TPS sensor

[Dragkid1917]

can any one let me know what a TPS sensor is, i was lookin at FAST 90 mm throttle bodies, and one was offered with a TPS sensor and one without. Also, what mass airflow sensor would be big enough as not to obstruct the air path of a 90 MM t/b

[Joe 1320]

TPS= Throttle Position Sensor. It is located on the side of the throttle body and provides an electronic measurement of the position of the throttle blade(s).

[Injuneer]

What ECU are you planning to run the system on? You would probably be better off getting rid of the MAF sensor and running speed-density.

Shoebox has a picture of a stock LT1 TPS. Its pretty much a "standard" GM piece, and most popular DFI systems and throttle bodies will accept it:

[Dragkid1917]

I was looking for speed density but i cant find it online maybe im just looking in the wrong place. I dont rele know what speed density is besides just another way to measure something, besides that idk if its a different type of sensor or like a program. Sorry for my lack of knowledge. If i get speed density, what goes in the place of my curren MAS

[fastTa]

can any one let me know what a TPS sensor is, i was lookin at FAST 90 mm throttle bodies, and one was offered with a TPS sensor and one without. Also, what mass airflow sensor would be big enough as not to obstruct the air path of a 90 MM t/b

The FAST 90mm intake along with a 90mm TB is slightly overkill on an LS1 until you do at least a cam. If you plan on doing a cam or heads in the near future, then the 90/90 setup will be fine. Most of the bolt on guys just use a LS6 or LS2 intake manifold, stock ported TB, and a 85mm MAF sensor.

[Dragkid1917]

i wanto get new heads all together, the package from slp looks nice with that huge cam, but having said that what exactly is speed density? and what do i need to use it

[fastTa]

i wanto get new heads all together, the package from slp looks nice with that huge cam, but having said that what exactly is speed density? and what do i need to use it

Just a harmless mistake by Fred, I think he thought you had an LT1 and were going to use a FAST EFI controller. There aren't very many LSx owners on this site. I've done it a million times myself. You don't want to run speed density with a stock PCM. Just stick with the MAF.

What size cam are you looking at?

[Dragkid1917]

the cam specs are something like 236/236 @ 50 and .590/.590 max lift with the stock rocker ratio, they also have another one thats like 250/246 (in/ex) at 50 and then .596/.596, even though i thought usually the exaust was the one with the bigger duration usually. I love the sound of the aggressive cams, but obviously u can use too big of a cam, however with the head package these were reccomended. Back to the t/b issue, if i have a 90 mm t/b and a 90mm. manifold opening, but my maf inside diameter is only 80 or 85... isnt that like... defeating the purpose of a 90 mm t/b, if so what do people do to fix it?

[Injuneer]

I realized what he was doing... I just figured if you were flowing enough air to need a 90mm MAF, you would be better off with no MAF at all. A 90mm inlet track should support 700HP.

Putting an 80 or 85mm MAF in the intake track doesn't defeat the purpose of going larger on the other components. The pressure lost in the intake track is the sum of each of the components. As long as the MAF has tapered transitions from the larger to the smaller diameter, and back up again, the contribution to total system pressure drop is going to be small. Putting an 80mm component in a 90mm system just means there's an increase (25% for the 80mm, 11% for 85mm) in pressure loss in that single component. It doesn't reduce the capacity of the total sytem to "80mm".

[fastTa]

the cam specs are something like 236/236 @ 50 and .590/.590 max lift with the stock rocker ratio, they also have another one thats like 250/246 (in/ex) at 50 and then .596/.596, even though i thought usually the exaust was the one with the bigger duration usually. I love the sound of the aggressive cams, but obviously u can use too big of a cam, however with the head package these were reccomended. Back to the t/b issue, if i have a 90 mm t/b and a 90mm. manifold opening, but my maf inside diameter is only 80 or 85... isnt that like... defeating the purpose of a 90 mm t/b, if so what do people do to fix it?

If you go with heads and the 236 cam or bigger, you would definitely want the 90/90 setup. The LSx's just outright defy conventional physics when it comes to flow and velocity. The 85mm MAF will work just fine along with the 90/90 intake/TB. Get a good lid and don't worry about ordering a new TPS as long as your current TPS is working correctly.

That 236 will have a little bit of a rough idle, but it will be fine on the street. That 250 cam will be another story, especially if you are on stock cubes. I personally could live with a well tuned 250 on the street, but you will have to be able to live with a pretty soggy bottom end. Under 3k-3.5k RPM, it will be pretty soft. Now over 3.5k it will pull like a raped ape.

As far as tuning, you can go with either a dedicated closed loop speed density tune or a CLSD tune and leave the MAF plugged in. Tuners will use what works best for you with your particular application. Some people find that a CLSD tune in conjunction with a functioning MAF is the way to go. Some will just use a dedicated SD tune. You can even program the tune to run in OLSD (open loop speed density) then at 95% TPS run it in CLFA. Either way you do it, only tune your WOT with the PE tables.

The nitrous guys that are spraying into the lid or above stream from the IAT like to use dedicated CLSD since the VE table looks to the to IAT as a fueling variable. An abnormally "cold" input from the IAT can cause the car to go abnormally fat and also screw with the Charge Blending table values. The default units are (grams*Kelvin/kPa), where the Kelvin is your temp input.

If you leave the MAF, which I suspect you will, it is really easy to calibrate. You will log your MAF FREQ and DYNAIR. Then your tuner will use that data to create your MAF table. Simple.

[Dragkid1917]

How can you run with no Maf, the last time i took it off it ran like sht, it was runnin extremly rich. If u ran no maf i assume you would need to program your car for that?... is that like, better?

[Injuneer]

The stock PCM is designed to run with the MAF. But it is also designed to keep the engine running when the MAF dies (you should be able to unplug the MAF and have the engine continue to run decently, unless you have a lot of mods). When the MAF fails, the PCM reverts to speed-density operation. You can program the stock PCM to run only in speed-density mode, or you can use an aftermarket engine control unit (ECU) that has increased speed-density capabilities.

The MAF sensor tells the PCM the mass flow rate (#/HR) of air entering the engine. The PCM then divides that number by the desired A/F ratio, and sets the injectcor pulse width to provide that many #/HR of fuel (simplified expanation).

In a speed-density setup, the PCM works ALMOST the same way, but it has to calculate the mass air flow rate from several pieces of data, including engine speed (RPM), volumetric efficiency (VE), intake air absolute temperature (IAT) and intake manifold absolute pressure (MAP). In order for the speed-density system to provide good performance, it need an accurate VE table.... the percent air fill of the cylinder, at a given RPM and MAP. If your VE table is correct, the engine will run identically, whether its running an MAF or running in speed-density mode.

The bottom line is that the MAF is able to adapt to modifications that affect volumetric efficiency.... heads, cam, exhaust, etc. The speed-density system can not, since anything the changes the engine's VE requires that a new VE table be programmed. That takes a bit of dyno time.

Which is better..... if you don't want to have to reprogram VE tables, the MAF makes life simple. It just has the potential of becoming a flow obstruction, as the air demands of the engine increase.

My 94 runs in speed-density, using a MoTeC M48Pro ECU. If I change anything in the setup, its fire up the wide-band O2 unit, or back to the dyno to tweek the VE tables. Its done that way largely to handle a big shot of dry nitrous.

[Dragkid1917]

Thank you, infact i think ill stay with MAF. I picked up an LS1 magazine, and they built an engine on the dyno exactly what i wanted to do, infact with just 1-7/8 headers with the Ws6 setup it put down 400 Crank hp and 413 C tq. (101 octane) There was no water pump or alternator but thats still pretty good.
They then put a monster cam in it, something like .649 intake/ .609 exaust, and with durations like 239/242 with 112 degree lobe and it put down 482 hp and 439 tq, now with this they changes pushrods and springs, but, nothin else, also from the pics it appears to have new spark wires but not blaster coils or an ignition system. Anyway they then put on stage 1 heads witch had 307 cfm intake at .600 lift and 220 cfm exaust at .600 lift (2 inch intake 1.55 exaust). After setting the A/F ratio it made 530 hp and 464 tq.
Finally they put a 90 MM fast intake and t/b. They also used an 85mm SLP MAF witch answeres my question weather thats a good idea or not, if they did it i guess its not so bad. With that the horsepower went to 551, and the torque 476. For a stock bottom end 346, with 60,000 miles on it id say that these motors can make quite a bit of power. Im sure with bigger heads they can pick it up to 575 h/p. I just thought id share the article i read about, and let everyone know that my question about the MAF and the 85MM maf to a 90 MM intake was solved.