Tuned Port Fuel Injection LT1?

[91 Black Convertible]

Can anyone quote a GM/Chevrolet/Corvette manual that gives a definition of TPI? That would be the ultimate answer for me. Otherwise, you're just giving your interpretation of TPI, what you or someone else thought they meant.

[91 Black Convertible]

edit:
The injector IN EACH PORT has it's own pulsewidth. The pulsewidth duration is TUNED for that cylinder. Tuned port injection.

I don't believe that is true. On the L98 each bank of four injectors is fired at the same time, so how can you have a different pulse width for each cylinder?

[vetteoz]

Yet another comment above, the one about being able to backdate a Gen II with a Gen I distributor by changing the intake manifold, is not correct.

Corrected

[Schrade]

I don't believe that is true. On the L98 each bank of four injectors is fired at the same time, so how can you have a different pulse width for each cylinder?

I don't remember where I read that. This LT1 scan shows 4 different pulsewidth readings for left bank, and 4 different readings for right bank. Not what I'm lookin' for tho'...

Desired Idle (RPM) 550 550 550 550
Engine RPM (RPM) 2025 2025 2025 2025
Coolant Temp (°F) 196.2 196.2 196.2 196.2
Oil Temp (°F) 173.3 173.3 173.3 173.3
Manifold Air Tmp (°F) 59.9 59.9 59.9 59.9
A/C Pressure (PSI) 62 62 62 62
MAP Sensor (Volts) 1.92 1.8 1.72 1.58
Throttle Sensor (Volts) 0.94 0.9 0.9 0.86
Throttle Angle (%) 11 10 10 8
Battery Voltage (Volts) 13.9 13.9 13.9 13.9
Barometric Press (Volts) 4.29 4.29 4.29 4.29
Left O2 Sensor (mVolts) 928 928 932 924
Right O2 Sensor (mVolts) 888 888 897 897
Block Learn Cell 7 7 7 7
Left Block Learn value 160 160 160 160
Right Block Learn value 160 160 160 160
Left Integrator value 128 128 128 128
Right Integrator value 128 128 128 128
Left Inj Pulse (mS) 6.6 6.3 6 5.6
Injector Pulse (mS) 6.5 6.1 6 5.6
Mass Air Flow (gr/sec) 27 25 25 23
CCP Duty Cycle (%) 99.4 99.4 99.4 99.4
Idle Air Mtr Pos (steps) 63 63 61 60
Learned Idle Pos (steps) 10 10 10 10
Spark Advance (°) 37 40 41 44
Knock Retard (°) 3 2 1 0
Knock Sensor 44 44 44 44
EGR Duty Cycle (%) 0 0 0 0
Vehicle Speed (MPH) 71 71 71 71
Engine Run Time (seconds) 550 551 552 553

[91 Black Convertible]

I don't remember where I read that. This LT1 scan shows 4 different pulsewidth readings for left bank, and 4 different readings for right bank. ...

That may be true for the LT1, but I doubt it for the L98.

[nelson84]

You can say I'm wrong, but GM is the one who built these engines and they say it is a Gen 1 and a Gen II and a Gen III. They are different engines. And the TPI does produce more torque at a certain rpm than the LT-1. Its a fact, don't try and twist it around to suit your mistaken post. Just admit you are wrong. My original post is all correct. If you don't like the truth than to bad.

L98 tpi 250 hp 350 lb/ft of torque

LT1 300 hp 340 lb/ft of torque

LT4 330 hp 340 lb/ft of torque

TPI rules in the torque department.

[Schrade]

92black made an interesting observation there. This is interesting... New plates for '96 were changed for LT4. BUT, new plates that started for '93-'95 LT5 were NOT changed... AND, '96 LT1 comes up Tuned Port Injection?







I don't know if anything definitive CAN be known...

[vetteoz]

That may be true for the LT1, but I doubt it for the L98.

L98 is batch fire , not sequential.If you log a L98 you only get one pulse width registering

[Hib Halverson]

(snip)
TPI rules in the torque department.

In 18 years of writing in-depth coverage about GM Powertrain products, I was bound to get some of the numbers confused...admittedly a piss-poor excuse.

I should have known better than to post to a discussion on engine specs and trivia that involves "nelson84" without confirming some of the numbers in the 24-model year collection of Chevrolet and GM media information I have stored up in the "stacks" above my office. I mean, hey the stuff was just up the stairs, but...I digress.

In seven model years of production, the L98's peak torque was specified variously from 330 lbs/ft to 350 lbs/ft. Interestingly, in the final year of production, MY91, GM quoted two numbers which were, depending on what part of the corp was dispensing the data, either 345 lbs/ft or 350 lbs/ft.

In five model years, the LT1's peak torque was specified variously from 330 lbs/ft to 340 lbs ft.

So, on one narrowly-focused issue, the L98's peak torque, "nelson84" is correct and I was wrong. Depending on what model year and what source you use for the numbers, L98 had between zero and 20 lbs/ft higher peak torque than did the LT1.

But (actually it's a big "but" so let's set it in all caps)...BUT, when you look at the full torque curve of each engine, the L98 sucks hind tit compared to the LT1. When you consider torque curves, people who actually know about engines (as well as knowing the their peak numbers) understand that it's the torque curve in totality that makes the car accelerate well.

I have the 1992 Chevrolet media information open on my desk and in that book, GM published a comparison chart of the L98's power and torque curves vs. the LT1's power and torque curves.

Looking at this data, right away one can see that the L98, by virtue of the long intake runners of the "tuned port" injection, is actually quite peaky, with a strong "hump" in the torque curve that begins at 2500 rpm, peaks at 3200 rpm and ends at 3600 rpm. In fact, that narrow range, 2500 rpm to 3600 rpm, is the only place the L98's torque exceeds the LT1s and in 1993, a camshaft change added 10 more lbs/ft torque to the LT1, decreasing the L98's lead in that range.

Everywhere else in the torque curve, from idle to 2500 rpm and from 3600 rpm to the L98s rev limit, the LT1 has more torque and it continues to make torque for 700 rpm beyond where the L98 quits. For example, at 1000 rpm, the LT1 is up 10 lbs ft and at 4200 rpm, the difference is huge with the L98 dropping off to 270 lbs/ft and the LT1 at 325 lbs/ft.

Obviously, the disparity is even bigger when we talk about power, with the LT1 making between 50 and 70 more horsepower, depending on model year.

Yeah, the L98's torque peak was higher, but the reason a stock 92-96 Corvette with the LT1 could clean the clock of any stock L98-powered car in a drag race, in a 0-60 contest or any other kind of useful acceleration contest, was the LT1's fatter torque curve.

So, "nelson84" is correct in saying that the L98's torque peak is higher, but he's wrong when he says the L98 has "more torque."

As for the persistent rumor which "Schrade" discusses, ie: either of those engines can vary injector pulse width on a per cylinder basis....it's urban myth. L98s used one pulse width for all eight cylinders. LT1s used two pulse widths, bank 1 and bank 2. In addtion, pulse widths were varied only when the engine was in closed loop. At WOT, the engines ran in open loop and on the base fuel schedule in the calibration.

[92BlackVette]

So check it out, I was searching ebay the other day and saw this auction:
Chevrolet : Corvette:eBay Motors (item 130305136911 end time May-14-09 17:46:42 PDT)

If your not wanting to follow the link here is the deal, it's a 1992 Corvette with the following stickers:



I sent him an message saying that 1992 used a Multi-port Injection, and it wasn't referred to as Tuned Port Injection, nevertheless he didn't like that his stickers were wrong.

He replied: "No this car has TPI. Car came right from the factory like such."

[nelson84]

But the LT-1 never reaches 350 lb/ft of torque. No wonde GM is bankrupt. They do a bunch of testing and make a crappy engine. Why didn't they make the runners a little longer on the LT-1 and atleast produce more torque than the L98. Even if they were able to get 360 lb/ft would have been decent. Good thing they dropped it after 4 years. Have you ever drove a LT-1 with a 2.59 rear gear, what a dog. Why did GM install granny gears in a corvette.

[vetteoz]

But the LT-1 never reaches 350 lb/ft of torque.

As Hib states above;
"people who actually know about engines (as well as knowing the their peak numbers) understand that it's the torque curve in totality that makes the car accelerate well."
Yes , by the numbers , the L98 has MORE torque.But the LT1 has more useible torque over a wider rev range as well as more Hp.

Maybe they should build a Renegade intake for a LT1?

[nelson84]

As Hib states above;
"people who actually know about engines (as well as knowing the their peak numbers) understand that it's the torque curve in totality that makes the car accelerate well."
Yes , by the numbers , the L98 has MORE torque.But the LT1 has more useible torque over a wider rev range as well as more Hp.

Maybe they should build a Renegade intake for a LT1?

Renegade intake? That is for a Gen I engine. Opti will not work with it. What would you plug the distributor whole with your head?

[91 Black Convertible]

Please explain to me why people buy Tuned Port Fuel Injection stickers for their LT1 (1992 and 1996) Corvettes?

Maybe I am not understanding something?

I'm not sure that any of the posts to this thread to date have actually answered your question.

I guess the answer might be: Because that is what is on the stickers that they sell, (the center console ones). I don't think anyone makes a sticker that says something different. One can only buy what is being sold.

So for me, the real question is: Are those stickers correct? That has not been answered to my satisfaction here yet. I have yet to read a post that quotes a GM/Chevy/Corvette source that defines what Tuned Port Injection really means. I will admit that up until this thread I thought that the L98 was the only Tuned Port Injection engine.


Inquiring minds want to know...


Jim S.

[Hib Halverson]

But the LT-1 never reaches 350 lb/ft of torque. No wonde GM is bankrupt. They do a bunch of testing and make a crappy engine.

A rediculous statement which deserves no additional comment.

Why didn't they make the runners a little longer on the LT-1 and atleast produce more torque than the L98. Even if they were able to get 360 lb/ft would have been decent.

An excellent question. Considering the first statement, I'm suprised at the contrast.

One good quality of the L98 was it's strong midrange and high peak torque. One bad quailty of the L98 was its lack of torque off-idle and at highe rpm. TPI's long intake runner length and modest port volume is responsible for the big mid-range number but it's, also, responsible for the lack of high rpm torque. To give the LT1 a wider torque band as discussed previously, it shortened runner length and increased port volume. Going the other way (longer) would have sacrificed the high rpm torque the engine rquired.

Good thing they dropped it after 4 years.

The Gen II engine was inproduction from MY92-96, a total of five years.

Have you ever drove a LT-1 with a 2.59 rear gear, what a dog. Why did GM install granny gears in a corvette.

The base axle ratio existed to enable the Corvette to meet the U.S. CAFE requirements.