I'm intrigued by the last hurrah effort the powertrain guys made for 1996 when they took the LT1 and dialed it up to what some claim were high-300s HP levels while retaining the factory standards of driveability, mileage, and emissions. It seems like they got a lot without sacrificing anything.

So let's say a guy wanted to take an L98 and turn it into the "L99." That is, increase the power significantly but without pushing it into "cleary non-stock" engine behavior. In other words, do something the factory would do, more or less. I'd like to hear peoples' ideas.

Is it as easy as swapping some AFR 180s, a Mini Ram, and a moderate cam? Could the stock ECM handle this? What kind of power is possible while retaining a stockish personality?

 

There was a guy recreating the Ten Times the Torque intake comparison of the late 2000s. However, he did his comparison with the stock cam and just swapped intakes. I bring this up because you mentioned programming the ECM. Maybe that's something you want to avoid? Maybe it's fine? Anyway, without doing much (except maybe increase fuel pressure?), he bumped L98 power into the 280s. For the best results, run a super ram or a hogged out large-tube intake (which eliminates some of the extra runner length challenge).

If you convert 280/290 rwhp into flywheel numbers (which you talk about above), that's somewhere around 335fwhp. A stock L98 is advertised in the 230-245hp range. So, that's a decent jump. IMO, 335fwhp is probably higher than most LT1's came rolling off the floor with. LT4's...around that 335 mark. So...Tom seemed to prove an intake swap could help an L98 equal LTx factory levels of power. FWIW, I don't think he had a stock exhaust on his "Kart" (which was used for the test). I can't remember if it was equipped with headers?

Tom's latest comparison (posted elsewhere):



NOTE: The miniram didn't fare as well. If you're familiar with the stock L98 tune (like I am), you'll know it lacks the PE fueling "curve" necessary to take advantage of a shorter-runner intake. IMO, that's why the MR didn't fare better this intake comparo.

 

The answer is yes... Any top end L98 can equal the LT1 as suggested by the above data adding 100hp to the stock 240hp to 250hp takes it into LT4 territory. The properly tuned computer to match the Mini-ram would definitely make more power. Cheers... My lowly stock bottom end 86' L98 with a weight of about 3,600lbs ran 109mph in the 1/4, that is LT5 ZR-1 realm and they made 375HP to 380HP to do that.

 

Fourteen years and never quite right

 

It's a lot more stark than that....lol.

If you don't tune properly for the Miniram, you're going to wish you never "wasted the money" on it.

 

Yep.

Before my 383 swap a few years ago, I was running a 350 with a 212@.050 cam with a 112 LSA, 180 AFR heads, and a Miniram. From what you're describing in terms of your objective, I think you'd be very happy with it. Stock sounding idle, very mild mannered around town, decent gas mileage, but plenty of power up to 6000 rpm.

Though like in my post above, I spent A LOT of time learning how to tune the Miniram to get it running good. I'm a bit of a perfectionist, so that probably played a lot into that. For you, you might consider something like a Super Ram. Might make the tuning easier, but still get better mid-upper range power than a TPI.

Not sure if you have a manual or automatic, but if you have an auto, then to take full advantage of the engine, you'll want a ~2500 rpm converter.

 

I would like to add my opinion on what I believe is a myth regarding LT4s.

I recently saw a video from C&S Corvettes where the business owner claims some shop in Jersey did dyno testing and/or collected dyno data from owners regarding "stock" horsepower production against advertised horsepower rating by GM. Apparently, some "bone stock" LT4s dynoed at nearly 400HP when converted to FW horsepower. Many were in the 380 range.
I have a hard time believing in the "freak” engine theory, for one simple reason: Based on what?

IF....IF...all LT4s are created equal, then how can one explain as much as 70HP difference between one and the other? What makes one so much stronger than the other?

To me, the only reasonable explanation is either wild variations in manufacturing, or LT4s purposely or conveniently built differently, or some people out there are full of *****.

From everything I've read, the primary HP producers in the LT4 were the heads, cam, and roller rockers. The cam is slightly larger than that of the LT1, which may not take full advantage of the heads. The RR are probably good for 10HP or so. The other changes were done to add reliability and durability given the increased RPM range.

In any case, I believe there is a fair amount of myth surrounding there engines.

As to the main point here, as others have said, the TPI is the biggest factor. It really should have been given to the trucks. It simply is not conducive to HP production. A head, cam, intake and full exhaust package will absolutely get the L98 near or right to the 400HP Mark.
As evidence, my absolutely butchered 88 Trans Am GTA had home ported SLP runners and plenum, Edelbrock base, a massive Comp Cams (230/236, 510/510 110LSA) and a half azzed exhaust. I ran it at 13.39@104 on a misfiring distributor from AutoZone and worn out it rings.
My guess is that it was making about 300HP...on a TPI system.
L98, LT1, and LT4 engine are all 350 in3, so the potential is there.

Ric

 

I see your frustration about dyno data not being logical.

Engine Dynos are usually using a water brake, and measure HP using a very precise load cell, and very low inertia. There are quite a few load cell chassis dynos out there, using eddy current brakes (electronically controlled large brake disk) and also a very precise load cell. These show HP and TQ in real time, and the time element is just a pre programmed RPM/Second load control.. or it can be a step type analyses for better tuning. The load cell is calibrated every so often, simply by placing a precise weight on a proper spot, which is calibrated to for example 62.347 lbs. The load cell reading will show that weight during the calibration process.

Then there's the Dynojet Inertia type dyno, measures rate of acceleration of a weighted drum. Calculates via algorythm for speed of drum, and acceleration over time. There's no native load cell, although there can be an eddy current brake and load cell add on for tuning partial throttle and accurate numbers.

They are all repeatable and reliable methods of analyses, but when it comes to measuring true HP using the Dynojet Inertia dyno, it comes up a little bit optimistic. Note, that there's NO acceleration as part of the HP formula (stating that as I've seen this touted as the definition of HP here many times, it's not). The load cell dyno uses a simple formula (load and RPM) to calculate HP, and the inertia dyno uses algorithms to estimate. There is no easy correlation between load cell and inertia dynos, as inertia dynos are more susceptible to changes in wheel and drive train inertia, even tire pressure. Whereas the eddy current load cell is much less so.

So if you use the same inertia dyno, same calibration settings, conditions, tire pressure, measuring the same car, with the same gearing for test, it's valid before/after comparison. But there are some limitations. One is, they tend to lead the tuner into using a little bit too much timing advance, and a liitle too much fuel. The other is, you can only tune the 100% throttle cells on the VE and ignition tables, so the other ~90% of the table is not addressed (although you can address some of it in other ways). What's NICE about the inertia dyno, is the simplicity for a rolling road type test, and it costs perhaps half as much. It's the ideal "dyno night" tool. Dyno operator can select STD or SAE calibration, so there's a good difference there also. Look at Tom's dyno chart, upper RH side it shows SAE. If another dyno run shows STD, it will be higher, so at least keep that consistant., and look for it when comparing dyno sheets.

The issues with the eddy current load cell dynos, is when you try to set it up to repeat a dynojet result. It's just not good at it. It can control a certain rate well, but that rate is independent of HP whereas the inertia dyno, they are completely dependant. So don't mix up comparisons.

 

Yes it basically is as easy as head/cam/Miniram, but the custom chip tuning side will take the time. It will not feel like an L98 though, not without rear gears (and TC on a A4 car).

 

Even more reason to believe some of us, LT4 owners, are a bit delusional regarding power levels on these engines.

I'd have a hard time believeing anything more than +- 10HP