I just found that out. Why the hell does it only get 250hp then?

The TSX puts out 200hp NA but it does 370hp at 13 psi. Does the LGT have really low compression ratio or something?

Just wondering...

 

the GT was also made to have a useable powerband, does the TSX have any useable power at 2500?

 

According to dyno results, the TSX puts out ~72hp at 2500rpm and the LGT puts out ~77hp.

 

I haven't been following the Legacy, but I have a Forester XT and have been otherwise somewhat abreast of Subaru stuff.

Subaru has tended to underrate HP/TQ numbers in their press releases compared to real life. Rumor has it that they don't want to make their non-STi cars look better then the WRX STi.

I know the Forester XT goes to 11.4 (11.something) PSI stock, but it'll only blip that high unless you're running other ECU and boost management stuff. It spends the remainder of it's life at much lower boost (which goes with the concept above of a 'useable powerband'). The compression ratio on the EJ255 is 10:1.

 

That's interesting.

 

link?

 

https://acurazine.com/forums/showthr...ighlight=370hp

 

Is the LGT under boost @ only 2500rpm? In several of the turbo apps I've seen, 2500rpm is the lag zone.

 

The Legacy turbo produces a peak 13.5 psi, compared to 11.6 in the Forester and Baja, and a high 14.5 in the mighty WRX STi.

 

CLUofI said it was, so I was just trying to compare the two. To me it looks like both engines have very linear power delivery.

 

i think i did read about that. i thought you meant it was a members car.

 

We need a fuel management system to make that power reliable. Most of the early conversions have required removal of the DBW system which also kills the VSA.

 

250 lbs tq > 160 lbs tq

 

but I just wish people would stop using torque as the way to compare engines.

Horsepower is a better way of comparing things. More torque means that it puts out more horsepower at that RPM.

At peak torque on the LGT (4400rpm), it's putting out 175hp to the wheels. The TSX puts out the same power at 7100rpm. This says that the powerband is lower on the LGT than the TSX.

 

The TSX puts out 175fwhp at 7100rpms?????

 

The engine is a little underrated.

 

That's about what my WRX did 13-14 psi.... .turbo motors normally run lower compression...


Again, I recommend staying far, FAR away from any Subaru product, but I'm biased cause I spent all that money putting a new motor in mine....

 

yeah but you FEEL the torque. Can anyone here honestly say the TSX feels as powerful as the Legacy

IMO torque is more important because i hate to have to ring out an engine all the time to get usable power. It is nice to be able to dip into the throttle at any speed and feel some go.

 

Torque is the single value of any real use. HP is just the rate at which torque is applied. Torque is the force which plants you back in the seat when throttle is applied. You can't feel HP. Looking at the torque curves gives an idea of how a car will feel and what it is capable of especially when gearing is inserted into the analysis.

Now why can that TSX make 370 WHP, because it was a one off kit. It was not meant for sale and wasn't an OEM installation where 100k mile warranty may be applicable. I beleive I had read about that TSX and it wasn't just a turbo kit either; more work had gone into it as well.

 

That's a fact.

 

My only thought is that if the TSX were pushing 13.5 psi, it would own the legacy.

Such is the nature of the discussion between NA and turbo engines.

 

Totally disagree. Especially since HP is a just an equation based off torque/rpm.

Scalbert worded it best, I won't say anymore...

 

Incorrect, if the TSX ran 13.5 PSI it wouldn't make it through many passes with its 10.5:1 CR.

 

In essence, the TSX would have to lose some HP with the lowering of its CR to 8.5:1 (or so)......this would then drop the K24A well below it's stock 200bhp. Then the boost would be added. What HP it winds up having, I cant say without actually doing the upgrade.

But Scalbert is correct, you DONT run 1lb short of one bar under a 10.5:1CR....that is unless you really hate your engine.

 

But even with a reduced compression ratio, Honda's engines have proven very responsive to properly sorted turbocharging. And considering that with stock internals and mild boost from a supercharger, Comptech was able to achieve 240 hp, even with a reduction of compression ratio, 13.5 psi of boost on the K24 should achieve well over 250 hp.

Heck, just look at the performance difference between the standard non-turbo Legacy and compare those numbers against the TSXs.

 

You do realize, it's all speculation.

One can also argue (with much validity) that Subaru knew they were going to develop a performance oriented Turbo 4 Legacy model and didnt see the need to overbuild an NA Boxer 4 into the same lineup. (I wont even regard the fact that the Scoobys are AWD...read: weight penalty)

Just food for thought.

 

HP is a better indicator of how fast a car is, period. your formula is wrong, -> hp = torque * rpm/5252. So you can increase hp by raising torque, OR raising RPM. Both will do the job. Does the integra type-r have alot of torque? What about an F1 car (Relatively speaking)

Yes, you "feel" torque, and it is the actual force that moves you. But looking at the torque your engine makes is not a good indicator of how fast your car is. (if anything torque at the wheels after gearing would be better).

In the end your HP will be the better indicator of your 1/4 mile.

 

Not need to inform me of what Honda/Acura engines can do. I did make 369 WHP and 310 WTQ on 7.5 PSI in my CL-S6 SC/IC. But would I throw 13.4 PSI at it and expect it to live, no way.

In addition to running lower CR's , an OEM is going to run less timing on a factory forced induction engine further limiting the power.

IMO, Honda would most likely out do Subaru with an OEM forced induction power plant if they produced one today. However, you can't compare a factory turbo application to an aftermarket system; there are too many variables.

 

Agreed. And I wasn't informing you, I was just using an example to better explain myself.

Regardless, I think an apples to apples comparison would be more conclusive. The TSX really focuses on something other than outright straight-line speed which the Legacy excels at.

 

You cannot calculate HP without knowing both Torque and RPM. Thus HP is a derived by the rate at which torque is applied. Torque is a single value; HP is comprised of two values but I believe you know this since it is shown in your equation. Even reading your own equation you should acknowledge this.

You want to look at the torque curve or HP curve if you know RPM. But torque is a better illustration of the vehicles acceleration through a gear. Looking at a HP curve requires the RPM to be known as it is nearly always climbing unless the torque curve slope is dropping quicker than RPM is climbing.

HP does matter. But it is all about the duration of the torque curve which is what creates high HP. Making torque is important, but making torque longer is pinnacle which is what HP measures. But more things are involved than that; gearing for one is very important when dissecting performance potential.

Here is a good read on HP and Torque and may help to illustrate things better:

http://www.vettenet.org/torquehp.html

Oh and BTW, torque is what gets you better ETs. HP increases your traps. This is a general rule-of-thumb but is certainly valid. Increase low or mid range torque and you will drop your short times and your ET's. But you may not increase your trap speed though.

 

I never wrote out the formula I was simply listing what its variables are... you can use the SEARCH function and find where I have posted the HP calculation in many other threads. So NO my formula wasn't wrong, I NEVER wrot/posted one...

Maybe read a bit closer next time. I'll make sure to use a comma to seperate my variables next time... lol
HP does not always increase as torque increases. Torque is the twisting force, HP is just a calculation of WORK over TIME. Not power.

So explain why a 500HP lighter M5 is slower than a heavier 460HP E55.

 

I would agree with that. The Legacy does have AWD to aid in low speed traction.

For instance, my current S4 would certainly take my CL-S6 SC/IC off the line. But once past 60 - 70 MPH where the CL-S6 SC/IC starts to get traction, there is no contest.

 

read my post again. I NEVER said torque didnt matter, and I acknowledge what it does. But I am saying HP is a BETTER overall indicator of accelration because it taking into consideration not only torque, but RPMs as well.

I think my type-r and F1 car examples alone prove my point.

 

On this I have to disagree.

The reason why you can feel torque is because it's being constantly applied. HP is torque AND the rate at which it's being applied. If you had a motor capable of 1000 lb ft at 1 rpm is that any better than a motor that can produce 1 lb ft at 1000rpm? No, they're the same.

Say you were to put both the LGT and TSX engines into identical cars with a CVT transmission. Rev the LGT to 4400rpm and the TSX to 7100rpm and let the CVT do the work. Both cars would accelerate at the same rate because they are putting out the same amount of horsepower.

Don't get me wrong, torque is certainly not a meaningless number. It can be very useful for things like calculating how much force a clutch needs to hold.

I understand that this kit wasn't going to be released by Honda as a factory-backed solution for the TSX. I wasn't trying to imply that.

I was just curious why the LGT needed 13.5psi to get up to 250hp. I figured they must have done something to the engine to reduce it's efficiency and increase it's reliability under boost. The whole point of this thread is to find out what they did and by the sounds of it, they just lowered the compression.


Sorry to anyone who mistook this thread to be a "TSX is better than LGT" thread. I fully admit that the LGT is a much more powerful car. I just wanted to have a discussion on the inner workings of the two cars.

 

HP does not indicate acceleration, torque does. If you take an engine which makes 200 HP at 10,000 RPM and put it in an Integra it would not be quick if gearing is left alone. Change the gearing to use that low, but extending, torque curve and it would fair better.

In a theoretical engine; you make 300 lb/ft of torque at 3000 RPM and 350 HP at 7000 RPM. For any given gear you will be accelerating harder at 3000 RPM than you will at 7000 RPM even though the HP number is higher. Why, because you are only making 262 lb/ft at 7000 RPM. Your torque curve is your acceleration rate for any given gear.

And your examples prove nothing because gearing is not considered. First of all, the ITR is not an acceleration monster. It only does OK and is designed for turning moreso than accelerating. F1 cars use low weight and aggressive gearing to acheive what they do as do most all purpose race cars.

 

acceleration is a tricky word, and I purposely left it out of my origional post. What I am talking about is the time is takes to get from 0 - 1/4 mile. Call it what you will. There are so many factors here ...gearing, weight, torque, etc. In order to really understand how fast a car will be you need to study all of these. Ideally you want to see the power curves graphed, and study the region under the curve.

That being said .... if you are just purely looking at numbers, your HP number will be a better indicator of how quickly your car will get through the 1/4 mile than torque will. Yes i realize HP is a limited indicator, but torque is even less usefull. HP is the better indicator, i never said it wasnt flawed. Thats my point.

 

This is BAR NONE the best discussion on torque vs HP in terms of acceleration: http://www.allpar.com/eek/hp-vs-torque.html

I highly recommend everyone should read it or at very least, his conclusion at the end.

 

great article.


we shift at peak power, not peak torque for best straight line performance.

 

Work/time = Power

It's because the cars don't start out and stay at peak power in a 0-60 or QM contest. The E55's got more torque, and thus more power at lower RPMs--making the car accelerate faster, earlier. I don't know the curves, but I'd bet that the M5's not making more power than the E55 until an RPM above the E55s redline. By that time, the MB already has a big distance advantage.

On the highway, when you can force the cars to be at or around peak power, the M5 wins because of the better peak power to weight ratio.

 

You can disagree all you want but you are still incorrect. I would wager I have a bit more experience in these things.

Your first example is irrelevant as it implies a constant force and not acceleration. This is fine if you are towing a heavy trailer or even mixing bread, etc. But we are discussing acceleration. To use your example for acceleration you would have to include gearing and maximum RPM to get an idea of the theoretical results.

The biggest thing to remember is that you will never accelerate harder for a given gear than what you do at your peak torque.

For your second example we will dissect it further. If we take the same weight car and use the same CVT but with a TSX engine turning 7100 RPM and an LGT engine turning 4400 RPM we need to determine the torque output at the two points.

For the TSX engine vehicle we can infer that it is making no more than 148 lb/ft at 7100 as the peak HP rating it 200 HP. It probably makes less than this as I suspect the peak HP number is not at 7100. But for the sake of argument we will leave it.

The LGT makes 250 lb/ft at 3600 RPM and 219 lb/ft at 6000 RPM. We could assume a somewhat linear progressive in the torque curve so 240 lb/ft would be a safe estimate at 4400 RPM.

Applying 240 lb/ft at 4400 RPM versus 148 lb/ft @ 7100 RPM in a CVT transmission holding the RPM still but increasing the ratio. The 240 lb/ft vehicle will be accelerating the vehicle quicker.