. So would it hold any water at all to say that a 50% bigger throttle body would be a better match?

Thoughts, discussion?

[NOMIEZVR4]

what IM did you purchase?

[TurboSinceBirth]

Size your throttle body for the intercooler piping. There's no reason to go bigger because that's the smallest restriction in the whole system. Most FMIC kits have 2.75" intercooler piping which should be a 70mm ID throttle body. For 3" intercooler piping on some of the older FMIC kits a 75mm ID throttle body would be good. 91-99 DSM aftermarket throttle bodies in these sizes bolt up to our cars and all of the sensors transfer over. An Evo 8/9 will bolt up but the sensors are slightly different in design so you'd need theirs plus pigtails to splice into our harness.

I have a 70mm ID throttle body I will be doing some testing on this summer with a stock intake manifold, a ported stock intake, and then an aftermarket one to see what the gains are. Given the lack of testing and general upgraded use on big turbo builds I'm not expecting as big of gains as other platforms will see, but it'll be interesting to note what happens. I need to hook up two map sensors one pre and one post throttle body to see if I have a loss in pressure right now with stock parts.

You probably won't see significant gains until you're pushing those 20Gs full tilt. I don't expect there to be pump gas benefits. I'd love to be proven wrong though so we at least have the hard data. People lose resolution with larger throttle bodies no matter what the size of the cold size piping is. 2" piping is not going to be outflowed at low loads even on a 2.5" throttle body. WOT it could depending on the size of the turbos. A larger throttle body will flow more at part throttle than stock. You can be 20% TPS cruising but the bigger throttle body is flowing 40% more than stock making low throttle inputs shift scaling to the left majorly thus losing resolution. If you think about the flow of the butterfly valve in the throttle body it makes sense.

[futurevr4man]

I am getting my IM from Von.

I am not wanting to go bigger than my already 90mm intercooler piping. Just get a throttle body to match.

As far as the resolution goes, I kept reading about people going bigger on the TB with their smaller piping... I guess it still makes sense that the extra airflow is there though. Hopefully I can make some adjustments in the ECU to compensate for it though... at least a little.


Anyone with more knowledge or experience than I know much about how the air velocity entering the chamber affects power output? I am interested in your pressure drop test as well TSB. When do you plan to start your trials?

[fastfalcon94]

Subscribing. I'm not an expert but I'm trying to keep all of my pipes roughly the same. To me the stock TB was my biggest limiting factor so I decided to try and even it out. These are my area calculations.

2" hotside piping is 1*1*3.14*2 = 6.28
3" codeside IC piping going in/out of an IC with 3" openings is 1.5 * 1.5 * 3.14 = 7.065
Q45TB is 83mm which is 3.27" is 1.635 * 1.635 * 3.14 = 8.39. Subtract the TB shaft area and it would probably be 7.x

The stock TB ID was 60mm which is 2.36". That's 1.18 * 1.18 * 3.14 = 4.37. It would be less subtracting the shaft area and by far the limiting factor.


I was also doing some research on other 6 cylinder platforms. The nissan 300zx has two 50mm (~ 6.02 area) ID TB's and they upgrade to 60mm (8.74 area).
Supra owners upgrade as well, but I was having trouble finding the stock TB size. I almost think it's 68mm which would be 5.59.

In the other plenum thread people were saying the exhaust housings will limit our power before the stock TB size becomes an issue. I'll be testing my stock setup vs q45 this year. I hope it's not all a waste of time. I am running bigger dnp precat housings now though which I hope helps.

[anyonebutme]

You feel a "loss in resolution" because at low throttle with a large TB, small movements result in lots of airflow changes. A throttle cam solves this and allows you to tune the throttle response.

[vr4tune]

Will the s90 74mm fit the stock manifold?

[futurevr4man]

Fast falcon: I read about the exhaust being the limiting factor as well but I'm hoping with my bigger td05 turbos, that doesn't hold true currently (with stock TB). If you do the math on two 2.5" pipes merging to a 3.5" pipe, it's 9.8 merging into 9.6... Can't get much closer. The ID of my MAF is 3.5" (3.75" z06 MAF) and so now with my dinky 60mm TB it's a big time restriction. I do have concern with the air velocity being too slow, but under pressure I'm not sure if that's just a moot point really. Also, we all know that DSM's can run significantly more boost pressure than we can, even from factory, and I wonder if our TB being too small is a contributing factor. None of the guys that mess with this stuff post on here much, or if they do I just haven't seen them post about it.

ABM: I'm not sure what a throttle cam is but ill do some research. There may be some adjustments in the ecu that can help as well. With flash able anything is possible... Right? Hahaha

Idk anything about the s90. I am leaning towards no, but I can't be sure.

[vr4tune]

I believe the throttle cam is the wheel attached to the throttle plate on the exterior of the body that the cable attaches to and rolls on. The bigger the wheel the less sensitive the gas petal is.

[anyonebutme]

There may be some adjustments in the ecu that can help as well. With flash able anything is possible... Right? Hahaha

The tune isn't really going to help the fact that the car will NOT go slow no matter how hard you try, it'll act like 0 throttle and goes straight to 25%, lol. What a throttle cam does is progressively speeds up the opening speed, so the pedal moves more distance at low throttle openings than high openings. It allows you to actually drive the speed limit in school zones, lol. You'll see what I'm talking about.