Tuned Port Fuel Injection LT1?

[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:Lotfl 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:Lotfl 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?:bash

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.

 

[Cadillac Tech]

There are a number of interesting assumptions in this thread...

An LT1 cannot be converted to an L98.

"Tuned Port Injection" like "Generation 2 Small Block V8" were marketing terms. "Tuned Port" was a name coined by Chevrolet marketing weenies back in the early 80s for the port fuel injection system used from 85-91 on the Corvette and until 92 on the Camaro and the Pontiac Firebird. It gets its name from its long intake runners, the lengths of which were selected or "tuned" to cause an increase in low-speed torque.

The "Tuned" name was dropped in 92 in favor of another, even less descriptive moniker "Multi", but the 92 LT1 (along with the later L99 and LT4), also, used intake port length tuning to affect torque...but the port length was much shorter, which raised the rpm for which the runner length was "tuned". This also allowed the LT1 its higher rpm range and greater power.

The Generation 2 (or "Gen 2") Small-Block V8 arrived in 1992 in Corvette and in 1993 in Camaro, Firebird and the GM B-car. While its block architecture was very much the same as the traditional small block (the so-called Gen 1 of 55-91), there was a big change in the cylinder head and cooling system to acomplish the "reverse flow" cooling discussed above.

"Nelson84" is incorrect in saying the L98 (350 cuin version) of the Tuned Port engines are "easier to mod". Reality is each engine has good points and bad points as far as their potential for modification, but, if "modification" means significant increases in horsepower and an extension of the engine's rpm range, the L98s big problem is the tuned port system itself. The intake manifold, the runners and the plenum are highly restrictive and a big problem when modification for high horsepower and high rpm are the goal.

"Nelson84" makes the misleading statment that the L98 makes "more torque". It is true that, in stock trim, the L98 engine has slightly more torque output between off-idle and the mid-range rpms but, if you consider the entire useable torque curve of the engine and the torque peak, the LT1 makes "more torque".

As for "no Optispark" well....yeah, the L98 had the rear-mounted distributor, but that "no Optispark" is an advantage, I think, is debateable to a certain extent. I'll admit that the early ABITS distributors where flawed by poor moisture sealing but that flaw was eventually eliminated. The later ABITS distributors were not the reliability/durability problems the first ones were and were a much more accurate way to control ignition.

No doubt, TPI systems look better under the hood. The long runners are pretty darn sexy.

Another comment above that Tuned Port means one injector per cylinder is not correct. The LT5 has two injectors per cyinder. "Tuned Port" refers to the length of the intake runner not the number of injectors per port.

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.

Someone asked about the Vortec 350 truck engine. GM called that "Gen IE" and they were basically the Gen I engine with the best of the Gen II cylinder head, but no reverse flow cooling.

Lastly, the final interation of the Gen II, the 330hp SAE net, LT4 was the most powerful production Small-Block V8 which used the traditional block design. If the old gross power rating system used in the muscle car era had still been valid, that engine would have been rated at about 410-430 hp. Such a power level would have been impossible using the L98 style induction and 2-bolt main cylinder block.

Thanks for the information. It is nice to read posts from someone that really knows what they are talking about.

 

[92BlackVette]

Reading these arguments between the L98 and LT1 remind me of listening to siblings argue.

If were feeling like an idiot and wanted to act like the locals where I live, I would find a 1992(LT1) & 1991(L98) and hook a chain to their bumpers(more like the frames) and see for myself who pulls who. I know makes no sense, it's really what people with trucks do for fun I guess.

See video for youtube example:
YouTube - Mike@uspmotorsports vs. Chris@uspmotorsports Truck pull

 

[vetteoz]

Reading these arguments between the L98 and LT1 remind me of listening to siblings argue.

It is a argument based on each's engines technical merits v one person's misguided personal opinion.
As they say; you can lead a horse to water ......

 

[Schrade]

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.

Dog? I have an LT1 with a 2.59:1, and I don't call it a dog. You got a bad attitude talkin' trash about ANYbody's car like that.

And LT1 wasn't dropped after 4 years either...

 

[nelson84]

Dog? I have an LT1 with a 2.59:1, and I don't call it a dog. You got a bad attitude talkin' trash about ANYbody's car like that.

And LT1 wasn't dropped after 4 years either...

I test drove a LT-1 with 2.59 gears with an auto and it was slow. The salesman told me before I test drove it that it was slow. But I thought he was an idiot, it was a new vette with 300 hp. It is obvious that the LT1 needs gears to get into its power range. With lower gears the LT1 is a good engine.

Sorry if I said 4 years. It was 5 and it was the shortest run of any of the 350 engines for a reason.

Don't get me wrong, if I could get a LT-1 vette cheap, say off ebay I would buy it in a second.

 

[LT4man]

I am trying to figure out what you think of the LT1 and LT4 engines which were installed in MY 1997 Chevrolet Camaros and Pontiac Firebirds. By my math, that makes six (6) years of engine production. Not four (4) or five (5).

The technology of the LS1 and subsequent later LS engines was so far advanced compared to the L98, LT1 & LT4 engines, GM was smart in developing the LS series and dropping the Gen I and Gen II engines.

Hib is spot on about the definition of "tuned port".

DON'T FORGET TO TRY TO SAVE THE !

 

[Hib Halverson]

I test drove a LT-1 with 2.59 gears with an auto and it was slow. The salesman told me before I test drove it that it was slow. But I thought he was an idiot, it was a new vette with 300 hp. It is obvious that the LT1 needs gears to get into its power range. With lower gears the LT1 is a good engine.

I'd say just about any Corvette with a 2.59 gear is a pooch, no matter what engine is in it. No on who drove even halfway hard bought that axle.

Sorry if I said 4 years. It was 5 and it was the shortest run of any of the 350 engines for a reason.

Corvette 350s in production less than 5 model years:
L46
L83
LT1 (the original)
LT4
LS6

 

[Hib Halverson]

I am trying to figure out what you think of the LT1 and LT4 engines which were installed in MY 1997 Chevrolet Camaros and Pontiac Firebirds. By my math, that makes six (6) years of engine production. Not four (4) or five (5).

!

"LT4 Man" is correct in that LT1 production in vehicles other than the Vette was longer than five years.

In this discussion I was talking about Corvette.

 

[MusclecarJohn]

My '92 has 2.59 gears and is a dog alright, a scalded dog wned

 

[vetteoz]

it was the shortest run of any of the 350 engines for a reason..

How many years was L83 Crossfire engine made?